places among those by which modern
astronomy is honoured.

On the 13th of March, 1781, between ten and eleven o'clock at night,
Herschel was examining the small stars near H Geminorum with a
seven-foot telescope, bearing a magnifying power of 227 times. One of
these stars seemed to him to have an unusual diameter. The celebrated
astronomer, therefore, thought it was a comet. It was under this
denomination that it was then discussed at the Royal Society of London.
But the researches of Herschel and of Laplace showed later that the
orbit of the new body was nearly circular, and Uranus was elevated to
the rank of a planet.

The immense distance of Uranus, its small angular diameter, the
feebleness of its light, did not allow the hope, that if that body had
satellites, the magnitudes of which were, relatively to its own size,
what the satellites of Jupiter, of Saturn are, compared to those two
large planets, any observer could perceive them, from the earth.
Herschel was not a man to be deterred by such discouraging conjectures.
Therefore, since powerful telescopes of the ordinary construction, that
is to say, with two mirrors conjugated, had not enabled him to discover
any thing, he substituted, in the beginning of January, 1787, _front
view_ telescopes, that is, telescopes throwing much more light on the
objects, the small mirror being then suppressed, and with it one of the
causes of loss of light is got rid of.

By patient labour, by observations requiring a rare perseverance,
Herschel attained (from the 11th of January, 1787, to the 28th of
February, 1794,) to the discovery of the six satellites of his planet,
and thus to complete the _world_ of a system that belongs entirely to
himself.

There are several of Herschel's memoirs on comets. In analyzing them, we
shall see that this great observer could not touch any thing without
making further discoveries in the subject.

Herschel applied some of his fine instruments to the study of the
physical constitution of a comet discovered by Mr. Pigott, on the 28th
September, 1807.

The nucleus was round and well determined. Some measures taken on the
day when the nucleus subtended only an angle of a single second, gave as
its real angle 6/100 of the diameter of the earth.

Herschel saw no phase at an epoch when only 7/10 of the nucleus could
be illuminated by the sun. The nucleus then must shine by its own light.

This is a legitimate inference in the opinion of every