14 Mayer — Phenomena of Simultaneous Contrast- Color, 



removed then a new departure was taken and a judgment 

 formed which resulted in his seeing yellow on a blue ground, 

 and all that in a minute interval of time. 



I do not know if psychologists have come to a conclusion as 

 to the smallest interval of time necessary to form a judgment, 

 either true or false, or in which to have a " fluctuation of the 

 judgment," or in which " to exercise judgment and divide 

 between two colors the difference in colors which really exist." 

 If such mental operations can be performed in the millionth, 

 the thousandth, or even in a few hundredths of a second then 

 the explanations of these phenomena, as generally given, may 

 be convincing. 



Yon Bezold in his " Theory of Color," Boston, 1876, in 

 explaining the fact that a rod seen by reflection from a piece of 

 green glass laid on a mirror gives two images one green the 

 other red, says : " As the observer does not know which of the 

 two images is the colored one he exercises his judgment, and 

 divides between the two images the difference in color which 

 really exists." Now this experiment is similar in its conditions 

 and in its effects of contrast-color to the one I made on the 

 contrast-colors of the electric flash, when the same colors were 

 distinctly seen apparently at the moment of the discharge. Can 

 one " exercise his judgment and divide between the two images 

 the differences in color which really exists " in an interval of 

 time wmich is less than -^ of a second ? 



In the experiment of the colored shadows cast by the candle 

 and by daylight, these colors are explained by Yon Bezold 

 (pp. 152,153), as follows: "The spot occupied by the blue 

 shadow is illuminated by the white daylight, the larger white 

 surface by daylight and by candle light, the other shadow by 

 candle light only. It might be presumed, therefore, that one 

 of the shadows would appear white the other yellow. This is 

 not the case, however ; for knowing the surface to be white 

 we still take it to be white after it has really received the yel- 

 low light of the candle. Our judgment is led astray regarding 

 white, and hence we believe the place occupied by the second 

 shadow to be blue, although it is actually white." Helmholtz 

 (" Lectures," IS". Y., 1873, p. 267), says : " Thus in the experi- 

 ment described above of colored shadows thrown by day-light 

 and candle light the doubly illuminated surface of the paper 

 being the brightest object seen gives a false criterion for white. 

 Compared with it, the really white but less bright shadow 

 thrown by the candle looks blue." These explanations assume 

 knowledge and conditions which are not essential. If this 

 knowledge and these conditions were necessary to see the phe- 

 nomena then these explanations of the phenomena might be 

 convincing ; but the conditions they assume are not necessary. 



