404 DR. J. C. MOTTRAM ON 



a point will be reached at which one half of the disc is blended 

 with one component of the background, whilst the other half is 

 seen as projecting into the other component. If the grey disc 

 more nearly approaches the black in tone than the white, then 

 at a distance it will appear as in text-fig. 14, 5; if it more 

 nearly approach the white, then as no. 2. 



The following experiment illustrates this appearance : — 



EXPEEIMENT No. 11. 



Caudles 1 ft. apai-t and 2 ft. distant from background. 

 Background half black and half white (7X5 ins.). 



Objects circular, 20'4 sq. mm., eight in number and ranging in tone from black to 

 white. Objects placed exactly over the junction of the black and white of the 

 background. 



Visibility distance. 



1- Black ^^^^^■.. , 1 Visible as a dark 



t- ^", t; " ^i»<='^®s- ]. projection into the white of 



3- Dark grey ^7 „ 5 „ C i' ^ the background. 



4). „ „ ^U „ J 



I- t'\, " io " t " 1 Visible as a light 



6. Light grey ... 23 „ 5 „ f projection into the black of 



si White ::....::: 35 ;; 9 :; 3 the background. 



An object was prepared of such a grey tone that it was neither seen as a white 

 nor as a black projection into the background's components. This object was the 

 least visible disc and visible at 16 ft. 4 ins. 



Some similar experiments were carried out with backgrounds 

 composed of different tones of grey instead of black and white, 

 and it was found that the objects likewise appeared as projectors 

 into one or other of the components, according as to whether 

 the object more nearly approached in tone one or other of the 

 components. 



If, for instance, the background was made of two dark grey 

 tones, then only the darkest objects appeared as black projectors 

 against the lighter of the two components. 



As in Nature backgrounds are- dark in tone rather than light, 

 it follows that light grey or white discs will be more visible 

 under these conditions, i. e., when seen against two or more 

 components of a patterned background, than dark discs. 



As mentioned in the last experiment, there is one tone of grey 

 against which black and white are equally visible, and when the 

 object is of this particular tone it never appears as a projective 

 from one component on to the other. Against backgrounds 

 composed of tones other than black and white, there is similarly 

 one grey tone which the object may have which will cause it to 

 give a similar appearance. 



An experiment was carried out with discs of this tone to 

 discover whether the effect of size of the object was similar or 

 not to that found when dealing with plain objects against plain 

 backgrounds. As seen in the following experiment, the effect is 

 similar : — 



