NEBULA. 811 



into clusters. This number may, perhaps, be increased to 

 4,000, if we take into account 300 or 400 seen by Sir Wil- 

 liam Herschel, 38 but not again determined, and the 629 

 observed by Dunlop at Paramatta, with a nine-inch Newto- 

 nian reflector, of which Sir John Herschel included only 206 

 in his catalogue. 87 Similar results have recently been pub- 

 lished by Bond and Madler. The number of nebulae, com- 

 pared with that of double stars appears, therefore, according 

 to the present condition of science, to be in the ratio of 

 2:3; although it must not be forgotten that under the 

 designation of double-stars are included those which are 

 merely optically double, and that hitherto alterations of posi- 

 tion have only been observed in a ninth, or perhaps but an 

 eighth portion of the whole number. 88 



The above numbers 2,299 nebulae, with 152 clusters ot 

 stars, in the Northern, and only 1,239 nebulae, with 23fi 

 clusters of stars, in the Southern Catalogue, show that the 

 southern hemisphere, with a smaller number of nebula?, 

 possesses a preponderance of clusters of stars. If we assume 

 that all nebulae are from their probable constitution resolvable, 

 as merely more remote clusters of stars or stellar groups, 

 composed of smaller and less thronged, self-luminous celestial 

 bodies, this apparent contrast (whose importance has been 

 the more noticed by Sir John Herschel 39 in consequence of 



* Sir John Herschel says, in his Observations at the Cape, 

 p. 134, '* There are between 300 and 400 nebulae of Sir 

 William Herschel's Catalogue still unobserved by me; foi 

 the most part very faint objects." 



37 Op. cit. 7. Compare Dunlop's Cat. of Ncbulce and 

 Clusters of the Southern Hemisphere, in the Philos. Transact. 

 for 1828, pp. 114-146. 



88 Cosmos, vol. iii. p. 272. 



Observations at the Cape, 105-107. 



