It was in the year 1774 that Herschel first had a view of the heavens
through the telescope he had himself constructed. During the early part
of his career he does not seem to have made any important discoveries.
He was gradually preparing himself for the great achievement by which
his name became famous.
It was on the 13th of March, 1781, that the organist of the Octagon
Chapel at Bath turned his telescope on the constellation of the Twins,
and began to look at one star after another. You must know that a star
merely looks like a little point in a telescope; even the greatest
instrument will only make a star look brighter, and will never show
it with a perceptible disk. In looking over the stars that night,
Herschel’s attention was arrested by one object that did look larger
when magnified, and therefore was not a star. The only other objects
which would behave in this way were the planets, or possibly a comet.
Indeed, at first Herschel imagined that what he saw must be a comet. It
could hardly have occurred to him that he was to have such good fortune
as to discover a new planet. The five great planets had been known from
all antiquity. Was it reasonable to suppose that there could be yet
another that had never been perceived? Fortunately, there was a test
available. A star remains in the same place from night to night and
from year to year; while a planet, as we have already had occasion to
mention, is a body which is wandering about. The movements of a planet
are, however, not at all like those of a comet. To decide on the nature
of Herschel’s newly discovered body, it was sufficient to observe the
character of its motion. A few nights sufficed to do this. The position
of the body was carefully marked relatively to the neighboring stars,
and it was soon shown that it was a planet.
Here, then, a great discovery was made. A new planet, now called
Uranus, was added to our system. It would be nothing to discover a
new star. You might as well talk of discovering a new grain of sand
on the seashore. The stars are in untold myriads. They are so far off
that they have no relation whatever to our system, which is presided
over by the sun. But by the detection of a new planet, revolving far
outside Saturn, Herschel showed that a new and most interesting member
had to be added to the five old planets which have been known from the
earliest records of history.
It may well be imagined that a discovery so startling as this excited
astonishment throughout the scientific world. “Who is this Bath
organist?” everybody asked. Accounts of him and his discoveries
appeared in the papers. His fellow-citizens were not so familiar with
the name as we are, happily, now; and the spelling of the unusual name
showed many varieties. When George III. heard of Herschel’s great
achievement, he directed the astronomer to be summoned to Windsor,
that the King might receive an account of the wonderful discovery from
the lips of the discoverer himself. Herschel of course obeyed, and he
brought with him his famous telescope, and also a map of the whole
solar system, to show to the King. No doubt he thought that his Majesty
had probably not paid much attention to astronomy. Herschel was,
therefore, prepared to explain to the King what it would be necessary
for him to know before he could fully appreciate the magnitude of the
discovery.
You will remember that Herschel while still a boy had deserted from the
army, many years previously. It appears that the King had learned this
fact in some way, so that when Herschel was ushered into his presence
his Majesty said that before the great astronomer could discuss science
there was a little matter of business that must be disposed of. The
King accordingly handed Herschel a paper, in which he was, I dare say,
greatly surprised to find a pardon to the deserter written out by the
King himself.
Then Herschel unfolded his wonderful discovery, which the King
thoroughly appreciated, and in the evening the telescope was set up in
the gardens, and the glories of the heavens were displayed. Herschel
made a most favorable impression on his Majesty, and when the King
told the ladies of the Castle next day of all that Herschel had shown
him, their astronomical ardor was also aroused, and they asked to see
through the marvellous tube. Of course Herschel was ready to comply,
and the telescope was accordingly carried to the windows of the Queen’s
apartments at Windsor, which would have commanded a fine view if the
clouds had not been in the way, which they unfortunately were. Even
for royalty the clouds would not disperse, so what was to be done?
Herschel was equal to the occasion. He specially wanted to exhibit
Saturn, for it is one of the most beautiful objects in the sky, and
will fascinate any intelligent beholder. No astronomers would have been
able to see Saturn through the clouds, but Herschel did not disappoint
his visitors; he directed the instrument, not to the sky (nothing was
there to be seen); he turned it towards a distant garden wall. Now what
would you expect to see by looking through a telescope at a garden
wall--bricks, perhaps, or ivy? What these ladies saw was a beautiful
image of Saturn, his globe in the centre and his rings all complete,
forming so true a resemblance to the planet that even an experienced
astronomer might have been deceived. In the afternoon Herschel had seen
that the clouds were thick, and that there would be little probability
of using the telescope properly. Accordingly he cut out a little
image of Saturn, illuminated it by lamps, and set it up at a suitable
distance on a garden wall.
