of Edinburgh, Session 1884-85. 
>321 
Hence we obtain 
T , p 4 - r 
R +p= 
x 
V 
. . (i) 
How, placing the battery between B and C, we get similarly 
R +p + p = r — — - (2) 
x ^ 
y' 
when x 7 and p 7 are the currents corresponding to x and y in the pre- 
vious arrangement. From (1) and (2) we get 
P = r 
xy - yx' 
xx — yy 
• (3) 
Hence the difference between the resistances of the two parts of the 
electrolyte may be calculated in terms of a known resistance and of 
known currents. In this form of the experiments, however, it is 
assumed that polarisation is proportional to the current density. 
Also there is the objection that heating is going on, usually to 
different extents, in the two parts, because of the currents being 
different. Both these sources of error vanish if x is equal to y , 
and then equation (3) reduces to 
p = r. 
I have as yet made only a very rough series of experiments with 
the view of testing the steadiness of the currents, but it seems to 
indicate that the method will be successful. The form in which the 
experiments were conducted is that to which equation (3) applies. 
In addition to the errors above indicated as affecting the results, 
there were causes tending to produce large variations arising from 
the roughness of the apparatus set up provisionally. Three cylin- 
drical glass cups were connected in series by two glass tubes inserted 
near their lower edge. The electrolyte (a 5 per cent, aqueous 
solution of sulphuric acid) was poured into this arrangement, and 
the electrodes (platinum) dipped into it through the open ends of 
the cups. The cups were of large volume, so that the resistance of 
the portion of liquid between the electrodes and the extremities of 
the tubes could be neglected. The lengths of the tubes were 9 '2 and 
8 -5 centimetres respectively, and their diameter was ‘65 centimetre. 
The metal wire used to connect the extreme electrodes had a resist- 
