356 



PRACTICAL PHYSIOLOGY. 



[LXXIV. 



(/.) H. Meyer's Experiments on simultaneous contrast, 

 (i.) Cut out a small oblong of white, or preferably of grey, paper, 

 and put it on a large piece of bright green paper (4 inches square) ; 

 the grey sufters no change. Cover the .whole with a thin semi- 

 transparent sheet of tissue paper. The grey oblong appears pinli. 



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

 it as l3efore ; a greenish-blue contrast colour is seen. 



(iii.) Repeat (a.), but place a red square on a grey ground ; the 

 red square will appear greenish. 



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



blue appears white, when 

 covered with tissue paper. 

 All the above are modifica- 

 tions of H. Meyer's experi- 

 ment. The tissue paper is 

 used, as contrast colours are 

 far more readily excited 

 by pale than by saturated 

 colours, so that differences 

 of sensation are much greater 

 with weak than with strong 

 stimulation. 



(v.) Surround the small 

 square with a broad black 

 line, each square appears in 

 its own colour. The effect 



Fig. 277--Disc for Simultaneous Contrast ^f contrast is destroyed. 



(Jc) Place side by side two strips of paper, green and red (6x3 in.). Over 

 the Hne of junction place a strip of grey paper (i x 6 in.), 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. 



(Z.) Arrange a disc like tig. 277 on the rotating wheel. 

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

 sectors, and interrupt each in the middle, as in the 

 figure, with a black and white stripe. On rotating the 

 disc, the ring, which one might expect to be grey from 

 the black and white, appeai-s reddish, i.e., the comple- 

 mentary colour of the greenish ground. 



{m.) Place a strip of grey paper on a black background 

 and a corresponding strip on a white ground. The 

 fonner will appear much lighter, the grey on white 

 much darker. Fix the eyes for a minute on a point mid- 

 way between the strips ; close and cover the eyes. The 

 after-images will show a great difference in luminosity, 

 (n.) Ragona Scina's Experiment. — Two pieces of wood fixed at right angles 

 to each other are covered by white paper, while a coloured sheet of glass is 

 held at an angle of 45° between them (fig. 27S), or the apparatus of Hering (fig. 



Fig. 273. — Kagona 

 Sciua's Experi- 

 ment. 



