BIBLIOGRAPHY OF HERSCHEL's WRITINGS. G21 



SUBJECT-IXDEX. PHILOSOFHICAL INSTRUCTIONS. Year. Page. 



Sun spots : are veiled over with nebulosity 1795 57 



: observed 1795 49-58 



: penumbra 1795 62 



Sun's emission of light and heat : is variable 1801 ) " 



i 354 



Sun's motion in space : its quantity assigned 1806 23:5 



Sweeps : method described 1786 458 



: with the 40-foot 1795 384 



: with 40-foot telescope it would require 812 years to view the 



whole heavens 1800 84 



Telescopes : (Herschel's 4-inch Newtonian described) 1780 513 



: Dolland's 3i-foot refractors 1780 518 



: (Herschel's 7, 10, 20 feet) 1~81 . 121 



: used by Herschel 1~83 249 



: (Herschel's 20-foot described) 1784 437 



: (Herschel's 20-foot sweeping telescope described) 1786 457 



: experiments with various magnifying powers 1786 500 



: the 20-foot was much tarnished in 1788. 



: those made in 1793 l~'^-l 50,51 



• (Herschel's 40-foot described) I'Oi' p47 



' 34/ 



. : account of Herschel's telescopes in general 1795 < 348 



( 349 



: their space-penetrating power, etc. ; general theory 1800 49 



: data as to Herschel's reiiectors 1800 68-81 



: advantages of large apertures 1800 255 



: light- gathering power , 1800 5.5 



: measure of their effectiveness ---- 1800 6o 



: description of one with a glass mirror 1803 214 



: investigation of the causes which often prevent their proper action 1803 214 



: spurious diameters -- 1803 345 



: power to determine very small angles 1805 31 



: there is a limit for each telescope below which it cannot distin- 

 guish a real from a spurious diameter 180> 62 



: (Herschel's 20-foot and 40-foot— their relative convenience) .... 1815 295 



: generally perform well in windy weather 1815 322 



: magnifying powers used. See Magnifying powers. 



Telescopes penetrate into space ' ' ~ 



Telescopes penetrate space : example on a terrestrial object 1800 07 



^, ^. .,, 1/91 /7 



Telescopic milky way - 



• •• ■■ 1790 456 



Teihys: observations i--oiP44l 



Titan : transit observed 1789, November 2 J^^^ ^«'^^^ 



: observations * ... ^ .,j, 



discovered January 11, 1787 (period 8f days) ^ 1^»J^ i^^ 



its elements I 1788 377 



1798 78 



1815 356 



is larger than O&ero/i , ^^ 



is variable in brightness ^^ ^.^ 



revolves in 8^ 16^ 5b™ 5^.2 



Titania . 



< 178& 

 I 178c 



is brighter than Oberon 



is larger than Oberon . . 

 is variable in brightness . 



5 



, ,,„, ,, , ... 1781 492 



Uranus: discovered 1781, Marcli i-i 



■ r/;n->> liO-i l/i 



: diameter is o' .022 



