workshop. A cabinet-maker making a tube and stands of all
descriptions in a handsomely furnished drawing-room; Alex. putting
up a huge turning-machine (which he had brought in the autumn from
Bristol, where he used to spend the summer) in a bed-room, for
turning patterns, grinding glasses, and turning eye-pieces, &c. At
the same time music durst not lie entirely dormant during the
summer, and my brother had frequent rehearsals at home."
Finally, in 1774, at the age of thirty-six, he had made himself a
5-1/2-foot telescope, and began to view the heavens. So attached was he
to the instrument that he would run from the concert-room between the
parts, and take a look at the stars.
He soon began another telescope, and then another. He must have made
some dozen different telescopes, always trying to get them bigger and
bigger; at last he got a 7-foot and then a 10-foot instrument, and began
a systematic survey of the heavens; he also began to communicate his
results to the Royal Society.
He now took a larger house, with more room for workshops, and a grass
plot for a 20-foot telescope, and still he went on grinding
mirrors--literally hundreds of them.
I read another extract from the diary of his sister, who waited on him
and obeyed him like a spaniel:--
"My time was taken up with copying music and practising, besides
attendance on my brother when polishing, since by way of keeping
him alive I was constantly obliged to feed him by putting the
victuals by bits into his mouth. This was once the case when, in
order to finish a 7-foot mirror, he had not taken his hands from it
for sixteen hours together. In general he was never unemployed at
meals, but was always at those times contriving or making drawings
of whatever came in his mind. Generally I was obliged to read to
him whilst he was at the turning-lathe, or polishing mirrors--_Don
Quixote_, _Arabian Nights' Entertainments_, the novels of Sterne,
Fielding, &c.; serving tea and supper without interrupting the work
with which he was engaged, ... and sometimes lending a hand. I
became, in time, as useful a member of the workshop as a boy might
be to his master in the first year of his apprenticeship.... But as
I was to take a part the next year in the oratorios, I had, for a
whole twelvemonth, two lessons per week from Miss Fleming, the
celebrated dancing-mistress, to drill me for a gentlewoman (God
knows how she succeeded). So we lived on without interruption. My
brother Alex. was absent from Bath for some months every summer,
but when at home he took much pleasure in executing some turning or
clockmaker's work for his brother."
The music, and the astronomy, and the making of telescopes, all went on
together, each at high pressure, and enough done in each to satisfy any
ordinary activity. But the Herschels knew no rest. Grinding mirrors by
day, concerts and oratorios in the evening, star-gazing at night. It is
strange his health could stand it.
The star-gazing, moreover, was no _dilettante_ work; it was based on a
serious system--a well thought out plan of observation. It was nothing
less than this--to pass the whole heavens steadily and in order through
the telescope, noting and describing and recording every object that
should be visible, whether previously known or unknown. The operation is
called sweeping; but it is not a rapid passage from one object to
another, as the term might suggest; it is a most tedious business, and
consists in following with the telescope a certain field of view for
some minutes, so as to be sure that nothing is missed, then shifting it
to the next overlapping field, and watching again. And whatever object
appears must be scrutinized anxiously to see what there is peculiar
about it. If a star, it may be double, or it may be coloured, or it may
be nebulous; or again it may be variable, and so its brightness must be
estimated in order to compare with a subsequent observation.
Four distinct times in his life did Herschel thus pass the whole visible
heavens under review; and each survey occupied him several years. He
discovered double stars, variable stars, nebulae, and comets; and Mr.
William Herschel, of Bath, the amateur astronomer, was gradually
emerging from his obscurity, and becoming a known man.
Tuesday, the 13th of March, 1781, is a date memorable in the annals of
astronomy. "On this night," he writes to the Royal Society, "in
examining the small stars near _[eta]_ Geminorum, I perceived one
visibly larger than the rest. Struck with its uncommon appearance, I
compared it to _[eta]_ Geminorum and another star, and finding it so
much larger than either, I suspected it to be a comet."
The "comet" was immediately observed by professional astronomers, and
its orbit was computed by some of them. It was thus found to move in
nearly a circle instead of an elongated ellipse, and to be nearly twice
as far from the sun as Saturn. It was no comet, it was a new planet;
more than 100 times as big as the earth, and nearly twice as far away as
Saturn. It was presently christened "Uranus."
