indicative of an increase of conductivity or diminution of resistance.
Fig. 55. Cyclic Curves showing Conductivity Hysteresis. In each curve the right half is due to increasing, the left half to decreasing E. M. F.
Experiments were next carried out to find whether similar residual effects could be observed when the sensitive substance was carried through a cycle of electromotive variation. I tried both single and multiple contacts.
As stated before, the E. M. F. can be continuously increased by turning the winding wheel which moves the platform uniformly in one direction; the E. M. F. is continuously diminished by turning the wheel in the opposite direction, and thus reversing the motion of the platform. By this means the receiver can be subjected to a cyclic electromotive variation through large or small range at will. I reproduce curves of cyclic variation taken with filings, when the range of electro-
