[allen] 



PHENOMENA OF THE PERSISTENCE OF VISION 



207 



ITiis is shown in the curves in figures 10 and 11, which are taken from 

 the paper referred to several times. 



When, however, the eye is fatigued with complementary red : and green 

 colours together, the curve (figure 7) has an elevation in tlie red, a de- 

 pression in the green, and a pronounced elevation in the violet. It is 

 remarkable that there is no green elevation, and still more remarkable 

 that the violet sensation is affected at all, or at least, to any very per- 

 ceptible amount. It is, perhaps, possible that the white light fonned 

 by combining complementary red and green hues is a compound with 

 properties of its own quite different from those possessed by the separate 



Fig. 11. 



Fig. 12. 



components, and, in virtue of its being white, stimulates all three sen- 

 sations, red, green and violet, even though no violet light is present. 

 The same idea would also apply to the curve in figure 6, though, as we 

 have seen, the occurrence of the elevations there is susceptible of 

 another explanation. 



Both persistency curves obtained when the retina was fatigued by 

 the compooinded complementary colours intersect the normal in two 

 places, one of which is in the orange at X = .62//. This colour was 

 ufied as a fatiguing stimulus and a persistency-* curve obtained which is 

 plotted in figure 12 from the data in table 7. The curve shows twol.ele- 



