PATTERNS CONSPICUOUS IN NATURE. 387 



ground is more visible than a black object on a white ground. 

 It can be seen (text-fig. 2) that the higher the illumination the 

 greater the difference ; at low illuminations the curves of visibility 

 approach one another (they would meet at complete darkness). 

 The same was found to be the case when object and background 

 were of different shades of grey, instead of black and white. The 

 light -grey object against the dark-grey background is more visible 

 than the dark -grey object against the light background. 



It was thought that the lower visibility of the black object on 

 the white ground might be due to the dazzling effect of the 

 large area of white. It was found that reduction in the area of 

 the white background by means of black diaphragms produced 

 the opposite effect, and, further, that the nearer the diaphragm 

 was brought to the object the less visible the object became. It 

 was further found that when the white squai-e on the black 

 background was similarly surrounded by white diaphragms, the 

 same effect resulted (see experiment no. 3). 



Experiment No. 3. 



Experimental conditions as in text-fig. 1. Candles 1 ft. 6 ins. apart; 

 distance of candles from object, 2 ft. 



Materials : — Backgrounds of white Bristol board and black needle-paper, 100 sq. cm. 

 Objects of same materials, 4'5 sq. cm. Black and white square diaphragms, 

 total size 100 sq. cm., with a central square hole : 



No. 1. Size of central hole was 6i sq. cm. 

 „ 2. ,, „ 36 



„ 3. ., „ 16 



„ 4. „ „ 4 



„ 5. „ ,, 1 



„ 6. „ „ 0-16 



White object on black background was visible at 45"5 feet. 



When surmounted by No. 1 white diaphragm, at 40"7 „ 



„ 2 „ „ 37-6 „ 



3 „ „ 34-8 „ 



» ,, 4 „ „ 29-5 „ 



5 „ „ 24-0 „ 



6 „ „ 13-4 „ 



Black object on white background was visible at 38"4 feet. 



When surmounted by No. 1 black diaphragm, at 32'2 „ 



2 „ „ 30-5 „ 



3 „ „ 30 „ 



4 „ „ 29-6 „ 



5 -> „ 21-7 „ 



6 „ „ 15-5 „ 



(Above readings are the mean of three observations.) 



It would thus appear that light tone on dark is more visible 

 than dark on light. This has been considered to be due to the 

 eye recognising the object, in one case by a positive image, 

 in the other by the absence of stimulation. This fact is of 

 considerable importance in regard to the visibility of animals 

 in Nature : those exhibiting large areas of light tone must 

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