ON THE INTERACTION OF NATUHAL FORCES. 193 



have given place to us and our fellow-creatures which 

 now exist. 



Thus the thread which was spun in darkness by those 

 who sought a perpetual motion has conducted us to a uni- 

 versal law of nature, which radiates light into the distant 

 nights of the beginning and of the end of the history of 

 the universe. To our own race it permits a long but not 

 an endless existence ; it threatens it with a day of judg- 

 ment, the dawn of which is still happily obscured. As 

 each of us singly must endure the thought of his death, 

 the race must endure the same. But above the forms of 

 life gone by, the human race has higher moral problems 

 before it, the bearer of which it is, and in the completion 

 of which it fulfils its destiny. 



