Biology Reference
In-Depth Information
of his experimental results was based on Newton's ideas of colour
mixture. Thus, he presumed that the method of determining the
position and strength of the resultant colour of mixed lights is
mathematically identical to that of finding the centre of gravity of
weights and placing a weight equal to the sum of the weights at the
point so found. This presumption presupposes that colour mixing
is additive. If, for example, the same light is added to or subtracted
from both test and comparison fields, which have been matched
with respect to all colour aspects, it is assumed that the match will
still hold; or if two matched lights (A and B) are added to two other
matched lights (C and D), the result is two lights that match, that
is, (A + C) match (B + D). As Helmholtz (
1855
, p. 24) puts it, 'Gleich
aussehende Farben gemischt geben gleich aussehende Mischungen'
(mixing equally appearing colours gives equally appearing mixtures).
Hence, Maxwell (taking account of Newton's laws of gravitation)
could express his colour-mixture results
algebraically
in the form of
equations with the colour under test on one side of the equation and
the mixture of three standard lights (red, green and blue) on the other.
Thus, Maxwell (
1860
) first made a colour match between
a mixture of his standard red, green and blue lights and a constant
reference white. He then replaced one of the standard primaries by the
monochromatic spectral light to be studied, and a new match of the
constant white was made. Now he had two equations for the match
of the same standard white and could subtract one from the other to
obtain the equation of the unknown spectral light investigated. By
this procedure, Maxwell (
1860
) discovered that the colour effects of all
monochromatic spectral lights could, in fact, be matched by using only
three primaries. Hence, he had proved that the retinal colour response
to spectral lights must involve a triplex mechanism. Since there was
no histological evidence for such a triplex mechanism at the time, the
triple subdivision had to occur on a sub-microscopic scale.
His mathematical treatment was as follows:
Given that the three standard lights are denoted
R
,
G
and
B
,
white sensation
W
, the spectral light to be studied
S
and
a
,
b
,
c
,