Herschel’s visit to Windsor was productive of important consequences.
The King said it was a pity that so great an astronomer should devote
himself to music, and that it would be far better for him to give up
that profession and come and live at Windsor. His Majesty promised that
he would pay him a salary, and he also undertook to provide the cost of
erecting great telescopes. His faithful sister Caroline came with him
as his assistant, and also received some bounty from the King. From
that moment Herschel renounced all his musical business, and devoted
himself to his great life-task of observing the heavens.
He built telescopes of proportions far exceeding those that had ever
been then thought of. He used to stand at night in the open air from
dusk to dawn gazing down the tube of his mighty reflector, watching the
stars and other objects in the heavens as they moved past. He would
dictate what he saw to Caroline, who sat near him. It was her business
to write down his notes and to record the position of the objects which
he was describing. Sometimes, she tells us, the cold was so great that
the ink used to freeze in her pen when she was at this work. Until he
became a very old man, Herschel devoted himself to his astronomical
labors. His discoveries are to be counted by thousands, though not one
of them was so striking or so important as the detection of the new
planet which first brought him fame.
The question of a name for the addition to the sun’s family had, of
course, to be settled. Herschel had surely a right to be heard at the
christening, and as a compliment to his Majesty he named the stranger
the Georgium Sidus. So, indeed, for a brief while, the planet was
actually styled. The Continental astronomers, however, would not accept
this designation; all the other planets were named after ancient
divinities, and it was thought that the King of England would seem
oddly associated with Jupiter and Saturn; perhaps also they considered
that the British dominions, on which the sun never sets, were already
quite large enough, without further extension to the celestial
regions. Accordingly a consultation was held, the result of which was
that George III. was deprived of his planetary honors, and the body was
given the name of Uranus, which, by universal consent, it now bears.
The planet Uranus lies just on the verge of visibility with the
unaided eye. It can sometimes be glimpsed like a faint star, and, of
course, with a telescope it is readily perceived. Many generations of
astronomers before Herschel’s time had been observing the heavens,
making maps of the stars, and compiling great catalogues in which the
places of the stars were accurately put down. It often happened that
Uranus came under their notice, but it never occurred to them that
what seemed so like a star was really a planet. I have, no doubt, said
that Uranus looked unlike a star when Herschel examined it; but then
that was because Herschel was a particularly skilful astronomer. To
an observer of a more ordinary type Uranus would not present any very
remarkable appearance, and would be passed over merely as a small star.
In fact, the planet was thus observed not once or twice, but no fewer
than seventeen times, before the acute eye of Herschel perceived its
true character. On many previous occasions the planet had been noted
as a star by astronomers who are in every way entitled to our respect.
It required a Herschel, determined to see everything in the very best
manner, to grasp the discovery which eluded so many others.
When Uranus was observed on these former occasions and mistaken for
a star, its place had been carefully put down. These records are at
present of the utmost use, because they show the past history of the
planet; and they appear all the more valuable when we remember that
Uranus requires no less than eighty-four years to accomplish a single
revolution around the sun. Thus, since the planet was discovered in
1781, it had completed one revolution by 1865, and is now (1899) about
one-third of the way around another. The earlier observations extend
backwards almost 200 years, so that altogether we have more or less
information about the movements of the planet during the completion of
two circuits and a half.
Uranus is a great deal bigger than the earth, as you will see in the
view of the comparative sizes of the planets (Fig. 47). It appears to
be of a bluish hue, but we cannot tell whether it turns round on its
axis, or rather, I should say, we are not able to _see_ whether it
turns round on its axis; for we can hardly doubt that it does so.
Notwithstanding that Uranus is at so great a distance from the earth,
we have been able to put this planet, no less than the nearer ones,
in the weighing scales, and we assert with confidence that Uranus is
fifteen times as heavy as our earth. We are indebted to the satellites
for this information.