582 Proceedings of the Boyal Society 
ence of the readings was tabulated as representing its electromotive 
force. 
In the earlier experiments I used a plate of gutta-percha in 
which the ten holes were bored, but for a time discontinued its use 
on suspecting that it sometimes led to irregular working of the 
apparatus by imperfect insulation. The cups were then separately 
mounted on insulators three inches high, but this was not found to 
be an improvement of any consequence ; and the holes are now 
made in a small, but thick, plate of vulcanite. 
In this note the numbers presented must be looked upon only as 
first approximations ; but the apparatus has now been carefully 
constructed by an instrument maker, and Mr Dewar has begun 
an elaborate series of experiments with it, from which valuable 
results may soon be expected. In the trials which have as yet 
been made we employed a temporary apparatus, rudely built up of 
wires, sealing-wax, and gutta-percha. We have rather been endea- 
vouring to determine whether the process, complicated as it is by 
the inertia of the movable part of the electrometer, the quickness 
with which the rocking can be conducted, and the rate at which 
the polarisation begins to diminish as soon as the polarised plates 
are detached from the decomposing battery, is capable of being 
made to give good results, than in actually attempting to get such. 
So far as I can yet see, the first of these complications is alone 
likely to cause any serious embarrassment; and should such be the 
case, which I do not anticipate, a form of experiment a little more 
laborious than that above described, and which I have already once 
or twice tried, seems to be well adapted to meet it. 
The following are, for the most part, means of a great number 
of determinations. The electrolyte was usually dilute commercial 
sulphuric acid, 1 part acid to 10 of water; and to the lead and 
other impurities it was found to contain, we may ascribe the fact 
that the results were not very accordant from day to day, so that it 
was not easy to decide how to take the means. Mr Dewar is now 
working with substances chemically pure, and obtains much more 
constant results. 
The unit employed is the electromotive force of an ordinary 
Daniell’s cell. The G-rove’s cells used in the electrolysis had (very 
constantly) an electromotive force about 1-74 times as great. 
