GEOMETRICAL COLOUR TABLE. 



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(tig. 537) two differently coloured pieces of glass ; the coloured rays of light passing through 

 the holes unite on the retina, and produce a mixed colour (Czermak). 



Complementary Colours. Investigation shows that the following colours of the spectrum are 

 complementary, i.e., every pair gives rise to white : 



Red and greenish-blue, Orange and Cyan-blue, 



Yellow and indigo-blue, Greenish-yellow and violet, 



while green has the compound complementary colour, purple (v. Helmholtz). 



The mixed colours may be determined from the following table. At the top of the vertical 

 and horizontal columns are placed the simple colours ; the mixed colours occur where they 

 intersect the corresponding vertical and horizontal columns (Dk. =dark ; wh. = whitish) : 



The following results have been obtained from observations on the mixture of 

 colours : 



1. If two simple, but non-complementary, spectral colours be mixed with each 

 other, they give rise to a colour sensation, which may be represented by a colour 

 lying in the spectrum between both, and mixed with a certain quantity of white. 

 Hence we may produce every impression of mixed colours by a colour of the spec- 

 trum + white (Grassmaii). 



2. The less white the colours contain, the more " saturated " they are said to 

 be ; the more white they contain, the more unsaturated do they appear. The 

 saturation of a colour diminishes with the intensity of the illumination. 



Geometrical Colour Table. Since the time of Newton, attempts have been made to construct 

 a so-called "geometrical colour table," which will enable any mixed colour to be readily found. 

 Fig. 561 shows such a colour table ; 

 white is placed in the middle, and from 

 it to every point in the curve, which is 

 marked with the names of the colours, 

 suppose eaph colour to be so placed 

 that, proceeding from white, the colours 

 are arranged, beginning with the bright- 

 est tone, always followed by the most 

 saturated tone, until the pure saturated 

 spectral colour lies in the point of the 

 curve marked with the name of the 

 colour. The mixed colour, purple, is 

 placed between violet and red. In order 

 to determine from this table the mixed 

 colour of any two spectral colours, unite 

 the points of these colours by a straight 

 line. Suppose weights corresponding to 

 the units of intensity of these colours, 

 to be placed on both points of the curve 

 indicating colours, then the position of 

 the centre of gravity of both in the line 

 connecting the colours indicates the posi- 

 tion of the mixed colour in the table. The mixed colour of two spectral colours always lies in 

 the colour table in the straight line connecting the two colour points. Further, the impression 

 of the mixed colour corresponds to an intermediate spectral colour mixed with white. The 

 complementary colour of any spectral colour is found at once by making a line from the point 

 of this colour through white, until it intersects the opposite margin of the colour table ; the 

 point of intersection indicates the complementary colour. If pure white be produced by mixing 

 two complementary colours, the colour lying nearest white on the connecting line must be 

 specially strong, as then only would the centre of gravity of the lines uniting both Colours lie 

 in the point marked white. 



Violet 



Cyan blue 



Yellow 



Orange 



Red 



Fig. 561. 

 Geometrical colour cone or table. 



