Measurement of the Electric Resistance of Liquids. 133 
ences when the same current was being sent through a known 
resistance. 
Figs. 1 and 2, PI. II., show the arrangement of the apparatus 
used in the experiments. B is the battery producing the cur- 
rent passing between the platinum plates P and P'. G is a 
delicate reflecting galvanometer measuring the current. E is 
a quadrant-electrometer which measures the difference of po- 
tentials between the two wires W and W f . These two platinum 
wires W and W 7 were immersed in glass tubes ; and their ends 
were above the bottom of the glass tubes as shown. Figure 1 
shows the connexions when the differences of potentials be- 
tween W and W were being measured by the electrometer, 
and figure 2 when the differences of potentials at the two ends of 
the known resistance-coil, of 10,000 ohms, were being measured. 
The following Table gives the dimensions of the various 
parts of the apparatus: — 
Diameter of the beaker at water-line 8'5 centim. 
Height of water-line above the bottom ... 5*76 „ 
Distance between centres of wire tubes 7 , S n 
(W, W in fig. 2) / 4 '^ » 
Distance between the platinum plates 7 - 3 
Part of the glass tube surrounding the") ^^ . 
wire dipped in water J 
Part of the platinum wire in water 0'91 „ 
Outside diameter of the glass tube - 87 „ 
Size of platinum plate : height 3 - 28 „ 
„ „ „ ■ width 2-29 „ 
Before each experiment, when no current was passing, the 
difference of potentials between the plates and wires was 
reduced to 0, if not already. The wires W and W were heated 
to redness before each experiment, and the platinum plates 
cleaned. 
At the beginning pure distilled water was used; and this 
water was not added to all the time : it therefore lost a little 
by evaporation during the course of the experiment, and may 
have become a little dusty ; but as the main object of the in- 
vestigation was to examine the method of testing, and not for 
the purpose of measuring the specific resistance of water or of 
any other particular liquid, this result was of little consequence. 
The following is a sample of the experiments made: — 
January 25, 1878. — Battery-power employed ■§■ of 23 
DanielPs cells, having an E.M.F. of 4*08 volts, and which 
gave a deflection of 468 divisions on the galvanometer when 
shunted with the -j^ shunt, and when a resistance of 
10,000 ohms was introduced in the circuit. 