This was a most striking discovery, and the news sped over Europe. To
understand the interest it excited we must remember that such a
discovery was unique. Since the most ancient times of which men had any
knowledge, the planets Mercury, Venus, Mars, Jupiter, Saturn, had been
known, and there had been no addition to their number. Galileo and
others had discovered satellites indeed, but a new primary planet was an
entire and utterly unsuspected novelty.
One of the most immediate consequences of the event was the discovery of
Herschel himself. The Royal Society made him a Fellow the same year. The
University of Oxford dubbed him a doctor; and the King sent for him to
bring his telescope and show it at Court. So to London and Windsor he
went, taking with him his best telescope. Maskelyne, the then
Astronomer-Royal, compared it with the National one at Greenwich, and
found Herschel's home-made instrument far the better of the two. He had
a stand made after Herschel's pattern, but was so disgusted with his own
instrument now that he scarcely thought it worthy of the stand when it
was made. At Windsor, George III. was very civil, and Mr. Herschel was
in great request to show the ladies of the Court Saturn and other
objects of interest. Mr. Herschel exhibited a piece of worldly wisdom
under these circumstances, that recalls faintly the behaviour of Tycho
Brahe under similar circumstances. The evening when the exhibition was
to take place threatened to become cloudy and wet, so Herschel rigged up
an artificial Saturn, constructed of card and tissue paper, with a lamp
behind it, in the distant wall of a garden; and, when the time came, his
new titled friends were regaled with a view of this imitation Saturn
through the telescope--the real one not being visible. They went away
much pleased.
He stayed hovering between Windsor and Greenwich, and uncertain what was
to be the outcome of all this regal patronizing. He writes to his sister
that he would much rather be back grinding mirrors at Bath. And she
writes begging him to come, for his musical pupils were getting
impatient. They had to get the better of their impatience, however, for
the King ultimately appointed him astronomer or rather telescope-maker
to himself, and so Caroline and the whole household were sent for, and
established in a small house at Datchet.
From being a star-gazing musician, Herschel thus became a practical
astronomer. Henceforth he lived in his observatory; only on wet and
moonlight nights could he be torn away from it. The day-time he devoted
to making his long-contemplated 20-foot telescope.
Not yet, however, were all their difficulties removed. The house at
Datchet was a tumble-down barn of a place, chosen rather as a workshop
and observatory than as a dwelling-house. And the salary allowed him by
George III. was scarcely a princely one. It was, as a matter of fact,
L200 a year. The idea was that he would earn his living by making
telescopes, and so indeed he did. He made altogether some hundreds.
Among others, four for the King. But this eternal making of telescopes
for other people to use or play with was a weariness to the flesh. What
he wanted was to observe, observe, observe.
Sir William Watson, an old friend of his, and of some influence at
Court, expressed his mind pretty plainly concerning Herschel's position;
and as soon as the King got to understand that there was anything the
matter, he immediately offered L2,000 for a gigantic telescope to be
made for Herschel's own use. Nothing better did he want in life. The
whole army of carpenters and craftsmen resident in Datchet were pressed
into the service. Furnaces for the speculum metal were built, stands
erected, and the 40-foot telescope fairly begun. It cost L4,000 before
it was finished, but the King paid the whole.
[Illustration: FIG. 83.--Herschel's 40-foot telescope.]
With it he discovered two more satellites to Saturn (five hitherto had
been known), and two moons to his own planet Uranus. These two are now
known as Oberon and Titania. They were not seen again till some forty
years after, when his son, Sir John Herschel, reobserved them. And in
1847, Mr. Lassell, at his house, "Starfield," near Liverpool, discovered
two more, called Ariel and Umbriel, making the number four, as now
known. Mr. Lassell also discovered, with a telescope of his own making,
an eighth satellite of Saturn--Hyperion--and a satellite to Neptune.
