II 
constancy of the glane at which they met was a proof of the con- 
stancy of the tension of the film. 
The lecturer next dealt with the colours of soap bubbles. These 
are due to the extreme thinness of the film. From each surface, 
external and internal, light is reflected. Colours result from the 
interference between the two reflections. He reflected the light 
of the arc from a film formed in a ring of metal held vertically. 
The thickness is less at the top of the circle and continually decreases 
until the film breaks. As this progresses bands of vivid colour 
travel downwards until, just before rupture, a black spot appears 
at the top. At this black spot the extreme thinness is such that 
no reflection of light is possible, and the soap film is here invisible. 
This experiment is of great interest, as, by the measurement of 
the thickness at this black spot, the late Lord Kelvin determined 
an approximate value of the size of the molecules of which matter 
is composed. The thickness is here about one hundred thousand 
millionth of an inch. 
Dr. Clay proceeded to give a demonstration of blowing bubbles 
inside one another. He succeeded in blowing a large bubble some 
fifteen inches across. 
The last experiment of the evening consisted in the formation of 
a “big drop.”” An ordinary drop of water hanging from a water 
tap is held together and derives its figure from the surface tension 
of the water referred to at the beginning of the lecture. This 
“big drop,” however, was enclosed by a film of rubber. Its shape — 
was that of an ordinary drop, but hugely large. The lecturer 
emptied two pails of water into it before it finally burst. 
On Friday, February 7th, the Annual General Meeting was 
held under the chairmanship of Mr. Walter Baily, M.A., Vice- 
President. The Report of the Council was read and adopted. 
The President, Vice-President, Officers and Council were elected. 
The meeting was resolved into an ordinary meeting. 
Mr. P. Macleod Yearsley, F.R.C.S., gave a lecture on 
‘« The Physiology of Hearing,” illustrated with lantern slides. 
Hearing was believed to be a development of the sense of touch. 
With the aid of lantern photographs and diagrams, the anatomy 
of the ear was first described. The external ear, or pinna, now 
nearly or quite incapable of movement, and apparently of little 
or no use as an aid to hearing, has been evolved from the pointed 
movable ear of the lower animals. A drawing of the pointed ear 
of an ape was exhibited to show the changes that had taken place. 
