178 WRITINGS OF JOSEPH HENRY. [1840 



of current electricity in a unit of length of the conductor, 

 we readily infer from it that by increasing the length of the 

 conductor, or the value of R, the quantity of current in a unit 

 of the length is lessened. And if the resistance of a unit 

 of the length of the conductor were very great in compari- 

 son with that of r, (the resistance of one element of the bat- 

 tery,) then the formula would become 



A 



R' 

 or the quantity in a single unit of the conductor would be 

 inversely as its entire length, and hence the amount of cur- 

 rent electricity in the whole conductor would be a constant 

 quantity, whatever might be its length. This however can 

 never be the case in any of our experiments, since in no in- 

 stance is the resistance of R very great in reference to r, and, 

 therefore, according to the formula, (73,) the whole quantity 

 of current electricity in a long conductor is always somewhat 

 greater than in a short one. 



74. Let us however in order to simplify the conditions of 

 the induction at the ending of a current, suppose that the 

 quantity in a unit of the conductor is inversely at its whole 

 length, or in other words that the quantity of current elec- 

 tricity is the same in a long conductor as in a short one ; 

 and let us also suppose for an example that the length of 

 the spiral conductor, (Fig. 3,) was increased from one spire to 

 twenty spires ; then, if the velocity of the diminution of the 

 section of the current is the same (69) in the long conductor 

 as in the short one, the shock which would be received by sub- 

 mitting the helix to the action of one spire of the long coil 

 would be nearly of the same intensity as that from one 

 spire of the short conductor; the quantity of induction 

 however as shown by the galvanometer, should be nearly 

 twenty times less ; and these inferences I have found in ac- 

 cordance with the results of experiments, (75.) If however 

 instead of placing the helix on one spire of the long con- 

 ductor, it be submitted at once to the influence of all the 

 twenty spires, then the intensity of the shock should be 

 twenty times greater, since twenty times the quantity of 



