123 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 mtensity 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 he- 

 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 with 

 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 evi- 

 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- 



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