ON ELECTRO-DYNAMIC INDUCTION. 327 



the outer riband, the needle was strongly magnetized in such a manner 

 as to indicate an induced current through the inner riband in the same 

 direction as that of the current of the jar. This experiment was re- 

 peated many times, and always with the same result. 



101. When the ends of one of the ribands were placed very nearly 

 in contact, a small spark was perceived at the opening, the moment 

 the discharge took place^ through the other riband. 



102. When the ends of the same riband were separated to a conside- 

 rable distance, a larger spark than the last could be drawn from each 

 end by presenting a ball, or the knuckle. 



103. Also if the ends of the outer riband were united, so as to form 

 a perfect metallic circuit, a spark could be drawn from any point of the 

 same, when a discharge was sent through the inner riband. 



104. The sparks in the two last experiments are evidently due to 

 the action known in ordinary electricity by the name of the lateral 

 discharge. To render this clear, it is perhaps necessary to recall the 

 well known fact, that when the knob of a jar is electrified positively, 

 and the outer coating in connection with the earth, then the jar con- 

 tains a small excess of positive electricity beyond what is necessary to 

 perfectly neutralize the negative surface. If the knob be put in com- 

 munication with the earth, the extra quantity, or the free electricity, as 

 it is sometimes called, will be on the negative side. When the dis- 

 charge took place in the above experiments, the inner riband became 

 for an instant charged with this free electricity, and consequently 

 threw off from the outer riband, by ordinary induction, the sparks de- 

 scribed. It therefore became a question of importance to determine, 

 whether the induced current described in paragraph 100 was not also 

 a result of the lateral discharge, instead of being a true case of a second- 

 ary current analogous to those produced from galvanism. For this 

 purpose the jar was charged, first with the outer coating in connection 

 with the earth, and again with the knob in connection with the same, 

 so that the extra quantity might be in the one case plus and in the 

 other minus ; but the direction of the induced current was not affected 

 by these changes ; it was always the same, namely, from the positive to 

 the negative side of the jar. 



VI.— 4 G 



