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COLOURS IN RIPPLED WATER or
surface entirely covered with minute spots of the
constituent colours at a distance sufficient to cause
them to blend completely in the eye. This system
of mixing coloured lights on the canvas has ad¬
vantages which would seem to recommend it for the
painting of the whole surface of the rippled water.
It not only gives increased luminosity, but also, as
pointed out by Rood, adds a lustre and transparency
not otherwise obtainable. “If the coloured lines or
dots are quite distant from the eye, the mixture is of
course perfect and presents nothing remarkable in
its appearance; but before this distance is reached
there is a stage in which the colours are blended,
shall receive simultaneously blue and yellow light, not the slightest
approach to green is produced, but a grey, slightly tinged with
yellow. By carefully reducing and adjusting the portion of the
yellow disc exposed it is possible to get rid of this yellowness and
to obtain an absolutely neutral grey . . . The light reflected from a
blue pigment, mingled with the light reflected from a yellow, in¬
variably produces white of small brightness, that is, a neutral grey”
(“Colour,” by Prof. A. H. Church, Cassell and Co., 1887,
page 80).
According to the Young-Helmholtz theory of colour-perception,
now generally accepted, there are three primary colour sensations,
viz., red, green and blue (or violet). The secondary colour-sensa¬
tions arise from mixtures of two of these primaries; thus a mixture
of red and green lights gives the sensation of yellow, green and
blue together give that of sea green, and red and blue that of purple.
A mixture of all three primaries in the right proportions gives
white. The complementary of any given colour is that colour which
must be added to it in order to produce the sensation of white.
Thus yellow is the complementary of blue, purple of green, and
sea green of red. For a complete account of Young’s theory and
its developments, see Church’s manual on “Colour,” from which
is taken the passage quoted above.