78 
Proceedings of the Royal Society 
will become a straight line, giving up its fluid to the other four 
films. At this instant the whole system changes, the oval film 
being reproduced in the angle of 135° ! 
Remarkable as this phenomenon is, there is one still more 
remarkable, which requires the testimony of the eye to make it 
credible. If when the rectangles are inclined 90° we blow upon 
the elliptical film, a bubble of such a size as to replace the system 
of films with a hollow curvilineal cube, and wait till it bursts, the 
system of liquid films which it expelled will reappear , as if it had left 
its ghost behind it to recover the elements which the bubble had appro- 
priated ! 
By uniting the upper and lower ends of all the wires in this 
system, and also by uniting the wires at various points in their 
length, the author obtained a number of beautiful and complex 
systems of films, which require numerous diagrams to make them 
intelligible. 
After treating of the equilibrium of liquid films, as seen in the 
union of spherical bubbles and other hollow solids, the author 
considers the formation of plane, convex, and concave films upon 
the mouths of open and closed vessels of different shapes, and their 
deposition on the same vessels from bubbles; and he describes 
various remarkable movements of the films, upwards and down- 
wards, when they are formed upon conical vessels open at both 
ends. 
4. On a Method of ascertaining the Specific Gravity of 
Water which holds a minute quantity of Foreign Matter 
in Solution ; or, on the Specific Gravity of Impure Water. 
By Edward Sang, Esq. 
The determination of the degree of impurity of spring or well 
water is every day becoming of more and more importance. In 
order to discover how much foreign matter is contained in a sample 
of water, the chemist is under the necessity of drying up a quan- 
tity of it, and of weighing the residue. This operation is tedious, 
and gives a trust-worthy result only when the evaporation has been 
carried on in closed vessels from which atmospheric impurities have 
