Oldal 144 [144]
82 LIGHT AND WATER
your head ; and thus the colours with which water is
painted are an indication of the position of the spec¬
tator, and connected inseparably with the perspective
of the shores. The most beautiful of all results that
I know in mountain streams is when the water is
shallow, and the stones at the bottom are rich reddish¬
orange and black, and the water is seen at an angle
which exactly divides the visible colours between
those of the stones and that of the sky, and the sky
is of clear, full blue. The resulting purple, obtained
by the blending of the blue and the orange red, broken
by the play of innumerable gradations in the stones,
is indescribably lovely. All this seems complicated
enough already; but if there be a strong colour in
the clear water itself,as of green or blue in the Swiss
lakes, all these phenomena are doubly involved ; for
the darker reflections now become of the colour of
the water. The reflection of a black gondola, for
instance, at Venice, is never black, but pure dark
93
STC: «5:5
NOTE ON THE COLOUR OF WATER.
The selective absorption theory of the colour of water is
now generally accepted in preference to the selective reflexion
theory, Dr. John Aitken, in his Paper “On the Colour of the
Mediterranean and other Waters” (Proc. R. S. E. vol. xi,
page 472), having shown conclusively that the former theory
is the correct one. “ According to the selective reflexion theory
the colour is due to the light reflected by extremely small
particles of matter suspended in the water. These particles
being so small they can reflect only the short waves of light,
or those which belong to the blue end of the spectrum. The