THE EARTH 



15 



too far from land for fear of encountering strange mon- 

 sters or falling over the " edge " of the earth. 



The great Greek philosopher, Aristotle, who lived 

 about the middle of the fourth century B.C., observed 



FIG. 12. Flames on the Edge of the Sun. 



the curved outline of the earth's shadow on the moon 

 at the time of an eclipse and concluded from this observa- 

 tion that the earth must have a curved surface like a 

 globe. About the beginning of the Christian Era, writers 

 began to refer to the argument for the curvature of the 

 earth based on the disappearance of the lower part of 

 a vessel when sailing out to sea (Figure 13) ; that fact 



FIG. 13. Showing the Curvature of the Earth. 



had evidently been noted by many for some time pre- 

 vious. 



The knowledge thus gained by the wise men of the 

 ancient Mediterranean countries concerning the shape 



