eyes, and also to extend as an external coat over the whole 
of the sclerotic, as far as its anterior margin in front of the 
lens. The demonstration of the retinal structure was 
postponed, and Dr. Fripp, indicating the results of his exa- 
mination, stated that they strongly corroborated the 
modern explanation of vision by direct transference of 
impressions of light through a radial system of fibres to the 
ganglionic layers of the optic nerve, where the conversion 
of the physical impressions into sensation might take place. 
Assuming this radial system to be correct, there existed no 
essential difference of plan or principle between the Mollusc 
Insect and Vertebrate eye, for the system in greater or less 
perfection existed in each, though not always recognised as 
such. 
Chemical, and Photographic Section, May 10.— 
Dr. W. B. Herapath, F.R.S., president in the chair. Mr. W. 
L. Carpenter made a verbal communication, entitled " N"otes 
on a Soap-bubble." The brilliant colours visible on a soap 
bobble were one among many illustrations of phenomenon 
known in optics as the colours of thin plates — the explana- 
tion of which, according to the emission theory very imper- 
fect, had been made extremely clear by the undulatory 
theory of light. Mr. Carpenter enunciated the four chief 
laws in connexion with them, giving the mathematical 
formulas, and describing the experimental proofs. 
It appeared that the colours were due to the inter- 
ference of two sets of waves, the incident ray striking 
upon the film, being reflected partly from its upper and 
partly from its under surface, and that the colours, which 
were not visible by homogeneous light, depended entirely 
upon the thickness of the film, which varied from 
l-178000th of an inch to about 1-17800. Many plans 
had been tried for keeping the colours constant in the soap- 
bubble, without much success, as they varied on account of 
the evaporation from the surface ; but the author had acci- 
dentally noticed that if the bubble were made in a flask con- 
t \ining a warm solution of soap, the application of heat frora 
beneath might be regulated in such a way that the 
evaporation from the surf^ice of the solution on the under 
surface of the babble should exactly compensate for the 
evaporation from its upper surface ; and in this way be had 
been able to retain a film of the unvarying thickness and 
constant shade of colour for a long period. The gentleman 
who had undertaken to provide a photographic subject for 
the evening having failed to keep his engagement, Dr. 
Herapath kindly gave the members an account of many 
novel scientific instruments exhibited at a recent soiree of 
the Royal Society, at which he had been present, amongst 
which may mentioned a new printing telegraph, Mr. 
Sarby's microspectroscope, some very curious photographs 
on porcelain, ind a new mode of giving stereoscopic effects 
to portraits, &c., by placing a single picture behind a very 
thick piece of glass, and viewing the whole by transmitted 
light. 
Geological Section, May 22. — The first geological walk 
of the season was taken along the left bank of the Avon, in 
