OF THE COSMOS. DISTRIBUTION OF THE FIXED STARS. 115 



as red or reddish. ( 221 ) I may name as exceptions Algol 

 in the head of Medusa, /3 Lyrse, and e Aurigse, which have 

 a pure white light. Mira Ceti, whose periodic variation of 

 light was the first recognised, ( 222 ) has a strongly reddish 

 light ; but the variability of Algol and /3 Lyrse shows that 

 the red colour is not a necessary condition of variability of 

 light ; and we know, moreover, that there are several reddish 

 stars which are not included among the variable stars. 

 According to Struve, the faintest stars in which colours can 

 still be distinguished are of the 9th and 10th magnitudes. 

 We find the first mention of blue stars ( 223 ) in Mariotte's 

 " Traite des Couleurs/' in 1686. The star n Lyrse is bluish. 

 A small cluster of 3 J minutes' diameter in the southern he- 

 misphere consists, according to Dunlop, exclusively of small 

 blue stars. Among the double stars there are many in 

 which the, principal star is white, and the companion blue ; 

 and some in which both the principal star and the companion 

 have a blue light, ( 224 ) as Serp. and 59 Androm. Some- 

 times, as in the cluster of stars near K of the Southern 

 Cross, which was taken by Lacaille for a nebula, above a 

 hundred small stars of different colours (red, green, blue, 

 and bluish-green) are so crowded together, that they appear, 

 in large telescopes, like gems of \nany colours ("like a 

 superb piece of fancy jewellery)." (^5) 



The ancients thought they recognised a remarkable sym- 

 metrical arrangement in the position of certain stars of the 

 1st magnitude. Thus their attention was particularly 

 directed to what they call ed the " four royal stars," which 

 are opposite to each ot'ner on the sphere Aldebaran and 

 Antares, Eegulus and 'Eomalhaut. This regular arrange 



