On Electro- Dynamic Inductio7i. 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. 

 O71 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 bodies as copper and other non-mag- 

 netic metals." 



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 from a 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. 



34. 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 suddenly 

 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. XLi, No. 1.— April-June, 1841, 17 



