THE PERCEPTION OF SIGHT. 



285 



picture g in the mirror 6, while the left saw the picture 

 k in the mirror a. 



A more convenient instrument, though it does not 



Fig. 35. 



give such sharply defined effects, is tlie ordinary stereo- 

 scope of Brewster,^ shown in Fig. 36. Here the two 



Fig. 36. 



pictures are placed on the same slide and laid in the 



' Sir David Brewster, Professor of Mathematics at Edinburgh, born 

 1781, died 1868.— Tr. 



