PHYSIOLOGICAL PARADOXES. 



existence of hills and hollows is made obvious 

 by the fact that the prominences obstruct the 

 view of the low ground beyond them. When 

 the point of view is very high, this guide to the 

 structure of the country is withdrawn, because 

 the eye looks down upon the surface of hills and 

 hollows alike ; while the difference of distance 

 between the higher and lower parts is so small 

 in comparison with the distance of both from 

 the observer as to be imperceptible, so that it 

 forms no guide to height. In such cases we 



A G B D 



FIG. 55.-VARIATION8 IN APPARENT STEEPNESS OF HILLS. 



actually see a view in which there is no repre- 

 sentation of higher and lower levels. 



Where we think that we see heights greater 

 than those which exist it is the thought, rather 

 than the sight, that is in error. 



Suppose A B (Fig. 55) to represent a stretch 

 of flat country, and B C D a hill. Familiar with 

 the level ground, we judge of the steepness 

 and height of the hill by the inclination of its 

 face, B C, to the level ground in other words, 

 by the size of the angle ABC. 



But if, instead of level ground at A B, there 

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