THE EFFECTS OF "FATIGUE" 113 



of colour vision. Earlier authors, including v. Helmholtz, and most 

 physicists make free use of the conception of fatigue to account for 

 successive induction, but the facts, and especially those of simultaneous 

 contrast {vide infra), negative so simple an explanation. There is, 

 however, a group of phenomena associated with prolonged or intense 

 stimulation to which the term may be fittingly applied, though even in 

 this case it should be done " without prejudice." These phenomena 

 have been studied particularly by Burch^. By flooding the eye with 

 bright sunlight which had passed through a lens of 2 inch focus and a 

 suitable colour screen or by a similar process with a spectrum of wide 

 dispersion Burch was able to study the after-effects of fatigue for the 

 various colours. 



After fatigue for red, scarlet geraniums appear black, calceolarias 

 and sunflowers various shades of green, and marigolds green shaded 

 with black in the parts that are orange to the normal eye. Purple 

 flowers, such as candytuft and clematis look violet, and pink roses 

 bright sky-blue. Short exposures — a few seconds to two or three 

 minutes^suffice, and the effect is transient, passing off in about 

 ten minutes. 



After fatigue for violet, violet wools look black, purple flowers 

 crimson, some blues greenish, green a richer hue. A noticeable effect 

 is the tinging of all objects which do not reflect violet with that colour, 

 and the same applies to " dazzling " with other colours. 



Fatiguing with green makes the landscape look like a picture painted 

 with vermilion, ultramarine and flake-white, variously blended. The 

 foliage is reddish-grey or bluish-grey, blue flowers are dirty blue, 

 red flowers are impure red, and every colour but green is tinged with 

 green. 



Fatiguing with jmrple {i.e. red and blue) makes everything look 

 monochromatic green. All red, purple or blue flowers look black, and 

 green looks a quite unnaturally brilliant green. The red fatigue passes 

 off first, the observer then being in a condition of violet fatigue, which 

 passes off in 15 — 60 minutes. 



Fatigue of one eye with purple and of the other with green produced 

 a very weird and exaggerated stereoscopic effect. 



In fatiguing the eye with the colours of the spectrum comparatively 

 simple changes, differing in degree but not in kind, occur with four 

 regions, viz. the regions which give the sensations of pure red, 



^ Phil. Trans. Roy. Soc. Land. B, cxci. 1, 1898; Proc. Roy. Soc. Lond. lxvi. 216, 

 1900. 



P. c. V. 8 



