166 Mr. A. M. Mayer on the Phenomena 



to fall, falling with two oscillations in intensity, so that all the 

 events of the phenomenon take place in about ^ of a second. 

 However, no vague impression of surfaces merely differing 

 in illumination and then suddenly changing into a colour and 

 its contrast-colour could be detected. I think that this interval 

 of no colour-sensation, if it exist, must be of exceeding short 

 duration ; but such a period of light without colour cannot 

 be detected, and if it cannot be perceived, then, so far as we 

 are concerned, it appears to me that there can be no hesitation 

 in the perception of the colours, and no " fluctuation of the 

 judgment " and " dividing between two images the difference 

 in colour which really exists " before the mind reaches its 

 conclusion as to the character of the colours. 



The following experiments were separately made on three 

 persons between whom no communication had passed as to 

 the nature of the experiments to be tried on them. I placed 

 a grey ring on a ultramarine disk in front of the Holtz 

 machine and requested the observer, who had implicit confi- 

 dence in my truthfulness, to describe to me as accurately as 

 possible the exact hue of the pink, or rose colour, or red he 

 would see on a green ground at the instant of the electric 

 flash. Each observer at once said : " It is not pink, the ring- 

 appears yellow on a blue ground." Now in each of these 

 experiments the observer was prepared, by my pardonable 

 lying, to see red on a green ground, and to see yellow on a 

 blue ground, his mental condition of anticipation to see red on 

 a green ground was first 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 judg- 

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

 of the judgment/' or in which " to exercise judgment and 

 divide between two colours the difference in colours 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 gene- 

 rally given, may be convincing. 



Yon Bezold in his i Theory of Colour/ Boston, 1876, in 

 explaining the fact that a rod seen by reflexion 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 coloured one he exercises his judg- 

 ment, and divides between the two images the difference in 

 colour which really exists. " Now this experiment is similar 

 in its conditions and in its effects of contrast-colour to the 



