On Electro-Dynamic Induction. 129 
rendered more interesting by causing the induction to take place 
through a number of persons standing in a row between the two 
conductors. 
Section II. 
On apparently two kinds of electro-dynamic induction. 
32. The investigations arranged under this head had their ori- 
gin in the following circumstances. After the publication of my 
last paper, I received, through the kindness of Dr. Faraday, a 
copy of the fourteenth series of his researches, and in this I was 
surprised to find a statement which appeared in direct opposition 
to one of the principal facts of my communication. In para- 
graph 59, I state, in substance, that when a plate of metal is in- 
terposed between the coil transmitting a galvanic current, and the 
helix placed above it to receive the induction, the shock from the 
secondary current is almost perfectly neutralized. Dr. Faraday, 
in the extension of his new and ingenious views of the agency 
of the intermediate particles in transmitting induction, was led 
to make an experiment on the same point, and apparently, under 
the same circumstances, he found that it ‘makes not the least 
difference, whether the intervening space between the two con- 
ductors is occupied by such insulating bodies as air, sulphur, and 
Shell-lac, or such conducting bod ies 2S Copper and other non-mag- 
hetic metals.” a ae bs 
33. As the investigation of the fact mentioned above forms an 
important part of my paper, and is intimately connected with al- 
most all the phenomena subsequently described in the communi- 
cation, I was, of course, anxious to discover the cause of so re- 
markable a discrepancy. There could be no doubt of the truth 
of my results, since a shock froma secondary current which 
would paralyze the arms was so much reduced by the interposi- 
tion of plates of metal as scarcely to be felt through the tongue. 
After some reflection, however, the thought occurred to me» 
that induction might be produced in such a way as not to be af 
fected by the interposition of a plate of metal. To understand 
this, suppose the end of a magnetic bar placed perpendicularly 
under the middle of a plate of copper, and a helix suddenl 
brought down on this; an induced current would be produced in 
the helix by its motion towards the plate, since the copper, in this. 
Vol. x11, No. 1.—April-June, 1841.17 ¢ 
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