to Electricity and Magnetism. 491 



form of a circle, and placing the helix within this. The shock 

 was felt in the hands at the moment of closing the circuit, but 

 the effect at opening the same was scarcely perceptible through 

 the tongue. An attempt was also made to get indications of 

 induction by placing the helix within a circle of dilute acid, 

 coimected with a battery instead of a coil, but the effect, if 

 any, was very feeble. 



29. I have shown, in the second number of my contribu- 

 tions, that if the body be introduced into a circuit with a bat- 

 tery of one hundred and twenty elements, without a coil, a 

 thrilling sensation will be felt during the continuance of the 

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

 interrupting the current by breaking the circuit at any point. 

 This result is evidently due to the induction of a secondary 

 current in the battery itself, and on this principle the remark- 

 able physiological effects produced by Dr. Ure, on the body 

 of a malefactor, may be explained. The body, in these ex- 

 periments, was made to form a part of the circuit, with a 

 compound galvanic apparatus in which a series of interrup- 

 tions was rapidly made by drawing the end of a conductor 

 over the edges of the plates of the battery. By this opera- 

 tion a series of induced currents must have been produced in 

 the battery itself, the intensity of which was greater than that 

 of die primary current. 



30. In this connexion I may mention that the idea has oc- 

 curred 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 ani- 

 mals may serve the purpose of a long conductor*. It ap- 

 pears to me, that in the present state of knowledge, this is the 

 only way in which we can conceive of such intense electricity 

 being produced in organs imperfecdy 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 se- 

 condary 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, the secondary current affords the 

 means of imitating the phaenomena 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 extremities of tiie 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 



• Since writing the above, I have found that M. Massou has suggested 

 the same idea in an interesting thesis lately published. 



