Biology Reference
In-Depth Information
Newton (
1730
, pp.179-185, 245-288), a pigment may absorb, transmit
and reflect the spectral lights that fall upon it and when two pigments
are mixed, the new compound pigment reflects and transmits only
those rays that are not absorbed by each of the two pigments. This
complexity, of course, prevented an adequate control of the spectral
composition of the light that entered the subject's eye. Moreover,
both Newton (
1730
, pp.132-134) and Helmholtz (
1852
) stressed that
the experimenter could not control the composition of the spectral
lights by the apparent colour of the pigment either, since the same
colour sensation could be a composite of different spectral lights (the
metamerism of colours).
On the other hand, when monochromatic
prismatic
lights
were mixed and focused on the retina, the different rays that entered
the eye were combined additively and could easily be controlled and
varied by the experimenter. Thus, as was first clearly explained by
Newton (
1730
) and later by Helmholtz (
1852
), mixing of pigments
and mixing of spectral lights generated a subtractive and an additive
result, respectively.
Another serious problem confronting the trichromatic colour
theory of Young (
1807
) was the observation of Helmholtz (
1852
) that
monochromatic spectral colours could
not
be reproduced by mixing
three primary spectral lights. Thus, he found that prismatic yellow
and blue colours could not be matched by mixing, respectively, red
and green, and green and violet lights. The spectral colours were found
to be more saturated than the mixtures. Adding another primary to
the mixture would only enhance the saturation differences found.
Helmholtz (
1852
) concluded that there had to be at least five so-called
primary colours.
2.7 Maxwell: triplicity of colour vision
proved
The results of Maxwell's (
1855
,
1860
) colour matching experiments,
however, showed this conclusion to be wrong and the trichromatic
colour theory of Young to be on the right lines. Maxwell's treatment
