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Title:  Great Astronomers

Author:  R. S. Ball

August, 2000  [Etext #2298]


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This etext was prepared by
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Pamela L. Hall  pamhall@www.edu





GREAT ASTRONOMERS

By

SIR ROBERT S. BALL D.Sc. LL.D. F.R.S.

Lowndean Professor of Astronomy and Geometry in the
University of Cambridge

Author of "In Starry Realms" " In the High Heavens" etc.


[PLATE:  GREENWICH OBSERVATORY.]



PREFACE.



It has been my object in these pages to present the life of each
astronomer in such detail as to enable the reader to realise in
some degree the man's character and surroundings; and I have
endeavoured to indicate as clearly as circumstances would permit
the main features of the discoveries by which he has become known.

There are many types of astronomers--from the stargazer who merely
watches the heavens, to the abstract mathematician who merely
works at his desk; it has, consequently, been necessary in the
case of some lives to adopt a very different treatment from that
which seemed suitable for others.

While the work was in progress, some of the sketches appeared in
"Good Words."  The chapter on Brinkley has been chiefly derived from
an article on the "History of Dunsink Observatory," which was
published on the occasion of the tercentenary celebration of the
University of Dublin in 1892, and the life of Sir William Rowan
Hamilton is taken, with a few alterations and omissions, from an
article contributed to the "Quarterly Review" on Graves' life of
the great mathematician.  The remaining chapters now appear for
the first time.  For many of the facts contained in the sketch of
the late Professor Adams, I am indebted to the obituary notice
written by my friend Dr. J.W.L. Glaisher, for the Royal Astronomical
Society; while with regard to the late Sir George Airy,  I have a
similar acknowledgment to make to Professor H.H. Turner.  To my
friend Dr. Arthur A. Rambaut I owe my hearty thanks for his
kindness in aiding me in the revision of the work.

R.S.B.
The Observatory, Cambridge.
October, 1895




CONTENTS.


INTRODUCTION.

PTOLEMY.

COPERNICUS.

TYCHO BRAHE.

GALILEO.

KEPLER.

ISAAC NEWTON.

FLAMSTEED.

HALLEY.

BRADLEY.

WILLIAM HERSCHEL.

LAPLACE.

BRINKLEY.

JOHN HERSCHEL.

THE EARL OF ROSSE.

AIRY.

HAMILTON.

LE VERRIER.

ADAMS.



LIST OF ILLUSTRATIONS.

THE OBSERVATORY, GREENWICH.

PTOLEMY.

PTOLEMY'S PLANETARY SCHEME.

PTOLEMY'S THEORY OF THE MOVEMENT OF MARS.

THORN, FROM AN OLD PRINT.

COPERNICUS.

FRAUENBURG, FROM AN OLD PRINT.

EXPLANATION OF PLANETARY MOVEMENTS.

TYCHO BRAHE.

TYCHO'S CROSS STAFF.

TYCHO'S "NEW STAR" SEXTANT OF 1572.

TYCHO'S TRIGONIC SEXTANT.

TYCHO'S ASTRONOMIC SEXTANT.

TYCHO'S EQUATORIAL ARMILLARY.

THE GREAT AUGSBURG QUADRANT.

TYCHO'S "NEW SCHEME OF THE TERRESTRIAL SYSTEM," 1577.

URANIBORG AND ITS GROUNDS.

GROUND-PLAN OF THE OBSERVATORY.

THE OBSERVATORY OF URANIBORG, ISLAND OF HVEN.

EFFIGY ON TYCHO'S TOMB AT PRAGUE.
  By Permission of Messrs. A. & C. Black.

TYCHO'S MURAL QUADRANT, URANIBORG.

GALILEO'S PENDULUM.

GALILEO.

THE VILLA ARCETRI.

FACSIMILE SKETCH OF LUNAR SURFACE BY GALILEO.

CREST OF GALILEO'S FAMILY.

KEPLER'S SYSTEM OF REGULAR SOLIDS.

KEPLER.

SYMBOLICAL REPRESENTATION OF THE PLANETARY SYSTEM.

THE COMMEMORATION OF THE RUDOLPHINE TABLES.

WOOLSTHORPE MANOR.

TRINITY COLLEGE, CAMBRIDGE.

DIAGRAM OF A SUNBEAM.

ISAAC NEWTON.

SIR ISAAC NEWTON'S LITTLE REFLECTOR.

SIR ISAAC NEWTON'S SUN-DIAL.

SIR ISAAC NEWTON'S TELESCOPE.

SIR ISAAC NEWTON'S ASTROLABE.

SIR ISAAC NEWTON'S SUN-DIAL IN THE ROYAL SOCIETY.

FLAMSTEED'S HOUSE.

FLAMSTEED.

HALLEY.

GREENWICH OBSERVATORY IN HALLEY'S TIME.

7, NEW KING STREET, BATH.
   From a Photograph by John Poole, Bath.

WILLIAM HERSCHEL.

CAROLINE HERSCHEL.

STREET VIEW, HERSCHEL HOUSE, SLOUGH.
   From a Photograph by Hill & Saunders, Eton.

GARDEN VIEW, HERSCHEL HOUSE, SLOUGH.
   From a Photograph by Hill & Saunders, Eton.

OBSERVATORY, HERSCHEL HOUSE, SLOUGH.
   From a Photograph by Hill & Saunders, Eton.

THE 40-FOOT TELESCOPE, HERSCHEL HOUSE, SLOUGH.
   From a Photograph by Hill & Saunders, Eton.

LAPLACE.

THE OBSERVATORY, DUNSINK.
   From a Photograph by W. Lawrence, Dublin.

ASTRONOMETER MADE BY SIR JOHN HERSCHEL.

SIR JOHN HERSCHEL.

NEBULA IN SOUTHERN HEMISPHERE.

THE CLUSTER IN THE CENTAUR.

OBSERVATORY AT FELDHAUSEN.

GRANITE COLUMN AT FELDHAUSEN.

THE EARL OF ROSSE.

BIRR CASTLE.
   From a Photograph by W. Lawrence, Dublin.

THE MALL, PARSONSTOWN.
   From a Photograph by W. Lawrence, Dublin.

LORD ROSSE'S TELESCOPE.
   From a Photograph by W. Lawrence, Dublin.

ROMAN CATHOLIC CHURCH, PARSONSTOWN.
   From a Photograph by W. Lawrence, Dublin.

AIRY.
   From a Photograph by E.P. Adams, Greenwich.

HAMILTON.

ADAMS.

THE OBSERVATORY, CAMBRIDGE.




INTRODUCTION.



Of all the natural sciences there is not one which offers such
sublime objects to the attention of the inquirer as does the
science of astronomy.  From the earliest ages the study of the
stars has exercised the same fascination as it possesses at the
present day.  Among the most primitive peoples, the movements of
the sun, the moon, and the stars commanded attention from their
supposed influence on human affairs.

The practical utilities of astronomy were also obvious in primeval
times.  Maxims of extreme antiquity show how the avocations of the
husbandman are to be guided by the movements of the heavenly
bodies.  The positions of the stars indicated the time to plough,
and the time to sow.  To the mariner who was seeking a way across
the trackless ocean, the heavenly bodies offered the only reliable
marks by which his path could be guided.  There was, accordingly,
a stimulus both from intellectual curiosity and from practical
necessity to follow the movements of the stars.  Thus began a
search for the causes of the ever-varying phenomena which the
heavens display.

Many of the earliest discoveries are indeed prehistoric.  The
great diurnal movement of the heavens, and the annual revolution
of the sun, seem to have been known in times far more ancient than
those to which any human monuments can be referred.  The acuteness
of the early observers enabled them to single out the more
important of the wanderers which we now call planets.  They saw
that the star-like objects, Jupiter, Saturn, and Mars, with the
more conspicuous Venus, constituted a class of bodies wholly
distinct from the fixed stars among which their movements lay, and
to which they bear such a superficial resemblance.  But the
penetration of the early astronomers went even further, for they
recognized that Mercury also belongs to the same group, though
this particular object is seen so rarely.  It would seem that
eclipses and other phenomena were observed at Babylon from a very
remote period, while the most ancient records of celestial
observations that we possess are to be found in the Chinese
annals.

The study of astronomy, in the sense in which we understand the
word, may be said to have commenced under the reign of the
Ptolemies at Alexandria.  The most famous name in the science of
this period is that of Hipparchus who lived and worked at Rhodes
about the year 160BC.  It was his splendid investigations that
first wrought the observed facts into a coherent branch of
knowledge.  He recognized the primary obligation which lies on the
student of the heavens to compile as complete an inventory as
possible of the objects which are there to be found.  Hipparchus
accordingly commenced by undertaking, on a small scale, a task
exactly similar to that on which modern astronomers, with all
available appliances of meridian circles, and photographic
telescopes, are constantly engaged at the present day.  He
compiled a catalogue of the principal fixed stars, which is of
special value to astronomers, as being the earliest work of its
kind which has been handed down.  He also studied the movements of
the sun and the moon, and framed theories to account for the
incessant changes which he saw in progress.  He found a much more
difficult problem in his attempt to interpret satisfactorily the
complicated movements of the planets.  With the view of
constructing a theory which should give some coherent account of
the subject, he made many observations of the places of these
wandering stars.  How great were the advances which Hipparchus
accomplished may be appreciated if we reflect that, as a
preliminary task to his more purely astronomical labours, he had
to invent that branch of mathematical science by which alone the
problems he proposed could be solved.  It was for this purpose
that he devised the indispensable method of calculation which we
now know so well as trigonometry.  Without the aid rendered by
this beautiful art it would have been impossible for any really
important advance in astronomical calculation to have been
effected.

But the discovery which shows, beyond all others, that Hipparchus
possessed one of the master-minds of all time was the detection of
that remarkable celestial movement known as the precession of the
equinoxes.  The inquiry which conducted to this discovery involved
a most profound investigation, especially when it is remembered
that in the days of Hipparchus the means of observation of the
heavenly bodies were only of the rudest description, and the
available observations of earlier dates were extremely scanty.
We can but look with astonishment on the genius of the man who, in
spite of such difficulties, was able to detect such a phenomenon
as the precession, and to exhibit its actual magnitude.  I shall
endeavour to explain the nature of this singular celestial
movement, for it may be said to offer the first instance in the
history of science in which we find that combination of accurate
observation with skilful interpretation, of which, in the
subsequent development of astronomy, we have so many splendid
examples.

The word equinox implies the condition that the night is equal to
the day.  To a resident on the equator the night is no doubt equal
to the day at all times in the year, but to one who lives on any
other part of the earth, in either hemisphere, the night and the
day are not generally equal.  There is, however, one occasion in
spring, and another in autumn, on which the day and the night are
each twelve hours at all places on the earth.  When the night and
day are equal in spring, the point which the sun occupies on the
heavens is termed the vernal equinox.  There is similarly another
point in which the sun is situated at the time of the autumnal
equinox.  In any investigation of the celestial movements the
positions of these two equinoxes on the heavens are of primary
importance, and Hipparchus, with the instinct of genius, perceived
their significance, and commenced to study them.  It will be
understood that we can always define the position of a point on
the sky with reference to the surrounding stars.  No doubt we do
not see the stars near the sun when the sun is shining, but they
are there nevertheless.  The ingenuity of Hipparchus enabled him
to determine the positions of each of the two equinoxes relatively
to the stars which lie in its immediate vicinity.  After
examination of the celestial places of these points at different
periods, he was led to the conclusion that each equinox was moving
relatively to the stars, though that movement was so slow that
twenty five thousand years would necessarily elapse before a
complete circuit of the heavens was accomplished.  Hipparchus
traced out this phenomenon, and established it on an impregnable
basis, so that all astronomers have ever since recognised the
precession of the equinoxes as one of the fundamental facts of
astronomy.  Not until nearly two thousand years after Hipparchus
had made this splendid discovery was the explanation of its cause
given by Newton.

From the days of Hipparchus down to the present hour the science
of astronomy has steadily grown.  One great observer after another
has appeared from time to time, to reveal some new phenomenon with
regard to the celestial bodies or their movements, while from time
to time one commanding intellect after another has arisen to
explain the true import of the facts of observations.  The history
of astronomy thus becomes inseparable from the history of the
great men to whose labours its development is due.

In the ensuing chapters we have endeavoured to sketch the lives
and the work of the great philosophers, by whose labours the
science of astronomy has been created.  We shall commence with
Ptolemy, who, after the foundations of the science had been laid
by Hipparchus, gave to astronomy the form in which it was taught
throughout the Middle Ages.  We shall next see the mighty
revolution in our conceptions of the universe which are associated
with the name of Copernicus.  We then pass to those periods
illumined by the genius of Galileo and Newton, and afterwards we
shall trace the careers of other more recent discoverers, by
whose industry and genius the boundaries of human knowledge have
been so greatly extended.  Our history will be brought down late
enough to include some of the illustrious astronomers who laboured
in the generation which has just passed away.





PTOLEMY.


[PLATE:  PTOLEMY.]

The career of the famous man whose name stands at the head of this
chapter is one of the most remarkable in the history of human
learning.  There may have been other discoverers who have done
more for science than ever Ptolemy accomplished, but there never
has been any other discoverer whose authority on the subject of
the movements of the heavenly bodies has held sway over the minds
of men for so long a period as the fourteen centuries during which
his opinions reigned supreme.  The doctrines he laid down in his
famous book, "The Almagest," prevailed throughout those ages.  No
substantial addition was made in all that time to the undoubted
truths which this work contained.  No important correction was
made of the serious errors with which Ptolemy's theories were
contaminated.  The authority of Ptolemy as to all things in
the heavens, and as to a good many things on the earth (for the
same illustrious man was also a diligent geographer), was
invariably final.

Though every child may now know more of the actual truths of the
celestial motions than ever Ptolemy knew, yet the fact that his
work exercised such an astonishing effect on the human intellect
for some sixty generations, shows that it must have been an
extraordinary production.  We must look into the career of this
wonderful man to discover wherein lay the secret of that
marvellous success which made him the unchallenged instructor of
the human race for such a protracted period.

Unfortunately, we know very little as to the personal history of
Ptolemy.  He was a native of Egypt, and though it has been
sometimes conjectured that he belonged to the royal families of
the same name, yet there is nothing to support such a belief.
The name, Ptolemy, appears to have been a common one in Egypt in
those days.  The time at which he lived is fixed by the fact that
his first recorded observation was made in 127 AD, and his last in
151 AD.  When we add that he seems to have lived in or near
Alexandria, or to use his own words, "on the parallel of
Alexandria," we have said everything that can be said so far as
his individuality is concerned.

Ptolemy is, without doubt, the greatest figure in ancient
astronomy.  He gathered up the wisdom of the philosophers who had
preceded him.  He incorporated this with the results of his
own observations, and illumined it with his theories.  His
speculations, even when they were, as we now know, quite
erroneous, had such an astonishing verisimilitude to the actual
facts of nature that they commanded universal assent.  Even in
these modern days we not unfrequently find lovers of paradox who
maintain that Ptolemy's doctrines not only seem true, but actually
are true.

In the absence of any accurate knowledge of the science of
mechanics, philosophers in early times were forced to fall back
on certain principles of more or less validity, which they derived
from their imagination as to what the natural fitness of things
ought to be.  There was no geometrical figure so simple and so
symmetrical as a circle, and as it was apparent that the heavenly
bodies pursued tracks which were not straight lines, the
conclusion obviously followed that their movements ought to be
circular.  There was no argument in favour of this notion, other
than the merely imaginary reflection that circular movement, and
circular movement alone, was "perfect," whatever "perfect" may
have meant.  It was further believed to be impossible that the
heavenly bodies could have any other movements save those which
were perfect.  Assuming this, it followed, in Ptolemy's opinion,
and in that of those who came after him for fourteen centuries,
that all the tracks of the heavenly bodies were in some way or
other to be reduced to circles.

Ptolemy succeeded in devising a scheme by which the apparent
changes that take place in the heavens could, so far as he knew
them, be explained by certain combinations of circular movement.
This seemed to reconcile so completely the scheme of things
celestial with the geometrical instincts which pointed to the
circle as the type of perfect movement, that we can hardly wonder
Ptolemy's theory met with the astonishing success that attended
it.  We shall, therefore, set forth with sufficient detail the
various steps of this famous doctrine.

Ptolemy commences with laying down the undoubted truth that the
shape of the earth is globular.  The proofs which he gives of this
fundamental fact are quite satisfactory; they are indeed the same
proofs as we give today.  There is, first of all, the well-known
circumstance of which our books on geography remind us, that when
an object is viewed at a distance across the sea, the lower part
of the object appears cut off by the interposing curved mass of
water.

The sagacity of Ptolemy enabled him to adduce another argument,
which, though not quite so obvious as that just mentioned,
demonstrates the curvature of the earth in a very impressive
manner to anyone who will take the trouble to understand it.
Ptolemy mentions that travellers who went to the south reported,
that, as they did so, the appearance of the heavens at night
underwent a gradual change.  Stars that they were familiar with in
the northern skies gradually sank lower in the heavens.  The
constellation of the Great Bear, which in our skies never sets
during its revolution round the pole, did set and rise when a
sufficient southern latitude had been attained.  On the other
hand, constellations new to the inhabitants of northern climes
were seen to rise above the southern horizon.  These
circumstances would be quite incompatible with the supposition
that the earth was a flat surface.  Had this been so, a little
reflection will show that no such changes in the apparent
movements of the stars would be the consequence of a voyage to the
south.  Ptolemy set forth with much insight the significance of
this reasoning, and even now, with the resources of modern
discoveries to help us, we can hardly improve upon his arguments.

Ptolemy, like a true philosopher disclosing a new truth to the
world, illustrated and enforced his subject by a variety of happy
demonstrations.  I must add one of them, not only on account of
its striking nature, but also because it exemplifies Ptolemy's
acuteness.  If the earth were flat, said this ingenious reasoner,
sunset must necessarily take place at the same instant, no matter
in what country the observer may happen to be placed.  Ptolemy,
however, proved that the time of sunset did vary greatly as
the observer's longitude was altered.  To us, of course, this is
quite obvious; everybody knows that the hour of sunset may have
been reached in Great Britain while it is still noon on the
western coast of America.  Ptolemy had, however, few of those
sources of knowledge which are now accessible.  How was he to show
that the sun actually did set earlier at Alexandria than it would
in a city which lay a hundred miles to the west?  There was no
telegraph wire by which astronomers at the two Places could
communicate.  There was no chronometer or watch which could be
transported from place to place; there was not any other reliable
contrivance for the keeping of time.  Ptolemy's ingenuity,
however, pointed out a thoroughly satisfactory method by which the
times of sunset at two places could be compared.  He was
acquainted with the fact, which must indeed have been known from
the very earliest times, that the illumination of the moon is
derived entirely from the sun.  He knew that an eclipse of the
moon was due to the interposition of the earth which cuts off the
light of the sun.  It was, therefore, plain that an eclipse of the
moon must be a phenomenon which would begin at the same instant
from whatever part of the earth the moon could be seen at the
time.  Ptolemy, therefore, brought together from various quarters
the local times at which different observers had recorded the
beginning of a lunar eclipse.  He found that the observers to the
west made the time earlier and earlier the further away their
stations were from Alexandria.  On the other hand, the eastern
observers set down the hour as later than that at which the
phenomenon appeared at Alexandria.  As these observers all
recorded something which indeed appeared to them simultaneously,
the only interpretation was, that the more easterly a place the
later its time.  Suppose there were a number of observers along a
parallel of latitude, and each noted the hour of sunset to be
six o'clock, then, since the eastern times are earlier than
western times, 6 p.m. at one station A will correspond to 5 p.m.
at a station B sufficiently to the west.  If, therefore, it is
sunset to the observer at A, the hour of sunset will not yet be
reached for the observer at B.  This proves conclusively that the
time of sunset is not the same all over the earth.  We have,
however, already seen that the apparent time of sunset would be
the same from all stations if the earth were flat.  When Ptolemy,
therefore, demonstrated that the time of sunset was not the same
at various places, he showed conclusively that the earth was not
flat.

As the same arguments applied to all parts of the earth where
Ptolemy had either been himself, or from which he could gain the
necessary information, it followed that the earth, instead of
being the flat plain, girdled with an illimitable ocean, as was
generally supposed, must be in reality globular.  This led at once
to a startling consequence.  It was obvious that there could be no
supports of any kind by which this globe was sustained; it
therefore followed that the mighty object must be simply poised in
space.  This is indeed an astonishing doctrine to anyone who
relies on what merely seems the evidence of the senses, without
giving to that evidence its due intellectual interpretation.
According to our ordinary experience, the very idea of an object
poised without support in space, appears preposterous.  Would it
not fall? we are immediately asked.  Yes, doubtless it could not
remain poised in any way in which we try the experiment.
We must, however, observe that there are no such ideas as upwards
or downwards in relation to open space.  To say that a body falls
downwards, merely means that it tries to fall as nearly as
possible towards the centre of the earth.  There is no one
direction along which a body will tend to move in space, in
preference to any other.  This may be illustrated by the fact that
a stone let fall at New Zealand will, in its approach towards the
earth's centre, be actually moving upwards as far as any locality
in our hemisphere is concerned.  Why, then, argued Ptolemy, may
not the earth remain poised in space, for as all directions are
equally upward or equally downward, there seems no reason why the
earth should require any support?  By this reasoning he arrives at
the fundamental conclusion that the earth is a globular body
freely lying in space, and surrounded above, below, and on all
sides by the glittering stars of heaven.

The perception of this sublime truth marks a notable epoch in the
history of the gradual development of the human intellect.  No
doubt, other philosophers, in groping after knowledge, may have
set forth certain assertions that are more or less equivalent to
this fundamental truth.  It is to Ptolemy we must give credit,
however, not only for announcing this doctrine, but for
demonstrating it by clear and logical argument.  We cannot easily
project our minds back to the conception of an intellectual state
in which this truth was unfamiliar.  It may, however, be well
imagined that, to one who thought the earth was a flat plain of
indefinite extent, it would be nothing less than an intellectual
convulsion for him to be forced to believe that he stood upon a
spherical earth, forming merely a particle relatively to the
immense sphere of the heavens.

What Ptolemy saw in the movements of the stars led him to the
conclusion that they were bright points attached to the inside of
a tremendous globe.  The movements of this globe which carried the
stars were only compatible with the supposition that the earth
occupied its centre.  The imperceptible effect produced by a
change in the locality of the observer on the apparent brightness
of the stars made it plain that the dimensions of the terrestrial
globe must be quite insignificant in comparison with those of the
celestial sphere.  The earth might, in fact, be regarded as a
grain of sand while the stars lay upon a globe many yards in
diameter.

So tremendous was the revolution in human knowledge implied by
this discovery, that we can well imagine how Ptolemy, dazzled as
it were by the fame which had so justly accrued to him, failed to
make one further step.  Had he made that step, it would have
emancipated the human intellect from the bondage of fourteen
centuries of servitude to a wholly monstrous notion of this
earth's importance in the scheme of the heavens.  The obvious fact
that the sun, the moon, and the stars rose day by day, moved
across the sky in a glorious never-ending procession, and duly set
when their appointed courses had been run, demanded some
explanation.  The circumstance that the fixed stars preserved
their mutual distances from year to year, and from age to age,
appeared to Ptolemy to prove that the sphere which contained those
stars, and on whose surface they were believed by him to be fixed,
revolved completely around the earth once every day.  He would
thus account for all the phenomena of rising and setting
consistently with the supposition that our globe was stationary.
Probably this supposition must have appeared monstrous, even to
Ptolemy.  He knew that the earth was a gigantic object, but, large
as it may have been, he knew that it was only a particle in
comparison with the celestial sphere, yet he apparently believed,
and certainly succeeded in persuading other men to believe, that
the celestial sphere did actually perform these movements.

Ptolemy was an excellent geometer.  He knew that the rising and
the setting of the sun, the moon, and the myriad stars, could have
been accounted for in a different way.  If the earth turned round
uniformly once a day while poised at the centre of the sphere of
the heavens, all the phenomena of rising and setting could be
completely explained.  This is, indeed, obvious after a moment's
reflection.  Consider yourself to be standing on the earth at the
centre of the heavens.  There are stars over your head, and half
the contents of the heavens are visible, while the other half are
below your horizon.  As the earth turns round, the stars over your
head will change, and unless it should happen that you have taken
up your position at either of the poles, new stars will pass into
your view, and others will disappear, for at no time can you have
more than half of the whole sphere visible.  The observer on the
earth would, therefore, say that some stars were rising, and that
some stars were setting.  We have, therefore, two totally distinct
methods, each of which would completely explain all the observed
facts of the diurnal movement.  One of these suppositions requires
that the celestial sphere, bearing with it the stars and other
celestial bodies, turns uniformly around an invisible axis, while
the earth remains stationary at the centre.  The other supposition
would be, that it is the stupendous celestial sphere which remains
stationary, while the earth at the centre rotates about the same
axis as the celestial sphere did before, but in an opposite
direction, and with a uniform velocity which would enable it to
complete one turn in twenty-four hours.  Ptolemy was mathematician
enough to know that either of these suppositions would suffice for
the explanation of the observed facts.  Indeed, the phenomena of
the movements of the stars, so far as he could observe them, could
not be called upon to pronounce which of these views was true, and
which was false.

Ptolemy had, therefore, to resort for guidance to indirect lines
of reasoning.  One of these suppositions must be true, and yet it
appeared that the adoption of either was accompanied by a great
difficulty.  It is one of his chief merits to have demonstrated
that the celestial sphere was so stupendous that the earth itself
was absolutely insignificant in comparison therewith.  If, then,
this stupendous sphere rotated once in twenty-four hours, the
speed with which the movement of some of the stars must be
executed would be so portentous as to seem well-nigh impossible.
It would, therefore, seem much simpler on this ground to adopt the
other alternative, and to suppose the diurnal movements were due
to the rotation of the earth.  Here Ptolemy saw, or at all events
fancied he saw, objections of the weightiest description.  The
evidence of the senses appeared directly to controvert the
supposition that this earth is anything but stationary.  Ptolemy
might, perhaps, have dismissed this objection on the ground that
the testimony of the senses on such a matter should be entirely
subordinated to the interpretation which our intelligence would
place upon the facts to which the senses deposed.  Another
objection, however, appeared to him to possess the gravest moment.
It was argued that if the earth were rotating, there is nothing to
make the air participate in this motion, mankind would therefore
be swept from the earth by the furious blasts which would arise
from the movement of the earth through an atmosphere at rest.
Even if we could imagine that the air were carried round with the
earth, the same would not apply, so thought Ptolemy, to any object
suspended in the air.  So long as a bird was perched on a tree, he
might very well be carried onward by the moving earth, but the
moment he took wing, the ground would slip from under him at a
frightful pace, so that when he dropped down again he would find
himself at a distance perhaps ten times as great as that which a
carrier-pigeon or a swallow could have traversed in the same time.
Some vague delusion of this description seems even still to crop
up occasionally.  I remember hearing of a proposition for balloon
travelling of a very remarkable kind.  The voyager who wanted to
reach any other place in the same latitude was simply to ascend in
a balloon, and wait there till the rotation of the earth conveyed
the locality which happened to be his destination directly beneath
him, whereupon he was to let out the gas and drop down!  Ptolemy
knew quite enough natural philosophy to be aware that such a
proposal for locomotion would be an utter absurdity; he knew that
there was no such relative shift between the air and the earth as
this motion would imply.  It appeared to him to be necessary that
the air should lag behind, if the earth had been animated by a
movement of rotation.  In this he was, as we know, entirely wrong.
There were, however, in his days no accurate notions on the
subject of the laws of motion.

Assiduous as Ptolemy may have been in the study of the heavenly
bodies, it seems evident that he cannot have devoted much thought
to the phenomena of motion of terrestrial objects.  Simple,
indeed, are the experiments which might have convinced a
philosopher much less acute than Ptolemy, that, if the earth did
revolve, the air must necessarily accompany it.  If a rider
galloping on horseback tosses a ball into the air, it drops again
into his hand, just as it would have done had he been remaining at
rest during the ball's flight; the ball in fact participates in
the horizontal motion, so that though it really describes a curve
as any passer-by would observe, yet it appears to the rider
himself merely to move up and down in a straight line.  This fact,
and many others similar to it, demonstrate clearly that if the
earth were endowed with a movement of rotation, the atmosphere
surrounding it must participate in that movement.  Ptolemy did
not know this, and consequently he came to the conclusion
that the earth did not rotate, and that, therefore,
notwithstanding the tremendous improbability of so mighty an
object as the celestial sphere spinning round once in every
twenty-four hours, there was no course open except to believe that
this very improbable thing did really happen.  Thus it came to
pass that Ptolemy adopted as the cardinal doctrine of his system a
stationary earth poised at the centre of the celestial sphere,
which stretched around on all sides at a distance so vast that the
diameter of the earth was an inappreciable point in comparison
therewith.

Ptolemy having thus deliberately rejected the doctrine of the
earth's rotation, had to make certain other entirely erroneous
suppositions.  It was easily seen that each star required exactly
the same period for the performance of a complete revolution
of the heavens.  Ptolemy knew that the stars were at enormous
distances from the earth, though no doubt his notions on this
point came very far short of what we know to be the reality.  If
the stars had been at very varied distances, then it would be so
wildly improbable that they should all accomplish their
revolutions in the same time, that Ptolemy came to the
conclusion that they must be all at the same distance, that is,
that they must be all on the surface of a sphere.  This view,
however erroneous, was corroborated by the obvious fact that the
stars in the constellations preserved their relative places
unaltered for centuries.  Thus it was that Ptolemy came to the
conclusion that they were all fixed on one spherical surface,
though we are not informed as to the material of this marvellous
setting which sustained the stars like jewels.

Nor should we hastily pronounce this doctrine to be absurd.  The
stars do appear to lie on the surface of a sphere, of which the
observer is at the centre; not only is this the aspect which the
skies present to the untechnical observer, but it is the aspect in
which the skies are presented to the most experienced astronomer
of modern days.  No doubt he knows well that the stars are at the
most varied distances from him; he knows that certain stars are
ten times, or a hundred times, or a thousand times, as far as
other stars.  Nevertheless, to his eye the stars appear on the
surface of the sphere, it is on that surface that his measurements
of the relative places of the stars are made; indeed, it may be
said that almost all the accurate observations in the observatory
relate to the places of the stars, not as they really are, but as
they appear to be projected on that celestial sphere whose
conception we owe to the genius of Ptolemy.

This great philosopher shows very ingeniously that the earth must
be at the centre of the sphere.  He proves that, unless this were
the case, each star would not appear to move with the absolute
uniformity which does, as a matter of fact, characterise it.  In
all these reasonings we cannot but have the most profound
admiration for the genius of Ptolemy, even though he had made an
error so enormous in the fundamental point of the stability of
the earth.  Another error of a somewhat similar kind seemed to
Ptolemy to be demonstrated.  He had shown that the earth was an
isolated object in space, and being such was, of course, capable
of movement.  It could either be turned round, or it could be
moved from one place to another.  We know that Ptolemy
deliberately adopted the view that the earth did not turn round;
he had then to investigate the other question, as to whether the
earth was animated by any movement of translation.  He came to the
conclusion that to attribute any motion to the earth would be
incompatible with the truths at which he had already arrived.  The
earth, argued Ptolemy, lies at the centre of the celestial sphere.
If the earth were to be endowed with movement, it would not lie
always at this point, it must, therefore, shift to some other part
of the sphere.  The movements of the stars, however, preclude the
possibility of this; and, therefore, the earth must be as devoid
of any movement of translation as it is devoid of rotation.  Thus
it was that Ptolemy convinced himself that the stability of the
earth, as it appeared to the ordinary senses, had a rational
philosophical foundation.

Not unfrequently it is the lot of the philosophers to contend
against the doctrines of the vulgar, but when it happens, as in
the case of Ptolemy's researches, that the doctrines of the vulgar
are corroborated by philosophical investigation which bear the
stamp of the highest authority, it is not to be wondered at that
such doctrines should be deemed well-nigh impregnable.  In this
way we may, perhaps, account for the remarkable fact that the
theories of Ptolemy held unchallenged sway over the human
intellect for the vast period already mentioned.

Up to the present we have been speaking only of those primary
motions of the heavens, by which the whole sphere appeared to
revolve once every twenty-four hours.  We have now to discuss the
remarkable theories by which Ptolemy endeavoured to account for
the monthly movement of the moon, for the annual movement of the
sun, and for the periodic movements of the planets which had
gained for them the titles of the wandering stars.

Possessed with the idea that these movements must be circular, or
must be capable, directly or indirectly, of being explained by
circular movements, it seemed obvious to Ptolemy, as indeed it had
done to previous astronomers, that the track of the moon through
the stars was a circle of which the earth is the centre.
A similar movement with a yearly period must also be attributed to
the sun, for the changes in the positions of the constellations in
accordance with the progress of the seasons, placed it beyond
doubt that the sun made a circuit of the celestial sphere, even
though the bright light of the sun prevented the stars in its
vicinity, from being seen in daylight.  Thus the movements both of
the sun and the moon, as well as the diurnal rotation of the
celestial sphere, seemed to justify the notion that all celestial
movements must be "perfect," that is to say, described uniformly
in those circles which were the only perfect curves.

The simplest observations, however, show that the movements of the
planets cannot be explained in this simple fashion.  Here the
geometrical genius of Ptolemy shone forth, and he devised a scheme
by which the apparent wanderings of the planets could be accounted
for without the introduction of aught save "perfect" movements.

To understand his reasoning, let us first set forth clearly those
facts of observation which require to be explained.  I shall take,
in particular, two planets, Venus and Mars, as these illustrate,
in the most striking manner, the peculiarities of the inner and
the outer planets respectively.  The simplest observations would
show that Venus did not move round the heavens in the same fashion
as the sun or the moon.  Look at the evening star when brightest,
as it appears in the west after sunset.  Instead of moving towards
the east among the stars, like the sun or the moon, we find, week
after week, that Venus is drawing in towards the sun, until it is
lost in the sunbeams.  Then the planet emerges on the other side,
not to be seen as an evening star, but as a morning star.  In
fact, it was plain that in some ways Venus accompanied the sun in
its annual movement.  Now it is found advancing in front of the
sun to a certain limited distance, and now it is lagging to an
equal extent behind the sun.

[FIG. 1.  PTOLEMY'S PLANETARY SCHEME.]

These movements were wholly incompatible with the supposition
that the journeys of Venus were described by a single motion of
the kind regarded as perfect.  It was obvious that the movement
was connected in some strange manner with the revolution of the
sun, and here was the ingenious method by which Ptolemy sought to
render account of it.  Imagine a fixed arm to extend from the
earth to the sun, as shown in the accompanying figure (Fig. 1),
then this arm will move round uniformly, in consequence of the
sun's movement.  At a point P on this arm let a small circle be
described.  Venus is supposed to revolve uniformly in this small
circle, while the circle itself is carried round continuously by
the movement of the sun.  In this way it was possible to account
for the chief peculiarities in the movement of Venus.  It will be
seen that, in consequence of the revolution around P, the
spectator on the earth will sometimes see Venus on one side of the
sun, and sometimes on the other side, so that the planet always
remains in the sun's vicinity.  By properly proportioning the
movements, this little contrivance simulated the transitions from
the morning star to the evening star.  Thus the changes of Venus
could be accounted for by a Combination of the "perfect" movement
of P in the circle which it described uniformly round the earth,
combined with the "perfect" motion of Venus in the circle which it
described uniformly around the moving centre.

In a precisely similar manner Ptolemy rendered an explanation of
the fitful apparitions of Mercury.  Now just on one side of the
sun, and now just on the other, this rarely-seen planet moved like
Venus on a circle whereof the centre was also carried by the line
joining the sun and the earth.  The circle, however, in which
Mercury actually revolved had to be smaller than that of Venus, in
order to account for the fact that Mercury lies always much closer
to the sun than the better-known planet.

[FIG. 2.  PTOLEMY'S THEORY OF THE MOVEMENT OF MARS.]

The explanation of the movement of an outer planet like Mars could
also be deduced from the joint effect of two perfect motions.  The
changes through which Mars goes are, however, so different from
the movements of Venus that quite a different disposition of the
circles is necessary.  For consider the facts which characterise
the movements of an outer planet such as Mars.  In the first
place, Mars accomplishes an entire circuit of the heaven.  In this
respect, no doubt, it may be said to resemble the sun or the moon.
A little attention will, however, show that there are
extraordinary irregularities in the movement of the planet.
Generally speaking, it speeds its way from west to east among the
stars, but sometimes the attentive observer will note that the
speed with which the planet advances is slackening, and then it
will seem to become stationary.  Some days later the direction of
the planet's movement will be reversed, and it will be found
moving from the east towards the west.  At first it proceeds
slowly and then quickens its pace, until a certain speed is
attained, which afterwards declines until a second stationary
position is reached.  After a due pause the original motion from
west to east is resumed, and is continued until a similar cycle of
changes again commences.  Such movements as these were obviously
quite at variance with any perfect movement in a single circle
round the earth.  Here, again, the geometrical sagacity of Ptolemy
provided him with the means of representing the apparent movements
of Mars, and, at the same time, restricting the explanation to
those perfect movements which he deemed so essential.  In Fig. 2
we exhibit Ptolemy's theory as to the movement of
Mars.  We have, as before, the earth at the centre, and the sun
describing its circular orbit around that centre.  The path of Mars
is to be taken as exterior to that of the sun.  We are to suppose
that at a point marked M there is a fictitious planet, which
revolves around the earth uniformly, in a circle called the
DEFERENT.  This point M, which is thus animated by a perfect
movement, is the centre of a circle which is carried onwards
with M, and around the circumference of which Mars revolves
uniformly.  It is easy to show that the combined effect of these
two perfect movements is to produce exactly that displacement of
Mars in the heavens which observation discloses.  In the position
represented in the figure, Mars is obviously pursuing a course
which will appear to the observer as a movement from west to east.
When, however, the planet gets round to such a position as R, it
is then moving from east to west in consequence of its revolution
in the moving circle, as indicated by the arrowhead.  On the other
hand, the whole circle is carried forward in the opposite
direction.  If the latter movement be less rapid than the former,
then we shall have the backward movement of Mars on the heavens
which it was desired to explain.  By a proper adjustment of the
relative lengths of these arms the movements of the planet as
actually observed could be completely accounted for.

The other outer planets with which Ptolemy was acquainted, namely,
Jupiter and Saturn, had movements of the same general character as
those of Mars.  Ptolemy was equally successful in explaining the
movements they performed by the supposition that each planet had
perfect rotation in a circle of its own, which circle itself had
perfect movement around the earth in the centre.

It is somewhat strange that Ptolemy did not advance one step
further, as by so doing he would have given great simplicity to
his system.  He might, for instance, have represented the
movements of Venus equally well by putting the centre of the
moving circle at the sun itself, and correspondingly enlarging the
circle in which Venus revolved.  He might, too, have arranged that
the several circles which the outer planets traversed should also
have had their centres at the sun.  The planetary system would
then have consisted of an earth fixed at the centre, of a sun
revolving uniformly around it, and of a system of planets each
describing its own circle around a moving centre placed in the
sun.  Perhaps Ptolemy had not thought of this, or perhaps he may
have seen arguments against it.  This important step was, however,
taken by Tycho.  He considered that all the planets revolved
around the sun in circles, and that the sun itself, bearing all
these orbits, described a mighty circle around the earth.  This
point having been reached, only one more step would have been
necessary to reach the glorious truths that revealed the structure
of the solar system.  That last step was taken by Copernicus.



COPERNICUS


[PLATE:  THORN, FROM AN OLD PRINT.]

The quaint town of Thorn, on the Vistula, was more than two
centuries old when Copernicus was born there on the 19th of
February, 1473.  The situation of this town on the frontier
between Prussia and Poland, with the commodious waterway offered
by the river, made it a place of considerable trade.  A view of
the town, as it was at the time of the birth of Copernicus, is
here given.  The walls, with their watch-towers, will be noted,
and the strategic importance which the situation of Thorn gave to
it in the fifteenth century still belongs thereto, so much so
that the German Government recently constituted the town a
fortress of the first class.

Copernicus, the astronomer, whose discoveries make him the great
predecessor of Kepler and Newton, did not come from a noble
family, as certain other early astronomers have done, for his
father was a tradesman.  Chroniclers are, however, careful to
tell us that one of his uncles was a bishop.  We are not
acquainted with any of those details of his childhood or youth
which are often of such interest in other cases where men have
risen to exalted fame.  It would appear that the young Nicolaus,
for such was his Christian name, received his education at home
until such time as he was deemed sufficiently advanced to be sent
to the University at Cracow.  The education that he there
obtained must have been in those days of a very primitive
description, but Copernicus seems to have availed himself of it
to the utmost.  He devoted himself more particularly to the study
of medicine, with the view of adopting its practice as the
profession of his life.  The tendencies of the future astronomer
were, however, revealed in the fact that he worked hard at
mathematics, and, like one of his illustrious successors,
Galileo, the practice of the art of painting had for him a very
great interest, and in it he obtained some measure of success.

By the time he was twenty-seven years old, it would seem that
Copernicus had given up the notion of becoming a medical
practitioner, and had resolved to devote himself to science.
He was engaged in teaching mathematics, and appears to have
acquired some reputation.  His growing fame attracted the notice
of his uncle the bishop, at whose suggestion Copernicus took holy
orders, and he was presently appointed to a canonry in the
cathedral of Frauenburg, near the mouth of the Vistula.

To Frauenburg, accordingly, this man of varied gifts retired.
Possessing somewhat of the ascetic spirit, he resolved to devote
his life to work of the most serious description.  He eschewed
all ordinary society, restricting his intimacies to very grave
and learned companions, and refusing to engage in conversation of
any useless kind.  It would seem as if his gifts for painting
were condemned as frivolous; at all events, we do not learn that
he continued to practise them.  In addition to the discharge of
his theological duties, his life was occupied partly in
ministering medically to the wants of the poor, and partly with
his researches in astronomy and mathematics.  His equipment in
the matter of instruments for the study of the heavens seems to
have been of a very meagre description.  He arranged apertures in
the walls of his house at Allenstein, so that he could observe in
some fashion the passage of the stars across the meridian.  That
he possessed some talent for practical mechanics is proved by his
construction of a contrivance for raising water from a stream,
for the use of the inhabitants of Frauenburg.  Relics of this
machine are still to be seen.

[PLATE:  COPERNICUS.]

The intellectual slumber of the Middle Ages was destined to be
awakened by the revolutionary doctrines of Copernicus.  It may be
noted, as an interesting circumstance, that the time at which he
discovered the scheme of the solar system has coincided with a
remarkable epoch in the world's history.  The great astronomer
had just reached manhood at the time when Columbus discovered the
new world.

Before the publication of the researches of Copernicus,
the orthodox scientific creed averred that the earth
was stationary, and that the apparent movements of the heavenly
bodies were indeed real movements.  Ptolemy had laid down this
doctrine 1,400 years before.  In his theory this huge error was
associated with so much important truth, and the whole presented
such a coherent scheme for the explanation of the heavenly
movements, that the Ptolemaic theory was not seriously questioned
until the great work of Copernicus appeared.  No doubt others,
before Copernicus, had from time to time in some vague fashion
surmised, with more or less plausibility, that the sun, and not
the earth, was the centre about which the system really revolved.
It is, however, one thing to state a scientific fact; it is
quite another thing to be in possession of the train of
reasoning, founded on observation or experiment, by which that
fact may be established.  Pythagoras, it appears, had indeed told
his disciples that it was the sun, and not the earth, which was
the centre of movement, but it does not seem at all certain that
Pythagoras had any grounds which science could recognise for the
belief which is attributed to him.  So far as information is
available to us, it would seem that Pythagoras associated his
scheme of things celestial with a number of preposterous notions
in natural philosophy.  He may certainly have made a correct
statement as to which was the most important body in the solar
system, but he certainly did not provide any rational
demonstration of the fact.  Copernicus, by a strict train of
reasoning, convinced those who would listen to him that the sun
was the centre of the system.  It is useful for us to consider
the arguments which he urged, and by which he effected that
intellectual revolution which is always connected with his name.

The first of the great discoveries which Copernicus made relates
to the rotation of the earth on its axis.  That general diurnal
movement, by which the stars and all other celestial bodies
appear to be carried completely round the heavens once every
twenty-four hours, had been accounted for by Ptolemy on the
supposition that the apparent movements were the real movements.
As we have already seen, Ptolemy himself felt the extraordinary
difficulty involved in the supposition that so stupendous a
fabric as the celestial sphere should spin in the way supposed.
Such movements required that many of the stars should travel with
almost inconceivable velocity.  Copernicus also saw that the
daily rising and setting of the heavenly bodies could be
accounted for either by the supposition that the celestial sphere
moved round and that the earth remained at rest, or by the
supposition that the celestial sphere was at rest while the earth
turned round in the opposite direction.  He weighed the arguments
on both sides as Ptolemy had done, and, as the result of his
deliberations, Copernicus came to an opposite conclusion from
Ptolemy.  To Copernicus it appeared that the difficulties
attending the supposition that the celestial sphere revolved,
were vastly greater than those which appeared so weighty to
Ptolemy as to force him to deny the earth's rotation.

Copernicus shows clearly how the observed phenomena could be
accounted for just as completely by a rotation of the earth as by
a rotation of the heavens.  He alludes to the fact that, to those
on board a vessel which is moving through smooth water, the
vessel itself appears to be at rest, while the objects on shore
seem to be moving past.  If, therefore, the earth were rotating
uniformly, we dwellers upon the earth, oblivious of our own
movement, would wrongly attribute to the stars the displacement
which was actually the consequence of our own motion.

Copernicus saw the futility of the arguments by which Ptolemy had
endeavoured to demonstrate that a revolution of the earth was
impossible.  It was plain to him that there was nothing whatever
to warrant refusal to believe in the rotation of the earth.  In
his clear-sightedness on this matter we have specially to admire
the sagacity of Copernicus as a natural philosopher.  It had been
urged that, if the earth moved round, its motion would not be
imparted to the air, and that therefore the earth would be
uninhabitable by the terrific winds which would be the result of
our being carried through the air.  Copernicus convinced himself
that this deduction was preposterous.  He proved that the air
must accompany the earth, just as his coat remains round him,
notwithstanding the fact that he is walking down the street.  In
this way he was able to show that all a priori objections to
the earth's movements were absurd, and therefore he was able to
compare together the plausibilities of the two rival schemes for
explaining the diurnal movement.

[PLATE:  FRAUENBURG, FROM AN OLD PRINT.]

Once the issue had been placed in this form, the result could not
be long in doubt.  Here is the question: Which is it more likely--
that the earth, like a grain of sand at the centre of a mighty
globe, should turn round once in twenty-four hours, or that the
whole of that vast globe should complete a rotation in the
opposite direction in the same time?  Obviously, the former is
far the more simple supposition.  But the case is really much
stronger than this. Ptolemy had supposed that all the stars were
attached to the surface of a sphere.  He had no ground whatever
for this supposition, except that otherwise it would have been
well-nigh impossible to have devised a scheme by which the
rotation of the heavens around a fixed earth could have been
arranged.  Copernicus, however, with the just instinct of a
philosopher, considered that the celestial sphere, however
convenient from a geometrical point of view, as a means of
representing apparent phenomena, could not actually have a
material existence.  In the first place, the existence of a
material celestial sphere would require that all the myriad stars
should be at exactly the same distances from the earth.
Of course, no one will say that this or any other arbitrary
disposition of the stars is actually impossible, but as there
was no conceivable physical reason why the distances of all the
stars from the earth should be identical, it seemed in the very
highest degree improbable that the stars should be so placed.

Doubtless, also, Copernicus felt a considerable difficulty as to
the nature of the materials from which Ptolemy's wonderful sphere
was to be constructed.  Nor could a philosopher of his penetration
have failed to observe that, unless that sphere were infinitely
large, there must have been space outside it, a consideration
which would open up other difficult questions.  Whether infinite
or not, it was obvious that the celestial sphere must have a
diameter at least many thousands of times as great as that of the
earth.  From these considerations Copernicus deduced the important
fact that the stars and the other celestial bodies must all be
vast objects.  He was thus enabled to put the question in such a
form that it could hardly receive any answer but the correct one.
Which is it more rational to suppose, that the earth should turn
round on its axis once in twenty-four hours, or that thousands of
mighty stars should circle round the earth in the same time, many
of them having to describe circles many thousands of times greater
in circumference than the circuit of the earth at the equator?
The obvious answer pressed upon Copernicus with so much force that
he was compelled to reject Ptolemy's theory of the stationary
earth, and to attribute the diurnal rotation of the heavens to the
revolution of the earth on its axis.

Once this tremendous step had been taken, the great difficulties
which beset the monstrous conception of the celestial sphere
vanished, for the stars need no longer be regarded as situated at
equal distances from the earth.  Copernicus saw that they might
lie at the most varied degrees of remoteness, some being hundreds
or thousands of times farther away than others.  The complicated
structure of the celestial sphere as a material object
disappeared altogether; it remained only as a geometrical
conception, whereon we find it convenient to indicate the places
of the stars.  Once the Copernican doctrine had been fully set
forth, it was impossible for anyone, who had both the
inclination and the capacity to understand it, to withhold
acceptance of its truth.  The doctrine of a stationary earth had
gone for ever.

Copernicus having established a theory of the celestial movements
which deliberately set aside the stability of the earth, it
seemed natural that he should inquire whether the doctrine of a
moving earth might not remove the difficulties presented in other
celestial phenomena.  It had been universally admitted that the
earth lay unsupported in space.  Copernicus had further shown
that it possessed a movement of rotation.  Its want of stability
being thus recognised, it seemed reasonable to suppose that
the earth might also have some other kinds of movements as well.
In this, Copernicus essayed to solve a problem far more difficult
than that which had hitherto occupied his attention.  It was a
comparatively easy task to show how the diurnal rising and
setting could be accounted for by the rotation of the earth.
It was a much more difficult undertaking to demonstrate that the
planetary movements, which Ptolemy had represented with so much
success, could be completely explained by the supposition that
each of those planets revolved uniformly round the sun, and that
the earth was also a planet, accomplishing a complete circuit of
the sun once in the course of a year.

[PLATE:  EXPLANATION OF PLANETARY MOVEMENTS.]

It would be impossible in a sketch like the present to enter into
any detail as to the geometrical propositions on which this
beautiful investigation of Copernicus depended.  We can only
mention a few of the leading principles.  It may be laid down in
general that, if an observer is in movement, he will, if
unconscious of the fact, attribute to the fixed objects around
him a movement equal and opposite to that which he actually
possesses.  A passenger on a canal-boat sees the objects on the
banks apparently moving backward with a speed equal to that by
which he is himself advancing forwards.  By an application of this
principle, we can account for all the phenomena of the movements
of the planets, which Ptolemy had so ingeniously represented by
his circles.  Let us take, for instance, the most characteristic
feature in the irregularities of the outer planets.  We have
already remarked that Mars, though generally advancing from west
to east among the stars, occasionally pauses, retraces his steps
for awhile, again pauses, and then resumes his ordinary onward
progress.  Copernicus showed clearly how this effect was produced
by the real motion of the earth, combined with the real motion of
Mars.  In the adjoining figure we represent a portion of the
circular tracks in which the earth and Mars move in accordance
with the Copernican doctrine.  I show particularly the case where
the earth comes directly between the planet and the sun, because
it is on such occasions that the retrograde movement (for so this
backward movement of Mars is termed) is at its highest.  Mars is
then advancing in the direction shown by the arrow-head, and the
earth is also advancing in the same direction.  We, on the earth,
however, being unconscious of our own motion, attribute, by the
principle I have already explained, an equal and opposite motion
to Mars.  The visible effect upon the planet is, that Mars has two
movements, a real onward movement in one direction, and an
apparent movement in the opposite direction.  If it so happened
that the earth was moving with the same speed as Mars, then the
apparent movement would exactly neutralise the real movement, and
Mars would seem to be at rest relatively to the surrounding stars.
Under the actual circumstances represented, however, the earth is
moving faster than Mars, and the consequence is, that the apparent
movement of the planet backwards exceeds the real movement
forwards, the net result being an apparent retrograde movement.

With consummate skill, Copernicus showed how the applications of
the same principles could account for the characteristic movements
of the planets.  His reasoning in due time bore down all
opposition.  The supreme importance of the earth in the system
vanished.  It had now merely to take rank as one of the planets.

The same great astronomer now, for the first time, rendered
something like a rational account of the changes of the seasons.
Nor did certain of the more obscure astronomical phenomena escape
his attention.

He delayed publishing his wonderful discoveries to the world
until he was quite an old man.  He had a well-founded apprehension
of the storm of opposition which they would arouse.  However, he
yielded at last to the entreaties of his friends, and his book was
sent to the press.  But ere it made its appearance to the world,
Copernicus was seized by mortal illness.  A copy of the book was
brought to him on May 23, 1543.  We are told that he was able to
see it and to touch it, but no more, and he died a few hours
afterwards.  He was buried in that Cathedral of Frauenburg, with
which his life had been so closely associated.




