12 Mayer — Phenomena of Simultaneous Contrast- Color, 



twice the thickness of the green glass. In this experiment 

 we obtain contrast-colors in the source of light itself. 



The explanation of the phenomena of simultaneous contrast- 

 colors, as generally given in works on chromatics, is that they 

 are due to " error of judgment," to " deception of judgment," 

 or to " fluctuation of judgment." The reasoning given may 

 be convincing if all the conditions really exist which the 

 writers assume to exist in their explanations of these phe- 

 nomena. One of these conditions is that a judgment can be 

 formed in the minute interval of time only necessary in which 

 to perceive contrast-colors. In the experiments just described 

 with the electric flash we have apparently instantaneous per- 

 ception of the contrast-colors in the gray ring placed on the 

 green and ultramarine grounds, in the candle and electric light 

 shadows and even in the very flash itself when this is seen 

 reflected from the top surface of a green glass and from the 

 mirror on which the green glass rests. 



Many careful experiments made by me and others, using as 

 chronometer three pairs of forks of the octave of UT 6 , giving 

 respectively 10, 12 and 15 beats per second, showed that cer- 

 tainly the interval between the flash and the perception of the 

 colors was much less than -^ of a second. Indeed, on viewing 

 the flash and the illuminated surfaces at the same time, or, hear- 

 ing the discharge and viewing only the illuminated ring, no 

 interval could he detected by this mode of observation as exist- 

 ing between the instant of the flash and the perception of the 

 colors, and we certainly could have detected a shorter interval 

 than -J-g- of a second had it existed. 



Incidentally, I will here state that when different geometrical 

 or irregular figures cut out of white paper and placed on an 

 ivory-black ground were illuminated by the electric flash, the 

 observer, so far as I could ascertain formed conclusions as to 

 the forms of the pieces of paper in an interval of time less 

 than the ^ of a second. Certainly the interval of time re- 

 quired to reach a conclusion as to the contrast-color was less 

 than the T ^- of a second. Professor Mendenhall in 1871 (this 

 Journal) gives 0*292 sec. for the time required by an observer 

 to respond, by means of an electric chronograph, to the appear- 

 ance of a white card. When the observer responds by 

 touching the circuit key with one hand when a white card 

 appears, and with the other hand when a red card appears, 

 Professor Mendenhall finds 0*143 sec. as the time required 

 for the response. Subtracting the first number from the 

 last he obtains '151, or i sec, as the time to form a judg- 

 ment between white and red. Similar experiments gave 

 him 202, or -J sec, as the time to judge whether a circle or a 

 triangle appeared to the observer. The intervention of the 



