Great Astronomers
by
R. S. Ball
Part 3 out of 5
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 somewhat 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
Back to Full Books
|