On Electro- Dynamic Induction. 233 



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 repeated 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 

 considerable 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 elec- 

 trified positively, and the outer coating in connection with the 

 earth, then the jar contains a small excess of positive electricity 

 beyond what is necessary to neutralize perfectly the negative sur- 

 face. If the knob be put in communication with the earth, the 

 extra quantity, or the free electricity, as it is sometimes called, 

 will be on the negative side. When the discharge 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 described. 

 It therefore became a question of importance to determine, whe- 

 ther the induced current described in paragraph 100 was not also 

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

 secondary 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 con- 

 nection 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. 



105. When, however, the quantity of free electricity was in- 

 creased, by connecting the knob of the jar with a globe about a 



Vol. zxxvxii, No. 2.— Jan.-March, 1840. 30 



