602 BIBLIOGRAPHY OF HERSCHEL's WRITINGS. 



Herschel, W.: Synopsis of the Writings of— Continued. 

 A.D. Vol. p. 



1814 104 254 The idea of a nebula with a nucleus which gradually assumed the 

 lustre of a star is more probable than the fortuitous central meet- 

 ing of a star and nebula. 

 V. Of nebulous stars. 

 Thirteen are noted — see also Phil. Trans., 1791. p. 71. 



255 Nebulous stars are not only connected Avith a nebulosity, which, from 



its great regularity, might be taken for an atmosphere, but also 

 with the luminous appearances belonging to the nebulous matter 

 ♦ which is so widely expanded in various regions of the heavens. 



What has been said of the gradual condensation of the nebulous 

 matter in the case of extended nebula, is supported by a much 

 greater number of nebulosities in aspherical form. [See Phil. Trans., 

 1811, pp. 301-8.] 322 cases are there mentioned, in which the fact 

 of the gradual condensation is rendered so evident as not to admit 

 of a doubt. 



256 Nebulous stars only differ from round nebula? containing a nucleus 



in the degree of condensation. 

 25G VI. Of Stars counccted with extensive xvindings of nebulosity. 



Three cases noted. The nebulosity which has been shown to be con- 

 nected with stars, may be fully proved to be of the same nature as the 

 general mass of nebulous matter. 



Stars of til is class are in a condition of growth. 



257 Possibility that stars were originally formed by a condensation of the 



nebulous matter. 

 We may conceive both the generation and growth of stars to be the 

 legitimate effects of the law of gravitation, to which the nebulous 

 matter is proved by observation to be subject. 



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. Nebulas are subject to great changes in 



their appearance, as the nebula of Orion. [^Phil. Trans., 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 continued. 



VIII. Of objects of an ambiguous construction. 



Clusters of stars at a great distance may assume a nebulous appear- 

 ance. IPhil. Trans., 1811, p. 270.] 



Telescopes of gradually increasing space-penetrating powers show 

 certain objects successively as nebula), mixtures of nebulosity and 

 stars, and as true clusters; other objects, so viewed, increase in 

 brightness, and the nebulosity becomes more uuiibrmly united and 

 of a milky appearance, aud these are purely nebulous. 



260 Definition of ambiguous objects, their classilicatlon 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. 



