112 P. C. on the Colours that enter into the [Aug. 



vivid impression from it than the other parts of the eye 

 which had not been removed from it ; and upon turning 

 the eyes from one object to the other in rapid succession, 

 both colours became exalted ; the crimson, though some- 

 what faded, being thus rendered very brilliant; and its acci- 

 dental colour, upon the oak ground, became a vivid green. 



I have made a great variety of experiments in the manner 

 before described, with all the different colours, and the 

 results have invariably confirmed the theory I have ad- 

 vanced, that red, green, and violet, are primitive colours ; 

 blue, crimson, and yellow, being complementary to them, 

 and, of course, compound colours. 



Another method by which I have analyzed the colours 

 of the spectrum, has been to direct the eye when impressed 

 with a primary colour, to a ground formed by a mixture 

 of this colour with some other, and thus exhibit the latter 

 colour only ; proving the compound character of the 

 coloured ground, and at the same time shewing its com- 

 ponent principles. 



If, when the eye is impressed with red, we look at a 

 white paper, the accidental colour is blue ; if we substitute 

 a yellow paper, the accidental colour is changed to green. 

 If we then impress the eye with green, the accidental colour 

 on a white ground will be crimson, and upon a yellow 

 ground red : thus, proving that yellow is a compound of 

 green and red, by exhibiting its component colours sepa- 

 rately. Crimson and blue may be analyzed in the same 

 manner. The colours exhibited in these experiments are 

 rendered much more vivid by repeatedly directing the eye 

 to the different objects in succession. 



Another method of analyzing compound colours, is to 

 allow light of two colours to fall upon a ground, also, of 

 two colours, only one of which corresponds with either of 

 the colours admitted to it ; the other being, of course, the 

 complementary colour of both. When, for instance, yellow 

 light, formed of red and green, is admitted to a blue 

 ground, it produces a green ; this being the only part of 

 yellow light which is reflected by a blue ground, or by 

 objects which appear blue in white light. It is upon this 

 principle that blue frequently appears green by candle 

 light ; the violet rays being deficient in this light, it 

 approaches to yellow. 



