1840] WRITINGS OF JOSEPH HENRY. 155 



the current, since we know that the latter is diminished in a 

 given unit of the conductor by increasing the length of the 

 whole. 



14. We have seen (8) that with a circuit composed of ten 

 elements of the compound battery and the coil No. 2, the 

 shock, at the beginning of the current, was fully equal to 

 that at the ending. It was however found that if in this 

 case the length of the coil was increased, this shock was di- 

 minished; and we may state as an inference from several 

 experiments, that however great may be the intensity of the 

 electricity from the battery, the shock at the beginning may 

 be so reduced, by a sufficient increase of the length of the 

 primary circuit, as to be scarcely perceptible. 



15. It was also found that when the thickness of tlie coil 

 was increased, the length and intensity of the circuit remain- 

 ing the same, the shock at the beginning of the battery 

 current was somewhat increased. This result was produced 

 by using a double coil; the electricity was made to pass 

 through one strand, and immediately afterwards through 

 both ; the shock from the helix in the latter case was ap- 

 parently the greater. 



16. By the foregoing results we are evidently furnished 

 with two methods of increasing at pleasure the intensity of 

 the induction at the beginning of a battery current; — the one 

 consisting in increasing the intensity of the source of the 

 electricity, and the other in diminishing the resistance to 

 conduction of the circuit while the intensity remains the 

 same. 



17. The explanation of the effects which we have given, 

 relative to the induction at the beginning, is apparently not 

 difficult. The resistance to conduction in the case of a long 

 conductor and a battery of a single element is so great that 

 the full development of the primary current may be sup- 

 posed not to take place with sufficient rapidity to produce 

 the instantaneous action on which the shock from the sec- 

 ondary current would seem to depend. But when a battery 

 of a number of elements is employed, the poles of this, pre- 

 vious to the moment of completing the circuit, are in a state 



