40 MECHANICAL EQUIVALENT OF ELECTRIC EFFECT. 



"The above examples will show pretty clearly the effects 

 of magnetic internal resistance. This resistance is the 

 prime obstacle to the perfection of the electro-magnetic 

 engine ; and in proportion as it is overcome will the 

 motive force increase. It therefore claims our first attention." 

 This suggests that he had become aware that this resistance 

 was previously known. A view, which is confirmed by 

 his attributing, in a subsequent paper, Feb. 16, 1841, the 

 discovery, without determining the laws of this internal resist- 

 ance, to Professor Jacobi, and also to his giving references 

 to Faraday s Experimental Researches ; Scoresbys Magnetic 

 Researches, Xesbit and Henry, in a paper, written in 

 August 28, 1840, which are almost the first reference 

 contained in his papers to the works of other investigators, 

 and thus indicate that he had recently been reading 

 as v.ell as investigating. Joule is not, however, content 

 with recognizing this internal resistance, but has made 

 a complete experimental determination of its law — "that 

 it is proportional to the product of the velocity of rotation 

 multiplied by the magnetism." This statement is equivalent 

 to saying that the electric action spent in overcoming the 

 resistance induced in the machine, namely, the product of 

 the current multiplied by the induced resistance, is pro- 

 portional under all circumstances to the product of the 

 square of the current multiplied by the velocity of the 

 machine ; and this is also proportional to the mechanical 

 effect ; so that Joule had now proved that there are quan- 

 titative equivalents in mechanical effect for the electric 

 action (product of electro-motive force multiplied by 

 current), and for the chemical action expended in pro- 

 ducing the mechanical effect. 



He then continues his researches on magnetic forces 



