Biology Reference
In-Depth Information
Fig. 2.1 The colour circle of Newton representing the visual spectrum.
Although Newton held that the prismatic spectrum consisted of
innumerable different sorts of rays, he assumed that the number of
primary colours was restricted to seven.
the centre of gravity principle of colour mixture (implying additivity
of colour matches) and the concept of spectral composition of light
stimuli were clearly spelled out by Newton.
Not all colour-mixture data, however, could readily be handled
by Newton's model. He found that when two colours opposite to
each other in the colour circle were mixed in due proportions, so
that the common centre of gravity fell on the centre of the circle, the
colour mixture did not generate a perfect white. Mixing four or five
(or possibly three) primary colours, however, was sufficient. A further
complication was observed when primary red and violet were mixed.
In such instances he found the resultant colour to be purple, which
was not a prismatic colour and, therefore, did not fit well with his
model of colour mixture. (See Helmholtz,
1855
, for a discussion.)
