402 DR. J. C. MOTTRAM ON. 



The most conspicuous pattern that an object can have against 

 a series of plain backgrounds may now be defined : — 



(1) The pattern must consist of two components. 



(2) The components must difier widely in tone (black and 



white). 



(3) The lighter component (white) must be concentrated at 



the centre in the form of a circle. 



(4) The darker component must sm-round the white so that 



nowhere is there an interrupted margin. 



(5) If the series of backgrounds be of low tone (as they are in 



Nature) then there must be more white than black in the 

 pattern. 



(C) Plain Objects against Patterned Backgrounds. 



(1) If the object is visible after the pattern has blended at 

 distance, then the factors which control its visibility are the 

 same as those of plain objects against plain backgrounds. The 

 outline of the object will, however, api^ear blurred just as when 

 a patterned object, whose pattern is interrupted at the margin, 

 appears blurred when viewed against a plain background. The 

 conckisions are similar, the only difference being, that in one 

 case the object is plain and the background patterned, whereas 

 in the other the object is patterned and the background plain. 



(2) If the object becomes invisible before the pattern of the 

 background blends at distance, then the object may be seen 

 against one component of the background ; in which case the 

 factors controlling visibility will be similar as are those of plain 

 objects against plain backgrounds, except that the near presence 

 of an area of different tone will afiect the visibility of the object. 

 A black square on the white component of a checkered back- 

 ground will be less visible than on a plain white background 

 (see experiments, nos. 2 & 3). With this exception, the factors 

 controlling visibility are similar- to those of a plain object against 

 a plain background. The object may be visible against two or 

 more components of the background. If the object is of the 

 same tone as one of the background components, then the object 

 will appear as a projection from the margin of one component. 



Experiments were carried out to discover whether the factors 

 controlling visibility were different from those of a black object 

 against a white background, and it was found that, except for 

 the decrease in visibility due to the presence of an area of black 

 (in this case touching the object), the visibility was similar to 

 that of a plain object on a plain background, except that the 

 effect of shape of the object was rather different from its effect 

 when dealing with plain objects against plain backgrounds, as 

 seen in the following experiment *. 



* This consideration has an important bearing on concealment b/ indented or 

 scalloped mai'gins ; a series of experiments has been carried out from this point of 

 view which, however, are only of present interest in so far as they show that an even 

 margin is a factor for conspicuousness. 



