386 



DR. J. C. MOTTRAM ON 



that a constant-in-tone contrast between object and background 

 does not result in a constant visibility. 



Text-fiijure 2. 



^r 















A 



-t; 



\ 



■^A-. 



^A^-. 



CX 



-X 



^-o--^ 



5 4 Sj^et. 



Relative visibility of objects. 



Ordinates = distance at which object is visible. 

 Abscissae = distance of candles from object. 



X = white object against black background. 

 © = black object against white background. 



EXPEEIMENX No. 2. 

 Experimental conditions as in text-fig. 1. Candles 1 ft. apart. 



Materials: — Backgrounds: white, of white Bristol board 100 sq. cm.; black, of 

 black needle-paper 100 sq. cm. Objects : — White, of white Bristol board 

 4'5 sq. cm. ; black, of black needle-paper 4'5 sq. cm. 



Results (mean of three observations). 

 When distance from white square was black square was 



This experiment shows that a white object on a black back- 