TYCHO BRAHE.



The most picturesque figure in the history of astronomy is
undoubtedly that of the famous old Danish astronomer whose name
stands at the head of this chapter.  Tycho Brahe was alike notable
for his astronomical genius and for the extraordinary vehemence of
a character which was by no means perfect.  His romantic career as
a philosopher, and his taste for splendour as a Danish noble, his
ardent friendships and his furious quarrels, make him an ideal
subject for a biographer, while the magnificent astronomical work
which he accomplished, has given him imperishable fame.

The history of Tycho Brahe has been admirably told by Dr. Dreyer,
the accomplished astronomer who now directs the observatory at
Armagh, though himself a countryman of Tycho.  Every student of
the career of the great Dane must necessarily look on Dr. Dreyer's
work as the chief authority on the subject.  Tycho sprang from an
illustrious stock.  His family had flourished for centuries, both
in Sweden and in Denmark, where his descendants are to be met with
at the present day.  The astronomer's father was a privy
councillor, and having filled important positions in the Danish
government, he was ultimately promoted to be governor of
Helsingborg Castle, where he spent the last years of his life.
His illustrious son Tycho was born in 1546, and was the second
child and eldest boy in a family of ten.

It appears that Otto, the father of Tycho, had a brother named
George, who was childless.  George, however, desired to adopt a
boy on whom he could lavish his affection and to whom he could
bequeath his wealth.  A somewhat singular arrangement was
accordingly entered into by the brothers at the time when Otto was
married.  It was agreed that the first son who might be born to
Otto should be forthwith handed over by the parents to George to
be reared and adopted by him.  In due time little Tycho appeared,
and was immediately claimed by George in pursuance of the compact.
But it was not unnatural that the parental instinct, which had
been dormant when the agreement was made, should here interpose.
Tycho's father and mother receded from the bargain, and refused to
part with their son.  George thought he was badly treated.
However, he took no violent steps until a year later, when a
brother was born to Tycho.  The uncle then felt no scruple in
asserting what he believed to be his rights by the simple process
of stealing the first-born nephew, which the original bargain had
promised him.  After a little time it would seem that the parents
acquiesced in the loss, and thus it was in Uncle George's home
that the future astronomer passed his childhood.

When we read that Tycho was no more than thirteen years old at the
time he entered the University of Copenhagen, it might be at
first supposed that even in his boyish years he must have
exhibited some of those remarkable talents with which he was
afterwards to astonish the world.  Such an inference should not,
however, be drawn.  The fact is that in those days it was
customary for students to enter the universities at a much earlier
age than is now the case.  Not, indeed, that the boys of thirteen
knew more then than the boys of thirteen know now.  But the
education imparted in the universities at that time was of a much
more rudimentary kind than that which we understand by university
education at present.  In illustration of this Dr. Dreyer tells us
how, in the University of Wittenberg, one of the professors, in
his opening address, was accustomed to point out that even the
processes of multiplication and division in arithmetic might be
learned by any student who possessed the necessary diligence.

It was the wish and the intention of his uncle that Tycho's
education should be specially directed to those branches of
rhetoric and philosophy which were then supposed to be a necessary
preparation for the career of a statesman.  Tycho, however,
speedily made it plain to his teachers that though he was an
ardent student, yet the things which interested him were the
movements of the heavenly bodies and not the subtleties of
metaphysics.

[PLATE:  TYCHO BRAHE.]

On the 21st October, 1560, an eclipse of the sun occurred, which
was partially visible at Copenhagen.  Tycho, boy though he was,
took the utmost interest in this event.  His ardour and
astonishment in connection with the circumstance were chiefly
excited by the fact that the time of the occurrence of the
phenomenon could be predicted with so much accuracy.  Urged by his
desire to understand the matter thoroughly, Tycho sought to
procure some book which might explain what he so greatly wanted
to know.  In those days books of any kind were but few and scarce,
and scientific books were especially unattainable.  It so
happened, however, that a Latin version of Ptolemy's astronomical
works had appeared a few years before the eclipse took place, and
Tycho managed to buy a copy of this book, which was then the chief
authority on celestial matters.  Young as the boy astronomer was,
he studied hard, although perhaps not always successfully, to
understand Ptolemy, and to this day his copy of the great work,
copiously annotated and marked by the schoolboy hand, is preserved
as one of the chief treasures in the library of the University at
Prague.

After Tycho had studied for about three years at the University of
Copenhagen, his uncle thought it would be better to send him, as
was usual in those days, to complete his education by a course of
study in some foreign university.  The uncle cherished the hope
that in this way the attention of the young astronomer might be
withdrawn from the study of the stars and directed in what
appeared to him a more useful way.  Indeed, to the wise heads of
those days, the pursuit of natural science seemed so much waste of
good time which might otherwise be devoted to logic or rhetoric or
some other branch of study more in vogue at that time.  To assist
in this attempt to wean Tycho from his scientific tastes, his
uncle chose as a tutor to accompany him an intelligent and upright
young man named Vedel, who was four years senior to his pupil, and
accordingly, in 1562, we find the pair taking up their abode at
the University of Leipzig.

The tutor, however, soon found that he had undertaken a most
hopeless task.  He could not succeed in imbuing Tycho with the
slightest taste for the study of the law or the other branches of
knowledge which were then thought so desirable.  The stars, and
nothing but the stars, engrossed the attention of his pupil.  We
are told that all the money he could obtain was spent secretly in
buying astronomical books and instruments.  He learned the name of
the stars from a little globe, which he kept hidden from Vedel,
and only ventured to use during the latter's absence.  No little
friction was at first caused by all this, but in after years a
fast and enduring friendship grew up between Tycho and his tutor,
each of whom learned to respect and to love the other.

Before Tycho was seventeen he had commenced the difficult task of
calculating the movements of the planets and the places which they
occupied on the sky from time to time.  He was not a little
surprised to find that the actual positions of the planets
differed very widely from those which were assigned to them by
calculations from the best existing works of astronomers.  With
the insight of genius he saw that the only true method of
investigating the movements of the heavenly bodies would be to
carry on a protracted series of measurements of their places.
This, which now seems to us so obvious, was then entirely new
doctrine.  Tycho at once commenced regular observations in such
fashion as he could.  His first instrument was, indeed, a very
primitive one, consisting of a simple pair of compasses, which
he used in this way.  He placed his eye at the hinge, and then
opened the legs of the compass so that one leg pointed to one
star and the other leg to the other star.  The compass was then
brought down to a divided circle, by which means the number of
degrees in the apparent angular distance of the two stars
was determined.

His next advance in instrumental equipment was to provide himself
with the contrivance known as the "cross-staff," which he
used to observe the stars whenever opportunity offered.  It must,
of course, be remembered that in those days there were no
telescopes.  In the absence of optical aid, such as lenses afford
the modern observers, astronomers had to rely on mechanical
appliances alone to measure the places of the stars.  Of such
appliances, perhaps the most ingenious was one known before
Tycho's time, which we have represented in the adjoining figure.

[PLATE:  TYCHO'S CROSS STAFF.]

Let us suppose that it be desired to measure the angle between two
stars, then if the angle be not too large it can be determined in
the following manner.  Let the rod AB be divided into inches and
parts of an inch, and let another rod, CD, slide up and down
along AB in such a way that the two always remain perpendicular
to each other.  "Sights," like those on a rifle, are placed at A
and C, and there is a pin at D. It will easily be seen that, by
sliding the movable bar along the fixed one, it must always be
possible when the stars are not too far apart to bring the sights
into such positions that one star can be seen along DC and the
other along DA.  This having been accomplished, the length from
A to the cross-bar is read off on the scale, and then, by means
of a table previously prepared, the value of the required angular
distance is obtained.  If the angle between the two stars were
greater than it would be possible to measure in the way already
described, then there was a provision by which the pin at D might
be moved along CD into some other position, so as to bring the
angular distance of the stars within the range of the instrument.

[PLATE:  TYCHO'S "NEW STAR" SEXTANT OF 1572.
(The arms, of walnut wood, are about 5 1/2 ft. long.)]

No doubt the cross-staff is a very primitive contrivance, but when
handled by one so skilful as Tycho it afforded results of
considerable accuracy.  I would recommend any reader who may have
a taste for such pursuits to construct a cross-staff for himself,
and see what measurements he can accomplish with its aid.

To employ this little instrument Tycho had to evade the vigilance
of his conscientious tutor, who felt it his duty to interdict all
such occupations as being a frivolous waste of time.  It was when
Vedel was asleep that Tycho managed to escape with his cross staff
and measure the places of the heavenly bodies.  Even at this
early age Tycho used to conduct his observations on those
thoroughly sound principles which lie at the foundation of all
accurate modern astronomy.  Recognising the inevitable errors of
workmanship in his little instrument, he ascertained their amount
and allowed for their influence on the results which he deduced.
This principle, employed by the boy with his cross-staff in 1564,
is employed at the present day by the Astronomer Royal at
Greenwich with the most superb instruments that the skill of
modern opticians has been able to construct.

[PLATE:  TYCHO'S TRIGONIC SEXTANT.
(The arms, AB and AC, are about 5 1/2 ft. long.)]

After the death of his uncle, when Tycho was nineteen years of
age, it appears that the young philosopher was no longer
interfered with in so far as the line which his studies were to
take was concerned.  Always of a somewhat restless temperament, we
now find that he shifted his abode to the University of Rostock,
where he speedily made himself notable in connection with an
eclipse of the moon on 28th October, 1566.  Like every other
astronomer of those days, Tycho had always associated astronomy
with astrology.  He considered that the phenomena of the heavenly
bodies always had some significance in connection with human
affairs.  Tycho was also a poet, and in the united capacity of
poet, astrologer, and astronomer, he posted up some verses
in the college at Rostock announcing that the lunar eclipse was a
prognostication of the death of the great Turkish Sultan,
whose mighty deeds at that time filled men's minds.  Presently
news did arrive of the death of the Sultan, and Tycho was
accordingly triumphant; but a little later it appeared that the
decease had taken place BEFORE the eclipse, a circumstance which
caused many a laugh at Tycho's expense.

[PLATE:  TYCHO'S ASTRONOMIC SEXTANT.
(Made of steel:  the arms, AB, AC, measure 4 ft.)

PLATE:  TYCHO'S EQUATORIAL ARMILLARY.
(The meridian circle, E B C A D, made of solid steel,
is nearly 6 ft. in diameter.)]

Tycho being of a somewhat turbulent disposition, it appears that,
while at the University of Rostock, he had a serious quarrel with
another Danish nobleman.  We are not told for certain what was the
cause of the dispute.  It does not, however, seem to have had any
more romantic origin than a difference of opinion as to which of
them knew the more mathematics.  They fought, as perhaps it was
becoming for two astronomers to fight, under the canopy of
heaven in utter darkness at the dead of night, and the duel
was honourably terminated when a slice was taken off Tycho's nose
by the insinuating sword of his antagonist.  For the repair of
this injury the ingenuity of the great instrument-maker was here
again useful, and he made a substitute for his nose "with a
composition of gold and silver."  The imitation was so good that
it is declared to have been quite equal to the original.  Dr.
Lodge, however, pointedly observes that it does not appear whether
this remark was made by a friend or an enemy.

[PLATE:  THE GREAT AUGSBURG QUADRANT.
(Built of heart of oak; the radii about 19 ft.)

PLATE:  TYCHO'S "NEW SCHEME OF THE TERRESTRIAL SYSTEM," 1577.]

The next few years Tycho spent in various places ardently pursuing
somewhat varied branches of scientific study.  At one time we hear
of him assisting an astronomical alderman, in the ancient city of
Augsburg, to erect a tremendous wooden machine--a quadrant of
19-feet radius--to be used in observing the heavens.  At another
time we learn that the King of Denmark had recognised the talents
of his illustrious subject, and promised to confer on him a
pleasant sinecure in the shape of a canonry, which would assist
him with the means for indulging his scientific pursuits.  Again
we are told that Tycho is pursuing experiments in chemistry with
the greatest energy, nor is this so incompatible as might at first
be thought with his devotion to astronomy.  In those early days
of knowledge the different sciences seemed bound together by
mysterious bonds.  Alchemists and astrologers taught that the
several planets were correlated in some mysterious manner with the
several metals.  It was, therefore hardly surprising that Tycho
should have included a study of the properties of the metals in
the programme of his astronomical work.

[PLATE:  URANIBORG AND ITS GROUNDS.

PLATE:  GROUND-PLAN OF THE OBSERVATORY.]

An event, however, occurred in 1572 which stimulated Tycho's
astronomical labours, and started him on his life's
work.  On the 11th of November in that year, he was returning home
to supper after a day's work in his laboratory, when he happened
to lift his face to the sky, and there he beheld a brilliant new
star.  It was in the constellation of Cassiopeia, and occupied a
position in which there had certainly been no bright star visible
when his attention had last been directed to that part of the
heavens.  Such a phenomenon was so startling that he found it
hard to trust the evidence of his senses.  He thought he must be
the subject of some hallucination.  He therefore called to the
servants who were accompanying him, and asked them whether they,
too, could see a brilliant object in the direction in which he
pointed.  They certainly could, and thus he became convinced that
this marvellous object was no mere creation of the fancy, but a
veritable celestial body--a new star of surpassing splendour which
had suddenly burst forth.  In these days of careful scrutiny of
the heavens, we are accustomed to the occasional outbreak of new
stars.  It is not, however, believed that any new star which has
ever appeared has displayed the same phenomenal brilliance as was
exhibited by the star of 1572.

This object has a value in astronomy far greater than it
might at first appear.  It is true, in one sense, that Tycho
discovered the new star, but it is equally true, in a different
sense, that it was the new star which discovered Tycho.  Had it
not been for this opportune apparition, it is quite possible that
Tycho might have found a career in some direction less beneficial
to science than that which he ultimately pursued.

[PLATE: THE OBSERVATORY OF URANIBORG, ISLAND OF HVEN.]

When he reached his home on this memorable evening, Tycho
immediately applied his great quadrant to the measurement of the
place of the new star.  His observations were specially directed
to the determination of the distance of the object.  He rightly
conjectured that if it were very much nearer to us than the stars
in its vicinity, the distance of the brilliant body might be
determined in a short time by the apparent changes in its distance
from the surrounding points.  It was speedily demonstrated that
the new star could not be as near as the moon, by the simple
fact that its apparent place, as compared with the stars in its
neighbourhood, was not appreciably altered when it was observed
below the pole, and again above the pole at an interval of twelve
hours.  Such observations were possible, inasmuch as the star was
bright enough to be seen in full daylight.  Tycho thus showed
conclusively that the body was so remote that the diameter of the
earth bore an insignificant ratio to the star's distance.  His
success in this respect is the more noteworthy when we find that
many other observers, who studied the same object, came to the
erroneous conclusion that the new star was quite as near as the
moon, or even much nearer.  In fact, it may be said, that with
regard to this object Tycho discovered everything which could
possibly have been discovered in the days before telescopes were
invented.  He not only proved that the star's distance was too
great for measurement, but he showed that it had no proper motion
on the heavens.  He recorded the successive changes in its
brightness from week to week, as well as the fluctuations in hue
with which the alterations in lustre were accompanied.

It seems, nowadays, strange to find that such thoroughly
scientific observations of the new star as those which Tycho made,
possessed, even in the eyes of the great astronomer himself, a
profound astrological significance.  We learn from Dr. Dreyer
that, in Tycho's opinion, "the star was at first like Venus and
Jupiter, and its effects will therefore, first, be pleasant; but
as it then became like Mars, there will next come a period of
wars, seditions, captivity, and death of princes, and destruction
of cities, together with dryness and fiery meteors in the
air, pestilence, and venomous snakes.  Lastly, the star became
like Saturn, and thus will finally come a time of want, death,
imprisonment, and all kinds of sad things!"  Ideas of this kind
were, however, universally entertained.  It seemed, indeed,
obvious to learned men of that period that such an apparition must
forebode startling events.  One of the chief theories then held
was, that just as the Star of Bethlehem announced the first coming
of Christ, so the second coming, and the end of the world, was
heralded by the new star of 1572.

The researches of Tycho on this object were the occasion of his
first appearance as an author.  The publication of his book was
however, for some time delayed by the urgent remonstrances of his
friends, who thought it was beneath the dignity of a nobleman to
condescend to write a book.  Happily, Tycho determined to brave
the opinion of his order; the book appeared, and was the first of
a series of great astronomical productions from the same pen.

[PLATE:  EFFIGY ON TYCHO'S TOMB AT PRAGUE.]

The fame of the noble Dane being now widespread, the King of
Denmark entreated him to return to his native country, and to
deliver a course of lectures on astronomy in the University of
Copenhagen.  With some reluctance he consented, and his
introductory oration has been preserved.  He dwells, in fervent
language, upon the beauty and the interest of the celestial
phenomena.  He points out the imperative necessity of
continuous and systematic observation of the heavenly bodies in
order to extend our knowledge.  He appeals to the practical
utility of the science, for what civilised nation could exist
without having the means of measuring time?  He sets forth how the
study of these beautiful objects "exalts the mind from earthly
and trivial things to heavenly ones;" and then he winds up by
assuring them that a special use of astronomy is that it enables
us to draw conclusions from the movements in the celestial regions
as to human fate."

An interesting event, which occurred in 1572, distracted Tycho's
attention from astronomical matters.  He fell in love.  The young
girl on whom his affections were set appears to have sprung from
humble origin.  Here again his august family friends sought to
dissuade him from a match they thought unsuitable for a nobleman.
But Tycho never gave way in anything.  It is suggested that he did
not seek a wife among the highborn dames of his
own rank from the dread that the demands of a fashionable lady
would make too great an inroad on the time that he wished to
devote to science.  At all events, Tycho's union seems to have
been a happy one, and he had a large family of children; none of
whom, however, inherited their father's talents.

[PLATE: TYCHO'S MURAL QUADRANT PICTURE, URANIBORG.]

Tycho had many scientific friends in Germany, among whom his work
was held in high esteem.  The treatment that he there met with
seemed to him so much more encouraging than that which he received
in Denmark that he formed the notion of emigrating to Basle and
making it his permanent abode.  A whisper of this intention was
conveyed to the large-hearted King of Denmark, Frederick II.  He
wisely realised how great would be the fame which would accrue to
his realm if he could induce Tycho to remain within Danish
territory and carry on there the great work of his life.  A
resolution to make a splendid proposal to Tycho was immediately
formed.  A noble youth was forthwith despatched as a messenger,
and ordered to travel day and night until he reached Tycho, whom
he was to summon to the king.  The astronomer was in bed on the
morning Of 11th February, 1576, when the message was delivered.
Tycho, of course, set off at once and had an audience of the king
at Copenhagen.  The astronomer explained that what he wanted was
the means to pursue his studies unmolested, whereupon the king
offered him the Island of Hven, in the Sound near Elsinore.
There he would enjoy all the seclusion that he could desire.  The
king further promised that he would provide the funds necessary
for building a house and for founding the greatest observatory
that had ever yet been reared for the study of the heavens.  After
due deliberation and consultation with his friends, Tycho accepted
the king's offer.  He was forthwith granted a pension, and a deed
was drawn up formally assigning the Island of Hven to his use all
the days of his life.

The foundation of the famous castle of Uraniborg was laid on 30th
August, 1576.  The ceremony was a formal and imposing one, in
accordance with Tycho's ideas of splendour.  A party of scientific
friends had assembled, and the time had been chosen so that the
heavenly bodies were auspiciously placed.  Libations of costly
wines were poured forth, and the stone was placed with due
solemnity.  The picturesque character of this wonderful temple for
the study of the stars may be seen in the figures with which this
chapter is illustrated.

One of the most remarkable instruments that has ever been employed
in studying the heavens was the mural quadrant which Tycho erected
in one of the apartments of Uraniborg.  By its means the altitudes
of the celestial bodies could be observed with much greater
accuracy than had been previously attainable.  This wonderful
contrivance is represented on the preceding page.  It will be
observed that the walls of the room are adorned by pictures with a
lavishness of decoration not usually to be found in scientific
establishments.

A few years later, when the fame of the observatory at Hven became
more widely spread, a number of young men flocked to Tycho to
study under his direction.  He therefore built another observatory
for their use in which the instruments were placed in subterranean
rooms of which only the roofs appeared above the ground.  There
was a wonderful poetical inscription over the entrance to this
underground observatory, expressing the astonishment of Urania at
finding, even in the interior of the earth, a cavern devoted to
the study of the heavens.  Tycho was indeed always fond of
versifying, and he lost no opportunity of indulging this taste
whenever an occasion presented itself.

Around the walls of the subterranean observatory were the pictures
of eight astronomers, each with a suitable inscription--one of
these of course represented Tycho himself, and beneath were
written words to the effect that posterity should judge of his work.
The eighth picture depicted an astronomer who has not yet come into
existence.  Tychonides was his name, and the inscription presses
the modest hope that when he does appear he will be worthy of his
great predecessor.  The vast expenses incurred in the erection and
the maintenance of this strange establishment were defrayed by a
succession of grants from the royal purse.

For twenty years Tycho laboured hard at Uraniborg in the pursuit
of science.  His work mainly consisted in the determination of
the places of the moon, the planets, and the stars on the
celestial sphere.  The extraordinary pains taken by Tycho
to have his observations as accurate as his instruments would
permit, have justly entitled him to the admiration of all
succeeding astronomers.  His island home provided the means of
recreation as well as a place for work.  He was surrounded by his
family, troops of friends were not wanting, and a pet dwarf seems
to have been an inmate of his curious residence.  By way of change
from his astronomical labours he used frequently to work with his
students in his chemical laboratory.  It is not indeed known what
particular problems in chemistry occupied his attention.  We are
told, however, that he engaged largely in the production of
medicines, and as these appear to have been dispensed gratuitously
there was no lack of patients.

Tycho's imperious and grasping character frequently brought him
into difficulties, which seem to have increased with his advancing
years.  He had ill-treated one of his tenants on Hven, and an
adverse decision by the courts seems to have greatly exasperated
the astronomer.  Serious changes also took place in his relations
to the court at Copenhagen.  When the young king was crowned in
1596, he reversed the policy of his predecessor with reference to
Hven.  The liberal allowances to Tycho were one after another
withdrawn, and finally even his pension was stopped.  Tycho
accordingly abandoned Hven in a tumult of rage and mortification.
A few years later we find him in Bohemia a prematurely aged man,
and he died on the 24th October, 1601.




GALILEO.



Among the ranks of the great astronomers it would be difficult
to find one whose life presents more interesting features and
remarkable vicissitudes than does that of Galileo.  We may
consider him as the patient investigator and brilliant discoverer.
We may consider him in his private relations, especially to his
daughter, Sister Maria Celeste, a woman of very remarkable
character; and we have also the pathetic drama at the close of
Galileo's life, when the philosopher drew down upon himself the
thunders of the Inquisition.

The materials for the sketch of this astonishing man are
sufficiently abundant.  We make special use in this place of
those charming letters which his daughter wrote to him from her
convent home.  More than a hundred of these have been preserved,
and it may well be doubted whether any more beautiful and touching
series of letters addressed to a parent by a dearly loved child
have ever been written.  An admirable account of this
correspondence is contained in a little book entitled "The Private
Life of Galileo," published anonymously by Messrs. Macmillan in
1870, and I have been much indebted to the author of that volume
for many of the facts contained in this chapter.

Galileo was born at Pisa, on 18th February, 1564.  He was the
eldest son of Vincenzo de' Bonajuti de' Galilei, a Florentine
noble.  Notwithstanding his illustrious birth and descent, it
would seem that the home in which the great philosopher's
childhood was spent was an impoverished one.  It was obvious at
least that the young Galileo would have to be provided with some
profession by which he might earn a livelihood.  From his father
he derived both by inheritance and by precept a keen taste for
music, and it appears that he became an excellent performer on the
lute.  He was also endowed with considerable artistic power, which
he cultivated diligently.  Indeed, it would seem that for some
time the future astronomer entertained the idea of devoting
himself to painting as a profession.  His father, however, decided
that he should study medicine.  Accordingly, we find that when
Galileo was seventeen years of age, and had added a knowledge of
Greek and Latin to his acquaintance with the fine arts, he was
duly entered at the University of Pisa.

Here the young philosopher obtained some inkling of mathematics,
whereupon he became so much interested in this branch of science,
that he begged to be allowed to study geometry.  In compliance
with his request, his father permitted a tutor to be engaged for
this purpose; but he did so with reluctance, fearing that the
attention of the young student might thus be withdrawn from that
medical work which was regarded as his primary occupation.  The
event speedily proved that these anxieties were not without some
justification.  The propositions of Euclid proved so engrossing to
Galileo that it was thought wise to avoid further distraction by
terminating the mathematical tutor's engagement.  But it was too
late for the desired end to be attained.  Galileo had now made
such progress that he was able to continue his geometrical studies
by himself.  Presently he advanced to that famous 47th proposition
which won his lively admiration, and on he went until he had
mastered the six books of Euclid, which was a considerable
achievement for those days.

The diligence and brilliance of the young student at Pisa did not,
however, bring him much credit with the University authorities.
In those days the doctrines of Aristotle were regarded as the
embodiment of all human wisdom in natural science as well as in
everything else.  It was regarded as the duty of every student
to learn Aristotle off by heart, and any disposition to doubt or
even  to question the doctrines of the venerated teacher was
regarded as intolerable presumption.  But young Galileo had the
audacity to think for himself about the laws of nature.  He would
not take any assertion of fact on the authority of Aristotle when
he had the means of questioning nature directly as to its truth or
falsehood.  His teachers thus came to regard him as a somewhat
misguided youth, though they could not but respect the unflagging
industry with which he amassed all the knowledge he could acquire.

[PLATE:  GALILEO'S PENDULUM.]

We are so accustomed to the use of pendulums in our clocks that
perhaps we do not often realise that the introduction of this
method of regulating time-pieces was really a notable invention
worthy the fame of the great astronomer to whom it was due.  It
appears that sitting one day in the Cathedral of Pisa, Galileo's
attention became concentrated on the swinging of a chandelier
which hung from the ceiling.  It struck him as a significant
point, that whether the arc through which the pendulum oscillated
was a long one or a short one, the time occupied in each vibration
was sensibly the same.  This suggested to the thoughtful observer
that a pendulum would afford the means by which a time-keeper
might be controlled, and accordingly Galileo constructed for the
first time a clock on this principle.  The immediate object sought
in this apparatus was to provide a means of aiding physicians in
counting the pulses of their patients.

The talents Of Galileo having at length extorted due recognition
from the authorities, he was appointed, at the age of twenty-five,
Professor of Mathematics at the University of Pisa.  Then came
the time when he felt himself strong enough to throw down the
gauntlet to the adherents of the old philosophy.  As a necessary
part of his doctrine on the movement of bodies Aristotle had
asserted that the time occupied by a stone in falling depends upon
its weight, so that the heavier the stone the less time would it
require to fall from a certain height to the earth.  It might
have been thought that a statement so easily confuted by the
simplest experiments could never have maintained its position
in any accepted scheme of philosophy.  But Aristotle had said it,
and to anyone who ventured to express a doubt the ready sneer
was forthcoming,  "Do you think yourself a cleverer man than
Aristotle?"  Galileo determined to demonstrate in the most
emphatic manner the absurdity of a doctrine which had for
centuries received the sanction of the learned.  The summit
of the Leaning Tower of Pisa offered a highly dramatic site for
the great experiment.  The youthful professor let fall from the
overhanging top a large heavy body and a small light body
simultaneously.  According to Aristotle the large body ought to
have reached the ground much sooner than the small one, but such
was found not to be the case.  In the sight of a large concourse
of people the simple fact was demonstrated that the two bodies
fell side by side, and reached the ground at the same time.
Thus the first great step was taken in the overthrow of that
preposterous system of unquestioning adhesion to dogma, which
had impeded the development of the knowledge of nature for nearly
two thousand years.

This revolutionary attitude towards the ancient beliefs was not
calculated to render Galileo's relations with the University
authorities harmonious.  He had also the misfortune to make
enemies in other quarters.  Don Giovanni de Medici, who was then
the Governor of the Port of Leghorn, had designed some contrivance
by which he proposed to pump out a dock.  But Galileo showed up
the absurdity of this enterprise in such an aggressive manner that
Don Giovanni took mortal offence, nor was he mollified when the
truths of Galileo's criticisms were abundantly verified by the
total failure of his ridiculous invention.  In various ways
Galileo was made to feel his position at Pisa so unpleasant that
he was at length compelled to abandon his chair in the University.
The active exertions of his friends, of whom Galileo was so
fortunate as to have had throughout his life an abundant supply,
then secured his election to the Professorship of Mathematics at
Padua, whither he went in 1592.

[PLATE:  PORTRAIT OF GALILEO.]

It was in this new position that Galileo entered on that
marvellous career of investigation which was destined to
revolutionize science.  The zeal with which he discharged his
professorial duties was indeed of the most unremitting character.
He speedily drew such crowds to listen to his discourses on
Natural Philosophy that his lecture-room was filled to
overflowing.  He also received many private pupils in
his house for special instruction.  Every moment that could be
spared from these labours was devoted to his private study and to
his incessant experiments.

Like many another philosopher who has greatly extended our
knowledge of nature, Galileo had a remarkable aptitude for the
invention of instruments designed for philosophical research.
To facilitate his practical work, we find that in 1599 he had
engaged a skilled workman who was to live in his house, and thus
be constantly at hand to try the devices for ever springing from
Galileo's fertile brain.  Among the earliest of his inventions
appears to have been the thermometer, which he constructed in
1602.  No doubt this apparatus in its primitive form differed in
some respects from the contrivance we call by the same name.
Galileo at first employed water as the agent, by the expansion of
which the temperature was to be measured.  He afterwards saw the
advantage of using spirits for the same purpose.  It was not until
about half a century later that mercury came to be recognised as
the liquid most generally suitable for the thermometer.

The time was now approaching when Galileo was to make that
mighty step in the advancement of human knowledge which followed
on the application of the telescope to astronomy.  As to how his
idea of such an instrument originated, we had best let him tell
us in his own words.  The passage is given in a letter which he
writes to his brother-in-law, Landucci.

"I write now because I have a piece of news for you, though
whether you will be glad or sorry to hear it I cannot say; for
I have now no hope of returning to my own country, though the
occurrence which has destroyed that hope has had results both
useful and honourable.  You must know, then, that two months ago
there was a report spread here that in Flanders some one had
presented to Count Maurice of Nassau a glass manufactured in such
a way as to make distant objects appear very near, so that a man
at the distance of two miles could be clearly seen.  This seemed
to me so marvellous that I began to think about it.  As it
appeared to me to have a foundation in the Theory of Perspective,
I set about contriving how to make it, and at length I found out,
and have succeeded so well that the one I have made is far
superior to the Dutch telescope.  It was reported in Venice that
I had made one, and a week since I was commanded to show it to his
Serenity and to all the members of the senate, to their infinite
amazement.  Many gentlemen and senators, even the oldest, have
ascended at various times the highest bell-towers in Venice to
spy out ships at sea making sail for the mouth of the harbour,
and have seen them clearly, though without my telescope they
would have been invisible for more than two hours.  The effect
of this instrument is to show an object at a distance of say
fifty miles, as if it were but five miles."

The remarkable properties of the telescope at once commanded
universal attention among intellectual men.  Galileo received
applications from several quarters for his new instrument, of
which it would seem that he manufactured a large number to be
distributed as gifts to various illustrious personages.

But it was reserved for Galileo himself to make that application
of the instrument to the celestial bodies by which its peculiar
powers were to inaugurate the new era in astronomy.  The first
discovery that was made in this direction appears to have been
connected with the number of the stars.  Galileo saw to his
amazement that through his little tube he could count ten
times as many stars in the sky as his unaided eye could detect.
Here was, indeed, a surprise.  We are now so familiar with the
elementary facts of astronomy that it is not always easy to
realise how the heavens were interpreted by the observers in
those ages prior to the invention of the telescope.  We can
hardly, indeed, suppose that Galileo, like the majority of those
who ever thought of such matters, entertained the erroneous
belief that the stars were on the surface of a sphere at equal
distances from the observer.  No one would be likely to have
retained his belief in such a doctrine when he saw how the number
of visible stars could be increased tenfold by means of Galileo's
telescope.  It would have been almost impossible to refuse to
draw the inference that the stars thus brought into view were
still more remote objects which the telescope was able to reveal,
just in the same way as it showed certain ships to the astonished
Venetians, when at the time these ships were beyond the reach of
unaided vision.

Galileo's celestial discoveries now succeeded each other rapidly.
That beautiful Milky Way, which has for ages been the object of
admiration to all lovers of nature, never disclosed its true
nature to the eye of man till the astronomer of Padua turned on it
his magic tube.  The splendid zone of silvery light was then
displayed as star-dust scattered over the black background of
the sky.  It was observed that though the individual stars were
too small to be seen severally without optical aid, yet such was
their incredible number that the celestial radiance produced that
luminosity with which every stargazer was so familiar.

But the greatest discovery made by the telescope in these early
days, perhaps, indeed, the greatest discovery that the telescope
has ever accomplished, was the detection of the system of four
satellites revolving around the great planet Jupiter.  This
phenomenon was so wholly unexpected by Galileo that, at first,
he could hardly believe his eyes.  However, the reality of the
existence of a system of four moons attending the great planet
was soon established beyond all question.  Numbers of great
personages crowded to Galileo to see for themselves this beautiful
miniature representing the sun with its system of revolving
planets.

Of course there were, as usual, a few incredulous people who
refused to believe the assertion that four more moving bodies
had to be added to the planetary system.  They scoffed at the
notion; they said the satellites may have been in the telescope,
but that they were not in the sky.  One sceptical philosopher is
reported to have affirmed, that even if he saw the moons of
Jupiter
himself he would not believe in them, as their existence was
contrary to the principles of common-sense!

There can be no doubt that a special significance attached to
the new discovery at this particular epoch in the history of
science.  It must be remembered that in those days the doctrine
of Copernicus, declaring that the sun, and not the earth, was
the centre of the system, that the earth revolved on its axis
once a day, and that it described a mighty circle round the sun
once a year, had only recently been promulgated.  This new view
of the scheme of nature had been encountered with the most
furious opposition.  It may possibly have been that Galileo
himself had not felt quite confident in the soundness of the
Copernican theory, prior to the discovery of the satellites of
Jupiter.  But when a picture was there exhibited in which a
number of relatively small globes were shown to be revolving
around a single large globe in the centre, it seemed impossible
not to feel that the beautiful spectacle so displayed was an
emblem of the relations of the planets to the sun.  It was
thus made manifest to Galileo that the Copernican theory of
the planetary system must be the true one.  The momentous import
of this opinion upon the future welfare of the great philosopher
will presently appear.

It would seem that Galileo regarded his residence at Padua as a
state of undesirable exile from his beloved Tuscany.  He had
always a yearning to go back to his own country and at last the
desired opportunity presented itself.  For now that Galileo's
fame had become so great, the Grand Duke of Tuscany desired to
have the philosopher resident at Florence, in the belief that he
would shed lustre on the Duke's dominions.  Overtures were
accordingly made to Galileo, and the consequence was that in 1616
we find him residing at Florence, bearing the title of
Mathematician and Philosopher to the Grand Duke.

Two daughters, Polissena and Virginia, and one son, Vincenzo,
had been born to Galileo in Padua.  It was the custom in those
days that as soon as the daughter of an Italian gentleman had
grown up, her future career was somewhat summarily decided.
Either a husband was to be forthwith sought out, or she was to
enter the convent with the object of taking the veil as a
professed nun.  It was arranged that the two daughters of
Galileo, while still scarcely more than children, should both
enter the Franciscan convent of St. Matthew, at Arcetri.  The
elder daughter Polissena, took the name of Sister Maria Celeste,
while Virginia became Sister Arcangela.  The latter seems to
have been always delicate and subject to prolonged melancholy,
and she is of but little account in the narrative of the life of
Galileo.  But Sister Maria Celeste, though never leaving the
convent, managed to preserve a close intimacy with her beloved
father.  This was maintained only partly by Galileo's visits,
which were very irregular and were, indeed, often suspended for
long intervals.  But his letters to this daughter were evidently
frequent and affectionate, especially in the latter part of his
life.  Most unfortunately, however, all his letters have been
lost.  There are grounds for believing that they were deliberately
destroyed when Galileo was seized by the Inquisition, lest they
should have been used as evidence against him, or lest they
should have compromised the convent where they were received.
But Sister Maria Celeste's letters to her father have happily
been preserved, and most touching these letters are.  We can
hardly read them without thinking how the sweet and gentle nun
would have shrunk from the idea of their publication.

Her loving little notes to her "dearest lord and father," as she
used affectionately to call Galileo, were almost invariably
accompanied by some gift, trifling it may be, but always the best
the poor nun had to bestow.  The tender grace of these endearing
communications was all the more precious to him from the fact that
the rest of Galileo's relatives were of quite a worthless
description.  He always acknowledged the ties of his kindred in the
most generous way, but their follies and their vices, their
selfishness and their importunities, were an incessant source of
annoyance to him, almost to the last day of his life.

On 19th December, 1625, Sister Maria Celeste writes:--

"I send two baked pears for these days of vigil.  But as the
greatest treat of all, I send you a rose, which ought to please
you extremely, seeing what a rarity it is at this season; and with
the rose you must accept its thorns, which represent the bitter
passion of our Lord, whilst the green leaves represent the hope we
may entertain that through the same sacred passion we, having
passed through the darkness of the short winter of our mortal
life, may attain to the brightness and felicity of an eternal
spring in heaven."

When the wife and children of Galileo's shiftless brother came to
take up their abode in the philosopher's home, Sister Maria
Celeste feels glad to think that her father has now some one who,
however imperfectly may fulfil the duty of looking after him.  A
graceful note on Christmas Eve accompanies her little gifts.  She
hopes that--

"In these holy days the peace of God may rest on him and all the
house.  The largest collar and sleeves I mean for Albertino, the
other two for the two younger boys, the little dog for baby, and
the cakes for everybody, except the spice-cakes, which are for
you.  Accept the good-will which would readily do much more."

The extraordinary forbearance with which Galileo continually
placed his time, his purse, and his influence at the service of
those who had repeatedly proved themselves utterly unworthy of his
countenance, is thus commented on by the good nun.--

"Now it seems to me, dearest lord and father, that your lordship
is walking in the right path, since you take hold of every
occasion that presents itself to shower continual benefits on
those who only repay you with ingratitude.  This is an action
which is all the more virtuous and perfect as it is the more
difficult."

When the plague was raging in the neighbourhood, the loving
daughter's solicitude is thus shown:--

"I send you two pots of electuary as a preventive against the
plague.  The one without the label consists of dried figs,
walnuts, rue, and salt, mixed together with honey.  A piece of the
size of a walnut to be taken in the morning, fasting, with a
little Greek wine."

The plague increasing still more, Sister Maria Celeste obtained
with much difficulty, a small quantity of a renowned liqueur, made
by Abbess Ursula, an exceptionally saintly nun.  This she sends to
her father with the words:--

"I pray your lordship to have faith in this remedy.
For if you have so much faith in my poor miserable prayers, much
more may you have in those of such a holy person; indeed, through
her merits you may feel sure of escaping all danger from the
plague."

Whether Galileo took the remedy we do not know, but at all events
he escaped the plague.

[PLATE:  THE VILLA ARCETRI.
Galileo's residence, where Milton visited him.]

From Galileo's new home in Florence the telescope was again
directed to the skies, and again did astounding discoveries reward
the atronomer's labours.  The great success which he had met with
in studying Jupiter naturally led Galileo to look at Saturn.  Here
he saw a spectacle which was sufficiently amazing, though he
failed to interpret it accurately.  It was quite manifest that
Saturn did not exhibit a simple circular disc like Jupiter, or
like Mars.  It seemed to Galileo as if the planet consisted of
three bodies, a large globe in the centre, and a smaller one on
each side.  The enigmatical nature of the discovery led Galileo
to announce it in an enigmatical manner.  He published a string
of letters which, when duly transposed, made up a sentence which
affirmed that the planet Saturn was threefold.  Of course we now
know that this remarkable appearance of the planet was due to the
two projecting portions of the ring.  With the feeble power of
Galileo's telescope, these seemed merely like small globes or
appendages to the large central body.

The last Of Galileo's great astronomical discoveries related to
the libration of the moon.  I think that the detection of this
phenomenon shows his acuteness of observation more remarkably than
does any one of his other achievements with the telescope.  It is
well known that the moon constantly keeps the same face turned
towards the earth.  When, however, careful measurements have been
made with regard to the spots and marks on the lunar surface, it
is found that there is a slight periodic variation which permits
us to see now a little to the east, or to the west, now a little
to the north or to the south of the average lunar disc.

But the circumstances which make the career of Galileo so
especially interesting from the biographer's point of view, are
hardly so much the triumphs that he won as the sufferings that he
endured.  The sufferings and the triumphs were, however, closely
connected, and it is fitting that we should give due consideration
to what was perhaps the greatest drama in the history of science.

On the appearance of the immortal work of Copernicus, in which it
was taught that the earth rotated on its axis, and that the earth,
like the other planets, revolved round the sun, orthodoxy stood
aghast.  The Holy Roman Church submitted this treatise, which bore
the name "De Revolutionibus Orbium Coelestium," to the
Congregation of the Index.  After due examination it was condemned
as heretical in 1615.  Galileo was suspected, on no doubt
excellent grounds, of entertaining the objectionable views of
Copernicus.  He was accordingly privately summoned before Cardinal
Bellarmine on 26th February 1616,
and duly admonished that he was on no account to teach or to
defend the obnoxious doctrines.  Galileo was much distressed by
this intimation.  He felt it a serious matter to be deprived of
the privilege of discoursing with his friends about the Copernican
system, and of instructing his disciples in the principles of the
great theory of whose truth he was perfectly convinced.  It pained
him, however, still more to think, devout Catholic as he was, that
such suspicions of his fervent allegiance to his Church should
ever have existed, as were implied by the words and monitions of
Cardinal Bellarmine.

In 1616, Galileo had an interview with Pope Paul V., who received
the great astronomer very graciously, and walked up and down with
him in conversation for three-quarters of an hour.  Galileo
complained to his Holiness of the attempts made by his enemies to
embarrass him with the authorities of the Church, but the Pope
bade him be comforted.  His Holiness had himself no doubts of
Galileo's orthodoxy, and he assured him that the Congregation of
the Index should give Galileo no further trouble so long as Paul
V. was in the chair of St. Peter.

On the death of Paul V. in 1623, Maffeo Barberini was elected
Pope, as Urban VIII.  This new Pope, while a cardinal, had been an
intimate friend of Galileo's, and had indeed written Latin verses
in praise of the great astronomer and his discoveries.  It was
therefore not unnatural for Galileo to think that the time had
arrived when, with the use of due circumspection, he might
continue his studies and his writings, without fear of incurring
the displeasure of the Church.  Indeed, in 1624, one of Galileo's
friends writing from Rome, urges Galileo to visit the city again,
and added that--

"Under the auspices of this most excellent, learned, and benignant
Pontiff, science must flourish.  Your arrival will be welcome to
his Holiness.  He asked me if you were coming, and when, and in
short, he seems to love and esteem you more than ever."

The visit was duly paid, and when Galileo returned to Florence,
the Pope wrote a letter from which the following is an extract,
commanding the philosopher to the good offices of the young
Ferdinand, who had shortly before succeeded his father in the
Grand Duchy of Tuscany.

"We find in Galileo not only literary distinction, but also the
love of piety, and he is also strong in those qualities by which
the pontifical good-will is easily obtained.  And now, when he has
been brought to this city to congratulate us on our elevation, we
have very lovingly embraced him; nor can we suffer him to return
to the country whither your liberality calls him, without an ample
provision of pontifical love.  And that you may know how dear he
is to us, we have willed to give him this honourable testimonial
of virtue and piety.  And we further signify that every benefit
which you shall confer upon him, imitating or even surpassing your
father's liberality, will conduce to our gratification."

The favourable reception which had been accorded to him by
Pope Urban VIII. seems to have led Galileo to expect that there
might be some corresponding change in the attitude of the Papal
authorities on the great question of the stability of the earth.
He accordingly proceeded with the preparation of the chief work
of his life, "The Dialogue of the two Systems."  It was submitted
for inspection by the constituted authorities.  The Pope himself
thought that, if a few conditions which he laid down were duly
complied with, there could be no objection to the publication of
the work.  In the first place, the title of the book was to be so
carefully worded as to show plainly that the Copernican doctrine
was merely to be regarded as an hypothesis, and not as a
scientific fact.  Galileo was also instructed to conclude the book
with special arguments which had been supplied by the Pope
himself, and which appeared to his Holiness to be quite conclusive
against the new doctrine of Copernicus.

Formal leave for the publication of the Dialogue was then given
to Galileo by the Inquisitor General, and it was accordingly sent
to the press.  It might be thought that the anxieties of the
astronomer about his book would then have terminated.  As a matter
of fact, they had not yet seriously begun.  Riccardi, the
Master of the Sacred Palace, having suddenly had some further
misgivings, sent to Galileo for the manuscript while the work was
at the printer's, in order that the doctrine it implied might be
once again examined.  Apparently, Riccardi had come to the
conclusion that he had not given the matter sufficient attention,
when the authority to go to press had been first and, perhaps,
hastily given.  Considerable delay in the issue of the book was
the result of these further deliberations.  At last, however, in
June, 1632, Galileo's great work, "The Dialogue of the two
Systems," was produced for the instruction of the world, though
the occasion was fraught with ruin to the immortal author.

[PLATE: FACSIMILE SKETCH OF LUNAR SURFACE BY GALILEO.]

The book, on its publication, was received and read with the
greatest avidity.  But presently the Master of The Sacred Palace
found reason to regret that he had given his consent to its
appearance.  He accordingly issued a peremptory order to
sequestrate every copy in Italy. This sudden change in the Papal
attitude towards Galileo formed the subject of a strong
remonstrance addressed to the Roman authorities by the Grand Duke
of Tuscany.  The Pope himself seemed to have become impressed all
at once with the belief that the work contained matter of an
heretical description.  The general interpretation put upon the
book seems to have shown the authorities that they had mistaken
its true tendency, notwithstanding the fact that it had been
examined again and again by theologians deputed for the duty.  To
the communication from the Grand Duke the Pope returned answer,
that he had decided to submit the book to a congregation of
"learned, grave, and saintly men," who would weigh every word in
it.  The views of his Holiness personally on the subject were
expressed in his belief that the Dialogue contained the most
perverse matter that could come into a reader's hands.

The Master of the Sacred Palace was greatly blamed by the
authorities for having given his sanction to its issue.  He
pleaded that the book had not been printed in the precise terms of
the original manuscript which had been submitted to him.  It was
also alleged that Galileo had not adhered to his promise of
inserting properly the arguments which the Pope himself had given
in support of the old and orthodox view.  One of these had, no
doubt, been introduced, but, so far from mending Galileo's case,
it had made matters really look worse for the poor philosopher.
The Pope's argument had been put into the mouth of one of the
characters in the Dialogue named "Simplicio."  Galileo's enemies
maintained that by adopting such a method for the expression of
his Holiness's opinion, Galileo had intended to hold the Pope
himself up to ridicule.  Galileo's friends maintained that nothing
could have been farther from his intention.  It seems, however,
highly probable that the suspicions thus aroused had something to
say to the sudden change of front on the part of the Papal
authorities.

On 1st October, 1632, Galileo received an order to appear before
the Inquisition at Rome on the grave charge of heresy.  Galileo,
of course, expressed his submission, but pleaded for a respite
from compliance with the summons, on the ground of his advanced
age and his failing health.  The Pope was, however, inexorable; he
said that he had warned Galileo of his danger while he was still
his friend.  The command could not be disobeyed.  Galileo might
perform the journey as slowly as he pleased, but it was
imperatively necessary for him to set forth and at once.

On 20th January, 1633, Galileo started on his weary journey to
Rome, in compliance with this peremptory summons.  On 13th
February he was received as the guest of Niccolini, the Tuscan
ambassador, who had acted as his wise and ever-kind friend
throughout the whole affair.  It seemed plain that the Holy Office
were inclined to treat Galileo with as much clemency and
consideration as was consistent with the determination that the
case against him should be proceeded with to the end.  The Pope
intimated that in consequence of his respect for the
Grand Duke of Tuscany he should permit Galileo to enjoy the
privilege, quite unprecedented for a prisoner charged with heresy,
of remaining as an inmate in the ambassador's house.  He ought,
strictly, to have been placed in the dungeons of the Inquisition.
When the examination of the accused had actually commenced,
Galileo was confined, not, indeed, in the dungeons, but in
comfortable rooms at the Holy Office.

By the judicious and conciliatory language of submission which
Niccolini had urged Galileo to use before the Inquisitors, they
were so far satisfied that they interceded with the Pope for his
release.  During the remainder of the trial Galileo was
accordingly permitted to go back to the ambassador's, where he was
most heartily welcomed.  Sister Maria Celeste, evidently thinking
this meant that the whole case was at an end, thus expresses
herself:--

"The joy that your last dear letter brought me, and the having to
read it over and over to the nuns, who made quite a jubilee on
hearing its contents, put me into such an excited state that at
last I got a severe attack of headache."

In his defence Galileo urged that he had already been acquitted
in 1616 by Cardinal Bellarmine, when a charge of heresy was
brought against him, and he contended that anything he might now
have done, was no more than he had done on the preceding occasion,
when the orthodoxy of his doctrines received solemn confirmation.
The Inquisition seemed certainly inclined to clemency, but the
Pope was not satisfied.  Galileo was accordingly summoned again on
the 21st June.  He was to be threatened with torture if he did not
forthwith give satisfactory explanations as to the reasons which
led him to write the Dialogue.  In this proceeding the Pope
assured the Tuscan ambassador that he was treating Galileo with
the utmost consideration possible in consequence of his esteem and
regard for the Grand Duke, whose servant Galileo was.  It was,
however, necessary that some exemplary punishment be meted out
to the astronomer, inasmuch as by the publication of the Dialogue
he had distinctly disobeyed the injunction of silence laid upon
him by the decree of 1616.  Nor was it admissible for Galileo to
plead that his book had been sanctioned by the Master of the
Sacred College, to whose inspection it had been again and again
submitted.  It was held, that if the Master of the Sacred College
had been unaware of the solemn warning the philosopher had already
received sixteen years previously, it was the duty of Galileo to
have drawn his attention to that fact.

On the 22nd June, 1633, Galileo was led to the great hall of the
Inquisition, and compelled to kneel before the cardinals there
assembled and hear his sentence.  In along document, most
elaborately drawn up, it is definitely charged against Galileo
that, in publishing the Dialogue, he committed the essentially
grave error of treating the doctrine of the earth's motion as
open to discussion.  Galileo knew, so the document affirmed,
that the Church had emphatically pronounced this notion to be
contrary to Holy Writ, and that for him to consider a doctrine so
stigmatized as having any shadow of probability in its favour was
an act of disrespect to the authority of the Church which could
not be overlooked.  It was also charged against Galileo that in
his Dialogue he has put the strongest arguments into the mouth,
not of those who supported the orthodox doctrine, but of those
who held the theory as to the earth's motion which the Church
had so deliberately condemned.

After due consideration of the defence made by the prisoner, it
was thereupon decreed that he had rendered himself vehemently
suspected of heresy by the Holy Office, and in consequence had
incurred all the censures and penalties of the sacred canons,
and other decrees promulgated against such persons.  The graver
portion of these punishments would be remitted, if Galileo would
solemnly repudiate the heresies referred to by an abjuration to
be pronounced by him in the terms laid down.

At the same time it was necessary to mark, in some emphatic
manner, the serious offence which had been committed, so that it
might serve both as a punishment to Galileo and as a warning to
others.  It was accordingly decreed that he should be condemned to
imprisonment in the Holy Office during the pleasure of the Papal
authorities, and that he should recite once a week for three years
the seven Penitential Psalms.

Then followed that ever-memorable scene in the great hall of the
Inquisition, in which the aged and infirm Galileo, the inventor of
the telescope and the famous astronomer, knelt down to abjure
before the most eminent and reverend Lords Cardinal, Inquisitors
General throughout the Christian Republic against heretical
depravity.  With his hands on the Gospels, Galileo was made to
curse and detest the false opinion that the sun was the centre of
the universe and immovable, and that the earth was not the centre
of the same, and that it moved.  He swore that for the future he
will never say nor write such things as may bring him under
suspicion, and that if he does so he submits to all the pains and
penalties of the sacred canons.  This abjuration was subsequently
read in Florence before Galileo's disciples, who had been
specially summoned to attend.

It has been noted that neither on the first occasion, in 1616, nor
on the second in 1633, did the reigning Pope sign the decrees
concerning Galileo.  The contention has accordingly been made that
Paul V. and Urban VIII. are both alike vindicated from any
technical responsibility for the attitude of the Romish Church
towards the Copernican doctrines.  The significance of this
circumstance has been commented on in connection with the doctrine
of the infallibility of the Pope.

