132 cosmos. 



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 rays, either in the pho- 

 tosphere of the star itself, or in the moving cosmical clouds 

 by which it is surrounded. It is to be wished that the epoch 

 of the disappearance of the red color of Sirius had been re- 

 corded by a definite reference to the time, as this subject has 

 excited a vivid interest in the minds of astronomers since 

 the great advance made in modern optics. At the time of 

 Tycho Brahe the light of Sirius was undoubtedly already 

 white, for when the new star which appeared in Cassiopeia 

 in 1572, was observed in the month of March, 1573, to 

 change from its previous dazzling white color to a reddish 

 hue, and again became white in January, 1574, the red ap- 

 pearance of the star was compared to the color of Mars and 

 Aldebaran, but not to that of Sirius. M. Sedillot, or other 

 philologists conversant with Arabic and Persian astronomy, 

 may perhaps some day succeed in discovering evidence of 

 the earlier color of Sirius, in the periods intervening from 

 El-Batani (Albategnius) and El-Fergani (Alfraganus) to Ab- 

 durrahman Sufi and Ebn-Junis (that is, from 880 to 1007), 

 and from Ebn-Junis to Nassir-Eddin and Ulugh Beg (from 

 1007 to 1437). 



El-Fergani (properly Mohammed Ebn-Kethir El-Fergani), 

 who conducted astronomical observations in the middle of 

 the tenth century at Rakka (Aracte) on the Euphrates, in- 

 dicates as red stars {stellce, ruffce of the old Latin translation 

 of 1590) Aldebaran, and, singularly enough,* Capella, which 

 is now yellow, and has scarcely a tinge of red, but he does 

 not mention Sirius. If at this period Sirius had been no 

 longer red, it would certainly be a striking fact that El-Fer 



* In Muhamedis Alfragani Chronologica et Astronomica Elementa, ed. 

 Jacobus Christmaimus, 1590, cap. 22, p. 97, we read, " Stella ruffa in 

 Tauro Aldebaran ; Stella ruffa in Geminis quae appellatur Hajok, hoc 

 est Capra." Alhajoc, Aijuk are, however, the ordinary names for Ca- 

 pella Auriga?, in the Arabic and Latin Almagest. Argelander justly ob- 

 serves, in reference to this subject, that Ftolemy, in the astrological 

 work (TerpaSiBXoc cvvra^ic), the genuine character of which is testi- 

 fied by the style as well as by ancient evidence, has associated planeta 

 with stars according to similarity of color, and has thus connected Mar 

 tis Stella, Quce urit sicut congruit igneo ipsius colori, with Aurigae Stella 

 or Capella. (Compare Ptol., Quadripart. Construct., libri iv., Basil 

 1551, p. 383.) Riccioli (Almagestum Novum, ed. 1650, torn, i., pars i. 

 lib. 6, cap. 2, p. 394) also reckons Capella, together with Ajitares, Aide 

 baran, and Arcturus, among red stars. 