A letter from a foreign astronomer about this period describes Herschel
and his sister's method of work:--
"I spent the night of the 6th of January at Herschel's, in Datchet,
near Windsor, and had the good luck to hit on a fine evening. He
has his 20-foot Newtonian telescope in the open air, and mounted in
his garden very simply and conveniently. It is moved by an
assistant, who stands below it.... Near the instrument is a clock
regulated to sidereal time.... In the room near it sits Herschel's
sister, and she has Flamsteed's atlas open before her. As he gives
her the word, she writes down the declination and right ascension,
and the other circumstances of the observation. In this way
Herschel examines the whole sky without omitting the least part. He
commonly observes with a magnifying power of one hundred and fifty,
and is sure that after four or five years he will have passed in
review every object above our horizon. He showed me the book in
which his observations up to this time are written, and I am
astonished at the great number of them. Each sweep covers 2 deg. 15' in
declination, and he lets each star pass at least three times
through the field of his telescope, so that it is impossible that
anything can escape him. He has already found about 900 double
stars, and almost as many nebulae. I went to bed about one o'clock,
and up to that time he had found that night four or five new
nebulae. The thermometer in the garden stood at 13 deg. Fahrenheit; but,
in spite of this, Herschel observes the whole night through, except
that he stops every three or four hours and goes into the room for
a few moments. For some years Herschel has observed the heavens
every hour when the weather is clear, and this always in the open
air, because he says that the telescope only performs well when it
is at the same temperature as the air. He protects himself against
the weather by putting on more clothing. He has an excellent
constitution, and thinks about nothing else in the world but the
celestial bodies. He has promised me in the most cordial way,
entirely in the service of astronomy, and without thinking of his
own interest, to see to the telescopes I have ordered for European
observatories, and he will himself attend to the preparation of the
mirrors."
[Illustration: _Painted by Abbott._
_Engraved by Ryder._
FIG. 84.--WILLIAM HERSCHEL.
_From an Original Picture in the Possession of_ WM. WATSON, M.D.,
F.R.S.]
In 1783, Herschel married an estimable lady who sympathized with his
pursuits. She was the only daughter of a City magnate, so his pecuniary
difficulties, such as they were (they were never very troublesome to
him), came to an end. They moved now into a more commodious house at
Slough. Their one son, afterwards the famous Sir John Herschel, was
born some nine years later. But the marriage was rather a blow to his
devoted sister: henceforth she lived in lodgings, and went over at
night-time to help him observe. For it must be remarked that this family
literally turned night into day. Whatever sleep they got was in the
day-time. Every fine night without exception was spent in observing: and
the quite incredible fierceness of the pursuit is illustrated, as
strongly as it can be, by the following sentence out of Caroline's
diary, at the time of the move from Datchet to Slough: "The last night
at Datchet was spent in sweeping till daylight, and by the next evening
the telescope stood ready for observation at Slough."
Caroline was now often allowed to sweep with a small telescope on her
own account. In this way she picked up a good many nebulae in the course
of her life, and eight comets, four of which were quite new, and one of
which, known since as Encke's comet, has become very famous.
The work they got through between them is something astonishing. He made
with his own hands 430 parabolic mirrors for reflecting telescopes,
besides a great number of complete instruments. He was forty-two when he
began contributing to the Royal Society; yet before he died he had sent
them sixty-nine long and elaborate treatises. One of these memoirs is a
catalogue of 1000 nebulae. Fifteen years after he sends in another 1000;
and some years later another 500. He also discovered 806 double stars,
which he proved were really corrected from the fact that they revolved
round each other (p. 309). He lived to see some of them perform half a
revolution. For him the stars were not fixed: they moved slowly among
themselves. He detected their proper motions. He passed the whole
northern firmament in review four distinct times; counted the stars in
3,400 gauge-fields, and estimated the brightness of hundreds of stars.
He also measured as accurately as he could their proper motions,
devising for this purpose the method which still to this day remains in
use.
And what is the outcome of it all? It is not Uranus, nor the satellites,
nor even the double stars and the nebulae considered as mere objects: it
is the beginning of a science of the stars.
[Illustration: FIG. 85.--CAROLINE HERSCHEL.
_From a Drawing from Life, by_ GEORGE MUeLLER, 1847.]
