Light and Colour Theories, and their relation to light and colour standardization

by Joseph W. Lovibond

The Red, Green, and Violet theory appears to be based on two principal assumptions: first that there are only three fundamental colours; and second that the rays taken from different colour areas are pure colours. Both assumptions are open to question. In regard to the first, there is no difficulty in isolating six colours; and as to the second, it can be demonstrated that the colours do overlap in every part, with a double overlapping in the middle colours, and are therefore not simple but complex.

PAST THEORIES.

In a work of this nature it is unnecessary to deal minutely with the theories which have been adopted from time to time since Newton’s discovery of the continuous spectrum. It will, however, be useful to touch on the principal points where theorists are agreed, and also on some of their points of difference, the latter in order to find, if possible, the causes of their difference.

TABLE I.

	No. of Rays.	Primary Colours.
Newton (later)	7	Red,	Orange,	Yellow,	Green,	Blue,	Indigo,	Violet
Werner	6	Red,	Orange,	Yellow,	Green,	Blue,		Violet
Newton and Helmholtz (early)	5	Red,		Yellow,	Green,	Blue,		Violet
Hering	4	Red,		Yellow,	Green,	Blue
Chevieul, Brewster, Hay, Redgrave, Field	3	Red,		Yellow,		Blue
Young, Helmholtz (later)	3	Red,			Green,			Violet

Note to Plate I.

The respective positions of the primaries of each theory in regard to the whole cycle of distinguishable colours are illustrated above, and the primaries of each theory are shown in their several spectrum positions, the spectrum being shown as bent in circular form.

The six principal theories of primary colours are given in Table I, and illustrated on Plate I, with the names of the primaries of each theory opposite the names of some of their principal advocates. It should not be forgotten when comparing these wide divergences, that each theory has been the result of experimental evidence, in what was, at the time, and remains up to the present, a new and progressive branch of science.

They agree that the spectrum colours are purer than the pigmentary colours, and that by reason of their being referable to wave length positions, they are most adaptable as standards of colour. There has also been common agreement that certain colours are primaries, and that all other colours are mixtures of these, but there has been wide divergence as to their number and even the colours themselves.