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Proceedings of the Royal Society 
reflections which would destroy the brilliancy of the coloured 
shadow experiments. 
These colour experiments explain why there is so little appear- 
ance of coloured light in our Cathedrals, even when there is much 
coloured light entering through the stained glass windows, and they 
show us that we might glaze the windows with the most brilliantly 
coloured glass, and yet the light in the interior might be quite 
white. 
It is hoped these colour-combining instruments will be found 
useful for teaching physiological optics, for experiments on colour 
perception, and also for measuring the qualities of lights from 
different sources. The possibility of making a perfect match, and 
the extreme nicety of the adjustment necessary to produce a perfect 
balance, indicate that these instruments are capable of considerable 
accuracy. 
2. On Chlorophyll from the Deep Sea. By W. W. Hartley, 
F.R.S., Royal College of Science, Dublin. 
The shells of certain molluscs which are obtainable on the sea- 
shore between tides are seen to be more or less coloured green. I 
have noticed a fine rich colour on the operculum of a Turbo from the 
Pacific Ocean, which had been killed and the shell preserved dry. 
The shell has a high polish, the colour is the rich green of an ivy 
leaf, and the pigment is contained in the shell material. When the 
mollusc dies, and the shell is left exposed to air, light, and water, the 
green becomes a brownish-yellow colour. Some specimens of spirit, 
which had been poured off shells and fragments of coral obtained 
by dredging in deep waters, were examined by me for Mr J. Y. 
Buchanan. He informed me that some of the shells were of a 
beautiful green colour, but there was no appearance of any growth 
of algse adhering to them. When placed in spirit, the colour became 
dissolved. After evaporation of the spirit, a mixture of green and 
yellow pigments was found in the residue, and nothing else. The 
green pigment was insoluble, while the yellow appeared to be 
slightly soluble in water. On shaking the substance with hydro- 
chloric acid and ether, I did not at first get Fremy’s reaction ; but 