We can judge of the anxiety felt by Sister Maria Celeste about her
beloved father during these terrible trials.  The wife of the
ambassador Niccolini, Galileo's steadfast friend, most kindly
wrote to give the nun whatever quieting assurances the case would
permit.  There is a renewed flow of these touching epistles from
the daughter to her father.  Thus she sends word--

"The news of your fresh trouble has pierced my soul with grief all
the more that it came quite unexpectedly."

And again, on hearing that he had been permitted to leave Rome,
she writes--

"I wish I could describe the rejoicing of all the mothers and
sisters on hearing of your happy arrival at Siena.  It was indeed
most extraordinary.  On hearing the news the Mother Abbess and
many of the nuns ran to me, embracing me and weeping for joy and
tenderness."

The sentence of imprisonment was at first interpreted leniently by
the Pope.  Galileo was allowed to reside in qualified durance in
the archbishop's house at Siena.  Evidently the greatest pain that
he endured arose from the forced separation from that daughter,
whom he had at last learned to love with an affection almost
comparable with that she bore to him.  She had often told him that
she never had any pleasure equal to that with which she rendered
any service to her father.  To her joy, she discovers that she can
relieve him from the task of reciting the seven Penitential Psalms
which had been imposed as a Penance:--

"I began to do this a while ago," she writes, "and it gives me
much pleasure.  First, because I am persuaded that prayer in
obedience to Holy Church must be efficacious; secondly, in order
to save you the trouble of remembering it.  If I had been able to
do more, most willingly would I have entered a straiter prison
than the one I live in now, if by so doing I  could have set you
at liberty."

[PLATE:  CREST OF GALILEO'S FAMILY.]

Sister Maria Celeste was gradually failing in health, but the
great privilege was accorded to her of being able once again to
embrace her beloved lord and master.  Galileo had, in fact, been
permitted to return to his old home; but on the very day when he
heard of his daughter's death came the final decree directing him
to remain in his own house in perpetual solitude.

Amid the advancing infirmities of age, the isolation from friends,
and the loss of his daughter, Galileo once again sought
consolation in hard work.  He commenced his famous dialogue on
Motion.  Gradually, however, his sight began to fail, and
blindness was at last added to his other troubles.  On January
2nd, 1638, he writes to Diodati:--

"Alas, your dear friend and servant, Galileo, has been for the
last month perfectly blind, so that this heaven, this earth, this
universe which I by my marvellous discoveries and clear
demonstrations have enlarged a hundred thousand times beyond the
belief of the wise men of bygone ages, henceforward is for me
shrunk into such a small space as is filled by my own bodily
sensations."

But the end was approaching--the great philosopher, was attacked
by low fever, from which he died on the 8th January, 1643.




KEPLER.



While the illustrious astronomer, Tycho Brahe, lay on his
death-bed, he had an interview which must ever rank as one of the
important incidents in the history of science.  The life of Tycho
had been passed, as we have seen, in the accumulation of vast
stores of careful observations of the positions of the heavenly
bodies.  It was not given to him to deduce from his splendid work
the results to which they were destined to lead.  It was reserved
for another astronomer to distil, so to speak, from the volumes in
which Tycho's figures were recorded, the great truths of the
universe which those figures contained.  Tycho felt that his work
required an interpreter, and he recognised in the genius of a
young man with whom he was acquainted the agent by whom the world
was to be taught some of the great truths of nature.  To the
bedside of the great Danish astronomer the youthful philosopher
was summoned, and with his last breath Tycho besought of him to
spare no labour in the performance of those calculations, by which
alone the secrets of the movements of the heavens could be
revealed.  The solemn trust thus imposed was duly accepted, and
the man who accepted it bore the immortal name of Kepler.

Kepler was born on the 27th December, 1571, at Weil, in the Duchy
of Wurtemberg.  It would seem that the circumstances of his
childhood must have been singularly unhappy.  His father, sprung
from a well-connected family, was but a shiftless and idle
adventurer; nor was the great astronomer much more fortunate in
his other parent.  His mother was an ignorant and ill-tempered
woman; indeed, the ill-assorted union came to an abrupt end
through the desertion of the wife by her husband when their eldest
son John, the hero of our present sketch, was eighteen years old.
The childhood of this lad, destined for such fame, was still
further embittered by the circumstance that when he was four years
old he had a severe attack of small-pox.  Not only was his
eyesight permanently injured, but even his constitution appears to
have been much weakened by this terrible malady.

It seems, however, that the bodily infirmities of young John
Kepler were the immediate cause of his attention being directed to
the pursuit of knowledge.  Had the boy been fitted like other boys
for ordinary manual work, there can be hardly any doubt that to
manual work his life must have been devoted.  But, though his body
was feeble, he soon gave indications of the possession of
considerable mental power.  It was accordingly thought that a
suitable sphere for his talents might be found in the Church
which, in those days, was almost the only profession that
afforded an opening for an intellectual career.  We thus find
that by the time John Kepler was seventeen years old he had
attained a sufficient standard of knowledge to entitle him to
admission on the foundation of the University at Tubingen.

In the course of his studies at this institution he seems to have
divided his attention equally between astronomy and divinity.  It
not unfrequently happens that when a man has attained considerable
proficiency in two branches of knowledge he is not able to see
very clearly in which of the two pursuits his true vocation lies.
His friends and onlookers are often able to judge more wisely than
he himself can do as to which Of the two lines it would be better
for him to pursue.  This incapacity for perceiving the path in
which greatness awaited him, existed in the case of Kepler.
Personally, he inclined to enter the ministry, in which a
promising career seemed open to him.  He yielded, however, to
friends, who evidently knew him better than he knew himself, and
accepted in 1594, the important Professorship of astronomy which
had been offered to him in the University of Gratz.

It is difficult for us in these modern days to realise the
somewhat extraordinary duties which were expected from an
astronomical professor in the sixteenth century.  He was, of
course, required to employ his knowledge of the heavens in the
prediction of eclipses, and of the movements of the heavenly
bodies generally.  This seems reasonable enough; but what we are
not prepared to accept is the obligation which lay on the
astronomers to predict the fates of nations and the destinies of
individuals.

It must be remembered that it was the almost universal belief in
those days, that all the celestial spheres revolved in some
mysterious fashion around the earth, which appeared by far the
most important body in the universe.  It was imagined that the
sun, the moon, and the stars indicated, in the vicissitudes of
their movements, the careers of nations and of individuals.
Such being the generally accepted notion, it seemed to follow that
a professor who was charged with the duty of expounding the
movements of the heavenly bodies must necessarily be looked to for
the purpose of deciphering the celestial decrees regarding the
fate of man which the heavenly luminaries were designed to
announce.

Kepler threw himself with characteristic ardour into even this
fantastic phase of the labours of the astronomical professor; he
diligently studied the rules of astrology, which the fancies of
antiquity had compiled.  Believing sincerely as he did in the
connection between the aspect of the stars and the state of human
affairs, he even thought that he perceived, in the events of
his own life, a corroboration of the doctrine which affirmed the
influence of the planets upon the fate of individuals.

[PLATE:  KEPLER'S SYSTEM OF REGULAR SOLIDS.]

But quite independently of astrology there seem to have been many
other delusions current among the philosophers of Kepler's time.
It is now almost incomprehensible how the ablest men of a few
centuries ago should have entertained such preposterous notions,
as they did, with respect to the system of the universe.  As an
instance of what is here referred to, we may cite the
extraordinary notion which, under the designation of a discovery,
first brought Kepler into fame.  Geometers had long known that
there were five, but no more than five, regular solid figures.
There is, for instance, the cube with six sides, which is, of
course, the most familiar of these solids.  Besides the cube there
are other figures of four, eight, twelve, and twenty sides
respectively.  It also happened that there were five planets, but
no more than five, known to the ancients, namely, Mercury, Venus,
Mars, Jupiter, and Saturn.  To Kepler's lively imaginations this
coincidence suggested the idea that the five regular solids
corresponded to the five planets, and a number of fancied
numerical relations were adduced on the subject.  The absurdity of
this doctrine is obvious enough, especially when we observe that,
as is now well known, there are two large planets, and a host of
small planets, over and above the magical number of the regular
solids.  In Kepler's time, however, this doctrine was so far from
being regarded as absurd, that its announcement was hailed as a
great intellectual triumph.  Kepler was at once regarded with
favour.  It seems, indeed, to have been the circumstance which
brought him into correspondence with Tycho Brahe.  By its means
also he became known to Galileo.

The career of a scientific professor in those early days appears
generally to have been marked by rather more striking vicissitudes
than usually befall a professor in a modern university.  Kepler
was a Protestant, and as such he had been appointed to his
professorship at Gratz.  A change, however, having taken place in
the religious belief entertained by the ruling powers of the
University, the Protestant professors were expelled.  It seems
that special influence having been exerted in Kepler's case on
account of	his exceptional eminence, he was recalled to Gratz
and reinstated in the tenure of his chair.  But his pupils had
vanished, so that the great astronomer was glad to accept a post
offered him by Tycho Brahe in the observatory which the latter had
recently established near Prague.

On Tycho's death, which occurred soon after, an opening
presented itself which gave Kepler the opportunity his genius
demanded.  He was appointed to succeed Tycho in the position of
imperial mathematician.  But a far more important point, both for
Kepler and for science, was that to him was confided the use of
Tycho's observations.  It was, indeed, by the discussion of
Tycho's results that Kepler was enabled to make the discoveries
which form such an important part of astronomical history.

Kepler must also be remembered as one of the first great
astronomers who ever had the privilege of viewing celestial
bodies through a telescope.  It was in 1610 that he first held in
his hands one of those little instruments which had been so
recently applied to the heavens by Galileo.  It should, however,
be borne in mind that the epoch-making achievements of Kepler did
not arise from any telescopic observations that he made, or,
indeed, that any one else made.  They were all elaborately deduced
from Tycho's measurements of the positions of the planets,
obtained with his great instruments, which were unprovided with
telescopic assistance.

To realise the tremendous advance which science received from
Kepler's great work, it is to be understood that all the
astronomers who laboured before him at the difficult subject of
the celestial motions, took it for granted that the planets must
revolve in circles.  If it did not appear that a planet moved in a
fixed circle, then the ready answer was provided by Ptolemy's
theory that the circle in which the planet did move was itself in
motion, so that its centre described another circle.

When Kepler had before him that wonderful series of observations
of the planet, Mars, which had been accumulated by the
extraordinary skill of Tycho, he proved, after much labour, that
the movements of the planet refused to be represented in a
circular form.  Nor would it do to suppose that Mars revolved in
one circle, the centre of which revolved in another circle.  On no
such supposition could the movements of the planets be made to
tally with those which Tycho had actually observed.  This led to
the astonishing discovery of the true form of a planet's orbit.
For the first time in the history of astronomy the principle was
laid down that the movement of a planet could not be represented
by a circle, nor even by combinations of circles, but that it
could be represented by an elliptic path.  In this path the sun is
situated at one of those two points in the ellipse which are known
as its foci.

[PLATE:  KEPLER.]

Very simple apparatus is needed for the drawing of one those
ellipses which Kepler has shown to possess such astonishing
astronomical significance.  Two pins are stuck through a sheet of
paper on a board, the point of a pencil is inserted in a loop of
string which passes over the pins, and as the pencil is moved
round in such a way as to keep the string stretched, that
beautiful curve known as the ellipse is delineated, while the
positions of the pins indicate the two foci of the curve.  If the
length of the loop of string is unchanged then the nearer the pins
are together, the greater will be the resemblance between the
ellipse and the circle, whereas the more the pins are separated
the more elongated does the ellipse become.  The orbit of a great
planet is, in general, one of those ellipses which approaches a
nearly circular form.  It fortunately happens, however, that the
orbit of Mars makes a wider departure from the circular form than
any of the other important planets.  It is, doubtless, to this
circumstance that we must attribute the astonishing success of
Kepler in detecting the true shape of a planetary orbit.  Tycho's
observations would not have been sufficiently accurate to have
exhibited the elliptic nature of a planetary orbit which, like
that of Venus, differed very little from a circle.

The more we ponder on this memorable achievement the more striking
will it appear.  It must be remembered that in these days we know
of the physical necessity which requires that a planet shall
revolve in an ellipse and not in any other curve.  But Kepler had
no such knowledge.  Even to the last hour of his life he remained
in ignorance of the existence of any natural cause which ordained
that planets should follow those particular curves which geometers
know so well.  Kepler's assignment of the ellipse as the true form
of the planetary orbit is to be regarded as a brilliant guess, the
truth of which Tycho's observations enabled him to verify.  Kepler
also succeeded in pointing out the law according to which the
velocity of a planet at different points of its path could be
accurately specified.  Here, again, we have to admire the sagacity
with which this marvellously acute astronomer guessed the deep
truth of nature.  In this case also he was quite unprovided with
any reason for expecting from physical principles that such a law
as he discovered must be obeyed.  It is quite true that Kepler had
some slight knowledge of the existence of what we now know as
gravitation.  He had even enunciated the remarkable doctrine that
the ebb and flow of the tide must be attributed to the attraction
of the moon on the waters of the earth.  He does not, however,
appear to have had any anticipation of those wonderful discoveries
which Newton was destined to make a little later, in which he
demonstrated that the laws detected by Kepler's marvellous acumen
were necessary consequences of the principle of universal
gravitation.

[PLATE: SYMBOLICAL REPRESENTATION OF THE PLANETARY SYSTEM.]

To appreciate the relations of Kepler and Tycho it is necessary to
note the very different way in which these illustrious astronomers
viewed the system of the heavens.  It should be observed that
Copernicus had already expounded the true system, which located
the sun at the centre of the planetary system.  But in the days of
Tycho Brahe this doctrine had not as yet commanded universal
assent.  In fact, the great observer himself did not accept the
new views of Copernicus.  It appeared to Tycho that the earth not
only appeared to be the centre of things celestial, but that it
actually was the centre.  It is, indeed, not a little remarkable
that a student of the heavens so accurate as Tycho should have
deliberately rejected the Copernican doctrine in favour of the
system which now seems so preposterous.  Throughout his great
career, Tycho steadily observed the places of the sun, the moon,
and the planets, and as steadily maintained that all those bodies
revolved around the earth fixed in the centre.  Kepler,
however, had the advantage of belonging to the new school.  He
utilised the observations of Tycho in developing the great
Copernican theory whose teaching Tycho stoutly resisted.

Perhaps a chapter in modern science may illustrate the
intellectual relation of these great men.  The
revolution produced by Copernicus in the doctrine of
the heavens has often been likened to the revolution
which the Darwinian theory produced in the views held by
biologists as to life on this earth.  The Darwinian theory did not
at first command universal assent even among those naturalists
whose lives had been devoted with the greatest success to the
study of organisms.  Take, for instance, that great naturalist,
Professor Owen, by whose labours vast extension has been given to
our knowledge of the fossil animals which dwelt on the earth in
past ages.  Now, though Owens researches were intimately connected
with the great labours of Darwin, and afforded the latter material
for his epoch-making generalization, yet Owen deliberately refused
to accept the new doctrines.  Like Tycho, he kept on rigidly
accumulating his facts under the influence of a set of ideas as to
the origin of living forms which are now universally admitted to
be erroneous.  If, therefore, we liken Darwin to Copernicus, and
Owen to Tycho, we may liken the biologists of the present day to
Kepler, who interpreted the results of accurate observation upon
sound theoretical principles.

In reading the works of Kepler in the light of our modern
knowledge we are often struck by the extent to which his
perception of the sublimest truths in nature was associated with
the most extravagant errors and absurdities.  But, of course, it
must be remembered that he wrote in an age in which even the
rudiments of science, as we now understand it, were almost
entirely unknown.

It may well be doubted whether any joy experienced by mortals is
more genuine than that which rewards the successful searcher after
natural truths.  Every science-worker, be his efforts ever so
humble, will be able to sympathise with the enthusiastic delight
of Kepler when at last, after years of toil, the glorious light
broke forth, and that which he considered to be the greatest of
his astonishing laws first dawned upon him.  Kepler rightly judged
that the number of days which a planet required to perform its
voyage round the sun must be connected in some manner with the
distance from the planet to the sun; that is to say, with the
radius of the planet's orbit, inasmuch as we may for our present
object regard the planet's orbit as circular.

Here, again, in his search for the unknown law, Kepler had no
accurate dynamical principles to guide his steps.  Of course, we
now know not only what the connection between the planet's
distance and the planet's periodic time actually is, but we also
know that it is a necessary consequence of the law of universal
gravitation.  Kepler, it is true, was not without certain surmises
on the subject, but they were of the most fanciful description.
His notions of the planets, accurate as they were in certain
important respects, were mixed up with vague ideas as to the
properties of metals and the geometrical relations of the
regular solids.  Above all, his reasoning was penetrated by the
supposed astrological influences of the stars and their
significant relation to human fate.  Under the influence of such a
farrago of notions, Kepler resolved to make all sorts of trials in
his search for the connection between the distance of a planet
from the sun and the time in which the revolution of that planet
was accomplished.

It was quite easily demonstrated that the greater the distance of
the planet from the sun the longer was the time required for its
journey.  It might have been thought that the time would be
directly proportional to the distance.  It was, however, easy to
show that this supposition did not agree with the fact.  Finding
that this simple relation would not do, Kepler undertook a vast
series of calculations to find out the true method of expressing
the connection.  At last, after many vain attempts, he found, to
his indescribable joy, that the square of the time in which a
planet revolves around the sun was proportional to the cube of the
average distance of the planet from that body.

The extraordinary way in which Kepler's views on celestial matters
were associated with the wildest speculations, is well illustrated
in the work in which he propounded his splendid discovery just
referred to.  The announcement of the law connecting the distances
of the planets from the sun with their periodic times, was then
mixed up with a preposterous conception about the properties of
the different planets.  They were supposed to be associated with
some profound music of the spheres inaudible to human ears, and
performed only for the benefit of that being whose soul formed the
animating spirit of the sun.

Kepler was also the first astronomer who ever ventured to predict
the occurrence of that remarkable phenomenon, the transit of a
planet in front of the sun's disc.  He published, in 1629, a
notice to the curious in things celestial, in which he announced
that both of the planets, Mercury and Venus, were to make a
transit across the sun on specified days in the winter of 1631.
The transit of Mercury was duly observed by Gassendi, and the
transit of Venus also took place, though, as we now know, the
circumstances were such that it was not possible for the
phenomenon to be witnessed by any European astronomer.

In addition to Kepler's discoveries already mentioned, with which
his name will be for ever associated, his claim on the gratitude
of astronomers chiefly depends on the publication of his famous
Rudolphine tables.  In this remarkable work means are provided for
finding the places of the planets with far greater accuracy than
had previously been attainable.

Kepler, it must be always remembered, was not an astronomical
observer.  It was his function to deal with the observations made
by Tycho, and, from close study and comparison of the results, to
work out the movements of the heavenly bodies.  It was, in fact,
Tycho who provided as it were the raw material, while it was the
genius of Kepler which wrought that material into a beautiful and
serviceable form.  For more than a century the Rudolphine tables
were regarded as a standard astronomical work.  In these days we
are accustomed to find the movements of the heavenly bodies set
forth with all desirable exactitude in the NAUTICAL ALMANACK,
and the similar publication issued by foreign Governments.  Let it
be remembered that it was Kepler who first imparted the proper
impulse in this direction.

[PLATE:  THE COMMEMORATION OF THE RUDOLPHINE TABLES.]

When Kepler was twenty-six he married an heiress from Styria, who,
though only twenty-three years old, had already had some
experience in matrimony.  Her first husband had died; and it was
after her second husband had divorced her that she received the
addresses of Kepler.  It will not be surprising to hear that his
domestic affairs do not appear to have been particularly happy,
and his wife died in 1611.  Two years later, undeterred by the
want of success in his first venture, he sought a second partner,
and he evidently determined not to make a mistake this time.
Indeed, the methodical manner in which he made his choice of the
lady to whom he should propose has been duly set forth by him and
preserved for our edification.  With some self-assurance he
asserts that there were no fewer than eleven spinsters desirous of
sharing his joys and sorrows.  He has carefully estimated and
recorded the merits and demerits of each of these would-be brides.
The result of his deliberations was that he awarded himself to an
orphan girl, destitute even of a portion.  Success attended his
choice, and his second marriage seems to have proved a much more
suitable union than his first.  He had five children by the first
wife and seven by the second.

The years of Kepler's middle life were sorely distracted by a
trouble which, though not uncommon in those days, is one which we
find it difficult to realise at the present time.  His mother,
Catherine Kepler, had attained undesirable notoriety by the
suspicion that she was guilty of witchcraft.  Years were spent in
legal investigations, and it was only after unceasing exertions on
the part of the astronomer for upwards of a twelvemonth that he
was finally able to procure her acquittal and release from prison.

It is interesting for us to note that at one time there was a
proposal that Kepler should forsake his native country and adopt
England as a home.  It arose in this wise.  The great man was
distressed throughout the greater part of his life by pecuniary
anxieties.  Finding him in a strait of this description, the
English ambassador in Venice, Sir Henry Wotton, in the year 1620,
besought Kepler to come over to England, where he assured him that
he would obtain a favourable reception, and where, he was able to
add, Kepler's great scientific work was already highly esteemed.
But his efforts were unavailing; Kepler would not leave his own
country.  He was then forty-nine years of age, and doubtless a
home in a foreign land, where people spoke a strange tongue, had
not sufficient attraction for him, even when accompanied with the
substantial inducements which the ambassador was able to offer.
Had Kepler accepted this invitation, he would, in transferring his
home to England, have anticipated the similar change which took
place in the career of another great astronomer two centuries
later.  It will be remembered that Herschel, in his younger days,
did transfer himself to England, and thus gave to England the
imperishable fame of association with his triumphs.

The publication of the Rudolphine tables of the celestial
movements entailed much expense.  A considerable part of this was
defrayed by the Government at Venice but the balance occasioned no
little trouble and anxiety to Kepler.  No doubt the authorities
of those days were even less Willing to spend money on scientific
matters than are the Governments of more recent times.  For
several years the imperial Treasury was importuned to relieve him
from his anxieties.  The effects of so much worry, and of the long
journeys which were involved, at last broke down Kepler's health
completely.  As we have already mentioned, he had never been
strong
from infancy, and he finally succumbed to a fever in November,
1630, at the age of fifty-nine.  He was interred at St. Peter's
Church at Ratisbon.

Though Kepler had not those personal characteristics which have
made his great predecessor, Tycho Brahe, such a romantic figure,
yet a picturesque element in Kepler's character is not wanting.
It was, however, of an intellectual kind.  His imagination, as
well as his reasoning faculties, always worked together.  He was
incessantly prompted by the most extraordinary speculations.  The
great majority of them were in a high degree wild and chimerical,
but every now and then one of his fancies struck right to the
heart of nature, and an immortal truth was brought to light.

I remember visiting the observatory of one of our greatest modern
astronomers, and in a large desk he showed me a multitude of
photographs which he had attempted but which had not been
successful, and then he showed me the few and rare pictures which
had succeeded, and by which important truths had been revealed.
With a felicity of expression which I have often since thought of,
he alluded to the contents of the desk as the "chips."  They were
useless, but they were necessary incidents in the truly successful
work.  So it is in all great and good work.  Even the most skilful
man of science pursues many a wrong scent.  Time after time he
goes off on some track that plays him false.  The greater the
man's genius and intellectual resource, the more numerous will be
the ventures which he makes, and the great majority of those
ventures are certain to be fruitless.  They are in fact, the
"chips."  In Kepler's case the chips were numerous enough.
They were of the most extraordinary variety and structure.
But every now and then a sublime discovery was made of such a
character as to make us regard even the most fantastic of Kepler's
chips with the greatest veneration and respect.



ISAAC NEWTON.



It was just a year after the death of Galileo, that an infant came
into the world who was christened Isaac Newton.  Even the great
fame of Galileo himself must be relegated to a second place in
comparison with that of the philosopher who first expounded the
true theory of the universe.

Isaac Newton was born on the 25th of December (old style), 1642,
at Woolsthorpe, in Lincolnshire, about a half-mile from
Colsterworth, and eight miles south of Grantham.  His father,
Mr. Isaac Newton, had died a few months after his marriage to
Harriet Ayscough, the daughter of Mr. James Ayscough, of Market
Overton, in Rutlandshire.  The little Isaac was at first so
excessively frail and weakly that his life was despaired of.
The watchful mother, however, tended her delicate child with such
success that he seems to have thriven better than might have been
expected from the circumstances of his infancy, and he ultimately
acquired a frame strong enough to outlast the ordinary span of
human life.

For three years they continued to live at Woolsthorpe, the widow's
means of livelihood being supplemented by the income from another
small estate at Sewstern, in a neighbouring part of
Leicestershire.

[PLATE:  WOOLSTHORPE MANOR.
Showing solar dial made by Newton when a boy.]

In 1645, Mrs. Newton took as a second husband the Rev. Barnabas
Smith, and on moving to her new home, about a mile from
Woolsthorpe, she entrusted little Isaac to her mother, Mrs.
Ayscough.  In due time we find that the boy was sent to the public
school at Grantham, the name of the master being Stokes.  For the
purpose of being near his work, the embryo philosopher was boarded
at the house of Mr. Clark, an apothecary at Grantham.  We learn
from Newton himself that at first he had a very low place in the
class lists of the school, and was by no means one of those model
school-boys who find favour in the eyes of the school-master by
attention to Latin grammar.  Isaac's first incentive to diligent
study seems to have been derived from the circumstance that he was
severely kicked by one of the boys who was above him in the class.
This indignity had the effect of stimulating young Newton's
activity to such an extent that he not only attained the desired
object of passing over the head of the boy who had maltreated him,
but continued to rise until he became the head of the school.

The play-hours of the great philosopher were devoted to pursuits
very different from those of most school-boys.  His chief
amusement was found in making mechanical toys and various
ingenious contrivances.  He watched day by day with great interest
the workmen engaged in constructing a windmill in the
neighbourhood of the school, the result of which was that the boy
made a working model of the windmill and of its machinery, which
seems to have been much admired, as indicating his aptitude for
mechanics.  We are told that Isaac also indulged in somewhat
higher flights of mechanical enterprise.  He constructed a
carriage, the wheels of which were to be driven by the hands of
the occupant, while the first philosophical instrument he made
was a clock, which was actuated by water.  He also devoted much
attention to the construction of paper kites, and his skill in
this respect was highly appreciated by his schoolfellows.  Like a
true philosopher, even at this stage he experimented on the best
methods of attaching the string, and on the proportions which the
tail ought to have.  He also made lanthorns of paper to provide
himself with light as he walked to school in the dark winter
mornings.

The only love affair in Newton's life appears to have commenced
while he was still of tender years.  The incidents are thus
described in Brewster's "Life of Newton," a work to which I am
much indebted in this chapter.

"In the house where he lodged there were some female inmates, in
whose company he appears to have taken much pleasure.  One of these,
a Miss Storey, sister to Dr. Storey, a physician at Buckminster,
near Colsterworth, was two or three years younger than Newton and
to great personal attractions she seems to have added more than
the usual allotment of female talent. The society of this young
lady and her companions was always preferred to that of his own
school-fellows, and it was one of his most agreeable occupations
to construct for them little tables and cupboards, and other
utensils for holding their dolls and their trinkets.  He had lived
nearly six years in the same house with Miss Storey, and there is
reason to believe that their youthful friendship gradually rose to
a higher passion; but the smallness of her portion, and the
inadequacy of his own fortune, appear to have prevented the
consummation of their happiness.  Miss Storey was afterwards twice
married, and under the name of Mrs. Vincent, Dr. Stukeley visited
her at Grantham in 1727, at the age of eighty-two, and obtained
from her many particulars respecting the early history of
our author.  Newton's esteem for her continued unabated during
his life.  He regularly visited her when he went to Lincolnshire,
and never failed to relieve her from little pecuniary difficulties
which seem to have beset her family."

The schoolboy at Grantham was only fourteen years of age when his
mother became a widow for the second time.  She then returned to
the old family home at Woolsthorpe, bringing with her the three
children of her second marriage.  Her means appear to have been
somewhat scanty, and it was consequently thought necessary to
recall Isaac from the school.  His recently-born industry had been
such that he had already made good progress in his studies, and
his mother hoped that he would now lay aside his books, and those
silent meditations to which, even at this early age, he had become
addicted.  It was expected that, instead of such pursuits, which
were deemed quite useless, the boy would enter busily into the
duties of the farm and the details of a country life.  But before
long it became manifest that the study of nature and the pursuit
of knowledge had such a fascination for the youth that he could
give little attention to aught else.  It was plain that he would
make but an indifferent farmer.  He greatly preferred
experimenting on his water-wheels to looking after labourers,
while he found that working at mathematics behind a hedge was much
more interesting than chaffering about the price of bullocks in
the market place.  Fortunately for humanity his mother, like a
wise woman, determined to let her boy's genius have the scope
which it required.  He was accordingly sent back to Grantham
school, with the object of being trained in the knowledge which
would fit him for entering the University of Cambridge.

[PLATE: TRINITY COLLEGE, CAMBRIDGE.
Showing Newton's rooms; on the leads of the gateway he placed
his telescope.]

It was the 5th of June, 1660, when Isaac Newton, a youth of
eighteen, was enrolled as an undergraduate of Trinity College,
Cambridge.  Little did those who sent him there dream that this
boy was destined to be the most illustrious student who ever
entered the portals of that great seat of learning.  Little could
the youth himself have foreseen that the rooms near the gateway
which he occupied would acquire a celebrity from the fact that he
dwelt in them, or that the ante-chapel of his college was in good
time to be adorned by that noble statue, which is regarded as one
of the chief art treasures of Cambridge University, both on
account of its intrinsic beauty and the fact that it commemorates
the fame of her most distinguished alumnus, Isaac Newton, the
immortal astronomer.  Indeed, his advent at the University seemed
to have been by no means auspicious or brilliant.  His birth was,
as we have seen, comparatively obscure, and though he had already
given indication of his capacity for reflecting on philosophical
matters, yet he seems to have been but ill-equipped with the
routine knowledge which youths are generally expected to take with
them to the Universities.

From the outset of his college career, Newton's attention seems to
have been mainly directed to mathematics.  Here he began to give
evidence of that marvellous insight into the deep secrets of
nature which more than a century later led so dispassionate a
judge as Laplace to pronounce Newton's immortal work as
pre-eminent above all the productions of the human intellect.
But though Newton was one of the very greatest mathematicians
that ever lived, he was never a mathematician for the mere sake
of mathematics.  He employed his mathematics as an instrument for
discovering the laws of nature.  His industry and genius soon
brought him under the notice of the University authorities.
It is stated in the University records that he obtained a
Scholarship in 1664.  Two years later we find that Newton, as well
as many residents in the University, had to leave Cambridge
temporarily on account of the breaking out of the plague.
The philosopher retired for a season to his old home at
Woolsthorpe, and there he remained until he was appointed a Fellow
of Trinity College, Cambridge, in 1667.  From this time onwards,
Newton's reputation as a mathematician and as a natural philosopher
steadily advanced, so that in 1669, while still but twenty-seven
years of age, he was appointed to the distinguished position of
Lucasian Professor of Mathematics at Cambridge.  Here he found the
opportunity to continue and develop that marvellous career of
discovery which formed his life's work.

The earliest of Newton's great achievements in natural philosophy
was his detection of the composite character of light.  That a
beam of ordinary sunlight is, in fact, a mixture of a very great
number of different-coloured lights, is a doctrine now familiar
to every one who has the slightest education in physical science.
We must, however, remember that this discovery was really a
tremendous advance in knowledge at the time when Newton announced
it.

[PLATE:  DIAGRAM OF A SUNBEAM.]

We here give the little diagram originally drawn by Newton, to
explain the experiment by which he first learned the composition
of light.  A sunbeam is admitted into a darkened room through an
opening, H, in a shutter.  This beam when not interfered with will
travel in a straight line to the screen, and there reproduce a
bright spot of the same shape as the hole in the shutter.
If, however, a prism of glass, A B C, be introduced so that the
beam traverse it, then it will be seen at once that the light is
deflected from its original track.  There is, however, a further
and most important change which takes place.  The spot of light is
not alone removed to another part of the screen, but it becomes
spread out into a long band beautifully coloured, and exhibiting
the hues of the rainbow.  At the top are the violet rays, and then
in descending order we have the indigo, blue, green, yellow,
orange, and red.

The circumstance in this phenomenon which appears to have
particularly arrested Newton's attention, was the elongation
which the luminous spot underwent in consequence of its passage
through the prism.  When the  prism was absent the spot was nearly
circular, but when the prism was introduced the spot was about
five times as long as it was broad.  To ascertain the explanation
of this was the first problem to be solved.  It seemed natural to
suppose that it might be due to the thickness of the glass in the
prism which the light traversed, or to the angle of incidence at
which the light fell upon the prism. He found, however, upon
careful trial, that the phenomenon could not be thus accounted
for.  It was not until after much patient labour that the true
explanation dawned upon him.  He discovered that though the beam
of white light looks so pure and so simple, yet in reality it is
composed of differently coloured lights blended together.  These
are, of course, indistinguishable in the compound beam, but they
are separated or disentangled, so to speak, by the action of the
prism.  The rays at the blue end of the spectrum are more
powerfully deflected by the action of the glass than are the rays
at the red end.  Thus, the rays variously coloured red, orange,
yellow, green, blue, indigo, violet, are each conducted to a
different part of the screen.  In this way the prism has the
effect of exhibiting the constitution of the composite beam of
light.

To us this now seems quite obvious, but Newton did not adopt it
hastily.  With characteristic caution he verified the explanation
by many different experiments, all of which confirmed his
discovery.  One of these may be mentioned.  He made a hole in the
screen at that part on which the violet rays fell.  Thus a violet
ray was allowed to pass through, all the rest of the light being
intercepted, and on this beam so isolated he was able to try
further experiments.  For instance, when he interposed another
prism in its path, he found, as he expected, that it was again
deflected, and he measured the amount of the deflection.  Again he
tried the same experiment with one of the red rays from the
opposite end of the coloured band. He allowed it to pass through
the same aperture in the screen, and he tested the amount by
which the second prism was capable of producing deflection.
He thus found, as he had expected to find, that the second prism
was more efficacious in bending the violet rays than in bending
the red rays.  Thus he confirmed the fact that the various hues
of the rainbow were each bent by a prism to a different extent,
violet being acted upon the most, and red the least.

[PLATE:  ISAAC NEWTON.]

Not only did Newton decompose a white beam into its constituent
colours, but conversely by interposing a second prism with its
angle turned upwards, he reunited the different colours, and thus
reproduced the original beam of white light.  In several other
ways also he illustrated his famous proposition, which then seemed
so startling, that white light was the result of a mixture of all
hues of the rainbow.  By combining painters' colours in the right
proportion he did not indeed succeed in producing a mixture which
would ordinarily be called white, but he obtained a grey pigment.
Some of this he put on the floor of his room for comparison with a
piece of white paper.  He allowed a beam of bright sunlight to
fall upon the paper and the mixed colours side by side, and a
friend he called in for his opinion pronounced that under these
circumstances the mixed colours looked the whiter of the two.

By repeated demonstrations Newton thus established his great
discovery of the composite character of light.  He at once
perceived that his researches had an important bearing upon
the principles involved in the construction of a telescope.
Those who employed the telescope for looking at the stars,
had been long aware of the imperfections which prevented all the
various rays from being conducted to the same focus.  But this
imperfection had hitherto been erroneously accounted for.  It had
been supposed that the reason why success had not been attained
in the construction of a refracting telescope was due to the fact
that the object glass, made as it then was of a single piece,
had not been properly shaped.  Mathematicians had abundantly
demonstrated that a single lens, if properly figured, must conduct
all rays of light to the same focus, provided all rays experienced
equal refraction in passing through the glass.  Until Newton's
discovery of the composition of white light, it had been taken for
granted that the several rays in a white beam were equally
refrangible.  No doubt if this had been the case, a perfect
telescope could have been produced by properly shaping the object
glass.  But when Newton had demonstrated that light was by no
means so simple as had been supposed, it became obvious that
a satisfactory refracting telescope was an impossibility when
only a single object lens was employed, however carefully that
lens might have been wrought.  Such an objective might, no doubt,
be made to conduct any one group of rays of a particular shade
to the same focus, but the rays of other colours in the beam of
white light must necessarily travel some-what astray.  In this
way Newton accounted for a great part of the difficulties which
had hitherto beset the attempts to construct a perfect refracting
telescope.

We now know how these difficulties can be, to a great extent,
overcome, by employing for the objective a composite lens made of
two pieces of glass possessing different qualities.  To these
achromatic object glasses, as they are called, the great
development of astronomical knowledge, since Newton's time, is
due.  But it must be remarked that, although the theoretical
possibility of constructing an achromatic lens was investigated by
Newton, he certainly came to the conclusion that the difficulty
could not be removed by employing a composite objective, with two
different kinds of glass.  In this his marvellous sagacity in the
interpretation of nature seems for once to have deserted him.
We can, however, hardly regret that Newton failed to discover
the achromatic objective, when we observe that it was in
consequence of his deeming an achromatic objective to be
impossible that he was led to the invention of the reflecting
telescope.  Finding, as he believed, that the defects of the
telescope could not be remedied by any application of the
principle of refraction he was led to look in quite a different
direction for the improvement of the tool on which the advancement
of astronomy depended.  The REFRACTION of light depended as he
had found, upon the colour of the light.  The laws of REFLECTION
were, however, quite independent of the colour.  Whether rays be
red or green, blue or yellow, they are all reflected in precisely
the same manner from a mirror.  Accordingly, Newton perceived that
if he could construct a telescope the action of which depended upon
reflection, instead of upon refraction, the difficulty which had
hitherto proved an insuperable obstacle to the improvement of the
instrument would be evaded.

[PLATE:  SIR ISAAC NEWTON'S LITTLE REFLECTOR.]

For this purpose Newton fashioned a concave mirror from a mixture
of copper and tin, a combination which gives a surface with almost
the lustre of silver.  When the light of a star fell upon the
surface, an image of the star was produced in the focus of this
mirror, and then this image was examined by a magnifying eye-
piece.  Such is the principle of the famous reflecting telescope
which bears the name of Newton.  The little reflector which he
constructed, represented in the adjoining figure, is still
preserved as one of the treasures of the Royal Society.  The
telescope tube had the very modest dimension of one inch in
diameter.  It was, however, the precursor of a whole series
of magnificent instruments, each outstripping the other in
magnitude, until at last the culminating point was attained in
1845, by the construction of Lord Rosse's mammoth reflector
of six feet in aperture.

Newton's discovery of the composition of light led to an
embittered controversy, which caused no little worry to the great
Philosopher.  Some of those who attacked him enjoyed considerable
and, it must be admitted, even well-merited repute in the ranks of
science.  They alleged, however, that the elongation of the
coloured band which Newton had noticed was due to this, to that,
or to the other--to anything, in fact, rather than to the true
cause which Newton assigned.  With characteristic patience and
love of truth, Newton steadily replied to each such attack.
He showed most completely how utterly his adversaries had
misunderstood the subject, and how slight indeed was their
acquaintance with the natural phenomenon in question.  In reply to
each point raised, he was ever able to cite fresh experiments and
adduce fresh illustrations, until at last his opponents retired
worsted from the combat.

It has been often a matter for surprise that Newton, throughout
his whole career, should have taken so much trouble to expose the
errors of those who attacked his views.  He used even to do this
when it plainly appeared that his adversaries did not understand
the subject they were discussing.  A philosopher might have said,
"I know I am right, and whether others think I am right or not may
be a matter of concern to them, but it is certainly not a matter
about which I need trouble.  If after having been told the truth
they elect to remain in error, so much the worse for them; my time
can be better employed than in seeking to put such people right."
This, however, was not Newton's method.  He spent much valuable
time in overthrowing objections which were often of a very futile
description.  Indeed, he suffered a great deal of annoyance from
the persistency, and in some cases one might almost say from the
rancour, of the attacks which were made upon him.  Unfortunately
for himself, he did not possess that capacity for sublime
indifference to what men may say, which is often the happy,
possession of intellects greatly inferior to his.

The subject of optics still continuing to engross Newton's
attention, he followed up his researches into the structure of the
sunbeam by many other valuable investigations in connection with
light.  Every one has noticed the beautiful colours manifested in
a soap-bubble.  Here was a subject which not unnaturally attracted
the attention of one who had expounded the colours of the spectrum
with such success.  He perceived that similar hues were produced
by other thin plates of transparent material besides soap-bubbles,
and his ingenuity was sufficient to devise a method by which the
thicknesses of the different films could be measured.  We can
hardly, indeed, say that a like success attended his
interpretation of these phenomena to that which had been so
conspicuous in his explanation of the spectrum.  It implies no
disparagement to the sublime genius of Newton to admit that the
doctrines he put forth as to the causes of the colours in the
soap-bubbles can be no longer accepted.  We must remember that
Newton was a pioneer in accounting for the physical properties
of light.  The facts that he established are indeed
unquestionable, but the explanations which he was led to offer
of some of them are seen to be untenable in the fuller light
of our present knowledge.

[PLATE:  SIR ISAAC NEWTON'S SUN-DIAL.]

Had Newton done nothing beyond making his wonderful discoveries
in light, his fame would have gone down to posterity as one of
the greatest of Nature's interpreters.  But it was reserved for
him to accomplish other discoveries, which have pushed even his
analysis of the sunbeam into the background; it is he who has
expounded the system of the universe by the discovery of the
law of universal gravitation.

The age had indeed become ripe for the advent of the genius of
Newton.  Kepler had discovered with marvellous penetration the
laws which govern the movements of the planets around the sun, and
in various directions it had been more or less vaguely felt that
the explanation of Kepler's laws, as well as of many other
phenomena, must be sought for in connection with the attractive
power of matter.  But the mathematical analysis which alone could
deal with this subject was wanting; it had to be created by
Newton.

At Woolsthorpe, in the year 1666, Newton's attention appears to
have been concentrated upon the subject of gravitation.
Whatever may be the extent to which we accept the more or less
mythical story as to how the fall of an apple first directed the
attention of the philosopher to the fact that gravitation must
extend through space, it seems, at all events, certain that this
is an excellent illustration of the line of reasoning which he
followed.  He argued in this way.  The earth attracts the apple;
it would do so, no matter how high might be the tree from which
that apple fell.  It would then seem to follow that this power
which resides in the earth by which it can draw all external
bodies towards it, extends far beyond the altitude of the loftiest
tree.  Indeed, we seem to find no limit to it.  At the greatest
elevation that has ever been attained, the attractive power of the
earth is still exerted, and though we cannot by any actual
experiment reach an altitude more than a few miles above the
earth, yet it is certain that gravitation would extend to
elevations far greater.   It is plain, thought Newton, that an
apple let fall from a point a hundred miles above this earth's
surface, would be drawn down by the attraction, and would
continually gather fresh velocity until it reached the ground.
From a hundred miles it was natural to think of what would happen
at a thousand miles, or at hundreds of thousands of miles.  No
doubt the intensity of the attraction becomes weaker with every
increase in the altitude, but that action would still exist to
some extent, however lofty might be the elevation which had been
attained.

It then occurred to Newton, that though the moon is at a distance
of two hundred and forty thousand miles from the earth, yet the
attractive power of the earth must extend to the moon.  He was
particularly led to think of the moon in this connection, not only
because the moon is so much closer to the earth than are any other
celestial bodies, but also because the moon is an appendage to the
earth, always revolving around it.  The moon is certainly
attracted to the earth, and yet the moon does not fall down; how
is this to be accounted for?  The explanation was to be found in
the character of the moon's present motion.  If the moon were left
for a moment at rest, there can be no doubt that the attraction of
the earth would begin to draw the lunar globe in towards our globe.
In the course of a few days our satellite would come down on the
earth with a most fearful crash.  This catastrophe is averted by
the circumstance that the moon has a movement of revolution around
the earth.  Newton was able to calculate from the known laws of
mechanics, which he had himself been mainly instrumental in
discovering, what the attractive power of the earth must be, so
that the moon shall move precisely as we find it to move.  It then
appeared that the very power which makes an apple fall at the
earth's surface is the power which guides the moon in its orbit.

[PLATE:  SIR ISAAC NEWTON'S TELESCOPE.]

Once this step had been taken, the whole scheme of the universe
might almost be said to have become unrolled before the eye of the
philosopher.  It was natural to suppose that just as the moon
was guided and controlled by the attraction of the earth, so the
earth itself, in the course of its great annual progress, should
be guided and controlled by the supreme attractive power of the
sun.  If this were so with regard to the earth, then it would be
impossible to doubt that in the same way the movements of the
planets could be explained to be consequences of solar attraction.

It was at this point that the great laws of Kepler became
especially significant.  Kepler had shown how each of the planets
revolves in an ellipse around the sun, which is situated on one of
the foci.  This discovery had been arrived at from the
interpretation of observations.  Kepler had himself assigned no
reason why the orbit of a planet should be an ellipse rather than
any other of the infinite number of closed curves which might be
traced around the sun.  Kepler had also shown, and here again he
was merely deducing the results from observation, that when the
movements of two planets were compared together, the squares of
the periodic times in which each planet revolved were proportional
to the cubes of their mean distances from the sun.  This also
Kepler merely knew to be true as a fact, he gave no demonstration of
the reason why nature should have adopted this particular relation
between the distance and the periodic time rather than any other.
Then, too, there was the law by which Kepler with unparalleled
ingenuity, explained the way in which the velocity of a planet
varies at the different points of its track, when he showed how
the line drawn from the sun to the planet described equal areas
around the sun in equal times.  These were the materials with
which Newton set to work.  He proposed to infer from these the
actual laws regulating the force by which the sun guides the
planets.  Here it was that his sublime mathematical genius came
into play.  Step by step Newton advanced until he had completely
accounted for all the phenomena.

In the first place, he showed that as the planet describes equal
areas in equal times about the sun, the attractive force which the
sun exerts upon it must necessarily be directed in a straight line
towards the sun itself.  He also demonstrated the converse truth,
that whatever be the nature of the force which emanated from a
sun, yet so long as that force was directed through the sun's
centre, any body which revolved around it must describe equal
areas in equal times, and this it must do, whatever be the actual
character of the law according to which the intensity of the force
varies at different parts of the planet's journey.  Thus the first
advance was taken in the exposition of the scheme of the universe.

The next step was to determine the law according to which the
force thus proved to reside in the sun varied with the distance of
the planet.  Newton presently showed by a most superb effort of
mathematical reasoning, that if the orbit of a planet were an
ellipse and if the sun were at one of the foci of that ellipse,
the intensity of the attractive force must vary inversely as the
square of the planet's distance.  If the law had any other
expression than the inverse square of the distance, then the orbit
which the planet must follow would not be an ellipse; or if
an ellipse, it would, at all events, not have the sun in the
focus.  Hence he was able to show from Kepler's laws alone that
the force which guided the planets was an attractive power
emanating from the sun, and that the intensity of this attractive
power varied with the inverse square of the distance between the
two bodies.

These circumstances being known, it was then easy to show that the
last of Kepler's three laws must necessarily follow.  If a number
of planets were revolving around the sun, then supposing the
materials of all these bodies were equally affected by
gravitation, it can be demonstrated that the square of the
periodic time in which each planet completes its orbit is
proportional to the cube of the greatest diameter in that orbit.

[PLATE:  SIR ISAAC NEWTON'S ASTROLABE.]

These superb discoveries were, however, but the starting point
from which Newton entered on a series of researches, which
disclosed many of the profoundest secrets in the scheme of
celestial mechanics.  His natural insight showed that not only
large masses like the sun and the earth, and the moon, attract
each other, but that every particle in the universe must attract
every other particle with a force which varies inversely as the
square of the distance between them.  If, for example, the two
particles were placed twice as far apart, then the intensity of
the force which sought to bring them together would be reduced to
one-fourth.  If two particles, originally ten miles asunder,
attracted each other with a certain force, then, when the distance
was reduced to one mile, the intensity of the attraction between
the two particles would be increased one-hundred-fold.  This
fertile principle extends throughout the whole of nature.  In some
cases, however, the calculation of its effect upon the actual
problems of nature would be hardly possible, were it not for
another discovery which Newton's genius enabled him to accomplish.
In the case of two globes like the earth and the moon, we must
remember that we are dealing not with particles, but with two
mighty masses of matter, each composed of innumerable myriads of
particles.  Every particle in the earth does attract every
particle in the moon with a force which varies inversely as the
square of their distance.  The calculation of such attractions is
rendered feasible by the following principle.  Assuming that the
earth consists of materials symmetrically arranged in shells
of varying densities, we may then, in calculating its attraction,
regard the whole mass of the globe as concentrated at its centre.
Similarly we may regard the moon as concentrated at the centre of
its mass.  In this way the earth and the moon can both be regarded
as particles in point of size, each particle having, however, the
entire mass of the corresponding globe.  The attraction of one
particle for another is a much more simple matter to investigate
than the attraction of the myriad different points of the earth
upon the myriad different points of the moon.

Many great discoveries now crowded in upon Newton.  He first of
all gave the explanation of the tides that ebb and flow around
our shores.  Even in the earliest times the tides had been shown
to be related to the moon.  It was noticed that the tides were
specially high during full moon or during new moon, and this
circumstance obviously pointed to the existence of some connection
between the moon and these movements of the water, though as to
what that connection was no one had any accurate conception until
Newton announced the law of gravitation.  Newton then made
it plain that the rise and fall of the water was simply a
consequence of the attractive power which the moon exerted
upon the oceans lying upon our globe.  He showed also that
to a certain extent the sun produces tides, and he was able
to explain how it was that when the sun and the moon both
conspire, the joint result was to produce especially high
tides, which we call "spring tides"; whereas if the solar
tide was low, while the lunar tide was high, then we had the
phenomenon of "neap" tides.

But perhaps the most signal of Newton's applications of the
law of gravitation was connected with certain irregularities
in the movements of the moon.  In its orbit round the earth
our satellite is, of course, mainly guided by the great
attraction of our globe.  If there were no other body in the
universe, then the centre of the moon must necessarily perform an
ellipse, and the centre of the earth would lie in the focus of
that ellipse.  Nature, however, does not allow the movements to
possess the simplicity which this arrangement would imply, for the
sun is present as a source of disturbance.  The sun attracts the
moon, and the sun attracts the earth, but in different degrees,
and the consequence is that the moon's movement with regard to the
earth is seriously affected by the influence of the sun.  It is
not allowed to move exactly in an ellipse, nor is the earth
exactly in the focus.  How great was Newton's achievement in the
solution of this problem will be appreciated if we realise that he
not only had to determine from the law of gravitation the nature
of the disturbance of the moon, but he had actually to construct
the mathematical tools by which alone such calculations could be
effected.

The resources of Newton's genius seemed, however, to prove
equal to almost any demand that could be made upon it.  He saw
that each planet must disturb the other, and in that way he was
able to render a satisfactory account of certain phenomena which
had perplexed all preceding investigators.  That mysterious
movement by which the pole of the earth sways about among the
stars had been long an unsolved enigma, but Newton showed that the
moon grasped with its attraction the protuberant mass at the
equatorial regions of the earth, and thus tilted the earth's
axis in a way that accounted for the phenomenon which had been
known but had never been explained for two thousand years.  All
these discoveries were brought together in that immortal work,
Newton's Principia."

Down to the year 1687, when the "Principia" was published, Newton
had lived the life of a recluse at Cambridge, being entirely
occupied with those transcendent researches to which we have
referred.  But in that year he issued from his seclusion under
circumstances of considerable historical interest.  King James the
Second attempted an invasion of the rights and privileges of the
University of Cambridge by issuing a command that Father Francis,
a Benedictine monk, should be received as a Master of Arts in the
University, without having taken the oaths of allegiance and
supremacy.  With this arbitrary command the University sternly
refused to comply.  The Vice-Chancellor was accordingly summoned
to answer for an act of contempt to the authority of the Crown.
Newton was one of nine delegates who were chosen to defend the
independence of the University before the High Court.  They were
able to show that Charles the Second, who had issued a MANDAMUS
under somewhat similar circumstances, had been induced after due
consideration to withdraw it.  This argument appeared
satisfactory, and the University gained their case.  Newton's next
step in public life was his election, by a narrow majority, as
member for the University, and during the years 1688 and 1689, he
seems to have attended to his parliamentary duties with
considerable regularity.

An incident which happened in 1692 was apparently the cause of
considerable disturbance in Newton's equanimity, if not in his
health.  He had gone to early morning chapel, leaving a lighted
candle among his papers on his desk.  Tradition asserts that his
little dog "Diamond" upset the candle; at all events, when Newton
came back he found that many valuable papers had perished in a
conflagration.  The loss of these manuscripts seems to have had a
serious effect.  Indeed, it has been asserted that the distress
reduced Newton to a state of mental aberration for a considerable
time.  This has, apparently, not been confirmed, but there is no
doubt that he experienced considerable disquiet, for in
writing on September 13th, 1693, to Mr. Pepys, he says:

"I am extremely troubled at the embroilment I am in, and have
neither ate nor slept well this twelvemonth, nor have my former
consistency of mind."

