Page:Collected Physical Papers.djvu/319

Rh cyclic curve (fig. 80, 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. 80, C). 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 the substitution of dilute Na$2$CO$3$ 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 Na$2$CO$3$ 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.

I reproduce photographic records of a few typical cases which will graphically illustrate the influence of chemical reagents. The mode of procedure is as follows. The cell is filled with water, and photographic records are taken of responses to single vibrations of constant amplitude, applied to one of the two wires at intervals of 1 minute. The responses are found to be uniform. Chemical reagents are now added, and responses obtained as before. These exhibit either an increase or a diminution, depending on the exciting or depressing nature of the reagent. It is also quite easy to obtain duplicated results by alternately vibrating the A and B wires. Uniform responses, alternately