556 BIBLIOGRAPHY OF HERSCHEL's WRITINGS. 



Herschel, W.: Synopsis of the Writings of— Continued. 



A. D. Vol. P. 



1795 bo 71 It seems, therefore, upon tlie whole not improbable that in many cases 

 stars are united in such close systems as not to leave miich room for 

 the orbits of planets or comets; and that consequently many stars, 

 unless Ave woukl make them mere useless brilliant points, may them- 

 selves be lucid planets, perhaps unattended by satellites. 

 71 Postscript. The following observations of the sun arc added. They 

 are decisive in regard to one of the conditions of the lucid matter 

 of the sun. 1794, Nov. 2G. The sun is mottled everywhere, equally 

 at poles and equator. This is owing to inequalities in its surface. 

 71 The lucid substauce of the sun is neither a liquid nor an clastic fluid, 

 as is evident from its not instantly filling up the cavities of the 

 spots, etc. It exists, therefore, in the manner of lucid clouds swim- 

 ming in the transparent atmosphere of the sun; or, rather, of lu- 

 minous decompositions taking place within that atmosphei'e. 



1795 85 317 Bcscripiionof aforti/-foot rejlcciing tclescojw. By William Herschel, 

 LL.D., F. R. S. Read June 11, 1795., 



347 When I resided at Bath I had long been acquainted with the theory 



of optics and mechanics and Avanted only that experience so neces- 

 sary in the practical part of these sciences. This I acquired by 

 degrees at that place, where in my leisure hours by way of amusL-- 

 ment I made several 2-foot, 5-foot, 7-foot, 10-foot and 20-foot New- 

 tonian telescopes, besides others of the Gregorian form of 8, 12, 18 

 inches and 2, 3, 5 and 10 feet focal length. 

 343 In this way I made not less than 200 7-foot, 150 more 10-foot, and 

 about SO 20-foot mirrors, not to mention tlie Gngorian telescopes. 



348 The number of stands I invented for these telescopes it would not bo 



easy to assign. My Newtonian stand was contrived about 1778. 



348 In 1781 1 began to construct a 30-foot aerial rellector, and having made 



a stand for it I cast the mirror 36 inclies in diameter, which was 

 cracked in cooling. I cast it a second time, and the furnace which 

 I had built in my house broke. Soon- after, the Georgian Planet 

 was discovered [and observations on this interrupted the making 

 of new telescopes. ] 



349 In 1783 I finished a very good 20-foot reflector, and in 1785 I began to 



construct the 40-foot. 



349 lu the whole of the apparatus none but common workmen were em- 



ployed, for I made drawings of every part of it and directed every 

 person's labor, though sometimes there were not less thau 40 em- 

 l)loyed at the same time. There was no iuterruiition except my re- 

 moval from Clay Hall to Slough. 



350 The 40-foot speculum was put into the tube and first used 1787, Feb. 



19. The first mirror being too thin, etc., could uot receive a good 

 figure, and a second was cast 1788, Jan. 2G, Avhich cracked in cool- 

 ing. It was recast Feb. IG, audon Oct. 24 it had a good figure and 

 I observed Saturn with it ; but not being satisfied I worked upon it 

 till Aug. 27, 1789. Aug. 28, 1789, I discovered a sixth satellite of 

 Saturn. I date the finishing of the telescope from that time. 



350 Description of the telescope. See Plates XXIV to XLII. 



350-365 The foundation and stand. 



365 The tube : it is 39 feet 4 inches long, 4 feet 10 inches diameter, made 

 of iron. 



377 Motions of the telescope. 



