HEAT IN METALLIC CONDUCTORS. 47 



tional to the electric action, in Oersted's measure, expended 

 in its production, and that the chemical action was also 

 proportional to the electric action. There were two possible 

 inferences to be drawn from these proportionalities. It 

 might be inferred, as Joule was subsequently led to infer, 

 that the chemical effect was convertible into mechanical 

 effect in a definite ratio, and thus had a definite mechanical 

 equivalent ; the electric action being the agent of conversion. 

 On the other hand, it might be inferred that without being 

 convertible, or being in any way primarily related, the 

 chemical effect and the mechanical effect were each quanti- 

 tatively related to the electric action. This second inference 

 was that which Joule at first drew. He does not explicitly 

 say so, but it may be clearly inferred from the subsequent 

 line of his work that the discovery of these proportionalities 

 suggested to him the existence of definite equivalents 

 amongst all the effects, resulting in or produced by a definite 

 amount of electric action, as a consequence of the existence 

 of quantitative relations between the several effects and the 

 electric action. 



In order to test these views he first investigates 

 the heat produced by a current, and establishes, for the 

 first time, that in a stationary conductor the amount of 

 heat produced by a given current is proportional to the 

 square of the current. He then proceeds to determine 

 the quantitative relations between the heat produced, 

 the current, and the resistance of his conductor. Taking 

 for his units the heat required to raise 2lb. of water 

 one degree Fahrenheit, the current necessary to effect the 

 separation of 9 grains of water in one hour, and the 

 resistance of a definite piece of copper wire, which he takes 

 as his standard throughout this paper, and subsequently 



