210 SPECIAL RESULTS IN THE URANOLOGICAL 



of the revolution of sidereal bodies in partial systems round 

 a common centre of gravity. A careful examination of the 

 brighter double stars (colour is still determinable in stars of 

 the 9th magnitude), teaches us that,, besides pure white, all 

 the colours of the solar spectrum are to be found in double 

 stars ; but that the principal star, when not white, generally 

 approximates to the red extreme, namely, that of the least 

 refrangible rays, and the companion to the violet extreme, 

 or that of the most refrangible rays. The reddish stars 

 are twice as frequent as the blue and bluish, and the 

 white are about twice and a half as numerous as the red and 

 reddish. It is also to be remarked, that usually a great 

 difference of colour is combined with a considerable differ- 

 ence in the intensity of the light. In two pairs of stars, 

 which, from their great brightness, can be easily measured 

 in the daytime with powerful telescopes, Bob'tis and y 

 Leonis, the first-named pair consists of two white stars of 

 the 3rd and 4th magnitudes, and the latter of a principal star 

 of the 2m., and a companion of the 3 '5m. This last-named 

 star (y Leonis) is said to be the finest double star of the 

 Northern Hemisphere, but a Centauri ( 352 ) and a Crucis, of 

 the Southern Heavens, surpass all other double stars in 

 brilliancy. As in ? Bobtis, so also in a Centauri and y 

 Virginis, we remark the rare combination of two large stars 

 having but little inequality of light. 



Eespecting variability of brightness in multiple stars, and 

 especially respecting variability in the companion, unanimity 

 and certainty do not yet prevail. '"We have already spoken 

 more than once ( 353 ) of the somewhat irregular variability of 

 the brightness of the principal star of a yellowish-red colour, 

 in aHerculis. Also the variation of brightness, observed by 



