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AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



the space between the two squares seems smaller than that between the two 

 oblong figures. 



In some case, however, an influence of the opposite sort l seems to be 



PIG. 254. To illustrate contrast in space-perception (Muller-Lyer). 



exerted, as is shown in Figure 256, in which the middle one of three parallel 

 lines seems longer when the outside lines are longer, and shorter when they 

 are shorter than it is itself, and in Figure 257, where a circle appears larger 



FIG. 255. To illustrate contrast in space-perception (Muller-Lyer). 



if surrounded by a circle larger than itself, and smaller if a smaller circle is 

 shown concentrically within it. 



Lines meeting at an angle appear longer when the included angle is large 



FIG. 256. To illustrate so-called "confluxion" in space-perception (Muller-Lyer). 



than when it is small, as is shown in Figure 258. This influence of the 

 included angle affords a partial explanation of the illusion shown in Figure 

 259, where the horizontal line at B seems longer than at A ; but the distance 



1 For this influence the name "confluxion" has been proposed by Muller-Lyer, from whose 

 article in the Archivfiir Physiologic, 1889, Sup. Bd., the above examples are taken. 



