290 EXPERIMENTAL PHYSIOLOGY. 



(6.) Instead of green paper, place the grey slip on red, and 

 cover it as before ; a greenish-blue contrast colour is seen. 



(c.) Repeat (a.\ but place a red square on a grey ground; 

 the red square will appear greenish. 



(d. ) A grey square upon blue appears yellow ; a yellow 

 upon blue appears white, when covered with tissue paper. 



(e.) Surround the small square with a broad black line, 

 each square appears in its own colour. The effect of con- 

 trast is destroyed. 



(f.) Place side by side two strips of paper, green and red 

 (6 x 3). Over the line of junction place a strip of grey 

 paper ( j x 6), and cover the whole with tissue paper, as 

 before. The grey appears pink on the green side, and 

 greenish on the red. This contrast is also set aside by 

 running a black margin round the grey strip. Do the same 

 with yellow and blue. 



(</.) Arrange a disc like Fig. 139 on the rotating wheel. 

 On a white disc fix four narrow, coloured (e.g., green) sectors, 



139. 



and interrupt each in the middle, as in the figure, with a 

 black and white stripe. On rotating the disc, the ring which 



