﻿Resonance and Electrical Interference. 183 



of the subject should be more developed in order to decide, if 

 possible, upon the truth of the various assumptions that have 

 been made, I have continued my studies on the oscillations of 

 electricity with the aid of more powerful methods of studying 

 periodic currents than I had hitherto used. In a paper on 

 the oscillations of lightning discharges *, I expressed the 

 opinion that the method first employed by Spottiswoode, of 

 exciting a Ruhmkorff coil or transformer by means of an 

 alternating-current dynamo, put in the hands of an experi- 

 menter a far more powerful method of studying electrical 

 oscillations than the old method of charging Leyden jars by 

 means of an electric machine, or by the use of a Ruhmkorff 

 coil with a battery. I have, therefore, in this investigation, 

 employed an alternating machine capable of giving 120 volts 

 and a current of from 15 to 25 amperes, and have employed 

 suitable transformers to obtain the necessary difference of 

 potential to produce the sparks which I wished to study. 



Generally I have employed one primary or exciting circuit 

 between two entirely separate and disconnected resonating or 

 secondary circuits. The image of the three sparks thus pro- 

 duced could then be compared upon the same plate. 



Before entering into a more detailed account of the appa- 

 ratus I employed, I will state the most striking results which 

 I have obtained. A unidirectional spark (non-oscillatory) 

 always excites an oscillatory discharge in a secondary circuit 

 if the self-induction, capacity, and resistance of this secondary 

 circuit permit an oscillatory movement. It is therefore not 

 necessary that the spark in a primary circuit should be an 

 oscillating one in order to excite oscillations in a neighbouring 

 conductor. In this respect two electrical circuits are not in 

 close analogy with two tuning-forks. It is difficult by a uni- 

 directional movement of the prongs of one tuning-fork to 

 excite the vibrations of another fork which is not in tune with 

 the first fork. In every secondary circuit, or circuits neigh- 

 bouring to the primary circuit, the first effect of the exciting- 

 unidirectional primary spark is to make the secondary circuits 

 act as if there were no capacity in their circuits. In these 

 circuits a thread-like spark results which is exactly like that 

 produced when all the capacity in the secondary circuits is 

 removed. After a short interval of time the electricity rushes 

 into the condensers and begins to oscillate, the strength of the 

 oscillations rising, after one or two vibrations, to a maximum 

 and then decreasing ; the rate of oscillation finally assumes a 

 steady state, and is expressed by the formula t=27r VLC. 



* Phil. Mag. October 1893. 



