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tain tones of colour (see § 231, Remark) more than they reflect
them. If this is the case the Spectroscope will show us, which
of our metals are contained as vapours in the sun's atmosphere.
Remark. For optical instruments this decomposition of light would be
very inconvenient, hence it was a great improvement, when Dolland in the
year 1757 combined two lenses: one of crown glass, the other of fint
glass (containing much lead and having a stronger dispersive power) in
such a way that they compensate each other as regards coloration. Such
lenses are called achromatic lenses. 397.
§ 227. 2) As to the colour of bodies it is Newton's theory,
that bodies are not coloured at all, but that they have the proper
ty to decompose the white sun-light, absorb most of the rays and
reflect only those rays, the colour of which they seem to have.
So, f.e.green leaves have the property to reflect green rays more
than any other colour. 402. White bodies reflect all rays and
black none. 403. (So white and black colours are no colours
at all.) Green and blue are but with great difficulty distin
guished in the light of a lamp. 404.
§ 228. The colours needed to complete the sensation of
white light are called complementary colours. They are: green
and red, orange and blue, indigo and yellow, etc. After
having looked at the setting sun we see a green disc upon a
white wall, because a mixture of the rays without red produces
green. 405. If we look for some time upon a sheet of common
red blotting paper on the ground and then upon the plank near
it, we shall see a corresponding green space. By the conjoint
light of the moon and of the light of a candle a body throws a
blue shadow upon a sheet of white paper. Snow exposed to the
sun's light on a clear day looks yellowish; if in the shade bluish.
We see that colours do not always correspond with the real con
dition of the object, but may be only subjective colours.
Any excessive irritation of our optical organ by one colour
