22 



OUR OWN WORLD 



Experiment 2. Attach a centrifugal hoop to a rotator apparatus 

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

 motion 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 greater than this below sea 

 level, yet these distances are so little in comparison to the 



size of the earth that the surface 

 is comparatively less irregular 

 than that of an orange. 



In these days many men have 

 sailed around the earth; but 

 valiant indeed was that little 

 company which in 1522 first 

 proved that it was possible to 

 sail continually in one 'direction 

 and yet reach the home port, 

 thus demonstrating that the earth 

 was probably round. Long be- 

 fore, wise men had come to 



believe that the earth was a sphere, for it had been noted 

 as far back as the time of Aristotle, the famous Greek 

 philosopher, that when the shadow of the earth fell upon 

 the moon, causing an eclipse of the moon, the boundaries 

 of the shadow were curved lines. It was also later noticed 

 that when ships are seen approaching at sea the masts ap- 

 pear first and then gradually the lower parts of the ship ; 

 and when ships sail away, the lower parts disappear first. 



PARTIAL ECLIPSE OF THE 

 MOON 



Showing the curved outline 

 of the earth's shadow. 



Experiment 3. Add alcohol to water until a solution is obtained 

 in which common lubricating oil will float at any depth. Insert with 



