Volume 5

Treasury of human inheritance / edited by Karl Pearson, R.A. Fisher, L.S. Penrose.

Date:
1909-
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Treasury of human inheritance / edited by Karl Pearson, R.A. Fisher, L.S. Penrose. Source: Wellcome Collection.

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    of colours. And for that purpose having darkened my chamber, and made a small hole in my window shuts, to let in a convenient quantity of the sun’s light, I placed my prism at his entrance, that it might be refracted to the opposite wall. It was at first a very pleasing diversion to view the vivid and intense colours produced thereby: but after a while applying myself to consider them more circumspectly, I was surprised to see them in an oblong form; which, according to the received laws of refraction, I expected would have been circular. They were terminated at the sides with strait lines, but at the ends the decay of light was so gradual, that it was difficult to determine justly what was their figure; yet they seemed semicircular. Comparing the length of this coloured spectrum with its breadth, I found it about five times greater; a disproportion so extravagant that it excited me to a more than ordinary curiosity of examining from whence it might proceed.” There follows the classical account of Newton’s experiments (too long to quote fully here and too beautiful to describe in words other than the author’s), with the conclusion: “And so the true cause of the length of that image was detected to be no other than that light consists of rays differently refrangible, which, without any respect to a difference in their incidence, were, according to their degrees of refrangi- bility, transmitted towards divers parts of the wall,” and the author’s doctrine of colours is propounded in thirteen propositions from which the following extracts are taken: “As the rays of light differ in degrees of refrangibility, so they also differ in their disposition to exhibit this or that particular colour. Colours are not qualifications of light, derived from refractions, or reflections of natural bodies (as it is generally believed,) but original and connate properties, which in divers rays are diverse. Some rays are disposed to exhibit a red colour, and no other; some a yellow and no other; some a green, and no other; and so of the rest To the same degree of refrangibility ever belongs the same colour, and to the same colour ever belongs the same degree of refrangibility....The species of colour, and degree of refrangibility proper to any particular sort of rays, is not mutable by refraction, nor by reflection from natural bodies, nor by any other cause, that I could yet observe. When any one sort of rays has been well parted from those of other kinds, it has afterwards obstinately retained its colour, notwithstanding my utmost endeavours to change it Yet seeming transmutations of colours may be made where there is any mixture of divers sorts of rays, for in such mixtures the component colours appear not, but, by their mutual allaying each other, constitute a middling colour There are therefore two sorts of colours. The one original and simple, the other compounded of these. The original or primary colours are red, yellow, green, blue, and a violet-purple, together with orange, indigo, and an indefinite variety of intermediate gradations. The same colours in specie with these primary ones may be also produced by composition: for a mixture of yellow and blue makes green. But the most surprising and wonderful composition was that of whiteness. There is no one sort of rays which alone can exhibit this. It is ever compounded, and to its composition are requisite all the aforesaid primary colours, mixed in a due proportion.” Newton would observe facts and deduce from his observations, but he must always have a foundation of experimental knowledge and had a fundamental dislike to pro pounding a theory which was not built upon this plan; it apparently gave him annoy ance to have his theory of colours referred to as an hypothesis. He says: “I do not take it amiss that the Rev. Father calls my theory an hypothesis inasmuch as he was not acquainted with it....if I had not considered them as true, I would rather have them rejected as vain and empty speculation, than acknowledged even as an hypo thesis 1 .” After discussing his experiments on colours, he says: “But to determine more absolutely what light is, after what manner refracted, and by what modes or action it produces in our minds the phantasms of colours, is not so easy. And I shall not mingle conjectures with certainties.” Newton, at a later date, after a much more detailed analytical investigation of the nature and phenomena of colours, propounds sixteen queries' 2 to encourage the search of others, and these queries are some of them concerned with the problem of the mechanism of colour vision. Thus: 1 Phil. Trans. Vol. vn, p. 4093. London, 1672. Sibl. No. 26, pp. 132-7.