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COLOURS IN STILL WATER 8: With regard to the unusually green and clear water on the west and south-west coast of Australia, Prof. Threlfall suggests that the greenness may be caused by the solution of a yellow colouring matter from dead or even living seaweed. Lord Avebury, in his work on “The Scenery of Switzerland,” page 217, describes the experiments of Forel, who showed that the blue water of the Lake of Geneva could be turned into a green exactly similar to that of the Lake of Lucerne by the addition of a small quantity of water coloured yellow by the infusion of peat. Since writing the above, my attention has been drawn to the fact that Sir Humphry Davy, in his anonymous work, “Salmonia, or Days of Fly-Fishing” (published in 1828, the year before his death) gave an account of the colour of water substantially in accordance with modern ideas. The only point in which his views seem incomplete is with regard to the luminosity of water, which as shown by Aitken, depends upon the number and colour of the suspended particles. As the book is now somewhat rare, and Davy’s work on the subject—almost his latest contribution to science—not generally known, I give the complete passage here. “ POIETES.—Y ou, Halieus, must certainly have considered the causes which produce the colours of waters. The streams of our own island are of a very different colour from these mountain rivers, and why should the same element or substance assume such a variety of tints? “ HALIEUS.—I certainly have often thought upon the subject, and I have made some observations and ove experiment in relation toit. I will give you my opinion with pleasure, and as far as I know, they have not been brought forward in any of the works on the properties of water, or on its consideration as a chemical element. The purest water with which we are acquainted is undoubtedly that which falls from the atmosphere. Having touched air alone, it can
