IV. 



ON Sm WILLIAM HERSCHEL'S OBSERVATIONS 

 OF THE SATELLITES OF URANUS. 



By E. S. HOLDEN. 

 (Read 1874, Junk 6.) 



It is well known that Sir William Herschel suspected that 

 the planet which he had discovered was accompanied by six 

 satellites. These he numbered in their order proceeding outwards 

 from the planet. 



I. Period 5 days, 21 hours. 



IL " 8 " 18 " 



IIL " 10 " 23 " 



IT. " 13 " U " 



Y. " 88 " 1 



YI. " lOY " 16 " 



Of the existence of satellites II. and lY. there is no manner of 

 doubt, since they were steadily observed by the elder Herschel 

 from 1787, Jan. 11, to 1810, May 25, and by his son in the years 

 1828 to 1832, as well as by Lamont, Struve, Lassell, and New- 

 comb since that time, and all of these observations have been 

 consistent. 



Satellites I., III., Y., and YI., have no such evidence in favor 

 of their existence as the brighter ones II. and lY. 



From the Philosophical Transactions, 1815, where Herschel 

 has collected all his observations of the satellites of Uranus, it 

 appears that he supposed satellite I. to have been observed on 

 four different occasions, viz. : — 



January 18, 1790. 

 March 27, 1794. 

 February 15, 1798. 

 April 17, 1801. 



Satellite III. was seen only twice, on March 26 and 27, 1794, 

 while Y. and YI. were suspected at various times. 



Lassell. in 1847, discovered two satellites interior to Herschel's 

 II. , and we owe to him and to his assistant, Marth, a good series 

 of observations of all four satellites. The periods as determined 

 by Lassell are — 



Ariel : 2^ 12'^ 29^" 20^7 

 Umbriel: 4 3 28 7.5 

 Titania : 8 16 56 25.6 

 Oberon : 13 11 6 55.4 

 (30) 



