204 



Mr. G. J. Burch. On the Relation of 



"On the Eelation of Artificial Colour-blindness to Successive 

 Contrast." By G-eorge J. Burch, M.A. Oxon., Eeading 

 College, Eeading. Communicated by Professor GoTCH, F.E.S. 

 Eeceived January 30 — Eead February 8, 1900. 



I have elsewhere pointed out that my observations on artificial 

 colour-blindness seem unfavourable to the theory of Hering, and 

 favourable to that of Young. The experiments on successive contrast 

 described in the following pages tend also to confirm in a remarkable 

 manner opinions held before the time of Young, and which must be 

 considered as incorporated in his theory. The method I have pursued 

 throughout this investigation consists essentially in the use of the 

 spectroscope to analyse sensations of contrast, and I have accordingly 

 been able to make certain experiments which would have been 

 beyond the resom'ces of those earlier writers ; but the following 

 account of their opinions, expressed as far as possible in the words of 

 the authors themselves, is intended to show in some detail how closely 

 their views agree with my own results. 



During the 18th century the phenomena of after-images and suc- 

 cessive contrast attracted a good deal of attention, and although in 

 most cases the physical conditions of the experiments were too com- 

 plex to aff'ord much information as to their true nature, there were 

 some remarkable exceptions, to which I desire to direct attention. 



The opinions enunciated during the 18th century may be divided 

 broadly into two groups. The one school held that after the stimulus 

 of a strong Hght of any given colour, a species of reaction sets in, by 

 which a sensation of the complementary colour is produced. This 

 view may be regarded as belonging to the same category as the theory 

 of Hering. It may be doubted whether it was definitely adopted by 

 Jurin,* who says only that this " contrary sensation is apt to arise in 

 us sometimes of itself, and sometimes from such causes as at another 

 time would not produce the sensation at all, or at least not to the same 

 degree," and preserves a like caution throughout his description of the 

 phenomena. Other experimenters, however, advocated this theory, 

 and it was strongly upheld in 1801 by Venturi,t who maintained that 

 the changing tints of after-images excited by the pure colours of the 

 spectrum proved the existence of a multiple function for each nerve- 

 fibre, as opposed to the theory of one nerve, one function, taught by 

 Bonnet. J 



* " Essay on Distinct and Indistinct Yision." In Smith's ' Opticks,' 1738. 

 t "Dei Colori Imniaginarii." ' Opusc. scelti sulle Scienze,' da Carlo Amoretti. 

 Soave, vol 21, p. 274. 



X " Essai Analytique sur I'Ame," and " Essai de Psychologie." Works. 1785. 



