1840] WRITINGS OF JOSEPH HENRY. 179 



current electricity collapses (if we may be allowed the expres- 

 sion) in the same time, and exerts at once all its influence 

 on the helix. If in addition to this we add the considera- 

 tion that the whole quantity of current electricity in a long 

 conductor is greater than that in a short one, (73,) we shall 

 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 repeat- 

 ing the experiment described in paragraph 13. In this, as 

 we have seen, the intensit}'^ of the shock remained the same, 

 although the length of the circuit was increased by the addi- 

 tion of coil No. 2. When however the galvanometer was 

 employed in the same arrangement, the whole quantity of 

 induction, 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 addition to the experi- 

 ment (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 shocks and sparks from a battery ol 

 a single element, discovered by myself in 1832; (see No. 

 II.) The induction in this case takes place in the con- 

 ductor of the primary current itself, and the secondary cur- 

 rent which is produced is generated by the joint action of 

 each unit of the length of the primary current. Let us sup- 

 pose for illustration that the conductor was at first one foot 

 long, and afterwards increased to twenty feet. In the first 

 case, because the short conductor would transmit a greater 

 quantity of electricity, the secondar}^ current produced by it 

 would be one of considerable quantity, or power to deflect di 

 galvanometer; but it would be of feeble intensity, for 

 although the primary current 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 



