376 PRACTICAL PHYSIOLOGY 



spectrum, and the results of their mixture yields various colours which 

 are largely mixed with grey. 



EXPERIMENT I. Take two large discs of red and green and two 

 small of black and yellow. Adjust the proportion of the red and green so 

 that rapid revolution produces a yellow. This will be dark in shade 

 and can be matched by the inner discs of yellow and black. 



EXPERIMENT II. Take large discs of green and violet and small 

 discs of blue and black. With the large discs a blue can be obtained 

 and matched with the smaller discs. 



EXPERIMENT III. Take three large discs of red, green, and violet. 

 To bring about a good result the red should correspond to the red in 

 the spectrum at wave-length 6300, the green to wave-length 5150, and 

 the blue to wave-length 4700. Arrange these so that red constitutes 

 about 118, green about 146, and blue about 96. Arrange also two 

 smaller discs of white and black. As the result of revolution the 

 larger discs will give a grey, which can be matched by about 285 black 

 and 75 degrees white of the smaller discs. 



EXPERIMENT IY. Using the three discs of Experiment III., work 

 gradually through the whole spectrum, using different sized sectors of 

 each for the different regions of the spectrum. The sizes of these 

 sectors will roughly correspond to the different degrees in which the 

 three primary colour sensations according to the Helmholtz theory are 

 evoked. 



The best method of fusing the colours sensations is to superimpose 

 the various colours of the spectrum by projection of the same on a 

 white screen. 1 By means of lenses the spectrum can be recomposed as 

 white light. By introducing shutters eliminating certain portions of 

 the spectrum the result of fusion of the remaining colours can be 

 examined. 



5. Complementary Colours. For every colour in any part of the 

 spectrum there is a colour in another part of the spectrum which, when 

 mixed with it, will yield a white or grey. Such colours are said to be 

 complementary. 



EXPERIMENT I. Take from the series of colour discs one of an 

 orange colour. If no disc can be found which in any proportion with 

 the orange disc will give a white or grey, take the blue and green discs 

 and adjust all three so that a grey is obtainable. (This should be 

 estimated by smaller discs of black and white). A certain proportion 

 will exist between the blue and the green. If now the whole circle be 



1 See Abney, Colour Vision, p. 18 et seq. 



