Dr. A. Schuster's Experiments on Electrical Vibrations. 319 



is set up in the circuit, owing to what we call self-induction. 

 It is assumed that this electromotive force is proportional to 

 the rate of increase of the current ; so that, if that rate is a 

 negative quantity, an electromotive force in the same direction is 

 set up. If we could imagine some state of things so that this 

 self-induction would not depend merely upon the rate of in- 

 crease of the current, but also in part upon the current passing 

 through the circuit, my experiments would find an easy expla- 

 nation. In order to fix our ideas I shall make certain hypo- 

 theses, and show how the different facts can be accounted for 

 by means of them. "While the current increases it has to 

 establish its own lines of force, and is therefore doing work. 

 The weakening of the current due to self-induction is assumed 

 to be due to this work. The establishment of the lines of 

 force may, however, not be the only work the current has to do. 

 Suppose the current places the particles of copper in a certain 

 way, and suppose that this magnetization of the copper par- 

 ticles, as it may be called, approaches a maximum as the current 

 increases. It is easy to see that in this hypothetical case the 

 self-induction of a current will be smaller if the original current 

 passing through the circuit was strong than if it was weak. It is 

 also evident that the self-induction will be weaker when a cur- 

 rent is increased than when it is decreased by a certain amount. 

 A rotating magnet will therefore induce currents of unequal 

 strength in a wire through which a permanent current passes, 

 as the current induced in the same direction as the original 

 current will be stronger than that induced in the opposite direc- 

 tion. This would agree with the observed facts. 



V. Conclusion. 



It is impossible to decide by the experiments which I have 

 made which of these two explanations is the correct one ; and 

 it will be very difficult to decide this by further experimenta- 

 tion. Whenever we use currents of varying intensity, both 

 the causes suggested will give the same result. We should 

 therefore have to use only constant currents. Unfortunately 

 we have to meet great practical difficulties if we want to use 

 constant currents. The greatest of these difficulties is the 

 change of resistance by increase of temperature. I need not go 

 into this any further here. 



The above paper was read in a slightly different form before 

 Section A of the British Association at Belfast. As it is of some 

 importance to see whether Ohm's law is rigidly correct or not, 

 the British Association has appointed a Committee for the pur- 

 pose of verifying the law experimentally. If the result should 

 be that the law is correct within the limits in which we should 



