CHAPTER I.

Introduction.

It may at first appear strange that colour, one of the most important indices of value in the Arts, Manufactures, and Natural Products, should have no common nomenclature or reliable standard for reference, the reproduction of a given colour depending for exactitude on the memory of a sensation; whereas this branch of science requires a physical means of recording a colour, with a power of recovery. It remains to be shown that this power of record and recovery is possible, and depends only on the observance of a few simple natural laws easy of application.

The study of colour is carried on by two principal methods: the spectroscopic, where the colours are partially separated as a continuous band by a regular variation in their indices of refraction, the colours gradually merging into each other by overlapping in opposite directions; or by absorption, where a colour is developed by absorbing its complementary, and is isolated as a single or complex colour. This latter is nature’s own method.

It is necessary to touch on some theoretical differences which exist between Scientists and Artists, as to which are Primary colours, as confusion of this character retards investigation. Scientists adopt Red, Green, and Violet as Primaries, regarding all other colours as mixtures of these; whilst Artists and Colourists adopt Red, Yellow and Blue as the Primaries, and all other colours as made from them.

The theory of the Scientists is based on the phenomena developed by mixing coloured lights taken from different parts of the spectrum. This is a method of synthesis, each added colour being a progressive stage towards the complexity of white light. In this case the colour developed is that of the preponderating ray of a complex beam. The theory of the Artists is based on the phenomena developed by mixed pigments. This is a method of analysis, tending towards ray simplicity, each added pigment reducing the complexity of the colour developed by its power of selective absorption.

The theoretical differences between the two schools appear to have arisen from supposing that a given colour developed by the two methods should correspond; but considering the differences in their ray composition, this would be impossible, for although both may be describable by one general colour term, as for instance a Red, they would be of two varieties. It remains to be shown that one theory may cover both sets of phenomena.

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 | Primary Colours. |Rays.| ----------------+-----+------------------------------------------------- Newton (later) | 7 | Red, Orange, Yellow, Green, Blue, Indigo, Violet | | Werner | 6 | Red, Orange, Yellow, Green, Blue, Violet | | Newton and | | Helmholtz | 5 | Red, Yellow, Green, Blue, Violet (early) | | | | 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.