348 Dr. A. Schuster's Experiments on Electrical Vibrations. 



If, therefore, dr be negative, the deflection will be greater when 

 the electrical vibrations and the permanent current are passing 

 than when the permanent current alone is passing. This means 

 that the experiments described above could be explained by as- 

 suming that the resistance decreases as the current increases. 

 As we can make e very large without introducing any difficulty 

 in the way of experimenting, we may produce a sensible effect 

 although dr may be very small. It can be shown that with the 

 instruments with which I worked I could have detected a differ- 

 ence in the resistance amounting to J of the whole resist- 

 ance. The change in the resistance which we should have to 

 assume in order to account for the effect observed is easily found. 

 Supposing the current which passes when the constant electro- 

 motive 2x acts alone to be c } the deflection will then be propor- 

 tional to c or ac. Similarly the resultant current which passes 

 when the constant electromotive force acts and the magnet 

 rotates shall be designated by c\ and the deflection observed 

 consequently by «c'. We have then 



2x 

 r 



, 2% x-\- e 7 



etc = 5- dr. 



r r 4. 



Dividing one of these equations by the other, we get 



dr _ c — c' • 2x 

 r s c x + e 



In this equation x means the integral electromotive force 



of the battery acting during half a revolution of the magnet, 



while e means the electromotive force of the moving magnet 



2x 

 during that time. The value of in my experiments was 



generally about 0001 ; was found by experiments to be 



nearly 0*05. It follows from this that 



- = -0-00005. 

 r 



A change in the resistance amounting to such a small frac- 

 tion of the resistance only could not have been detected by the 

 methods which have been hitherto used to verify Ohm's law. 



I shall now pass to a second explanation of the phenome- 

 non, which is, however, a little complicated. If a current of 

 electricity passing through a circuit is increased by any elec- 

 tromotive force, an electromotive force in the opposite direction 



