Stranica 147 [147]
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 sug¬
gests 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 Switzer¬
land,” 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 sub¬
stance assume such a variety of tints?
“ HALIEUS.—I certainly have often thought upon the
subject, and I have made some observations and ove experi¬
ment in relation toit. I will give you my opinion with plea¬
sure, and as far as I know, they have not been brought for¬
ward 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