1866] WRITINGS OF JOSEPH HENRY. 457 



REMARKS ON "VITALITY."* 

 (From the Smithsonian Annual Keport for 18C6, pp. 886-388.) 



In the early study of mechanical and physiological phe- 

 nomena, the energy which was exhibited by animals, or in 

 other words, their power to perform what is technically 

 called work, that is to overcome the inertia and change the 

 form of matter, was referred to the vital force. A more criti- 

 cal study of these phenomena has however shown that this 

 energy results from the mechanical power stored away in 

 the food and material which the body consumes; that the 

 body is a machine for applying and modifying power, pre- 

 cisely similar to those machines invented by man for a 

 similar purpose. Indeed, it has been shown by accurate 

 experiments that the amount of energy developed in animal 

 exertion is just in proportion to the material consumed. To 

 give a more definite idea of this, we may state the general 

 fact that matter may be considered under two aspects, namely 

 matter in a condition of power, and matter in a state of entire 

 inertness. For example, the weight of a clock or the spring 

 of a w^atch when wound up is in a state of power, and in its 

 running down gives out, tick by tick, an amount of power 

 precisely equal to the muscular energy expended in winding 

 it up. When the weight or the spring has run down, it is 

 then in a condition of inertness, and will continue in this 

 state, incapable of producing motion, unless it be again 

 put in a condition of power by the application of an extrane- 

 ous force. Again, coal and other combustible bodies consist 

 of matter in a condition of power, and in their running down 

 into carbonic acid and water, during their combustion, evolve 

 the energy exhibited in the operations of the steam engine. 

 The combustible material may be considered the food of the 

 steam engine, and experiments have been made to ascertain 



* [Remarks on a communication "On Vitalitj," by the Rev. H. H. Hig- 

 gin.9, in the Proceedings of the Literary and Philosophical Society of Lirer- 

 pool, (England,) 1864. Re-printed in the Smithsonian Report for 1866, pp. 

 879-886.] 



