NEBULAR HYPOTHESIS. 187 



in which the nebulous matter was more and more 

 diffuse, the nucleus being less and less luminous. 

 We arrive," Laplace says, " in this manner, at 

 a nebulosity so diffuse, that its existence could 

 scarcely be suspected." 



" Such is," he adds, " in fact, the first state 

 of the nebulae which Herschel carefully observed 

 by means of his powerful telescopes. He traced 

 the progress of condensation, not indeed on one 

 nebula, for this progress can only become per- 

 ceptible to us in the course of centuries ; but in 

 the assemblage of nebulae ; much in the same 

 manner as in a large forest we may trace the 

 growth of trees among the examples of different 

 ages which stand side by side. He saw in the 

 first place the nebulous matter dispersed in 

 patches, in the different parts of the sky. He 

 saw in some of these patches this matter feebly 

 condensed round one or more faint nuclei. In 

 other nebulae, these nuclei were brighter in pro- 

 portion to the surrounding nebulosity ; when by 

 a further condensation the atmosphere of each 

 nucleus becomes separate from the others, the 

 result is multiple nebulous stars, formed by bril- 

 liant nuclei very near each other, and each sur- 

 rounded by an atmosphere : sometimes the nebu- 

 lous matter condensing in a uniform manner has 

 produced nebulous systems which are called 

 planetary. Finally, a still greater degree of con- 

 densation transforms all these nebulous systems 



