﻿230 Mr. J. A. Brown on the Potential required 



the original direction. In other words, if, for example, at 

 first the sparking potential was taken with the top plate (A) 

 positive, and then the poles reversed, and without running the 

 current further the sparking potential determined with A 

 negative, its value now would be considerably lower than it 

 was at first with A positive. Running the current with A 

 negative, however, would bring the sparking potential up to 

 the same value as that obtained originally for A positive. 

 If now the poles were again reversed without running the 

 current, A positive would in turn be at first lower, gradually 

 rising to its original value. Table IV. shows a typical set of 

 observations which will make this effect clear. 



It looks as if there might perhaps be some kind of polari- 

 zation-effect on the glass walls of the spark-gap, caused possibly 

 by ions adhering to the sides which would tend to affect the 

 uniformity of the field between the plates. Whatever the 

 cause, it is an effect that only enters into the determination 

 of the sparking potential, as no similar phenomenon was 

 noticed in the value for the current on reversing the poles. 



D. Other Effects. 



(a) The effect of capacity in the circuit already noticed by 

 previous investigators w T as also confirmed. When the electro- 

 static voltmeter was thrown in, the current in general in- 

 creased, sometimes as much as 10 per cent. This effect was 

 entirely got rid of by having a large resistance in the main 

 circuit. With the series given in Part I. of this investigation, 

 there was not the slightest indication of any error due to this 

 cause. 



(b) Another result observed by previous experiment was 

 that the current is not always steady, even though not the 

 slightest flickering in the glow of the spark could be de- 

 tected, and the galvanometer deflexion remained absolutely 

 stationary. The effect was noticed when a telephone-receiver 

 was put in the circuit. Frequently there would be a shrill 

 whistling noise in the instrument, which would change with 

 the capacity, as when the metallic conductor was touched 

 with the hand. It also varied with the resistance, and seemed 

 quite erratic, as one could never be certain what the pitch 

 of the note would be, nor even if it would be present in 

 a given case. With the large resistance, however, the value 

 of the current seemed entirely independent of the presence 

 or absence of the noise ; so in general, except for noting 

 when the phenomenon was present, no attention was paid 

 to it. 



