296 RECENT PROGRESS OF THE THEORY OF VISION. 



as the attention is fixed upon one of them we become 

 conscious of the colour of the corresponding glass. 



These experiments on the rivalry of colours have given 

 rise to a singular controversy among the best observers ; 

 and the possibility of such difference of opinion is an 

 instructive hint as to the nature of the phenomenon 

 itself. One party, including the names of Dove, Reg- 

 nault,^ Briicke, Ludwig,^ Panum,^ and Hering,^ main- 

 tains that the result of a binocular view of two colours 

 is the true combination-colour. Other observers, as 

 Heinrich Meyer of Ziirich, Yolkm^ann, Meissner,^ and 

 Funke,^ declare quite as positively that, under these 

 conditions, they have never seen the combination-colour. 

 I myself entirely agree with the latter, and a careful 

 examination of the cases in which I might have imagined 

 that I saw tlie combination-colour, has always proved to 

 me that it was the result of phenomena of contrast. 

 Each time that I brought the true combination-colour 

 side by side with the binocular mixture of colours, the 

 difference between the two was very apparent. On the 

 other hand, there can of course be no doubt that the ob- 

 servers I first naDied really saw what they profess, so that 

 there mast here be great individual difference. Indeed 

 with certain experiments which Dove recommends as par- 

 ticularly well fitted to prove the correctness of his con- 

 clusion, such as the binocular combination of comple- 

 mentary polarisation-colours into white, I could not 

 myself see the slightest trace of a combination-colour. 



' The distinguished French chemist, father of the well-known painter 

 who was killed in the second siege of Paris. 



* Professor of Physiology in the University of Leipzig. 

 ' Professor of Physiology in the University of Kiel. 



* Ewald Hering, Professor of Physiology in the University of Prague, 

 lately in the Josephsakademie of Vienna. 



* Professor of Physiology in the University of Gottingen. 



* Professor of Physiology in the University of Freiburg. — Tk. 



