320 PHYSIOGRAPHY. [chap. 



are presented ; the first points which are visible to him are 

 the peaks of hills, or the tops of buildings. He is prevented 

 from seeing the bases of these objects by the bulge of 

 water, which rises between him and the shore. Now, as 

 these appearances are not confined to any one locality, but 

 are seen in every part of the world, it follows that the earth 

 must have a general curvature. In fact, it can be shown 

 that the convexity is everywhere very nearly the same ; and 

 it is, therefore, clear that the earth is a globe-shaped body. 



It is possible to obtain similar proof of the earth's round- 

 ness by pbserving a vessel which is stationary. Suppose that 

 a person who is about to bathe in a calm sea, sees a small 

 boat a mile or two from shore. Let him then get into the 

 water, and, with his eye only a few inches above sea-level, 

 look along the surface of the water in the direction of the 

 boat. He will now find that the boat is more or less 

 hidden, or perhaps altogether lost from sight. In fact the 

 curved surface of the sea obstructs the view ; and the 

 obstruction is greater, the lower the position of the bather's 

 eye. When a man is standing on shore, his eyes are raised 

 something like five feet above ground ; but, when his head 

 is in the water, they are only a few inches above the sea 

 level, and his view is accordingly obstructed. When the 

 observer is in an elevated position, he is able to look over 

 the low hill of water which interferes with the prospect at 

 lower levels : hence, more of a distant ship can be seen 

 from the top of a tower than from its base. 



If a person standing on a wide plain, with nothing to 

 obstruct his view, looks round about him, he finds that the 

 boundary of his vision extends equally in all directions, and 

 thus forms a circle. This boundary is called the horizon} 

 The term horizon, at least as used in this sense, therefore 

 ' Horizon, from boi^ui, horizo, to bound. 



