116 COLOUR VISION 



so that the after-image formed a band across the middle of the spectrum. 

 After fatigue with 654 — 675 /x/x the extreme red was slightly diminished, 

 there was no change in the orange, yellow, or green, and the blue and 

 violet became darker and bluer. If only red and orange were viewed 

 the red disappeared and the orange remained. The sodium flame 

 appeared unchanged (Porter), slightly greener (Edridge-Green). After 

 fatigue with orange, 619 — 631 /x/u,, the dark blue after-image was seen 

 right across the spectrum except in the region of the orange, which 

 appeared unaffected. If only red and orange were viewed the red was 

 replaced by the green-blue after-image, whilst the orange appeared 

 unaffected. After fatigue with orange-yellow, 585 — 595 /x/x, the purple 

 after-image appeared as if painted over the spectrum, the red being 

 affected most. Fatigue with yellow-green, 545 — 550 /x/x, gave a similar 

 result, with least effect in the orange. Fatigue with blue-green, 496 — 

 500 /x/A, gave the same effect,a purple (not red) after-image, with orange 

 least affected : the sodium flame appeared unchanged (Porter), slightly 

 redder (Edridge-Green). After fatigue with blue, 478 — 480 /x/x, there was 

 no change in the red and orange, and the reddish purple after-image 

 was seen over the rest of the spectrum. With blue, 445 — 455 /x/i, the 

 after-image was yellow-green (Porter), orange (Edridge-Green) ; the 

 violet and blue were cut off, red and green became yellower ; if only 

 green and red were viewed the former was obliterated, the latter un- 

 affected. With violet, 425 — 436 /x/x, the after-image was green ; the red 

 and orange were unchanged, the green became yellow-green, and the 

 violet and blue appeared green. 



The authors found that ' ' the stability of the after-image was remark- 

 able ; it did not change colour, and was not influenced by subsequent 

 light falling on the retina when this was not of too great intensity." 

 Thus, if after viewing the reacting spectrum the eyes were turned to 

 the dark screen the after-image appeared as a uniform dark band, 

 darker than the screen. In contradiction to previous observers the 

 authors found that " the complementary to the exciting light is never 

 strengthened in the spectrum on the screen by the after-image." They 

 also found no change in colour of the after-image as it fades. 



Wanach^ found that the eye fatigues more quickly for some 

 spectral colours than for others, and least for the more refrangible. 

 Macular fatigue lasts longer than peripheral. 



The consideration of Abney's researches on colour fatigue will be 

 postponed (Part III). 



^ Ztsch. /. Sinnesphysiol. XLni. 443, 1908. 



