Prof. Rijke on some Properties of the Induced Current. 253 



7. Dr. Levoir, who assisted me in these experiments, surprised, 

 like myself, at the result at which we had arrived, and which we 

 were far from expecting, proposed to me to try whether, if the 

 circuit were broken in a current of gas not lighted, we should 

 not also find the striking distance increased. We immediately 

 made the experiment, and found, in fact, that gas not lighted 

 produced an action but little less than that offtame 3 as will-be seen 

 from the following Table : — 



Medium in which the rupture of 

 the inducing circuit took place. 



Greatest striking distance. 



Coal-gas not lighted 



1 millims. 



f 63-2 

 163-6 



Mean 63-4 



J 64-1 



\67-3 



The electrodes between which the induction spark passed were 

 the circular plate and the tapering conductor described above. 

 We found analogous results in working with hydrogen. 



Medium in which the rupture of 

 the inducing circuit took place. 



Greatest striking distance. 





millims. 



[401 



140-3 



Mean 40-2 



J 29 



133 



Mean... 31 





The following arc a series of experiments made with other 

 gases* : — 



* It is very rare that a spark is produced in a current of hydrogen with- 

 out an explosion ensuing. The diffusion of air into hydrogen takes place 

 so rapidly, that an explosive mixture is soon formed. This difficulty may 

 be easily overcome by arranging the experiment in the following manner : — 

 A glass "funnel, so large that the two hands can be introduced, is fixed by 

 means of a support in a vertical position, with the tube upwards. When a 

 somewhat rapid current of hydrogen is passed into this tube, the circuit 

 may be broken in the funnel without danger of an explosion. Moreover, 

 an explosion under these circumstances would not present the same danger. 



