THE HUMAN COLOUE SENSE. ^ 171 



laws of musical harmony to painting, with no reservation 

 whatever, only observing that juxtaposition is to colour what 

 synchronous co-operation is to sound. The visual faculty 

 deals with space and the auditory Avitli time ; but this simple 

 physiological fact can scarcely be taken into account by 

 those experimentalists who mix rays of colour in the hope 

 of obtaining a harmonious combination, and further, if they 

 don't succeed good names may go to swell the list of the 

 opponents of the ^'■analogy of sound and colour.'' Moreover, 

 they don't appear to be aware that they are only dealing 

 with " overhues,'' as physical mixture would seem to be 

 impossible, except in the case of pigments. Thus great 

 stress is laid on the fact that green cannot be produced 

 by the mixture of yellow and blue light, but the cause 

 of this is not far to seek. In the first place the mean of 

 the two sets of vibrations would be a blue green {^^) and 

 not pure spectral green (Ftj), and 2ndly, the sum of the 

 two would be theoretically the octave of the same green, 

 and consequently overreach the limit of colour vision. In 

 the prism itself the formation of green is always coincident 

 with the overlapping of the yellow and blue bands, though 

 it is assumed that the fact admits of some other explanation. 



In all the experimental mixtures of coloured light hitherto 

 carried out, no reference has been made to the analogy ot 

 " overhues " in colour to " overtones " in sound, and the 

 result has been the reception of green and violet as 

 primitives so called to the exclusion of ^yellow and blue, 

 and so lend support to the " Young- Helmlwltz theory.'' 



Whatever progress had been made in tlie study of music 

 up to the days of Pythagoras it is clear that he made good 

 use of the monochord, and handed it down to us as the 

 only test of musical perfection, so that the validity of the 

 deductions drawn from any other means must still be 

 submitted to the same test, which is satisfactorily applied in 

 Table II. We talk familiarly of the scale of colour as being 

 composed of red, orange, yellow, green, blue, indigo and 

 violet, but as in the iris there are numerous grades of hue in 

 all the colours, and the human colour sense is not always to 

 be depended upon, without the application of the musical 

 ratios it would be quite impossible to furnish so perfect a 

 scale of colour as that given in Table I. 



As might be expected whenever the analogy of sound and 

 colour is ignored, all reference to tones and semitones of 

 colour must be indefinite and uncertain. Thus red spoken 



