SUCCESSIVE INDUCTION OR AFTER-IMAGES 111 



then red- violet or red. The yellow phase is shortest. After longer and 

 stronger stimulation by white light the after-image in the darkened eye 

 passes through white, blue, green, red, blue, and on exposure to dim 

 white light blue-green and yellow. Different authors give different 

 phases with stronger excitation, but blue always starts the series. 

 The after-images from direct exposure to sunlight are still more 

 complicated 1 . 



The fading phases of after-images have been more recently in- 

 vestigated by Miss Washburn 2 and McDougall 3 . The latter has shown 

 that it is unnecessary to use stimuli of excessive strength. He found 

 that after excitation with white light a very constant feature was the 

 tendency of the three simple colours to follow one another in a recurring 

 cycle of the order green, red, blue, green, red, blue. If the white 

 light be only moderately bright, red is usually the first colour to appear 

 and is then succeeded by green, which persists to the end. After 

 brighter light green comes first, and is succeeded by red, then blue, 

 and then green again. If the light is still a little brighter, McDougall 

 describes the green as being " usually mixed with red from the first, 

 i.e., it appears yellow with a red edge." If the light be very bright then 

 the first phase of the after-image is white or bright blue of very low 

 saturation ; the blue soon passes through blue-green to green, which is 

 then followed by the cycle of pure colours. 



According to McDougall " an important feature of the after-images 

 of bright white light is that, after a first short period in which two colours 

 fuse to give yellow, or, as is the case after the brightest lights, all three 

 fuse to give white, the colours that in turn occupy the area of the after- 

 image, alone and unchanging for considerable periods, are red, green, 

 and blue only, and these are in every case of exactly the same colour- 

 tone although varying in brightness in different cases and in different 

 stages of one after-image. The red is a rich crimson red, decidedly 

 less orange than the red of the solar spectrum, the blue is a rich ultra- 

 marine, and the green a pure green having no inclination towards blue 

 or yellow 4 ." McDougall states that " they are the purest, richest, 

 most saturated colours that I have ever experienced, and I believe that 

 in this way, and this way only, one may experience absolutely simple, 

 i.e.., unmixed and fully saturated colour-sensations." 



The fading phases of the after-images from coloured lights are also 

 not limited to the homochromatic positive and the complementary 



1 v. Helmholtz, loc. cit. n. 211. 2 Psycliol. Rev. vn. 1900. 



3 Mind, x. N. S. 235, 1901. * Cf. Part III. 



