214 INTERACTION OF NATURAL FORCES. 



ing brains, to lead them round a circle for years, deceiving 

 ever with new expectations, which vanished upon nearer ap- 

 proach, and finally reducing these dupes of hope to open in- 

 sanity. 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 

 proceedings 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 mathemati- 

 cal 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 compar- 

 ing their arrangements with those of men and animals to 

 replace which they were applied. We still reckon the work 

 of steam engines according to horse-power. The value of 

 manual labor is determined partly by the force which is ex- 

 pended in it (a strong laborer is valued more highly than a 

 weak one) , partly however, by the skill which is brought into 

 action. A machine, on the contrary, which executes work 

 skilfully, can always be multiplied to any extent ; hence its 

 skill has not the high value of human skill in domains where 

 the latter cannot be supplied by machines. Thus the idea of 

 the quantity of work in the case of machines has been limited 

 to the consideration of the expenditure of force ; this was the 

 more important, as indeed most machines are constructed for 

 the express purpose of exceeding, by the magnitude of their 



