COLOR or THE STARS. 131 



Eiope, ill the radiant fields of the starry heaven, as in the 

 blossoms of the phancrogamia, and in the metallic oxyds, 

 almost all the frradations of the prismatic spectrum between 

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

 Ptolemy enumerates in his catalogue of the fixed stars six 

 {yioKLppoL) fiery red stars, viz. :^ Arcturus, Aldcbaran, Pol- 

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

 Cleomcdes even compares Antares in Scorpio with the fiery 

 red Mars,t which is called both irvppdg and rrvpoeidrjg. 



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

 dish lisrht. Pollux is still indicated as a reddish, but Castor 

 as a greenish star.t Sirius therefore afibrds 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 vTTOKtp^og, which Ptolemy employs indiscriminate- 

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

 marked transition from Jiery yellow to Jieri/ red; it therefore refers, 

 Btrictly speaking, to b. fiery reddish color. He seems to attach the gen- 

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

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

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

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

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

 QucEst., i., 1) to be redder than Mars, and belongs to the stars called in 

 the Almagest VTzoKippoi, there can be no doubt that the word implies 

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

 The assertion that the affix iTocKt?.og, which Aratus, v. 327, attaches to 

 Sirius, has been translated by Cicero as " rutilus," is erroneoa'^. Cicero 

 says, indeed, v. 348: 



" Namque pedes subter rutilo cum lumine claret, 

 Fervidus ille Canis stellar um luce retulgens ;" 



but '* rutilo cum lumine" is not a translation of ttolkc^.o^, but the mere 

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

 fessor Franz.) " If," as Arago observes {Annuaire, 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 Schum., 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 

 actually 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 ignorant," (Compare Arago, in the Annuaire pour 1842, p. 350- 

 353.) 



