THE EAETII C 9 



inch in height to a ball of ten feet in diameter ; therefore, 

 with all its valleys and high hills, the surface of the earth is 

 smoother in proportion to its bulk than the rind of an 

 orange. The earth is not a perfect sphere, but has a slightly 

 flattened form, as though it had been compressed at the 

 poles. The diameter at the poles is the smallest, and is 

 7899 miles, while that at the equator (its greatest) is 7925 

 miles, being a difference of twenty-six miles ; but this is so 

 small, when compared with the size of the earth, that if an 

 exact model of it were made, four inches in diameter, it 

 would require the most accurate measurement to determine 

 that it was not a perfect sphere. 



The form of the earth has been demonstrated by accurate 

 experiments and calculations, but there are many things we 

 may observe, convincing us of its rotundity ; one of the 

 most evident of these is the fact that as a ship at sea goes 

 from the land, the hull first disappears, then the lower sails, 

 and lastly the tops, while a ship approaching the shore 



shows first the topsails, and lastly the hull ; see fig. 7, 

 where A shows a ship on the horizon, B hull-down, c out of 

 sight. In the same way, the tops of distant mountains are 

 seen at sea long before the lower lands. Another proof is 

 drawn from the fact, that ships have been sailed quite 

 round the earth ; by steering as nearly as possible in one 

 direction, they have arrived at the place from which they 



