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.