178 P. C. on the Colours that enter into the [Sept. 



tary colour. When, for instance, we look for some time at 

 the lackered knob of a lock, upon a door, originally white, 

 but rendered yellow by the usual effect of time, the white 

 appears to recover its former purity ; and when the eye 

 directed to it has been too much impressed to stop at this 

 point, it is converted to violet, its complementary colour ; 

 or, if we look for a short time at crimson and red, alter- 

 nately, the former approaches to violet, and the latter 

 appears of a dull brick colour. 



It may be supposed that when two colours are brought 

 near to each other, as in a picture, for instance, the eye 

 does not rest long enough upon one of these colours to pro- 

 duce any effect with regard to the other; or, that the 

 colours occupy different parts of the eye, and, therefore, do 

 not interfere with each other ; but the facts are otherwise ; 

 if the eye rests upon a colour for a few seconds only, or 

 when the transition from one colour to the other is so rapid 

 as only to give time to observe the different colours, as 

 exemplified in the two coloured shadows we have been 

 treating of, it produces a very decided effect ; and it will be 

 found that however near the colours are to each other, 

 there is a slight motion of the eye, when the attention is 

 turned from one to the other, which brings them in succes- 

 sion to the same part of it. 



These observations are verified by several of the preceding 

 t experiments ; and by many others which I have not con- 

 sidered it necessary to insert. It appears, from them, that 

 to exalt a colour it might be placed near its complementary 

 colour ; and that to depress it, the eye must be prepared by 

 the same colour, or a compound colour in which it takes a 

 part. Nature has given us many examples ; her finest 

 productions are frequently heightened by contrast ; even 

 the bloom of the rose derives additional beauty from the 

 green leaves which surround it. 



The phenomena of accidental colours are highly interesting 

 and instructive ; the colours are produced with a facility 

 which those who are not familiar with the subject are not 

 prepared to expect ; and there is no appearance connected 

 with them, that I am acquainted with, which does not admit 

 of an easy and simple explanation upon the received theory. 

 We cannot, however, attribute the appearance of accidental 



