M? J 



456 Prof. J. J. Thomson on the Discharge of Electricity 



produces it. Thus a high maximum value, lasting only for 

 a short time, might produce a discharge, while a more 

 equable distribution of electromotive intensity having the 

 same average value might leave the tube quite dark. 



I have employed these discharges to study the behaviour of 

 bodies under the action of very rapid electrical oscillations 

 in the following way. In the primary circuit connecting 

 the outside coatings of the jar, two loops A and B (fig. 15) 

 were made, in one of which, A, an 

 exhausted bulb was placed, the spark- Fig. 15. 



length and the pressure of the gas on 

 it being adjusted until the discharge 

 was sensitive, i. e. until a small alter- 

 ation in the electromotive intensity 

 acting on the bulb produced a con- 

 siderable effect upon the appearance 



presented by the discharge. The ^^-P Q/B 



substance whose behaviour under ^^___-^ 



rapid electrical vibrations was to be 



examined was placed in the loop B. The results got at first 

 were very perplexing, and at first sight contradictory, and it 

 was some time before I could see their explanation. The 

 following are some of these results. When a highly exhausted 

 bulb was placed in B a brilliant discharge passed through it, 

 while the discharge in A stopped. A bulb of the same size, 

 filled with a dilute solution of electrolyte, produced no appre- 

 ciable effect; when filled with a strong solution it dimmed the 

 discharge in A, but not to the same extent as the exhausted 

 bulb. A piece of brass rod or tube increased the brightness of 

 the discharge in A ; on the other hand, a similar piece of iron 

 rod or tube stopped the discharge in A at once. The most 

 decided effect, however, was produced by a small crucible 

 made of plumbago and clay : this when put in the loop B 

 stopped the discharge in A completely. I found, however, 

 that by considering the work spent on the substance placed 

 in B, the preceding results could be explained. When a 

 large amount of work is spent in B, the discharge in A will 

 be dimmed, while no appreciable effect will be produced on A 

 when the work spent in B is small. Now let us consider the 

 work done in a secondary circuit whose resistance is R, whose 

 coefficient of self-induction is L, and which has a coefficient 

 of mutual induction M with the primary circuit. If the 

 frequency of the current circulating in the primary is p, we 

 can easily prove that the rate of absorption of work by the 

 secondary is proportional to 



BMy 

 hy+R 2 ' 



