90 COLOUR VISION 



the tertiary image its hue is best appreciated when red is chosen as the 

 stimulus. With increasing dark adaptation the tertiary gains in bright- 

 ness but loses in chromatic value. There is some difference of opinion 

 as to whether the tertiary image can be seen at the fovea. 



Hamaker described the secondary image as coloured with the 

 complementary colour and lasting | sec, the tertiary as homochromatic 

 and lasting several seconds. Dark adaptation had little influence. The 

 secondary image was the better seen for all colours ; the tertiary better 

 for red and yellow than green and blue. With stationary light he 

 found the following phases : (1) the primary image ; (2) a dark interval, 

 often absent ; (3) the secondary image ; (4) a dark interval (| sec.) ; 

 (5) the tertiary image ; (6) a dark interval, often absent ; (7) with 

 stimulus of 1 to 4 sees, a quaternary image, accompanied by shortening 

 of the tertiary. The quaternary is a true negative after-image, of 

 complementary colour and surrounded by a bright halo. With moving 

 light he found the following phases : (1) the primary image {e.g., 3°), 

 passing into (2) a short homochromatic or white tail (6°) ; (3) a dark 

 interval (10° — 15°) ; (4) the complementary, coloured or colourless 

 secondary image (satellite, 3°, absent with red light) ; (5) a dark interval 

 (50°) ; (6) the tertiary, faintly coloured homochromatic image (about 

 360°). As regards the region of retina stimulated, with stationary 

 light, red and green gave a very marked complementary secondary 

 foveal image, which was absent for yellow and blue ; the tertiary image 

 was absent with foveal stimulation. With moving light the fovea gave 

 no secondary and apparently also no tertiary image. 



The " action-time " of a light stimulus (McDougall), i.e., the least 

 time during which a light of given intensity must act upon the retina 

 in order to excite the most intense sensation it is capable of exciting, 

 has been studied by Swan^, Exuer^, KunkeP, Charpentier'*, Martins^, 

 and McDougall^. It is a necessary preliminary to the proper under- 

 standing of flicker phenomena. 



It may be accepted that the sensation curve rises rapidly to a 

 maximum and falls gradually. The rapidity of the rise varies with 



Ophth. XLiv. 3, 445, 1897 ; SamojlofE, Ztsch. f. Psychol, u. Physiol, d. Sinnesorg. xx. 118, 

 1899 ; Hamaker, loc. cit. xxi. 1, 1899; P. Miiller, Arch. f. d. yes. Psychol, xiv. 358, 1909; 

 Kinoshita, Ztsch. /. SijDiesphysiol. xixn. 420, 434, 1909; Hering, Arch. f. d. grs. Physiol. 

 cxxvi. 604, 1909; Dittler and Eisenmeier, ;6/(7. cxxvi. 610, 1909. 



1 Trmis. R. S. Edin. Ii. 230, 1849 ; xxn. 33, 1861. 



2 Sitz. d. Wiener Akad. Lvm. 2, 601, 1868. 



» Arch.f. d. ges. Physiol, ix. 197, 1874. « C. r. soc. de hiol iv. 1887. 



^ Btitr. z. Psychol, u. Philos. i. 2, 1902. « Brit. Jl. of Psychol, i. 151, 1904. 



