THE PERCEPTION OF SIGHT. 259 



partly by the elements of the retina which are affected by each 

 of them being tired, and partly by the complementary after- 

 images which result. The alternation then ceases, and there 

 ensues a kind of mixture of the two original colours. 



It is much more difficult to fix the attention upon a colour 

 than upon such an object as an engraving. For the attention 

 upon which, as we have seen, the whole phenomenon of ' rivalry ' 

 depends, fixes itself with constancy only upon such a picture as 

 continually offers something new for the eye to follow. But we 

 may assist this by reflecting on the side of the glasses next the 

 eye letters or other lines upon which the attention can fix. 

 These reflected images themselves are not coloured, but as soon 

 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, includ- 

 ing the names of Dove, Regnault, 1 Briicke, Ludwig, 2 Panum, 3 

 and Hering, 4 maintains that the result of a binocular view of 

 two colours is the true combination-colour. Other observers, as 

 Heinrich Meyer of Zurich, Volkmann, Meissner, 5 and Funke, 6 

 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 the 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 diffe- 

 rence between the two was very apparent. On the other hand, 



1 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, 

 late y in the Josephsakademie of Vienna. 



Professor of Physiology in the University of Gottingen. 

 Professor of Physiology in the University of Freiburg. TR. 

 s 2 



