320 NOTES TO BOOK VII. 



just been said of the observations of Double Stars ; 

 that they probably contain the materials of important 

 future discoveries. It is impossible not to regard these 

 phenomena with reference to the Nebular Hypothesis, 

 which has been propounded by Laplace, and much more 

 strongly insisted upon by other persons ; namely the 

 hypothesis that systems of revolving planets, of which the 

 Solar System is an example, arise from the gradual con- 

 traction and separation of vast masses of nebulous matter. 

 Yet it does not appear that any changes have been ob- 

 served in nebulae 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 shewn 

 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 refer- 

 ence 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 Palcetiological Sciences ; namely, 

 those Sciences which contemplate the universe, the earth, 

 and its inhabitants, with reference to their historical 

 changes and the causes of those changes. 



I have, in this note as in other places, used freely 

 Professor Airy's valuable Report on tlie Progress of Astro- 

 nomy during the present Century, printed in the Reports of 

 the British Association for 1832. 



