ACCIDENTAL COLOURS. 545 



If a strong impression is created by some definite 

 colour, the eye perceives the complementary colour, 

 although it has no real existence. Thus, let a burning 

 candle be placed at a small distance from a white sheet 

 of paper, and near a window, so that two nearly 

 equally dark shadows of a pencil may be thrown upon 

 the paper, due respectively to the light of the window 

 and to that of the candle. The shadows will not appear 

 both grey, but one will have a bluish, the other a 

 reddish tinge. The reason is, that the light of the 

 candle is not white, but yellowish, and that there- 

 fore the sheet of paper upon which the light of the 

 candle and diffused daylight fall reflects a yellowish 

 light. That portion of the paper, however, upon which 

 the shadow caused by the candle is projected receives 

 none of the yellowish light, and by contrast with the 

 adjoining large yellow space it appears bluish. On 

 the other hand, the shadow caused by the daylight re- 

 ceives the yellowish light of the candle, hence by con- 

 trast with the much less yellow adjoining space, and 

 with the bluish shadow caused by the candle, it appears 

 reddish. If a small piece of grey paper is placed upon 

 a surface which is of a bright colour, for example, 

 on a piece of coloured fabric or (unglazed) paper, and 

 both are looked at while exposed to the direct rays of 

 the sun, or strongly illuminated by some other means, 

 the grey paper will exhibit the complementary colour 

 of that of the surface below it ; if the latter is blue, the 

 paper appears yellow ; if red, the grey paper appears 

 green, and so on. The name of ' accidental colours ' has 

 been given to those colours which are perceived in such 

 cases without their having an actual existence. 



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