CYCLIC MOLECULAR VARIATION 621 



similar, is obtained from filings of a substance belonging 

 to the negative class under increasing electro-motive force 

 (fig. 379). Taking first the substance in a low or indifferent 

 condition, we find the curve in its earliest stage, A, to be 

 almost horizontal. That is to say, the molecular distortion 

 induced is here very slight. We next arrive, however, at a 

 stage, B, which I shall call transitional, where increasing 

 force induces change at a rapid rate. In the third stage, 

 subsequent to this, there is a decline in the rate of change, 

 the molecules now approaching their maximum distortion. 



FIG. 379. Characteristic Conductivity Curve of Sensitive Metallic 

 Particles belonging to Negative Class, under increasing Electro- 



mrvfixr^ TTrvrr** 



motive Force 



These principal features are common to characteristic curves 

 in general, slight deviations from the type being met with 

 occasionally. In the cases given, for example, the substance 

 starts from an indifferent condition. But it might have been 

 in a still lower, or a-tonic, condition at starting. Under such 

 circumstances I find that the tendency of the first part of 

 the curve is to fall below the zero-line, crossing it, however, 

 in an upward direction, at the transitional point B. When 

 the curve, again, has reached the highest point, C, it may 

 remain horizontal for a considerable time, or there may be a 

 decline, owing, as we shall see, to fatigue. 



