Theory of the Capillary Electrometer. 333 



The presence of even a trace of impurity is soon manifested by the 

 blocking of the capillary, and if this block is removed by electrolysis, 

 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 "Pol arisations-geschwindig- 

 keit " 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 first 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 

 sufncient to detach any part of it until the stress is intense enough 

 to break down all similar molecules simultaneously. 



But if by polarisation is meant this condition of the interface, then 

 I maintain that it must precede the movement, and must be deve- 

 loped 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 : 



dpjdt+rprof(t) = 0, 



where r and e are constants, and cf(t) = 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.F. expressed as a differential equation. 



For dp/dt is, in the polar curves taken with my machine, merely 

 the subnormal N", and rp is identical with &Ar, whence 



dpjdt + rp rcf(t) 



is identical with 



K + *Ar - / () volt, 



which being interpreted signifies 



fThesub-1 f A constant mul- 1 f The 



I normal I , J tiple of the dis- I f A constant! I E.M.F. at 

 1 to the (^ 1 tan ce from the f " \ multiple of /] time t (m 

 curve. J zero-line. J I volts). 



