516 
PROFESSOHS A. W. RETNOLD ARD A. RUCKER OX THE 
battery of from fourteen to twenty-eight Leclanche cells was passed through the film 
from the moment of its formation, in others no current was used until the time for 
measurement arrived, and then it was produced by seven Leclanche cells only, and 
was applied intermittently so that the circuit was not completed unless an observa¬ 
tion was actually in progress. 
The following results were obtained with an unsalted oleate of potash solution. 
Each of the values of ^ was derived from a different film, and the number of cells 
indicated is in each case that employed to pass a continuous current from the first 
formation of the film. Of course in all cases a current was used at the moment of 
measurement. 
Table X. 
Number of 
P (apparent tbickness of black 
cells. 
film measured electrically). 
0 
150, 171, 148, 150 
14 
151, 145, 142 
28 
150, 157, 179 
These numbers prove that the results were not affected by the strength or duration 
of the current which was passed through the film before the measurements were 
actually made. 
These observations were supplemented by others in which the resistance of films 
could be compared by means of currents which were practically instantaneous. For 
this purpose the needles were connected with the terminals of the secondary of a 
Ruhmkorfif coil, a ballistic galvanometer being included in the circuit. 
The primary circuit could be completed or broken by an independent key. In 
experiments on different films the circuit was always completed for the first time 
when the black had descended to the same distance below the lower needle, so that 
the throw would be nearly inversely proportional to the resistance of the black film. 
The deflections of the galvanometer were identical in two cases, in one of which a 
current from twenty cells had been passed through the film (formed of an unsalted 
hard soap solution) from the time of its formation, while in the other a film formed of 
the same liquid had not been subjected to any electrical action until the transient 
current used in the measurement was employed. It might possibly be urged in 
answer to this that we have no evidence that the thickness of the black was the same 
in each case—that we may have been dealing with in the one case and /3o in the 
other. If this were so the equality of the throws could only be explained by the 
hypothesis that the product of the thickness and specific conductivity is the same for 
Pi and ySj, and this is inconsistent with the large change in resistance which the 
substitution of one for the other has been proved above to produce. 
