400 DR. J. C. MOTTRAM ON 



background, nevertheless, when a series of backgrounds are used, 

 then the object will appear inconspicuous against those similar, in 

 tone. On the other hand, with a patterned object, when the 

 background is similar in tone to one of the components, then the 

 other will make a strong contrast and cause the object to be 

 easily visible. 



It has been seen that the greatest blending distance which a 

 pattern can have is one in which the white or lighter component 

 is concentrated in the form of a circle, and that an object is most 

 conspicuous against a wide series of backgrounds when it presents 

 a pattern of only two components. Experiments were therefore 

 made to discover which of two component patterns, the light- 

 centre one or the dark, is the more conspicuous against a wide 

 series of backgrounds. A series of discs were made, as shown in 

 text-iig. 9, and examined against a series of backgrounds in the 

 following manner : — 



Text-fig. 1, B (p. 385) gives a ground-plan of the experimental 

 conditions ; it can be seen that the backgrounds are illuminated 

 separately from the discs, which ai-e fixed to a glass plate. By 

 moving the backgrounds towards or away from the light, a 

 continuous and wide i-ange of tone in the background can be 

 obtained. First, the background of white paper was moved so 

 as to exactly match in tone that of the white in the discs. 

 Under these conditions the all-white disc was invisible ; of the 

 rest, the disc with a white centre, 7/8 of the whole, was found to 

 be the least visible, and next the disc with 6/8 Avhite centre. 

 The most visible disc was the all black. 



The discs were examined in a. similar manner over a wide 

 series, and in each case the three least visible discs and the most 

 visible were noted ; the following table gives the results. 



It can be seen that, except against 1 ackgrounds lighter than 

 the white in the discs, the black-centre eye-spots are less visible 

 than the white, and the appearances of the discs as seen from a, 

 distance show that the white-centre discs are the more visible. 



The greater visibility of the white-centre eye-spots is especially 

 marked when the backgrounds approach the dark end of the 

 series; and as, as already shown-, the backgrounds in Nature are, 

 for the most part, of dark tone, it follows that white-centi'e eye- 

 spot patterns of two components must be more conspicuous than 

 black-centre patterns. Similarly, the white-centre pattern must 

 be more visible than any other combination of black and white, 

 because in this pattern the white is most concentrated, and there- 

 fore has the greatest visibility and the longest blending distance. 

 It follows that against a sei-ies of plain backgrounds, and especially 

 a series of relatively dark tone, the white-centre eye-spot pattern 

 is the most visible one that an object can have. 



