96 Professors Reinold and Riicker on the Injluence of an 
More recently we have employed the current from a Siemens’ 
dynamo. ‘The current passed through a sensitive reflecting 
galvanometer, the deflection on the scale measuring approxi- 
mately the strength of the current. This varied from about 
100 microamperes to half a microampere. 
We began our experiments by observing the behaviour of 
a number of films, each 40 millim. long, formed of potash- 
soap solution without any glycerine, which were allowed to 
thin in the ordinary way, no current passing through them. 
In less than a minute after the adjustment of the film to the 
cylindrical form narrow rings of colour appeared, and white 
of the first order of Newton’s rings was soon seen at the top, 
generally bordered by a narrow band of deep blue, the blue 
of the second order. The coloured bands did not extend 
beyond 10 miliim. from the top, the rest of the film being 
colourless. ‘This was the state of the case at the end of five or 
six minutes. In from eight to fifteen minutes from the moment 
of formation of the film a black ring appeared and slowly 
extended downwards. Nine films were examined, and all 
behaved substantially in the same way. 
We now tried the effect of passing a current through the films. 
It is unnecessary to describe all the observations that were 
made, as the object of many of them was merely to obtain 
confirmation of previous results. A few typical cases may be 
described. 
i. Downward Current. Plain Potash-soap Solution. 
(1) Film 40 millim. long. A current was passed through 
from the moment of its formation. Broad bands of colour 
formed and spread with great rapidity, soon occupying the 
whole area of the film. After six minutes the current was 
2°6 microampéres (m.a.). In eleven minutes there was a ring 
of black, which in two minutes more increased to 8 millim. 
The curr ant was then stopped. 
It appears from this and a number of other experiments 
made in the same way that the effect of the downward current 
is to promote the thinning of the film. The bands are broader 
and spread out more rapidly than when no current is applied. 
(2) A film 40 millim. long had thinned until 2°5 millim. of 
black were formed. Next to the black came a band of deep 
blue. A downward current of 5°18 m.a. was applied. The 
blue changed to white, the black not being altered. After 
nine minutes the bine was still of about thes same breadth and 
the white had increased to 16 millim., the current being now 
4-06 m.a. In two minutes after breakin g the circuit the white 
