BIBLIOGRAPHY OF HERSCHEl's WRITINGS. 



(;2i 



Subject-Index. PniLOSOPHicAL Lnstulctions. Trar. 



Sun spots : are veiled over with nebulosity IT'jf) 



: observed 1705 



: penumbra 17'jr, 



Sun's emission of light and heat : is variable isoi 



Sun's motion in space : its quantity assigned 1806 



Sweeps : method described 1780 



: with the 40-foot 171)5 



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



whole heavens 1800 



r)7 

 49-58 



62 

 ^ 205 



23:$ 

 458 

 384 



84 



Telescopes : (Herschel's 4-iuch Newtonian described) 



Dolland's 3i-foot refractors 



(Herschel's 7, 10, 20 feet) 



used by Herschel 



(Herschel's 20-foot described) 



(Herschel's 20-foot sweeping telescope described) 



experiments with various magnifying powers 



the 20-foot was much tarnished in 1788. 



those made in 1793 



(Herschel's 40-foot described) 



account of Herschel's telescopes in general 



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



: data as to Herschel's reflectors 



: advantages of large apertures 



: light- gathering power 



: measure of their etfectiveness 



: description of one with a glass mirror 



: investigation of the causes which often prevent their proper action 



: spurious diameters 



: power to determine very small angles 



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

 guish a real from a spurious diameter 



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



: generally perform well in windy weather 



: magnifying powers used. See Magnifying powers. 



Telescopes penetrate into space 



Telescopes penetrate space : example on a terrestrial object 



Telescopic milky way 



Teihys: observations - 



Titan : transit observed 1789, November 2 



: observations • 



Titania : discovered January 11, 1787 (period Sf days) . 



— : its elements 



: is brighter than Oberon . . 



: is larger than Oberon 



: is variable in brightness. 



: revolves in 8^ 16^ SO"" 5^; 



Uranus : discovered 1781, March 13 

 : diameter is 5" .022 



I 17 



