388 DR. J. C. MOTTRAM ON 



be considered to be, other things being equal, much more 

 conspicuous than those which do not. For instance, a light- 

 coloured butterfly flying across a meadow, or down a hedgerow, 

 is visible at a much greater distance than a dark one. 



This greater visibility of light-toned objects in Nature can 

 easily be demonstrated by comparing the visibility of black 

 and white discs against a great nvimber of natural backgrounds : 

 only against snow and certain parts of the sky is the whita 

 the less visible ; against the vast majority of backgrounds the 

 white is very much more visible. 



Text-figure 3. 



% 



^ 



^^ 





^ 



A' 



/^ 





V 



c 



.J2f 



cr 



r i 5 H »S- 3 3S /f 5 6 7 B 9 



Visibility of objects in pi-oportion to size. 



Ordinates = distance (in feet) at which object is visible. 

 Abscissse = size of object, in square millimetres. 



EXPEEIMENT No. 4. 



Experimental conditions as in text-fig. 1. Candles 1 ft. apart and 2 ft. from object. 



Materials : — Black and white backgrounds of Bristol board and black needle-paper. 

 Objects:' — Black needle-paper of the following sizes: 2'5, 3'7, 4'8, 7'2, and 

 8'8 sq. mm. ; and white paper of the following sizes : 1, VQ, IQ. 2'8, and 

 3'5 sq. mm. 



The above diagram shows the distance at which the black objects were visible 

 against the white background (X) and at which the white objects were visible 

 against the black background (0). 



An even more convincing way of demonstrating this fact is to 

 take a series of artificial backgrounds, from white, through grey, 



