Fig. 86.—Incomplete and Complete Fusion of Effect in Tin
As the frequency of stimulation is increased the fusion becomes more and more complete. Vertical line to the right represents ·1 volt.
Hysteresis.—Allusion has already been made to the increased responsiveness conferred by preliminary stimulation (see [p. 127]). Being desirous of finding out in what manner this is brought about, I took a series of observations for an entire cycle, that is to say, a series of observations were taken for maximum effects, starting from amplitude of vibration of 10° and ending in 100°, and backwards from 100° to 10°. Effect of hysteresis is very clearly seen (see A, [fig. 87]); there is a considerable divergence between the forward and return curves, the return curve being higher. On repeating the cycle several times, the divergence is found very much reduced, the wire on the whole is found to assume a more constant sensitiveness. In this steady condition, generally speaking, the sensitiveness for smaller amplitude of vibration is found to be greater than at the very beginning, but the reverse is the case for stronger intensity of stimulation.
Fig. 87.—Cyclic Curve for Maximum Effects showing Hysteresis
Effect of annealing.—I repeated the experiment with the same wire, after pouring hot water into the cell and allowing it to cool to the old temperature. From the cyclic curve (B, [fig. 87]) it will be seen (1) that the sensitiveness has become very much enhanced; (2) that there is relatively less divergence between the forward and return curves. Even this divergence practically disappeared at the third cycle, when the forward and backward curves coincided (C, [fig. 87]). The above results show in what manner the excitability of the wire is enhanced by purely physical means.
It is very curious to notice that addition of Na2CO3 solution (see Chap. XV—Action of Stimulants) produces enhancement of responsive power similar to that produced by annealing; that is to say, not only is there a great increase of sensitiveness, but there is also a reduction of hysteresis.