CHAPTER LI!' 



THE EAKTH 



HE earth is round, as proved by the follow- 

 ing facts. When, in order to reach the town 

 he is journeying toward, a traveler crosses a level 

 plain where nothing intercepts his view, from a cer- 

 tain distance the highest points of the town, the 

 summits of towers and steeples, are seen first. 

 From a lesser distance the spires of the steeples be- 

 come entirely visible, then the roofs of buildings 

 themselves ; so that the view embraces a great num- 



ber of objects, beginning with the highest and end- 

 ing with the lowest, as the distance diminishes. The 

 curvature of the ground is the cause of it. ' ' 



Uncle Paul took a pencil and traced on paper the 

 picture that you see here ; then he continued : 



"To an observer at A the tower is quite invisible 

 because the curvature of the ground hides the view. 

 To the observer at B the upper half of the tower is 

 visible, but the lower half is still hidden. Finally, 

 when the observer is at C he can see the whole tower. 

 It would not be thus if the earth were flat. From 



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