Notwithstanding the fame which Newton had achieved, by the
publication of his, "Principia," and by all his researches, the
State had not as yet taken any notice whatever of the most
illustrious man of science that this or any other country has ever
produced.  Many of his friends had exerted themselves to procure
him some permanent appointment, but without success.  It happened,
however, that Mr. Montagu, who had sat with Newton in Parliament,
was appointed Chancellor of the Exchequer in 1694.  Ambitious of
distinction in his new office, Mr. Montagu addressed himself to
the improvement of the current coin, which was then in a very
debased condition.  It fortunately happened that an opportunity
occurred of appointing a new official in the Mint; and Mr. Montagu
on the 19th of March, 1695, wrote to offer Mr. Newton the position
of warden.  The salary was to be five or six hundred a year, and
the business would not require more attendance than Newton could
spare.  The Lucasian professor accepted this post, and forthwith
entered upon his new duties.

The knowledge of physics which Newton had acquired by his
experiments was of much use in connection with his duties at the
Mint.  He carried out the re-coinage with great skill in the
course of two years, and as a reward for his exertions, he was
appointed, in 1697, to the Mastership of the Mint, with a salary
between 1,200 Pounds and 1,500 Pounds per annum.  In 1701 his
duties at the Mint being so engrossing, he resigned his Lucasian
professorship at Cambridge, and at the same time he had to
surrender his fellowship at Trinity College.  This closed his
connection with the University of Cambridge.  It should, however,
be remarked that at a somewhat earlier stage in his career he
was very nearly being appointed to an office which might have
enabled the University to retain the great philosopher within
its precincts.  Some of his friends had almost succeeded in
securing his nomination to the Provostship of King's College,
Cambridge; the appointment, however, fell through, inasmuch as
the statute could not be evaded, which required that the Provost
of King's College should be in holy orders.

In those days it was often the custom for illustrious
mathematicians, when they had discovered a solution for some new
and striking problem, to publish that problem as a challenge to
the world, while withholding their own solution.  A famous
instance of this is found in what is known as the Brachistochrone
problem, which was solved by John Bernouilli.  The nature of this
problem may be mentioned.  It was to find the shape of the curve
along which a body would slide down from one point (A) to another
point (B) in the shortest time.  It might at first be thought that
the straight line from A to B, as it is undoubtedly the shortest
distance between the points, would also be the path of quickest
descent; but this is not so.  There is a curved line, down which a
bead, let us say, would run on a smooth wire from A to B in a
shorter time than the same bead would require to run down the
straight wire.  Bernouilli's problem was to find out what that
curve must be.  Newton solved it correctly; he showed that the
curve was a part of what is termed a cycloid--that is to say, a
curve like that which is described by a point on the rim of a
carriage-wheel as the wheel runs along the ground.  Such was
Newton's geometrical insight that he was able to transmit a
solution of the problem on the day after he had received it, to
the President of the Royal Society.

In 1703 Newton, whose world wide fame was now established, was
elected President of the Royal Society.  Year after year he was
re-elected to this distinguished position, and his tenure, which
lasted twenty-five years, only terminated with his life.
It was in discharge of his duties as President of the Royal
Society that Newton was brought into contact with Prince George of
Denmark.  In April, 1705, the Queen paid a visit to Cambridge as
the guest of Dr. Bentley, the then Master of Trinity, and in a
court held at Trinity Lodge on April 15th, 1705, the honour of
knighthood was conferred upon the discoverer of gravitation.

Urged by illustrious friends, who sought the promotion of
knowledge, Newton gave his attention to the publication of a new
edition of the "Principia."  His duties at the Mint, however,
added to the supreme duty of carrying on his original
investigations, left him but little time for the more ordinary
task of the revision.  He was accordingly induced to associate
with himself for this purpose a distinguished young mathematician,
Roger Coates, a Fellow of Trinity College, Cambridge, who had
recently been appointed Plumian Professor of Astronomy.  On July
27th, 1713, Newton, by this time a favourite at Court, waited on
the Queen, and presented her with a copy of the new edition of the
"Principia."

Throughout his life Newton appears to have been greatly interested
in theological studies, and he specially devoted his attention to
the subject of prophecy.  He left behind him a manuscript on the
prophecies of Daniel and the Apocalypse of St. John, and he also
wrote various theological papers.  Many other subjects had from
time to time engaged his attention.  He studied the laws of heat;
he experimented in pursuit of the dreams of the Alchymist; while
the philosopher who had revealed the mechanism of the heavens
found occasional relaxation in trying to interpret hieroglyphics.
In the last few years of his life he bore with fortitude a painful
ailment, and on Monday, March 20th, 1727, he died in the
eighty-fifth year of his age.  On Tuesday, March 28th, he was
buried in Westminster Abbey.

Though Newton lived long enough to receive the honour that his
astonishing discoveries so justly merited, and though for many
years of his life his renown was much greater than that of any
of his contemporaries, yet it is not too much to say that, in
the years which have since elapsed, Newton's fame has been ever
steadily advancing, so that it never stood higher than it does
at this moment.

We hardly know whether to admire more the sublime discoveries at
which he arrived, or the extraordinary character of the
intellectual processes by which those discoveries were reached.
Viewed from either standpoint, Newton's "Principia" is
incomparably the greatest work on science that has ever yet been
produced.

[PLATE:  SIR ISAAC NEWTON'S SUN-DIAL IN THE ROYAL SOCIETY.]




FLAMSTEED.



Among the manuscripts preserved at Greenwich Observatory are
certain documents in which Flamsteed gives an account of his own
life.  We may commence our sketch by quoting the following passage
from this autobiography:--"To keep myself from idleness, and to
recreate myself, I have intended here to give some account of my
life, in my youth, before the actions thereof, and the providences
of God therein, be too far passed out of my memory; and to observe
the accidents of all my years, and inclinations of my mind, that
whosoever may light upon these papers may see I was not so wholly
taken up, either with my father's business or my mathematics, but
that I both admitted and found time for other as weighty
considerations."

The chief interest which attaches to the name of Flamsteed arises
from the fact that he was the first of the illustrious series of
Astronomers Royal who have presided over Greenwich Observatory.
In that capacity Flamsteed was able to render material assistance
to Newton by providing him with the observations which his lunar
theory required.

John Flamsteed was born at Denby, in Derbyshire, on the 19th of
August, 1646.  His mother died when he was three years old, and
the second wife, whom his father took three years later, only
lived until Flamsteed was eight, there being also two younger
sisters.  In his boyhood the future astronomer tells us that he
was very fond of those romances which affect boy's imagination,
but as he writes, "At twelve years of age I left all the wild ones
and betook myself to read the better sort of them, which, though
they were not probable, yet carried no seeming impossibility in
the picturing."  By the time Flamsteed was fifteen years old he
had embarked in still more serious work, for he had read
Plutarch's "Lives," Tacitus' "Roman History," and many other books
of a similar description.  In 1661 he became ill with some serious
rheumatic affection, which obliged him to be withdrawn from
school.  It was then for the first time that he received the
rudiments of a scientific education.  He had, however, attained
his sixteenth year before he made any progress in arithmetic.
He tells us how his father taught him "the doctrine of fractions,"
and "the golden rule of three"--lessons which he seemed to have
learned easily and quickly.  One of the books which he read at
this time directed his attention to astronomical instruments, and
he was thus led to construct for himself a quadrant, by which he
could take some simple astronomical observations.  He further
calculated a table to give the sun's altitudes at different hours,
and thus displayed those tastes for practical astronomy which he
lived to develop so greatly.  It appears that these scientific
studies were discountenanced by his father, who designed that his
son should follow a business career.  Flamsteed's natural
inclination, however, forced him to prosecute astronomical work,
notwithstanding the impediments that lay in his path.
Unfortunately, his constitutional delicacy seems to have
increased, and he had just completed his eighteenth year, "when,"
to use his own words, "the winter came on and thrust me again into
the chimney, whence the heat and the dryness of the preceding
summer had happily once before withdrawn me.  But, it not being a
fit season for physic, it was thought fit to let me alone this
winter, and try the skill of another physician on me in the
spring."

It appears that at this time a quack named Valentine Greatrackes,
was reputed to have effected most astonishing cures in Ireland
merely by the stroke of his hands, without the application of any
medicine whatever.  Flamsteed's father, despairing of any remedy
for his son from the legitimate branch of the profession,
despatched him to Ireland on August 26th, 1665, he being then, as
recorded with astronomical accuracy, "nineteen years, six days,
and eleven hours old."  The young astronomer, accompanied by a
friend, arrived on a Tuesday at Liverpool but the wind not being
favourable, they remained there till the following Friday, when a
shift of the wind to the east took place.  They embarked
accordingly on a vessel called the SUPPLY at noon, and on Saturday
night came in sight of Dublin.  Ere they could land, however, they
were nearly being wrecked on Lambay Island.  This peril safely
passed, there was a long delay for quarantine before they were at
last allowed on shore.  On Thursday, September 6th, they set out
from Dublin, where they had been sojourning at the "Ship" Hotel,
in Dame Street, towards Assaune, where Greatrackes received his
patients.

[PLATE:  FLAMSTEED'S HOUSE.]

Flamsteed gives an interesting account of his travels in Ireland.
They dined at Naas on the first day, and on September 8th they
reached Carlow, a town which is described as one of the fairest
they saw on their journey.  By Sunday morning, September 10th,
having lost their way several times, they reached Castleton,
called commonly Four Mile Waters.  Flamsteed inquired of the
host in the inn where they might find a church, but was told that
the minister lived twelve miles away, and that they had no sermon
except when he came to receive his tithes once a year, and a woman
added that "they had plenty enough of everything necessary except
the word of God."  The travellers accordingly went on to
Cappoquin, which lies up the river Blackwater, on the road to
Lismore, eight miles from Youghal.  Thence they immediately
started on foot to Assaune.  About a mile from Cappoquin, and
entering into the house of Mr. Greatrackes, they saw him touch
several patients, "whereof some were nearly cured, others were on
the mending hand, and some on whom his strokes had no effect."
Flamsteed was touched by the famous quack on the afternoon of
September 11th, but we are hardly surprised to hear his remark
that "he found not his disease to stir."  Next morning the
astronomer came again to see Mr. Greatrackes, who had "a kind of
majestical yet affable presence, and a composed carriage."  Even
after the third touching had been submitted to, no benefit seems
to have been derived.  We must, however record, to the credit of
Mr. Greatrackes, that he refused to accept any payment from
Flamsteed, because he was a stranger.

Finding it useless to protract his stay any longer, Flamsteed and
his friend set out on their return to Dublin.  In the course of
his journey he seems to have been much impressed with Clonmel,
which he describes as an "exceedingly pleasantly seated town."
But in those days a journey to Ireland was so serious an
enterprise that when Flamsteed did arrive safely back at Derby
after an absence of a month, he adds, "For God's providence in
this journey, His name be praised, Amen."

As to the expected benefits to his health from the expedition we
may quote his own words: "In the winter following I was
indifferent hearty, and my disease was not so violent as it used
to be at that time formerly.  But whether through God's mercy I
received this through Mr. Greatrackes' touch, or my journey and
vomiting at sea, I am uncertain; but, by some circumstances, I
guess that I received a benefit from both."

It is evident that by this time Flamsteed's interest in all
astronomical matters had greatly increased.  He studied the
construction of sun-dials, he formed a catalogue of seventy of
the fixed stars, with their places on the heavens, and he computed
the circumstances of the solar eclipse which was to happen on June
22nd, 1666.  It is interesting to note that even in those days the
doctrines of the astrologers still found a considerable degree of
credence, and Flamsteed spent a good deal of his time in
astrological studies and computations.  He investigated the
methods of casting a nativity, but a suspicion, or, indeed, rather
more than a suspicion, seems to have crossed his mind as to the
value of these astrological predictions, for he says in fine, "I
found astrology to give generally strong conjectural hints, not
perfect declarations."

All this time, however, the future Astronomer Royal was steadily
advancing in astronomical inquiries of a recondite nature.  He had
investigated the obliquity of the ecliptic with extreme care, so
far as the circumstances of astronomical observation would at that
time permit.  He had also sought to discover the sun's distance
from the earth in so far as it could be obtained by determining
when the moon was exactly half illuminated, and he had measured,
with much accuracy, the length of the tropical year.  It will thus
be seen that, even at the age of twenty, Flamsteed had made marked
progress, considering how much his time had been interfered with
by ill-health.

Other branches of astronomy began also to claim his attention.
We learn that in 1669 and 1670 he compared the planets Jupiter
and Mars with certain fixed stars near which they passed.  His
instrumental means, though very imperfect, were still sufficient
to enable him to measure the intervals on the celestial sphere
between the planets and the stars.  As the places of the stars
were known, Flamsteed was thus able to obtain the places of the
planets.  This is substantially the way in which astronomers of
the present day still proceed when they desire to determine the
places of the planets, inasmuch as, directly or indirectly those
places are always obtained relatively to the fixed stars.  By his
observations at this early period, Flamsteed was, it is true, not
able to obtain any great degree of accuracy; he succeeded,
however, in proving that the tables by which the places of the
planets were ordinarily given were not to be relied upon.

[PLATE:  FLAMSTEED.]

Flamsteed's labours in astronomy and in the allied branches of
science were now becoming generally known, and he gradually came
to correspond with many distinguished men of learning.  One of the
first occasions which brought the talents of the young astronomer
into fame was the publication of some calculations concerning
certain astronomical phenomena which were to happen in the year
1670.  In the monthly revolution of the moon its disc passes over
those stars which lie along its track.  The disappearance of a
star by the interposition of the moon is called an "occultation."
Owing to the fact that our satellite is comparatively near us, the
position which the moon appears to occupy on the heavens varies
from different parts of the earth, it consequently happens
that a star which would be occulted to an observer in one
locality, would often not be occulted to an observer who was
situated elsewhere.  Even when an occultation is visible from
both places, the times at which the star disappears from view
will, generally speaking, be different.  Much calculation is
therefore necessary to decide the circumstances under which the
occultations of stars may be visible from any particular station.
Having a taste for such computations, Flamsteed calculated the
occultations which were to happen in the year 1670, it being the
case that several remarkable stars would be passed over by the
moon during this year.  Of course at the present time, we find
such information duly set forth in the NAUTICAL ALMANAC, but a
couple of centuries ago there was no such source of astronomical
knowledge as is now to be found in that invaluable publication,
which astronomers and navigators know so well.  Flamsteed
accordingly sent the results of his work to the President of the
Royal Society.  The paper which contained them was received very
favourably, and at once brought Flamsteed into notice among the
most eminent members of that illustrious body, one of whom,
Mr. Collins, became through life his faithful friend and constant
correspondent.  Flamsteed's father was naturally gratified with
the remarkable notice which his son was receiving from the great
and learned; accordingly he desired him to go to London, that he
might make the personal acquaintance of those scientific friends
whom he had only known by correspondence previously.  Flamsteed
was indeed glad to avail himself of this opportunity.  Thus he
became acquainted with Dr. Barrow, and especially with Newton, who
was then Lucasian Professor of Mathematics at Cambridge.  It seems
to have been in consequence of this visit to London that Flamsteed
entered himself as a member of Jesus College, Cambridge.  We have
but little information as to his University career, but at all
events he took his degree of M.A. on June 5th, 1674.

Up to this time it would seem that Flamsteed had been engaged, to
a certain extent, in the business carried on by his father.  It is
true that he does not give any explicit details, yet there are
frequent references to journeys which he had to take on business
matters.  But the time now approached when Flamsteed was to start
on an independent career, and it appears that he took his degree
in Cambridge with the object of entering into holy orders, so that
he might settle in a small living near Derby, which was in the
gift of a friend of his father, and would be at the disposal of
the young astronomer.  This scheme was, however, not carried out,
but Flamsteed does not tell us why it failed, his only remark
being, that "the good providence of God that had designed me for
another station ordered it otherwise."

Sir Jonas Moore, one of the influential friends whom Flamsteed's
talents had attracted, seems to have procured for him the position
of king's astronomer, with a salary of 100 pounds per annum.  A
larger
salary appears to have been designed at first for this office,
which was now being newly created, but as Flamsteed was resolved
on taking holy orders, a lesser salary was in his case deemed
sufficient.  The building of the observatory, in which the first
Astronomer Royal was to be installed, seems to have been brought
about, or, at all events, its progress was accelerated, in a
somewhat curious manner.

A Frenchman, named Le Sieur de S. Pierre, came over to London to
promulgate a scheme for discovering longitudes, then a question of
much importance.  He brought with him introductions to
distinguished people, and his mission attracted a great deal of
attention.  The proposals which he made came under Flamsteed's
notice, who pointed out that the Frenchman's projects were quite
inapplicable in the present state of astronomical science,
inasmuch as the places of the stars were not known with the degree
of accuracy which would be necessary if such methods were to be
rendered available.  Flamsteed then goes on to say:--"I heard no
more of the Frenchman after this; but was told that my letters had
been shown King Charles.  He was startled at the assertion of the
fixed stars' places being false in the catalogue, and said, with
some vehemence, he must have them anew observed, examined,
and corrected, for the use of his seamen."

The first question to be settled was the site for the new
observatory.  Hyde Park and Chelsea College were both mentioned as
suitable localities, but, at Sir Christopher Wren's suggestion,
Greenwich Hill was finally resolved upon.  The king made a grant
of five hundred pounds of money.  He gave bricks from Tilbury
Fort, while materials, in the shape of wood, iron, and lead, were
available from a gatehouse demolished in the Tower.  The king also
promised whatever further material aid might be shown to be
necessary.  The first stone of the Royal Observatory was laid on
August 10th, 1675, and within a few years a building was erected
in which the art of modern practical astronomy was to be created.
Flamsteed strove with extraordinary diligence, and in spite of
many difficulties, to obtain a due provision of astronomical
instruments, and to arrange for the carrying on of his
observations.  Notwithstanding the king's promises, the astronomer
was, however, but scantily provided with means, and he had no
assistants to help him in his work.  It follows that all the
observations, as well as the reductions, and, indeed, all the
incidental work of the observatory, had to be carried on by
himself alone.  Flamsteed, as we have seen, had, however, many
staunch friends.  Sir Jonas Moore in particular at all times
rendered him most valuable assistance, and encouraged him by the
warm sympathy and keen interest which he showed in astronomy.  The
work of the first Astronomer Royal was frequently interrupted by
recurrent attacks of the complaints to which we have already
referred.  He says himself that "his distempers stick so close
that that he cannot remove them," and he lost much time by
prostration from headaches, as well as from more serious
affections.

The year 1678 found him in the full tide of work in his
observatory.  He was specially engaged on the problem of the
earth's motion, which he sought to derive from observations of the
sun and of Venus.  But this, as well as many other astronomical
researches which he undertook, were only subsidiary to that which
he made the main task of his life, namely, the formation of a
catalogue of fixed stars.  At the time when Flamsteed commenced
his career, the only available catalogue of fixed stars was that
of Tycho Brahe.  This work had been published at the commencement
of the seventeenth century, and it contained about a thousand
stars.  The positions assigned to these stars, though obtained
with wonderful skill, considering the many difficulties under
which Tycho laboured, were quite inaccurate when judged by our
modern standards.  Tycho's instruments were necessarily most
rudely divided, and he had, of course, no telescopes to aid him.
Consequently it was merely by a process of sighting that he could
obtain the places of the stars.  It must further be remembered
that Tycho had no clocks, and no micrometers.  He had, indeed, but
little correct knowledge of the motions of the heavenly bodies to
guide him.  To determine the longitudes of a few principal stars
he conceived the ingenious idea of measuring by day the position
of Venus with respect to the sun, an observation which the
exceptional brightness of this planet rendered possible without
telescopic aid, and then by night he observed the position of
Venus with regard to the stars.

It has been well remarked by Mr. Baily, in his introduction
to the "British Catalogue of Stars," that "Flamsteed's
observations, by a fortunate combination of circumstances,
commenced a new and a brilliant era.  It happened that, at that
period, the powerful mind of Newton was directed to this subject;
a friendly intercourse then existed between these two
distinguished characters; and thus the first observations that
could lay any claim to accuracy were at once brought in aid of
those deep researches in which our illustrious geometer was then
engaged.  The first edition of the `Principia' bears testimony to
the assistance afforded by Flamsteed to Newton in these inquiries;
although the former considers that the acknowledgment is not so
ample as it ought to have been."

Although Flamsteed's observations can hardly be said to possess
the accuracy of those made in more recent times, when instruments
so much superior to his have been available, yet they possess
an interest of a special kind from their very antiquity.  This
circumstance renders them of particular importance to the
astronomer, inasmuch as they are calculated to throw light on the
proper motions of the stars.  Flamsteed's work may, indeed, be
regarded as the origin of all subsequent catalogues, and the
nomenclature which he adopted, though in some respects it can
hardly be said to be very defensible, is, nevertheless, that which
has been adopted by all subsequent astronomers.  There were also a
great many errors, as might be expected in a work of such extent,
composed almost entirely of numerical detail.  Many of these
errors have been corrected by Baily himself, the assiduous editor
of "Flamsteed's Life and Works," for Flamsteed was so harassed
from various causes in the latter part of his life, and was so
subject to infirmities all through his career, that he was unable
to revise his  computations with the care that would have been
necessary.  Indeed, he observed many additional stars which he
never included in the British Catalogue.  It is, as Baily well
remarks, "rather a matter of astonishment that he accomplished so
much, considering his slender means, his weak frame, and the
vexations which he constantly experienced."

Flamsteed had the misfortune, in the latter part of his life, to
become estranged from his most eminent scientific contemporaries.
He had supplied Newton with places of the moon, at the urgent
solicitation of the author of the "Principia," in order that the
lunar theory should be carefully compared with observation.  But
Flamsteed appears to have thought that in Newton's further request
for similar information, he appeared to be demanding as a right
that which Flamsteed considered he was only called upon to render
as a favour.  A considerable dispute grew out of this matter, and
there are many letters and documents, bearing on the difficulties
which subsequently arose, that are not, perhaps, very creditable
to either party.

Notwithstanding his feeble constitution, Flamsteed lived to the
age of seventy-three, his death occurring on the last day of the
year 1719.




HALLEY.



Isaac Newton was just fourteen years of age when the birth of
Edmund Halley, who was destined in after years to become Newton's
warmly attached friend, and one of his most illustrious scientific
contemporaries, took place.  There can be little doubt that the
fame as an astronomer which Halley ultimately acquired, great as
it certainly was, would have been even greater still had it not
been somewhat impaired by the misfortune that he had to shine in
the same sky as that which was illumined by the unparalleled
genius of Newton.

Edmund Halley was born at Haggerston, in the Parish of
St. Leonard's, Shoreditch, on October 29th, 1656.  His father, who
bore the same name as his famous son, was a soap-boiler in
Winchester Street, London, and he had conducted his business with
such success that he accumulated an ample fortune.  I have been
unable to obtain more than a very few particulars with respect to
the early life of the future astronomer.  It would, however,
appear that from boyhood he showed considerable aptitude for the
acquisition of various kinds of learning, and he also had some
capacity for mechanical invention.  Halley seems to have received
a sound education at St. Paul's School, then under the care of
Dr. Thomas Gale.

Here, the young philosopher rapidly distanced his competitors in
the various branches of ordinary school instruction.  His
superiority was, however, most conspicuous in mathematical
studies, and, as a natural development of such tastes, we learn
that by the time he had left school he had already made good
progress in astronomy.  At the age of seventeen he was entered as
a commoner at Queen's College, Oxford, and the reputation that he
brought with him to the University may be inferred from the remark
of the writer of "Athenae Oxonienses," that Halley came to Oxford
with skill in Latin, Greek, and Hebrew, and such a knowledge of
geometry as to make a complete dial."  Though his studies were
thus of a some-what multifarious nature, yet it is plain that from
the first his most favourite pursuit was astronomy.  His earliest
efforts in practical observation were connected with an eclipse
which he observed from his father's house in Winchester Street.
It also appears that he had studied theoretical branches of
astronomy so far as to be conversant with the application of
mathematics to somewhat abstruse problems.

Up to the time of Kepler, philosophers had assumed almost as an
axiom that the heavenly bodies must revolve in circles and that
the motion of the planet around the orbit which it described must
be uniform.  We have already seen how that great philosopher,
after very persevering labour, succeeded in proving that the
orbits of the planets were not circles, but that they were
ellipses of small eccentricity.  Kepler was, however, unable to
shake himself free from the prevailing notion that the angular
motion of the planet ought to be of a uniform character around
some point.  He had indeed proved that the motion round the focus
of the ellipse in which the sun lies is not of this description.
One of his most important discoveries even related to the fact
that at some parts of its orbit a planet swings around the sun
with greater angular velocity than at others.  But it so happens
that in elliptic tracks which differ but little from circles, as
is the case with all the more important planetary orbits, the
motion round the empty focus of the ellipse is very nearly
uniform.  It seemed natural to assume, that this was exactly the
case, in which event each of the two foci of the ellipse would
have had a special significance in relation to the movement of the
planet.  The youthful Halley, however, demonstrated that so	far as
the empty focus was concerned, the movement of the planet around
it, though so nearly uniform, was still not exactly so, and at the
age of nineteen, he published a treatise on the subject which at
once placed him in the foremost rank amongst theoretical
astronomers.

But Halley had no intention of being merely an astronomer with his
pen.  He longed to engage in the practical work of observing.  He
saw that the progress of exact astronomy must depend largely on
the determination of the positions of the stars with all
attainable accuracy.  He accordingly determined to take up this
branch of work, which had been so successfully initiated by Tycho
Brahe.

At the present day, astronomers of the great national
observatories are assiduously engaged in the determination of the
places of the stars.  A knowledge of the exact positions of these
bodies is indeed of the most fundamental importance, not alone
for the purposes of scientific astronomy, but also for navigation
and for extensive operations of surveying in which accuracy is
desired.  The fact that Halley determined to concentrate himself
on this work shows clearly the scientific acumen of the young
astronomer.

Halley, however, found that Hevelius, at Dantzig, and Flamsteed,
the Astronomer Royal at Greenwich, were both engaged on
work of this character.  He accordingly determined to direct his
energies in a way that he thought would be more useful to
science.  He resigned to the two astronomers whom I have named the
investigation of the stars in the northern hemisphere, and he
sought for himself a field hitherto almost entirely unworked.  He
determined to go to the southern hemisphere, there to measure and
survey those stars which were invisible in Europe, so that his
work should supplement the labours of the northern astronomers,
and that the joint result of his labours and of theirs might be a
complete survey of the most important stars on the surface of the
heavens.

In these days, after so many ardent students everywhere have
devoted themselves to the study of Nature, it seems difficult for
a beginner to find a virgin territory in which to commence his
explorations.  Halley may, however, be said to have enjoyed the
privilege of commencing to work in a magnificent region, the
contents of which were previously almost entirely unknown.  Indeed
none of the stars which were so situated as to have been
invisible from Tycho Brahe's observatory at Uraniborg, in
Denmark, could be said to have been properly observed.  There was,
no doubt, a rumour that a Dutchman had observed southern stars
from the island of Sumatra, and certain stars were indicated in
the southern heavens on a celestial globe.  On examination,
however, Halley found that no reliance could be placed on the
results which had been obtained, so	that practically the field
before him may be said to have been unworked.

At the age of twenty, without having even waited to take that
degree at the university which the authorities would have been
glad to confer on so promising an undergraduate, this ardent
student of Nature sought his father's permission to go to the
southern hemisphere for the purpose of studying the stars which
lie around the southern pole.  His father possessed the necessary
means, and he had likewise the sagacity to encourage the young
astronomer.  He was indeed most anxious to make every thing as
easy as possible for so hopeful a son.  He provided him with an
allowance of 300 pounds a year, which was regarded as a very
munificent provision in those days.  Halley was also furnished
with letters of recommendation  from King Charles II., as well as
from the directors of the East India Company.  He accordingly set
sail with his instruments in the year 1676, in one of the East
India Company's ships, for the island of St. Helena, which he had
selected as the scene of his labours.

[PLATE:  HALLEY.]

After an uneventful voyage of three months, the astronomer
landed on St. Helena, with his sextant of five and a half feet
radius, and a telescope 24 feet long, and forthwith plunged with
ardour into his investigation of the southern skies.  He met,
however, with one very considerable disappointment.  The climate
of this island had been represented to him as most favourable for
astronomical observation; but instead of the pure blue skies he
had been led to expect, he found that they were almost always more
or less clouded, and that rain was frequent, so that his
observations were very much interrupted.  On this account he only
remained at St. Helena for a single year, having, during that
time, and in spite of many difficulties, accomplished a piece of
work which earned for him the title of "our southern Tycho."  Thus
did Halley establish his fame as an astronomer on the same lonely
rock in mid-Atlantic, which nearly a century and a-half later
became the scene of Napoleon's imprisonment, when his star, in
which he believed so firmly, had irretrievably set.

On his return to England, Halley prepared a map which showed the
result of his labours, and he presented it to the king, in 1677.
Like his great predecessor Tycho, Halley did not altogether
disdain the arts of the courtier, for he endeavoured to squeeze
a new constellation into the group around the southern pole
which he styled "The Royal Oak," adding a description to the
effect that the incidents of which "The Royal Oak" was a symbol
were of sufficient importance to be inscribed on the surface of
the heavens.

There is reason to think that Charles II. duly appreciated the
scientific renown which one of his subjects had achieved, and it
was probably through the influence of the king that Halley was
made a Master of Arts at Oxford on November 18th, 1678.  Special
reference was made on the occasion to his observations at
St. Helena, as evidence of unusual attainments in mathematics and
astronomy.  This degree was no small honour to such a young man,
who, as we have seen, quitted his university before he had the
opportunity of graduating in the ordinary manner.

On November 30th, in the same year, the astronomer
received a further distinction in being elected a Fellow of
the Royal Society.  From this time forward he took a most active
part in the affairs of the Society, and the numerous papers which
he read before it form a very valuable part of that notable series
of volumes known as the "Philosophical Transactions."  He was
subsequently elected to the important office of secretary to the
Royal Society, and he discharged the duties of his post until his
appointment to Greenwich necessitated his resignation.

Within a year of Halley's election as a Fellow of the Royal
Society, he was chosen by the Society to represent them in a
discussion which had arisen with Hevelius.  The nature of this
discussion, or rather the fact that any discussion should have
been necessary, may seem strange to modern astronomers, for the
point is one on which it would now seem impossible for there to be
any difference of opinion.  We must, however, remember that the
days of Halley were, comparatively speaking, the days of infancy
as regards the art of astronomical observation, and issues that now
seem obvious were often, in those early times, the occasions of
grave and anxious consideration.  The particular question on which
Halley had to represent the Royal Society may be simply stated.
When Tycho Brahe made his memorable investigations into the places
of the stars, he had no telescopes to help him.  The famous
instruments at Uraniborg were merely provided with sights, by
which the telescope was pointed to a star on the same principle as
a rifle is sighted for a target.  Shortly after Tycho's time,
Galileo invented the telescope.  Of course every one admitted at
once the extraordinary advantages which the telescope had to
offer, so far as the mere question of the visibility of objects
was concerned.  But the bearing of Galileo's invention upon what
we may describe as the measuring part of astronomy was not so
immediately obvious.  If a star be visible to the unaided eye, we
can determine its place by such instruments as those which Tycho
used, in which no telescope is employed.  We can, however, also
avail ourselves of an instrument in which we view the star not
directly but through the intervention of the telescope.  Can the
place of the star be determined more accurately by the latter
method than it can when the telescope is dispensed with?  With our
present knowledge, of course, there is no doubt about the answer;
every one conversant with instruments knows that we can determine
the place of a star far more accurately with the telescope than is
possible by any mere sighting apparatus.  In fact an observer
would be as likely to make an error of a minute with the sighting
apparatus in Tycho's instrument, as he would be to make an error
of a second with the modern telescope, or, to express the matter
somewhat differently, we may say, speaking quite generally, that
the telescopic method of determining the places of the stars does
not lead to errors more than one-sixtieth part as great as which
are unavoidable when we make use of Tycho's method.

But though this is so apparent to the modern astronomer, it
was not at all apparent in the days of Halley, and  accordingly he
was sent off to discuss the question with the Continental
astronomers.  Hevelius, as the representative of the older method,
which Tycho had employed with such success, maintained that an
instrument could be pointed more accurately at a star by the use
of sights than by the use of a telescope, and vigorously disputed
the claims put forward by those who believed that the latter
method was the more suitable.  On May 14th, 1679, Halley started
for Dantzig, and the energetic character of the man may be judged
from the fact that on the very night of his arrival he commenced
to make the necessary observations.  In those days astronomical
telescopes had only obtained a fractional part of the perfection
possessed by the instruments in our modern observatories, and
therefore it may not be surprising that the results of the trial
were not immediately conclusive.  Halley appears to have devoted
much time to the investigation; indeed, he remained at Dantzig for
more than a twelvemonth.  On his return to England, he spoke
highly of the skill which Hevelius exhibited in the use of his
antiquated methods, but Halley was nevertheless too sagacious an
observer to be shaken in his preference for the telescopic method
of observation.

The next year we find our young astronomer starting for a
Continental tour, and we, who complain if the Channel passage
lasts more than an hour or two, may note Halley's remark in
writing to Hooke on June 15th, 1680: "Having fallen in with bad
weather we took forty hours in the journey from Dover to Calais."
The scientific distinction which he had already attained was such
that he was received in Paris with marked attention.  A great deal
of his time seems to have been passed in the Paris observatory,
where Cassini, the presiding genius, himself an astronomer of
well-deserved repute, had extended a hearty welcome to his English
visitor.  They made observations together of the place of the
splendid comet which was then attracting universal attention, and
Halley found the work thus done of much use when he subsequently
came to investigate the path pursued by this body.  Halley was
wise enough to spare no pains to derive all possible advantages
from his intercourse with the distinguished savants of the
French capital.  In the further progress of his tour he visited
the principal cities of the Continent, leaving behind him
everywhere the memory of an amiable disposition and of a rare
intelligence.

After Halley's return to England, in 1682, he married a young lady
named Mary Tooke, with whom he lived happily, till her death
fifty-five years later.  On his marriage, he took up his abode in
Islington, where he erected his instruments and recommenced his
observations.

It has often been the good fortune of astronomers to render
practical services to humanity by their investigations, and
Halley's achievements in this respect deserve to be noted.  A few
years after he had settled in England, he published an important
paper on the variation of the magnetic compass, for so the
departure of the needle from the true north is termed.  This
subject had indeed early engaged his attention, and he continued
to feel much interest in it up to the end of his life.  With
respect to his labours in this direction, Sir John Herschel says:
"To Halley we owe the first appreciation of the real complexity of
the subject of magnetism.  It is wonderful indeed, and a striking
proof of the penetration and sagacity of this extraordinary
man, that with his means of information he should have been able
to draw such conclusions, and to take so large and comprehensive a
view of the subject as he appears to have done."  In 1692, Halley
explained his theory of terrestrial magnetism, and begged captains
of ships to take observations of the variations of the compass in
all parts of the world, and to communicate them to the Royal
Society, "in order that all the facts may be readily available to
those who are hereafter to complete this difficult and complicated
subject."

The extent to which Halley was in advance of his contemporaries,
in the study of terrestrial magnetism, may be judged from the fact
that the subject was scarcely touched after his time till the year
1811.  The interest which he felt in it was not of a merely
theoretical kind, nor was it one which could be cultivated in an
easy-chair.  Like all true investigators, he longed to submit his
theory to the test of experiment, and for that purpose Halley
determined to observe the magnetic variation for himself.  He
procured from King William III. the command of a vessel called the
"Paramour Pink," with which he started for the South Seas in 1694.
This particular enterprise was not, however, successful; for, on
crossing the line, some of his men fell sick and one of his
lieutenants mutinied, so that he was obliged to return the
following year with his mission unaccomplished.  The government
cashiered the lieutenant, and Halley having procured a second
smaller vessel to accompany the "Paramour Pink," started once more
in September, 1699.  He traversed the Atlantic to the 52nd degree
of southern latitude, beyond which his further advance was
stopped.  "In these latitudes," he writes to say, "we fell in with
great islands of ice of so incredible height and magnitude, that I
scarce dare write my thoughts of it."

On his return in 1700, Halley published a general chart, showing
the variation of the compass at the different places which he had
visited.  On these charts he set down lines connecting those
localities at which the magnetic variation was identical.  He
thus set an example of the graphic representation of large masses
of complex facts, in such a manner as to appeal at once to the
eye, a method of which we make many applications in the present
day.

But probably the greatest service which Halley ever rendered to
human knowledge was the share in which he took in bringing
Newton's "Principia" before the world.  In fact, as Dr. Glaisher,
writing in 1888, has truly remarked, "but for Halley the
'Principia' would not have existed."

It was a visit from Halley in the year 1684 which seems to have
first suggested to Newton the idea of publishing the results of
his investigations on gravitation.  Halley, and other scientific
contemporaries, had no doubt some faint glimmering of the great
truth which only Newton's genius was able fully to reveal.  Halley
had indeed shown how, on the assumptions that the planets move in
circular orbits round the sun, and that the squares of their
periodic times are proportional to the cubes of their mean
distances, it may be proved that the force acting on each planet
must vary inversely as the square of its distance from the sun.
Since, however, each of the planets actually moves in an ellipse,
and therefore, at continually varying distances from the sun, it
becomes a much more difficult matter to account mathematically for
the body's motions on the supposition that the attractive force
varies inversely as the square of the distance.  This was the
question with which Halley found himself confronted, but which his
mathematical abilities were not adequate to solve.  It would seem
that both Hooke and Sir Christopher Wren were interested in
the same problem; in fact, the former claimed to have arrived
at a solution, but declined to make known his results, giving as
an excuse his desire that others having tried and failed might
learn to value his achievements all the more.  Halley, however,
confessed that his attempts at the solution were unsuccessful, and
Wren, in order to encourage the other two philosophers to pursue
the inquiry, offered to present a book of forty shillings value to
either of them who should in the space of two months bring him a
convincing proof of it.  Such was the value which Sir Christopher
set on the Law of Gravitation, upon which the whole fabric of
modern astronomy may be said to stand.

Finding himself unequal to the task, Halley went down to Cambridge
to see Newton on the subject, and was delighted to learn that the
great mathematician had already completed the investigation.  He
showed Halley that the motions of all the planets could be
completely accounted for on the hypothesis of a force of
attraction directed towards the sun, which varies inversely as the
square of the distance from that body.

Halley had the genius to perceive the tremendous importance of
Newton's researches, and he ceased not to urge upon the recluse
man of science the necessity for giving his new discoveries
publication.  He paid another visit to Cambridge with the object
of learning more with regard to the mathematical methods which
had already conducted Newton to such sublime truths, and he again
encouraged the latter both to pursue his investigations, and to
give some account of them to the world.  In December of the same
year Halley had the gratification of announcing to the Royal
Society that Newton had promised to send that body a paper
containing his researches on Gravitation.

It seems that at this epoch the finances of the Royal Society
were at a very low ebb.  This impecuniosity was due to the fact
that a book by Willoughby, entitled "De Historia Piscium," had
been recently printed by the society at great expense.  In fact,
the coffers were so low that they had some difficulty in paying
the salaries of their permanent officials.  It appears that the
public did not care about the history of fishes, or at all events
the volume did not meet with the ready demand which was expected
for it.  Indeed, it has been recorded that when Halley had
undertaken to measure the length of a degree of the earth's
surface, at the request of the Royal Society, it was ordered that
his expenses be defrayed either in 50 pounds sterling, or in fifty
books of fishes.  Thus it happened that On June 2nd, the Council, after
due consideration of ways and means in connection with the issue
of the Principia," ordered that Halley should undertake the
business of looking after the book and printing it at his own
charge," which he engaged to do.

It was, as we have elsewhere mentioned, characteristic of Newton
that he detested controversies, and he was, in fact, inclined to
suppress the third book of the "Principia" altogether rather than
have any conflict with Hooke with respect to the discoveries there
enunciated.  He also thought of changing the name of the work to
De Motu Corporum Libri Duo, but upon second thoughts, he
retained the original title, remarking, as he wrote to Halley, "It
will help the sale of the book, which I ought not to diminish, now
it is yours," a sentence which shows conclusively, if further
proof were necessary, that Halley had assumed the responsibility
of its publication.

Halley spared no pains in pushing forward the publication of
his illustrious friend's great work, so that in the same year he
was in a position to present a complete copy to King James II.,
with a proper discourse of his own.  Halley also wrote a set of
Latin hexameters in praise of Newton's genius, which he printed at
the beginning of the work.  The last line of this specimen of
Halley's poetic muse may be thus rendered: Nor mortals nearer may
approach the gods."

The intimate friendship between the two greatest astronomers of
the time continued without interruption till the death of Newton.
It has, indeed, been alleged that some serious cause of
estrangement arose between them.  There is, however, no
satisfactory ground for this statement; indeed, it may be regarded
as effectually disposed of by the fact that, in the year 1727,
Halley took up the defence of his friend, and wrote two learned
papers in support of Newton's "System of Chronology," which had
been seriously attacked by a certain ecclesiastic.  It is quite
evident to any one who has studied these papers that Halley's
friendship for Newton was as ardent as ever.

The generous zeal with which Halley adopted and defended the
doctrines of Newton with regard to the movements of the celestial
bodies was presently rewarded by a brilliant discovery, which has
more than any of his other researches rendered his name a familiar
one to astronomers.  Newton, having explained the movement of the
planets, was naturally led to turn his attention to comets.  He
perceived that their journeyings could be completely accounted for
as consequences of the attraction of the sun, and he laid down the
principles by which the orbit of a comet could be determined,
provided that observations of its positions were obtained at three
different dates.  The importance of these principles was by no
one more quickly recognised than by Halley, who saw at once that
it provided the means of detecting something like order in the
movements of these strange wanderers.  The doctrine of Gravitation
seemed to show that just as the planets revolved around the sun in
ellipses, so also must the comets.  The orbit, however, in the
case of the comet, is so extremely elongated that the very small
part of the elliptic path within which the comet is both near
enough and bright enough to be seen from the earth, is
indistinguishable from a parabola.  Applying these principles,
Halley thought it would be instructive to study the movements of
certain bright comets, concerning which reliable observations
could be obtained.  At the expense of much labour, he laid down
the paths pursued by twenty-four of these bodies, which had
appeared between the years 1337 and 1698.  Amongst them he noticed
three, which followed tracks so closely resembling each other,
that he was led to conclude the so called three comets could only
have been three different appearances of the same body.  The first
of these occurred in 1531, the second was seen by Kepler in 1607,
and the third by Halley himself in 1682.  These dates suggested
that the observed phenomena might be due to the successive returns
of one and the same comet after intervals of seventy-five or
seventy-six years.  On the further examination of ancient records,
Halley found that a comet had been seen in the year 1456, a date,
it will be observed, seventy-five years before 1531.  Another had
been observed seventy-six years earlier than 1456, viz., in 1380,
and another seventy-five years before that, in 1305.

As Halley thus found that a comet had been recorded on several
occasions at intervals of seventy-five or seventy-six years, he
was led to the conclusion that these several apparitions related
to one and the same object, which was an obedient vassal of the
sun, performing an eccentric journey round that luminary in a
period of seventy-five or seventy-six years.  To realise the
importance of this discovery, it should be remembered that before
Halley's time a comet, if not regarded merely as a sign of divine
displeasure, or as an omen of intending disaster, had at least
been regarded as a chance visitor to the solar system, arriving no
one knew whence, and going no one knew whither.

A supreme test remained to be applied to Halley's theory.  The
question arose as to the date at which this comet would be seen
again.  We must observe that the question was complicated by the
fact that the body, in the course of its voyage around the sun,
was exposed to the incessant disturbing action produced by the
attraction of the several planets.  The comet therefore, does not
describe a simple ellipse as it would do if the attraction of the
sun were the only force by which its movement were controlled.
Each of the planets solicits the comet to depart from its track,
and  though the amount of these attractions may be insignificant
in comparison with the supreme controlling force of the sun, yet
the departure from the ellipse is quite sufficient to produce
appreciable irregularities in the comet's movement.  At the time
when Halley lived, no means existed of calculating with precision
the effect of the disturbance a comet might experience from the
action of the different planets.  Halley exhibited his usual
astronomical sagacity in deciding that Jupiter would retard the
return of the comet to some extent.  Had it not been for this
disturbance the comet would apparently have been due in 1757 or
early in 1758.  But the attraction of the great planet would cause
delay, so that Halley assigned, for the date of its re-appearance,
either the end of 1758 or the beginning of 1759.  Halley knew that
he could not himself live to witness the fulfilment of his
prediction, but he says: "If it should return, according to our
predictions, about the year 1758, impartial posterity will not
refuse to acknowledge that this was first discovered by an
Englishman."  This was, indeed, a remarkable prediction of an
event to occur fifty-three years after it had been uttered.  The
way in which it was fulfilled forms one of the most striking
episodes in the history of astronomy.  The comet was first seen on
Christmas Day, 1758, and passed through its nearest point to the
sun on March 13th, 1759.  Halley had then been lying in his grave
for seventeen years, yet the verification of his prophecy reflects
a glory on his name which will cause it to live for ever in the
annals of astronomy.  The comet paid a subsequent visit in 1835,
and its next appearance is due about 1910.

Halley next entered upon a labour which, if less striking to
the imagination than his discoveries with regard to comets, is
still of inestimable value in astronomy.  He undertook a series of
investigations with the object of improving our knowledge of the
movements of the planets.  This task was practically finished in
1719, though the results of it were not published until after his
death in 1749.  In the course of it he was led to investigate
closely the motion of Venus, and thus he came to recognise for the
first time the peculiar importance which attaches to the
phenomenon of the transit of this planet across the sun.  Halley
saw that the transit, which was to take place in the year 1761,
would afford a favourable opportunity for determining the distance
of the sun, and thus learning the scale of the solar system.  He
predicted the circumstances of the phenomenon with an astonishing
degree of accuracy, considering his means of information, and it
is unquestionably to the exertions of Halley in urging the
importance of the matter upon astronomers that we owe the
unexampled degree of interest taken in the event, and the energy
which scientific men exhibited in observing it.  The illustrious
astronomer had no hope of being himself a witness of the event,
for it could not happen till many years after his death.  This did
not, however, diminish his anxiety to impress upon those who would
then be alive, the importance of the occurrence, nor did it lead
him to neglect anything which might contribute to the success of
the observations.  As we now know, Halley rather over-estimated
the value of the transit of Venus, as a means of determining the
solar distance.  The fact is that the circumstances are such that
the observation of the time of contact between the edge of the
planet and the edge of the sun cannot be made with the accuracy
which he had expected.

In 1691, Halley became a candidate for the Savilian Professorship
of Astronomy at Oxford.  He was not, however, successful, for his
candidature was opposed by Flamsteed, the Astronomer Royal of the
time, and another was appointed.  He received some consolation for
this particular disappointment by the fact that, in 1696, owing to
Newton's friendly influence, he was appointed deputy Controller of
the Mint at Chester, an office which he did not retain for long,
as it was abolished two years later.  At last, in 1703, he
received what he had before vainly sought, and he was appointed to
the Savilian chair.

His observations of the eclipse of the sun, which occurred in
1715, added greatly to Halley's reputation.  This phenomenon
excited special attention, inasmuch as it was the first total
eclipse of the sun which had been visible in London since the
year 1140.  Halley undertook the necessary calculations,
and predicted the various circumstances with a far higher degree
of precision than the official announcement.  He himself observed
the phenomenon from the Royal Society's rooms, and he minutely
describes the outer atmosphere of the sun, now known as the
corona; without, however, offering an opinion as to whether it
was a solar or a lunar appendage.

At last Halley was called to the dignified office which he of all
men was most competent to fill.  On February 9th, 1720, he was
appointed Astronomer Royal in succession to Flamsteed.  He found
things at the Royal Observatory in a most unsatisfactory state.
Indeed, there were no instruments, nor anything else that was
movable; for such things, being the property of Flamsteed,
had been removed by his widow, and though Halley attempted
to purchase from that lady some of the instruments which
his predecessor had employed, the unhappy personal differences
which had existed between him and Flamsteed, and which, as we have
already seen, prevented his election as Savilian Professor of
Astronomy, proved a bar to the negotiation.  Greenwich Observatory
wore a very different appearance in those days, from that which
the modern visitor, who is fortunate enough to gain admission, may
now behold.  Not only did Halley find it bereft of instruments, we
learn besides that he had no assistants, and was obliged to
transact the whole business of the establishment single-handed.

In 1721, however, he obtained a grant of 500 pounds from the Board
of Ordnance, and accordingly a transit instrument was erected in
the same year.  Some time afterwards he procured an eight-foot
quadrant, and with these instruments, at the age of sixty-four, he
commenced a series of observations on the moon.  He intended, if
his life was spared, to continue his observations for a period of
eighteen years, this being, as astronomers know, a very important
cycle in connection with lunar movements.  The special object of
this vast undertaking was to improve the theory of the moon's
motion, so that it might serve more accurately to determine
longitudes at sea.  This self-imposed task Halley lived to carry
to a successful termination, and the tables deduced from his
observations, and published after his death, were adopted almost
universally by astronomers, those of the French nation being the
only exception.

Throughout his life Halley had been singularly free from illness
of every kind, but in 1737 he had a stroke of paralysis.
Notwithstanding this, however, he worked diligently at his
telescope till 1739, after which his health began rapidly to give
way.  He died on January 14th, 1742, in the eighty-sixth year of
his age, retaining his mental faculties to the end.  He was buried
in the cemetery of the church of Lee in Kent, in the same grave as
his wife, who had died five years previously.  We are informed by
Admiral Smyth that Pond, a later Astronomer Royal, was afterwards
laid in the same tomb.

Halley's disposition seems to have been generous and candid, and
wholly free from anything like jealousy or rancour.  In person he
was rather above the middle height, and slight in build; his
complexion was fair, and he is said to have always spoken, as well
as acted, with uncommon sprightliness.  In the eloge pronounced
upon him at the Paris Academie Des Sciences, of which Halley had
been made a member in 1719 it was said, "he possessed all the
qualifications which were necessary to please princes who were
desirous of instruction, with a great extent of knowledge and a
constant presence of mind; his answers were ready, and at the same
time pertinent, judicious, polite and sincere."

[PLATE:  GREENWICH OBSERVATORY IN HALLEY'S TIME.]

Thus we find that Peter the Great was one of his most ardent
admirers.  He consulted the astronomer on matters connected with
shipbuilding, and invited him to his own table.  But Halley
possessed nobler qualifications than the capacity of pleasing
Princes.  He was able to excite and to retain the love and
admiration of his equals.  This was due to the warmth of his
attachments, the unselfishness of his devotion to his friends,
and to a vein of gaiety and good-humour which pervaded all his
conversation.





BRADLEY.



James Bradley was descended from an ancient family in the county
of Durham.  He was born in 1692 or 1693, at Sherbourne, in
Gloucestershire, and was educated in the Grammar School at
Northleach.  From thence he proceeded in due course to Oxford,
where he was admitted a commoner at Balliol College, on March
15th, 1711.  Much of his time, while an undergraduate, was
passed in Essex with his maternal uncle, the Rev. James Pound,
who was a well-known man of science and a diligent observer of the
stars.  It was doubtless by intercourse with his uncle that young
Bradley became so expert in the use of astronomical instruments,
but the immortal discoveries he subsequently made show him to have
been a born astronomer.

The first exhibition of Bradley's practical skill seems to be
contained in two observations which he made in 1717 and 1718.
They have been published by Halley, whose acuteness had led him to
perceive the extraordinary scientific talents of the young
astronomer.  Another illustration of the sagacity which Bradley
manifested, even at the very commencement of his astronomical
career, is contained in a remark of Halley's, who says: Dr. Pound
and his nephew, Mr. Bradley, did, myself being present, in the
last opposition of the sun and Mars this way demonstrate the
extreme minuteness of the sun's parallax, and that it was not more
than twelve seconds nor less than nine seconds."  To make the
significance of this plain, it should be observed that the
determination of the sun's parallax is equivalent to the
determination of the distance from the earth to the sun.  At the
time of which we are now writing, this very important unit of
celestial measurement was only very imperfectly known, and the
observations of Pound and Bradley may be interpreted to mean that,
from their observations, they had come to the conclusion that the
distance from the earth to the sun must be more than 94 millions
of miles, and less than 125 millions.  We now, of course, know
that they were not exactly right, for the true distance of the sun
is about 93 millions of miles.  We cannot, however, but think
that it was a very remarkable approach for the veteran astronomer
and his brilliant nephew to make towards the determination of a
magnitude which did not become accurately known till fifty years
later.