Hitherto the stars had only been observed for nautical and practical
purposes. Their times of rising and southing and setting had been noted;
they had been treated as a clock or piece of dead mechanism, and as
fixed points of reference. All the energies of astronomers had gone out
towards the solar system. It was the planets that had been observed.
Tycho had observed and tabulated their positions. Kepler had found out
some laws of their motion. Galileo had discovered their peculiarities
and attendants. Newton and Laplace had perceived every detail of their
laws.
But for the stars--the old Ptolemaic system might still have been true.
They might still be mere dots in a vast crystalline sphere, all set at
about one distance, and subservient to the uses of the earth.
Herschel changed all this. Instead of sameness, he found variety;
instead of uniformity of distance, limitless and utterly limitless
fields and boundless distances; instead of rest and quiescence, motion
and activity; instead of stagnation, life.
[Illustration: FIG. 86.--The double-double star [epsilon] Lyrae as seen
under three different powers.]
Yes, that is what Herschel discovered--the life and activity of the
whole visible universe. No longer was our little solar system to be the
one object of regard, no longer were its phenomena to be alone
interesting to man. With Herschel every star was a solar system. And
more than that: he found suns revolving round suns, at distances such as
the mind reels at, still obeying the same law of gravitation as pulls an
apple from a tree. He tried hard to estimate the distance of the stars
from the earth, but there he failed: it was too hopeless a problem. It
was solved some time after his death by Bessel, and the distances of
many stars are now known but these distances are awful and unspeakable.
Our distance from the sun shrinks up into a mere speck--the whole solar
system into a mere unit of measurement, to be repeated hundreds of
thousands of times before we reach the stars.
Yet their motion is visible--yes, to very accurate measurement quite
plain. One star, known as 61 Cygni, was then and is now rushing along at
the rate of 100 miles every second. Not that you must imagine that this
makes any obvious and apparent change in its position. No, for all
ordinary and practical purposes they are still fixed stars; thousands of
years will show us no obvious change; "Adam" saw precisely the same
constellations as we do: it is only by refined micrometric measurement
with high magnifying power that their flight can be detected.
But the sun is one of the stars--not by any means a specially large or
bright one; Sirius we now know to be twenty times as big as the sun. The
sun is one of the stars: then is it at rest? Herschel asked this
question and endeavoured to answer it. He succeeded in the most
astonishing manner. It is, perhaps, his most remarkable discovery, and
savours of intuition. This is how it happened. With imperfect optical
means and his own eyesight to guide him, he considered and pondered over
the proper motion of the stars as he had observed it, till he discovered
a kind of uniformity running through it all. Mixed up with
irregularities and individualities, he found that in a certain part of
the heavens the stars were on the whole opening out--separating slowly
from each other; on the opposite side of the heavens they were on the
average closing up--getting slightly nearer to each other; while in
directions at right angles to this they were fairly preserving their
customary distances asunder.
Now, what is the moral to be drawn from such uniformity of behaviour
among unconnected bodies? Surely that this part of their motion is only
apparent--that it is we who are moving. Travelling over a prairie
bounded by a belt of trees, we should see the trees in our line of
advance opening out, and those behind closing up; we should see in fact
the same kind of apparent motion as Herschel was able to detect among
the stars: the opening out being most marked near the constellation
Hercules. The conclusion is obvious: the sun, with all its planets, must
be steadily moving towards a point in the constellation Hercules. The
most accurate modern research has been hardly able to improve upon this
statement of Herschel's. Possibly the solar system may ultimately be
found to revolve round some other body, but what that is no one knows.
All one can tell is the present direction of the majestic motion: since
it was discovered it has continued unchanged, and will probably so
continue for thousands of years.
[Illustration: FIG. 87.--Old drawing of the cluster in Hercules.]
And, finally, concerning the nebulae. These mysterious objects exercised
a strong fascination for Herschel, and many are the speculations he
indulges in concerning them. At one time he regards them all as clusters
of stars, and the Milky Way as our cluster; the others he regards as
other universes almost infinitely distant; and he proceeds to gauge and
estimate the shape of our own universe or galaxy of suns, the Milky Way.
