SECT. xxxvii.J NUMBEK OF NEBULE. 433 



As the sun is only a unit in the stellar system, so the 

 Milky Way, and all the stars that adorn the firmament of 

 both hemispheres, constitute a group which is but a unit 

 among the infinite numbers of starry clusters and nebulae 

 that are profusely scattered throughout the universe. 



By the aid of a good telescope there may be seen on the 

 clear vault of heaven, between the stars of our own stellar 

 system, and far in the depths of space, an immense multi- 

 tude of objects like clouds of white vapour of all forms and 

 sizes. Some are mixed with stars, others are entirely formed 

 of them. Many appear as if they were stellar, but required 

 a telescope of higher power to resolve them, and vast 

 numbers appear to be matter rarefied in the highest pos- 

 sible degree, giving no indication of a stellar nature ; and 

 these are in every state of condensation, from a vague film 

 hardly to be discerned to such as have actually arrived at a 

 solid nucleus. Probably the cloudy appearance in many 

 instances is merely the blending of the rays of innumerable 

 stars, which are themselves invisible from their extreme 

 distance, like parts of the Milky Way. . Sir William Her- 

 schel was at first of that opinion, and the nebulae that have 

 been resolved by Lord Ross's telescope have led astronomers 

 to believe that such may be the case. Yet the tails of 

 comets, the zodiacal light, and the extensive luminous 

 atmospheres which encompass many of the stars, show that, 

 in all probability, a self-luminous phosphorescent material 

 substance in a highly diluted or gaseous form exists in 

 vast abundance. 



The number of the nebulae, like that of the stars, is only 

 limited by the imperfection of our instruments, for each 

 improvement in the telescope only enables us to penetrate 

 a little farther into the infinity of space to see a few more 

 of these shadowy existences in the far distance, and to 

 resolve a few more of those that are comparatively near; 

 Sir William Herschel examined the nature and determined 

 the position of 2500 nebulae in the northern hemisphere 



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