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Abstract of Proceedings, 
1908. 
$4444 44 
GENERAL MEETINGS. 
Friday, January 3rd. Mr. Walter Baily, M.A., Vice-President, 
in the chair. 
Principal Reginald S. Clay, D.Sc., gave a holiday lecture 
on ‘* Soap Bubbles,’’ illustrated with experiments. The lecturer 
explained that the free surface of water behaves as if a taut mem- 
brane were spread over it, always tending to reduce the area of the 
surface to the smallest dimensions. Force is required to enlarge 
this surface. This he showed in several ways. If a film of soap 
solution containing a loop of cotton thread be pricked within the 
loop, the latter instantly expands into a circle, this being the 
greatest area a given length of thread can enclose. The film out- 
side the loop contracts to its greatest extent, leaving a circular 
hole where the film has been broken. And, again, a wire sieve, 
waxed so as to be incapable of being wetted, though full of holes, 
will hold a small quantity of water, the tension of the water 
surface, at each hole through which the water is endeavouring to 
pass, being sufficient to retain it. For a similar reason the iron 
sieve could be made to float on water. In the case of a bubble of 
soap solution the film, in its endeavour to contract as much as 
possible, compresses the enclosed air into a sphere, for a sphere is 
that figure which has the smallest surface with a given volume. 
The lecturer also showed that, whereas a piece of rubber re- 
quires more force to stretch it the more it is stretched, this is not 
so with a soap film. The tension is the same, however large and 
however small. He blew a mass of bubbles between two glass 
plates in the lantern, and showed that, under all conditions of 
size of the bubbles, three films always meet at one point, never 
more nor less, and that the three films made equal angles with one 
another at this point. He showed the same principle with some 
wire frames, bent into simple geometrical figures—cube, pyramid, 
etc. On dipping these into soap solution a film was left on each 
side and films met in the inside. Whenever this was the case the 
