1054 



THE SENSES 



less by the medium, and still less by the long waves. The curves 

 in Fig. 44^7 illustrate these relations. 



The theory explains as follows the phenomena of colour- mixture 

 referred to above. When all the rays of the spectrum act upon 

 the retina together, the three components are about equally affected, 

 and this equal effect is supposed to be the condition of the sensation 

 of white light. When the green of the spectrum alone falls on the 

 retina, the ' green ' component is strongly excited, the other two 



Fig. 447. Curves of Excitability of Primary Sensations from Observations on 

 Colour Mixtures (Konig). The numbers give wave-lengths of the spectrum in 

 millionths of a millimetre. 



only slightly ; this is the relation between the amount of excitation 

 in the three components which is associated with a sensation of 

 spectral green. When two complementary colours, such as red and 

 bluish-green, fall together on the same portion of the retina, the 

 three components are excited in the relative proportions associated 

 with the sensation of white light. 



The colour triangle is a graphic method of representing various facts 

 in colour-mixture (Fig. 44 Q ). 



The chief points to be noted are the following: (i) On the curve 



the spectral colours are 

 arranged at such dis- 

 tances that the angle con- 

 tained between straight 

 lines drawn from the 

 point marked ' white,' 

 and intersecting the 

 curve at the positions 

 corresponding to any two 

 colours is proportional to 

 their difference in tone. 

 (2) The distance of any 

 Fig. 448. Colour Triangle. point of the curve from 



the point marked ' white ' 



is proportional to the stimulation intensity of the colour corresponding 

 to it. (If the stimulation intensities of all the colours be represented by 



