118 WRITINGS OF JOSEPH HENRY. [1838 



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 a battery, 

 of intensity. 



41. This experiment was considered of so much impor- 

 tance, that it was varied and repeated many times, but always 

 with the same result; it therefore establishes the fact that an 

 ^'intensity" current can induce one of " quantity, ^^ and, by the 

 preceding 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 favor 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 

 expended (to use the language of theory) in giving a great 

 velocity to a small quantity of the fluid, and in the other in 

 producing a slower motion in a larger current; but in the 

 two cases, were it not for the increased resistance to conduc- 

 tion in the longer wire, the quantity multiplied by the 

 square of the velocity would be the same. This however 

 is as yet a hypothesis, but it enables us to conceive how in- 

 tensity 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 



