08 SPECIAL RESULTS IN THE URANOLOGICAL 



In the Southern Hemisphere, we have from Sir John Her- 

 schel, the unexpected result that, "in the extra-tropical 

 parts, the number of multiple stars is much less than in the 

 corresponding parts of the Northern Hemisphere/'' And yet 

 these fair southern regions were examined with an excellent 

 20 -feet reflector, which separated stars of the 8th magnitude 

 in distances of only three-fourths of a second apart, under the 

 most favourable atmospheric conditions, and by a most prac- 

 tised observer. ( 344 ) 



An exceedingly remarkable peculiarity of multiple stars, 

 consists in the occurrence among them of contrasted co- 

 lours. Struve, in his great work published in 1837, gave 

 the following results in respect to colours, derived from 

 600 of the brightest double stars. ( 845 ) In 375 cases, the 

 colour of the principal star and the companion was the 

 same, and equally intense. In 101, the colour was the same, 

 but a difference of intensity was perceived. The cases of 

 double or multiple stars having entirely different colours, 

 were 120 in number, or one-fifth of the whole ; whereas 

 uniformity of colour between the principal stars and their 

 companions, extended to four-fifths of the entire carefully 

 examined mass. In almost half the 600 cases, both the 

 principal star and the companion are white. Among those 

 in which the colours are different, combinations of yellow 

 and blue (as in t Cancri), and of reddish-yellow and green (as 

 in the ternary star y Andromedse), ( 346 ) are very frequent. 



It was Arago who in 1825 first called attention to the 

 circumstance, that in most, or at least in very many cases, 

 the diversity of colour in binary systems appeared to have 

 reference to complementary colours (i. e. to the subjective re- 

 lation between colours, the union of which forms white). ( 347 ) 



