and the Intensities of Lights of different Colors. 15 



The following experiments show that there is no necessity at 

 all in "knowing the surface to be white" or to see "the 

 doubly illuminated surface of the paper." 



The experiment of the colored shadows cast by the candle 

 and by daylight was arranged behind a screen, so that no one 

 could divine what was there. A tube blackened on the inside 

 went obliquely through the side of the screen and was so 

 adjusted that the circular field of view through the tube was 

 entirely filled by equal portions of the two shadows, which 

 formed two semicircles, one colored orange the other blue. 

 The two persons on whom I experimented were ignorant of 

 the phenomena of contrast- color and moreover were misled as 

 to what they would see on looking into the tube, and I was 

 specially careful not to speak to them about color. These per- 

 sons were strangers to each other and neither knew that the 

 other had been the subject of my experimenting. The first 

 observer at once reported : " I see a circle half yellow and half 

 blue." The other said : " I see a golden band next to a sky- 

 blue band and the golden band is rather deeper in color where 

 it is next to the blue," which is certainly a very good descrip- 

 tion. 



Having in mind the facts established by the foregoing ex- 

 periments it seems to me that we have either to regard the 

 phenomena of simultaneous-contrast color as psychical phe- 

 nomena of which no satisfactory explanation has been given, 

 or, we must discard the Young-Helmholtz hypothesis of color 

 sensation and adopt one similar to that of Hering, which gives a 

 direct physiological explanation of contrast-color effects without 

 the psychological considerations which those who adopt the 

 Young-Helmholtz hypothesis are obliged to resort to in their 

 explanation of these phenomena ; and which explanations, as I 

 have attempted to show, are faulty, and have to be modified to 

 be convincing. 



According to Hering's hypothesis of color sensations when 

 a portion of the retina is stimulated, adjoining portions of the 

 field of view are affected by a sort of inductive action ; so 

 that changes are produced which are antagonistic or comple- 

 mentary to those portions of the retina actually stimulated. 



M. Foster in his " Physiology, Lond., 1891," Part IY, bk. 

 Ill, gives an excellent discussion of the relative merits of the 

 Young-Helmholtz hypothesis and Hering's in explaining color 

 sensations. In conclusion he writes . . "so far as we are 

 aware no crucial test between the two has as yet been brought 

 forward. We may now leave the matter with the remark 

 that while the Young-Helmholtz theory tends to lead us 

 direct from the retinal image to the psychological questioning 

 of the sensations, and seems to offer no bridge between the 



