Effect of Annealing.—I repeated the experiment with the same wire, after pouring hot water and allowing it to cool to the old temperature. It will be seen from the cyclic curve (fig. 10, B), (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 (fig. 10, C). The above results show in what
Fig. 10.—Cyclic curves for maximum effects due to increasing and decreasing amplitude of vibration. A, fresh wire; B, after annealing; C. the same after three cycles. Abscissa represents the amplitude of vibration; the ordinate represents the corresponding electromotive variation.
manner the excitability of the wire is enhanced by purely physical means.
It is very curious to notice that the substitution. of Na2CO3 solution as electrolyte produces results very similar to that produced by annealing; that is to say, not only is there a great enhancement of sensitiveness, but there is also a reduction of hysteresis. Another curious point is that, whereas with ordinary fresh wire the addition of Na2CO3 greatly enhances the sensitiveness, after the wire has been annealed there is comparatively little further increase of sensitiveness due to the addition of the reagent.
