The relation of light perception to colour perception

Abstract

Since the majority of the theories of colour perception which have been propounded have been really theories of light perception, the two subjects, namely, colour and light perception, though really quite distinct, have become so interwoven in the discussion of the question that many seem quite incapable of distinguishing the two. Yet it may be easily shown that light perception and colour perception are quite distinct. In fact, we can divide cases of colour blindness into two classes, according as the defect is ( a ) one of light perception, or ( b ) one of colour perception or differentiation without any defect in light perception. Of course, both defects may be present in the same individual. The investigation of these two classes of defective vision is much facilitated by the use of a spectrometer which I have devised for the purpose, and which is so arranged as to make it possible to expose to view in the eye-piece the portion of a spectrum between any two desired wave-lengths. It consists of the usual parts of a prism spectroscope, i. e . a collimator with adjustable slit, prism, and telescope with eye-piece of the following dimensions :─ The prism is of flint glass, 1.65 refractive index for D. Eye-piece, Ramsden form, focussing on to the shutters described below.