On Electro-Dynamic Induction. 219 
current ; but in the two eases, were it not for the increased resist- 
ance to eondecticnad in the longer wire, the quantity multiplied 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, i 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 Ill. 
On the Induction of Secondary Currents at a distance. 
A5. In the experiments given in the two preceding mien 
the conductor which received the induction, was se 
that which transmitted the primary current by the thickness = 
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 
istance. 
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 
