ON ELECTRO-DYNAMIC INDUCTION. 5 



conductor, then a slight increase in the induction should take place, since, 

 according to theory, the current is somewhat increased in quantity, in the case 

 of a long coil, by the increase of the intensity of the battery. Although very 

 little, if any, difference could be observed in the intensity of the shock from 

 the secondary current, yet the snap and deflagration of the murcury appeared 

 to be greater from the primary current, when ten elements of the battery were 

 included in the circuit, than with a single one. The other results which are 

 mentioned in my last paper in reference to the compound battery are, I believe, 

 correctly given. 



10. The intensity of the different shocks in the foregoing experiments was 

 compared by gradually raising the helix from the coil, (see Fig. 3,) until, on 

 account of the distance of the conductors, the shock in one case would be so 

 much reduced as to be scarcely perceptible through the fingers or the tongue, 

 while the shock from another arrangement, but with the same distance of the 

 conductors, would be evident, perhaps, in the hands. The same method was 

 generally employed in the experiments in which 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 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 men- 

 tioned 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 diminu- 

 tion 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 helix, was continually shortened, until the whole of it 

 was excluded from the circuit; in this case the intensity of the shock at the 



VIII. — B 



