75 



matic analysis of the fullest and most vivid yellows (those which 

 excite the sensation of yellowness in the greatest perfection), as the 

 colours of bright yellow flowers, or that of the yellow chromate of 

 mercury, clearly demonstrates the fullness, richness, and brilliancy 

 of their colour to arise from their reflexion of the whole, or nearly 

 the whole of the red, orange, yellow, and green rays, and the sup- 

 pression of all, or nearly all the blue, indigo, and violet portion of the 

 spectrum. On the hypothesis of an analysis of sensation correspond- 

 ing to an analysis of coloured light, these facts would seem incom- 

 patible with the simplicity of the sensation yellow, and it would 

 appear impossible (on that hypothesis) to express them otherwise 

 than by declaring red and green to be primary sensations, and yellow 

 a mixture of them a proposition which needs only to be understood 

 to be repudiated quite as decidedly as that the sensation of green- 

 ness is a mixture of the sensations of blueness and yellowness, and for 

 the same reason ; the complete want of suggestion of the so-called 

 simple sensations by the asserted complex ones. 



Mr. Maxwell's assertion that blue and yellow do not make green, 

 assuredly appears startling as contradictory to all common experience ; 

 but the common experience appealed to is that of artists, dyers, and 

 others in the habit of mixing natural colours as they are presented to 

 us in pigments, coloured tissues, &c., who have for the most part 

 never seen a prismatic spectrum, or at least attended to its phseno- 

 rnena. The perceptions of colour afforded by such objects are those 

 of white light from which certain rays have been abstracted by ab- 

 sorption, that is to say, they are negative hues, or hues of darkness 

 rather than of light, inasmuch as all the colouring of the artist is 

 based, not on the generation, but on the destruction of light. This 

 circumstance, which is not generally recognized, even among edu- 

 cated artists, has vitiated all the language of chromatics as applied to 

 art, and so placed a barrier between the painter and the photologist, 

 which has to be surmounted before they can come to a right under- 

 standing of each other's meaning. It is evident, that, to make 

 experiments on the subject free from this objection, absorptive 

 colours must be discarded, at least in bodily mixture with each other. 

 Thus it is true that a dingy green may be produced by rubbing 

 together in powder prussian blue and the yellow chromate of mer- 

 cury above mentioned ; but both these agree in reflecting a con- 