Later on, however, he pictures to himself the nebulae as nascent suns:
solar systems before they are formed. Some he thinks have begun to
aggregate, while some are still glowing gas.
[Illustration: FIG. 88.--Old drawing of the Andromeda nebula.]
He likens the heavens to a garden in which there are plants growing in
all manner of different stages: some shooting, some in leaf, some in
flower, some bearing seed, some decaying; and thus at one inspection we
have before us the whole life-history of the plant.
Just so he thinks the heavens contain worlds, some old, some dead, some
young and vigorous, and some in the act of being formed. The nebulae are
these latter, and the nebulous stars are a further stage in the
condensation towards a sun.
And thus, by simple observation, he is led towards something very like
the nebular hypothesis of Laplace; and his position, whether it be true
or false, is substantially the same as is held to-day.
[Illustration: FIG. 89.--The great nebula in Orion.]
We _know_ now that many of the nebulae consist of innumerable isolated
particles and may be spoken of as gas. We know that some are in a state
of whirling motion. We know also that such gas left to itself will
slowly as it cools condense and shrink, so as to form a central solid
nucleus; and also, if it were in whirling motion, that it would send off
rings from itself, and that these rings could break up into planets. In
two familiar cases the ring has not yet thus aggregated into planet or
satellite--the zone of asteroids, and Saturn's ring.
The whole of this could not have been asserted in Herschel's time: for
further information the world had to wait.
These are the problems of modern astronomy--these and many others, which
are the growth of this century, aye, and the growth of the last thirty
or forty, and indeed of the last ten years. Even as I write, new and
very confirmatory discoveries are being announced. The Milky Way _does_
seem to have some affinity with our sun. And the chief stars of the
constellation of Orion constitute another family, and are enveloped in
the great nebula, now by photography perceived to be far greater than
had ever been imagined.
What is to be the outcome of it all I know not; but sure I am of this,
that the largest views of the universe that we are able to frame, and
the grandest manner of its construction that we can conceive, are
certain to pale and shrink and become inadequate when confronted with
the truth.
NOTES TO LECTURE XIII
BODE'S LAW.--Write down the series 0, 3, 6, 12, 24, 48, &c.; add 4 to
each, and divide by 10; you get the series:
.4 .7 1.0 1.6 2.8 5.2 10.0 19.6 38.8
Mercury Venus Earth Mars ---- Jupiter Saturn Uranus ----
numbers which very fairly represent the distances of the then known
planets from the sun in the order specified.
Ceres was discovered on the 1st of January, 1801, by Piazzi; Pallas in
March, 1802, by Olbers; Juno in 1804, by Harding; and Vesta in 1807, by
Olbers. No more asteroids were discovered till 1845, but there are now
several hundreds known. Their diameters range from 500 to 20 miles.
Neptune was discovered from the perturbations of Uranus by sheer
calculation, carried on simultaneously and independently by Leverrier in
Paris, and Adams in Cambridge. It was first knowingly seen by Galle, of
Berlin, on the 23rd of September, 1846.
LECTURE XIII
THE DISCOVERY OF THE ASTEROIDS
Up to the time of Herschel, astronomical interest centred on the solar
system. Since that time it has been divided, and a great part of our
attention has been given to the more distant celestial bodies. The solar
system has by no means lost its interest--it has indeed gained in
interest continually, as we gain in knowledge concerning it; but in
order to follow the course of science it will be necessary for us to
oscillate to and fro, sometimes attending to the solar system--the
planets and their satellites--sometimes extending our vision to the
enormously more distant stellar spaces.
Those who have read the third lecture in Part I. will remember the
speculation in which Kepler indulged respecting the arrangements of the
planets, the order in which they succeeded one another in space, and the
law of their respective distances from the sun; and his fanciful guess
about the five regular solids inscribed and circumscribed about their
orbits.
The rude coincidences were, however, accidental, and he failed to
discover any true law. No thoroughly satisfactory law is known at the
present day. And yet, if the nebular hypothesis or anything like it be
true, there must be some law to be discovered hereafter, though it may
be a very complicated one.
An empirical relation is, however, known: it was suggested by Tatius,
and published by Bode, of Berlin, in 1772. It is always known as Bode's
law.