OF THE COSMOS. VARIABLE STARS. 175 



convincingly that Bayer did not follow the principle of 

 always indicating the brightest stars by the first letters ; but 

 that, oil the contrary, in the same star-magnitude he distri- 

 buted the letters in the order of position in such manner 

 as to pass usually from the head of the figure, in each con- 

 stellation, to its feet. The alphabetical order of the letters 

 employed in Bayer's Uranometry has long given prevalence 

 to a belief in changes having taken place in the light of a 

 Aquilse, of Castor, and of Alphard. 



Struve (1838) and Sir John Herschel saw Capella increase 

 in light. Sir John Herschel now estimates Capella as 

 much brighter than Vega, whereas he formerly always 

 considered it fainter ( 285 ). Galle and Heis form the same 

 judgment from a present comparison of Capella and Vega : 

 Heis considers the latter star to be between five and six 

 gradations, or more than half a magnitude, fainter than 

 Capella. 



The alterations in the light of some stars in the constella- 

 tions of the Great and Little Bear, are deserving of particular 

 attention. "The star / Ursae majoris," says Sir John 

 Herschel, " is now certainly the brightest of the seven bright 

 stars in the Great Bear, whilst in 1837 the first rank belonged 

 incontestably to e" This remark occasioned me to make 

 inquiries from Heis, who occupies himself with so much 

 ardour, and so extensively, with the variability of the light 

 of stars. He wrote to me in reply to the following effect : 

 " From the mean of the observations made by me at Aix-la- 

 Chapelle from 1842 to 1850, I find the order of succession 

 thus : 1. e Ursse maj., or Alioth ; 2. or Dubhe; 3. rj or 

 Benetnasch; 4. <T or Mizar; 5. |3; 6. y; 7. 3. In respect 

 to the differences of brightness between these seven stars, E, 



