ON ELECTRO-DYNAMIC INDUCTION. 11 



ance of the current, and a shock will be experienced at the moment of inter- 

 rupting the current by breaking the circuit at any point. This result is evi- 

 dently due to the induction of a secondary current in the battery itself, and on 

 this principle the remarkable physiological effects produced by Dr. Ure, on the 

 body of a malefactor, may be explained. The body, in these experiments, was 

 made to form a part of the circuit, with a compound galvanic apparatus in 

 which a series of interruptions was rapidly made by drawing the end of a con- 

 ductor over the edges of the plates of the battery. By this operation a series 

 of induced currents must have been produced in the battery itself, the intensity 

 of which would be greater than that of the primary current. 



30. In this connexion I may mention that the idea has occurred to me that 

 the intense shocks given by the electrical fish may possibly be from a secondary 

 current, and that the great amount of nervous organization found in these 

 animals may serve the purpose of a long conductor.* It appears to me, that 

 in the present state of knowledge, this is the only way in which we can con- 

 ceive of such intense electricity being produced in organs imperfectly insulated 

 and immersed in a conducting medium. But we have seen that an original 

 current of feeble intensity can induce, in a long wire, a secondary current 

 capable of giving intense shocks, although the several strands of the wire are 

 separated from each other only by a covering of cotton thread. Whatever 

 may be the worth of this suggestion, on which I place but little value, the 

 secondary current affords the means of imitating the phenomena of the shock 

 from the electrical eel, as described by Dr. Faraday. By immersing the apparatus 

 (Fig. 3) in a shallow vessel of water, the handles being placed at the two ex- 

 tremities of the diameter of the helix, and the hands plunged into the water 

 parallel to a line joining the two poles, a shock is felt through the arms; but 

 when the contact with the water is made in a line at right angles to the last, 

 only a slight sensation is felt in each hand, but no shock. 



31. Since the publication of my last paper, I have exhibited to my class the 

 experiment (No. III. Sec. 3d) relative to the induction at a distance on a much 

 larger scale. All my coils were united so as to form a single length of conductor 

 of about four hundred feet, and this was rolled into a ring of five and a half 

 feet in diameter, and suspended vertically against the inside of the large folding 



* Since writing the above, I have found that M. Masson has suggested the same idea, in an 

 interesting thesis lately published. 



