136 CELESTIAL PHENOMENA. 



covered luminous or non-luminous central body, however 

 naturally we may be disposed to an inference which would 

 gratify alike the imaginative faculty, and that intellectual 

 activity which ever seeks after the last and highest generalisa- 

 tion. Even the Stagirite has said, " All that moves leads 

 us back to the cause of the motion which we perceive ; and 

 it would be but an endless derivation of causes, were there 

 not a primary mover itself at rest( 103 )." 



Amongst the manifold changes of place of stars in groups, 

 not occasioned by parallax depending on the place of 

 the observer, but actual changes taking place progressively 

 and uninterruptedly in space, we have revealed to us in 

 the most incontestable manner by one phenomenon, the 

 orbital movements of double stars, and their variable 

 motion in different parts of their elliptical orbits, the 

 dominion of the laws of gravitation, extending far beyond 

 the limits of our solar system, even to the remotest regions 

 of creation. On this subject man's desire of knowledge need 

 no longer rest on vague conjecture, or seek satisfaction in 

 the boundless but uncertain field of analogy, for here also 

 the progress of astronomical observation* and calculation has 

 at length placed us on firm ground. It is not so much the 

 astonishing number already discovered of double or multiple 

 etars revolving round a common center of gravity 

 (a number which, in 1837, amounted to 2800), as it 

 is the extension of our knowledge of the fundamental forces 

 of the whole material world, and the evidence thus afforded 

 of the universal prevalence of the law of gravitation, 

 which excites our admiration, and constitutes one of the 

 most brilliant discoveries of our epoch. The time of 

 revolution of differently -coloured double stars varies ex- 

 ceedingly in different instances, from 43 years in 77 Coronse, 



