COLOUR OF THE STARS. 177 



and Sirius. Cleomedes even compares Antares in Scorpio 

 with the fiery red Mars,* 7 which is called both irvppos and 



7TVpOtl8f]S. 



Of the six above named stars, five still retain a red or 

 reddish light. Pollux is still indicated as a reddish, but 

 Castor as a greenish star. 48 Sirius therefore affords the 

 only example of an historically proved change of colour, 

 for it has at present a perfectly white light. A great 

 physical revolution* 9 must therefore have occurred at the 

 surface or in the photosphere of this fixed star, (or remote 

 sun, as Aristarchus of Samos called the fixed stars) before 

 the process could have been disturbed by means of which 

 the less refrangible red rays had obtained the preponderance, 

 through the abstraction or absorption of other complementary 



Sirius, has been translated by Cicero as " rutilus," is erro- 

 neous. Cicero says, indeed, v. 348 : 



ik Namque pedes subter rutilo cum lumine claret, 



Fervidus ille Canis stellarum luce refulgens ;" 

 but " rutilo cum lumine" is not a translation of irowoXos, but 

 the mere addition of a free translation. (From letters ad- 

 dressed to me by Professor Franz.) " If," as Arago observes 

 (Annuaire. 1842, p. 351), "the Roman orator, in using the 

 term rittilus, purposely departs from the strict rendering of 

 the Greek of Aratus, we must suppose that he recognized the 

 reddish character of the light of Sirius." 



47 Cleom., Cycl. Theor., i. ii. p. 59. 



43 Madler, Astr. 1849, s. 391. 



49 Sir John Herschel, in the Edinb. Review, vol. 87, 

 1848, p. 189, and in Schum. Astr. Nachr., 1839, no. 372: 

 " It seems much more likely that in Sirius a red colour should 

 be the effect of a medium interfered, than that in the short 

 space of 2000 years so vast a body should have actually under- 

 gone such a material change in its physical constitution. It 

 may be supposed owing to the existence of some sort of cos- 

 mical cloudiness, subject to internal movements, depending on 

 causes of which we are ignorant." (Compare Arago in thfj 

 Annuaire pour 1642, pp. 350-353.) 



VOL. in. N 



