On Electro-Dynamic Induction. 219 



current ; but in the two cases, were it not for the increased resist- 

 ance to conduction in the longer wire, the quantity multiphed by 

 the velocity would be the same. This, however, is as yet a hy- 

 pothesis, but it enables us to conceive how intensity and quantity 

 may both be produced from the same induction. 



43. From some of the foregoing experiments we may con- 

 clude, that the quantity of electricity in motion in the helix is 

 really less than in the coil, of the same weight of metal ; but 

 this may possibly be owing simply to the greater resistance offer- 

 ed by the longer wire. It would also appear, if the above reason- 

 ing be correct, that to produce the most energetic physiological 

 effects, only a small quantity of electricity, moving with great 

 velocity, is necessary. 



44. In this and the preceding section, I have attempted to give 

 only the general conditions which influence the galvanic induc- 

 tion. To establish the law, would require a great number of more 

 refined experiments, and the consideration of several circumstan- 

 ces which would affect the results, such as the conduction of the 

 wires, the constant state of the battery, the method of breaking 

 the circuit with perfect regularity, and also more perfect means 

 than we now possess of measuring the amount of the inductive 

 action. All these circumstances render the problem very complex. 



SECTION III. 



On the Induction of Secondary Currents at a distance. 



AS. In the experiments given in the two preceding sections, 

 the conductor which received the induction, was separated from 

 that which transmitted the primary current by the thickness only 

 of a pane of glass ; but the action from this arrangement was so 

 energetic, that I was naturally led to try the effect at a greater 

 distance. 



46. For this purpose coil No. 1 was formed into a ring of about 

 two feet in diameter, and helix No. 4 placed as is shown in the 

 figure. When the helix was at the distance of about sixteen 

 inches from the middle of the plane of the ring, shocks could be 

 perceived through the tongue, and these rapidly increased in in- 

 tensity as the helix was lowered, and when it reached the plane 

 of the ring they were quite severe. The effect, however, was 

 still greater when the helix was moved from the centre to the 



