ON THE INTERACTION OF NATURAL FORCES. 155 



experience which a later time knew how to take advan- 

 tage of. We no longer seek to build machines which 

 shall fulfil the thousand services required of one man, 

 but desire, on the contrary, that a machine shall perform 

 one service, and shall occupy in doing it the place of a 

 thousand men. 



From these efforts to imitate living creatures, another 

 idea, also by a misunderstanding, seems to have developed 

 itself, and which, as it were, formed the new philosopher's 

 stone of the seventeenth and eighteenth centuries. It 

 was now the endeavour to ..construct a perpetual motion. 

 Under this term was understood a machine, which, 

 without being wound up, without consuming in the 

 working of it falling water, wind, or any other natural 

 force, should still continue in motion, the motive power 

 being perpetually supplied by the machine itself. Beasts 

 and human beings seemed to correspond to the idea of 

 such an apparatus, for they moved themselves ener- 

 getically and incessantly as long as they lived, and 

 were never wound up ; nobody set them in motion. A 

 connexion between the supply of nourishment and the 

 development of force did not make itself apparent. The 

 nourishment seemed only necessary to grease, as it 

 were, the wheelwork of the animal machine, to replace 

 what was used up, and to renew the old. The develop- 

 ment of force out of itself seemed to be the essential 

 peculiarity, the real quintessence of organic life. If, 

 therefore, men were to be constructed, a perpetual motion 

 must first be found. 



Another hope also seemed to take up incidentally the 

 second place, which in our wiser age would certainly have 

 claimed the first rank in the thoughts of men. The per- 

 petual motion was to produce work inexhaustibly without 

 corresponding consumption, that is to say, out of nothing. 

 Work, however, is money. Here, therefore, the great 

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