488 HISTORY OF PHYSICAL ASTRONOMY. 



sisted upon by other persons ; — namely, the hypothesis that systems of 

 revolving planets, of which the Solar System is an example, arise from 

 the gradual contraction and separation of vast masses of nebulous mat- 

 ter. Yet it does not appear that any changes have been observed in 

 nebulas which tend to confirm this hypothesis ; and the most powerful 

 telescope in the world, recently erected by the Earl of Rosse, has given 

 results which militate against the hypothesis; inasmuch as it has 

 shown that what appeared a diffused nebulous mass is, by a greater 

 power of vision, resolved, in all cases yet examined, into separate stars. 

 When astronomical phenomena are viewed with reference to the 

 Nebular Hypothesis, they do not belong so properly to Astronomy, in 

 the view here taken of it, as to Cosmogony. If such speculations 

 should acquire any scientific value, we shall have to arrange them 

 among those which I have called Pal (Etiological Sciences; namely, 

 those Sciences which contemplate the universe, the earth, and its in- 

 habitants, with reference to their historical changes and the causes of 

 those changes.] 