Among the earliest parts of astronomical work to which Bradley's
attention was directed, were the eclipses of Jupiter's satellites.
These phenomena are specially attractive inasmuch as they can be
so readily observed, and Bradley found it extremely interesting to
calculate the times at which the eclipses should take place, and
then to compare his observations with the predicted times.  From
the success that he met with in this work, and from his other
labours, Bradley's reputation as an astronomer increased so
greatly that on November the 6th, 1718, he was elected a Fellow of
the Royal Society.

Up to this time the astronomical investigations of Bradley had
been more those of an amateur than of a professional astronomer,
and as it did not at first seem likely that scientific work would
lead to any permanent provision, it became necessary for the
youthful astronomer to choose a profession.  It had been all
along intended that he should enter the Church, though for some
reason which is not told us, he did not take orders as soon as
his age would have entitled him to do so.  In 1719, however, the
Bishop of Hereford offered Bradley the Vicarage of Bridstow, near
Ross, in Monmouthshire, and on July 25th, 1720, he having then
taken priest's orders, was duly instituted in his vicarage.  In
the beginning of the next year,  Bradley had some addition to his
income from the proceeds of a Welsh living, which, being a
sinecure, he was able to hold with his appointment at Bridstow.
It appears, however, that his clerical occupations were not very
exacting in their demands upon his time, for he was still able to
pay long and often-repeated visits to his uncle at Wandsworth,
who, being himself a clergyman, seems to have received occasional
assistance in his ministerial duties from his astronomical nephew.

The time, however, soon arrived when Bradley was able to make a
choice between continuing to exercise his profession as a divine,
or devoting himself to a scientific career.  The Savilian
Professorship of Astronomy in the University of Oxford became
vacant by the death of Dr. John Keill.  The statutes forbade that
the Savilian Professor should also hold a clerical appointment,
and Mr. Pound would certainly have been elected to the
professorship had he consented to surrender his preferments in the
Church.  But Pound was unwilling to sacrifice his clerical
position, and though two or three other candidates appeared in the
field, yet the talents of Bradley were so conspicuous that he was
duly elected, his willingness to resign the clerical profession
having been first ascertained.

There can be no doubt that, with such influential friends as
Bradley possessed, he would have made great advances had he
adhered to his profession as a divine.  Bishop Hoadly, indeed,
with other marks of favour, had already made the astronomer his
chaplain.  The engrossing nature of Bradley's interest in
astronomy decided him, however, to sacrifice all other prospects
in comparison with the opening afforded by the Savilian
Professorship.  It was not that Bradley found himself devoid of
interest in clerical matters, but he felt that the true scope for
such abilities as he possessed would be better found in the
discharge of the scientific duties of the Oxford chair than in the
spiritual charge of a parish.  On April the 26th, 1722, Bradley
read his inaugural lecture in that new position on which he was
destined to confer such lustre.

It must, of course, be remembered that in those early days the art
of constructing the astronomical telescope was very imperfectly
understood.  The only known method for getting over the peculiar
difficulties presented in the construction of the refracting
telescope, was to have it of the most portentous length.  In fact,
Bradley made several of his observations with an instrument of two
hundred and twelve feet focus.  In such a case, no tube could be
used, and the object glass was merely fixed at the top of a high
pole.  Notwithstanding the inconvenience and awkwardness of such
an instrument, Bradley by its means succeeded in making many
careful measurements.  He observed, for example, the transit of
Mercury over the sun's disc, on October 9th, 1723, he also
observed the dimensions of the planet Venus, while a comet which
Halley discovered on October the 9th, 1723, was assiduously
observed at Wanstead up to the middle of the ensuing month.  The
first of Bradley's remarkable contributions to the "Philosophical
Transactions" relates to this comet, and the extraordinary amount
of work that he went through in connection therewith may
be seen from an examination of his book of Calculations which is
still extant.

The time was now approaching when Bradley was to make the first of
those two great discoveries by which his name has acquired a
lustre that has placed him in the very foremost rank of
astronomical discoverers.  As has been often the case in the
history of science, the first of these great successes was
attained while he was pursuing a research intended for a wholly
different purpose.  It had long been recognised that as the earth
describes a vast orbit, nearly two hundred million miles in
diameter, in its annual journey round the sun, the apparent
places of the stars should alter, to some extent, in
correspondence with the changes in the earth's position.  The
nearer the star the greater the shift in its apparent place on the
heavens, which must arise from the fact that it was seen from
different positions in the earth's orbit.  It had been pointed out
that these apparent changes in the places of the stars, due to the
movement of the earth, would provide the means of measuring the
distances of the stars.  As, however, these distances are
enormously great in comparison with the orbit which the earth
describes around the sun, the attempt to determine the distances
of the stars by the shift in their positions had hitherto proved
ineffectual.  Bradley determined to enter on this research once
again; he thought that by using instruments of greater power, and
by making measurements of increased delicacy, he would be able to
perceive and to measure displacements which had proved so small as
to elude the skill of the other astronomers who had previously
made efforts in the same direction.  In order to simplify the
investigation as much as possible, Bradley devoted his attention
to one particular star, Beta Draconis, which happened to pass near
his zenith.  The object of choosing a star in this position was to
avoid the difficulties which would be introduced by refraction had
the star occupied any other place in the heavens than that
directly overhead.

We are still able to identify the very spot on which the telescope
stood which was used in this memorable research.  It was erected
at the house then occupied by Molyneux, on the western extremity
of Kew Green.  The focal length was 24 feet 3 inches, and the eye-
glass was 3 and a half feet above the ground floor.  The
instrument was first set up on November 26th, 1725.  If there had
be any appreciable disturbance in the place of Beta Draconis in
consequence of the movement of the earth around the sun, the star
must appear to have the smallest latitude when in conjunction with
the sun, and the greatest when in opposition.  The star passed the
meridian at noon in December, and its position was particularly
noticed by Molyneux on the third of that month.  Any perceptible
displacement by parallax--for so the apparent change in position,
due to the earth's motion, is called--would would have made the
star shift towards the north.  Bradley, however, when observing it
on the 17th, was surprised to find that the apparent place of the
star, so far from shifting towards the north, as they had perhaps
hoped it would, was found to lie a little more to the south than
when it was observed before.  He took extreme care to be sure that
there was no mistake in his observation, and, true astronomer as
he was, he scrutinized with the utmost minuteness all the
circumstances of the adjustment of his instruments.  Still the
star went to the south, and it continued so advancing in the same
direction until the following March, by which time it had moved no
less than twenty seconds south from the place which it occupied
when the first observation was made.  After a brief pause, in
which no apparent movement was perceptible, the star by the middle
of April appeared to be returning to the north.  Early in June it
reached the same distance from the zenith which it had in
December.  By September the star was as much as thirty-nine
seconds more to the north than it had been in March, then it
returned towards the south, regaining in December the same
situation which it had occupied twelve months before.

This movement of the star being directly opposite to the movements
which would have been the consequence of parallax, seemed to show
that even if the star had any parallax its effects upon the
apparent place were entirely masked by a much larger motion of a
totally different description.  Various attempts were made to
account for the phenomenon, but they were not successful.  Bradley
accordingly determined to investigate the whole subject in a more
thorough manner.  One of his objects was to try whether the same
movements which he had observed in one star were in any similar
degree possessed by other stars.  For this purpose he set up a new
instrument at Wanstead, and there he commenced a most diligent
scrutiny of the apparent places of several stars which passed at
different distances from the zenith.  He found in the course of
this research that other stars exhibited movements of a similar
description to those which had already proved so perplexing.  For
a long time the cause of these apparent movements seemed a
mystery.  At last, however, the explanation of these remarkable
phenomena dawned upon him, and his great discovery was made.

One day when Bradley was out sailing he happened to remark that
every time the boat was laid on a different tack the vane at the
top of the boat's mast shifted a little, as if there had been a
slight change in the direction of the wind.  After he had noticed
this three or four times he made a remark to the sailors to the
effect that it was very strange the wind should always happen to
change just at the moment when the boat was going about.  The
sailors, however, said there had been no change in the wind, but
that the alteration in the vane was due to the fact that the
boat's course had been altered.  In fact, the position of the
vane was determined both by the course of the boat and the
direction of the wind, and if either of these were altered there
would be a corresponding change in the direction of the vane.
This meant, of course, that the observer in the boat which was
moving along would feel the wind coming from a point different
from that in which the wind appeared to be blowing when the boat
was at rest, or when it was sailing in some different direction.
Bradley's sagacity saw in this observation the clue to the
Difficulty which had so long troubled him.

It had been discovered before the time of Bradley that the passage
of light through space is not an instantaneous phenomenon.  Light
requires time for its journey.  Galileo surmised that the sun may
have reached the horizon before we see it there, and it was indeed
sufficiently obvious that a physical action, like the transmission
of light, could hardly take place without requiring some lapse of
time.  The speed with which light actually travelled was, however,
so rapid that its determination eluded all the means of
experimenting which were available in those days.  The penetration
of Roemer had previously detected irregularities in the observed
times of the eclipses of Jupiter's satellites, which were
undoubtedly due to the interval which light required for
stretching across the interplanetary spaces.  Bradley argued that
as light can only travel with a certain speed, it may in a
measure be regarded like the wind, which he noticed in the boat.
If the observer were at rest, that is to say, if the earth were a
stationary object, the direction in which the light actually does
come would be different from that in which it appears to come when
the earth is in motion.  It is true that the earth travels but
eighteen miles a second, while the velocity with which light is
borne along attains to as much as 180,000 miles a second.  The
velocity of light is thus ten thousand times greater than the
speed of the earth.  But even though the wind blew ten
thousand times faster than the speed with which the boat was
sailing there would still be some change, though no doubt a very
small change, in the position of the vane when the boat was in
progress from the position it would have if the boat were at rest.
It therefore occurred to this most acute of astronomers that when
the telescope was pointed towards a star so as to place it
apparently in the centre of the field of view, yet it was not
generally the true position of the star.  It was not, in fact,
the position in which the star would have been observed had the
earth been at rest.  Provided with this suggestion, he explained
the apparent movements of the stars by the principle known as the
"aberration of light."  Every circumstance was accounted for as a
consequence of the relative movements of the earth and of the
light from the star.  This beautiful discovery not only
established in the most forcible manner the nature of the movement
of light; not only did it illustrate the truth of the Copernican
theory which asserted that the earth revolved around the sun, but
it was also of the utmost importance in the improvement of
practical astronomy.  Every observer now knows that, generally
speaking, the position which the star appears to have is not
exactly the position in which the star does actually lie.  The
observer is, however, able, by the application of the principles
which Bradley so clearly laid down, to apply to an observation the
correction which is necessary to obtain from it the true place in
which the object is actually situated.  This memorable achievement
at once conferred on Bradley the highest astronomical fame.  He
tested his discovery in every way, but only to confirm its truth
in the most complete manner.

Halley, the Astronomer Royal, died on the 14th, January, 1742, and
Bradley was immediately pointed out as his successor.  He was
accordingly appointed Astronomer Royal in February, 1742.
On first taking up his abode at Greenwich he was unable to conduct
his observations owing to the wretched condition in which he found
the instruments.  He devoted himself, however, assiduously to
their repair, and his first transit observation is recorded on the
25th July, 1742.  He worked with such energy that on one day it
appears that 255 transit observations were taken by himself alone,
and in September, 1747, he had completed the series of
observations which established his second great discovery, the
nutation of the earth's axis.  The way in which he was led to the
detection of the nutation is strikingly illustrative of the
extreme care with which Bradley conducted his observations.  He
found that in the course of a twelvemonth, when the star had
completed the movement which was due to aberration, it did not
return exactly to the same position which it had previously
occupied.  At first he thought this must be due to some
instrumental error, but after closer examination and
repeated study of the effect as manifested by many different
stars, he came to the conclusion that its origin must be sought in
some quite different source.  The fact is that a certain change
takes place in the apparent position of the stars which is not due
to the movement of the star itself, but is rather to be attributed
to changes in the points from which the star's positions are
measured.

We may explain the matter in this way.  As the earth is not a
sphere, but has protuberant parts at the equator, the attraction
of the moon exercises on those protuberant parts a pulling effect
which continually changes the direction of the earth's axis, and
consequently the position of the pole must be in a state of
incessant fluctuation.  The pole to which the earth's axis points
on the sky is, therefore, slowly changing.  At present it happens
to lie near the Pole Star, but it will not always remain there.
It describes a circle around the pole of the Ecliptic, requiring
about 25,000 years for a complete circuit.  In the course of its
progress the pole will gradually pass now near one star and now
near another, so that many stars will in the lapse of ages
discharge the various functions which the present Pole Star does
for us.  In about 12,000 years, for instance, the pole will have
come near the bright star, Vega.  This movement of the pole had
been known for ages.  But what Bradley discovered was that the
pole, instead of describing an uniform movement as had been
previously supposed, followed a sinuous course now on one side and
now on the other of its mean place.  This he traced to the
fluctuations of the moon's orbit, which undergoes a continuous
change in a period of nineteen years.  Thus the efficiency with
which the moon acts on the protuberant mass of the earth
varies, and thus the pole is caused to oscillate.

This subtle discovery, if perhaps in some ways less impressive
than Bradley's earlier achievements of the detection of the
aberration of light, is regarded by astronomers as testifying even
in a higher degree to his astonishing care and skill as an
observer, and justly entitles him to a unique place among the
astronomers whose discoveries have been effected by consummate
practical skill in the use of astronomical instruments.

Of Bradley's private or domestic life there is but little
to tell.  In 1744, soon after he became Astronomer Royal,
he married a daughter of Samuel Peach, of Chalford, in
Gloucestershire.  There was but one child, a daughter, who became
the wife of her cousin, Rev. Samuel Peach, rector of Compton,
Beauchamp, in Berkshire.

Bradley's last two years of life were clouded by a melancholy
depression of spirits, due to an apprehension that he should
survive his rational faculties.  It seems, however, that the ill
he dreaded never came upon him, for he retained his mental powers
to the close.  He died on 13th July, 1762, aged seventy, and was
buried at Michinghamton.




WILLIAM HERSCHEL.



William Herschel, one of the greatest astronomers that has ever
lived, was born at Hanover, on the 15th November, 1738.  His
father, Isaac Herschel, was a man evidently of considerable
ability, whose life was devoted to the study and practice of
music, by which he earned a somewhat precarious maintenance.  He
had but few worldly goods to leave to his children, but he more
than compensated for this by bequeathing to them a splendid
inheritance of genius.  Touches of genius were, indeed, liberally
scattered among the members of Isaac's large family, and in the
case of his forth child, William, and of a sister several years
younger, it was united with that determined perseverance and rigid
adherence to principle which enabled genius to fulfil its perfect
work.

A faithful chronicler has given us an interesting account of
the way in which Isaac Herschel educated his sons; the narrative
is taken from the recollections of one who, at the time we are
speaking of, was an unnoticed little girl five or six years old.
She writes:--

"My brothers were often introduced as solo performers and
assistants in the orchestra at the Court, and I remember that I
was frequently prevented from going to sleep by the lively
criticisms on music on coming from a concert.  Often I would keep
myself awake that I might listen to their animating remarks, for
it made me so happy to see them so happy.  But generally their
conversation would branch out on philosophical subjects, when my
brother William and my father often argued with such warmth that
my mother's interference became necessary, when the names--Euler,
Leibnitz, and Newton--sounded rather too loud for the repose of her
little ones, who had to be at school by seven in the morning."
The child whose reminiscences are here given became afterwards the
famous Caroline Herschel.  The narrative of her life, by Mrs. John
Herschel, is a most interesting book, not only for the account it
contains of the remarkable woman herself, but also because it
provides the best picture we have of the great astronomer to whom
Caroline devoted her life.

This modest family circle was, in a measure, dispersed at the
outbreak of the Seven Years' War in 1756.  The French proceeded to
invade Hanover, which, it will be remembered, belonged at this
time to the British dominions.  Young William Herschel had already
obtained the position of a regular performer in the regimental
band of the Hanoverian Guards, and it was his fortune to obtain
some experience of actual warfare in the disastrous battle of
Hastenbeck.  He was not wounded, but he had to spend the night
after the battle in a ditch, and his meditations on the occasion
convinced him that soldiering was not the profession exactly
adapted to his tastes.  We need not attempt to conceal the fact
that he left his regiment by the very simple but somewhat risky
process of desertion.  He had, it would seem, to adopt disguises
to effect his escape.  At all events, by some means he succeeded
in eluding detection and reached England in safety.  It is
interesting to have learned on good authority that many years
after this offence was committed it was solemnly forgiven.  When
Herschel had become the famous astronomer, and as such visited
King George at Windsor, the King at their first meeting handed to
him his pardon for deserting from the army, written out in due
form by his Majesty himself.

It seems that the young musician must have had some difficulty in
providing for his maintenance during the first few years of his
abode in England.  It was not until he had reached the age of
twenty-two that he succeeded in obtaining any regular appointment.
He was then made Instructor of Music to the Durham Militia.
Shortly afterwards, his talents being more widely recognised, he
was appointed as organist at the parish church at Halifax, and his
prospects in life now being fairly favourable, and the Seven
Years' War being over, he ventured to pay a visit to Hanover to
see his father.  We can imagine the delight with which old Isaac
Herschel welcomed his promising son, as well as his parental pride
when a concert was given at which some of William's compositions
were performed.  If the father was so intensely gratified on this
occasion, what would his feelings have been could he have lived to
witness his son's future career?  But this pleasure was not to be
his, for he died many years before William became an astronomer.

In 1766, about a couple of years after his return to England from
This visit to his old home, we find that Herschel had received a
further promotion to be organist in the Octagon Chapel, at Bath.
Bath was then, as now, a highly fashionable resort, and many
notable personages patronised the rising musician.  Herschel had
other points in his favour besides his professional skill; his
appearance was good, his address was prepossessing, and even his
nationality was a distinct advantage, inasmuch as he was a
Hanoverian in the reign of King George the Third.  On Sundays he
played the organ, to the great delight of the congregation, and on
week-days he was occupied by giving lessons to private pupils, and
in preparation for public performances.  He thus came to be busily
employed, and seems to have been in the enjoyment of comfortable
means.

[PLATE:  7, NEW KING STREET, BATH, WHERE HERSCHEL LIVED.]

From his earliest youth Herschel had been endowed with that
invaluable characteristic, an eager curiosity for knowledge.  He
was naturally desirous of perfecting himself in the theory of
music, and thus he was led to study mathematics.  When he had once
tasted the charms of mathematics, he saw vast regions of knowledge
unfolded before him, and in this way he was induced to direct his
attention to astronomy.  More and more this pursuit seems to have
engrossed his attention, until at last it had become an absorbing
passion.  Herschel was, however, still obliged, by the exigency of
procuring a livelihood, to give up the best part of his time to
his profession as a musician; but his heart was eagerly fixed on
another science, and every spare moment was steadily devoted to
astronomy.  For many years, however, he continued to labour at his
original calling, nor was it until he had attained middle age and
become the most celebrated astronomer of the time, that he was
enabled to concentrate his attention exclusively on his favourite
pursuit.

It was with quite a small telescope which had been lent him by a
friend that Herschel commenced his career as an observer.
However, he speedily discovered that to see all he wanted to see,
a telescope of far greater power would be necessary, and he
determined to obtain this more powerful instrument by actually
making it with his own hands.  At first it may seem scarcely
likely that one whose occupation had previously been the study and
practice of music should meet with success in so technical an
operation as the construction of a telescope.  It may, however, be
mentioned that the kind of instrument which Herschel designed to
construct was formed on a very different principle from the
refracting telescopes with which we are ordinarily familiar.  His
telescope was to be what is termed a reflector.  In this type of
instrument the optical power is obtained by the use of a mirror at
the bottom of the tube, and the astronomer looks down through the
tube TOWARDS HIS MIRROR and views the reflection of the stars
with its aid.  Its efficiency as a telescope depends entirely on
the accuracy with which the requisite form has been imparted to
the mirror.  The surface has to be hollowed out a little, and this
has to be done so truly that the slightest deviation from good
workmanship in this essential particular would be fatal to
efficient performance of the telescope.

[PLATE:  WILLIAM HERSCHEL.]

The mirror that Herschel employed was composed of a mixture of two
parts of copper to one of tin; the alloy thus obtained is an
intensely hard material, very difficult to cast into the proper
shape, and very difficult to work afterwards.  It possesses,
however, when polished, a lustre hardly inferior to that of silver
itself.  Herschel has recorded hardly any particulars as to the
actual process by which he cast and figured his reflectors.
We are however, told that in later years, after his telescopes had
become famous, he made a considerable sum of money by the
manufacture and sale of great instruments.  Perhaps this may be
the reason why he never found it expedient to publish any very
explicit details as to the means by which his remarkable
successes were obtained.

[PLATE:  CAROLINE HERSCHEL.]

Since Herschel's time many other astronomers, notably the late
Earl of Rosse, have experimented in the same direction, and
succeeded in making telescopes certainly far greater, and probably
more perfect, than any which Herschel appears to have constructed.
The details of these later methods are now well known, and have
been extensively practised.  Many amateurs have thus been able to
make telescopes by following the instructions so clearly laid
down by Lord Rosse and the other authorities.  Indeed, it would
seem that any one who has a little mechanical skill and a good
deal of patience ought now to experience no great difficulty in
constructing a telescope quite as powerful as that which first
brought Herschel into fame.  I should, however, mention that in
these modern days the material generally used for the mirror is
of a more tractable description than the metallic substance which
was employed by Herschel and by Lord Rosse.  A reflecting
telescope of the present day would not be fitted with a mirror
composed of that alloy known as speculum metal, whose composition
I have already mentioned.  It has been found more advantageous to
employ a glass mirror carefully figured and polished, just as a
metallic mirror would have been, and then to impart to the
polished glass surface a fine coating of silver laid down by a
chemical process.  The silver-on-glass mirrors are so much lighter
and so much easier to construct that the more old-fashioned
metallic mirrors may be said to have fallen into almost total
disuse.  In one respect however, the metallic mirror may still
claim the advantage that, with reasonable care, its surface will
last bright and untarnished for a much longer period than can the
silver film on the glass.  However, the operation of re-silvering
a glass has now become such a simple one that the advantage this
indicates is not relatively so great as might at first be supposed.

[PLATE:  STREET VIEW, HERSCHEL HOUSE, SLOUGH.]

Some years elapsed after Herschel's attention had been first
directed to astronomy, before he reaped the reward of his
exertions in the possession of a telescope which would adequately
reveal some of the glories of the heavens.  It was in 1774, when
the astronomer was thirty-six years old, that he obtained his
first glimpse of the stars with an instrument of his own
construction.  Night after night, as soon as his musical labours
were ended, his telescopes were brought out, sometimes into the
small back garden of his house at Bath, and sometimes into the
street in front of his hall-door.  It was characteristic of him
that he was always endeavouring to improve his apparatus.  He was
incessantly making fresh mirrors, or trying new lenses, or
combinations of lenses to act as eye-pieces, or projecting
alterations in the mounting by which the telescope was supported.
Such was his enthusiasm that his house, we are told, was
incessantly littered with the usual indications of the workman's
presence, greatly to the distress of his sister, who, at this
time, had come to take up her abode with him and look after his
housekeeping.  Indeed, she complained that in his astronomical
ardour he sometimes omitted to take off, before going into his
workshop, the beautiful lace ruffles which he wore while
conducting a concert, and that consequently they became soiled
with the pitch employed in the polishing of his mirrors.

This sister, who occupies such a distinct place in scientific
history is the same little girl to whom we have already referred.
From her earliest days she seems to have cherished a passionate
admiration for her brilliant brother William.  It was the
proudest delight of her childhood as well as of her mature years
to render him whatever service she could; no man of science was
ever provided with a more capable or energetic helper than
William Herschel found in this remarkable woman.  Whatever work
had to be done she was willing to bear her share in it, or even to
toil at it unassisted if she could be allowed to do so.  She not
only managed all his domestic affairs, but in the grinding of the
lenses and in the polishing of the mirrors she rendered every
assistance that was possible.  At one stage of the very delicate
operation of fashioning a reflector, it is necessary for the
workman to remain with his hand on the mirror for many hours in
succession.  When such labours were in progress, Caroline used to
sit by her brother, and enliven the time by reading stories aloud,
sometimes pausing to feed him with a spoon while his hands were
engaged on the task from which he could not desist for a moment.

When mathematical work had to be done Caroline was ready for it;
she had taught herself sufficient to enable her to perform the
kind of calculations, not, perhaps, very difficult ones, that
Herschel's work required; indeed, it is not too much to say that
the mighty life-work which this man was enabled to perform could
never have been accomplished had it not been for the self-
sacrifice of this ever-loving and faithful sister.  When Herschel
was at the telescope at night, Caroline sat by him at her desk,
pen in hand, ready to write down the notes of the observations as
they fell from her brother's lips.  This was no insignificant
toil.  The telescope was, of course, in the open air, and as
Herschel not unfrequently continued his observations throughout
the whole of a long winter's night, there were but few women who
could have accomplished the task which Caroline so cheerfully
executed.  From dusk till dawn, when the sky was clear, were
Herschel's observing hours, and what this sometimes implied we can
realise from the fact that Caroline assures us she had sometimes
to desist because the ink had actually frozen in her pen.  The
night's work over, a brief rest was taken, and while William had
his labours for the day to attend to, Caroline carefully
transcribed the observations made during the night before,
reduced all the figures and prepared everything in readiness for
the observations that were to follow on the ensuing evening.

But we have here been anticipating a little of the future which
lay before the great astronomer; we must now revert to the
history of his early work, at Bath, in 1774, when Herschel's
scrutiny of the skies first commenced with an instrument of his
own manufacture.  For some few years he did not attain any result
of importance; no doubt he made a few interesting observations,
but the value of the work during those years is to be found, not
in any actual discoveries which were accomplished, but in the
practice which Herschel obtained in the use of his instruments.
It was not until 1782 that the great achievement took place by
which he at once sprang into fame.

[PLATE:  GARDEN VIEW, HERSCHEL HOUSE, SLOUGH.]

It is sometimes said that discoveries are made by accident,
and, no doubt, to a certain extent, but only, I fancy to a
very small extent, this statement may be true.  It is, at all
events, certain that such lucky accidents do not often fall to
the lot of people unless those people have done much to deserve
them.  This was certainly the case with Herschel.  He appears to
have formed a project for making a close examination of all the
stars above a certain magnitude.  Perhaps he intended to confine
this research to a limited region of the sky, but, at all events,
he seems to have undertaken the work energetically and
systematically.  Star after star was brought to the centre of the
field of view of his telescope, and after being carefully examined
was then displaced, while another star was brought forward to be
submitted to the same process.  In the great majority of cases
such observations yield really nothing of importance; no doubt
even the smallest star in the heavens would, if we could find out
all about it, reveal far more than all the astronomers that were
ever on the earth have even conjectured.  What we actually learn
about the great majority of stars is only information of the most
meagre description.  We see that the star is a little point of
light, and we see nothing more.

In the great review which Herschel undertook he doubtless examined
hundreds, or perhaps thousands of stars, allowing them to pass
away without note or comment.  But on an ever-memorable night in
March, 1782, it happened that he was pursuing his task among
the stars in the Constellation of Gemini.  Doubtless, on that
night, as on so many other nights, one star after another was
looked at only to be dismissed, as not requiring further
attention.  On the evening in question, however, one star was
noticed which, to Herschel's acute vision seemed different from
the stars which in so many thousands are strewn over the sky.  A
star properly so called appears merely as a little point of light,
which no increase of magnifying power will ever exhibit with a
true disc.  But there was something in the star-like object which
Herschel saw that immediately arrested his attention and made him
apply to it a higher magnifying power.  This at once disclosed the
fact that the object possessed a disc, that is, a definite,
measurable size, and that it was thus totally different from any
one of the hundreds and thousands of stars which exist elsewhere
in space.  Indeed, we may say at once that this little object was
not a star at all; it was a planet.  That such was its true nature
was confirmed, after a little further observation, by perceiving
that the body was shifting its place on the heavens relatively to
the stars.  The organist at the Octagon Chapel at Bath had,
therefore, discovered a new planet with his home-made telescope.

I can imagine some one will say, "Oh, there was nothing so
wonderful in that; are not planets always being discovered? Has
not M. Palisa, for instance discovered about eighty of such
objects, and are there not hundreds of them known nowadays?"  This
is, to a certain extent, quite true.  I have not the least desire
to detract from the credit of those industrious and sharp-sighted
astronomers who have in modern days brought so many of these
little objects within our cognisance.  I think, however, it must
be admitted that such discoveries have a totally different
importance in the history of science from that which belongs to
the peerless achievement of Herschel.  In the first place, it must
be observed that the minor planets now brought to light are so
minute that if a score of them were rolled to together into one
lump it would not be one-thousandth part of the size of the grand
planet discovered by Herschel.  This is, nevertheless, not the
most important point.  What marks Herschel's achievement as one of
the great epochs in the history of astronomy is the fact that the
detection of Uranus was the very first recorded occasion of the
discovery of any planet whatever.

For uncounted ages those who watched the skies had been aware of
the existence of the five old planets-Jupiter, Mercury, Saturn,
Venus, and Mars.  It never seems to have occurred to any of the
ancient philosophers that there could be other similar objects as
yet undetected over and above the well-known five.  Great then was
the astonishment of the scientific world when the Bath organist
announced his discovery that the five planets which had been known
from all antiquity must now admit the company of a sixth.  And
this sixth planet was, indeed, worthy on every ground to be
received into the ranks of the five glorious bodies of antiquity.
It was, no doubt, not so large as Saturn, it was certainly very
much less than Jupiter; on the other hand, the new body was very
much larger than Mercury, than Venus, or than Mars, and the earth
itself seemed quite an insignificant object in comparison with
this newly added member of the Solar System.  In one respect, too,
Herschel's new planet was a much more imposing object than any one
of the older bodies; it swept around the sun in a majestic orbit,
far outside that of Saturn, which had previously been regarded as
the boundary of the Solar System, and its stately progress
required a period of not less than eighty-one years.

King George the Third, hearing of the achievements of the
Hanoverian musician, felt much interest in his discovery, and
accordingly Herschel was bidden to come to Windsor, and to
bring with him the famous telescope, in order to exhibit the new
planet to the King, and to tell his Majesty all about it.  The
result of the interview was to give Herschel the opportunity for
which he had so long wished, of being able to devote himself
exclusively to science for the rest of his life.

[PLATE:  VIEW OF THE OBSERVATORY, HERSCHEL HOUSE, SLOUGH.]

The King took so great a fancy to the astronomer that he first, as
I have already mentioned, duly pardoned his desertion from the
army, some twenty-five years previously.  As a further mark of his
favour the King proposed to confer on Herschel the title of his
Majesty's own astronomer, to assign to him a residence near
Windsor, to provide him with a salary, and to furnish such funds
as might be required for the erection of great telescopes, and
for the conduct of that mighty scheme of celestial observation on
which Herschel was so eager to enter.  Herschel's capacity for
work would have been much impaired if he had been deprived of the
aid of his admirable sister, and to her, therefore, the King also
assigned a salary, and she was installed as Herschel's assistant
in his new post.

With his usually impulsive determination, Herschel immediately cut
himself free from all his musical avocations at Bath, and at once
entered on the task of making and erecting the great telescopes at
Windsor.  There, for more than thirty years, he and his faithful
sister prosecuted with unremitting ardour their nightly scrutiny
of the sky.  Paper after paper was sent to the Royal Society,
describing the hundreds, indeed the thousands, of objects such as
double stars; nebulae and clusters, which were first revealed to
human gaze during those midnight vigils.  To the end of his life
he still continued at every possible opportunity to devote himself
to that beloved pursuit in which he had such unparalleled success.
No single discovery of Herschel's later years was, however, of the
same momentous description as that which first brought him to
fame.

[PLATE:  THE 40-FOOT TELESCOPE AS IT WAS IN THE YEAR 1863,
HERSCHEL HOUSE, SLOUGH.]

Herschel married when considerably advanced in life and he lived
to enjoy the indescribable pleasure of finding that his only
son, afterwards Sir John Herschel, was treading worthily in his
footsteps, and attaining renown as an astronomical observer,
second only to that of his father.  The elder Herschel died in
1822, and his illustrious sister Caroline then returned to
Hanover, where she lived for many years to receive the respect and
attention which were so justly hers.  She died at a very advanced
age in 1848.




LAPLACE.



The author of the "Mecanique Celeste" was born at Beaumont-en-
Auge, near Honfleur, in 1749, just thirteen years later than his
renowned friend Lagrange.  His father was a farmer, but appears to
have been in a position to provide a good education for a son who
seemed promising.  Considering the unorthodoxy in religious
matters which is generally said to have characterized Laplace in
later years, it is interesting to note that when he was a boy the
subject which first claimed his attention was theology.  He was,
however, soon introduced to the study of mathematics, in which he
presently became so proficient, that while he was still no more
than eighteen years old, he obtained employment as a mathematical
teacher in his native town.

Desiring wider opportunities for study and for the acquisition of
fame than could be obtained in the narrow associations of
provincial life, young Laplace started for Paris, being provided
with letters of introduction to D'Alembert, who then occupied
the most prominent position as a mathematician in France, if not
in the whole of Europe.  D'Alembert's fame was indeed so
brilliant that Catherine the Great wrote to ask him to undertake
the education of her Son, and promised the splendid income of a
hundred thousand francs.  He preferred, however, a quiet life of
research in Paris, although there was but a modest salary attached
to his office.  The philosopher accordingly declined the alluring
offer to go to Russia, even though Catherine wrote again to say:
"I know that your refusal arises from your desire to cultivate
your studies and your friendships in quiet.  But this is of no
consequence: bring all your friends with you, and I promise you
that both you and they shall have every accommodation in my
power."  With equal firmness the illustrious mathematician
resisted the manifold attractions with which Frederick the Great
sought to induce him, to take up his residence at Berlin.  In
reading of these invitations we cannot but be struck at the
extraordinary respect which was then paid to scientific
distinction.  It must be remembered that the discoveries of such
a man as D'Alembert were utterly incapable of  being appreciated
except by those who possessed a high degree of mathematical
culture.  We nevertheless find the potentates of Russia and
Prussia entreating and, as it happens, vainly entreating, the
most distinguished mathematician in France to accept the
positions that they were proud to offer him.

It was to D'Alembert, the profound mathematician, that young
Laplace, the son of the country farmer, presented his letters of
introduction.  But those letters seem to have elicited no reply,
whereupon Laplace wrote to D'Alembert submitting a discussion on
some point in Dynamics.  This letter instantly produced the
desired effect.  D'Alembert thought that such mathematical talent
as the young man displayed was in itself the best of introductions
to his favour.  It could not be overlooked, and accordingly he
invited Laplace to come and see him.  Laplace, of course,
presented himself, and ere long D'Alembert obtained for the rising
philosopher a professorship of mathematics in the Military School
in Paris.  This gave the brilliant young mathematician the opening
for which he sought, and he quickly availed himself of it.

Laplace was twenty-three years old when his first memoir on a
profound mathematical subject appeared in the Memoirs of the
Academy at Turin.  From this time onwards we find him publishing
one memoir after another in which he attacks, and in many cases
successfully vanquishes, profound difficulties in the application
of the Newtonian theory of gravitation to the explanation of the
solar system.  Like his great contemporary Lagrange, he loftily
attempted problems which demanded consummate analytical skill for
their solution.  The attention of the scientific world thus became
riveted on the splendid discoveries which emanated from these two
men, each gifted with extraordinary genius.

Laplace's most famous work is, of course, the "Mecanique
Celeste," in which he essayed a comprehensive attempt to carry out
the principles which Newton had laid down, into much greater
detail than Newton had found practicable.  The fact was that
Newton had not only to construct the theory of gravitation, but he
had to invent the mathematical tools, so to speak, by which his
theory could be applied to the explanation of the movements of the
heavenly bodies.  In the course of the century which had elapsed
between the time of Newton and the time of Laplace, mathematics
had been extensively developed.  In particular, that potent
instrument called the infinitesimal calculus, which Newton had
invented for the investigation of nature, had become so far
perfected that Laplace, when he attempted to unravel the movements
of the heavenly bodies, found himself provided with a calculus far
more efficient than that which had been available to Newton.  The
purely geometrical methods which Newton employed, though they are
admirably adapted for demonstrating in a general way the
tendencies of forces and for explaining the more obvious phenomena
by which the movements of the heavenly bodies are disturbed, are
yet quite inadequate for dealing with the more subtle effects of
the Law of Gravitation.  The disturbances which one planet
exercises upon the rest can only be fully ascertained by the aid
of long calculation, and for these calculations analytical methods
are required.

With an armament of mathematical methods which had been perfected
since the days of Newton by the labours of two or three
generations of consummate mathematical inventors, Laplace essayed
in the "Mecanique Celeste" to unravel the mysteries of the
heavens.  It will hardly be disputed that the book which he has
produced is one of the most difficult books to understand that has
ever been written.  In great part, of course, this difficulty
arises from the very nature of the subject,  and is so far
unavoidable.  No one need attempt to read the "Mecanique Celeste"
who has not been naturally endowed with considerable mathematical
aptitude which he has cultivated by years of assiduous study.  The
critic will also note that there are grave defects in Laplace's
method of treatment.  The style is often extremely obscure, and
the author frequently leaves great gaps in his argument, to the
sad discomfiture of his reader.  Nor does it mend matters to say,
as Laplace often does say, that it is "easy to see" how
one step follows from another.  Such inferences often present
great difficulties even to excellent mathematicians.  Tradition
indeed tells us that when Laplace had occasion to refer to his own
book, it sometimes happened that an argument which he had
dismissed with his usual formula, "Il est facile a voir," cost the
illustrious author himself an hour or two of hard thinking
before he could recover the train of reasoning which had been
omitted.  But there are certain parts of this great work which
have always received the enthusiastic admiration of
mathematicians.  Laplace has, in fact, created whole tracts of
science, some of which have been subsequently developed with much
advantage in the prosecution of the study of Nature.

Judged by a modern code the gravest defect of Laplace's great work
is rather of a moral than of a mathematical nature.  Lagrange and
he advanced together in their study of the mechanics of the
heavens, at one time perhaps along parallel lines, while at other
times they pursued the same problem by almost identical methods.
Sometimes the important result was first reached by Lagrange,
sometimes it was Laplace who had the good fortune to make the
discovery.  It would doubtless be a difficult matter to draw the
line which should exactly separate the contributions to astronomy
made by one of these illustrious mathematicians, and
the contributions made by the other.  But in his great work
Laplace in the loftiest manner disdained to accord more than the
very barest recognition to Lagrange, or to any of the other
mathematicians, Newton alone excepted, who had advanced our
knowledge of the mechanism of the heavens.  It would be quite
impossible for a student who confined his reading to the
"Mecanique Celeste" to gather from any indications that it
contains whether the discoveries about which he was reading had
been really made by Laplace himself or whether they had not been
made by Lagrange, or by Euler, or by Clairaut.  With our present
standard of morality in such matters, any scientific man who now
brought forth a work in which he presumed to ignore in this
wholesale fashion the contributions of others to the subject on
which he was writing, would be justly censured and bitter
controversies would undoubtedly arise.  Perhaps we ought not
to judge Laplace by the standard of our own time, and in any case
I do not doubt that Laplace might have made a plausible
defence.  It is well known that when two investigators are working
at the same subjects, and constantly publishing their results, it
sometimes becomes difficult for each investigator himself to
distinguish exactly between what he has accomplished and that
which  must be credited to his rival.  Laplace may probably have
said to himself that he was going to devote his energies to a
great work on the interpretation of Nature, that it would take all
his time and all his faculties, and all the resources of knowledge
that he could command, to deal justly with the mighty problems
before him.  He would not allow himself to be distracted by any
side issue.  He could not tolerate that pages should be wasted in
merely discussing to whom we owe each formula, and to whom each
deduction from such formula is due.  He would rather endeavour to
produce as complete a picture as he possibly could of the
celestial mechanics, and whether it were by means of his
mathematics alone, or whether the discoveries of others may have
contributed in any degree to the result, is a matter so
infinitesimally insignificant in comparison with the grandeur of
his subject that he would altogether neglect it.  "If Lagrange
should think,"  Laplace might say, "that his discoveries had been
unduly appropriated, the proper course would be for him to do
exactly what I have done.  Let him also write a "Mecanique
Celeste," let him employ those consummate talents which he
possesses in developing his noble subject to the utmost.  Let him
utilise every result that I or any other mathematician have
arrived at, but not trouble himself unduly with unimportant
historical details as to who discovered this, and who discovered
that; let him produce such a work as he could write, and I shall
heartily welcome it as a splendid contribution to our science."
Certain it is that Laplace and Lagrange continued the best of
friends, and on the death of the latter it was Laplace who was
summoned to deliver the funeral oration at the grave of his great
rival.

The investigations of Laplace are, generally speaking, of too
technical a character to make it possible to set forth any account
of them in such a work as the present.  He did publish, however,
one treatise, called the " Systeme du Monde," in which, without
introducing mathematical symbols, he was able to give a general
account of the theories of the celestial movements, and of the
discoveries to which he and others had been led.  In this work the
great French astronomer sketched for the first time that
remarkable doctrine by which his name is probably most generally
known to those readers of astronomical books who are not specially
mathematicians.  It is in the "Systeme du Monde" that Laplace laid
down the principles of the Nebular Theory which, in modern days,
has been generally accepted by those philosophers who are
competent to judge, as substantially a correct expression of a
great historical fact.

[PLATE:  LAPLACE.]

The Nebular Theory gives a physical account of the origin of the
solar system, consisting of the sun in the centre, with the
planets and their attendant satellites.  Laplace perceived the
significance of the fact that all the planets revolved in the same
direction around the sun; he noticed also that the movements of
rotation of the planets on their axes were performed in the same
direction as that in which a planet revolves around the sun; he
saw that the orbits of the satellites, so far at least as he knew
them, revolved around their primaries also in the same direction.
Nor did it escape his attention that the sun itself rotated on its
axis in the same sense.  His philosophical mind was led to reflect
that such a remarkable unanimity in the direction of the movements
in the solar system demanded some special explanation.  It would
have been in the highest degree improbable that there should have
been this unanimity unless there had been some physical reason to
account for it.  To appreciate the argument let us first
concentrate our attention on three particular bodies, namely the
earth, the sun, and the moon.  First the earth revolves around the
sun in a certain direction, and the earth also rotates on its
axis.  The direction in which the earth turns in accordance with
this latter movement might have been that in which it revolves
around the sun, or it might of course have been opposite thereto.
As a matter of fact the two agree.  The moon in its monthly
revolution around the earth follows also the same direction, and
our satellite rotates on its axis in the same period as its
monthly revolution, but in doing so is again observing this same
law.  We have therefore in the earth and moon four movements, all
taking place in the same direction, and this is also identical
with that in which the sun rotates once every twenty-five days.
Such a coincidence would be very unlikely unless there were some
physical reason for it.  Just as unlikely would it be that in
tossing a coin five heads or five tails should follow each other
consecutively.  If we toss a coin five times the chances that it
will turn up all heads or all tails is but a small one.  The
probability of such an event is only one-sixteenth.

There are, however, in the solar system many other bodies besides
the three just mentioned which are animated by this common
movement.  Among them are, of course, the great planets, Jupiter,
Saturn, Mars, Venus, and Mercury, and the satellites which attend
on these planets.  All these planets rotate on their axes in the
same direction as they revolve around the sun, and all their
satellites revolve also in the same way.  Confining our attention
merely to the earth, the sun, and the five great planets with
which Laplace was acquainted, we have no fewer than six motions of
revolution and seven motions of rotation, for in the latter we
include the rotation of the sun.  We have also sixteen satellites
of the planets mentioned whose revolutions round their primaries
are in the same direction.  The rotation of the moon on its axis
may also be reckoned, but as to the rotations of the satellites of
the other planets we cannot speak with any confidence, as they are
too far off to be observed with the necessary accuracy.  We have
thus thirty circular movements in the solar system connected with
the sun and moon and those great planets than which no others were
known in the days of Laplace.  The significant fact is that all
these thirty movements take place in the same direction.  That
this should be the case without some physical reason would be just
as unlikely as that in tossing a coin thirty times it should turn
up all heads or all tails every time without exception.

We can express the argument numerically.  Calculation proves that
such an event would not generally happen oftener than once out of
five hundred millions of trials.  To a philosopher of Laplace's
penetration, who had made a special study of the theory of
probabilities, it seemed well-nigh inconceivable that there
should have been such unanimity in the celestial movements,
unless there had been some adequate reason to account for it.
We might, indeed, add that if we were to include all the objects
which are now known to belong to the solar system, the argument
from probability might be enormously increased in strength.  To
Laplace the argument appeared so conclusive that he sought for
some physical cause of the remarkable phenomenon which the solar
system presented.  Thus it was that the famous Nebular Hypothesis
took its rise.  Laplace devised a scheme for the origin of the sun
and the planetary system, in which it would be a necessary
consequence that all the movements should take place in the same
direction as they are actually observed to do.

Let us suppose that in the beginning there was a gigantic mass of
nebulous material, so highly heated that the iron and other
substances which now enter into the composition of the earth and
planets were then suspended in a state of vapour.  There is
nothing unreasonable in such a supposition indeed, we know as a
matter of fact that there are thousands of such nebulae to be
discerned at present through our telescopes.  It would be
extremely unlikely that any object could exist without possessing
some motion of rotation; we may in fact assert that for rotation
to be entirety absent from the great primeval nebula would be
almost infinitely improbable.  As ages rolled on, the nebula
gradually dispersed away by radiation its original stores of heat,
and, in accordance with well-known physical principles, the
materials of which it was formed would tend to coalesce.  The
greater part of those materials would become concentrated in a
mighty mass surrounded by outlying uncondensed vapours.  There
would, however, also be regions throughout the extent of the
nebula, in which subsidiary centres of condensation would be
found.  In its long course of cooling, the nebula would,
therefore, tend ultimately to form a mighty central body with a
number of smaller bodies disposed around it.  As the nebula was
initially endowed with a movement of rotation, the central mass
into which it had chiefly condensed would also revolve, and the
subsidiary bodies would be animated by movements of revolution
around the central body.  These movements would be all pursued in
one common direction, and it follows, from well-known mechanical
principles, that each of the subsidiary masses, besides
participating in the general revolution around the central body,
would also possess a rotation around its axis, which must likewise
be performed in the same direction.  Around the subsidiary bodies
other objects still smaller would be formed, just as they
themselves were formed relatively to the great central mass.

As the ages sped by, and the heat of these bodies became
gradually dissipated, the various objects would coalesce,
first into molten liquid masses, and thence, at a further
stage of cooling, they would assume the appearance of solid
masses, thus producing the planetary bodies such as we now
know them.  The great central mass, on account of its
preponderating dimensions, would still retain, for further
uncounted ages, a large quantity of its primeval heat, and
would thus display the splendours of a glowing sun.  In this way
Laplace was able to account for the remarkable phenomena presented
in the movements of the bodies of the solar system.  There are
many other points also in which the nebular theory is known
to tally with the facts of observation.  In fact, each advance in
science only seems to make it more certain that the Nebular
Hypothesis substantially represents the way in which our solar
system has grown to its present form.

Not satisfied with a career which should be merely scientific,
Laplace sought to connect himself with public affairs.  Napoleon
appreciated his genius, and desired to enlist him in the service
of the State.  Accordingly he appointed Laplace to be Minister of
the Interior.  The experiment was not successful, for he was not
by nature a statesman.  Napoleon was much disappointed at the
ineptitude which the great mathematician showed for official life,
and, in despair of Laplace's capacity as an administrator,
declared that he carried the spirit of his infinitesimal
calculus into the management of business.  Indeed, Laplace's
political conduct hardly admits of much defence.  While he
accepted the honours which Napoleon showered on him in the time of
his prosperity, he seems to have forgotten all this when Napoleon
could no longer render him service.  Laplace was made a Marquis by
Louis XVIII., a rank which he transmitted to his son, who was
born in 1789.  During the latter part of his life the philosopher
lived in a retired country place at Arcueile.  Here he pursued his
studies, and by strict abstemiousness, preserved himself from many
of the infirmities of old age.  He died on March the 5th, 1827,
in his seventy-eighth year, his last words being, "What we know is
but little, what we do not know is immense."




BRINKLEY.



Provost Baldwin held absolute sway in the University of Dublin for
forty-one years.  His memory is well preserved there.  The Bursar
still dispenses the satisfactory revenues which Baldwin left to
the College.  None of us ever can forget the marble angels round
the figure of the dying Provost on which we used to gaze during
the pangs of the Examination Hall.

Baldwin died in 1785, and was succeeded by Francis Andrews, a
Fellow of seventeen years' standing.  As to the scholastic
acquirements of Andrews, all I can find is a statement that he was
complimented by the polite Professors of Padua on the elegance and
purity with which he discoursed to them in Latin.  Andrews was
also reputed to be a skilful lawyer.  He was certainly a Privy
Councillor and a prominent member of the Irish House of Commons,
and his social qualities were excellent.  Perhaps it was Baldwin's
example that stimulated a desire in Andrews to become a
benefactor to his college.  He accordingly bequeathed a sum of
3,000 pounds and an annual income of 250 pounds wherewith to build
and endow an astronomical Observatory in the University.  The
figures just stated ought to be qualified by the words of cautious
Ussher (afterwards the first Professor of Astronomy), that "this
money was to arise from an accumulation of a part of his property,
to commence upon a particular contingency happening to his
family."  The astronomical endowment was soon in jeopardy by
litigation.  Andrews thought he had provided for his relations by
leaving to them certain leasehold interests connected with the
Provost's estate.  The law courts, however, held that these
interests were not at the disposal of the testator, and handed
them over to Hely Hutchinson, the next Provost.  The disappointed
relations then petitioned the Irish Parliament to redress this
grievance by transferring to them the moneys designed by Andrews
for the Observatory.  It would not be right, they contended, that
the kindly intentions of the late Provost towards his kindred
should be frustrated for the sake of maintaining what they
described as "a purely ornamental institution."  The authorities
of the College protested against this claim.  Counsel were heard,
and a Committee of the House made a report declaring the situation
of the relations to be a hard one.  Accordingly, a compromise was
made, and the dispute terminated.

The selection of a site for the new astronomical Observatory was
made by the Board of Trinity College.  The beautiful neighbourhood
of Dublin offered a choice of excellent localities.  On the north
side of the Liffey an Observatory could have been admirably
placed, either on the remarkable promontory of Howth or on the
elevation of which Dunsink is the summit.  On the south side of
Dublin there are several eminences that would have been suitable:
the breezy heaths at Foxrock combine all necessary conditions; the
obelisk hill at Killiney would have given one of the most
picturesque sites for an Observatory in the world; while near
Delgany two or three other good situations could be mentioned.
But the Board of those pre-railway days was naturally guided by
the question of proximity.  Dunsink was accordingly chosen as the
most suitable site within the distance of a reasonable walk from
Trinity College.

The northern boundary of the Phoenix Park approaches the little
river Tolka, which winds through a succession of delightful bits
of sylvan scenery, such as may be found in the wide demesne of
Abbotstown and the classic shades of Glasnevin.  From the
banks of the Tolka, on the opposite side of the park, the pastures
ascend in a gentle slope to culminate at Dunsink, where at a
distance of half a mile from the stream, of four miles from
Dublin, and at a height of 300 feet above the sea, now stands the
Observatory.  From the commanding position of Dunsink a
magnificent view is obtained.  To the east the sea is visible,
while the southern prospect over the valley of the Liffey is
bounded by a range of hills and mountains extending from Killiney
to Bray Head, thence to the little Sugar Loaf, the Two Rock and
the Three Rock Mountains, over the flank of which the summit of
the Great Sugar Loaf is just perceptible.  Directly in front opens
the fine valley of Glenasmole, with Kippure Mountain, while the
range can be followed to its western extremity at Lyons.  The
climate of Dunsink is well suited for astronomical observation.
No doubt here, as elsewhere in Ireland, clouds are abundant, but
mists or haze are comparatively unusual, and fogs are almost
unknown.

The legal formalities to be observed in assuming occupation
exacted a delay of many months; accordingly, it was not until the
10th December, 1782, that a contract could be made with Mr. Graham
Moyers for the erection of a meridian-room and a dome for an
equatorial, in conjunction with a becoming residence for the
astronomer.  Before the work was commenced at Dunsink, the Board
thought it expedient to appoint the first Professor of Astronomy.
They met for this purpose on the 22nd January, 1783, and chose the
Rev. Henry Ussher, a Senior Fellow of Trinity College, Dublin.
The wisdom of the appointment was immediately shown by the
assiduity with which Ussher engaged in founding the observatory.
In three years he had erected the buildings and equipped them with
instruments, several of which were of his own invention.  On the
19th of February, 1785, a special grant of 200 pounds was made by
the Board to Dr. Ussher as some recompense for his labours.  It
happened that the observatory was not the only scientific
institution which came into being in Ireland at this period; the
newly-kindled ardour for the pursuit of knowledge led, at the same
time, to the foundation of the Royal Irish Academy.  By a fitting
coincidence, the first memoir published in the "Transactions Of The
Royal Irish Academy," was by the first Andrews, Professor of
Astronomy.  It was read on the 13th of June, 1785, and bore the
title, "Account of the Observatory belonging to Trinity College,"
by the Rev. H. Ussher, D.D., M.R.I.A., F.R.S.  This communication
shows the extensive design that had been originally intended for
Dunsink, only a part of which was, however, carried out.  For
instance, two long corridors, running north and south from the
central edifice, which are figured in the paper, never developed
into bricks and mortar.  We are not told why the original scheme
had to be contracted; but perhaps the reason may be not
unconnected with a remark of Ussher's, that the College had
already advanced from its own funds a sum considerably exceeding
the original bequest.  The picture of the building shows also the
dome for the South equatorial, which was erected many years later.

