650 
PROFESSORS A. W. REINOLD AND A. W. RUCKER 
means—the right film displayed five millimetres of black at the top, and the tint of 
the remainder varied between the middle of the white of the first order, which was in 
contact with the black, and the beginning of the orange of the first order at the 
bottom. 
Results of Preliminary Experiments. 
The first experiments which we performed were designed to test the observations 
of Ludtge and Van der Mensbrugghe as to the difference of tension between two 
films, of which one had been formed more recently than the other. 
The symbols p and A. indicate the principal diameters of the right and left films 
respectively, and §=p —X. 
The diameter of the rings is 2Y, the distance between them 2X. 
All lengths are given in millimetres except when otherwise stated. In calculations 
in which the sensitiveness is used they must be expressed in centimetres. 
The following experiment was made as a test of the rapidity with which the films 
would return to their position of equilibrium when disturbed. This gave an idea of 
the readiness with which the arrangement would respond to a change of tension. 
Experiment I. 
2Y = 20-8, 2X = 2-5Y=26'0. 
Two films were made, flooded, and put into communication. Five minutes and 
eight minutes afterwards the diameters were measured. The time elapsed since the 
formation of the films is indicated by t. The results were as follows :— 
t 
O r 
c, 
P 
X 
8 
ID. 
5 
Colourless 
20-90 
20-83 
0-07 
8 
0 (4, 5) 
R (4, 5) 
20-94 
20-89 
0-05 
The two films were now separated, and the right hand one was blown out a little. 
The diameters were then measured. 
t 
Or 
C , 
p | x : 8 
m. 
ii 
G (3, 5) 
Ct (3, 5) 
22-18 20-91 1-27 
13 
5 ? 
22-20 20-88 132 
At 17 m the stop-cock was opened, so that the interiors of the films were again m 
communication, and the following observations taken. The colour of both films was 
still the green of the third order. 
