1908-9.] 
Note on a Study of Polarisation. 
165 
X. — Laboratory Note on a Study of Polarisation by means 
of the Dolezalek Electrometer. By A. F. Ewan, Physical 
Laboratory, Edinburgh University. (Communicated by Professor 
J. G. MacGregor.) 
(Read July 20, 1908. MS. received September 15, 1908 ; revised January 23, 1909.) 
The following experiments originated in a series of laboratory exercises 
which I performed on the use of the Dolezalek electrometer. The 
instrument which I used was made by Bartels, and had its needle suspended 
by a phosphor-bronze strip. This needle was raised to a potential of 
about 160 volts by being connected to one terminal of a battery of 
eighty small secondary cells, the other terminal of which was connected to 
earth. When at this potential the instrument gave, for a potential difference 
of 1 volt between its two pairs of quadrants, a deflection of 200 divisions 
on a scale 200 centimetres distant from it. The maximum deflection in the 
experiments described was 166 divisions, i.e. 332 cms., giving tan -1 T66 as 
maximum angle of deflection ; and therefore, by taking the deflection as 
proportional to the potential difference, a maximum error of 0*7 per cent, is 
introduced. 
Although these experiments are merely preliminary ones, I desire to 
give an account of the results obtained, as I am unable to go on with them 
at present. They refer to two subjects — (1) the variation of the electro- 
motive force of polarisation of a cell with the difference of potential between 
the electrodes, and (2) the applicability of Wiedeburg’s formula for the 
variation, with time, of the electromotive force of polarisation during the 
flow of the current. 
1. Variation of the Electromotive Force of Polarisation with the 
Difference of Potential between the Electrodes. 
It is usually held that there is no such variation, but that, for a given 
electrolyte, given electrodes, etc., it depends only on the current density. 
This assumption seems never to have been tested ; and as it underlies 
certain methods of using the Wheatstone bridge in the measurement of the 
conductivity of electrolytes, a test is desirable. For this purpose I passed 
a current through two cells of very different resistances, but otherwise 
