THE COLOUK OF THE STABS. 183 



stars Betelgeux, Arcturus, Aldebaran, Antares, and Pollux. 

 Riimker finds y Crucis of a fine red colour, and my old friend, 

 Captain Berard, who is an admirable observer, wrote from 

 Madagascar in 1847, that he had for some years seen a 

 Crucis growing red. The star TJ Argus, which has been 

 rendered celebrated by Sir John HerscheFs observations, and 

 to which I shall soon refer more circumstantially, is under- 

 going a change in colour, as well as in intensity of light. In 

 the year 1843, Mr. Mackay noticed at Calcutta that this star 

 was similar in colour to Arcturus, and was therefore reddish 

 yellow; 54 but in letters from Santiago de Chili, in Feb. 

 1850, Lieutenant Gilliss speaks of it as being of a darker 

 colour than Mars. Sir John Herschel, at the conclusion of 

 his Observations at the Cape, gives a list of seventy-six ruby- 

 coloured small stars, of the 7th to the 9th magnitude, some of 

 which appear in the telescope like drops of blood. The majo- 

 rity of the variable stars are also described as red and reddish,* 

 the exceptions being Algol in Caput Medusae, /3 Lyrse and e 

 Auriga, which have a. pure white light. Mira Ceti, in which 

 a periodical change of light was first recognized, has a strong 

 reddish light; 56 but the variability observed in Algol and 

 3 Lyrse, proves that this red colour is not a necessary condi- 

 tion of a change of light, since many red stars are not 

 variable. The faintest stars in which colours can be dis- 

 tinguished belong, according to Struve, to the 9th and 10th 

 magnitudes. Blue stars were first mentioned by Mariotte, 67 

 1686, in his Traite des Couleurs. The light of a Lyra3 is 

 bluish ; and a smaller stellar mass of 3^ minutes in diameter 

 in the southern hemisphere consists, according to Dunlop, of 

 blue stars alone. Among the double stars there are many in 



** Sir John Herschel, Observations at the Cape, p. 34. 



M Madler's Astronomic, s. 436. 



56 Cosmos, vol. ii. p. 713. 



m Arago, Annuaire pour 1842, p. 348. 



