72 ON COLOUR. Paet I. 



ries. But this is a philosophical view of them which does 

 not appertain to the question of their employment for orna- 

 mentation. Whatever may be their properties, or their right 

 to the name of colours, the eye has positive evidence of their 

 holding a place, and having their own effect, when in com- 

 bination with other colours. 



47. The tones and gradations of each primary, as well as of 

 any other colour, belong, of course, to the same class as its 

 fundamental hue ; but the moment a simple colour is mixed 

 with any other, it ceases to belong to the same class ; and if 

 it is sometimes the custom to classify crimson, scarlet, pink, 

 and others with the reds, they cannot be reckoned among the 

 primaries ; scarlet, for instance, having a certain quantity of 

 yellow mixed with the red, and therefore being a compound 

 colour. It is, therefore, only for convenience' sake, or in 

 accordance with a conventional custom, that we are justified 

 in classing them among the reds. 



48. Accidental Colours. — The accidental colour to any one of 

 the three primaries, as is well known, is the union of the other 

 remaining two. Thus, green {i.e. blue and yellow) is acci- 

 dental to red, orange to blue, and purple to yellow. Black 

 and white are also accidental to each other. As the simple 

 primary is accidental to the compound secondary colour (red 

 to green, blue to orange, and yellow to purple), so a tertiary, 

 in like manner, has its accidental colour, in the remaining one 

 not forming part of its composition. 



Though the existence of accidental colours was known 

 before Newton's time, he was the first to make any careful 

 experiments respecting them, an account of which he sent to 

 Locke; but this was not published till 1829, in Lord 

 King's life of that philosopher. The following are among 

 the observations made by Sir David Brewster on the subject of 

 accidental colours. If we place a red wafer on a sheet of white 

 paper, and fix the eye on the red spot, and then turn the eye 



