all their spare time in measuring the heights of about one hundred
mountains in the moon, which William gauged by three different methods.
In the same year, he made an acquaintance of some importance to him, as
forming his first introduction to the wider world of science in London
and elsewhere. Dr. Watson, a Fellow of the Royal Society, happened to
see him working at his telescope; and this led to a visit from the
electrician to the amateur astronomer. Dr. Watson was just then engaged
in getting up a Philosophical Society at Bath (a far rarer institution
at that time in a provincial town than now), and he invited William
Herschel to join it. Here Herschel learned for the first time to mix
with those who were more nearly his intellectual equals, and to measure
his strength against other men's.

It was in 1781 that Herschel made the great discovery which immediately
established his fame as an astronomer, and enabled him to turn from
conducting concerts to the far higher work of professionally observing
the stars. On the night of Tuesday, March 13th, Herschel was engaged in
his usual systematic survey of the sky, a bit at a time, when his
telescope lighted among a group of small fixed stars upon what he at
first imagined to be a new comet. It proved to be no comet, however, but
a true planet--a veritable world, revolving like our own in a nearly
circular path around the sun as centre, though far more remote from it
than the most distant planet then known, Saturn. Herschel called his new
world the _Georgium Sidus_ (King George's star) in honour of the
reigning monarch; but it has since been known as Uranus. Astronomers all
over Europe were soon apprised of this wonderful discovery, and the path
of the freshly found planet was computed by calculation, its distance
from the sun being settled at nineteen times that of our own earth.

In order faintly to understand the importance attached at the time to