On Electro-Dynamic Induction. 123 



ceived. We have, therefore, the remarkable result, that the in- 

 tensity of the ending induction of each unit of length of the 

 battery current is not materially altered, at least within certain 

 limits, by changing the length of the whole conductor. From 

 this we would infer that the shock depends more on the intensity 

 of the action than on the quantity of 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 ele- 

 ments of the compound battery and the coil No. 2, the shock, at 

 the beginning of the current, was fully equal to that at the end- 

 ing. It was, however, found that if, in this case, the length of 

 the coil was increased, this shock was diminished ; 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 in- 

 crease of the length of the primary circuit, as to be scarcely per- 

 ceptible. 



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

 was increased, the length and intensity of the circuit remaining 

 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 apparently the greater. 



16. By the foregoing results we are evidently furnished with 

 two methods of increasing, at pleasure, the intensity of the in- 

 duction at the beginning of a battery current, the one consist- 

 ing 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, rel- 

 ative to the induction at the beginning, is apparently not difficult. 

 The resistance to condnction in the case of a long conductor and 

 a battery of a single element is so great that the full develop- 

 ment of the primary current may be supposed not to take place 

 with sufficient rapidity to produce the instantaneous action on 

 which the shock from the secondary current would seem to de- 

 pend. But when a battery of a number of elements is employed, 

 the poles of this, previous to the moment of completing the cir- 



