VARIABLE STARS. 181 



served by him. He also conjecUircs (3 to be variable.* Since 

 1843, I have, as a rule, foimd Polaris fainter than (3 Ursae 

 miuoris ; but irom October, 1813, to July, 1819, Polaris was. 

 accordiii<^ to my registers, fourteen times brighter than (3. I 

 have had irequent opportunities of convincing myself that the 

 color of the last-named star is not always equally red ; it is 

 at times more or less yellow, at others most decidedly red."t 

 All the pains and labor spent in determining the relative 

 brightness of the stars will never attain any certain result 

 until the arrangement of their magnitudes from mere esti- 

 mation shall have given place to methods of measurement 

 founded on the progress of modern optical science.! The 

 possibility of attaining such an object need not be despaired 

 of by astronomers and physicists. 



The probably great physical similarity in the process of 

 light in all self-luminous stars (in the central body of our own 

 planetary system, and in the distant suns or fixed stars) has 

 long and justly directed attention to the importance^ and 

 significance which attach to the periodical or non-periodical 

 variation in the light of the stars in reference to climatology 

 generally ; to Ijie history of the atmosphere, or the varying 

 temperature which our planet has derived in the course of 

 thousands of years from the radiation of the sun ; with the 

 condition of organic life, and its forms of development in dif- 

 ferent degrees of latitude. The variable star in the neck of 

 the Whale (Mira Ceti) changes from the second magnitude 

 to the eleventh, and sometimes vanishes altogether ; we have 

 seen that rj Argus has increased from the fourth to the first 

 magnitude, and among the stars of this class has attained to 

 the brilliancy of Canopus, and almost to that of Sirius. Sup- 

 posing that our own sun has passed through only a very few 

 of these variations in intensity of light and heat, either in an 

 increasing or decreasing ratio (and why should it differ from 

 other suns ?), such a change, such a weakening or augment- 



* Observations at the Cape, $ 2.59, note 260. 



t Heis, ill his Manuscrij)t Notices of May, 1850 ; also Observations at 

 the Cape, p. 325 ; and P. vou Boguslawski, Uranus for 1818. p. 186. 

 The asserted variation of ??, a, and 6 Ursse majoris is also confirmed in 

 Outlines, p. 559. See Madler, Astr., p. 432. On the succession of the 

 stars which, from their proximity, will in time mark the north pole, 

 until, after the lapse of 12,000 years, Vega, the brightest of all possible 

 polar stars, will take their place. t Vide supra, p, 96 



§ William Herschel, On the Changes that happen to the Fixed Stars, 

 in the Philos. Transact, for 1796, p. 18G. Sir John Herschel, in the 

 Observations at the Cape, p. 350-352; as also in Mrs. Somerville's !^x« 

 cellent work, Connection of the Physical Sciences, 1846, p. 407. 



