On Water and Air. 
[January, 
64 
and we can easily balance that plate of glass by a weight (w), 
and then bring the glass down upon a sheet of water (Fig. 3) ; 
then, by adding more weights upon the scale-pan, we can 
determine the weight necessary to sever one part of the water 
from the other. Take the case of a soap-bubble. If I had 
time I could show you the beautiful zones of colour which 
a soap-bubble produces ; and, by means of the zones of 
colour, we can approximately determine the thickness of the 
bubble. You sometimes see a heavy drop of water pendant 
from a soap-bubble ; and if you reflect upon this you will 
see that the film of the bubble must have a tremendous 
amount of tenacity in order to support the drop of water 
which hangs from it. Prof. Henry, of Washington, esti- 
mated the tenacity of water at several hundred pounds per 
Fig. 3. 
square inch. But you will say, perhaps, that the soap 
confers this tenacity upon the water of the bubble. Well, 
Prof. Henry says that it is not so, and that water, if pro- 
perly dealt with, is really more tenacious than water with 
soap in it. But, however true that may be, I want, at all 
events, to show you that we can get beautiful bubbles and 
beautiful films of water without any soap whatever. 
Here is a tube connected with a cistern at the top of the 
house, and I am going to make an experiment with it upon 
a grand scale. It is an experiment which was made by an 
eminent French investigator, M. Felix Savart. Savart pro- 
duced films of water by allowing jets of water to fall upon 
small surfaces. It is wonderful what care we must take in 
this experiment. The slightest agitation would destroy the 
