278 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK in. 



moon, and planets, and of tliose more distant masses of matter, 

 star-clusters and nebulae. 



But it is not the curiosities or tlie wonders of the heavens 

 alone which we must pass under review; it is not only the depths 

 of infinite space where the systems of stars and nebulae shine that 

 must be explored. We must insist above and before all upon the 

 progress which the use of these instruments has rendered possible 

 in exact astronomy, and in the sublime theories which now explain 

 all the laws of the heavenly movements by considering the entire 

 universe as a system of bodies and. forces reacting one against the 

 other a system offering to geometry, on an infinite scale, the most 

 admirable applications of the theories of rational mechanics. 



