ON ELECTRO-DYNAMIC INDtJCtlON. 2^ 



have a further reason for the increase of the terminal shock, when we increase 

 the length of the battery conductor. 



75. The inference given in the last paragraph, relative to the change in the 

 quantity of the induction, but not in the intensity of the shock from a single 

 spire, by increasing the whole length of the conductor, is shown to be true by 

 repeating the experiment described in paragraph 13. In this, as we have seen, 

 the intensity of the shock remained the same, although the length of the cir- 

 cuit was increased by the addition of coil No. 2. When, however, the gal- 

 vanometer was employed in the same arrangement, the whole quantity of in- 

 duction, as indicated by the deflection of the needle, was diminished almost in 

 proportion to the increased length of the circuit. I was led to make this addi- 

 tion to the experiment (13) by my present views. 



76. The explanation given in paragraph 74 also includes that of the peculiar 

 action of a long conductor, either coiled or extended, in giving shock and sparks 

 from a battery of a single element, discovered by myself in 1831; (see Contrib. 

 No. II.) The induction, in this case, takes place in the conductor of the pri- 

 mary current itself, and the secondary current which is produced is generated 

 by the joint action of each unit of the length of the primary current. Let us 

 suppose, for illustration, that the conductor was at first one foot long, and after- 

 wards increased to twenty feet. In the first case, because the short conductor 

 would transmit a greater quantity of electricity, the secondary current pro- 

 duced by it would be one of considerable quantity, or power to deflect a gal- 

 vanometer; but it would be of feeble intensity, for although the primary cur- 

 rent would collapse with its usual velocity, (69,) yet, acting on only a foot of 

 conducting matter, the effect (74) would be feeble. In the second case, each 

 foot of the twenty feet of the primary current would severally produce an in- 

 ductive action of the same intensity as that of the short conductor, the velocity 

 of coUapsion being the same ; and as they are all at once exerted on the same 

 conductor, a secondary current would result of twenty times the intensity of 

 the current in the former case. 



77. To render this explanation more explicit, it may be proper to mention 

 that a current produced by an induction on one part of a long conductor of 

 uniform diameter, must exist, of the same intensity, in every other part of the 

 conductor; hence, the action of the several units of length of the primary cur- 

 rent must enforce each other, and produce the same effect on its own conductor 



