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AN AMERICAN TEXT-BOOK OF PHYSIOLOGY 



spots in Figure 161, when viewed from a distance of three or four meters, 

 appear hexagonal, since the irradiation is most marked in the triangular dark 

 space between three adjacent circles. A familiar example of the effect of irra- 



Fig. 161.— To illustrate the phenomenon of irradiation. 



diation is afforded by the appearance of the new moon, whose sun-illuminated 

 crescent seems to be part of a much larger circle than the remainder of the 

 disk, which shines only by the light reflected upon it from the surface of the 

 earth. 



D E 



Pig. L62.— To illustrate the illusion of subdivided space. 



Subdivided Space. — A space subdivided into smaller portions by inter- 

 mediate objects seems more extensive than a space of the same size not so sub- 

 divided. Thus the distance from A to B (Fig. 1 62) seems longer than that from 

 B to C, though both are of the same length, and for the same reason the square 



