How is this?"
The cases are entirely different, as I shall proceed to show. In
speaking of the first, the complementary colours, we speak of pure
spectral colours, coloured rays of light; in the latter, of pigment or
dye colours. As we shall see, in the first, we have an addition direct
of coloured lights producing white; in the latter, the green colour,
appearing as the result of the mixture of the blue and yellow pigments,
is obtained by the subtraction of colours; it is due to the absorption,
by the blue and yellow pigments, of all the spectrum, practically,
except the green portion. In the case of coloured objects, we are then
confronted with the fact that these objects appear coloured because of
an absorption by the colouring matter of every part of the rays of light
falling thereupon, except that of the colour of the object, which colour
is thrown off or reflected. This will appear clearer as we proceed. Now
let me point out a further fact and indicate another step which will
show you the value of such knowledge as this if properly applied.
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