168 Mr. A. M. Mayer on a Photometer for Measuring 



band next to a sky-blue band and the golden band is rather 

 deeper in colour where it is next to the blue/' which is cer- 

 tainly a very good description. 



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-colour as psychical phe- 

 nomena of which no satisfactory explanation has been given, 

 or we must discard the Young-Helmholtz hypothesis of colour- 

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

 a direct physiological explanation of contrast-colour effects 

 without the psychological considerations which those who 

 adopt the Young-Helmholtz r^pothesis are obliged to resort 

 to in their explanation of these phenomena ; and which ex- 

 planations, as I have attempted to show, are faulty, and have 

 to be modified to be convincing. 



According to Hering's hypothesis of colour-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 actuallv stimulated. 



M. Foster in his 'Physiology,' Lond. 1891, Part IV., 

 bk. iii., gives an excellent discussion of the relative merits of 

 the Young-Helmholtz hypothesis and Hering's in explaining 

 colour-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 question- 

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

 the first step and the last, Hering's theory is distinctly a 

 physiological theory, and at least holds out for us the promise 

 of being able to push the physiological explanation nearer 

 and nearer home before we are obliged to take refuge in the 

 methods of psychology." 



A Photometer for Measuring the Intensities of Differently 

 Coloured Lights. 



It has already been shown that, in certain conditions of 

 illumination and in certain directions of sight, a screen 

 formed of perforated cardboard covered with translucent 

 paper appears with complementary colours, and that if the 

 screen be in the form of a disk with alternate sectors cut 

 out of it, and is illuminated on one side by daylight and on 

 the other side by lamp-light, that the blue of one side of the 

 disk and the orange of the other appear intensified on slowly 

 rotating the disk. On increasing the velocity of rotation the 



