Helmholtz theory of color, of the truth of which it affords at 
the same time new evidence. ach wave-length produces three 
sient and violet the most persistent. Upon this suppos 
is easy to see that whatever may be the predominant tint of @ 
subjective” colors in these cases. Taken in conjunction, 
two causes are capable of producing a great variety of “8!” 
jective ” tints. Those produced by the more rapid disappe™ 
ance of the yellow and green portions of the image are similar 
to the colors which white assumes to green-blind persons, | 
* Von Helmholtz: Handbuch der physiologischen Optik, p. 389. 
