54 



COLOUR VISION 



2Q 



10 



6 8 10 \i 14 16 18 20 !i 24 26 28 30 32 .54 36 58 40 4f 44 46 48 50 52 54- 56 58 60 62 64 66 

 22-& 3839-8 506 581597613 



Fig. 14. Normal trichromat's photopic and scotopic luminosity curves. (One amy] 

 acetate or Hefner unit is equal to 0-9 international candle power. ) Abscissae, arbitrary 

 scale of the prismatic spectrum of the arc light ; orclinates, arbitrary scale, the maxi- 

 mum of luminosity being in each case 100. (Abney and Festing.) 



300 



280 



260 



240 



220 



200 



180 



160 



14 



120 



100 



80 



60 



40 



20 



01 2 



3456 



ui 



7 8 9 10 111213 1415 17 



en o o en en oi _ 



-*J 01 co -* o co -vj cnoiAcoKDro-'O 



o * A co co to ~j en o> en -N| (Drocnco 



ID 

 O 



19 



cp 

 en 



21 



A 



O) 



m 



23 25 27 





Fig. 15. Scotopic luminosity curves. 



SchaternikofF s curve (normal 

 trichromat). - Nagel's curve (deuteranope). X X X X X and o o o o o, 



other observations by Nagel. Abscissae, wave-lengths of the prismatic spectrum 

 of gas light; ordinates. arbitrary scale. (Schaternikoff.) 



