494 



MEASUREMENT OF CAPACITY. DIELECTRICS. 



force may be constructed. If the capacity were constant this curve 

 would reduce to a straight line passing through the origin. It does 

 really turn its convexity towards the axis of abscissae in other words, 

 the charges increase far more rapidly than the electromotive forces. 

 The angular coefficient of the tangent represents the true capacity at 

 each point. We may consider as the initial capacity the limiting value 

 of this coefficient when the electromotive force tends towards zero. 



1085. The difference of potential of the two electrodes repre- 

 sents the difference which polarization establishes between the 

 electromotive forces of contact of the two electrodes with the liquid, 

 which were originally equal. If the surface of one electrode is very 

 great, and as it were infinite in reference to the other, it may be 

 assumed that the surface of the first, and therefore its electromotive 



Fig. 232. 



force of contact, is not modified ; the difference observed represents 

 then the variation of the electromotive force of contact of the second. 

 If we take this latter alternately as positive or negative electrode 

 that is to say, charging it with oxygen or hydrogen, experiment gives 

 the same value for the initial capacity defined as above. This then 

 is independent of the direction of the polarization. If the electro- 

 motive forces and the corresponding charges are counted as positive 

 or negative according as the active electrode is itself positive or 

 negative, we obtain two curves which run into one another at the 

 origin, as seen in Fig. 232. 



Experiment shows that the capacity of a given electrode only 

 depends on the difference of potential between this electrode and 

 the liquid with which it is in contact, and not on the nature of the 