Ussher died in 1790.  During his brief career at the observatory,
he observed eclipses, and is stated to have done other scientific
work.  The minutes of the Board declare that the infant
institution had already obtained celebrity by his labours, and
they urge the claims of his widow to a pension, on the ground that
the disease from which he died had been contracted by his nightly
vigils.  The Board also promised a grant of fifty guineas as a
help to bring out Dr. Ussher's sermons.  They advanced twenty
guineas to his widow towards the publication of his astronomical
papers.  They ordered his bust to be executed for the observatory,
and offered "The Death of Ussher" as the subject of a prize essay;
but, so far as I can find, neither the sermons nor the papers,
neither the bust nor the prize essay, ever came into being.

There was keen competition for the chair of Astronomy which the
death of Ussher vacated.  The two candidates were Rev. John
Brinkley, of Caius College, Cambridge, a Senior Wrangler (born at
Woodbridge, Suffolk, in 1763), and Mr. Stack, Fellow of Trinity
College, Dublin, and author of a book on Optics.  A majority of
the Board at first supported Stack, while Provost Hely Hutchinson
and one or two others supported Brinkley.  In those days the
Provost had a veto at elections, so that ultimately Stack was
withdrawn and Brinkley was elected.  This took place on the 11th
December, 1790.  The national press of the day commented on the
preference shown to the young Englishman, Brinkley, over his Irish
rival.  An animated controversy ensued.  The Provost himself
condescended to enter the lists and to vindicate his policy by a
long letter in the "Public Register" or "Freeman's Journal," of
21st December, 1790.  This letter was anonymous, but its
authorship is obvious.  It gives the correspondence with Maskelyne
and other eminent astronomers, whose advice and guidance had been
sought by the Provost.  It also contends that "the transactions of
the Board ought not to be canvassed in the newspapers."  For this
reference, as well as for much other information, I am indebted
to my friend, the Rev. John Stubbs, D.D.

[PLATE: THE OBSERVATORY, DUNSINK.
From a Photograph by W. Lawrence, Upper Sackville Street, Dublin.]

The next event in the history of the Observatory was the issue of
Letters Patent (32 Geo. III., A.D 1792), in which it is recited
that "We grant and ordain that there shall be forever hereafter a
Professor of Astronomy, on the foundation of Dr. Andrews, to be
called and known by the name of the Royal Astronomer of Ireland."
The letters prescribe the various duties of the astronomer and
the mode of his election.  They lay down regulations as to the
conduct of the astronomical work, and as to the choice of an
assistant.  They direct that the Provost and the Senior Fellows
shall make a thorough inspection of the observatory once every
year in June or July; and this duty was first undertaken on the
5th of July, 1792.  It may be noted that the date on which the
celebration of the tercentenary of the University was held happens
to coincide with the centenary of the first visitation of the
observatory.  The visitors on the first occasion were A. Murray,
Matthew Young, George Hall, and John Barrett.  They record that
they find the buildings, books and instruments in good condition;
but the chief feature in this report, as well as in many which
followed it, related to a circumstance to which we have not yet
referred.

In the original equipment of the observatory, Ussher, with the
natural ambition of a founder, desired to place in it a telescope
of more magnificent proportions than could be found anywhere else.
The Board gave a spirited support to this enterprise, and
negotiations were entered into with the most eminent instrument-
maker of those days.  This was Jesse Ramsden (1735-1800), famous
as the improver of the sextant, as the constructor of the great
theodolite used by General Roy in the English Survey, and as the
inventor of the dividing engine for graduating astronomical
instruments.  Ramsden had built for Sir George Schuckburgh the
largest and most perfect equatorial ever attempted.  He
had constructed mural quadrants for Padua and Verona, which
elicited the wonder of astronomers when Dr. Maskelyne declared he
could detect no error in their graduation so large as two seconds
and a half.  But Ramsden maintained that even better results would
be obtained by superseding the entire quadrant by the circle.  He
obtained the means of testing this prediction when he completed a
superb circle for Palermo of five feet diameter.  Finding his
anticipations were realised, he desired to apply the same
principles on a still grander scale.  Ramsden was in this mood
when he met with Dr. Ussher.  The enthusiasm of the astronomer and
the instrument-maker communicated itself to the Board, and a
tremendous circle, to be ten feet in diameter, was forthwith
projected.

Projected, but never carried out.  After Ramsden had to some
extent completed a 10-foot circle, he found such difficulties that
he tried a 9-foot, and this again he discarded for an 8-foot,
which was ultimately accomplished, though not entirely by himself.
Notwithstanding the contraction from the vast proportions
originally designed, the completed instrument must still be
regarded as a colossal piece of astronomical workmanship.  Even
at this day I do not know that any other observatory can show a
circle eight feet in diameter graduated all round.

I think it is Professor Piazzi Smith who tells us how grateful he
was to find a large telescope he had ordered finished by the
opticians on the very day they had promised it.  The day was
perfectly correct; it was only the year that was wrong.  A
somewhat remarkable experience in this direction is chronicled by
the early reports of the visitors to Dunsink Observatory.  I
cannot find the date on which the great circle was ordered from
Ramsden, but it is fixed with sufficient precision by an allusion
in Ussher's paper to the Royal Irish Academy, which shows that by
the 13th June, 1785, the order had been given, but that the
abandonment of the 10-foot scale had not then been contemplated.
It was reasonable that the board should allow Ramsden ample time
for the completion of a work at once so elaborate and so novel.
It could not have been finished in a year, nor would there have
been much reason for complaint if the maker had found he
required two or even three years more.

Seven years gone, and still no telescope, was the condition in
which the Board found matters at their first visitation in 1792.
They had, however, assurances from Ramsden that the instrument
would be completed within the year; but, alas for such promises,
another seven years rolled on, and in 1799 the place for the great
circle was still vacant at Dunsink.  Ramsden had fallen into bad
health, and the Board considerately directed that "inquiries
should be made."  Next year there was still no progress, so the
Board were roused to threaten Ramsden with a suit at law; but
the menace was never executed, for the malady of the great
optician grew worse, and he died that year.

Affairs had now assumed a critical aspect, for the college had
advanced much money to Ramsden during these fifteen years, and the
instrument was still unfinished.  An appeal was made by the
Provost to Dr. Maskelyne, the Astronomer Royal of England, for his
advice and kindly offices in this emergency.  Maskelyne responds--
in terms calculated to allay the anxiety of the Bursar--"Mr.
Ramsden has left property behind him, and the College can be in no
danger of losing both their money and the instrument."  The
business of Ramsden was then undertaken by Berge, who proceeded to
finish the circle quite as deliberately as his predecessor.  After
four years Berge promised the instrument in the following August,
but it did not come.  Two years later (1806) the professor
complains that he can get no answer from Berge.  In 1807, it is
stated that Berge will send the telescope in a month.  He did not;
but in the next year (1808), about twenty-three years after the
great circle was ordered, it was erected at Dunsink, where it is
still to be seen.

The following circumstances have been authenticated by the
signatures of Provosts, Proctors, Bursars, and other College
dignitaries:--In 1793 the Board ordered two of the clocks at the
observatory to be sent to Mr. Crosthwaite for repairs.  Seven
years later, in 1800, Mr. Crosthwaite was asked if the clocks
were ready.  This impatience was clearly unreasonable, for even in
four more years, 1804, we find the two clocks were still in hand.
Two years later, in 1806, the Board determined to take vigorous
action by asking the Bursar to call upon Crosthwaite.  This
evidently produced some effect, for in the following year, 1807,
the Professor had no doubt that the clocks would be speedily
returned.  After eight years more, in 1815, one of the clocks was
still being repaired, and so it was in 1816, which is the last
record we have of these interesting timepieces.  Astronomers are,
however, accustomed to deal with such stupendous periods in their
calculations, that even the time taken to repair a clock seems
but small in comparison.

The long tenure of the chair of Astronomy by Brinkley is
divided into two nearly equal periods by the year in which
the great circle was erected.  Brinkley was eighteen years
waiting for his telescope, and he had eighteen years more in
which to use it.  During the first of these periods Brinkley
devoted himself to mathematical research; during the latter he
became a celebrated astronomer.  Brinkley's mathematical labours
procured for their author some reputation as a mathematician.
They appear to be works of considerable mathematical elegance, but
not indicating any great power of original thought.  Perhaps it
has been prejudicial to Brinkley's fame in this direction, that he
was immediately followed in his chair by so mighty a genius as
William Rowan Hamilton.

After the great circle had been at last erected, Brinkley was able
to begin his astronomical work in earnest.  Nor was there much
time to lose.  He was already forty-five years old, a year older
than was Herschel when he commenced his immortal career at Slough.
Stimulated by the consciousness of having the command of an
instrument of unique perfection, Brinkley loftily attempted the
very highest class of astronomical research.  He resolved to
measure anew with his own eye and with his own hand the constants
of aberration and of nutation.  He also strove to solve that great
problem of the universe, the discovery of the distance of a fixed
star.

These were noble problems, and they were nobly attacked.  But to
appraise with justice this work of Brinkley, done seventy years
ago, we must not apply to it the same criterion as we would think
right to apply to similar work were it done now.  We do not any
longer use Brinkley's constant of aberration, nor do we now think
that Brinkley's determinations of the star distances were
reliable.  But, nevertheless, his investigations exercised a
marked influence on the progress of science; they stimulated the
study of the principles on which exact measurements were to be
conducted.

Brinkley had another profession in addition to that of an
astronomer.  He was a divine.  When a man endeavours to pursue two
distinct occupations concurrently, it will be equally easy to
explain why his career should be successful, or why it should be
the reverse.  If he succeeds, he will, of course, exemplify the
wisdom of having two strings to his bow.  Should he fail, it is,
of course, because he has attempted to sit on two stools at once.
In Brinkley's case, his two professions must be likened to the two
strings rather than to the two stools.  It is true that his
practical experience of his clerical life was very slender.  He
had made no attempt to combine the routine of a parish with his
labours in the observatory.  Nor do we associate a special
eminence in any department of religious work with his name.  If,
however, we are to measure Brinkley's merits as a divine by the
ecclesiastical preferment which he received, his services to
theology must have rivalled his services to astronomy.  Having
been raised step by step in the Church, he was at last appointed
to the See of Cloyne, in 1826, as the successor of Bishop
Berkeley.

Now, though it was permissible for the Archdeacon to be also the
Andrews Professor, yet when the Archdeacon became a Bishop, it was
understood that he should transfer his residence from the
observatory to the palace.  The chair of Astronomy accordingly
became vacant.  Brinkley's subsequent career seems to have been
devoted entirely to ecclesiastical matters, and for the last ten
years of his life he did not contribute a paper to any scientific
society.  Arago, after a characteristic lament that Brinkley
should have forsaken the pursuit of science for the temporal and
spiritual attractions of a bishopric, pays a tribute to the
conscientiousness of the quondam astronomer, who would not even
allow a telescope to be brought into the palace lest his mind
should be distracted from his sacred duties.

The good bishop died on the 13th September, 1835.  He was buried
in the chapel of Trinity College, and a fine monument to his
memory is a familiar object at the foot of the noble old staircase
of the library.  The best memorial of Brinkley is his admirable
book on the "Elements of Plane Astronomy."  It passed through many
editions in his lifetime, and even at the present day the same
work, revised first by Dr. Luby, and more recently by the Rev. Dr.
Stubbs and Dr. Brunnow, has a large and well-merited circulation.




JOHN HERSCHEL.



This illustrious son of an illustrious father was born at Slough,
near Windsor, on the 7th March, 1792.  He was the only child of
Sir William Herschel, who had married somewhat late in life, as
we have already mentioned.

[PLATE: ASTRONOMETER MADE BY SIR J. HERSCHEL to compare the light
of certain stars by the intervention of the moon.]

The surroundings among which the young astronomer was reared
afforded him an excellent training for that career on which he was
to enter, and in which he was destined to attain a fame only less
brilliant than that of his father.  The circumstances of his youth
permitted him to enjoy one great advantage which was denied to the
elder Herschel.  He was able, from his childhood, to devote
himself almost exclusively to intellectual pursuits.  William
Herschel, in the early part of his career, had only been able to
snatch occasional hours for study from his busy life as a
professional musician.  But the son, having been born with
a taste for the student's life, was fortunate enough to have been
endowed with the leisure and the means to enjoy it from the
commencement.  His early years have been so well described by the
late Professor Pritchard in the "Report of the Council of the
Royal Astronomical Society for 1872," that I venture to make an
extract here:--

"A few traits of John Herschel's boyhood, mentioned
by himself in his maturer life, have been treasured up by those
who were dear to him, and the record of some of them may satisfy a
curiosity as pardonable as inevitable, which craves to learn
through what early steps great men or great nations become
illustrious.  His home was singular, and singularly calculated to
nurture into greatness any child born as John Herschel was with
natural gifts, capable of wide development.  At the head of the
house there was the aged, observant, reticent philosopher, and
rarely far away his devoted sister, Caroline Herschel, whose
labours and whose fame are still cognisable as a beneficent
satellite to the brighter light of her illustrious brother.  It
was in the companionship of these remarkable persons, and under
the shadow of his father's wonderful telescope, that John Herschel
passed his boyish years.  He saw them, in silent but ceaseless
industry, busied about things which had no apparent concern with
the world outside the walls of that well-known house, but which,
at a later period of his life, he, with an unrivalled eloquence,
taught his countrymen to appreciate as foremost among those living
influences which but satisfy and elevate the noblest instincts of
our nature.  What sort of intercourse passed between the father
and the boy may be gathered from an incident or two which he
narrated as having impressed themselves permanently on the memory
of his youth.  He once asked his father what he thought was the
oldest of all things.  The father replied, after the Socratic
method, by putting another question: 'And what do you yourself
suppose is the oldest of all things?'  The boy was not successful
in his answers, thereon the old astronomer took up a small stone
from the garden walk: "There, my child, there is the oldest of all
the things that I certainly know.'  On another occasion his father
is said to have asked the boy, 'What sort of things, do you think,
are most alike?'  The delicate, blue-eyed boy, after a short pause,
replied, 'The leaves of the same tree are most like each other.'
'Gather, then, a handful of leaves of that tree,' rejoined the
philosopher, 'and choose two that are alike.'  The boy failed; but
he hid the lesson in his heart, and his thoughts were revealed
after many days.  These incidents may be trifles; nor should we
record them here had not John Herschel himself, though singularly
reticent about his personal emotions, recorded them as having made
a strong impression on his mind.  Beyond all doubt we can trace
therein, first, that grasp and grouping of many things in one,
implied in the stone as the oldest of things; and, secondly, that
fine and subtle discrimination of each thing out of many like
things as forming the main features which characterized the habit
of our venerated friend's philosophy."

John Herschel entered St. John's College, Cambridge, when he was
seventeen years of age.  His university career abundantly
fulfilled his father's eager desire, that his only son should
develop a capacity for the pursuit of science.  After obtaining
many lesser distinctions, he finally came out as Senior Wrangler
in 1813.  It was, indeed, a notable year in the mathematical
annals of the University.  Second on that list, in which
Herschel's name was first, appeared that of the illustrious
Peacock, afterwards Dean of Ely, who remained throughout life
one of Herschel's most intimate friends.

Almost immediately after taking his degree, Herschel gave evidence
of possessing a special aptitude for original scientific
investigation.  He sent to the Royal Society a mathematical paper
which was published in the PHILOSOPHICAL TRANSACTIONS.  Doubtless
the splendour that attached to the name he bore assisted him in
procuring early recognition of his own great powers.  Certain it
is that he was made a Fellow of the Royal Society at the
unprecedentedly early age of twenty-one.  Even after this
remarkable encouragement to adopt a scientific career as the
business of his life, it does not seem that John Herschel at first
contemplated devoting himself exclusively to science.  He
commenced to prepare for the profession of the Law by entering as
a student at the Middle Temple, and reading with a practising
barrister.

But a lawyer John Herschel was not destined to become.
Circumstances brought him into association with some leading
scientific men.  He presently discovered that his inclinations
tended more and more in the direction of purely scientific
pursuits.  Thus it came to pass that the original intention as to
the calling which he should follow was gradually abandoned.
Fortunately for science Herschel found its pursuit so attractive
that he was led, as his father had been before him, to give up his
whole life to the advancement of knowledge.  Nor was it unnatural
that a Senior Wrangler, who had once tasted the delights of
mathematical research, should have been tempted to devote much
time to this fascinating pursuit.  By the time John Herschel was
twenty-nine he had published so much mathematical work, and his
researches were considered to possess so much merit, that the
Royal Society awarded him the Copley Medal, which was the highest
distinction it was capable of conferring.

At the death of his father in 1822, John Herschel, with his tastes
already formed for a scientific career, found himself in the
possession of ample means.  To him also passed all his father's
great telescopes and apparatus.  These material aids, together
with a dutiful sense of filial obligation, decided him to make
practical astronomy the main work of his life.  He decided to
continue to its completion that great survey of the heavens which
had already been inaugurated, and, indeed, to a large extent
accomplished, by his father.

The first systematic piece of practical astronomical work which
John Herschel undertook was connected with the measurement of what
are known as "Double Stars."  It should be observed, that there
are in the heavens a number of instances in which two stars are
seen in very close association.  In the case of those objects to
which the expression "Double Stars" is generally applied, the two
luminous points are so close together that even though they might
each be quite bright enough to be visible to the unaided eye, yet
their proximity is such that they cannot be distinguished as two
separate objects without optical aid.  The two stars seem fused
together into one.  In the telescope, however, the bodies may be
discerned separately, though they are frequently so close together
that it taxes the utmost power of the instrument to indicate the
division between them.

The appearance presented by a double star might arise from the
circumstance that the two stars, though really separated from each
other by prodigious distances, happened to lie nearly in the same
line of vision, as seen from our point of view.  No doubt, many of
the so-called double stars could be accounted for on this
supposition.  Indeed, in the early days when but few double stars
were known, and when telescopes were not powerful enough to
exhibit the numerous close doubles which have since been brought
to light, there seems to have been a tendency to regard all double
stars as merely such perspective effects.  It was not at first
suggested that there could be any physical connection between the
components of each pair.  The appearance presented was regarded as
merely due to the circumstance that the line joining the two
bodies happened to pass near the earth.

[PLATE:  SIR JOHN HERSCHEL.]

In the early part of his career, Sir William Herschel seems to
have entertained the view then generally held by other astronomers
with regard to the nature of these stellar pairs.  The great
observer thought that the double stars could therefore be made to
afford a means of solving that problem in which so many of the
observers of the skies had been engaged, namely, the determination
of the distances of the stars from the earth.  Herschel saw that
the displacement of the earth in its annual movement round the sun
would produce an apparent shift in the place of the nearer of the
two stars relatively to the other, supposed to be much more
remote.  If this shift could be measured, then the distance of the
nearer of the stars could be estimated with some degree of
precision.

As has not unfrequently happened in the history of science, an
effect was perceived of a very different nature from that which
had been anticipated.  If the relative places of the two stars had
been apparently deranged merely in consequence of the motion of
the earth, then the phenomenon would be an annual one.  After the
lapse of a year the two stars would have regained their original
relative positions.  This was the effect for which William
Herschel was looking.  In certain of the so called double stars,
he, no doubt, did find a movement.  He detected the remarkable
fact that both the apparent distance and the relative positions of
the two bodies were changing.  But what was his surprise to
observe that these alterations were not of an annually periodic
character.  It became evident then that in some cases one of the
component stars was actually revolving around the other, in an
orbit which required many years for its completion.  Here was
indeed a remarkable discovery.  It was clearly impossible to
suppose that movements of this kind could be mere apparent
displacements, arising from the annual shift in our point of view,
in consequence of the revolution of the earth.  Herschel's
discovery established the interesting fact that, in certain of
these double stars, or binary stars, as these particular objects
are more expressively designated, there is an actual orbital
revolution of a character similar to that which the earth performs
around the sun.  Thus it was demonstrated that in these particular
double stars the nearness of the two components was not merely
apparent.  The objects must actually lie close together at a
distance which is small in comparison with the distance at which
either of them is separated from the earth.  The fact that the
heavens contain pairs of twin suns in mutual revolution was thus
brought to light.

In consequence of this beautiful discovery, the attention of
astronomers was directed to the subject of double stars with a
degree of interest which these objects had never before excited.
It was therefore not unnatural that John Herschel should have been
attracted to this branch of astronomical work.  Admiration for his
father's discovery alone might have suggested that the son should
strive to develop this territory newly opened up to research.  But
it also happened that the mathematical talents of the younger
Herschel inclined his inquiries in the same direction.  He saw
clearly that, when sufficient observations of any particular
binary star had been accumulated, it would then be within the
power of the mathematician to elicit from those observations the
shape and the position in space of the path which each of the
revolving stars described around the other.  Indeed, in some cases
he would be able to perform the astonishing feat of determining
from his calculations the weight of these distant suns, and thus
be enabled to compare them with the mass of our own sun.

[PLATE:  NEBULA IN SOUTHERN HEMISPHERE, drawn by Sir John
Herschel.]

But this work must follow the observations, it could not precede
them.  The first step was therefore to observe and to measure with
the utmost care the positions and distances of those particular
double stars which appear to offer the  greatest promise in this
particular research.  In 1821, Herschel and a friend of his, Mr.
James South, agreed to work together with this object.  South was
a medical man with an ardent devotion to science, and possessed of
considerable wealth.  He procured the best astronomical
instruments that money could obtain, and became a most
enthusiastic astronomer and a practical observer of tremendous
energy.

South and John Herschel worked together for two years in the
observation and measurement of the double stars discovered by Sir
William Herschel.  In the course  of this time their assiduity was
rewarded by the accumulation of so great a mass of careful
measurements that when published, they formed quite a volume in
the "Philosophical Transactions."  The value and accuracy of the
work, when estimated by standards which form proper criteria for
that period, is universally recognised.  It greatly promoted the
progress of sidereal astronomy, and the authors were in
consequence awarded medals from the  Royal Society, and the
Royal Astronomical Society, as well as similar testimonials from
various foreign institutions.

This work must, however, be regarded as merely introductory to the
main labours of John Herschel's life.  His father devoted the
greater part of his years as an observer to what he called his
"sweeps" of the heavens.  The great reflecting telescope, twenty
feet long, was moved slowly up and down through an arc of about
two degrees towards and from the pole, while the celestial
panorama passed slowly in the course of the diurnal motion before
the keenly watching eye of the astronomer.  Whenever a double star
traversed the field Herschel described it to his sister Caroline,
who, as we have already mentioned, was his invariable assistant in
his midnight watches.  When a nebula appeared, then he estimated
its size and its brightness, he noticed whether it had a nucleus,
or whether it had stars disposed in any significant manner with
regard to it.  He also dictated any other circumstance which he
deemed worthy of record.  These observations were duly committed
to writing by the same faithful and indefatigable scribe, whose
business it also was to take a memorandum of the exact position of
the object as indicated by a dial placed in front of her desk, and
connected with the telescope.

John Herschel undertook the important task of re-observing the
various double stars and nebulae which had been discovered during
these memorable vigils.  The son, however, lacked one inestimable
advantage which had been possessed by the father.  John Herschel
had no assistant to discharge all those duties which Caroline had
so efficiently accomplished.  He had, therefore, to modify the
system of sweeping previously adopted in order to enable all the
work both of observing and of recording to be done by himself.
This, in many ways, was a great drawback to the work of the
younger astronomer.  The division of labour between the observer
and the scribe enables a greatly increased quantity of work to be
got through.  It is also distinctly disadvantageous to an observer
to have to use his eye at the telescope directly after he has been
employing it for reading the graduations on a circle, by the light
of a lamp, or for entering memoranda in a note book.  Nebulae,
especially, are often so excessively faint that they can only
be properly observed by an eye which is in that highly sensitive
condition which is obtained by long continuance in darkness.  The
frequent withdrawal of the eye from the dark field of the
telescope, and the application of it to reading by artificial
light, is very prejudicial to its use for the more delicate
purpose.  John Herschel, no doubt, availed himself of every
precaution to mitigate the ill effects of this inconvenience as
much as possible, but it must have told upon his labours as
compared with those of his father.

But nevertheless John Herschel did great work during his "sweeps."
He was specially particular to note all the double stars which
presented themselves to his observation.  Of course some little
discretion must be allowed in deciding as to what degree of
proximity in adjacent stars does actually bring them within the
category of "double stars."  Sir John set down all such objects as
seemed to him likely to be of interest, and the results of his
discoveries in this branch of astronomy amount to some thousands.
Six or seven great memoirs in the TRANSACTIONS of the Royal
Astronomical Society have been devoted to giving an account of his
labours in this department of astronomy.

[PLATE:  THE CLUSTER IN THE CENTAUR, drawn by Sir John Herschel.]

One of the achievements by which Sir John Herschel is best known
is his invention of a method by which the orbits of binary stars
could be determined.  It will be observed that when one star
revolves around another in consequence of the law of gravitation,
the orbit described must be an ellipse.  This ellipse, however,
generally speaking, appears to us more or less foreshortened, for
it is easily seen that only under highly exceptional circumstances
would the plane in which the stars move happen to be directly
square to the line of view.  It therefore follows that what we
observe is not exactly the track of one star around the other; it
is rather the projection of that track as seen on the surface of
the sky.  Now it is remarkable that this apparent path is still
an ellipse.  Herschel contrived a very ingenious and simple method
by which he could discover from the observations the size and
position of the ellipse in which the revolution actually takes
place.  He showed how, from the study of the apparent orbit of the
star, and from certain measurements which could easily be
effected upon it, the determination of the true ellipse in which
the movement is performed could be arrived at.  In other words,
Herschel solved in a beautiful manner the problem of finding the
true orbits of double stars.  The importance of this work may be
inferred from the fact that it has served as the basis on which
scores of other investigators have studied the fascinating subject
of the movement of binary stars.

The labours, both in the discovery and measurement of the double
stars, and in the discussion of the observations with the object
of finding the orbits of such stars as are in actual revolution,
received due recognition in yet another gold medal awarded by the
Royal Society.  An address was delivered on the occasion by the
Duke of Sussex (30th November, 1833), in the course of which,
after stating that the medal had been conferred on Sir John
Herschel, he remarks:--

"It has been said that distance of place confers the same
privilege as distance of time, and I should gladly avail myself
of the privilege which is thus afforded me by Sir John Herschel's
separation from his country and friends, to express my
admiration of his character in stronger terms than I should
otherwise venture to use; for the language of panegyric, however
sincerely it may flow from the heart, might be mistaken for that
of flattery, if it could not thus claim somewhat of an historical
character; but his great attainments in almost every department of
human knowledge, his fine powers as a philosophical writer, his
great services and his distinguished devotion to science, the high
principles which have regulated his conduct in every relation of
life, and, above all, his engaging modesty, which is the crown of
all his other virtues, presenting such a model of an accomplished
philosopher as can rarely be found beyond the regions of
fiction, demand abler pens than mine to describe them in adequate
terms, however much inclined I might feel to undertake the task."

The first few lines of the eulogium just quoted allude to
Herschel's absence from England.  This was not merely an episode
of interest in the career of Herschel, it was the occasion of one
of the greatest scientific expeditions in the whole history of
astronomy.

Herschel had, as we have seen, undertaken a revision of his
father's "sweeps" for new objects, in those skies which are
visible from our latitudes in the northern hemisphere.  He had
well-nigh completed this task.  Zone by zone the whole of the
heavens which could be observed from Windsor had passed under his
review.  He had added hundreds to the list of nebulae discovered
by his father.  He had announced thousands of double stars.  At
last, however, the great survey was accomplished.  The contents of
the northern hemisphere, so far at least as they could be
disclosed by his telescope of twenty feet focal length, had been
revealed.

[PLATE:  SIR JOHN HERSCHEL'S OBSERVATORY AT FELDHAUSEN,
Cape of Good Hope.]

But Herschel felt that this mighty task had to be supplemented by
another of almost equal proportions, before it could be said that
the twenty-foot telescope had done its work.  It was only the
northern half of the celestial sphere which had been fully
explored.  The southern half was almost virgin territory, for no
other astronomer was possessed of a telescope of such power as
those which the Herschels had used.  It is true, of course, that
as a certain margin of the southern hemisphere was visible from
these latitudes, it had been more or less scrutinized by observers
in northern skies.  And the glimpses which had thus been obtained
of the celestial objects in the southern sky, were such as to make
an eager astronomer long for a closer acquaintance with the
celestial wonders of the south.  The most glorious object in the
sidereal heavens, the Great Nebula in Orion, lies indeed in that
southern hemisphere to which the younger Herschel's attention now
became directed.  It fortunately happens, however, for votaries of
astronomy all the world over, that Nature has kindly placed her
most astounding object, the great Nebula in Orion, in such a
favoured position, near the equator, that from a considerable
range of latitudes, both north and south, the wonders of the
Nebula can be explored.  There are grounds for thinking that the
southern heavens contain noteworthy objects which, on the whole,
are nearer to the solar system than are the noteworthy objects in
the northern skies.  The nearest star whose distance is known,
Alpha Centauri, lies in the southern hemisphere, and so also does
the most splendid cluster of stars.

Influenced by the desire to examine these objects, Sir John
Herschel determined to take his great telescope to a station in
the southern hemisphere, and thus complete his survey of the
sidereal heavens.  The latitude of the Cape of Good Hope is such
that a suitable site could be there found for his purpose.  The
purity of the skies in South Africa promised to provide for the
astronomer those clear nights which his delicate task of surveying
the nebulae would require.

On November 13, 1833, Sir John Herschel, who had by this time
received the honour of knighthood from William IV., sailed from
Portsmouth for the Cape of Good Hope, taking with him his
gigantic instruments.  After a voyage of two months, which was
considered to be a fair passage in those days, he landed in Table
Bay, and having duly reconnoitred various localities, he decided
to place his observatory at a place called Feldhausen, about six
miles from Cape Town, near the base of the Table Mountain.  A
commodious residence was there available, and in it he settled
with his family.  A temporary building was erected to contain the
equatorial, but the great twenty-foot telescope was accommodated
with no more shelter than is provided by the open canopy of
heaven.

As in his earlier researches at home, the attention of the great
astronomer at the Cape of Good Hope was chiefly directed to the
measurement of the relative positions and distances apart of the
double stars, and to the close examination of the nebulae.  In the
delineation of the form of these latter objects Herschel found
ample employment for his skilful pencil.  Many of the drawings he
has made of the celestial wonders in the southern sky are
admirable examples of celestial portraiture.

The number of the nebulae and of those kindred objects, the star
clusters, which Herschel studied in the southern heavens, during
four years of delightful labour, amount in all to one thousand
seven hundred and seven.  His notes on their appearance, and the
determinations of their positions, as well as his measurements of
double stars, and much other valuable astronomical research, were
published in a splendid volume, brought out at the cost of the
Duke of Northumberland.  This is, indeed, a monumental work, full
of interesting and instructive reading for any one who has a
taste for astronomy.

Herschel had the good fortune to be at the Cape on the occasion of
the periodical return of Halley's great comet in 1833.  To the
study of this body he gave assiduous attention, and the records of
his observations form one of the most interesting chapters in that
remarkable volume to which we have just referred.

[PLATE:  COLUMN AT FELDHAUSEN, CAPE TOWN, to commemorate Sir John
Herschel's survey of the Southern Heavens.]

Early in 1838 Sir John Herschel returned to England.  He had made
many friends at the Cape, who deeply sympathised with his self-
imposed labours while he was resident among them.  They desired to
preserve the recollection of this visit, which would always, they
considered, be a source of gratification in the colony.
Accordingly, a number of scientific friends in that part of the
world raised a monument with a suitable inscription, on the
spot which had been occupied by the great twenty-foot reflector at
Feldhausen.

His return to England after five years of absence was naturally
an occasion for much rejoicing among the lovers of astronomy.  He
was entertained at a memorable banquet, and the Queen, at her
coronation, made him a baronet.  His famous aunt Caroline, at that
time aged eighty, was still in the enjoyment of her faculties, and
was able to estimate at its true value the further
lustre which was added to the name she bore.  But there is reason
to believe that her satisfaction was not quite unmixed with
other feelings.  With whatever favour she might regard her nephew,
he was still not the brother to whom her life had been devoted.
So jealous was this vigorous old lady of the fame of the great
brother William, that she could hardly hear with patience of the
achievements of any other astronomer, and this failing existed in
some degree even when that other astronomer happened to be her
illustrious nephew.

With Sir John Herschel's survey of the Southern Hemisphere it may
be said that his career as an observing astronomer came to a close.
He did not again engage in any systematic telescopic research.
But it must not be inferred from this statement that he desisted
from active astronomical work.  It has been well observed that Sir
John Herschel was perhaps the only astronomer who has studied with
success, and advanced by original research, every department of
the great science with which his name is associated.  It was to
some other branches of astronomy besides those concerned with
looking through telescopes, that the rest of the astronomer's life
was to be devoted.

To the general student Sir John Herschel is best known by the
volume which he published under the title of "Outlines of
Astronomy."  This is, indeed, a masterly work, in which the
characteristic difficulties of the subject are resolutely faced
and expounded with as much simplicity as their nature will admit.
As a literary effort this work is admirable, both on account of
its picturesque language and the ennobling conceptions of the
universe which it unfolds.  The student who desires to become
acquainted with those recondite departments of astronomy, in which
the effects of the disturbing action of one planet upon the
motions of another planet are considered, will turn to the
chapters in Herschel's famous work on the subject.  There he will
find this complex matter elucidated, without resort to difficult
mathematics.  Edition after edition of this valuable work has
appeared, and though the advances of modern astronomy have left it
somewhat out of date in certain departments, yet the expositions
it contains of the fundamental parts of the science still remain
unrivalled.

Another great work which Sir John undertook after his return from
the Cape, was a natural climax to those labours on which his
father and he had been occupied for so many years.  We have
already explained how the work of both these observers had been
mainly devoted to the study of the nebulae and the star clusters.
The results of their discoveries had been announced to the world
in numerous isolated memoirs.  The disjointed nature of these
publications made their use very inconvenient.  But still it was
necessary for those who desired to study the marvellous objects
discovered by the Herschels, to have frequent recourse to the
original works.  To incorporate all the several observations of
nebular into one great systematic catalogue, seemed, therefore, to
be an indispensable condition of progress in this branch of
knowledge.  No one could have been so fitted for this task as Sir
John Herschel.  He, therefore, attacked and carried through the
great undertaking.  Thus at last a grand catalogue of nebulae and
clusters was produced.  Never before was there so majestic an
inventory.  If we remember that each of the nebulae is an object
so vast, that the whole of the solar system would form an
inconsiderable speck by comparison, what are we to think of a
collection in which these objects are enumerated in thousands?  In
this great catalogue we find arranged in systematic order all the
nebulae and all the clusters which had been revealed by the
diligence of the Herschels, father and son, in the Northern
Hemisphere, and of the son alone in the Southern Hemisphere.  Nor
should we omit to mention that the labours of other astronomers
were likewise incorporated.  It was unavoidable that the
descriptions given to each of the objects should be very slight.
Abbreviations are used, which indicate that a nebula is bright, or
very bright, or extremely bright, or faint, or very faint, or
extremely faint.  Such phrases have certainly but a relative and
technical meaning in such a catalogue.  The nebulae entered as
extremely bright by the experienced astronomer are only so
described by way of contrast to the great majority of these
delicate telescopic objects.  Most of the nebulae, indeed, are so
difficult to see, that they admit of but very slight description.
It should be observed that Herschel's catalogue augmented the
number of known nebulous objects to more than ten times that
collected into any catalogue which had ever been compiled before
the days of William Herschel's observing began.  But the study of
these objects still advances, and the great telescopes now in use
could probably show at least twice as many of these objects as are
contained in the list of Herschel, of which a new and enlarged
edition has since been brought out by Dr. Dreyer.

One of the best illustrations of Sir John Herschel's literary
powers is to be found in the address which he delivered at the
Royal Astronomical Society, on the occasion of presenting a medal
to Mr. Francis Baily, in recognition of his catalogue of stars.
The passage I shall here cite places in its proper aspect the true
merit of the laborious duty involved in such a task as that which
Mr. Baily had carried through with such success:--

"If we ask to what end magnificent establishments are maintained
by states and sovereigns, furnished with masterpieces of art, and
placed under the direction of men of first-rate talent and high-
minded enthusiasm, sought out for those qualities among the
foremost in the ranks of science, if we demand QUI BONO? for
what good a Bradley has toiled, or a Maskelyne or a Piazzi has
worn out his venerable age in watching, the answer is--not to
settle mere speculative points in the doctrine of the universe;
not to cater for the pride of man by refined inquiries into the
remoter mysteries of nature; not to trace the path of our system
through space, or its history through past and future eternities.
These, indeed, are noble ends and which I am far from any thought
of depreciating; the mind swells in their contemplation, and
attains in their pursuit an expansion and a hardihood which fit it
for the boldest enterprise.  But the direct practical utility of
such labours is fully worthy of their speculative grandeur.  The
stars are the landmarks of the universe; and, amidst the endless
and complicated fluctuations of our system, seem placed by its
Creator as guides and records, not merely to elevate our minds by
the contemplation of what is vast, but to teach us to direct our
actions by reference to what is immutable in His works.  It is,
indeed, hardly possible to over-appreciate their value in this
point of view.  Every well-determined star, from the moment its
place is registered, becomes to the astronomer, the geographer,
the navigator, the surveyor, a point of departure which can never
deceive or fail him, the same for ever and in all places, of a
delicacy so extreme as to be a test for every instrument yet
invented by man, yet equally adapted for the most ordinary
purposes; as available for regulating a town clock as for
conducting a navy to the Indies; as effective for mapping down the
intricacies of a petty barony as for adjusting the boundaries of
Transatlantic empires.  When once its place has been thoroughly
ascertained and carefully recorded, the brazen circle with which
that useful work was done may moulder, the marble pillar may
totter on its base, and the astronomer himself survive only in the
gratitude of posterity; but the record remains, and transfuses
all its own exactness into every determination which takes it for
a groundwork, giving to inferior instruments--nay, even to
temporary contrivances, and to the observations of a few weeks or
days--all the precision attained originally at the cost of so much
time, labour, and expense."

Sir John Herschel wrote many other works besides those we have
mentioned.  His "Treatise on Meteorology" is, indeed, a standard
work on this subject, and numerous articles from the same pen on
miscellaneous subjects, which have been collected and reprinted,
seemed as a relaxation from his severe scientific studies.  Like
certain other great mathematicians Herschel was also a poet, and
he published a translation of the Iliad into blank verse.

In his later years Sir John Herschel lived a retired life.  For a
brief period he had, indeed, been induced to accept the office of
Master of the Mint.  It was, however, evident that the routine of
such an occupation was not in accordance with his tastes, and he
gladly resigned it, to return to the seclusion of his study in his
beautiful home at Collingwood, in Kent.

His health having gradually failed, he died on the 11th May,
1871, in the seventy-ninth year of his age.




THE EARL OF ROSSE.



The subject of our present sketch occupies quite a distinct
position in scientific history.  Unlike many others who have risen
by their scientific discoveries from obscurity to fame, the great
Earl of Rosse was himself born in the purple.  His father, who,
under the title of Sir Lawrence Parsons, had occupied a
distinguished position in the Irish Parliament, succeeded on the
death of his father to the Earldom which had been recently
created.  The subject of our present memoir was, therefore, the
third of the Earls of Rosse, and he was born in York on June
17, 1800.  Prior to his father's death in 1841, he was known as
Lord Oxmantown.

The University education of the illustrious astronomer was begun
in Dublin and completed at Oxford.  We do not hear in his case of
any very remarkable University career.  Lord Rosse was, however, a
diligent student, and obtained a first-class in mathematics.  He
always took a great deal of interest in social questions, and was
a profound student of political economy.  He had a seat in the
House of Commons, as member for King's County, from 1821 to
1834, his ancestral estate being situated in this part of
Ireland.

[PLATE:  THE EARL OF ROSSE.]

Lord Rosse was endowed by nature with a special taste for
mechanical pursuits.  Not only had he the qualifications of a
scientific engineer, but he had the manual dexterity which
qualified him personally to carry out many practical arts.  Lord
Rosse was, in fact, a skilful mechanic, an experienced founder,
and an ingenious optician.  His acquaintances were largely among
those who were interested in mechanical pursuits, and it was his
delight to visit the works or engineering establishments where
refined processes in the arts were being carried on.  It has often
been stated--and as I have been told by members of his family,
truly stated--that on one occasion, after he had been shown over
some large works in the north of England, the proprietor bluntly
said that he was greatly in want of a foreman, and would indeed be
pleased if his visitor, who had evinced such extraordinary
capacity for mechanical operations, would accept the post.  Lord
Rosse produced his card, and gently explained that he was not
exactly the right man, but he appreciated the compliment, and this
led to a pleasant dinner, and was the basis of a long friendship.

I remember on one occasion hearing Lord Rosse explain how it was
that he came to devote his attention to astronomy.  It appears
that when he found himself in the possession of leisure and of
means, he deliberately cast around to think how that means and
that leisure could be most usefully employed.  Nor was it
surprising that he should search for a direction which would offer
special scope for his mechanical tastes.  He came to the
conclusion that the building of great telescopes was an art which
had received no substantial advance since the great days of
William Herschel.  He saw that to construct mighty instruments for
studying the heavens required at once the command of time and the
command of wealth,  while he also felt that this was a subject the
inherent difficulties of which would tax to the uttermost whatever
mechanical skill he might possess.  Thus it was he decided that
the construction of great telescopes should become the business of
his life.

[PLATE:  BIRR CASTLE.

PLATE:  THE MALL, PARSONSTOWN.]

In the centre of Ireland, seventy miles from Dublin, on the border
between King's County and Tipperary, is a little town whereof we
must be cautious before writing the name.  The inhabitants of that
town frequently insist that its name is Birr,* while the official
designation is Parsonstown, and to this day for every six people
who apply one name to the town, there will be half a dozen who use
the other.  But whichever it may be, Birr or Parsonstown--and I
shall generally call it by the latter name--it is a favourable
specimen of an Irish county town.  The widest street is called the
Oxmantown Mall.  It is bordered by the dwelling-houses of the
chief residents, and adorned with rows of stately trees.  At one
end of this distinctly good feature in the town is the Parish
Church, while at the opposite end are the gates leading into Birr
Castle, the ancestral home of the house of Parsons.  Passing
through the gates the visitor enters a spacious demesne,
possessing much beauty of wood and water, one of the most pleasing
features being the junction of the two rivers, which unite at a
spot ornamented by beautiful timber.  At various points
illustrations of the engineering skill of the great Earl will be
observed.  The beauty of the park has been greatly enhanced by the
construction of an ample lake, designed with the consummate art by
which art is concealed.  Even in mid-summer it is enlivened by
troops of wild ducks preening themselves in that confidence which
they enjoy in those happy localities where the sound of a gun is
seldom heard.  The water is led into the lake by a tube which
passes under one of the two rivers just mentioned, while the
overflow from the lake turns a water-wheel, which works a pair of
elevators ingeniously constructed for draining the low-lying parts
of the estate.

*Considering the fame acquired by Parsonstown from Lord Rosse's
mirrors, it may be interesting to note the following extract from
"The Natural History of Ireland," by Dr. Gerard Boate, Thomas
Molyneux M.D., F.R.S., and others, which shows that 150 years ago
Parsonstown was famous for its glass:--

"We shall conclude this chapter with the glass, there having been
several glasshouses set up by the English in Ireland, none in
Dublin or other cities, but all of them in the country; amongst
which the principal was that of Birre, a market town, otherwise
called Parsonstown, after one Sir Lawrence Parsons, who, having
purchased that lordship, built a goodly house upon it; his son
William Parsons having succeeded him in the possession of it;
which town is situate in Queen's County, about fifty miles
(Irish) to the southwest of Dublin, upon the borders of the two
provinces of Leinster and Munster; from this place Dublin was
furnished with all sorts of window and drinking glasses, and such
other as commonly are in use.  One part of the materials, viz.,
the sand, they had out of England; the other, to wit the ashes,
they made in the place of ash-tree, and used no other.  The
chiefest difficulty was to get the clay for the pots to melt the
materials in; this they had out of the north."--Chap. XXI., Sect.
VIII. "Of the Glass made in Ireland."

Birr Castle itself is a noble mansion with reminiscences from the
time of Cromwell.  It is surrounded by a moat and a drawbridge of
modern construction, and from its windows beautiful views can be
had over the varied features of the park.  But while the visitors
to Parsonstown will look with great interest on this residence of
an Irish landlord, whose delight it was to dwell in his own
country, and among his own people, yet the feature which they have
specially come to observe is not to be found in the castle itself.
On an extensive lawn, sweeping down from the moat towards the
lake, stand two noble masonry walls.  They are turreted and clad
with ivy, and considerably loftier than any ordinary house.  As
the visitor approaches, he will see between those walls what may
at first sight appear to him to be the funnel of a steamer lying
down horizontally.  On closer approach he will find that it is an
immense wooden tube, sixty feet long, and upwards of six feet in
diameter.  It is in fact large enough to admit of a tall man
entering into it and walking erect right through from one end to
the other.  This is indeed the most gigantic instrument which has
ever been constructed for the purpose of exploring the heavens.
Closely adjoining the walls between which the great tube swings,
is a little building called "The Observatory."  In this the
smaller instruments are contained, and there are kept the books
which are necessary for reference.  The observatory also offers
shelter to the observers, and provides the bright fire and the cup
of warm tea, which are so acceptable in the occasional intervals
of a night's observation passed on the top of the walls with no
canopy but the winter sky.

Almost the first point which would strike the visitor to Lord
Rosse's telescope is that the instrument at which he is looking is
not only enormously greater than anything of the kind that he has
ever seen before, but also that it is something of a totally
different nature.  In an ordinary telescope he is accustomed to
find a tube with lenses of glass at either end, while the large
telescopes that we see in our observatories are also in general
constructed on the same principle.  At one end there is the
object-glass, and at the other end the eye-piece, and of course it
is obvious that with an instrument of this construction it is to
the lower end of the tube that the eye of the observer must be
placed when the telescope is pointed to the skies.  But in Lord
Rosse's telescope you would look in vain for these glasses, and it
is not at the lower end of the instrument that you are to take
your station when you are going to make your observations.  The
astronomer at Parsonstown has rather to avail himself of the
ingenious system of staircases and galleries, by which he
is enabled to obtain access to the mouth of the great tube.  The
colossal telescope which swings between the great walls, like
Herschel's great telescope already mentioned, is a reflector, the
original invention of which is due of course to Newton.  The
optical work which is accomplished by the lenses in the ordinary
telescope is effected in the type of instrument constructed by
Lord Rosse by a reflecting mirror which is placed at the lower end
of the vast tube.  The mirror in this instrument is made
of a metal consisting of two parts of copper to one of tin.  As we
have already seen, this mixture forms an alloy of a very peculiar
nature.  The copper and the tin both surrender their distinctive
qualities, and unite to form a material of a very different
physical character.  The copper is tough and brown, the tin is no
doubt silvery in hue, but soft and almost fibrous in texture.
When the two metals are mixed together in the proportions I have
stated, the alloy obtained is intensely hard and quite brittle
being in both these respects utterly unlike either of the two
ingredients of which it is composed.  It does, however, resemble
the tin in its whiteness, but it acquires a lustre far brighter
than tin; in fact, this alloy hardly falls short of silver itself
in its brilliance when polished.

[PLATE:  LORD ROSSE'S TELESCOPE.
From a photograph by W. Lawrence, Upper Sackville Street, Dublin.]

The first duty that Lord Rosse had to undertake was the
construction of this tremendous mirror, six feet across, and about
four or five inches thick.  The dimensions were far in excess of
those which had been contemplated in any previous attempt of the
same kind.  Herschel had no doubt fashioned one mirror of four
feet in diameter, and many others of smaller dimensions, but the
processes which he employed had never been fully published, and it
was obvious that, with a large increase in dimensions,
great additional difficulties had to be encountered.  Difficulties
began at the very commencement of the process, and were
experienced in one form or another at every subsequent stage.  In
the first place, the mere casting of a great disc of this mixture
of tin and copper, weighing something like three or four tons,
involved very troublesome problems.  No doubt a casting of this
size, if the material had been, for example, iron, would
have offered no difficulties beyond those with which every
practical founder is well acquainted, and which he has to
encounter daily in the course of his ordinary work.  But speculum
metal is a material of a very intractable description.  There is,
of course, no practical difficulty in melting the copper, nor
in adding the proper proportion of tin when the copper has been
melted.  There may be no great difficulty in arranging an
organization by which several crucibles, filled with the molten
material, shall be poured simultaneously so as to obtain the
requisite mass of metal, but from this point the difficulties
begin.  For speculum metal when cold is excessively brittle, and
were the casting permitted to cool like an ordinary copper or iron
casting, the mirror would inevitably fly into pieces.  Lord Rosse,
therefore, found it necessary to anneal the casting with extreme
care by allowing it to cool very slowly.  This was accomplished by
drawing the disc of metal as soon as it had entered into the solid
state, though still glowing red, into an annealing oven.  There
the temperature was allowed to subside so gradually, that six
weeks elapsed before the mirror had reached the temperature of the
external air.  The necessity for extreme precaution in the
operation of annealing will be manifest if we reflect on one of
the accidents which happened.  On a certain occasion, after the
cooling of a great casting had been completed, it was found, on
withdrawing the speculum, that it was cracked into two pieces.
This mishap was eventually traced to the fact that one of the
walls of the oven had only a single brick in its thickness, and
that therefore the heat had escaped more easily through that side
than through the other sides which were built of double thickness.
The speculum had, consequently, not cooled uniformly, and hence
the fracture had resulted.  Undeterred, however, by this failure,
as well as by not a few other difficulties, into a description of
which we cannot now enter, Lord Rosse steadily adhered to his
self-imposed task, and at last succeeded in casting two perfect
discs on which to commence the tedious processes of grinding and
polishing.  The magnitude of the operations involved may perhaps
be appreciated if I mention that the value of the mere copper and
tin entering into the composition of each of the mirrors was about
500 pounds.

In no part of his undertaking was Lord Rosse's mechanical
ingenuity more taxed than in the devising of the mechanism for
carrying out the delicate operations of grinding and polishing the
mirrors, whose casting we have just mentioned.  In the ordinary
operations of the telescope-maker, such processes had hitherto
been generally effected by hand, but, of course, such methods
became impossible when dealing with mirrors which were as large as
a good-sized dinner table, and whose weight was measured by
tons.  The rough grinding was effected by means of a tool of cast
iron about the same size as the mirror, which was moved by
suitable machinery both  backwards and forwards, and round and
round, plenty of sand and water being supplied between the mirror
and the tool to produce the necessary attrition.  As the process
proceeded and as the surface became smooth, emery was used instead
of sand; and when this stage was complete, the grinding tool was
removed and the polishing tool was substituted.  The essential
part of this was a surface of pitch, which, having been
temporarily softened by heat, was then placed on the mirror, and
accepted from the mirror the proper form.  Rouge was then
introduced as the polishing powder, and the operation was
continued about nine hours, by which time the great mirror
had acquired the appearance of highly polished silver.  When
completed, the disc of speculum metal was about six feet across
and four inches thick.  The depression in the centre was about
half an inch.  Mounted on a little truck, the great speculum was
then conveyed to the instrument, to be placed in its receptacle at
the bottom of the tube, the length of which was sixty feet, this
being the focal distance of the mirror.  Another small reflector
was inserted in the great tube sideways, so as to direct the gaze
of the observer down upon the great reflector.  Thus was completed
the most colossal instrument for the exploration of the heavens
which the art of man has ever constructed.

[PLATE:  ROMAN CATHOLIC CHURCH AT PARSONSTOWN.]

It was once my privilege to be one of those to whom the
illustrious builder of the great telescope entrusted its use.  For
two seasons in 1865 and 1866 I had the honour of being Lord
Rosse's astronomer.  During that time I passed many a fine night
in the observer's gallery, examining different objects in the
heavens with the aid of this remarkable instrument.  At the
time I was there, the objects principally studied were the
nebulae, those faint stains of light which lie on the background
of the sky.  Lord Rosse's telescope was specially suited for the
scrutiny of these objects, inasmuch as their delicacy required all
the light-grasping power which could be provided.

