PORTION OF THE COSMOS. CONCLUSION. 449 



The examination of the means, or methods, by which we 

 have thus arrived at the comprehension of the Universe, 

 and the explanation of the intricate phenomena of the 

 heavens, do not belong to the plan of the present work. 

 The " Physical Description of the Universe" tells of the con- 

 tents of space, and of the organic life which animates it, in 

 the two spheres of uranologic and telluric relations. It 

 dwells on the discovered laws of nature, and treats them as 

 facts achieved and ascertained, as the direct results of empi- 

 rical induction. In order that a work on the Cosmos might 

 be executed within its appropriate limits, and without ac- 

 quiring an immoderate extension, it was necessary that it 

 should not attempt to propound theoretically the bases of 

 the connection of phsenomena. In the view of this limita- 

 tion of the proposed plan, I have devoted the more dili- 

 gent care, in this astronomical volume of the Cosmos, to 

 the several facts and to the order of their arrangement. 

 From the consideration of cosmical space, i. e. its tempera- 

 ture, its degree of transparency, and the resisting medium 

 which fills it, I have proceeded to the subjects of natural and 

 telescopic vision ; the limits of visibility ; the velocity of 

 light according to its different sources ; our imperfect mea- 

 surements of the intensity of light ; and the new optical 

 means of discriminating between direct and reflected light. 

 Then follow, the heaven of the fixed stars ; the numbers of 

 its self-luminous suns, so far as their positions are known to 

 us, and their probable distribution ; the variable stars which 

 have well-measured periods; the proper motions of the 

 fixed stars ; the hypothesis of the existence of dark bodies, 

 and their influence on the motions of double stars ; and 



