to Electricity and Magnetism. 259 



put on the top of the heh'x, and in this position, although the 

 neutrahzation was not as perfect as before, jet a great reduc- 

 tion was observed in the intensity of the shock. 



67. But here a very interesting and puzzling question oc- 

 curs. How does it happen that two currents, both in the 

 same direction, can neutralize each other? I was at first dis- 

 posed to consider the phsenomenon as a case of real electrical 

 interference, in which the impulses succeed each other by 

 some regular interval. But if this were true the effect should 

 depend on the length and other conditions of the current in 

 the interposed conductor. In order to investigate this, several 

 modifications of the experiments were instituted. 



b'8. First a flat coil (No. 3) was interposed instead of the 

 plates. When the two ends of this were separated, the shocks 

 were received as if the coil were not present; but when the 

 ends were joined, so as to form a perfect metallic circuit, no 

 shocks could be obtained. The neutralization with the coil 

 in this experiment was even more perfect than with the plate. 



69. Again, coil No. 2, in the form of a ring, was placed not 

 between the conductors, but around the helix. With this 

 disposition of the apparatus, and the ends of the coil joined, 

 the shocks were scarcely perceptible ; but when the ends were 

 separated, the presence of the coil has no effect. 



70. Also when helix No. 1 and 2 were together submitted 

 to the influence of coil No. J, the ends of the one being joined, 

 the other gave no shock. 



71. The experiments were further varied by placing helix 

 No. 2 within a hollow cylinder of sheet brass, and this again 

 within coil No. 2 in a manner similar to that shown in fig. 12, 

 which is intended to illustrate another experiment. In this 

 arrangement the neutralizing action was exhibited, as in the 

 case of the plate. 



72. A hollow cylinder of iron was next substituted for the 

 one of brass, and with this also no shocks could be obtained. 



73. From these experiments it is evident that the neutrali- 

 zation takes place with currents in the interposed or adjoining 

 conductors of all lengths and intensities, and therefore can- 

 not, as it appears to me, be referred to the interference of two 

 systems of vibrations. 



74. This part of the investigation was, for a time, giveij 

 up almost in despair, and it was not until new light had been 

 obtained from another part of the inquiry, that any further 

 advances could be made towards a solution of the mystery. 



75. Before proceeding to the next section, I may here 

 state that the phaenomenon mentioned, paragraph 54, in re- 

 ference to helix No. 4, is connected with the neutrahzing ac- 



S2 



