180 



COSMOS. 



the stars in a constellation, beginning usually at the head, 

 and proceeding, in regular order, down to the feet. The or- 

 der of letters in Bayer's Uranometria has long led to a be- 

 lief that a change of light has taken place in a Aquilae, in 

 Castor Geminorum, and in Alphard of Hydra. 



Stmve, in 1838, and Sir John Hersohel, observed Capella 

 increase in light. The latter now finds Capella much bright- 

 er than Vega, though he had always before considered it 

 fainter.* Galle and Heis come to the same conclusion, from 

 their present comparison of Capella and Vega. The latter 

 finds Vega between five and six gradations, consequently 

 more than half a magnitude, the fainter of the two. 



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

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

 especial notice. " The star rj Ursae majoris," says Sir John 

 Herschel, "is at present certainly the most brilliant of the 

 seven bright stars in the Great Bear, although, in 1837, e 

 unquestionably held the first place among them." This re- 

 mark induced me to consult Heis, who so zealously and care- 

 fully occupies himself with the variability of stellar light. 

 " The following," he writes, " is the order of magnitude which 

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

 between 1842 and 1850 : 1. e Ursse majoris, or Alioth ; 2. 

 a, or Dubhe ; 3. 7], or Benetnasch ; 4. 6, or Mizar ; 5. (3 ; 6. 

 y ; 1.6. The three stars, e, a, and r\, of this group, are near- 

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

 in the atmosphere might render their order doubtful ; £ is de- 

 cidedly fainter than the three before mentioned. The two 

 stars j3 and y (both of which are decidedly duller than £) are 

 nearly equal to each other ; lastly, 6, which in ancient maps is 

 usually set down as of the same magnitude with and y, is 

 by more than a magnitude fainter than these ; e is decided- 

 ly variable. Although in general tins star is brighter, I have 

 nevertheless, in three years, observed it on five occasions to 

 be undoubtedly fainter than a. I also consider (3 Ursse ma- 

 joris to be variable, though I am unable to give any fixed 

 periods. In the years 1840 and 1841, Sir John Herschel 

 found (3 Ursae minoris much brighter than the Polar star ; 

 whereas still earlier, in May, 1846, the contrary was ob- 



* Sir John Herschel (Observations at the Cape, p. 334, 350, note 1, and 

 440). For older observations of Capella and Vega, see William Her- 

 schel, in the Philot. Transact., 1797, p. 307, 1799, p. 121 ; and Bode's 

 Jakrbnch fur 1810, s. 148. Argelander, on the other hand, advances 

 many doubts as to the variation of Capella and of the stars of the Bear. 



