156 ON THE INTERACTION OF NATURAL FORCES. 



practical problem which the cunning heads of all cen- 

 turies have followed in the most diverse ways, namely, to 

 fabricate money out of nothing, invited solution. The 

 similarity with the philosopher's stone sought by the 

 ancient chemists was complete. That also was thought 

 to contain the quintessence of organic life, and to be 

 capable of producing gold. 



The spur which drove men to inquiry was sharp, and 

 the talent of some of the seekers must not be estimated 

 as small. The nature of the problem was quite calcu- 

 lated to entice poring brains, to lead them round a circle 

 for years, deceiving ever with new expectations which 

 vanished upon nearer approach, and finally reducing these 

 dupes of hope to open insanity. The phantom could not 

 be grasped. It would be impossible to give a history of 

 these efforts, as the clearer heads, among whom the elder 

 Droz must be ranked, convinced themselves of the futility 

 of their experiments, and were naturally not inclined to 

 speak much about them. Bewildered intellects, however, 

 proclaimed often enough that they had discovered the 

 grand secret ; and as the incorrectness of their proceed- 

 ings was always speedily manifest, the matter fell into bad 

 repute, and the opinion strengthened itself more and 

 more that the problem was not capable of solution ; one 

 difficulty after another was brought under the dominion 

 of mathematical mechanics, and finally a point was 

 reached where it could be proved, that at least by the use 

 of pure mechanical forces no perpetual motion could be 

 generated. 



We have here arrived at the idea of the driving force 

 or power of a machine, and shall have much to do with it 

 in future. I must therefore give an explanation of it. 

 The idea of work is evidently transferred to machines by 

 comparing their performances with those of men and 

 animals, to replace which they were applied. We still 



