Proceedings of the Royal Institution. 401 



white ones, lilac, or purple combined with white, the intensity of the 

 spectrum of colour being exactly in proportion to the actual light 

 which is reflected from the black or white parts, and which dilutes 

 tlie colour; on green paper the black letters are brownish-red, the 

 white letters rose-colour, &c.' k>t. * /? p • . < i , '. ;; 

 , A curious instance of deception was mentioned as arising out of 

 these spectra. Mr. Brockedon stated, that one day, when walking in 

 the street, he slipt, and, like most people, turned suddenly round to 

 see the cause, when, looking on the ground, there was the appearance 

 of blood upon the spot where he looked, but in a moment after he 

 perceived that wherever he directed his eyes the blood still appeared ; 

 but the impression soon weakened. Aware then that this was a de- 

 ception, he looked for the cause, and found that he had been uncon- 

 sciously following a man with a slop-pail painted of a bright green, 

 of which the complementary spectrum presented was the red, which 

 surprised him. A knowledge of these contrasts of colour is, in many 

 ways, of great utility in decoration, in manufactures of pattern and 

 shot silks, and other tissues ; in dress, in the arrangement of an artist's 

 colours in his picture. It does not in the least degree dispense with 

 genius, but it is a means which talent may employ to facilitate its 

 productions, to give vividness without intensity, and in compounding 

 colours on the pallet, to obtain the requisite tints without muddling. 

 It is important to the painter, too, to know that long gazing on one 

 colour, renders his perception of another impure for a time. It ex- 

 plains, or at least offers a conjecture upon the cause of our percep- 

 tions of harmony in general arrangement. When two of the primitive 

 colours, as red and blue, alone or chiefly, impinge upon the eye, the 

 organ becomes distressed. If united, and forming purple, the eye is 

 excited to compensate its impression by a yellow spectrum ; these 

 preserve the tone of the organ, or, if yellow and purple separately 

 appear, they excite spectra which are complementary. But if, in- 

 stead of blue and red united, and forming purple, they in separate 

 colours affect the eye, then, each requiring its complement, yellow 

 would be found in both, the red exciting green, a compound of blue 

 and yellow^ and blue exciting orange, a compound of red and yellow ; 

 the excess of yellow thus excited produces a painful emotion. Har- 

 mony may be restored by placing on the picture a small quantity of 



