-1859] WRITINGS OF JOSEPH HENRY. 135 



The general conclusion which has been arrived at is that 

 the different physical energies — whether called chemical 

 action, heat, light, electricity, magnetism, muscular mo- 

 tion, or mechanical power, are all referable to the disturbance 

 of the equilibrium of the atoms and the subsequent resto- 

 ration due to their attractions and repulsions; and that all 

 these forms of energy are in one sense convertible into each 

 other, or in other words the force generated in the restora- 

 tion of the equilibrium in one case is sufficient to disturb it, 

 though in a different form perhaps, in another. We must 

 guard against the erroneous idea w-hich some have incon- 

 siderately adopted, that one form of power can be actually 

 converted into another, as heat into electricity, or the con- 

 verse. The theory of energy merely declares that the 

 power exhibited in the electrical discharge is the equiva- 

 lent of the muscular energy expended in charging the 

 battery, and not that muscular energy is converted into 

 electricity. 



The origin of heat produced by friction for a long time 

 perplexed the most sagacious philosophers. Our celebrated 

 and ingenious countryman, Count Rumford, caused a quan- 

 tity of water to boil for several hours by the heat generated 

 in boring a cannon; and after the process was ended, he 

 found that the borings and the cannon contained as much 

 heat as at the commencement of the experiment. From 

 this result he boldly proclaimed that heat was not matter, 

 but the vibrations of the atoms of matter, and that in his 

 experiment the heat was generated by the friction of the 

 drill on the metal. 



Later researches have constantly tended to strengthen 

 the probability of this view, and even to establish the gen- 

 eral fact, that when mechanical power is produced by the 

 expenditure of heat, a quantity of heat disappears, bearing 

 a fixed proportion to the power produced ; and conversely, 

 that when heat is produced by the expenditure of mechani- 

 cal power, the quantity of heat produced bears a fixed pro- 

 portion to the power expended. Thus in the case of a 

 steam engine doing no work, the quantity of heat given 



