William Herschel 91 



had carefully and thoroughly perfected the great instru- 

 ment in all its parts, I made systematic use of it in my 

 observations of the heavens, first forming a determi- 

 nation never to pass by any, the smallest, portion of 

 them without due investigation." 



Even the largest of the instruments, mentioned in this 

 letter, did not satisfy him, and he determined to improve 

 upon it by constructing one of twice its size. This was 

 finally mounted at Slough, where he had settled with his 

 sister in 1782. The polishing of concave mirrors was at 

 that time a serious business. On one occasion he kept 

 the tool on the mirror continuously for sixteen hours, and 

 with both hands engaged had to be fed by his sister, Caro- 

 line, who then kept house for him. His desire to obtain 

 larger and larger instruments did not, however, prevent 

 Herschel from making good use of those he had completed. 

 Surveying systematically the whole of the heavens he was 

 soon rewarded by a brilliant discovery. 



Struck by the peculiar appearance of a star that crossed 

 his field of view, he examined it with higher magnifying 

 powers, and found its apparent disc increased. Two days 

 later, a slight change of position could be detected. At 

 first it was thought to be a comet, but, ultimately, Saron, 

 at Paris, and Lexell, at Petrograd, found that its path in- 

 dicated an orbit round the sun of a nearly circular shape. 

 It then took its place as a new planet, the first that had 

 been discovered in historic times. The name " Georgium 

 Sidus," suggested by Herschel, was not generally accepted, 

 and was subsequently replaced by " Uranus." The dis- 

 covery was a fortunate one for Herschel, as it established 

 his reputation, and, what was more important, led 

 George III. to appoint him his private astronomer, with 

 a salary which, though modest, set him free to give up 

 his professional work and devote his entire energies to 

 astronomy. For a time, he increased his income by making 

 and selling telescope mirrors, but this ceased to be necessary 

 when, a few years later, he married a lady of independent 

 means. 



The leading feature of Herschel's work was his strong 

 faith in the unity of design which he tried to trace in the 