One of the greatest discoveries made by Lord Rosse, when his huge
instrument was first turned towards the heavens, consisted in the
detection of the spiral character of some of the nebulous forms.
When the extraordinary structure of these objects was first
announced, the discovery was received with some degree of
incredulity.  Other astronomers looked at the same objects, and
when they failed to discern--and they frequently did fail to
discern--the spiral structure which Lord Rosse had indicated, they
drew the conclusion that this spiral structure did not exist.
They thought it must be due possibly to some instrumental defect
or to the imagination of the observer.  It was, however, hardly
possible for any one who was both willing and competent to examine
into the evidence, to doubt the reality of Lord Rosse's
discoveries.  It happens, however, that they have been recently
placed beyond all doubt by testimony which it is impossible to
gainsay.  A witness never influenced by imagination has now come
forward, and the infallible photographic plate has justified Lord
Rosse.  Among the remarkable discoveries which Dr. Isaac Roberts
has recently made in the application of his photographic apparatus
to the heavens, there is none more striking than that which
declares, not only that the nebulae which Lord Rosse described as
spirals, actually do possess the character so indicated, but that
there are many others of the same description.  He has even
brought to light the astonishingly interesting fact that there are
invisible objects of this class which have never been seen by
human eye, but whose spiral character is visible to the peculiar
delicacy of the photographic telescope.

In his earlier years, Lord Rosse himself used to be a diligent
observer of the heavenly bodies with the great telescope which was
completed in the year 1845.  But I think that those who knew Lord
Rosse well, will agree that it was more the mechanical processes
incidental to the making of the telescope which engaged his
interest than the actual observations with the telescope when it
was completed.  Indeed one who was well acquainted with him
believed Lord Rosse's special interest in the great telescope
ceased when the last nail had been driven into it.  But the
telescope was never allowed to lie idle, for Lord Rosse always had
associated with him some ardent young astronomer, whose delight it
was to employ to the uttermost the advantages of his position in
exploring the wonders of the sky.  Among those who were in this
capacity in the early days of the great telescope, I may mention
my esteemed friend Dr. Johnston Stoney.

Such was the renown of Lord Rosse himself, brought about by his
consummate mechanical genius and his astronomical discoveries, and
such the interest which gathered around the marvellous workshops
at Birr castle, wherein his monumental exhibitions of optical
skill were constructed, that visitors thronged to see him from all
parts of the world.  His home at Parsonstown became one of
the most remarkable scientific centres in Great Britain; thither
assembled from time to time all the leading men of science in the
country, as well as many illustrious foreigners.  For many years
Lord Rosse filled with marked distinction the exalted position of
President of the Royal Society, and his advice and experience in
practical mechanical matters were always at the disposal of those
who sought his assistance.  Personally and socially Lord
Rosse endeared himself to all with whom he came in contact.  I
remember one of the attendants telling me that on one occasion he
had the misfortune to let fall and break one of the small mirrors
on which Lord Rosse had himself expended many hours of hard
personal labour.  The only remark of his lordship was that
"accidents will happen."

The latter years of his life Lord Rosse passed in comparative
seclusion; he occasionally went to London for a brief sojourn
during the season, and he occasionally went for a cruise in his
yacht; but the greater part of the  year he spent at Birr Castle,
devoting himself largely to the study of political and social
questions, and rarely going outside the walls of his demesne,
except to church on Sunday mornings.  He died on October 31, 1867.

He was succeeded by his eldest son, the present Earl of Rosse, who
has inherited his father's scientific abilities, and done much
notable work with the great telescope.




AIRY.



In our sketch of the life of Flamsteed, we have referred to the
circumstances under which the famous Observatory that crowns
Greenwich Hill was founded.  We have also had occasion to mention
that among the illustrious successors of Flamsteed both Halley and
Bradley are to be included.  But a remarkable development of
Greenwich Observatory from the modest establishment of early days
took place under the direction of the distinguished astronomer
whose name is at the head of this chapter.  By his labours this
temple of science was organised to such a degree of perfection
that it has served in many respects as a model for other
astronomical establishments in various parts of the world.  An
excellent account of Airy's career has been given by Professor H.
H. Turner, in the obituary notice published by the Royal
Astronomical Society.  To this I am indebted for many of the
particulars here to be set down concerning the life of the
illustrious Astronomer Royal.

The family from which Airy took his origin came from Kentmere, in
Westmoreland.  His father, William Airy, belonged to a
Lincolnshire branch of the same stock.  His mother's maiden name
was Ann Biddell, and her family resided at Playford, near Ipswich.
William Airy held some small government post which necessitated an
occasional change of residence to different parts of the country,
and thus it was that his son, George Biddell, came to be born at
Alnwick, on 27th July, 1801.  The boy's education, so far as
his school life was concerned was partly conducted at Hereford and
partly at Colchester.  He does not, however, seem to have derived
much benefit from the hours which he passed in the schoolroom.
But it was delightful to him to spend his holidays on the farm at
Playford, where his uncle, Arthur Biddell, showed him much
kindness.  The scenes of his early youth remained dear to Airy
throughout his life, and in subsequent years he himself owned a
house at Playford, to which it was his special delight to resort
for relaxation during the course of his arduous career.  In spite
of the defects of his school training he seems to have manifested
such remarkable abilities that his uncle decided to enter him in
Cambridge University.  He accordingly joined Trinity College as a
sizar in 1819, and after a brilliant career in mathematical and
physical science he graduated as Senior Wrangler in 1823.  It may
be noted as an exceptional circumstance that, notwithstanding the
demands on his time in studying for his tripos, he was able, after
his second term of residence, to support himself entirely by
taking private pupils.  In the year after he had taken his degree
he was elected to a Fellowship at Trinity College.

Having thus gained an independent position, Airy immediately
entered upon that career of scientific work which he prosecuted
without intermission almost to the very close of his life.  One of
his most interesting researches in these early days is on the
subject of Astigmatism, which defect he had discovered in his own
eyes.  His investigations led him to suggest a means of correcting
this defect by using a pair of spectacles with lenses so shaped as
to counteract the derangement which the astigmatic eye impressed
upon the rays of light.  His researches on this subject were of
a very complete character, and the principles he laid down are
to the present day practically employed by oculists in the
treatment of this malformation.

On the 7th of December, 1826, Airy was elected to the Lucasian
Professorship of Mathematics in the University of Cambridge, the
chair which Newton's occupancy had rendered so illustrious.  His
tenure of this office only lasted for two years, when he exchanged
it for the Plumian Professorship.  The attraction which led him to
desire this change is doubtless to be found in the circumstance
that the Plumian Professorship of Astronomy carried with it at
that time the appointment of director of the new astronomical
observatory, the origin of which must now be described.

Those most interested in the scientific side of University life
decided in 1820 that it would be proper to found an astronomical
observatory at Cambridge.  Donations were accordingly sought for
this purpose, and upwards of 6,000 pounds were contributed by
members of the University and the public.  To this sum 5,000
pounds were added by a grant from the University chest, and in
1824 further sums amounting altogether to 7,115 pounds were given
by the University for the same object.  The regulations as to the
administration of the new observatory placed it under the
management of the Plumian Professor, who was to be provided with
two assistants.  Their duties were to consist in making meridian
observations of the sun, moon, and the stars, and the observations
made each year were to be printed and published.  The observatory
was also to be used in the educational work of the University, for
it was arranged that smaller instruments were to be provided by
which students could be instructed in the practical art of making
astronomical observations.

The building of the Cambridge Astronomical Observatory was
completed in 1824, but in 1828, when Airy entered on the discharge
of his duties as Director, the establishment was still far from
completion, in so far as its organisation was concerned.  Airy
commenced his work so energetically that in the next year after
his appointment he was able to publish the first volume of
"Cambridge Astronomical Observations," notwithstanding that every
part of the work, from the making of observations to the revising
of the proof-sheets, had to be done by himself.

It may here be remarked that these early volumes of the
publications of the Cambridge Observatory contained the first
exposition of those systematic methods of astronomical work which
Airy afterwards developed to such a great extent at Greenwich, and
which have been subsequently adopted in many other places.  No
more profitable instruction for the astronomical beginner can be
found than that which can be had by the study of these volumes, in
which the Plumian Professor has laid down with admirable clearness
the true principles on which meridian work should be conducted.

[PLATE:  SIR GEORGE AIRY.
From a Photograph by Mr. E.P. Adams, Greenwich.]

Airy gradually added to the instruments with which the observatory
was originally equipped.  A mural circle was mounted in 1832, and
in the same year a small equatorial was erected by Jones.  This
was made use of by Airy in a well-known series of observations of
Jupiter's fourth satellite for the determination of the mass of
the great planet.  His memoir on this subject fully ex pounds the
method of finding the weight of a planet from observations of the
movements of a satellite by which the planet is attended.  This
is, indeed, a valuable investigation which no student of astronomy
can afford to neglect.  The ardour with which Airy devoted himself
to astronomical studies may be gathered from a remarkable report
on the progress of astronomy during the present century, which he
communicated to the British Association at its second meeting in
1832.  In the early years of his life at Cambridge his most famous
achievement was connected with a research in theoretical astronomy
for which consummate mathematical power was required.  We can only
give a brief account of the Subject, for to enter into any full
detail with regard to it would be quite out of the question.

Venus is a planet of about the same size and the same weight as
the earth, revolving in an orbit which lies within that described
by our globe.  Venus, consequently, takes less time than the earth
to accomplish one revolution round the sun, and it happens that
the relative movements of Venus and the earth are so proportioned
that in the time in which our earth accomplishes eight of her
revolutions the other planet will have accomplished almost exactly
thirteen.  It, therefore, follows that if the earth and Venus are
in line with the sun at one date, then in eight years later both
planets will again be found at the same points in their orbits.
In those eight years the earth has gone round eight times, and
has, therefore, regained its original position, while in the same
period Venus has accomplished thirteen complete revolutions, and,
therefore, this planet also has reached the same spot where it was
at first.  Venus and the earth, of course, attract each other, and
in consequence of these mutual attractions the earth is swayed
from the elliptic track which it would otherwise pursue.  In like
manner Venus is also forced by the attraction of the earth to
revolve in a track which deviates from that which it would
otherwise follow.  Owing to the fact that the sun is of such
preponderating magnitude (being, in fact, upwards of 300,000 times
as heavy as either Venus or the earth), the disturbances induced
in the motion of either planet, in consequence of the attraction
of the other, are relatively insignificant to the main controlling
agency by which each of the movements is governed.  It is,
however, possible under certain circumstances that the disturbing
effects produced upon one planet by the other can become so
multiplied as to produce peculiar effects which attain measurable
dimensions.  Suppose that the periodic times in which the earth
and Venus revolved had no simple relation to each other, then the
points of their tracks in which the two planets came into line
with the sun would be found at different parts of the orbits, and
consequently the disturbances would to a great extent neutralise
each other, and produce but little appreciable effect.  As,
however, Venus and the earth come back every eight years to nearly
the same positions at the same points of their track, an
accumulative effect is produced.  For the disturbance of one
planet upon the other will, of course, be greatest when those two
planets are nearest, that is, when they lie in line with the sun
and on the same side of it.  Every eight years a certain part of
the orbit of the earth is, therefore, disturbed by the attraction
of Venus with peculiar vigour.  The consequence is that, owing to
the numerical relation between the movements of the planets to
which I have referred, disturbing effects become appreciable which
would otherwise be too small to permit of recognition.  Airy
proposed to himself to compute the effects which Venus would have
on the movement of the earth in consequence of the circumstance
that eight revolutions of the one planet required almost the same
time as thirteen revolutions of the other.  This is a mathematical
inquiry of the most arduous description, but the Plumian Professor
succeeded in working it out, and he had, accordingly, the
gratification of announcing to the Royal Society that he had
detected the influence which Venus was thus able to assert on the
movement of our earth around the sun.  This remarkable investigation
gained for its author  the gold medal of the Royal Astronomical
Society in the year 1832.

In consequence Of his numerous discoveries, Airy's scientific fame
had become so well recognised that the Government awarded him a
special pension, and in 1835, when Pond, who was then Astronomer
Royal, resigned, Airy was offered the post at Greenwich.  There
was in truth, no scientific inducement to the Plumian Professor to
leave the comparatively easy post he held at Cambridge, in which
he had ample leisure to devote himself to those researches which
specially interested him, and accept that of the much more arduous
observatory at Greenwich.  There were not even pecuniary
inducements to make the change; however, he felt it to be his duty
to accede to the request which the Government had made that he
would take up the position which Pond had vacated, and accordingly
Airy went to Greenwich as Astronomer Royal on October 1st, 1835.

He immediately began with his usual energy to organise the
systematic conduct of the business of the National Observatory.
To realise one of the main characteristics of Airy's great work at
Greenwich, it is necessary to explain a point that might not
perhaps be understood without a little explanation by those who
have no practical experience in an observatory.  In the work of an
establishment such as Greenwich, an observation almost always
consists of a measurement of some kind.  The observer may, for
instance, be making a measurement of the time at which a star
passes across a spider line stretched through the field of view;
on another occasion his object may be the measurement of an angle
which is read off by examining through a microscope the lines of
division on a graduated circle when the telescope is so pointed
that the star is placed on a certain mark in the field of view.
In either case the immediate result of the astronomical
observation is a purely numerical one, but it rarely happens,
indeed we may say it never happens, that the immediate numerical
result which the observation gives expresses directly the quantity
which we are really seeking for.  No doubt the observation has
been so designed that the quantity we want to find can be obtained
from the figures which the measurement gives, but the object
sought is not those figures, for there are always a multitude of
other influences by which those figures are affected.  For
example, if an observation were to be perfect, then the telescope
with which the observation is made should be perfectly placed in
the exact position which it ought to occupy; this is, however,
never the case, for no mechanic can ever construct or adjust a
telescope so perfectly as the wants of the astronomer demand.  The
clock also by which we determine the time of the observation
should be correct, but this is rarely if ever the case.  We have
to correct our observations for such errors, that is to say, we
have to determine the errors in the positions of our telescopes
and the errors in the going of our clocks, and then we have to
determine what the observations would have been had our telescopes
been absolutely perfect, and had our clocks been absolutely
correct.  There are also many other matters which have to be
attended to in order to reduce our observations so as to obtain
from the figures as yielded to the observer at the telescope the
actual quantities which it is his object to determine.

The work of effecting these reductions is generally a very
intricate and laborious matter, so that it has not unfrequently
happened that while observations have accumulated in an
observatory, yet the tedious duty of reducing these observations
has been allowed to fall into arrear.  When Airy entered on his
duties at Greenwich he found there an enormous mass of
observations which, though implicitly containing materials of the
greatest value to astronomers, were, in their unreduced form,
entirely unavailable for any useful purpose.  He, therefore,
devoted himself to coping with the reduction of the observations
of his predecessors.  He framed systematic methods by which the
reductions were to be effected, and he so arranged the work that
little more than careful attention to numerical accuracy
would be required for the conduct of the operations.  Encouraged
by the Admiralty, for it is under this department that Greenwich
Observatory is placed, the Astronomer Royal employed a large force
of computers to deal with the work.  BY his energy and admirable
organisation he managed to reduce an extremely valuable series of
planetary observations, and to publish the results, which have
been of the greatest importance to astronomical investigation.

The Astronomer Royal was a capable, practical engineer as well
as an optician, and he presently occupied himself by designing
astronomical instruments of improved pattern, which should
replace the antiquated instruments he found in the observatory.
In the course of years the entire equipment underwent a total
transformation.  He ordered a great meridian circle, every part
of which may be said to have been formed from his own designs.
He also designed the mounting for a fine equatorial telescope
worked by a driving clock, which he had himself invented.
Gradually the establishment at Greenwich waxed great under his
incessant care.  It was the custom for the observatory to be
inspected every year by a board of visitors, whose chairman was
the President of the Royal Society.  At each annual visitation,
held on the first Saturday in June, the visitors received a report
from the Astronomer Royal, in which he set forth the business
which had been accomplished during the past year.  It was on these
occasions that applications were made to the Admiralty, either for
new instruments or for developing the work of the observatory in
some other way.  After the more official business of the
inspection was over, the observatory was thrown open to visitors,
and hundreds of people enjoyed on that day the privilege of seeing
the national observatory.  These annual gatherings are happily
still continued, and the first Saturday in June is known to be
the occasion of one of the most interesting reunions of scientific
men which takes place in the course of the year.

Airy's scientific work was, however, by no means confined to the
observatory.  He interested himself largely in expeditions for the
observation of eclipses and in projects for the measurement of
arcs on the earth. He devoted much attention to the collection of
magnetic observations from various parts of the world.  Especially
will it be remembered that the circumstances of the transits of
Venus, which occurred in 1874 and in 1882, were investigated by
him, and under his guidance expeditions were sent forth to observe
the transits from those localities in remote parts of the earth
where observations most suitable for the determination of
the sun's distance from the earth could be obtained.  The
Astronomer Royal also studied tidal phenomena, and he rendered
great service to the country in the restoration of the standards
of length and weight which had been destroyed in the great fire at
the House of Parliament in October, 1834.  In the most practical
scientific matters his advice was often sought, and was
as cheerfully rendered.  Now we find him engaged in an
investigation of the irregularities of the compass in iron ships,
with a view to remedying its defects; now we find him reporting on
the best gauge for railways.  Among  the most generally useful
developments of the observatory must be mentioned the telegraphic
method for the  distribution of exact time.  By arrangement with
the Post Office, the astronomers at Greenwich despatch each
morning a signal from the observatory to London at ten o'clock
precisely.  By special apparatus, this signal is thence
distributed automatically over the country, so as to enable the
time to be known everywhere accurately to a single second.  It was
part of the same system that a time ball should be dropped daily
at one o'clock at Deal, as well as at other places, for the
purpose of enabling ship's chronometers to be regulated.

Airy's writings were most voluminous, and no fewer than forty-
eight memoirs by him are mentioned in the "Catalogue of Scientific
Memoirs," published by the Royal Society up to the year 1873,
and this only included ten years out of an entire life of most
extraordinary activity.  Many other subjects besides those of a
purely scientific character from time to time engaged his
attention.  He wrote, for instance, a very interesting treatise on
the Roman invasion of Britain, especially with a view of
determining the port from which Caesar set forth from Gaul, and
the point at which he landed on the British coast.  Airy was
doubtless led to this investigation by his study of the tidal
phenomena in the Straits of Dover.  Perhaps the Astronomer Royal
is best known to the general reading public by his excellent
lectures on astronomy, delivered at the Ipswich Museum in 1848.
This book has passed through many editions, and it gives a most
admirable account of the manner in which the fundamental problems
in astronomy have to be attacked.

As years rolled by almost every honour and distinction that
could be conferred upon a scientific man was awarded to Sir George
Airy.  He was, indeed, the recipient of other honours not often
awarded for scientific distinction.  Among these we may mention
that in 1875 he received the freedom of the City of London, "as a
recognition of his indefatigable labours in astronomy, and of his
eminent services in the advancement of practical science, whereby
he has so materially benefited the cause of commerce and
civilisation."

Until his eightieth year Airy continued to discharge his labours
at Greenwich with unflagging energy.  At last, on August 15th,
1881, he resigned the office which he had held so long with such
distinction to himself and such benefit to his country.  He had
married in 1830 the daughter of the Rev. Richard Smith, of
Edensor.  Lady Airy died in 1875, and three sons and three
daughters survived him.  One daughter is the wife of Dr. Routh, of
Cambridge, and his other daughters were the constant companions of
their father during the declining years of his life.  Up to the
age of ninety he enjoyed perfect physical health, but an
accidental fall which then occurred was attended with serious
results. He died on Saturday, January 2nd, 1892, and was buried in
the churchyard at Playford.




HAMILTON.



William Rowan Hamilton was born at midnight between the 3rd and
4th of August, 1805, at Dublin, in the house which was then 29,
but subsequently 36, Dominick Street.  His father, Archibald
Hamilton, was a solicitor, and William was the fourth of a family
of nine.  With reference to his descent, it may be sufficient to
notice that his ancestors appear to have been chiefly of gentle
Irish families, but that his maternal grandmother was of Scottish
birth.  When he was about a year old, his father and mother
decided to hand over the education of the child to his uncle,
James Hamilton, a clergyman of Trim, in County Meath.  James
Hamilton's sister, Sydney, resided with him, and it was in their
home that the days of William's childhood were passed.

In Mr. Graves' "Life of Sir William Rowan Hamilton" a series
of letters will be found, in which Aunt Sydney details the
progress of the boy to his mother in Dublin. Probably there is no
record of an infant prodigy more extraordinary than that which
these letters contain.  At three years old his aunt assured the
mother that William is "a hopeful blade," but at that time it
was his physical vigour to which she apparently referred; for the
proofs of his capacity, which she adduces, related to his prowess
in making boys older than himself fly before him.  In the second
letter, a month later, we hear that William is brought in to read
the Bible for the purpose of putting to shame other boys double
his age who could not read nearly so well.  Uncle James appears to
have taken much pains with William's schooling, but his aunt said
that "how he picks up everything is astonishing, for he never
stops playing and jumping about."  When he was four years and three
months old, we hear that he went out to dine at the vicar's, and
amused the company by reading for them equally well whether the
book was turned upside down or held in any other fashion.  His
aunt assures the mother that " Willie is a most sensible little
creature, but at the same time has a great deal of roguery."  At
four years and five months old he came up to pay his mother a
visit in town, and she writes to her sister a description of the
boy;-

"His reciting is astonishing, and his clear and accurate
knowledge of geography is beyond belief; he even draws the
countries with a pencil on paper, and will cut them out,
though not perfectly accurate, yet so well that a anybody
knowing the countries could not mistake them; but, you will
think this nothing when I tell you that he reads Latin, Greek,
and Hebrew."

Aunt Sydney recorded that the moment Willie got back to Trim he
was desirous of at once resuming his former pursuits.  He would
not eat his breakfast till his uncle had heard him his Hebrew,
and he comments on the importance of proper pronunciation.  At
five he was taken to see a friend, to whom he repeated long
passages from Dryden.  A gentleman present, who was not
unnaturally sceptical about Willie's attainments, desired to
test him in Greek, and took down a copy of Homer which happened
to have the contracted type, and to his amazement Willie went on
with the greatest ease.  At six years and nine months he was
translating Homer and Virgil; a year later his uncle tells us
that William finds so little difficulty in learning French and
Italian, that he wishes to read Homer in French.  He is
enraptured with the Iliad, and carries it about with him,
repeating from it whatever particularly pleases him.  At eight
years and one month the boy was one of a party who visited
the Scalp in the Dublin mountains, and he was so delighted
with the scenery that he forthwith delivered an oration in
Latin.  At nine years and six months he is not satisfied until
he learns Sanscrit; three months later his thirst for the
Oriental languages is unabated, and at ten years and four months
he is studying Arabic and Persian.  When nearly twelve he
prepared a manuscript ready for publication.  It was a "Syriac
Grammar," in Syriac letters and characters compiled from that of
Buxtorf, by William Hamilton, Esq., of Dublin and Trim.  When he
was fourteen, the Persian ambassador, Mirza Abul Hassan Khan, paid
a visit to Dublin, and, as a practical exercise in his Oriental
languages, the young scholar addressed to his Excellency a letter
in Persian; a translation of which production is given by Mr.
Graves.  When William was fourteen he had the misfortune to lose
his father; and he had lost his mother two years previously.  The
boy and his three sisters were kindly provided for by different
members of the family on both sides.

It was when William was about fifteen that his attention began to
be turned towards scientific subjects.  These were at first
regarded rather as a relaxation from the linguistic studies with
which he had been so largely occupied.  On November 22nd, 1820, he
notes in his journal that he had begun Newton's "Principia": he
commenced also the study of astronomy by observing eclipses,
occultations, and similar phenomena.  When he was sixteen we learn
that he had read conic sections, and that he was engaged in the
study of pendulums.  After an attack of illness, he was moved for
change to Dublin, and in May, 1822, we find him reading the
differential calculus and  Laplace's "Mecanique Celeste." He
criticises an important part of Laplace's work relative to the
demonstration of the parallelogram of forces.  In this same year
appeared the first gushes of those poems which afterwards flowed
in torrents.

His somewhat discursive studies had, however, now to give place to
a more definite course of reading in preparation for entrance to
the University of Dublin.  The tutor under whom he entered,
Charles Boyton, was himself a distinguished man, but he frankly
told the young William that he could be of little use to him as a
tutor, for his pupil was quite as fit to be his tutor.  Eliza
Hamilton, by whom this is recorded, adds, "But there is one thing
which Boyton would promise to be to him, and that was a FRIEND;
and that one proof he would give of this should be that, if ever
he saw William beginning to be UPSET by the sensation he would
excite, and the notice he would attract, he would tell him of it."
At the beginning of his college career he distanced all his
competitors in every intellectual pursuit.  At his first term
examination in the University he was first in Classics and first
in Mathematics, while he received the Chancellor's prize for a
poem on the Ionian Islands, and another for his poem on Eustace de
St. Pierre.

There is abundant testimony that Hamilton had "a heart for
friendship formed."  Among the warmest of the friends whom he made
in these early days was the gifted Maria Edgeworth, who writes to
her sister about "young Mr. Hamilton, an admirable Crichton of
eighteen, a real prodigy of talents, who Dr. Brinkley says may be
a second Newton, quiet, gentle, and simple."  His sister Eliza,
to whom he was affectionately attached, writes to him in 1824:--

"I had been drawing pictures of you in my mind in your study at
Cumberland Street with 'Xenophon,' &c., on the table, and you,
with your most awfully sublime face of thought, now sitting down,
and now walking about, at times rubbing your hands with an air of
satisfaction, and at times bursting forth into some very heroical
strain of poetry in an unknown language, and in your own internal
solemn ventriloquist-like voice, when you address yourself to the
silence and solitude of your own room, and indeed, at times, even
when your mysterious poetical addresses are not quite unheard."

This letter is quoted because it refers to a circumstance which
all who ever met with Hamilton, even in his latest years, will
remember.  He was endowed with two distinct voices, one a high
treble, the other a deep bass, and he alternately employed these
voices not only in ordinary conversation, but when he was
delivering an address on the profundities of Quaternions to the
Royal Irish Academy, or on similar  occasions.  His friends had
long grown so familiar with this peculiarity that they were
sometimes rather surprised to find how ludicrous it appeared to
strangers.

Hamilton was fortunate in finding, while still at a very early
age, a career open before him which was worthy of his talents.
He had not ceased to be an undergraduate before he was called to
fill an illustrious chair in his university.  The circumstances
are briefly as follows.

We have already mentioned that, in 1826, Brinkley was appointed
Bishop of Cloyne, and the professorship of astronomy thereupon
became vacant.  Such was Hamilton's conspicuous eminence that,
notwithstanding he was still an undergraduate, and had only just
completed his twenty-first year, he was immediately thought of as
a suitable successor to the chair.  Indeed, so remarkable were his
talents in almost every direction that had the vacancy been in the
professorship of classics or of mathematics, of English literature
or of metaphysics, of modern or of Oriental languages, it seems
difficult to suppose that he would not have occurred to every one
as a possible successor.  The chief ground, however, on which the
friends of Hamilton urged his appointment was the earnest of
original power which he had already shown in a research on the
theory of Systems of Rays.  This profound work created a new
branch of optics, and led a few years later to a superb discovery,
by which the fame of its author became world-wide.

At first Hamilton thought it would be presumption for him to apply
for so exalted a position; he accordingly retired to the country,
and resumed his studies for his degree.  Other eminent candidates
came forward, among them some from Cambridge, and a few of the
Fellows from Trinity College, Dublin, also sent in their
claims.  It was not until Hamilton received an urgent letter from
his tutor Boyton, in which he was assured of the favourable
disposition of the Board towards his candidature, that he
consented to come forward, and on June 16th, 1827, he was
unanimously chosen to succeed the Bishop of Cloyne as Professor of
Astronomy in the University.  The appointment met with almost
universal approval.  It should, however, be noted that Brinkley,
whom Hamilton succeeded, did not concur in the general sentiment.
No one could have formed a higher opinion than he had done of
Hamilton's transcendent powers; indeed, it was on that very
ground that he seemed to view the appointment with disapprobation.
He considered that it would have been wiser for Hamilton to have
obtained a Fellowship, in which capacity he would have been able
to exercise a greater freedom in his choice of intellectual
pursuits.  The bishop seems to have thought, and not without
reason, that Hamilton's genius would rather recoil from much of
the routine work of an astronomical establishment.  Now that
Hamilton's whole life is before us, it is easy to see that the
bishop was entirely wrong.  It is quite true that Hamilton never
became a skilled astronomical observer; but the seclusion of the
observatory was eminently favourable to those gigantic labours to
which his life was devoted, and which have shed so much lustre,
not only on Hamilton himself, but also on his University and his
country.

In his early years at Dunsink, Hamilton did make some attempts at
a practical use of the telescopes, but he possessed no natural
aptitude for such work, while exposure which it involved seems
to have acted injuriously on his health.  He, therefore,
gradually allowed his attention to be devoted to those
mathematical researches in which he had already given such promise
of distinction.  Although it was in pure mathematics that he
ultimately won his greatest fame, yet he always maintained and
maintained with justice, that he had ample claims to
the title of an astronomer.  In his later years he set forth this
position himself in a rather striking manner.  De Morgan had
written commending to Hamilton's notice Grant's "History of
Physical Astronomy."  After becoming acquainted with the book,
Hamilton writes to his friend as follows:--

"The book is very valuable, and very creditable to its composer.
But your humble servant may be pardoned if he finds himself
somewhat amused at the title, `History of Physical Astronomy
from the Earliest Ages to the Middle of the Nineteenth Century,'
when he fails to observe any notice of the discoveries of Sir W.
R. Hamilton in the theory of the 'Dynamics of the Heavens.'"

The intimacy between the two correspondents will account for the
tone of this letter; and, indeed, Hamilton supplies in the
lines which follow ample grounds for his complaint.  He tells how
Jacobi spoke of him in Manchester in 1842 as "le Lagrange de votre
pays," and how Donkin had said that, "The Analytical Theory of
Dynamics as it exists at present is due mainly to the labours of
La Grange Poisson, Sir W. R. Hamilton, and Jacobi, whose
researches on this subject present a series of discoveries hardly
paralleled for their elegance and importance in any other branch
of mathematics."  In the same letter Hamilton also alludes to the
success which had attended the applications of his methods in
other hands than his own to the elucidation of the difficult
subject of Planetary Perturbations.  Even had his contributions to
science amounted to no more than these discoveries, his tenure of
the chair would have been an illustrious one.  It happens,
however, that in the gigantic mass of his intellectual work these
researches, though intrinsically of such importance, assume what
might almost be described as a relative insignificance.

The most famous achievement of Hamilton's earlier years at the
observatory was the discovery of conical refraction.  This was one
of those rare events in the history of science, in which a
sagacious calculation has predicted a result of an almost
startling character, subsequently confirmed by observation.  At
once this conferred on the young professor a world-wide renown.
Indeed, though he was still only twenty-seven, he had already
lived through an amount of intellectual activity which would have
been remarkable for a man of threescore and ten.

Simultaneously with his growth in fame came the growth of his
several friendships.  There were, in the first place, his
scientific friendships with Herschel, Robinson, and many others
with whom he had copious correspondence.  In the excellent
biography to which I have referred, Hamilton's correspondence with
Coleridge may be read, as can also the letters to his lady
correspondents, among them being Maria Edgeworth, Lady Dunraven,
and Lady Campbell.  Many of these sheets relate to literary
matters, but they are largely intermingled With genial pleasantry,
and serve at all events to show the affection and esteem with
which he was regarded by all who had the privilege of knowing him.
There are also the letters to the sisters whom he adored, letters
brimming over with such exalted sentiment, that most ordinary
sisters would be tempted to receive them with a smile in
the excessively improbable event of their still more ordinary
brothers attempting to pen such effusions.  There are also
indications of letters to and from other young ladies who from
time to time were the objects of Hamilton's tender admiration.  We
use the plural advisedly, for, as Mr. Graves has set forth,
Hamilton's love affairs pursued a rather troubled course.  The
attention which he lavished on one or two fair ones was not
reciprocated, and even the intense charms of mathematical
discovery could not assuage the pangs which  the disappointed
lover experienced.  At last he reached the haven of matrimony in
1833, when he was married to Miss Bayly.  Of his married life
Hamilton said, many years later to De Morgan, that it was as
happy as he expected, and happier than he deserved.  He had two
sons, William and Archibald, and one daughter, Helen, who became
the wife of Archdeacon O'Regan.

[PLATE:  SIR W. ROWAN HAMILTON.]

The most remarkable of Hamilton's friendships in his early years
was unquestionably that with Wordsworth.  It commenced with
Hamilton's visit to Keswick; and on the first evening, when the
poet met the young mathematician, an incident occurred which
showed the mutual interest that was aroused.  Hamilton thus
describes it in a letter to his sister Eliza:--

"He (Wordsworth) walked back with our party as far as their
lodge, and then, on our bidding Mrs. Harrison good-night, I
offered to walk back with him while my party proceeded to the
hotel.  This offer he accepted, and our conversation had become so
interesting that when we had arrived at his home, a distance of
about a mile, he proposed to walk back with me on my way to
Ambleside, a proposal which you may be sure I did not reject; so
far from it that when he came to turn once more towards his home I
also turned once more along with him.  It was very late when I
reached the hotel after all this walking."

Hamilton also submitted to Wordsworth an original poem, entitled
"It Haunts me Yet."  The reply of Wordsworth is worth repeating:--

"With a safe conscience I can assure you that, in my judgment,
your verses are animated with the poetic spirit, as they are
evidently the product of strong feeling.  The sixth and seventh
stanzas affected me much, even to the dimming of my eyes and
faltering of my voice while I was reading them aloud.  Having
said this, I have said enough.  Now for the per contra.  You
will not, I am sure, be hurt when I tell you that the
workmanship (what else could be expected from so young a
writer?) is not what it ought to be. . .

"My household desire to be remembered to you in no formal way.
Seldom have I parted--never, I was going to say--with one whom after
so short an acquaintance I lost sight of with more regret.  I
trust we shall meet again."

The further affectionate intercourse between Hamilton and
Wordsworth is fully set forth, and to Hamilton's latest years
a recollection of his "Rydal hours" was carefully treasured and
frequently referred to.  Wordsworth visited Hamilton at the
observatory, where a beautiful shady path in the garden is to the
present day spoken of as "Wordsworth's Walk."

It was the practice of Hamilton to produce a sonnet on almost
every occasion which admitted of poetical treatment, and it was
his delight to communicate his verses to his friends all round.
When Whewell was producing his "Bridgewater Treatises," he writes
to Hamilton in 1833:--

"Your sonnet which you showed me expressed much better than I
could express it the feeling with which I tried to write this
book, and I once intended to ask your permission to prefix the
sonnet to my book, but my friends persuaded me that I ought to
tell my story in my own prose, however much better your verse
might be."

The first epoch-marking contribution to Theoretical Dynamics after
the time of Newton was undoubtedly made by Lagrange, in his
discovery of the general equations of Motion.  The next great step
in the same direction was that taken by Hamilton in his discovery
of a still more comprehensive method.  Of this contribution
Hamilton writes to Whewell, March 31st, 1834:--

"As to my late paper, a day or two ago sent off to London, it is
merely mathematical and deductive.  I ventured, indeed, to call
it the 'Mecanique Analytique' of Lagrange, 'a scientific poem';
and spoke of Dynamics, or the Science of Force, as treating of
'Power acting by Law in Space and Time.'  In other respects it is
as unpoetical and unmetaphysical as my gravest friends could
desire."

It may well be doubted whether there is a more beautiful chapter
in the whole of mathematical philosophy than that which contains
Hamilton's dynamical theory.  It is disfigured by no tedious
complexity of symbols; it condescends not to any particular
problems; it is an all embracing theory, which gives an
intellectual grasp of the most appropriate method for discovering
the result of the application of force to matter.  It is the very
generality of this doctrine which has somewhat impeded the
applications of which it is susceptible.  The exigencies of
examinations are partly responsible for the fact that the method
has not become more familiar to students of the higher
mathematics.  An eminent professor has complained that
Hamilton's essay on dynamics was of such an extremely abstract
character, that he found himself unable to extract from it
problems suitable for his examination papers.

The following extract is from a letter of Professor Sylvester to
Hamilton, dated 20th of September, 1841.  It will show how his
works were appreciated by so consummate a mathematician as the
writer:--

"Believe me, sir, it is not the least of my regrets in quitting
this empire to feel that I forego the casual occasion of meeting
those masters of my art, yourself chief amongst the number, whose
acquaintance, whose conversation, or even notice, have in
themselves the power to inspire, and almost to impart fresh vigour
to the understanding, and the courage and faith without which the
efforts of invention are in vain.  The golden moments I enjoyed
under your hospitable roof at Dunsink, or moments such as they
were, may probably never again fall to my lot.

At a vast distance, and in an humble eminence, I still promise
myself the calm satisfaction of observing your blazing course in
the elevated regions of discovery.  Such national honour as you
are able to confer on your country is, perhaps, the only species
of that luxury for the rich (I mean what is termed one's glory)
which is not bought at the expense of the comforts of the
million."

The study of metaphysics was always a favourite recreation when
Hamilton sought for a change from the pursuit of mathematics.  In
the year 1834 we find him a diligent student of Kant; and, to show
the views of the author of Quaternions and of Algebra as the
Science of Pure Time on the "Critique of the Pure Reason," we
quote the following letter, dated 18th of July, 1834, from
Hamilton to Viscount Adare:--

"I have read a large part of the 'Critique of the Pure Reason,'
and find it wonderfully clear, and generally quite convincing.
Notwithstanding some previous preparation from Berkeley, and from
my own thoughts, I seem to have learned much from Kant's own
statement of his views of 'Space and Time.'  Yet, on the whole, a
large part of my pleasure consists in recognising through Kant's
works, opinions, or rather views, which have been long familiar to
myself, although far more clearly and systematically expressed and
combined by him.. . . Kant is, I think, much more indebted than
he owns, or, perhaps knows, to Berkeley, whom he calls by a sneer,
`GUTEM Berkeley'. . . as it were, `good soul, well meaning
man,' who was able for all that to shake to its centre the world
of human thought, and to effect a revolution among the early
consequences of which was the growth of Kant himself."

At several meetings of the British Association Hamilton was a very
conspicuous figure.  Especially was this the case in 1835, when
the Association met in Dublin, and when Hamilton, though then but
thirty years old, had attained such celebrity that even among a
very brilliant gathering his name was perhaps the most renowned.
A banquet was given at Trinity College in honour of the meeting.
The distinguished visitors assembled in the Library of the
University.  The Earl of Mulgrave, then Lord Lieutenant of
Ireland, made this the opportunity of conferring on Hamilton the
honour of knighthood, gracefully adding, as he did so: "I but set
the royal, and therefore the national mark, on a distinction
already acquired by your genius and labours."

The banquet followed, writes Mr. Graves.  "It was no little
addition to the honour Hamilton had already received that, when
Professor Whewell returned thanks for the toast of the University
of Cambridge, he thought it appropriate to add the words, 'There
was one point which strongly pressed upon him at that moment: it
was now one hundred and thirty years since a great man in another
Trinity College knelt down before his sovereign, and rose up Sir
Isaac Newton.'  The compliment was welcomed by immense applause."

A more substantial recognition of the labours of Hamilton took
place subsequently.  He thus describes it in a letter to
Mr. Graves of 14th of November, 1843:--

"The Queen has been pleased--and you will not doubt that it was
entirely unsolicited, and even unexpected, on my part--'to express
her entire approbation of the grant of a pension of two hundred
pounds per annum from the Civil List' to me for scientific
services.  The letters from Sir Robert Peel and from the Lord
Lieutenant of Ireland in which this grant has been communicated or
referred to have been really more gratifying to my feelings than
the addition to my income, however useful, and almost necessary,
that may have been."

The circumstances we have mentioned might lead to the supposition
that Hamilton was then at the zenith of his fame but this was not
so.  It might more truly be said, that his achievements up to
this point were rather the preliminary exercises which fitted him
for the gigantic task of his life.  The name of Hamilton is now
chiefly associated with his memorable invention of the calculus of
Quaternions.  It was to the creation of this branch of mathematics
that the maturer powers of his life were devoted; in fact he
gives us himself an illustration of how completely habituated he
became to the new modes of thought which Quaternions originated.
In one of his later years he happened to take up a copy of his
famous paper on Dynamics, a paper which at the time created such a
sensation among mathematicians, and which is at this moment
regarded as one of the classics of dynamical literature.  He read,
he tells us, his paper with considerable interest, and expressed
his feelings of gratification that he found himself still able to
follow its reasoning without undue effort.  But it seemed to him
all the time as a work belonging to an age of analysis
now entirely superseded.

In order to realise the magnitude of the revolution which Hamilton
has wrought in the application of symbols to mathematical
investigation, it is necessary to think of what Hamilton did
beside the mighty advance made by Descartes.  To describe the
character of the quaternion calculus would be unsuited to the
pages of this work, but we may quote an interesting letter,
written by Hamilton from his deathbed, twenty-two years later, to
his son Archibald, in which he has recorded the circumstances of
the discovery:--

Indeed, I happen to be able to put the finger of memory upon the
year and month--October, 1843--when having recently returned from
visits to Cork and Parsonstown, connected with a meeting of the
British Association, the desire to discover the laws of
multiplication referred to, regained with me a certain strength
and earnestness which had for years been dormant, but was
then on the point of being gratified, and was occasionally
talked of with you.  Every morning in the early part of the above-
cited month, on my coming down to breakfast, your (then) little
brother William Edwin, and yourself, used to ask me, 'Well papa,
can you multiply triplets?'  Whereto I was always obliged to reply,
with a sad shake of the head:  'No, I can only ADD and subtract
them,'

But on the 16th day of the same month--which happened to be
Monday, and a Council day of the Royal Irish Academy--I was walking
in to attend and preside, and your mother was walking with me
along the Royal Canal, to which she had perhaps driven; and
although she talked with me now and then, yet an UNDERCURRENT of
thought was going on in my mind which gave at last a RESULT,
whereof it is not too much to say that I felt AT ONCE the
importance.  An ELECTRIC circuit seemed to CLOSE; and a spark
flashed forth the herald (as I FORESAW IMMEDIATELY) of many long
years to come of definitely directed thought and work by MYSELF,
if spared, and, at all events, on the part of OTHERS if I should
even be allowed to live long enough distinctly to communicate the
discovery.  Nor could I resist the impulse--unphilosophical as it
may have been--to cut with a knife on a stone of Brougham Bridge as
we passed it, the fundamental formula which contains the SOLUTION
of the PROBLEM, but, of course, the inscription has long since
mouldered away.  A more durable notice remains, however, on the
Council Books of the Academy for that day (October 16, 1843),
which records the fact that I then asked for and obtained leave to
read a Paper on 'Quaternions,' at the First General Meeting of the
Session; which reading took place accordingly, on Monday,
the 13th of November following."

Writing to Professor Tait, Hamilton gives further particulars of
the same event.  And again in a letter to the Rev. J. W. Stubbs:--

"To-morrow will be the fifteenth birthday of the Quaternions.
They started into life full-grown on the 16th October, 1843, as I
was walking with Lady Hamilton to Dublin, and came up to Brougham
Bridge--which my boys have since called Quaternion Bridge.  I
pulled out a pocketbook which still exists, and made entry, on
which at the very moment I felt that it might be worth my while to
expend the labour of at least ten or fifteen years to come.  But
then it is fair to say that this was because I felt a problem to
have been at that moment solved, an intellectual want relieved
which had haunted me for at least fifteen years before.

But did the thought of establishing such a system, in which
geometrically opposite facts--namely, two lines (or areas) which
are opposite IN SPACE give ALWAYS a positive product--ever come
into anybody's head till I was led to it in October, 1843, by
trying to extend my old theory of algebraic couples, and of
algebra as the science of pure time?  As to my regarding
geometrical addition of lines as equivalent to composition of
motions (and as performed by the same rules), that is indeed
essential in my theory but not peculiar to it; on the contrary, I
am only one of many who have been led to this view of addition."

Pilgrims in future ages will doubtless visit the spot commemorated
by the invention of Quaternions.  Perhaps as they look at that by
no means graceful structure Quaternion Bridge, they will regret
that the hand of some Old Mortality had not been occasionally
employed in cutting the memorable inscription afresh.  It is now
irrecoverably lost.

It was ten years after the discovery that the great volume
appeared under the title of "Lectures on Quaternions," Dublin,
1853.  The reception of this work by the scientific world was
such as might have been expected from the extraordinary reputation
of its author, and the novelty and importance of the new calculus.
His valued friend, Sir John Herschel, writes to him in that style
of which he was a master:--

"Now, most heartily let me congratulate you on getting out your
book--on having found utterance, ore rotundo, for all that
labouring and seething mass of thought which has been from time to
time sending out sparks, and gleams, and smokes, and shaking the
soil about you; but now breaks into a good honest eruption, with a
lava stream and a shower of fertilizing ashes.

Metaphor and simile apart, there is work for a twelve-month to
any man to read such a book, and for half a lifetime to digest it,
and I am glad to see it brought to a conclusion."

We may also record Hamilton's own opinion expressed to Humphrey
Lloyd:--

"In general, although in one sense I hope that I am actually
growing modest about the quaternions, from my seeing so many peeps
and vistas into future expansions of their principles, I still
must assert that this discovery appears to me to be as important
for the middle of the nineteenth century as the discovery of
fluxions was for the close of the seventeenth."

Bartholomew Lloyd died in 1837.  He had been the Provost of
Trinity College, and the President of the Royal Irish Academy.
Three candidates were put forward by their respective friends for
the vacant Presidency.  One was Humphrey Lloyd, the son of the
late Provost, and the two others were Hamilton and Archbishop
Whately.  Lloyd from the first urged strongly the claims of
Hamilton, and deprecated the putting forward of his own name.
Hamilton in like manner desired to withdraw in favour of Lloyd.
The wish was strongly felt by many of the Fellows of the College
that Lloyd should be elected, in consequence of his having a more
intimate association with collegiate life than Hamilton; while his
scientific eminence was world-wide.  The election ultimately gave
Hamilton a considerable majority over Lloyd, behind whom the
Archbishop followed at a considerable distance.  All concluded
happily, for both Lloyd and the Archbishop expressed, and no doubt
felt, the pre-eminent claims of Hamilton, and both of them
cordially accepted the office of a Vice-President, to which,
according to the constitution of the Academy, it is the privilege
of the incoming President to nominate.

In another chapter I have mentioned as a memorable episode in
astronomical history, that Sir J. Herschel went for a prolonged
sojourn to the Cape of Good Hope, for the purpose of submitting
the southern skies to the same scrutiny with the great telescope
that his father had given to the northern skies.  The occasion of
Herschel's return after the brilliant success of his enterprise,
was celebrated by a banquet.  On June 15th, 1838, Hamilton was
assigned the high honour of proposing the health of Herschel.
This banquet is otherwise memorable in Hamilton's career as being
one of the two occasions in which he was in the company of his
intimate friend De Morgan.

In the year 1838 a scheme was adopted by the Royal Irish Academy
for the award of medals to the authors of papers which appeared to
possess exceptionally high merit.  At the institution of the medal
two papers were named in competition for the prize.  One was
Hamilton's "Memoir on Algebra, as the Science of Pure Time."  The
other was Macullagh's paper on the "Laws of Crystalline
Reflection and Refraction."  Hamilton expresses his gratification
that, mainly in consequence of his own exertions, he succeeded in
having the medal awarded to Macullagh rather than to himself.
Indeed, it would almost appear as if Hamilton had procured a
letter from Sir J. Herschel, which indicated the importance of
Macullagh's memoir in such a way as to decide the issue.  It then
became Hamilton's duty to award the medal from the chair, and to
deliver an address in which he expressed his own sense of
the excellence of Macullagh's scientific work.  It is the
more necessary to allude to these points, because in the whole of
his scientific career it would seem that Macullagh was the only
man with whom Hamilton had ever even an approach to a dispute
about priority.  The incident referred to took place in connection
with the discovery of conical refraction, the fame of which
Macullagh made a preposterous attempt to wrest from Hamilton.
This is evidently alluded to in Hamilton's letter to the Marquis
of Northampton, dated June 28th, 1838, in which we read:--

And though some former circumstances prevented me from applying to
the person thus distinguished the sacred name of FRIEND, I had the
pleasure of doing justice...to his high intellectual merits...I
believe he was not only gratified but touched, and may,
perhaps, regard me in future with feelings more like those which I
long to entertain towards him."

Hamilton was in the habit, from time to time, of commencing the
keeping of a journal, but it does not appear to have been
systematically conducted.  Whatever difficulties the biographer
may have experienced from its imperfections and irregularities,
seem to be amply compensated for by the practice which Hamilton
had of preserving copies of his letters, and even of comparatively
insignificant memoranda.  In fact, the minuteness with which
apparently trivial matters were often noted down appears almost
whimsical.  He frequently made a memorandum of the name of the
person who carried a letter to the post, and of the hour in which
it was despatched.  On the other hand, the letters which he
received were also carefully preserved in a mighty mass of
manuscripts, with which his study was encumbered, and with which
many other parts of the house were not unfrequently invaded.  If a
letter was laid aside for a few hours, it would become lost to
view amid the seething mass of papers, though occasionally, to use
his own expression, it might be seen "eddying" to the surface in
some later disturbance.

The great volume of "Lectures on Quaternions" had been issued, and
the author had received the honours which the completion of such a
task would rightfully bring him.  The publication of an immortal
work does not, however, necessarily provide the means for paying
the printer's bill.  The printing of so robust a volume was
necessarily costly; and even if all the copies could be sold,
which at the time did not seem very likely, they would hardly have
met the inevitable expenses.  The provision of the necessary funds
was, therefore, a matter for consideration.  The Board of Trinity
College had already contributed 200 pounds to the printing, but
yet another hundred was required.  Even the discoverer of
Quaternions found this a source of much anxiety.  However, the
board, urged by the representation of Humphrey Lloyd, now one of
its members, and, as we have already seen, one of Hamilton's
staunchest friends, relieved him of all liability.  We may here
note that, notwithstanding the pension which Hamilton enjoyed in
addition to the salary of his chair, he seems always to have been
in some what straitened circumstances, or, to use his own words in
one of his letters to De Morgan, "Though not an embarrassed man, I
am anything rather than a rich one."  It appears that,
notwithstanding the world-wide fame of Hamilton's discoveries,
the only profit in a pecuniary sense that he ever obtained from
any of his works was by the sale of what he called his Icosian
Game.  Some enterprising publisher, on the urgent representations
of one of Hamilton's friends in London, bought the copyright of
the Icosian Game for 25 pounds.  Even this little speculation
proved unfortunate for the purchaser, as the public could not be
induced to take the necessary interest in the matter.

After the completion of his great book, Hamilton appeared for
awhile to permit himself a greater indulgence than usual in
literary relaxations.  He had copious correspondence
with his intimate friend, Aubrey de Vere, and there were
multitudes of letters from those troops of friends whom it was
Hamilton's privilege to possess.  He had been greatly affected by
the death of his beloved sister Eliza, a poetess of much taste and
feeling.  She left to him her many papers to preserve or to
destroy, but he said it was only after the expiration of four
years of mourning that he took courage to open her pet box of
letters.

The religious side of Hamilton's character is frequently
illustrated in these letters; especially is this brought out in
the correspondence with De Vere, who had seceded to the Church of
Rome.  Hamilton writes, August 4, 1855:--

"If, then, it be painfully evident to both, that under such
circumstances there CANNOT (whatever we may both DESIRE) be NOW in
the nature of things, or of minds, the same degree of INTIMACY
between us as of old; since we could no longer TALK with the same
degree of unreserve on every subject which happened to present
itself, but MUST, from the simplest instincts of courtesy, be each
on his guard not to say what might be offensive, or, at least,
painful to the other; yet WE were ONCE so intimate, an retain
still, and, as I trust, shall always retain, so much of regard and
esteem and appreciation for each other, made tender by so
many associations of my early youth and your boyhood, which can
never be forgotten by either of us, that (as times go) TWO OR
THREE VERY RESPECTABLE FRIENDSHIPS might easily be carved out from
the fragments of our former and ever-to-be-remembered INTIMACY.
It would be no exaggeration to quote the words:  'Heu! quanto minus
est cum reliquis versari, quam tui meminisse!'"

In 1858 a correspondence on the subject of Quaternions; commenced
between Professor Tait and Sir William Hamilton.  It was
particularly gratifying to the discoverer that so competent a
mathematician as Professor Tait should have made himself
acquainted with the new calculus.  It is, of course, well known
that Professor Tait subsequently brought out a most valuable
elementary treatise on Quaternions, to which those who are anxious
to become acquainted with the subject will often turn in
preference to the tremendous work of Hamilton.

