1838] WRITINGS OF JOSEPH HENRY. 125 



disposed to consider the phenomenon as a case of real elec- 

 trical interference, in which the impulses succeed each other 

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

 should dejDend 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. 1, 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 experi- 

 ment. In this arrangement the neutralizing action was ex- 

 hibited, 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 neutral- 

 ization takes place with currents in the interposed or ad- 

 joining conductors of all lengths and intensities, and there- 

 fore cannot, as it appears to me, be referred to the interfer- 

 ence 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. 



