PORTION OF THE COSMOS. MULTIPLE STARS. 211 



Struve (1831-1833), in the nearly equally bright yellowish 

 stars (3rd magnitude) of the double star y Virginis and 

 Anon. 2718, may perhaps indicate a very slow rotation 

 around the axes of those two suns. ( 354 ) "Whether any actual 

 change of colour has ever taken place in double stars (y 

 Leonis and y Delphini ?), whether white light ever becomes 

 coloured in them, as we know that inversely in Sirius, 

 which is a single star, coloured light has become white, is 

 still undecided ; ( 3 ' 5 ) when the differences in question only 

 have reference to faint shades of colour, organic indivi- 

 duality in the observers, and when refractors are not 

 employed, the often reddening influence of the metallic 

 speculum in telescopes, are to be taken into account. 



Among the multiple stars, or systems, I may cite : 

 ternary; Librae, Cancri, 12 Lyncis, 11 Monoceritis : 

 quaternary; 102 and 2681 of Struve's catalogue, a Andro- 

 medae and e Lyrae : and a six-fold combination in Oripnis, 

 the celebrated trapezium in the great nebula in Orion, pro- 

 bably forming a single physical system united by laws of mu- 

 tual attraction, since the five smaller stars (6 '3m.; 7m.; 8m.; 

 ll'3m. ; and 12m.) follow the proper motion of the principal 

 star (4'7m). As yet, however, no change in their relative 

 positions has been observed. ( 356 ) In two ternary multiple 

 stars, ? Librae and Cancri, the movement of revolution of 

 both companions has been recognised with great certainty ; 

 Cancri consists of three stars differing but little in bright- 

 ness, being all of the 3rd magnitude, and the nearer com- 

 panion appears to have a ten times quicker motion than 

 the more distant one. 



The number of double stars, in which it has been possible 

 to compute the elements of the orbits, is given at present 