In the year 1861 gratifying information came to hand of the
progress which the study of Quaternions was making abroad.
Especially did the subject attract the attention of that
accomplished mathematician, Moebius, who had already in his
"Barycentrische Calculus" been led to conceptions which bore
more affinity to Quaternions than could be found in the writings
of any other mathematician.  Such notices of his work were
always pleasing to Hamilton, and they served, perhaps, as
incentives to that still closer and more engrossing labour by
which he became more and more absorbed.  During the last few
years of his life he was observed to be even more of a
recluse than he had hitherto been.  His powers of long and
continuous study seemed to grow with advancing years, and his
intervals of relaxation, such as they were, became more brief
and more infrequent.

It was not unusual for him to work for twelve hours at a stretch.
The dawn would frequently surprise him as he looked up to snuff
his candles after a night of fascinating labour at original
research.  Regularity in habits was impossible to a student who
had prolonged fits of what he called his mathematical trances.
Hours for rest and hours for meals could only be snatched in the
occasional the lucid intervals between one attack of Quaternions
and the next.  When hungry, he would go to see whether any thing
could be found on the sideboard; when thirsty, he would visit the
locker, and the one blemish in the man's personal character is
that these latter visits were sometimes paid too often.

As an example of one of Hamilton's rare diversions from the all-
absorbing pursuit of Quaternions, we find that he was seized with
curiosity to calculate back to the date of the Hegira, which he
found on the 15th July, 622.  He speaks of the satisfaction with
which he ascertained subsequently that Herschel had assigned
precisely the same date.  Metaphysics remained also, as it had
ever been, a favourite subject of Hamilton's readings and
meditations and of correspondence with his friends.  He wrote a
very long letter to Dr. Ingleby on the subject of his
"Introduction to Metaphysics."  In it Hamilton alludes, as he has
done also in other places, to a peculiarity of his own vision.  It
was habitual to him, by some defect in the correlation of his
eyes, to see always a distinct image with each; in fact, he speaks
of the remarkable effect which the use of a good stereoscope had
on his sensations of vision.  It was then, for the first time,
that he realised how the two images which he had always seen
hitherto would, under normal circumstances, be blended into one.
He cites this fact as bearing on the phenomena of binocular
vision, and he draws from it the inference that the necessity of
binocular vision for the correct appreciation of distance is
unfounded.  "I am quite sure," he says, "that I SEE DISTANCE with
EACH EYE SEPARATELY."

The commencement of 1865, the last year of his life saw Hamilton
as diligent as ever, and corresponding with Salmon and Cayley.  On
April 26th he writes to a friend to say, that his health has not
been good for years past, and that so much work has injured his
constitution; and he adds, that it is not conducive to good
spirits to find that he is accumulating another heavy bill with
the printer for the publication of the "Elements."  This was,
indeed, up to the day of his death, a cause for serious anxiety.
It may, however, be mentioned that the whole cost, which amounted
to nearly 500 pounds, was, like that of the previous volume,
ultimately borne by the College.  Contrary to anticipation, the
enterprise, even in a pecuniary sense, cannot have been a very
unprofitable one.  The whole edition has long been out of print,
and as much as 5 pounds has since been paid for a single copy.

It was on the 9th of May, 1865, that Hamilton was in Dublin for
the last time.  A few days later he had a violent attack of gout,
and on the 4th of June he became alarmingly ill, and on the next
day had an attack of epileptic convulsions.  However, he slightly
rallied, so that before the end of the month he was again at work
at the "Elements."  A gratifying incident brightened some of the
last days of his life.  The National Academy of Science in America
had then been just formed.  A list of foreign Associates had to be
chosen from the whole world, and a discussion took place as to
what name should be placed first on the list.  Hamilton was
informed by private communication that this great distinction was
awarded to him by a majority of two-thirds.

In August he was still at work on the table of contents of the
"Elements," and one of his very latest efforts was his letter to
Mr. Gould, in America, communicating his acknowledgements of the
honour which had been just conferred upon him by the National
Academy.  On the 2nd of September Mr. Graves went to the
observatory, in response to a summons, and the great
mathematician at once admitted to his friend that he felt the end
was approaching.  He mentioned that he had found in the 145th
Psalm a wonderfully suitable expression of his thoughts and
feelings, and he wished to testify his faith and thankfulness as a
Christian by partaking of the Lord's Supper.  He died at half-past
two on the afternoon of the 2nd of September, 1865, aged sixty
years and one month.  He was buried in Mount Jerome Cemetery on
the 7th of September.

Many were the letters and other more public manifestations of the
feelings awakened by Hamilton's death.  Sir John Herschel wrote to
the widow:--

"Permit me only to add that among the many scientific friends whom
time has deprived me of, there has been none whom I more deeply
lament, not only for his splendid talents, but for the excellence
of his disposition and the perfect simplicity of his manners--so
great, and yet devoid of pretensions."

De Morgan, his old mathematical crony, as Hamilton affectionately
styled him, also wrote to Lady Hamilton:--

"I have called him one of my dearest friends, and most truly; for
I know not how much longer than twenty-five years we have been in
intimate correspondence, of most friendly agreement or
disagreement, of most cordial interest in each other.  And yet we
did not know each other's faces.  I met him about 1830 at
Babbage's breakfast table, and there for the only time in our
lives we conversed.  I saw him, a long way off, at the dinner
given to Herschel (about 1838) on his return from the Cape and
there we were not near enough, nor on that crowded day could we
get near enough, to
exchange a word.  And this is all I ever saw, and, so it has
pleased God, all I shall see in this world of a man whose friendly
communications were among my greatest social enjoyments, and
greatest intellectual treats."

There is a very interesting memoir of Hamilton written by De
Morgan, in the "Gentleman's Magazine" for 1866, in which he produces
an excellent sketch of his friend, illustrated by personal
reminiscences and anecdotes.  He alludes, among other things, to
the picturesque confusion of the papers in his study.  There was
some sort of order in the mass, discernible however, by Hamilton
alone, and any invasion of the domestics, with a view to tidying
up, would throw the mathematician as we are informed, into "a good
honest thundering passion."

Hardly any two men, who were both powerful mathematicians, could
have been more dissimilar in every other respect than were
Hamilton and De Morgan.  The highly poetical temperament of
Hamilton was remarkably contrasted with the practical realism of
De Morgan.  Hamilton sends sonnets to his friend, who replies by
giving the poet advice about making his will.  The metaphysical
subtleties, with which Hamilton often filled his sheets, did not
seem to have the same attraction for De Morgan that he found in
battles about the quantification of the Predicate.  De Morgan was
exquisitely witty, and though his jokes were always appreciated by
his correspondent, yet Hamilton seldom ventured on anything of the
same kind in reply; indeed his rare attempts at humour only
produced results of the most ponderous description.  But never
were two scientific correspondents more perfectly in sympathy with
each other.  Hamilton's work on Quaternions, his labours in
Dynamics, his literary tastes, his metaphysics, and his poetry,
were all heartily welcomed by his friend, whose letters in reply
invariably evince the kindliest interest in all Hamilton's
concerns.  In a similar way De Morgan's letters to Hamilton always
met with a heartfelt response.

Alike for the memory of Hamilton, for the credit of his
University, and for the benefit of science, let us hope that a
collected edition of his works will ere long appear--a collection
which shall show those early achievements in splendid
optical theory, those achievements of his more mature powers which
made him the Lagrange of his country, and finally those creations
of the Quaternion Calculus by which new capabilities have been
bestowed on the human intellect.




LE VERRIER.



The name of Le Verrier is one that goes down to fame on account of
very different discoveries from those which have given renown to
several of the other astronomers whom we have mentioned.  We are
sometimes apt to identify the idea of an astronomer with that of a
man who looks through a telescope at the stars; but the word
astronomer has really much wider significance.  No man who ever
lived has been more entitled to be designated an astronomer than
Le Verrier, and yet it is certain that he never made a telescopic
discovery of any kind.  Indeed, so far as his scientific
achievements have been concerned, he might never have looked
through a telescope at all.

For the full interpretation of the movements of the heavenly
bodies, mathematical knowledge of the most advanced character is
demanded.  The mathematician at the outset calls upon the
astronomer who uses the instruments in the observatory, to
ascertain  for him at various times the exact positions occupied
by the sun, the moon, and the planets.  These observations,
obtained with the greatest care, and purified as far as possible
from the errors by which they may be affected form, as it were,
the raw material on which the mathematician exercises his skill.
It is for him to elicit from the observed places the true laws
which govern the movements of the heavenly bodies.  Here is indeed
a task in which the highest powers of the human
intellect may be worthily employed.

Among those who have laboured with the greatest success in the
interpretation of the observations made with instruments of
precision, Le Verrier holds a highly honoured place.  To him it
has been given to provide a superb illustration of the success
with which the mind of man can penetrate the deep things of
Nature.

The illustrious Frenchman, Urban Jean Joseph Le Verrier, was
born on the 11th March, 1811, at St. Lo, in the department of
Manche.  He received his education in that famous school for
education in the higher branches of science, the Ecole
Polytechnique, and acquired there considerable fame as a
mathematician.  On leaving the school Le Verrier at first purposed
to devote himself to the public service, in the department of
civil engineering; and it is worthy of note that his earliest
scientific work was not in those mathematical researches in which
he was ultimately to become so famous.  His duties in the
engineering department involved practical chemical research in the
laboratory.  In this he seems to have become very expert, and
probably fame as a chemist would have been thus attained, had not
destiny led him into another direction.  As it was, he did engage
in some original chemical research.  His first contributions to
science were the fruits of his laboratory work; one of his papers
was on the combination of phosphorus and hydrogen, and another on
the combination of phosphorus and oxygen.

His mathematical labours at the Ecole Polytechnique had, however,
revealed to Le Verrier that he was endowed with the powers
requisite for dealing with the subtlest instruments
of mathematical analysis.  When he was twenty-eight years old,
his first great astronomical investigation was brought forth.
It will be necessary to enter into some explanation as to the
nature of this, inasmuch as it was the commencement of the life-
work which he was to pursue.

If but a single planet revolved around the sun, then the orbit
of that planet would be an ellipse, and the shape and size, as
well as the position of the ellipse, would never alter.  One
revolution after another would be traced out, exactly in the same
manner, in compliance with the force continuously exerted by the
sun.  Suppose, however, that a second planet be introduced into
the system.  The sun will exert its attraction on this second
planet also, and it will likewise describe an orbit round the
central globe.  We can, however, no longer assert that the orbit
in which either of the planets moves remains exactly an ellipse.
We may, indeed, assume that the mass of the sun is enormously
greater than that of either of the planets.  In this case the
attraction of the sun is a force of such preponderating magnitude,
that the actual path of each planet remains nearly the same as if
the other planet were absent.  But it is impossible for the orbit
of each planet not to be affected in some degree by the attraction
of the other planet.  The general law of nature asserts that every
body in space attracts every other body.  So long as there is only
a single planet, it is the single attraction between the sun and
that planet which is the sole controlling principle of the
movement, and in consequence of it the ellipse is described.  But
when a second planet is introduced, each of the two bodies is not
only subject to the attraction of the sun, but each one of the
planets attracts the other.  It is true that this mutual
attraction is but small, but, nevertheless, it produces some
effect.  It "disturbs," as the astronomer says, the elliptic
orbit which would otherwise have been pursued.  Hence it follows
that in the actual planetary system where there are several
planets disturbing each other, it is not true to say that the
orbits are absolutely elliptic.

At the same time in any single revolution a planet may for most
practical purposes be said to be actually moving in an ellipse.
As, however, time goes on, the ellipse gradually varies.  It
alters its shape, it alters its plane, and it alters its position
in that plane.  If, therefore, we want to study the movements of
the planets, when great intervals of time are concerned, it is
necessary to have the means of learning the nature of the movement
of the orbit in consequence of the disturbances it has
experienced.

We may illustrate the matter by supposing the planet to be
running like a railway engine on a track which has been laid in
a long elliptic path.  We may suppose that while the planet is
coursing along, the shape of the track is gradually altering.
But this alteration may be so slow, that it does not
appreciably affect the movement of the engine in a single
revolution.  We can also suppose that the plane in which the
rails have been laid has a slow oscillation in level, and that
the whole orbit is with more or less uniformity moved slowly
about in the plane.

In short periods of time the changes in the shapes and positions
of the planetary orbits, in consequence of their mutual
attractions, are of no great consequence.  When, however, we bring
thousands of years into consideration, then the displacements of
the planetary orbits attain considerable dimensions, and have, in
fact, produced a profound effect on the system.

It is of the utmost interest to investigate the extent to
which one planet can affect another in virtue of their mutual
attractions.  Such investigations demand the exercise of the
highest mathematical gifts.  But not alone is intellectual
ability necessary for success in such inquiries.  It must be
united with a patient capacity for calculations of an arduous
type, protracted, as they frequently have to be, through many
years of labour.  Le Verrier soon found in these profound
inquiries adequate scope for the exercise of his peculiar
gifts.  His first important astronomical publication contained
an investigation of the changes which the orbits of several of
the planets, including the earth, have undergone in times past,
and which they will undergo in times to come.

As an illustration of these researches, we may take the case of
the planet in which we are, of course, especially
interested, namely, the earth, and we can investigate the
changes which, in the lapse of time, the earth's orbit has
undergone, in consequence of the disturbance to which it has
been subjected by the other planets.  In a century, or even in
a thousand years, there is but little recognisable difference
in the shape of the track pursued by the earth.  Vast periods
of time are required for the development of the large
consequences of planetary perturbation.  Le Verrier has,
however, given us the particulars of what the earth's journey
through space has been at intervals of 20,000 years
back from the present date.  His furthest calculation throws
our glance back to the state of the earth's track 100,000
years ago, while, with a bound forward, he shows us what the
earth's orbit is to be in the future, at successive intervals
of 20,000 years, till a date is reached which is 100,000
years in advance Of A.D. 1800.

The talent which these researches displayed brought Le Verrier
into notice.  At that time the Paris Observatory was presided
over by Arago, a SAVANT who occupies a distinguished position in
French scientific annals.  Arago at once perceived that
Le Verrier was just the man who possessed the qualifications
suitable for undertaking a problem of great importance and
difficulty that had begun to force itself on the attention of
astronomers.  What this great problem was, and how astonishing
was the solution it received, must now be considered.

Ever since Herschel brought himself into fame by his superb
discovery of the great planet Uranus, the movements of this new
addition to the solar system were scrutinized with care and
attention.  The position of Uranus was thus accurately
determined from time to time.  At length, when sufficient
observations of this remote planet had been brought together,
the route which the newly-discovered body pursued through the
heavens was ascertained by those calculations with which
astronomers are familiar.  It happens, however, that Uranus
possesses a superficial resemblance to a star.  Indeed the
resemblance is so often deceptive that long ere its detection as
a planet by Herschel, it had been observed time after time by
skilful astronomers, who little thought that the star-like point
at which they looked was anything but a star.  From these early
observations it was possible to determine the track of Uranus, and
it was found that the great planet takes a period of no less than
eighty-four years to accomplish a circuit.  Calculations were made
of the shape of the orbit in which it revolved before its
discovery by Herschel, and these were compared with the orbit
which observations showed the same body to pursue in those later
years when its planetary character was known.  It could not, of
course, be expected that the orbit should remain unaltered; the
fact that the great planets Jupiter and Saturn revolve in the
vicinity of Uranus must necessarily imply that the orbit of the
latter undergoes considerable changes.  When, however, due
allowance has been made for whatever influence the attraction of
Jupiter and Saturn, and we may add of the earth and all the other
Planets, could possibly produce, the movements of Uranus were
still inexplicable.  It was perfectly obvious that there must be
some other influence at work besides that which could be
attributed to the planets already known.

Astronomers could only recognise one solution of such a
difficulty.  It was impossible to doubt that there must be some
other planet in addition to the bodies at that time known, and
that the perturbations of Uranus hitherto unaccounted for, were
due to the disturbances caused by the action of this unknown
planet.  Arago urged Le Verrier to undertake the great problem of
searching for this body, whose theoretical existence seemed
demonstrated.  But the conditions of the search were such that it
must needs be conducted on principles wholly different from any
search which had ever before been undertaken for a celestial
object.  For this was not a case in which mere survey with a
telescope might be expected to lead to the discovery.

Certain facts might be immediately presumed with reference to
the unknown object.  There could be no doubt that the unknown
disturber of Uranus must be a large body with a mass far exceeding
that of the earth.  It was certain, however, that it must be so
distant that it could only appear from our point of view as a very
small object.  Uranus itself lay beyond the range, or almost
beyond the range, of unassisted vision.  It could be shown that
the planet by which the disturbance was produced revolved in an
orbit which must lie outside that of Uranus.  It seemed thus
certain that the planet could not be a body visible to the unaided
eye.  Indeed, had it been at all conspicuous its planetary
character would doubtless have been detected ages ago.  The
unknown body must therefore be a planet which would have to be
sought for by telescopic aid.

There is, of course, a profound physical difference between a
planet and a star, for the star is a luminous sun, and the planet
is merely a dark body, rendered visible by the sunlight which
falls upon it.  Notwithstanding that a star is a sun thousands of
times larger than the planet and millions of times more remote,
yet it is a singular fact that telescopic planets possess an
illusory resemblance to the stars among which their course happens
to lie.  So far as actual appearance goes, there is indeed only
one criterion by which a planet of this kind can be discriminated
from a star.  If the planet be large enough the telescope will
show that it possesses a disc, and has a visible and measurable
circular outline.  This feature a star does not exhibit.  The
stars are indeed so remote that no matter how large they may be
intrinsically, they only exhibit radiant points of light, which
the utmost powers of the telescope fail to magnify into objects
with an appreciable diameter.  The older and well-known planets,
such as Jupiter and Mars, possess discs, which, though not visible
to the unaided eye, were clearly enough discernible with the
slightest telescopic power.  But a very remote planet like Uranus,
though it possessed a disc large enough to be quickly appreciated
by the consummate observing skill of Herschel, was nevertheless so
stellar in its appearance, that it had been observed no fewer than
seventeen times by experienced astronomers prior to Herschel.  In
each case the planetary nature of the object had been overlooked,
and it had been taken for granted that it was a star.  It
presented no difference which was sufficient to arrest attention.

As the unknown body by which Uranus was disturbed was certainly
much more remote than Uranus, it seemed to be certain that though
it might show a disc perceptible to very close inspection, yet
that the disc must be so minute as not to be detected except with
extreme care.  In other words, it seemed probable that the body
which was to be sought for could not readily be discriminated from
a small star, to which class of object it bore a superficial
resemblance, though, as a matter of fact, there was the
profoundest difference between the two bodies.

There are on the heavens many hundreds of thousands of stars, and
the problem of identifying the planet, if indeed it should lie
among these stars, seemed a very complex matter.  Of course it is
the abundant presence of the stars which causes the difficulty.
If the stars could have been got rid of, a sweep over the heavens
would at once disclose all the planets which are bright enough to
be visible with the telescopic power employed.  It is the
fortuitous resemblance of the planet to the stars which enables it
to escape detection.  To discriminate the planet among stars
everywhere in the sky would be almost impossible.  If, however,
some method could be devised for localizing that precise region in
which the planet's existence might be presumed, then the search
could be undertaken with some prospect of success.

To a certain extent the problem of localizing the region on the
sky in which the planet might be expected admitted of an immediate
limitation.  It is known that all the planets, or perhaps I ought
rather to say, all the great planets, confine their movements to a
certain zone around the heavens.  This zone extends some way on
either side of that line called the ecliptic in which the earth
pursues its journey around the sun.  It was therefore to be
inferred that the new planet need not be sought for outside this
zone.  It is obvious that this consideration at once reduces the
area to be scrutinized to a small fraction of the entire heavens.
But even within the zone thus defined there are many thousands of
stars.  It would seem a hopeless task to detect the new planet
unless some further limitation to its position could be assigned.

It was accordingly suggested to Le Verrier that he should
endeavour to discover in what particular part of the strip of the
celestial sphere which we have indicated the search for the
unknown planet should be instituted.  The materials available to
the mathematician for the solution of this problem were to be
derived solely from the discrepancies between the calculated
places in which Uranus should be found, taking into account the
known causes of disturbance, and the actual places in which
observation had shown the planet to exist.  Here was indeed an
unprecedented problem, and one of extraordinary difficulty.  Le
Verrier, however, faced it, and, to the astonishment of the world,
succeeded in carrying it through to a brilliant solution.
We cannot here attempt to enter into any account of the
mathematical investigations that were necessary.  All that we can
do is to give a general indication of the method which had to be
adopted.

Let us suppose that a planet is revolving outside Uranus, at a
distance which is suggested by the several distances at which the
other planets are dispersed around the sun.  Let us assume that
this outer planet has started on its course, in a prescribed path,
and that it has a certain mass.  It will, of course, disturb the
motion of Uranus, and in consequence of that disturbance Uranus
will follow a path the nature of which can be determined by
calculation.  It will, however, generally be found that the path
so ascertained does not tally with the actual path which
observations have indicated for Uranus.  This demonstrates that
the assumed circumstances of the unknown planet must be in some
respects erroneous, and the astronomer commences afresh with an
amended orbit.  At last after many trials, Le Verrier ascertained
that, by assuming a certain size, shape, and position for the
unknown Planet's orbit, and a certain value for the mass of
the hypothetical body, it would be possible to account for the
observed disturbances of Uranus.  Gradually it became clear to
the perception of this consummate mathematician, not only that
the difficulties in the movements of Uranus could be thus
explained, but that no other explanation need be sought for.  It
accordingly appeared that a planet possessing the mass which
he had assigned, and moving in the orbit which his calculations
had indicated, must indeed exist, though no eye had ever beheld
any such body.  Here was, indeed, an astonishing result.  The
mathematician sitting at his desk, by studying the observations
which had been supplied to him of one planet, is able to
discover the existence of another planet, and even to assign the
very position which it must occupy, ere ever the telescope is
invoked for its discovery.

Thus it was that the calculations of Le Verrier narrowed greatly
the area to be scrutinised in the telescopic search
which was presently to be instituted.  It was already known, as we
have just pointed out, that the planet must lie somewhere on
the ecliptic.  The French mathematician had now further
indicated the spot on the ecliptic at which, according to his
calculations, the planet must actually be found.  And now for an
episode in this history which will be celebrated so long as
science shall endure.  It is nothing less than the telescopic
confirmation of the existence of this new planet, which had
previously been indicated only by mathematical calculation.  Le
Verrier had not himself the instruments necessary for studying the
heavens, nor did he possess the skill of the practical astronomer.
He, therefore, wrote to Dr. Galle, of the Observatory at Berlin,
requesting him to undertake a telescopic search for the new planet
in the vicinity which the mathematical calculation had indicated
for the whereabouts of the planet at that particular time.  Le
Verrier added that he thought the planet ought to admit of being
recognised by the possession of a disc sufficiently definite to
mark the distinction between it and the surrounding stars.

It was the 23rd September, 1846, when the request from Le Verrier
reached the Berlin Observatory, and the night was clear, so that
the memorable search was made on the same evening.  The
investigation was facilitated by the circumstance that a diligent
observer had recently compiled elaborate star maps for certain
tracts of the heavens lying in a sufficiently wide zone on both
sides of the equator.  These maps were as yet only partially
complete, but it happened that Hora. XXI., which included the very
spot which Le Verrier's results referred to, had been just issued.
Dr. Galle had thus before his, eyes a chart of all the stars which
were visible in that part of the heavens at the time when the map
was made.  The advantage of such an assistance to the search could
hardly be over-estimated.  It at once gave the astronomer another
method of recognising the planet besides that afforded by its
possible possession of a disc.  For as the planet was a moving
body, it would not have been in the same place relatively to the
stars at the time when the map was constructed, as it occupied
some years later when the search was being made.  If the body
should be situated in the spot which Le Verrier's calculations
indicated in the autumn of 1846, then it might be regarded
as certain that it would not be found in that same place on a
map drawn some years previously.

The search to be undertaken consisted in a comparison made point
by point between the bodies shown on the map, and those stars in
the sky which Dr. Galle's telescope revealed.  In the course of
this comparison it presently appeared that a star-like object of
the eighth magnitude, which was quite a conspicuous body in the
telescope, was not represented in the map.  This at once attracted
the earnest attention of the astronomer, and raised his hopes that
here was indeed the planet.  Nor were these hopes destined to be
disappointed.  It could not be supposed that a star of the eighth
magnitude would have been overlooked in the preparation of a chart
whereon stars of many lower degrees of brightness were set down.
One other supposition was of course conceivable.  It might have
been that this suspicious object belonged to the class of
variables, for there are many such stars whose brightness
fluctuates, and if it had happened that the map was constructed at
a time when the star in question had but feeble brilliance, it
might have escaped notice.  It is also well known that sometimes
new stars suddenly develop, so that the possibility that what
Dr. Galle saw should have been a variable star or should have been
a totally new star had to be provided against.

Fortunately a test was immediately available to decide whether
the new object was indeed the long sought for planet, or whether
it was a star of one of the two classes to which I have just
referred.  A star remains fixed, but a planet is in motion.
No doubt when a planet lies at the distance at which this new
planet was believed to be situated, its apparent motion would be
so slow that it would not be easy to detect any change in the
course of a single night's observation.  Dr. Galle, however,
addressed himself with much skill to the examination of the place
of the new body.  Even in the course of the night he thought he
detected slight movements, and he awaited with much anxiety the
renewal of his observations on the subsequent evenings.  His
suspicions as to the movement of the body were then amply
confirmed, and the planetary nature of the new object was thus
unmistakably detected.

Great indeed was the admiration of the scientific world
at this superb triumph.  Here was a mighty planet whose very
existence was revealed by the indications afforded by refined
mathematical calculation.  At once the name of Le Verrier, already
known to those conversant with the more profound branches of
astronomy, became everywhere celebrated.  It soon, however,
appeared, that the fame belonging to this great achievement had to
be shared between Le Verrier and another astronomer, J. C. Adams,
of Cambridge.  In our chapter on this great English mathematician
we shall describe the manner in which he was independently led to
the same discovery.

Directly the planetary nature of the newly-discovered body had
been established, the great observatories naturally included this
additional member of the solar system in their working lists, so
that day after day its place was carefully determined.  When
sufficient time had elapsed the shape and position of the orbit of
the body became known.  Of course, it need hardly be said that
observations applied to the planet itself must necessarily provide
a far more accurate method of determining the path which it
follows, than would be possible to Le Verrier, when all he had to
base his calculations upon was the influence of the planet
reflected, so to speak, from Uranus.  It may be noted that the
true elements of the planet, when revealed by direct observation,
showed that there was a considerable discrepancy between the track
of the planet which Le Verrier had announced, and that which the
planet was actually found to pursue.

The name of the newly-discovered body had next to be considered.
As the older members of the system were already known by the same
names as great heathen divinities, it was obvious that some
similar source should be invoked for a suggestion as to a name for
the most recent planet.  The fact that this body was so remote in
the depths of space, not unnaturally suggested the name "Neptune."
Such is accordingly the accepted designation of that mighty globe
which revolves in the track that at present seems to trace out the
frontiers of our system.

Le Verrier attained so much fame by this discovery, that when,
in 1854, Arago's place had to be filled at the head of the great
Paris Observatory, it was universally felt that the discoverer of
Neptune was the suitable man to assume the office which
corresponds in France to that of the Astronomer Royal in England.
It was true that the work of the astronomical mathematician had
hitherto been of an abstract character.  His discoveries had been
made at his desk and not in the observatory, and he had no
practical acquaintance with the use of astronomical instruments.
However, he threw himself into the technical duties of the
observatory with vigour and determination.  He endeavoured to
inspire the officers of the establishment with enthusiasm for that
systematic work which is so necessary for the accomplishment of
useful astronomical research.  It must, however, be admitted that
Le Verrier was not gifted with those natural qualities which would
make him adapted for the successful administration of such an
establishment.  Unfortunately disputes arose between the Director
and his staff.  At last the difficulties of the situation became
so great that the only possible solution was to supersede Le
Verrier, and he was accordingly obliged to retire.  He was
succeeded in his high office by another eminent mathematician, M.
Delaunay, only less distinguished than Le Verrier himself.

Relieved of his official duties, Le Verrier returned to the
mathematics he loved.  In his non-official capacity he continued
to work with the greatest ardour at his researches on the
movements of the planets.  After the death of M. Delaunay, who was
accidentally drowned in 1873, Le Verrier was restored to the
directorship of the observatory, and he continued to hold the
office until his death.

The nature of the researches to which the life of Le Verrier was
subsequently devoted are not such as admit of description in a
general sketch like this, where the language, and still less the
symbols, of mathematics could not be suitably introduced.  It
may, however, be said in general that he was particularly engaged
with the study of the effects produced on the movements of the
planets by their mutual attractions.  The importance of this work
to astronomy consists, to a considerable extent, in the fact that
by such calculations we are enabled to prepare tables by which the
places of the different heavenly bodies can be predicted for
our almanacs.  To this task Le Verrier devoted himself, and the
amount of work he has accomplished would perhaps have been deemed
impossible had it not been actually done.

The superb success which had attended Le Verrier's efforts to
explain the cause of the perturbations of Uranus, naturally led
this wonderful computer to look for a similar explanation of
certain other irregularities in planetary movements.  To a large
extent he succeeded in showing how the movements of each of the
great planets could be satisfactorily accounted for by the
influence of the attractions of the other bodies of the same
class.  One circumstance in connection with these investigations
is sufficiently noteworthy to require a few words here.  Just as
at the opening of his career, Le Verrier had discovered that
Uranus, the outermost planet of the then known system, exhibited
the influence of an unknown external body, so now it appeared to
him that Mercury, the innermost body of our system, was also
subjected to some disturbances, which could not be satisfactorily
accounted for as consequences of any known agents of attraction.
The ellipse in which Mercury revolved was animated by a slow
movement, which caused it to revolve in its plane.  It appeared to
Le Verrier that this displacement was incapable of explanation by
the action of any of the known bodies of our system.  He was,
therefore, induced to try whether he could not determine from the
disturbances of Mercury the existence of some other planet, at
present unknown, which revolved inside the orbit of the known
planet.  Theory seemed to indicate that the observed alteration in
the track of the planet could be thus accounted for.  He naturally
desired to obtain telescopic confirmation which might verify the
existence of such a body in the same way as Dr. Galle verified the
existence of Neptune.  If there were, indeed, an intramercurial
planet, then it must occasionally cross between the earth and
the sun, and might now and then be expected to be witnessed in
the actual act of transit.  So confident did Le Verrier feel in
the existence of such a body that an observation of a dark
object in transit, by Lescarbault on 26th March, 1859, was
believed by the mathematician to be the object which his theory
indicated.  Le Verrier also thought it likely that another transit
of the same object would be seen in March, 1877.  Nothing of the
kind was, however, witnessed, notwithstanding that an assiduous
watch was kept, and the explanation of the change in Mercury's
orbit must, therefore, be regarded as still to be sought for.

Le Verrier naturally received every honour that could be
bestowed upon a man of science.  The latter part of his life was
passed during the most troubled period of modern French history.
He was a supporter of the Imperial Dynasty, and during the
Commune he experienced much anxiety; indeed, at one time grave
fears were entertained for his personal safety.

Early in 1877 his health, which had been gradually failing for
some years, began to give way.  He appeared to rally somewhat in
the summer, but in September he sank rapidly, and died on
Sunday, the 23rd of that month.

His remains were borne to the cemetery on Mont Parnasse in a
public funeral.  Among his pallbearers were leading men of
science, from other countries as well as France, and the
memorial discourses pronounced at the grave expressed their
admiration of his talents and of the greatness of the services he
had rendered to science.




ADAMS.



The illustrious mathematician who, among Englishmen, at all
events, was second only to Newton by his discoveries in
theoretical astronomy, was born on June the 5th, 1819, at the
farmhouse of Lidcot, seven miles from Launceston, in Cornwall.
His early education was imparted under the guidance of the Rev.
John Couch Grylls, a first cousin of his mother.  He appears to
have received an education of the ordinary school type in classics
and mathematics, but his leisure hours were largely devoted to
studying what astronomical books he could find in the library of
the Mechanics' Institute at Devonport.  He was twenty years old
when he entered St. John's College, Cambridge.  His career in the
University was one of almost unparalleled distinction, and it is
recorded that his answering at the Wranglership examination, where
he came out at the head of the list in 1843, was so high that he
received more than double the marks awarded to the Second
Wrangler.

Among the papers found after his death was the following
memorandum, dated July the 3rd, 1841: "Formed a design at the
beginning of this week of investigating, as soon as possible after
taking my degree, the irregularities in the motion of Uranus,
Which are as yet unaccounted for, in order to find whether they
may be attributed to the action of an undiscovered planet beyond
it; and, if possible, thence to determine the elements of its
orbit approximately, which would lead probably to its discovery."

After he had taken his degree, and had thus obtained a little
relaxation from the lines within which his studies had
previously been necessarily confined, Adams devoted himself to
the study of the perturbations of Uranus, in accordance with the
resolve which we have just seen that he formed while he was
still an undergraduate.  As a first attempt he made the
supposition that there might be a planet exterior to Uranus, at
a distance which was double that of Uranus from the sun.  Having
completed his calculation as to the effect which such a
hypothetical planet might exercise upon the movement of Uranus,
he came to the conclusion that it would be quite possible to
account completely for the unexplained difficulties by the
action of an exterior planet, if only that planet were of
adequate size and had its orbit properly placed.  It was
necessary, however, to follow up the problem more precisely,
and accordingly an application was made through Professor
Challis, the Director of the Cambridge Observatory, to the
Astronomer Royal, with the object of obtaining from the
observations made at Greenwich Observatory more accurate values
for the disturbances suffered by Uranus.  Basing his work on the
more precise materials thus available, Adams undertook his
calculations anew, and at last, with his completed results, he
called at Greenwich Observatory on October the 21st, 1845.  He
there left for the Astronomer Royal a paper which contained the
results at which he had arrived for the mass and the mean distance
of the hypothetical planet as well as the other elements necessary
for calculating its exact position.

[PLATE:  JOHN COUCH ADAMS.]

As we have seen in the preceding chapter, Le Verrier had been also
investigating the same problem.  The place which Le Verrier
assigned to the hypothetical disturbing planet for the beginning
of the year 1847, was within a degree of that to which Adams's
computations pointed, and which he had communicated to the
Astronomer Royal seven months before Le Verrier's work appeared.
On July the 29th, 1846, Professor Challis commenced to search for
the unknown object with the Northumberland telescope belonging to
the Cambridge Observatory.  He confined his attention to a limited
region in the heavens, extending around that point to which Mr.
Adams' calculations pointed.  The relative places of all the
stars, or rather star-like objects within this area, were to be
carefully measured.  When the same observations were repeated a
week or two later, then the distances of the several pairs of
stars from each other would be found unaltered, but any planet
which happened to lie among the objects measured would disclose
its existence by the alterations in distance due to its motion in
the interval.  This method of search, though no doubt it must
ultimately have proved successful, was necessarily a very tedious
one, but to Professor Challis, unfortunately, no other method was
available.  Thus it happened that, though Challis commenced his
search at Cambridge two months earlier than Galle at Berlin, yet,
as we have already explained, the possession of accurate star-maps
by Dr. Galle enabled him to discover the planet on the very first
night that he looked for it.

The rival claims of Adams and Le Verrier to the discovery of
Neptune, or rather, we should say, the claims put forward by their
respective champions, for neither of the illustrious investigators
themselves condescended to enter into the personal aspect of the
question, need not be further discussed here.  The main points of
the controversy have been long since settled, and we cannot do
better than quote the words of Sir John Herschel when he
addressed the Royal Astronomical Society in 1848:--

"As genius and destiny have joined the names of Le Verrier and
Adams, I shall by no means put them asunder; nor will they ever be
pronounced apart so long as language shall celebrate the triumphs
Of science in her sublimest walks.  On the great discovery of
Neptune, which may be said to have surpassed, by intelligible and
legitimate means, the wildest pretensions of clairvoyance, it
Would now be quite superfluous for me to dilate.  That glorious
event and the steps which led to it, and the various lights
in which it has been placed, are already familiar to every one
having the least tincture of science.  I will only add that as
there is not, nor henceforth ever can be, the slightest rivalry on
the subject between these two illustrious men--as they have met as
brothers, and as such will, I trust, ever regard each other--we
have made, we could make, no distinction between then, on this
occasion.  May they both long adorn and augment our science, and
add to their own fame already so high and pure, by fresh
achievements."

Adams was elected a Fellow of St. John's College, Cambridge, in
1843; but as he did not take holy orders, his Fellowship, in
accordance with the rules then existing came to an end in 1852.
In the following year he was, however, elected to a Fellowship at
Pembroke College, which he retained until the end of his life.  In
1858 he was appointed Professor of Mathematics in the University
of St. Andrews, but his residence in the north was only a brief
one, for in the same year he was recalled to Cambridge as Lowndean
Professor of Astronomy and Geometry, in succession to Peacock.  In
1861 Challis retired from the Directorship of the Cambridge
Observatory, and Adams was appointed to succeed him.

The discovery of Neptune was a brilliant inauguration of the
astronomical career of Adams.  He worked at, and wrote upon, the
theory of the motions of Biela's comet; he made important
corrections to the theory of Saturn; he investigated the mass of
Uranus, a subject in which he was naturally interested from its
importance in the theory of Neptune; he also improved the methods
of computing the orbits of double stars.  But all these must be
regarded as his minor labours, for next to the discovery of
Neptune the fame of Adams mainly rests on his researches upon
certain movements of the moon, and upon the November meteors.

The periodic time of the moon is the interval required for one
circuit of its orbit.  This interval is known with accuracy at the
present day, and by means of the ancient eclipses the period of
the moon's revolution two thousand years ago can be also
ascertained.  It had been discovered by Halley that the period
which the moon requires to accomplish each of its revolutions
around the earth has been steadily, though no doubt slowly,
diminishing.  The change thus produced is not appreciable when
only small intervals of time are considered, but it becomes
appreciable when we have to deal with intervals of thousands of
years.  The actual effect which is produced by the lunar
acceleration, for so this phenomenon is called, may be thus
estimated.  If we suppose that the moon had, throughout the ages,
revolved around the earth in precisely the same periodic time
which it has at present, and if from this assumption we calculate
back to find where the moon must have been about two thousand
years ago, we obtain a position which the ancient eclipses show to
be different from that in which the moon was actually situated.
The interval between the position in which the moon would have
been found two thousand years ago if there had been no
acceleration, and the position in which the moon was actually
placed, amounts to about a degree, that is to say, to an arc
on the heavens which is twice the moon's apparent diameter.

If no other bodies save the earth and the moon were present in
the universe, it seems certain that the motion of the moon
would never have exhibited this acceleration.  In such a simple
case as that which I have supposed the orbit of the moon would
have remained for ever absolutely unchanged.  It is, however,
well known that the presence of the sun exerts a disturbing
influence upon the movements of the moon.  In each revolution our
satellite is continually drawn aside by the action of the sun from
the place which it would otherwise have occupied.  These
irregularities are known as the perturbations of the lunar
orbit, they have long been studied, and the majority of them
have been satisfactorily accounted for.  It seems, however, to
those who first investigated the question that the phenomenon of
the lunar acceleration could not be explained as a consequence of
solar perturbation, and, as no other agent competent to produce
such effects was recognised by astronomers, the lunar acceleration
presented an unsolved enigma.

At the end of the last century the illustrious French
mathematician Laplace undertook a new investigation of the famous
problem, and was rewarded with a success which for a long time
appeared to be quite complete.  Let us suppose that the moon lies
directly between the earth and the sun, then both earth and moon
are pulled towards the sun by the solar attraction; as, however,
the moon is the nearer of the two bodies to the attracting centre
it is pulled the more energetically, and consequently there is an
increase in the distance between the earth and the moon.
Similarly when the moon happens to lie on the other side of the
earth, so that the earth is interposed directly between the moon
and the sun, the solar attraction exerted upon the earth is more
powerful than the same influence upon the moon.  Consequently in
this case, also, the distance of the moon from the earth is
increased by the solar disturbance.  These instances will
illustrate the general truth, that, as one of the consequences of
the disturbing influence exerted by the sun upon the earth-moon
system, there is an increase in the dimensions of the average
orbit which the moon describes around the earth.  As the time
required by the moon to accomplish a journey round the earth
depends upon its distance from the earth, it follows that among
the influences of the sun upon the moon there must be an
enlargement of the periodic time, from what it would have been
had there been no solar disturbing action.

This was known long before the time of Laplace, but it did not
directly convey any explanation of the lunar acceleration.  It no
doubt amounted to the assertion that the moon's periodic time was
slightly augmented by the disturbance, but it did not give any
grounds for suspecting that there was a continuous change in
progress.  It was, however, apparent that the periodic time was
connected with the solar disturbance, so that, if there were any
alteration in the amount of the sun's disturbing effect, there
must be a corresponding alteration in the moon's periodic time.
Laplace, therefore, perceived that, if he could discover any
continuous change in the ability of the sun for disturbing the
moon, he would then have accounted for a continuous change in
the moon's periodic time, and that thus an explanation of the
long-vexed question of the lunar acceleration might be
forthcoming.

The capability of the sun for disturbing the earth-moon system
is obviously connected with the distance of the earth from the
sun.  If the earth moved in an orbit which underwent no change
whatever, then the efficiency of the sun as a disturbing agent
would not undergo any change of the kind which was sought for.
But if there were any alteration in the shape or size of the
earth's orbit, then that might involve such changes in the
distance between the earth and the sun as would possibly afford
the desired agent for producing the observed lunar effect.  It
is known that the earth revolves in an orbit which, though
nearly circular, is strictly an ellipse.  If the earth were the
only planet revolving around the sun then that ellipse would
remain unaltered from age to age.  The earth is, however, only one
of a large number of planets which circulate around the great
luminary, and are guided and controlled by his supreme attracting
power.  These planets mutually attract each other, and in
consequence of their mutual attractions the orbits of the planets
are disturbed from the simple elliptic form which they would
otherwise possess.  The movement of the earth, for instance, is
not, strictly speaking, performed in an elliptical orbit.  We may,
however, regard it as revolving in an ellipse provided we admit
that the ellipse is itself in slow motion.

It is a remarkable characteristic of the disturbing effects of
the planets that the ellipse in which the earth is at any moment
moving always retains the same length; that is to say, its longest
diameter is invariable.  In all other respects the ellipse is
continually changing.  It alters its position, it changes its
plane, and, most important of all, it changes its eccentricity.
Thus, from age to age the shape of the track which the earth
describes may at one time be growing more nearly a circle, or at
another time may be departing more widely from a circle.  These
alterations are very small in amount, and they take place with
extreme slowness, but they are in incessant progress, and their
amount admits of being accurately calculated.  At the present
time, and for thousands of years past, as well as for thousands of
years to come, the eccentricity of the earth's orbit is
diminishing, and consequently the orbit described by the earth
each year is becoming more nearly circular.  We must, however,
remember that under all circumstances the length of the longest
axis of the ellipse is unaltered, and consequently the size of the
track which the earth describes around the sun is gradually
increasing.  In other words, it may be said that during the
present ages the average distance between the earth and the sun is
waxing greater in consequence of the perturbations which the earth
experiences from the attraction of the other planets.  We have,
however, already seen that the efficiency of the solar attraction
for disturbing the moon's movement depends on the distance between
the earth and the sun.  As therefore the average distance between
the earth and the sun is increasing, at all events during the
thousands of years over which our observations extend, it follows
that the ability of the sun for disturbing the moon must be
gradually diminishing.

[PLATE:  CAMBRIDGE OBSERVATORY.]

It has been pointed out that, in consequence of the solar
disturbance, the orbit of the moon must be some what enlarged.
As it now appears that the solar disturbance is on the whole
declining, it follows that the orbit of the moon, which has to
be adjusted relatively to the average value of the solar
disturbance, must also be gradually declining.  In other words,
the moon must be approaching nearer to the earth in consequence
of the alterations in the eccentricity of the earth's orbit
produced by the attraction of the other planets.  It is true that
the change in the moon's position thus arising is an extremely
small one, and the consequent effect in accelerating the moon's
motion is but very slight.  It is in fact almost imperceptible,
except when great periods of time are involved.  Laplace undertook
a calculation on this subject.  He knew what the efficiency of the
planets in altering the dimensions of the earth's orbit amounted
to; from this he was able to determine the changes that would be
propagated into the motion of the moon.  Thus he ascertained, or
at all events thought he had ascertained, that the acceleration of
the moon's motion, as it had been inferred from the observations
of the ancient eclipses which have been handed down to us, could
be completely accounted for as a consequence of planetary
perturbation.  This was regarded as a great scientific triumph.
Our belief in the universality of the law of gravitation would, in
fact, have been seriously challenged unless some explanation of
the lunar acceleration had been forthcoming.  For about fifty
years no one questioned the truth of Laplace's investigation.
When a mathematician of his eminence had rendered an explanation
of the remarkable facts of observation which seemed so complete,
it is not surprising that there should have been but little
temptation to doubt it.  On undertaking a new calculation of the
same question, Professor Adams found that Laplace had not pursued
this approximation sufficiently far, and that consequently there
was a considerable error in the result of his analysis.  Adams,
it must be observed, did not impugn the value of the lunar
acceleration which Halley had deduced from the observations,
but what he did show was, that the calculation by which Laplace
thought he had provided an explanation of this acceleration was
erroneous.  Adams, in fact, proved that the planetary influence
which Laplace had detected only possessed about half the
efficiency which the great French mathematician had attributed to
it.  There were not wanting illustrious mathematicians who came
forward to defend the calculations of Laplace.  They computed the
question anew and arrived at results practically coincident with
those he had given.  On the other hand certain distinguished
mathematicians at home and abroad verified the results of
Adams.  The issue was merely a mathematical one.  It had only one
correct solution.  Gradually it appeared that those who opposed
Adams presented a number of different solutions, all of them
discordant with his, and, usually, discordant with each other.
Adams showed distinctly where each of these investigators had
fallen into error, and at last it became universally admitted that
the Cambridge Professor had corrected Laplace in a very
fundamental point of astronomical theory.

Though it was desirable to have learned the truth, yet the breach
between observation and calculation which Laplace was believed to
have closed thus became reopened.  Laplace's investigation, had it
been correct, would have exactly explained the observed facts.  It
was, however, now shown that his solution was not correct, and
that the lunar acceleration, when strictly calculated as a
consequence of solar perturbations, only produced about half the
effect which was wanted to explain the ancient eclipses
completely.  It now seems certain that there is no means of
accounting for the lunar acceleration as a direct consequence of
the laws of gravitation, if we suppose, as we have been in the
habit of supposing, that the members of the solar system concerned
may be regarded as rigid particles.  It has, however, been
suggested that another explanation of a very interesting kind may
be forthcoming, and this we must endeavour to set forth.

It will be remembered that we have to explain why the period of
revolution of the moon is now shorter than it used to be.  If we
imagine the length of the period to be expressed in terms of days
and fractions of a day, that is to say, in terms of the rotations
of the earth around its axis, then the difficulty encountered is,
that the moon now requires for each of its revolutions around the
earth rather a smaller number of rotations of the earth around its
axis than used formerly to be the case.  Of course this may be
explained by the fact that the moon is now moving more swiftly
than of yore, but it is obvious that an explanation of quite a
different kind might be conceivable.  The moon may be moving just
at the same pace as ever, but the length of the day may be
increasing.  If the length of the day is increasing, then, of
course, a smaller number of days will be required for the moon to
perform each revolution even though the moon's period was itself
really unchanged.  It would, therefore, seem as if the phenomenon
known as the lunar acceleration is the result of the two causes.
The first of these is that discovered by Laplace, though its value
was overestimated by him, in which the perturbations of the earth
by the planets indirectly affect the motion of the moon.  The
remaining part of the acceleration of our satellite is apparent
rather than real, it is not that the moon is moving more quickly,
but that our time-piece, the earth, is revolving more slowly, and
is thus actually losing time.  It is interesting to note that we
can detect a physical explanation for the apparent checking of the
earth's motion which is thus manifested.  The tides which ebb and
flow on the earth exert a brake-like action on the revolving
globe, and there can be no doubt that they are gradually reducing
its speed, and thus lengthening the day.  It has accordingly been
suggested that it is this action of the tides which produces the
supplementary effect necessary to complete the physical
explanation of the lunar acceleration, though it would perhaps be
a little premature to assert that this has been fully
demonstrated.

The third of Professor Adams' most notable achievements was
connected with the great shower of November meteors which
astonished the world in 1866.  This splendid display concentrated
the attention of astronomers on the theory of the movements of the
little objects by which the display was produced.  For the
definite discovery of the track in which these bodies revolve, we
are indebted to the labours of Professor Adams, who, by a
brilliant piece of mathematical work, completed the edifice whose
foundations had been laid by Professor Newton, of Yale, and other
astronomers.

Meteors revolve around the sun in a vast swarm, every individual
member of which pursues an orbit in accordance with the well-known
laws of Kepler.  In order to understand the movements of these
objects, to account satisfactorily for their periodic recurrence,
and to predict the times of their appearance, it became necessary
to learn the size and the shape of the track which the swarm
followed, as well as the position which it occupied.  Certain
features of the track could no doubt be readily assigned.  The
fact that the shower recurs on one particular day of the year,
viz., November 13th, defines one point through which the orbit
must pass.  The position on the heavens of the radiant point from
which the meteors appear to diverge, gives another element in the
track.  The sun must of course be situated at the focus, so that
only one further piece of information, namely, the periodic time,
will be necessary to complete our knowledge of the movements of
the system.  Professor H. Newton, of Yale, had shown that the
choice of possible orbits for the meteoric swarm is limited to
five.  There is, first, the great ellipse in which we now know the
meteors revolve once every thirty three and one quarter years.
There is next an orbit of a nearly circular kind in which the
periodic time would be a little more than a year.  There is a
similar track in which the periodic time would be a few days short
of a year, while two other smaller orbits would also be
conceivable.  Professor Newton had pointed out a test by which it
would be possible to select the true orbit, which we know must be
one or other of these five.  The mathematical difficulties which
attended the application of this test were no doubt great, but
they did not baffle Professor Adams.

There is a continuous advance in the date of this meteoric shower.
The meteors now cross our track at the point occupied by the
earth on November 13th, but this point is gradually altering.
The only influence known to us which could account for the
continuous change in the plane of the meteor's orbit arises from
the attraction of the various planets.  The problem to be solved
may therefore be attacked in this manner.  A specified amount of
change in the plane of the orbit of the meteors is known to
arise, and the changes which ought to result from the attraction
of the planets can be computed for each of the five possible
orbits, in one of which it is certain that the meteors must
revolve.  Professor Adams undertook the work.  Its difficulty
principally arises from the high eccentricity of the largest of
the orbits, which renders the more ordinary methods of
calculation inapplicable.  After some months of arduous labour the
work was completed, and in April, 1867, Adams announced his
solution of the problem.  He showed that if the meteors revolved
in the largest of the five orbits, with the periodic time of
thirty three and one quarter years, the perturbations of Jupiter
would account for a change to the extent of twenty minutes of arc
in the point in which the orbit crosses the earth's track.  The
attraction of Saturn would augment this by seven minutes, and
Uranus would add one minute more, while the influence of the Earth
and of the other planets would be inappreciable.  The
accumulated effect is thus twenty-eight minutes, which is
practically coincident with the observed value as determined by
Professor Newton from an examination of all the showers of which
there is any historical record.  Having thus showed that the great
orbit was a possible path for the meteors, Adams next proved that
no one of the other four orbits would be disturbed in the same
manner.  Indeed, it appeared that not half the observed amount of
change could arise in any orbit except in that one with the long
period.  Thus was brought to completion the interesting research
which demonstrated the true relation of the meteor swarm to the
solar system.

Besides those memorable scientific labours with which his
attention was so largely engaged, Professor Adams found time for
much other study.  He occasionally allowed himself to undertake as
a relaxation some pieces of numerical calculation, so tremendously
long that we can only look on them with astonishment.  He has
calculated certain important mathematical constants accurately to
more than two hundred places of decimals.  He was a diligent
reader of works on history, geology, and botany, and his arduous
labours were often beguiled by novels, of which, like many other
great men, he was very fond.  He had also the taste of a
collector, and he brought together about eight hundred volumes of
early printed works, many of considerable rarity and value.  As to
his personal character, I may quote the words of Dr. Glaisher when
he says, "Strangers who first met him were invariably struck by
his simple and unaffected manner.  He was a delightful companion,
always cheerful and genial, showing in society but few traces of
his really shy and retiring disposition.  His nature was
sympathetic and generous, and in few men have the moral and
intellectual qualities been more perfectly balanced.

In 1863 he married the daughter of Haliday Bruce, Esq., of
Dublin and up to the close of his life he lived at the Cambridge
Observatory, pursuing his mathematical work and enjoying the
society of his friends.

He died, after a long illness, on 21st January, 1892, and was
interred in St. Giles's Cemetery, on the Huntingdon Road,
Cambridge.





End of The Project Gutenberg Etext of Great Astronomers, by R. S. Ball