62 HERSCHEL. 



was eighteen, to which Herschel added nine namely Uranus and 

 six satellites, and two satellites of Saturn. His discovery of the 

 rotation of Saturn's ring, his measurements of the rotation of Saturn 

 and Venus, his observations of the belts of the former, and his con- 

 jectural theory derived from observation of the rotation of Jupi- 

 ter's satellites, with a large number of minor observations, prove 

 that no one individual ever added so much to the facts on Avhich 

 our knowledge of the solar system is founded. His leading dis- 

 coveries in siderial astronomy include the discovery of binary 

 systems of stars, and the orbits of several revolving stars; the 

 discovery and classification of a prodigious multitude of nebula ; 

 the law of grouping of the entire firmament, and its connection 

 with the great nebula of the Milky Way; and lastly, the determina- 

 tion of the motion of our sun and system in space, and the direction 

 of that motion. 



Herschel's magnificent speculations on the Milky Way, the con- 

 stitution of nebulae, &c., first opened the road to the conception, 

 that what was called the universe was, in all probability, but a 

 detached and minute portion of that fathomless series of similar 

 formations which ought to bear the name. Imagination roves with 

 ease upon such subjects ; but before Herschel's observations, even 

 that daring faculty would have rejected ideas which afterwards 

 proved to be but sober philosophy. These great and arduous 

 enquiries occupied Herschel during nearly the whole of his scientific 

 career, extending to almost half a century, and, excepting the con- 

 tinuation of his labours by his illustrious son, Sir John, little has 

 been added to our knowledge of ' the constitution of the heavens' 

 since his death. 



As an optician, Herschel deserves equal notice for the wonderful 

 improvements which he effected in the dimensions and magnifying 

 power of telescopes, and by the skill with which he applied them 

 to celestial observations. The reflecting telescope was the one to 

 the improvement of which he so successfully devoted himself; and 

 the real secret of his success in this, was his astonishing persever- 

 ance ; his determination being to obtain telescopes of twenty feet 

 focal length or more, and of a perfection equal or superior to the 

 small ones then in use. He himself relates, that whilst at Bath he 

 had constructed 200 specula of seven feet focus, 150 often feet, and 

 about 80 of twenty feet; a proof of extraordinary resolution in a 

 man of limited means, and at that time engaged in a laborious 

 profession. 



Herschel at last succeeded in constructing his enormous telescope 

 of forty feet focal length, which he erected in the grounds of his 

 house at Slough. This instrument was begun in 1785, and finally 

 completed on August 28th, 1789, on which day Ilerschel discovered 

 with it the sixth satellite of Saturn; the diameter of the tube was 

 4 feet 10 inches, the speculum having a useful area of 4 feet: the 



