The Special Senses 



275 



Experiment 137. Mark off a round piece of cardboard into black 

 and white sectors modeled after the disk in A (Fig. 147). Attach 

 it so as to rotate it rapidly, as on a sewing machine. An even gray 

 tint will be produced as in B. 



Experiment 138. To illustrate imperfect visual judgments. 

 Make three round black dots, A, B, C, of the same size, in the same 



line, and let A and C be equidistant from B. Between A and B 

 make several more dots of the same size. A and B will then appear 

 to be farther apart than B and C. 



Experiment 139. Make on a white card two squares of equal size. 

 Across the one draw horizontal lines at equal distances, and in the 

 other make similar vertical lines. Hold them at some distance. 

 The one with horizontal lines appears higher than it really is, while 

 the one with vertical lines appears broader, i.e., both appear oblong. 



Experiment 140. Look at the row of letters (S) and figures (8). 

 SSSSSSSS 88888888 



To some the upper halves of the letters and figures may appear to be 



of the same size as the lower halves, 



to others the lower halves may appear 



larger. Hold the figure upside down 



and observe that there is a considerable 



difference between the two, the lower 



halves being considerably larger. 



Experiment 141. The length of a 

 line appears to vary according to the 

 angle and direction of certain other 

 lines in relation to it (Fig. 148). The 

 length of the two vertical lines is 



the same, yet B appears much longer F IG . I4 g. TO show False 

 than A. Estimate of Size. 



