4-86 Prof. J. Henry's Contributions 



battery remaining the same. For this purpose, the battery 

 consisting 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-mentioned 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 

 fifteen 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 foct 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 ri- 

 band, which did not act on the helix, was continually short- 

 ened, until the whole of it was excluded from the circuit; in 

 this case the intensity of the shock at the beginning was con- 

 stantly increased. We may therefore state generally, that, 

 at the beginning of the battery current, the induction 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 eiidi7ig 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 evident from an experiment similar to the last, in 

 which the helix was placed on a coil consisting of only two 

 turns or spires of copper 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 perceived. 

 We have, therefore, the remarkable result, that the intensity 

 of the ending induction of each unit of length of the battery 

 current is not materially altered, at least within certain limits, 

 by changing the length of the whole conductor. From this 

 we would infer that the shock depends more on the intensity 

 of the action than on the quantity of the current, since we 



