.[ 438 J 



LI. Further Data on Colour-Blindness. — No. II. 

 By Dr. William Pole, F.R.S.* 



IN the July number of the Phil. Mag., seeing the 

 importance that had been attached to the subject of 

 Colour-blindness, I contributed some data as to certain early 

 investigations of my own. Since that time the interest in 

 the matter has been much increased by the prominence given 

 to it at the late meeting of the British Association in Edin- 

 burgh, and by criticisms made on some of the views still held 

 on it in this country. It may therefore be useful to invite 

 more attention than has yet been given, to opinions 

 expressed on it by foreign writers of eminence and authority 

 who have made it their special study ; and I propose to add 

 some notes with this object. 



I will begin with a writer whose reputation as physicist, 

 physiologist, and practical oculist was second to none, — 

 the late Professor F. C. Donders of Utrecht. He took 

 great interest in Colour-blindness, made many valuable 

 investigations, and wrote much thereupon. The position he 

 took was peculiarly independent. He embraced and strongly 

 advocated Young's trichromic theory, but entirely dissented 

 from the application of it so commonly made to dichromic 

 vision. At the same time, though he agreed with some of 

 Hering's fundamental principles, he opposed his colour theory. 

 And, consistently enough, having objected to the current 

 explanations, he brought forward a hypothesis of his own, 

 remarkable for its originality and its consonance with modern 

 biological science. 



Professor Donders came over to the meeting of the British 

 Medical Association at Cambridge in August 1880, and gave 

 there an able lecture on Colour ; but his views are still but 

 little known here. They are contained chiefly in two elaborate 

 articles, namely : — 



u Ueber Farbensysteme," in GraefVs Arckivfur OphtliaU 

 mologie, vol. xxvii. part i. 1881. 



" Noch einmal die Farbensysteme," Ibid. vol. xxx. part i. 

 1884. 



In giving his ideas about Normal Vision, he considers that 

 our natural impressions point to four " simple " colours — 

 red, yellow, green, and blue (which is one of the starting- 

 points of Hering's theory) ; but he believes these sensations 

 are caused by the combinations of three more-highly satu- 



* Communicated by the Author. 



2R2 



