THE HERSCHELS AND THE STAR-DEPTHS. 19 



opinion of the arrangement of the stars and their 

 magnitudes, and of some other particulars, has under- 

 gone a gradual change ; and, indeed, when the novelty 

 of the subject is considered, we cannot be surprised that 

 many things, formerly taken for granted, should on 

 examination prove to be different from what they were 

 generally but incautiously supposed to be. For instance, 

 an equal scattering of the stars may be admitted in 

 certain calculations ; but when we examine the Milky 

 Way, or the closely-compressed clusters of stars, this 

 supposed equality of scattering must be given up. We 

 may also have surmised nebulae to be no other than 

 clusters of stars disguised by their very great distance, 

 but a longer experience and better acquaintance with 

 the nature of nebulae will not allow a general admission 

 of such a principle, although undoubtedly a cluster of 

 stars may assume a nebulous appearance when it is 

 too remote for us to discern the stars of which it is 

 composed. 



The new views respecting the constitution of the 

 heavens, introduced in this paper, related chiefly to 

 those nebulae which, though otherwise conspicuous, yet 

 when examined even under the highest powers of Sir 

 W. Hersdjel's largest telescope, presented a milky 

 appearance. He now for the first time expressed the 

 opinion that such nebulae do not consist of multitudes 

 of stars, but of some self-luminous substance of exceed- 

 ing tenuity. He recognised the existence of this 

 luminous vapour amidst large tracts of the heavens ; 

 and he regarded it as certainly lying within the limits 



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