98 Professors Reinold and Riicker on the Influence of an 
ward current flows through a film from the moment of its 
formation, although the film thins more or less rapidly to the 
white of the first order, it generally does not show the black 
so soon as it would have done if no current had been flowing. 
So long as a thick liquid fringe remains on the upper support, 
liquid is being carried downwards and the film prevented from 
thinning beyond a certain limit. As soon as the circuit is 
broken this downward passage of liquid ceases, and the white 
of the first order rapidly thins to black. The fact that the 
current sometimes does and sometimes does not destroy the 
black may be understood by reflecting that the increase or 
decrease in the thickness of any part of the film depends upon 
whether the quantity of matter carried into it exceeds or falls 
short of that transported away from it in the same time. Since 
both these effects are produced in part by gravity and in 
part by the action of the current, and are also probably 
modified by the thickness of the different parts of the film, 
it is possible that very slight differences in the conditions of 
the experiment may determine which of the two shall obtain 
the predominance. 
(4) Film 30 millim. long. A downward current of 24 m.a. 
applied from the beginning. In ten minutes the white ex- 
tended more than halfway down, and the current fell to 2°5 m.a. 
The circuit was then broken. The white turned to black so 
rapidly that in less than one minute the entire transformation 
was effected. 
In this case, the film being shorter, the same battery gave 
a stronger current, and the changes due to the current were 
accelerated. 
We will now describe a few typical cases of the action of 
an upward current. 
il. Upward Current. Plain Potash-soap Solution. 
(1) Film 40 millim. long. Current (9:2 m.a.) applied 
from the beginning. In twenty-four minutes there was a 
narrow band of white at the top succeeded by a narrow band 
of indigo-blue. Faint uniform tint below. The film was 
left for three quarters of an hour, but no black appeared. 
The current fell to 1°95 m.a. We have evidence here of the 
retarding action of the current, as the film would have ex- 
hibited black in ten or twelve minutes had there been no 
current. The current was too feeble to produce more marked 
changes. 
(2) Film 40 millim. long. There were 3 millim. of black 
and three millim. of white immediately below. An upward 
current of 4°9 m.a. was used. The lower edge of the black 
