INDUCED RESISTANCE. 39 



accurately the relative current with the galvanometer, the 

 resistance and velocity of the machine, obtaining what 

 he now calls work, and perhaps most important, he now 

 estimates that portion of the zinc consumed in his batteries, 

 which is effective in producing current ; thus obtaining 

 the work done per pound of zinc, which he expresses, after 

 the manner of engineers, as ' duty.' He has thus made 

 complete tests of the machine in every particular, varying 

 the resistance, the velocity, and the quantity and intensity 

 of the current. 



All this implies that since his last paper he has received 

 much fresh light ; whether or not this is solely the result of 

 his own researches, is not stated in the paper, but from the 

 manner in which he commences the discussion of the 

 results, it may be inferred that it is not. 



The results, as stated, show clearly, that although the 

 resistance overcome is as the square of the current in all 

 cases, verifying his law of attraction as applied to the 

 moving armature, the current and resistance overcome 

 diminish as the speed increases — indicating clearly the 

 induced resistance (Faraday's) in the wire caused by the 

 motion of the machine, showing him that with a constant 

 battery the force of his engine diminishes as the 

 speed increases ; thus revealing the fundamental limit to 

 speed. Considering that he, in consequence of not 

 being aware of this induced resistance, or having 

 over-looked it, has been labouring for more than two 

 years trying to realize impossibilities, and that at the very 

 first start his experiments suggested to him the existence 

 of some limit to speed, he could hardly have discovered 

 this internal resistance for himself without making some 

 comment upon his discovery — whereas what he says is : 



