259 
to Electricity and Magnetism, 
put on the top of the helix, and in this position, although the 
neutralization was not as perfect as before, yet 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 phaenomenon 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. 
68. 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, given 
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 neutralizing ac« 
S 2 
