22 COLOUR VISION 



the nervous apparatus of vision constitutes an " inner eye," which 

 builds up a new visual world under the compulsion of the stimuli derived 

 from the real objects of the outer world. 



Things seen, visual objects, or colour forms must therefore be clearly 

 distinguished from the real objects. The untutored regard the green 

 of a leaf as an attribute of the leaf. The physicist, however, knows that 

 colour depends upon the light reflected from the leaf and calls the reflected 

 light green. The physiologist knows that the leaf, which appears green 

 when looked at directly may appear yellow or grey when its image falls 

 upon the peripheral part of the retina. He is therefore inclined to regard 

 the colour as an attribute of the eye itself. Finally, to the psychologist 

 the green is neither an attribute of the leaf, nor of the light, nor of the 

 eye, but a psychical phenomenon, a definite qualitative entity in con- 

 sciousness. 



Colours therefore are visual qualities, and we are only justified in 

 speaking of red or green objects, red or green rays, and so on in the broad 

 sense that the obj ects or rays appear red or green respectively under the 

 ordinary conditions of vision. Brightness and darkness, again, are not 

 attributes of the objects or light rays, but of the colours as visual 

 qualities. White, grey, and black must be included amongst the colours 

 as visual qualities, but may be distinguished from the variegated or 

 toned colours as untoned colours. 



The common attribution of colours to the objects themselves, thus 

 implying that the colours are properties of the objects, is largely a matter 

 of memory. We say that snow is white, soot black, blood red, because 

 under the ordinary conditions of life these objects appear to be of those 

 hues. In this sense the colours may be well termed " memory colours '' 

 (Geddchtnisfarben, Hering 1 ). The appearance of a given object at a given 

 moment is by no means determined solely by the nature and intensity 

 of the rays falling upon the eye and the condition of the nervous appara- 

 tus of vision at the time. These are but the primary and fundamental 

 exciting factors. They awaken unconscious reproductions or memories 

 of bygone experiences, which act as secondary but potent factors in the 

 subconscious sphere, modifying and in many cases determining the 

 ultimate conception. Thus it is that, though we are firmly convinced 

 that snow is white and blood is red, the pink glow of a snow-clad mountain 

 and the pallid hue of a face seen by the light of the mercury arc are 

 regarded as accidental colours in no wise modifying our impressions of 

 the actual colours of the objects. Every object with which we are 



1 Cf. Katz, Centralbl. /. Physiol, xx. 1906. 



