THE EARTH 



any distance the whole of a tower would be visible. 

 Ai'nr off, no doubt, it would be seen with less clear- 

 ness than near to, on account of the distance ; but it 

 could be seen more or less well from top to bottom." 



Here is another drawing of Uncle Paul's, repre- 

 senting two spectators, A and B, who, placed at very 

 different distances, nevertheless see the tower from 

 top to bottom on a flat surface. He resumed his 

 talk. 



"On dry land it is rare to find a surface that in 



ut and regularity is adapted to the observation 



I have just told you about. Nearly always hills, 



ridges, or screens of verdure intercept the view and 

 prevent one's seeing the gradual appearance, from 

 summit to base, of the tower or steeple that one is 

 approaching. On the sea no obstacle bars the view 

 mi loss it be the convexity of the waters, which follow 

 the general curvature of the earth. It is, accord- 

 ingly, there especially that it is easy to study the 

 ])li'iiomena produced by the rounded form of the 

 earth. 



" When a ship coming from the open sea ap- 

 proaches the coast, the first points of the shore visi- 

 ble to those on board are the highest points, like the 

 crests of mountains. Later the tops of high towers 

 come into sight; still hit IT the edge of the shore it- 

 self. In the same way an observer \\lio witnesses 

 from the shore the arrival of a vessel begins by per- 



