becoming famous in the world of science. On 1st August, 1786, during Herschel's absence in Germany, she discovered a comet, the first of eight similar objects to her credit. The small annuity conferred upon her was a recognition—painfully inadequate—of her own work in astronomical science.
The construction of the great telescope occupied nearly four years. The erection of this immense instrument took up a great deal of Herschel's attention. His sister asserted that "there is not one screwbolt about the whole apparatus but what was fixed under the immediate eye of my brother. I have seen him lie stretched many an hour in a burning sun, across the top beam while the iron-work for the various motions was being fixed. At one time, no fewer than twenty-four men (twelve and twelve relieving each other) kept polishing day and night; my brother, of course, never leaving them all the while, taking his food without allowing himself time to sit down to table."
This ceaseless industry bore fruit when in August, 1789, the great telescope was ready for use. Herschel's former telescopes had been Newtonians, with small secondary mirrors. In January, 1787, however, he made a novel experiment with his 20-foot telescope. In order to save the light lost by the second reflection, Herschel removed the small mirror and slightly tilted the tube. The result more than justified expectations, and the experiment resulted in the discovery of two satellites of Uranus. Accordingly, he decided to make the 40-foot telescope on this "front-view" principle. This particular form of the reflector is known as the Herschelian.
Herschel was very proud of his large telescope and in 1795 sent a description of it to the Royal Society. Yet, on the whole, its performances were disappointing. Immediately it was erected Herschel succeeded in con-
