CHAPTER II 



THE PLANET EAKTH 



5. The Shape of the Earth. Men who have in different 

 ways made careful measurements of the shape of the earth 

 tell us that it is an oblate spheroid (Fig. 6), that is, a 

 sphere which is somewhat flattened at 

 two opposite points. An ordinary 

 orange has this shape. The earth has 

 been so little flattened, however, that 

 its shape is very much nearer that of 

 a perfect sphere than is that of an 

 orange. Its polar diameter is only 27 

 miles shorter than its equatorial di- 

 ameter, so when we consider that each of its diameters 

 is nearly 8000 miles, a shortening of only 27 miles in 

 one of these would not change its shape from that of a 

 sphere enough to be noticed except by the most care- 

 ful measurements. 



Experiment 6. Attach a centrifugal hoop to a rotator apparatus 

 and revolve. The hoop bulges at the center or point of greatest mo- 

 tion and flattens at the top and bottom or points of least motion. 

 The earth revolves in a way similar to the hoop and is very slightly 

 flattened at the poles. 



Although some of the mountains of the earth rise above 

 sea level to a height of over five miles, and there are 

 depths in the sea which are somewhat deeper than this 

 below sea level, yet these distances are so little in* com- 

 parison to the size of the earth that the surface is com- 

 paratively less irregular than that of an orange. 



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