260 Prof. Rijke on some Properties of the Induced Current, 



induced, the two others as inducing helix. The depressions of 

 the column of liquid are given in the following Table : — 



Depressions obtained by breaking the inducing circuit in 

 Air. Flame. 



0-9 0*8 



1-3 1-3 



07 07 



Mean . . 0*9 Mean. . 09 



Hence the mode of breaking contact is without influence on the 

 quantity of heat developed, 



13. I ought especially, from the theoretical point of view, to 

 attach importance to knowing the kind of action which the 

 medium in which the rupture of the inducing circuit is made 

 exerts on the extra current. 



With this view I compared the physiological effect which the 

 extra current produces when the circuit is broken in air, to the 

 action which it exerts when the rupture takes place in the middle 

 of a flame. For this experiment I used a plane spiral, consist- 

 ing of a copper ribbon 130 metres long, 26 millims. w r ide, and 

 03 millim. in thickness. Holding in each hand a mandril 

 connected with the two ends of the spiral, the shock was in- 

 comparably stronger when contact was broken in a flame than 

 when it was broken in air. I repeated this experiment with a 

 small-sized Ruhmkorff's apparatus, and I again found that the 

 physiological effect produced by the extra current was stronger 

 when contact was broken in flame than it was when broken in air. 



To measure the action which the extra current exerts on the 

 dynamometer, I used a method which depends upon the follow- 

 ing theorem. Suppose a system of six conductors united, as 

 shown in the annexed figure. If, in 

 the conductors APB and AM, there 

 are electromotive forces which we 

 shall represent by e and e } , the inten- 

 sity of the current which traverses the 

 conductor M N will be independent 

 of the resistance of the conductor 

 APB and of the electromotive force 

 which resides in it, provided the resistances of the conductors 

 A M, M B, A N, and N B, which we will represent by r u r 2 , r^ 

 and r 4 , are in the proportion 



r \ • 7 *2 = r 3 • 7*4 • 



In fact, let r be the resistance of the conductor M N, r that of the 

 conductor APB, and let us represent by 



