* 
122 Contributions to Electricity and Magnetism. 
shocks are mentioned as being compared, in the other parts of this 
paper. 
11. Experiments were next made to determine the influence 
of a variation in the length of the coil, the intensity of the bat- 
tery remaining the same. For this purpose, the battery consist- 
ing of a single element, and the arrangement of the apparatus as 
represented in Fig. 3, the coil was diminished in length from sixty 
feet to forty five, then to thirty, and so on. With the first mention- 
ed length the shock, at making contact with the battery, was, of 
course, very feeble, and could be felt only in the tongue ; with 
the next shorter length it was more perceptible, and increased in 
intensity with each diminution of the coil, until a length of about 
fifteen feet appeared to give a maximum result. 
12. The diminution of the intensity of the shock in the last 
experiment, after the length of the coil was diminished below fif- 
teen feet, was due to the diminution of the number of spires of 
the coil, each of which, by acting on the helix, tends to increase 
the intensity of the secondary current, unless the combined length 
of the whole is too great for the intensity of the battery. That 
this is the fact is shown by the following experiment: the helix 
was placed on a single spire or turn of the coil, and the length of 
the other part of the copper riband, which did not act on the be- 
lix, was continually shortened, until the whole of it was exclu- 
ded from the circuit; in this case the intensity of the shock at 
the beginning was constantly increased. We may therefore state 
generally, that at the beginning of the battery current, the induc- 
tion of a unit of its length, is increased by every diminution of 
the length of the conductor. 
13. In the experiment given in paragraph 11, the intensity of 
the shock at the ending of the battery current diminishes wit 
each diminution of the length of the coil ; and this is also due 
to the decrease of the number of the spires of the coil, as is ev 
dent from an experiment similar to the last, in which the helix 
was placed on a coil consisting of only two turns or spires of cop- 
per riband; the shock at the ending, with this arrangement, was 
comparatively feeble, but could be felt in the hands. Different 
lengths of coil No. 2 were now introduced into the same circuit, 
but not so as to act on the helix; but although these were varied 
from four or five feet to the whole length of the coil, (sixty feet,) 
not the least difference in the intensity of the shock could be per- 
