PORTION OF THE COSMOS. ASTEOGN03Y. 29 



In order to divide conveniently into groups the principal 

 results of actual observation,, and the conclusions or con^ 

 jectures to which they lead, I propose to distinguish, in the 

 astrognostic portion of the description of the Universe, the 

 following heads : 



I. Considerations on space, and on what is supposed to 

 occupy it. 



II. Natural and telescopic vision; the scintillation of stars ; 

 the velocity of light ; and photometric experiments on the 

 intensity of sidereal light. 



III. The number, distribution, and colour of stars; clusters 

 of stars ; and the milky way, in which are only a few nebulae. 



IY. Newly appeared stars; vanished stars; and stars 

 which vary periodically. 



V. The proper motion of the fixed stars ; the problematical 

 existence of dark bodies ; the parallax and measured distance 

 of some fixed stars. 



VI. Double stars, and their periods of revolution round a 

 common centre of gravity. 



VII. Nebulae, which in the Magellanic clouds are inter- 

 mixed with many clusters of stars ; and the black spots or 

 patches in the sky (" coal-bags"). 



