230 SPECIAL RESULTS IN THE UEANOLOGICAL 



ing to the present state of our knowledge, therefore, the 

 proportion of the number of nebulae to that of double stars 

 is about as 2 I 3 ; but it should not be forgotten, that under 

 the denomination of double stars are included those which 

 are merely optically double, and that up to the present time 

 changes of position have only been recognised in an eighth, 

 or perhaps even a ninth part of the whole ( 395 ). 



The numbers found above, viz. 22 9 U nebulae with 152 

 star-clusters in the northern, and only 1239 nebulas with 

 236 clusters in the southern catalogues, shew a compara- 

 tively smaller number of nebulae and a preponderance of 

 star-clusters in the southern hemisphere. Even assuming 

 the probability of all nebulae being truly in their own nature 

 alike resolvable, i. e., of their being either -more remote 

 clusters, or groups composed of smaller, less crowded, self- 

 luminous cosmical bodies, yet this apparent contrast, (to the 

 importance of which Sir John Herschel himself called atten- 

 tion, ( 396 ) and that the more strongly as he had employed 

 reflecting telescopes of equal power in the two hemispheres), 

 must at least be held to indicate a striking diversity in 

 distribution in space, i. e. in respect to the directions in 

 which they present themselves on the northern or southern 

 firmament to the inhabitants of the earth. 



We owe to the same great observer the first exact know- 

 ledge and general cosmical view of the distribution of nebulae 

 and star-clusters over the entire surface of the heavens. In 

 order to examine their situation, their relative abundance 

 in different parts, and the probability or improbability of 

 their succession in certain groupings or lines, he entered be- 

 tween three and four thousand objects graphically in squares 

 of which the sides corresponded to 3 of Declination and 



