Prof. Rijke on some Properties of the Induced Current. 255 



8. We found that when the circuit was broken in nitrogen, 

 the greatest striking distances were the following : — 



17*5 



16 



22-5 



The gas issued from the gas-holder under various pressures. 

 The greatest pressure having coincided with the greatest striking 

 distance, I was led to inquire if this increase in the length of the 

 spark arose simply from an accidental cause, or if it must be 

 admitted that a certain degree of velocity imparted to the gaseous 

 molecules exerted a favourable influence on the length of the 

 spark. I undertook some experiments to settle this question. 

 At first I found that sparks were obtained which had virtually 

 the same length whether the rupture took place in air at rest, 

 or in a current escaping from a Pepys's gas-holder. The case 

 was different when the rupture took place in a souffiet d'enfer. 

 By raising the air in this apparatus to its greatest pressure, in 

 other words, giving to its molecules the greatest velocity, I 

 obtained sparks 41 millims. in length, while the length was only 

 20 millims. when the rupture took place in air at rest. 



In the reservoir of a Natterer's apparatus I condensed air 

 under a pressure of 25 atmospheres. Effecting the rupture of 

 the circuit in one case in the current of air which issued from 

 the efflux-tube used for collecting carbonic acid, and in the other 

 in air at rest, I obtained the results given in the following Table. 

 Two copper knobs formed the electrodes between which the in- 

 duction spark passed : — 



Medium in which the 



rupture of the inducing 



circuit took place. 



Greatest striking 

 distance. 



Ratio of the striking 



distance in the given 



medium to that in 



air. 





millims. 

 69-6 



8-6 

 78-6 



M 



millims. 

 8-09 

 1 

 1107 

 1 







Hence we see that the length of the induction spark increases 

 considerably when the rupture of the inducing circuit takes place 

 in air in rapid motion. 



9. It is known that a greater striking distance is obtained 

 when the rupture of the inducing circuit is effected in water 

 instead of in air. I found that this distance is still m,ore increased 

 when a certain velocity is imparted to the liquid particles. The 

 following are the results obtained : — 



