COLOU OF THE STARS. 131 



ifiope, ill the radiant fields of the starry heaven, as in tha 

 blossoms of the phanerogamia, and in the metallic oxyds, 

 almost all the gradations of the prismatic spectrum between 

 the extremes of refrangibility of the red and the violet ray. 

 Ptolemy enumerates in his catalogue of the fixed stars six 

 [vnoKi^poL) fiery red stars, viz. '.^ Arcturus, Aldebaran, Pol- 

 lux, Antares, a Orionis (in the right shoulder), and Sirius. 

 Cleomedes even compares Antares in Scorpio with the fiery 

 red Mars,t which is called both TTvppbg and TTvpoeidijq. 



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

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

 as a greenish star.$ Sirius therefore affords the only ex- 

 ample of an historically proved change of color, for it has at 

 present a perfectly white light. A great physical revolu- 

 tion^ must therefore have occurred at the surface or in the 

 photosphere of this fixed star (or remote sun, as Aristarchus 



* The expression VnOKippoQ, which Ptolemy employs indiscriminate- 

 ly to designate the six stars named in his catalogue, implies a slightly- 

 marked transition ivoxn. fiery yellow to fiery red; it therefore refers, 

 strictly speaking, to ^ fiery reddish color. He seems to attach the gen- 

 eral predicate ^avdog, fiery yellow, to all the other fixed stars. {Almag., 

 viii., 3d ed., Halma, torn, ii., p. 94.) Kip^oc is, according to Galen 

 (Metk. Med., 12), a pale fiery red inclining to yellow. Gellius com- 

 pares the word with melinns, which, according to Servius, has the same 

 meaning as " gilvus" and " fulvus." As Sirius is said by Seneca {Nai. 

 Qucesi., i., 1) to be redder thaii Mars, and belongs to the stars called in 

 !he Almagest v-oKippot, there can be no doubt that the word implies 

 llie predominance, or, at all events, a certain proportion of red rays. 

 The assertion that the affix Troi/c/Aof, which Aratus, v. 327, attaches to 

 Sirius, has been translated by Cicero as " rutilus," is erroneous. Cicero 

 says, indeed, v. 348 : 



" Nam que pedes subter rutilo cum hi mine claret, 

 Fervidus ille Canis stellarum luce refulgens ;*' 



but " rutilo cum lumine" is not a translation of ttoikHoc, but the mere 

 addition of a free translation. (From letters addressed to me by Pro 

 fessor Franz.) " If," as Arago observes (AnJinaire, 1842, p. 351), " the 

 Roman orator, in using the term rutilus, purposely departs from the 

 strict rendering of the Greek of Aratus, we must suppose that he rec- 

 ognized the reddish character of the light of Sirius." 



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



X Madler, Astr., 1849, s. 391. 



\ Sir John Herschel, in the Edinh. Review, vol. 87, 1848, p. 189, and 

 in Sebum., Astr. Nachr., 1839, No. 372: " It seems much more likely 

 that in Sirius a red color should be the effect of a medium interfered, 

 than that in the short space of 2000 years so vast a body should have 

 Rctually undergone such a material change in its physical constitution. 

 It may be supposed owing to the existence of some sort of cosmical 

 cloudiness, subject to internal movements, depending on causes of which 

 we are i:rnoiant." (Compare Aragn,in ilie Annuair^ pour 1842. p. 350- 

 353.) 



