244 COSMOS. 



Bayer's Uranometria has long led to a belief that a change 

 of light has taken place in Aquilae, in Castor Geminorum, 

 and in Alphard of Hydra. 



Struve, in 1838, and Sir John Herschel, observed Capella 

 increase in light. The latter now finds Capella much brighter 

 than Vega, though he had always before considered it fainter. 1 * 

 Galle and Heis come to the same conclusion, from their pre- 

 sent comparison of Capella and Vega. The latter finds Vega 

 between 5 and 6 gradations, consequently more than half a 

 magnitude, the fainter of the two. 



The variations in the light of some stars in the constellations 

 of the Greater and of the Lesser Bear are deserving of especia 

 notice. " The star D Ursai majoris," says Sir John Herschel 

 " is at present certainly the most brilliant of the seven brigh ; 

 stars in the Great Bear, although, in 1837, t unquestionably 

 held the first place among them." This remark induced me 

 to consult Heis, who so zealously and carefully occupies 

 himself with the variability of stellar light. "The follow- 

 ing," he writes, " is the order of magnitude which results 

 from my observations, carried on at Aix-la-Chapelle between 

 1842 and 1850: 1. c Ursse majoris, or Alioth ; 2. a, or 

 Dubhe; 3. , or Benetnasch ; 4. S, orMizar; 5. /3; 6. <y; 7. 

 The three stars, e, a, and *j, of this group are nearly equal 

 in brightness, so that the slightest want of clearness in the 

 atmosphere might render their order doubtful; ( is decidedly 

 fainter than the three before mentioned. The two stars /3 

 and y, (both of which are decidedly duller than ) are nearly 

 equal to each other ; lastly ^, which in ancient maps is usually 



19 Sir John Herschel (Observations at the Cape, pp. 334, 

 350, note 1, and 440). For older observations of Capeila and 

 Vega, see William Herschel, in the Philos. Transact., 1797, 

 p. 307, 1799, p. 121; and Boae's Jahrluch fur 1810, s. 148. 

 Argelander, on the other Land, advances many doubts as 

 to the variation of Capella and of the stars of the Bear. 



