30 INDEX CATALOGUE. 



Herschel, W. : Abstracts of Memoirs — Continued. 



A.D. Vol. P. 



which the nebulous matter is proved by observation to 

 be subject. 



1814 104 257 VII. Of small patches consisting of Stars mixed with 

 nebulosity . 



Thirty-seven cases noted. 



The connection may be only apparent — admitting it to be 

 real : 



1st, it may happen that the nebulosity still mixed with the 

 stars is some remaining unsubsided part of that from 

 which they were formed; or, 2d, the union of stars and 

 nebulosity may have been affected by the motion of either 

 the stars or the nebulosity. 



258 Such motions do take place. Nebulae are subject to great 



changes in their appearance, as the nebula of Orion. 

 [P. T., 1811, p. 320.] 



259 Every nebulosity which is carried into the region of a 



small patch of stars will probably be gradually arrested 

 and absorbed by them, and the growth of stars thus con- 

 tinued. 



VIII. Of objects of an ambiguous construction. 



Clusters of stars at a great distance may assume a nebulous 

 appearance. [P. T:, 1811, p. 270.] 



Telescopes of gradually increasing space-penetrating powers 

 show certain objects successively as nebulas, mixtures of 

 nebulosity and stars, and as true clusters ; other objects, 

 so viewed, increase in brightness, and the nebulosity be- 

 comes more uniformly united and of a milky appearance, 

 and these are purely nebulous. 

 2G0 Definition of ambiguous objects, their classification and 

 examples. Seventy-one such noted in four classes. 



Class 1. Seven objects, which may be supposed to consist 

 of stars, but where observations leave it doubtful. 

 261 Class 2. Twenty-six objects of round or nearly round 

 figure. The round figure of these show them to be glob- 

 ular. They must either be in a condensed state purely 

 nebulous, or else if consisting of stars, they must be in 

 an advanced order of compression, and only appear neb- 

 ulous on account of their very great distance from us. 



A middle state between the progressive condensation of a 

 globular nebula and a cluster of stars can have no ex- 

 istence, because a globular nebulosity when condensed 

 can only produce a single star. A globular cluster may, 

 however, intercept a mass of nebulous matter in motion, 



