176 SPECIAL RESULTS IN THE URANOLOGICAL PORTION 



a and y are nearly equal to each other ; so that, when the 

 atmosphere is not quite clear, their order of succession may 

 appear doubtful : is decidedly fainter than t, a, and i?. 

 The two stars |3 and y, both sensibly fainter than '(, are almost 

 equal to each other. Lastly, 3, which in old maps is given 

 as equal with /3 and y, is more than an entire order of magni- 

 tude fainter than those stars, e is certainly variable : although 

 usually brighter than a, I have five times in three years seen 

 it decidedly fainter than a. I also regard |3 Ursa3 majoris 

 as variable, but without being able to assign any determinate 

 period. Sir John Herschel, in 1840 and 1841, found /3 

 Ursse min. much brighter than Polaris ; whereas, in May 

 1846, the contrary was observed by him. He surmises 

 variability in /3 ( 286 ). Since 1843, I have usually found 

 Polaris fainter than ]3 Ursse min. ; but between October 1843 

 and July 1849 my registers show that, on fourteen occasions, 

 Polaris was seen to exceed /3 in brightness. I have repeatedly 

 had an opportunity of convincing myself that the last-named 

 star is not always equally reddish : it is sometimes more or 

 less yellow, and sometimes very decidedly red" ( 287 ). All 

 laborious investigations of the relative brightness of stars 

 will gain essentially in certainty, when successive arrangement 

 according to mere estimation shall be finally superseded by 

 methods of measurement founded on the progress of modern 

 optical science ( 288 ), and astronomers and physicists ought 

 not to doubt the possibility of attaining such an object. 



From the probably great physical similarity of the luminous 

 process in all self-luminous celestial bodies (in the central 

 body of our own planetary system, and in the remoter suns 

 or fixed stars), it has long been justly pointed out, ( 289 ) how 

 important a bearing the periodical or non-periodical variation 



