Page:Proceedings of the Royal Society of London Vol 60.djvu/360

Rh The presence of even a trace of impurity is soon manifested by the blocking of the capillary, and if this block is removed by electrolyse the instrument behaves for some time in an abnormal way. It shows signs of a residual charge, like that of a Leyden jar, the mercury rising again after the short-circuiting key is opened, instead of simply ceasing to fall.

This I ascribe to polarisation of the kind met with between solids and electrolytes, and to this the term “ Polarisations-geschwindigkeit ” would be applicable. But no good electrometer will show it, except with electromotive forces greater than ought to be employed. I* have held from the iirst that the capillary electrometer acts by transforming electrical into mechanical energy without any chemical interchange, and that this is possible because at the interface between two liquids which do not diffuse into each other the stress is so evenly distributed that no one molecule can be strained to a degree sufficient to detach any part of it until the stress is intense enoug 1 to break down all similar molecules simultaneously.

But if by polarisation is meant this condition ox the interface, then I maintain that it must precede the movement, and must be developed with almost inconceivable rapidity.

In order to investigate the form of curve produced by recording the motion of the meniscus when the electrometer is acted upon by an electromotive force varying with the time according to some known law, e.g., the pulsating or alternating current of a dynamo, Professor Hermann puts his equation into a somewhat different form, namely :

dpidt+rp—rc f(f) = 0 ,

Theory of the Capillary Electrometer. where r and G are constants, and ef( E is the electromotive force represented as a function of the time. But this is simply my own formula for the estimation of the E.M.E. expressed as a differential equation. For dpldt is, in the polar curves taken with my machine, merely the subnormal N, and rpis identical with Mr, whence

dpldt + is identical with N + rp JcAr rrf(t) 1 0-0133 /(0 volt,

which being interpreted signifies fThe sub-'l f A constant mul-l J normal I J tiple of the dis- l ] to the | | tance from the ( [_ curve. J zero-line. J / A constant \ \ multiple of J r 1 I E.M.F. at 1 volts). J
 * time t (in f