132 SCIENTIFIC THOUGHT. 



mechanism, they will have this property of a perfect 



machine, namely, that it can work backward as well as 



25. forward. It is against all reason and common-sense 



Summary 



i ts integrity and completeness. 



Kelvin). " The essence of Joule's discovery is the subjection of 

 physical phenomena to dynamical law. If, then, the 

 motion of every particle of matter in the universe were 

 precisely reversed at any instant, the course of nature 

 would be simply reversed for ever after. The bursting 

 bubble of foam at the foot of a waterfall would reunite 

 and descend into the water ; the thermal motions would 

 reconcentrate their energy and throw the mass up the 

 fall in drops, re-forming into a close column of ascending 

 water. Heat which had been generated by the friction 

 of solids and dissipated by conduction and radiation with 

 absorption, would come again to the place of contact and 

 throw the moving body back against the force to which 

 it had previously yielded. Boulders would recover from 

 the mud the materials required to rebuild them into 

 their previous jagged forms, and would become re-united 

 to the mountain - peak from which they had formerly 

 broken away. And also, if the materialistic hypothesis 

 of life were true, living creatures would grow backwards 

 with conscious knowledge of the future, but with no 

 memory of the past, and would become again unborn. 

 But the real phenomena of life infinitely transcend 

 human science ; and speculation regarding consequences 

 of their imagined reversal is utterly unprofitable. Far 

 otherwise, however, is it in respect to the reversal of the 

 motions of matter uninfluenced by life, a very elementary 

 consideration of which leads to the full explanation of 



