On Electro-Dynamie 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 deseribed. 
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. xxxvim, No, 2.~Jan.-March, 1840. 
