134 WKITINGS OF JOSEPH HENRY. [1838 



opening, the moment the discharge took place through the 

 other ribbon. 



102. When the ends of the same ribbon 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 ribbon 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 ribbon. 



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 coat- 

 ing is connected with the earth, then the jar contains a 

 small excess of positive electricity beyond what is necessary 

 to perfectly neutralize the negative surface. 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 ribbon became for an instant charged 

 with this free electricity, and consequently threw off from 

 the outer ribbon, by ordinary induction, the sparks de- 

 scribed. It therefore became a question of importance to 

 determine whether the induced current described in para- 

 graph 100 was not also a result of the lateral discharge, in- 

 stead 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 connection with 

 the same, so that the extra quantity might be in the one 

 case jdus and in the other minus; but the direction of the in- 

 duced 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 

 increased, by connecting the knob of the jar with a globe 

 about a foot in diameter, the intensity of magnetism ap- 



