200 COLOUR VISION 



light of all kinds excited all three kinds of fibres, though in varying 

 degrees. 



Young's hypothesis received scant acknowledgment, largely owing 

 to his resuscitation of the undulatory theory of light, which was regarded 

 as a grave heresy by the majority of scientists, who firmly adhered to 

 Newton's corpuscular theory. It remained unheeded until the middle 

 of the nineteenth century, when v. Helmholtz 1 and Clerk-Maxwell 2 

 adopted it as the explanation of their experiments on the mixture of 

 colours. Grassmann 3 simultaneously enunciated the laws of colour 

 mixture which bear his name. 



An essential feature of the Young-Helmholtz theory is the additive 

 process, especially as applied to colourless light sensations. Addition 

 of physical stimuli entails additive physiological reactions resulting in 

 compounded psychical end results. Goethe 4 approached the subject 

 from the psychologist's point of view and quickly accumulated facts 

 which were difficult to explain on the Newtonian basis. Such are 

 particularly the phenomena of after-images and simultaneous contrast. 

 The addition theory seemed incapable of supplying a satisfactory 

 explanation 5 . The claims of four fundamental colours as opposed to 

 three were emphasised by Aubert 6 , and this psychological point of view 

 became crystallised into the theory of opponent colours which bears 

 the name of Hering 7 . 



The clash of the contending theories led to modifications of each. 

 The psychophysical difficulties led Bonders 8 , Ad. Fick 9 and v. Kries to 

 limit what the latter calls the components theory (the Young-Helrnholtz 

 theory) to the peripheral link in the visual path. v. Kries has elaborated 

 this view in the theory of zones. 



Hering, regarding the question from the psychological point of view, 

 and endeavouring to bring the facts into a universal common relation- 

 ship with other physiological processes, emphasised the complementary 

 and opponent characters of certain fundamental colour sensations. 

 From the psychological point of view black, white, red, green, yellow, 

 and blue are fundamental sensations (Mach 10 ). All other hues appear to 



1 Miiller's Arch. f. Anat. 1852. 2 Trans. Roy. Soc. Edin. xxi. 1855. 



8 Ann. d. Physik LXXXIX. 1853. 4 Zur Farbenlehre, 1810. 



6 See, however, McDougall, infra. 



6 Physiologic dcr Netzhaut, Breslau, 1865 ; Graefe-Saemisch, Handb. d. ges. Augerihe.il- 

 kunde, 1st ed. n. 1876. 



7 Sitz. d. Wiener Akad. 1872-1874 ; Zur Lehre vom Lichtsinne, 1876. 



8 Arch. f. Ophth. xxvn. 2, 155, 1881 ; xxx. 1, 15, 1884. 



9 Arch. f. d. ges. Physiol. xvn. 152, 1878 ; XLIII. 441, 1888. 

 10 Sitz. d. Wiener Akad. LII. 2, 320, 1865. 



