470 
PROFESSORS A. W. REINOLD AND A. W. RUCKER OX 
were going on. When a film was to be examined the connecting pieces, A l5 Ao, A 3 , 
being all inserted in the corresponding mercury cups, the deflections right and left of 
the three electrometers were observed, the time of each reading being noted. A l was 
then removed, and G inserted in its place, and the deflections right and left again 
observed. These observations were repeated without cessation so long as the film 
lasted. The time occupied in taking a complete set of readings for the three needles 
and for the resistance was from 2 to 3 minutes. 
Fig. 7. 
F is the film with the three needles inserted in it, connected respectively to the mercury cups 1, 2, 3. 
E (1) the electrometer which measures the difference of potentials between needles 1 and 2. 
E (2) „ „ „ „ 1 and 3. 
E (3) „ „ „ „ 2 and 3. 
R, box of resistance coils. 
B, battery of 4 Grove’s cells. 
The deflections being plotted down on curve paper, as before described, curves 
representing the actual resistances between needles 1-2, 2-3, and 1-3 were deduced. 
The resistance between needles 1 3 ought of course to be equal to the sum of the 
resistances between needles 1-2 and 2-3. Sometimes the agreement was perfect, and 
the difference was rarely in excess of 1 per cent. 
IX. Description of the Apparatus for measuring the resistance of the liquid in mass. 
The method finally adopted for measuring the electrical resistance of the soap 
solutions was in principle the same as that employed in the examination of the films. 
A current was passed through a known resistance and a tube containing the liquid 
to be examined; and the difference of potential between two points in the tube 
which could be connected with an electrometer was compared with that between two 
other points in the same circuit separated by a known resistance. 
A piece of tube was selected, as nearly cylindrical as possible, about '8 centim. in 
diameter and 32 centims. in length. Its two ends were bent at right angles to it, as 
shown in the accompanying diagram, and two short pieces of the same tubing were 
fused into it near the turned up ends for the insertion of thermometers. At a, a', about 
