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 1 determined the peripheral 

 luminosity values and compared them with Nagel's corresponding 

 values for the achromatic scotopic luminosity curve : 



Wave lengths 

 Periphery values 

 Scotopio values 



The curves are shown in Fig. 25. 



350 



325 



300 



275 



250 



225 



200 



17 5 



150 



125 



100 



75 



50 



25 



Fig. 25.. 



680 651 629 6O8 589 573 558 530 513 



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 /z/z instead 

 of 544 /z/z, 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 different 

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

 qualitative. 



1 Ztvch. f. Psychol. u. Physiol. d. Sinneaonj. xv. 247, 1897. 



