XIX.] 



THE FIGURE OF THE EARTH. 



321 



denotes the circle of vision which seems to separate the 

 sky from the earth on land, or the sky from the water on 

 sea. But, if the observer mounts a hill, or ascends a 

 tower, or climbs to the mast-head of a ship, he finds that 

 his circle of vision becomes extended, and he can see 

 objects which were before beyond his range ; in other 

 words, his horizon increases, or becomes a larger circle. 

 This is illustrated by Fig. 100. A person standing at the 



Fig. 100. — Knlargement of horizon by ascending a hiil. 



i 



foot of the mountain at k, has his view limited by the 

 circle t) if he goes half-way up the mountain to c, his 

 horizon expands to the circle marked e; and, if he goes 

 quite to the top, s, it enlarges to the circle a-. If a man's 

 eyes are five faet above ground, as they might be if he 

 stood at the base of the hill, the radius of his horizon will 

 be less than two miles and three-quarters ; but, if he went to 



k 



