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Proceedings of the Royal Society 
in our choice of platinum electrodes. Professor Beetz’ own expe- 
rience,* and that of other workers in this department, shew that 
platinum electrodes are the best to form part , of an apparatus 
for the investigation of electrolytes generally. 
The method which we used certainly cannot be regarded as com- 
pletely eliminating the effects of electrolytic action. Like the 
other general methods which have been tried, it is an approximation 
method. It aims, just as Kohlrausch ’s does, at measuring resistance 
when the effects of polarisation are so slight that they may he 
neglected. If the weight of the mirror were indefinitely small, 
its first deflection might he regarded as due to the main current 
alone. But it is impossible to obtain such a mirror; and the 
first deflection must be regarded as caused by the sum of the forces 
of the first few moments, which sum includes the electromotive 
force of polarisation. It is generally admitted, however, that 
polarisation, beginning at zero, must during the first few moments 
be exceedingly slight. The mirror, therefore, being sufficiently 
light, the observation will take place when its electromotive force 
is so small as to warrant its being neglected. The lighter the 
mirror, the more rapid the deflection, the smaller the influence of 
polarisation and the error. Whether or not, with the lightest mirror 
which can at present be made, the error is really small enough to 
be neglected, can only be determined by a comparison of results with 
those of some standard method which eliminates completely the 
effects of electrolytic action. Our method guards for a single 
observation not only against polarisation, but in the same way 
against the effect of the production of substances which, while 
giving rise to no new electro motive force, differ in conductivity 
from the original liquid. The observation is made before such 
products can be formed in any appreciable amount. The necessity 
of repeated observations in the same liquid, however, renders the 
elimination of this error only slightly less defective than in the 
methods of Kohlrausch and Nippoldt, Kohlrausch and G-rotrian, 
Paalzow, and perhaps even Professor Beetz. 
In passing to consider the numerical results which we published, 
Professor Beetz refers to two remarks which we made about his 
results, in one of which he finds the only Verstandnissfehler , of 
* Pogg. Ann., cxvii. p. 26. 
