68 COLOUR VISION 



Charpentier^ obtained the following results with coloured paper of 

 20 sq. mm. 



Violet Blue- Yellow- Red Orange Yellow Blue 



Hess's field for invariable red and green {vide infra, p. 70) with an 

 object subtending 3° was 21° inwards, 43° outwards, 17° upwards, and 

 14° downwards. 



The fields for colours are approximately concentric with that for 

 white. The colours change in appearance in passing from the point 

 of fixation towards the periphery. Those at the red end of the spectrum 

 pass through yellow to grey ; those at the violet end through blue to 

 grey. Blue-green becomes green, then yellow-green, then yellowish 

 white (Hering). 



Baird'^, who has paid particular attention to this point, finds that 

 the changes in colour in passing from the periphery towards the centre 

 are as follow. Red first appeared yellowish, then passed through 

 yellow, orange and orange-red before it finally appeared red. Orange 

 first appeared yellow, becoming more and more orange. Yellow 

 appeared yellowish and gradually increased in saturation. Green 

 appeared yellowish at first, gradually increased in saturation, assuming 

 a greenish and finally a green tint. Blue became more and more 

 saturated. Violet appeared bluish, then blue, and finally violet. 

 Purple gave the longest and richest series of transitions : beginning 

 with yellowish, its tone gradually moved down the spectrum, passing 

 through orange-yellow, orange, red, and purplish red, before the pure 

 tone finally appeared. 



Aubert^ found the limits of the coloured fields determined by the 

 intensity of the light, and this result was confirmed by Landolt, Char- 

 pentier and others. The periphery is therefore dyschromatopic rather 

 than achromatopic (Charpentier). The diminution in intensity, as 

 measured by the distance of visibility of coloured spots, is given in 

 Fig. 24. The sudden curve in the blue at the macula is due to macular 

 pigmentation and also probably to dark adaptation. 



1 La Lumiere d les Couleurs, p. 193. 



2 The Color Sensitivity of the Peripheral Retina, AVasliington, 1905. 

 ^ Physiologie der Netzhaut, p. 116, 1865. 



