306 



has taken place. This spark is due to two causes. One is the tendency of the 

 Leyden jars forming the capacity C to lake on whal is known as a residual 

 charge. The other results from the oscillatory character of a Leyden jar 

 discharge, the jars having a charge after each spark depending on the direc- 

 tion of the last oscillation. With a charge on the capacity (' varying as to 

 both sign and magnitude, one can not expect a constant time interval between 

 the sparks L and S. In my later experiments I have been able to eliminate 

 much of this trouble by short-circuiting the terminals of the capacity (' 

 through a high resistance R and an inductance I. The resistance R is merely 

 a tube of water with wires passing through corks at either end of the tube. 

 The inductance 1 is an electromagnet of about a thousand turns of wire. 

 The result may be obtained with either a resistance or an inductance, if suffi- 

 ciently large. Using both one can, without reducing the intensity of the 

 illuminating spark, reduce the resistance R by shortening the water resis- 

 tance until the jars discharge themselves completely very soon after every 

 spark. Thus the condenser is brought into the same electrical < ondition before 

 every spark and consequently the time required to charge it to sparking 

 potential is made constant. 



The arrangement here described does not completely eliminate all varia- 

 tions in the time interval between the sparks because much of the variation is 

 due to change in the effective resistance of the spark gaps themselves, some- 

 thing the writer has been unable to control. The arrangement does, however, 

 reduce the variation about 50 per cent. 



Physics Laboratory, Indiana University, November, 1915. 



