Kn;. 1. Two biicUnioclels, just 

 ulikc except that the one on the left 

 is eon liter-shaded, the other not, 

 tlioii^Ii covered uniformly with the 

 vmy uiatorial of its hackgroiuid. 

 This ri.sht-hand model, therefore, 

 is tirliiaihj as light helow as above. 



r[f;. :;. liinl-iiinilc'K a^ in Fig. I, 

 but with the top-light cut ofl froTii 

 the iihlitt ratively-shaded one, A. 



l-'ir.. 2. Obliteratively-shadcd bird-nifKk'l. 

 as ill Fig. lA, but iiiverted. (Sniiicwhat 

 huU'-lightod.) 



Via. 4. Two hird-models as in J''ig. 1, hut out of doors against 

 hare ground. The one on the right is obliteratively-shaded, tlu- 

 other nut. 



Fig. 5. Two bird-models jireeisely as above save that the 

 right hand one is still better 'obliterated.' The reader will 

 have to take it on faith that this is a genuine photograph, and 

 that there is a right-hand model of the same size as the other, 

 unless he can detect its position by its faint visibility in Fig. -t. 



