112 



Dr. F. W. Edridge- Green. 



[Oct. 4, 



again examining the spectrum, there was no marked change in the orange or 

 any other part, with the exception of the green, which looked paler and more 

 yellow. I picked out the yellow of the spectrum by means of the shutters 

 of the spectrometer at exactly the same wave-lengths with and without the 

 blue-green spectacles, and with shorter and longer periods of colour adapta- 

 tion. The sodium flame appears less red through the blue-green glasses, 

 and there is no change to red after there has been colour adaptation. This 

 shows conclusively that yellow is a simple sensation and not compounded of 

 red and green sensations. If it were a compound sensation it should appear 

 red after colour adaptation to green. The results are in accordance with 

 those of colour fatigue.* The experiments on colour adaptation with the 

 sodium light and the subsequent disappearance of yellow from the spectrum 

 show that the yellow sensation is stimulated by the green, orange, and red 

 rays as well as by the yellow. This is in accordance with the facts of colour 

 mixing, and explains why red and green light make a yellow when mixed. 



An examination of definite regions in the green isolated in my spectro- 

 meter shows that the region corresponding to the dominant wave-length of 

 the glasses is most affected ; the regions on the blue side and the yellow 

 side appear bluer and yellower respectively. 



The following coloured cards were used for comparison in the photo- 

 meter : — 



Colour by daylight. 



Colour by electric light 

 (Osram incandescent). 



Colour by daylight. 



Colour by electric light 

 (Osram incandescent). 



1. Yellow 



2. Orange 



3. Slate 



4. Blue 



5. Yellow-green 



6. Green 



7. Brown 



8. Dark green 



9. Olive green 



10. Yellow 



11. Orange-yellow 



Pale orange 

 Orange 

 Grey 

 Blue 



Yellow-green 

 Green 



Light brown 

 Greenish -black 

 Dark green 

 Yellow 



Orange-yellow 



12. Chocolate brown 



13. Blue 



14. Brown 



15. Dark slate 



16. Eose red 



17. Rose 



18. Orange 



19. Black 



20. Brown 



Terra-cotta brown 

 Saturated ultramarine 



blue 

 Chocolate brown 

 Dark grey 

 Red 

 Rose 

 Orange 

 Black 

 Brown 



It will be noticed that there is very little difference in the appearance 

 of the colours by daylight and by electric light. This is due to colour 

 adaptation. If, however, two cards of the same colour be placed in a simple 

 photometer which I have had constructed for the purpose, and one side be 

 illuminated by daylight and the other side by an Osram electric light the 

 difference is very striking. The eye which examines the colours in the 



* ' Eoy. Soc. Proc.,' 1912, B, vol. 85, p. 434. 



