ON THE CONSEHVATION OF FORCE. 361 



You see how, starting from considerations based on the 

 immediate practical interests of technical work, we have 

 been led up to a universal natural law, which, as far as 

 all previous experience extends, rules and embraces all 

 natural processes ; which is no longer restricted to the 

 practical objects of human utility, but expresses a per- 

 fectly general and particularly characteristic property of 

 all natural forces, and which, as regards generality, is 

 to be placed by the side of the laws of the unalter- 

 ability of mass, and the unalterability of the chemical 

 elements. 



At the same time, it also decides a great practical 

 question which has been much discussed in the last two 

 centuries, to the decision of which an infinity of experi- 

 ments have been made and an infinity of apparatus con- 

 structed — that is, the question of the possibility of a per- 

 petual motion. By this was understood a machine which 

 was to work continuously without the aid of any external 

 driving force. The solution of this problem promised 

 enormous gains. Such a machine would have had all the 

 advantages of steam without requiring the expenditure of 

 fuel. Work is wealth. A machine which could produce 

 work from nothing was as good as one which made gold. 

 This problem had thus for a long time occupied the place 

 of gold making, and had confused many a pondering 

 brain. That a perpetual motion could not be produced 

 by the aid of the then known mechanical forces could be 

 demonstrated in the last century by the aid of the mathe- 

 matical mechanics which had at that time been developed. 

 But to show also that it is not possible even if heat, 

 chemical forces, electricity, and mag-netism were made to 

 co-operate, could not be done without a knowledge of 

 our law in all its generality. The possibility of a per- 

 petual motion was first finally negatived by the law of 

 the conservation of force, and this law might also be ex- 



