Now, if this be so, and if all the light available in
this world were of such a character, then such a colour as blue would be
unknown. We will now ask ourselves another question, "We have a new blue
colouring matter, and we desire to know if we may expect it to be one of
the greatest possible brilliancy, what spectroscopic conditions ought it
to fulfil?" On examining a solution of it, or rather the light passing
through a solution of it, with the spectroscope, we ought to find that
all the rays of the spectrum lying between and nearly to H and b (Fig.
16), _i.e._ all the bluish-violet, blue, and blue-green rays pass
through it unchanged, unabsorbed, whilst all the rest should be
completely absorbed. In like manner a pure yellow colour would allow all
the rays lying between orange-red and greenish-yellow (Fig. 16) to pass
through unchanged, but would absorb all the other colours of the
spectrum.
Now we come to the, for you, most-important subject of mixtures of
colours and their effects. Let us take the popular case of blue and
yellow producing green.
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