220 WRITINGS OP JOSEPH HENRY. [1844 



numerical details of these are reserved however until the 

 experiments can be repeated with a more delicate balance. 



The comparative cohesion of pure water and soap water 

 was determined by the weight necessary to detach the same 

 plate from each ; and in all cases the pure water required 

 the greater force. The want of permanency in the bubble 

 of pure water is therefore not due to feeble attraction, but 

 to the perfect mobility of the molecules, which causes the 

 equilibrium, as in the case of the arch without friction of 

 parts, to be destroyed by the slightest extraneous force. 



Several other experiments with films of soap water were 

 also described, which afford striking illustrations of the 

 principles of capillarity, and which apparently have an im- 

 portant bearing on the whole subject of cohesion.* 



ON THE ORIGIN AND CLASSIFICATION OF THE NATURAL MOTORS. 



(Proceedings of the American Philosophical Society, vol. iv,pp. 127-129.) 



December 20, 1844. 



Professor Henry made an oral communication in regard 

 to some speculations in which he had indulged relative to 

 the classification and origin of mechanical power. 



He stated that he was indebted for the origin of this train 

 of thought to some remarks made by Mr. Babbage in his 

 work on the economy of machinery, and to the late researches 

 of the German and French chemists on the subject of vital 

 chemistry; indeed all the views contained in the communi- 

 cation might perhaps be found in detached portions in 

 diflPerent works, but he believed that they had never before 

 been brought together and presented as a whole. 



He defined mechanical power to be that which is capable 

 of overcoming a constant resistance, and of producing a con- 

 tinued motion; or in the language of the engineer, it is that 

 which can be employed to "do work." It is here used in a 



*[Reprinted in Silliman's American Journal of Science, October, 1844. 

 Vol. XLViii, pp. 215-217. Also in the London and Edinburgh Philosophi- 

 cal Magazine, June, 1845. Vol. xxvi, pp. 541-543.] 



