THE FIELD OF VISION FOR COLOURS 



71 



eye. He used gelatine filters which transmitted approximately mono- 

 chromatic lights. 



The yellow-blue zone is " dichromatic." Beyond this zone there 

 is an extreme peripheral zone which is " monochromatic " or totally 

 colour-blind. It is best demonstrated in the nasal and upper and 

 lower portions of the field, but only with very small test objects in the 

 peripheral portion. If the luminosity curve for different colours is 

 worked out for this zone it is found to be quite different from the achro- 

 matic scotopic luminosity curve, v. Kries^ determined the peripheral 

 luminosity values and compared them with Nagel's corresponding 

 values for the achromatic scotopic luminosity curve : 



Wavelengths 680 651 629 608 589 573 558 



Periphery values 0-6 37-5 77-5 101 100 796 52-2 



Scotopic values ? 3-4 14 355 100 256 351 



The curves are shown in Fig. 25. 



530 512 

 28-5 14-6 

 321 198 



680 651 629 608 589 573 558 530 



513 



Fig. 2a. 



Photopic luminosity curve for the totally colour-blind peripheral 



zone of the retina Scotopic luminosity curve. Abscissae, wave-lengths of 



the prismatic spectrum of gas light; ordinates, arbitrary scale, (v. Kries.) 



The peripheral luminosity curve is highest at about 608 /m/x instead 

 of 544 ju.^, thus nearly approximating the luminosity curve for the fovea. 

 We have here a further proof that peripheral vision is to be regarded 

 as central vision diminished in sensibility, whereas scotopia is a difTerent 

 form of vision ; the former is a quantitative variation, the latter 

 qualitative. 



^ Ztsch. f. Psychol, u. Physiol, d. Sinnesortj. xv. 247, 1897. 



