I. 



CONSTITUTION OF NATURE. 1 



WE cannot think of space as finite, for wherever 

 in imagination we erect a boundary, we are com- 

 pelled to think of space as existing beyond it. Thus 

 by the incessant dissolution of limits we arrive at a 

 more or less adequate idea of the infinity of space. 

 But, though compelled to think of space as unbounded, 

 there is no mental necessity compelling us to think of 

 it either as filled or empty ; whether it is so or not must 

 be decided by experiment and observation. That it is 

 not entirely void, the starry heavens declare ; but the 

 question stiIT~rernains, Are the stars themselves hung 

 in vacuo ? Are the vast regions which surround them, 

 and across which their light is propagated, absolutely 

 empty ? A century ago the answer to this question, 

 founded on the Newtonian theory, would have been, 

 ' No, for particles of light are incessantly shot through 

 space.' The reply of modern science is also negative, 

 but on different grounds. It has the best possible 

 reasons for rejecting the idea of luminiferous particles ; 

 but, in support of the conclusion that the celestial 

 spaces are occupied by matter, it is able to offer proofs 



1 'Fortnightly Review,' 1865, vol. iii. p. 129. 



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