I 



1836.] Composition of White Light. 1 1 1 



are made in this way, the spectra are equal in intensity to 

 the primary colours. 



In the centre of the crimson silk there is a gilt ornament, 

 which in the accidental spectrum is violet ; the different 

 shades produced by the folds of the silk are also distinctly 

 marked. 



The crimson moreen is trimmed with black cord, which 

 in the spectrum, with the eyes closed, appears on the blue 

 as a pure white. The accidental blue, which is light and 

 very brilliant, is seen some time before the white makes its 

 appearance. 



When both objects are included in the same view, the 

 spectrum is formed of blue and green, quite distinct, and 

 in the proportions in which the primary colours fall on 

 the eyes. 



It is not necessary to direct the attention to the distinct 

 colours, or part of an object, to obtain a correct spectrum. 

 I have frequently been struck with the appearance of an 

 accidental colour, the primary of which, not being very- 

 conspicuous, had previously escaped my notice. 



The following accidental occurrence is a proof that no 

 attention is required to produce the complementary colours 

 of objects which fall on the eye. Happening while waiting 

 in a chapel for the commencement of the service, to sit 

 with a table before me covered with crimson cloth, my eyes 

 having been fixed for some time partly on the cloth, and 

 partly on the pulpit in front of it, I was surprised upon 

 changing my position to observe that the pulpit, which is 

 painted to represent oak, appeared of two different colours, 

 divided from each other by a distinct line of separation, 

 one green and the other its proper colour. My eyes being 

 very defective I was at first alarmed, fearing it was the 

 effect of some additional malady ; but it almost instantly 

 occurred to me that the green must be the accidental colour 

 of the crimson cloth ; and, upon repeating the experiment 

 with attention, I found this to be the case, the slightest 

 motion of the eye being sufficient to produce a stripe of the 

 accidental colour. 



I observed at the same time that the part of the eye 

 which had been occupied with the green accidental colour, 

 when again directed to the cloth, received a much more 



