to Electricity and Magnetism. 209 
fore one of intensity, and was induced by a battery current 
also of intensity. 
40. Instead of the helix used in the last experiment for 
receiving the induction, one of the coils (No. 3) was now 
placed on helix No. 1, the battery remaining as before. With 
this arrangement the induced current gave no shocks, but it 
magnetized the small horseshoe ; and when the ends of the 
coil were rubbed together, produced bright sparks. It had 
therefore the properties of a current of quantity ; and it was 
produced by the induction of a current, from the battery, of 
intensity. 
41. This experiment was considered of so much importance, 
that it was varied and repeated many times, but always with 
the same result ; it therefore establishes the fact that an in- 
tensity current can mduce one of quantity^ and by the prece-- 
ding experiments, the converse has also been shown, that a 
quantity current can induce one of intensity. 
42. This fact appears to have an important bearing on the 
law of the inductive action, and would seem to favour the 
supposition that the lower coil, in the two experiments with 
the long and short secondary conductors, exerted the same 
amount of inductive force, and that in one case this was ex- 
pended (to use the language of theory) in giving a great velo- 
city to a small quantity of the fluid, and in the other in pro- 
ducing a slower motion in a larger current; but in the two 
cases, were it not for the increased resistance to conduction in 
the longer wire, the quantity multiplied by the velocity would 
be the same. This, however, is as yet a hypothesis, but it en- 
ables 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 resist- 
ance offered by the longer wire. It would also appear, if 
the above reasoning be correct, that to produce the most 
energetic physiological effects, only a small quantity of elec- 
tricity, 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 
induction. To establish the law would require a great num- 
ber of more refined experiments, and the consideration of 
several circumstances 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, 
Phil. Mag. S. 3. V^ol. 16. No. 102. March 1840. P 
