CONCEALMENT BY THE APPARENT DISRUPTION OF SURFACE. 



253 



17. Some Observations upon Concealment by the apparent 

 Disruption of Surface in a Plane at Right Angles to 

 the Surface. By J. C. Mottram, M.B. (Lond.) *. 



[Received October 22, 1917 : Read November 6, 1917.] 

 (Text-figures 1-4.) 

 Index. , 



Morphology : Page 



Analysis of patterns 254 



Ethology : 



Concealing power of patterns 256 



The forms of animals are often rendered inconspicuous by the 

 methods which the artist usually employs in the representation 

 of three dimensions on a flat surface. 



Attempt is here made to show, first, what use the artist 

 makes of Simultaneous Contrast for the apparent disruption of 

 the surface of his paper or canvas : and subsequently to ascertain 

 whether similar arrangements occur in the patterns of animals. 



The Artistes Use of Simultaneous Contrast. — When a dark 

 object is viewed against a light background or vice versa, it will 

 be seen that where the dark and light areas join, the dark tone 

 appears darker than the rest of the dark area, and the light, 

 lighter than the remainder of the light area. 



The same appearance will be seen on the artist's paper if 

 he copies exactly the tones of the original. If, however, he 

 exaggerates the contrast by surrounding dark objects with dark 

 lines and light objects with light, then the objects will appear to 

 stand out from the background, and different portions of his 

 paper to occupy different planes. For this purpose, foreground 

 figures are often surrounded with dark lines, clouds are edged 

 with light tone, and trees against the sky are outlined with black, 

 whilst the neighbouring sky is greatly heightened in tone. 



It is not uncommon to find a series of receding hills outlined 

 with dark lines of gradually decreasing intensity : it is remark- 

 able how realistically distance is thus represented. 



The introduction of dark tone between coloured areas results 

 in disruption of surface for another reason. On viewing the 

 junction of two coloured areas, there will be seen for a short 

 distance a flowing-over of each colour into its neighbour. This 

 is well seen by drawing a narrow white line across red and blue 

 surfaces : where the white lies on the red, it appears reddish, 

 where on the blue, light blue. If the white line be surrounded 

 on both sides with black lines, then this flowing-over is prevented 

 and the white line retains its purity. By thus preventing this 



* Communicated by the Secretary, 



