652 
PROFESSORS A. W. REIXOLD ANT) A. W. RUCKER 
In the first place, we may state that we were most scrupulously careful about the 
cleanliness of the apparatus. It was always taken to pieces as soon as the experi¬ 
ments were over, and the glass box, rings, tubes, linen bands, &c., were all washed in 
distilled water. The bands were left to soak all night, and when required were wrung 
out and dried with blotting paper. The films were always flooded before an experi¬ 
ment began, so that the cups and bands were well washed down with the solution. 
We found also that successive films, when thus treated, behaved in a much more 
uniform way than if the flooding was omitted. We have at times replaced the metal 
rings by the glass ones, and been most careful that the liquid should touch nothing 
but glass and linen, but the phenomenon above described was as marked as before. 
Lastly, if one of the films was thickened by the electric current it contracted just as 
it would do if thickened by flooding. The fact that the thicker film displayed the 
greater surface tension cannot, therefore, be due to any peculiarity of the apparatus 
or mode of thickening adopted. 
Experiment III. 
As a crucial test as to whether the weight of the thicker film had anything to do 
with the phenomenon, we placed the larger rings on the upper and the smaller rings 
on the lower supports. We thus obtained two unduloidal films, which may be 
described as approximately cones with the smaller ends below. It is evident that if 
one of these films were heavier than the other the pressure exerted on the enclosed air 
would thereby be diminished, and the heavier film would bulge. Experiment proved 
that, on the contrary, it contracted, thus indicating that the pressure was increased. 
Experiment IV. 
The question as to whether the phenomenon was due to the fact that in the thicker 
film the liquid is falling more or less rapidly was answered by closing the cock until 
the down-rush was practically over. When communication between the films was 
restored the thicker one contracted as usual. 
The fact that the film contracted if it was slowly thickened from below by the 
electric current pointed to the same conclusion. 
Experiment V. 
It was, in the next place, important to determine whether the-gradual disappearance 
of the liquid rings by which the thinning film is attached to the solid supports could 
produce changes in the value of Y which would account wholly or partially for the 
phenomenon observed. 
If an unduloid differs but little from a cylinder of radius Y, we may write for its 
maximum and minimum ordinates Y-j- dot and Y -\-dfi. Any other ordinate maybe 
expressed by Y + dy. 
