114 



Colour Adaptation. 



and this was viewed with an eye adapted to electric light, the two no longer 

 matched, the blue now appeared blue and the brown pale purple. 



No colour is seen by colour adaptation unless the corresponding physical 

 stimuli are present in the light reaching the eye. On remaining in a room 

 illuminated by light through red glass windows, green will become 

 increasingly noticeable, but only when a certain amount of green light is 

 transmitted by the red glass. If, however, a red glass be used which is 

 impervious to green, not a trace of green will be seen in green or black 

 objects. A simple yellow still appears yellow after adaptation to electric 

 light, but a compound yellow, which appears pure yellow by daylight, and 

 which is compounded of red and green, appears greenish-yellow after- 

 adaptation to electric light. 



Colour adaptation appears to produce its effect by subtraction, and not by the 

 addition of any new colour sensation which is not previously present. The 

 ultramarine blue, which, when illuminated by electric light, matches a 

 chocolate brown illuminated by daylight, appears blue after colour adaptation 

 to electric light through the subtraction of the yellow element of the light 

 reflected from the card. A blue sky appears much bluer when viewed from a 

 room illuminated by electric light than it does when seen from an unlighted 

 street, because, when viewed in the latter position, the eyes are adapted for 

 the light of the sky, and, when viewed from the room, any yellow element is 

 subtracted. 



Summary. 



1. In colour adaptation, the retino-cerebral apparatus appears to become 

 less and less sensitive to the colour corresponding to the dominant wave- 

 length, and to set up a new system of differentiation. 



2. When light of a composition differing from that of daylight is employed 

 to illuminate objects, an immediate and unconscious estimation of the colours 

 of these objects is made in relation to this light, the light employed being- 

 considered as white light. 



3. No colour is seen of which the physical basis is not present in the light 

 employed. 



4. When spectral regions are examined with a colour-adapted eye, that of 

 the dominant wave-length appears colourless, whilst those immediately on 

 either side of it appear to be shifted higher and lower in the scale respectively. 



5. There is immediate colour adaptation, as well as colour adaptation after 

 a longer stimulation with the adapting light. 



6. Colours which correspond to the dominant wave-length of an artificial 

 light are with difficulty discriminated from white by this light. 



7. Colour adaptation may bring two colours below the threshold of 



