134 THE GREEK ASTRONOMY. 



elephants, which are said to be of the same species (yivog) towards 

 each extreme ; as if this circumstance was a consequence of the con- 

 junction of the extremes. The mathematicians, who try to calculate 

 the measure of the circumference, make it amount to 400,000 stadia ; 

 whence we collect that the earth is not only spherical, but is not large 

 compared with the magnitude of the other stars." 



When this notion was once suggested, it was defended and confirm- 

 ed by such arguments as we find in later writers : for instance, 51 that 

 the tendency of all things was to fall to the place of heavy bodies, and 

 that this place being the centre of the earth, the whole earth had no 

 such tendency ; that the inequalities on the surface were so small as 

 not materially to affect the shape of so vast a mass ; that drops of 

 water naturally form themselves into figures with a convex surface ; 

 that the end of the ocean would fall if it were not rounded off; that 

 we see ships, when they go out to sea, disappearing downwards, which 

 shows the surface to be convex. These are the arguments still em- 

 ployed in impressing the doctrines of astronomy upon the student of 

 our own days ; and thus we find that, even at the early period of 

 which we are now speaking, truths had begun to accumulate which 

 form a part of our present treasures. 



Sect. 10. The Phases of the Moon. 



WHEN men had formed a steady notion of the Moon as a solid body, 

 revolving about the earth, they had only further to conceive it spheri- 

 cal, and to suppose the sun to be beyond the region of the moon, and 

 they would find that they had obtained an explanation of the varying 

 forms which the bright part of the moon assumes in the course of a 

 month. For the convex side of the crescent-moon, and her full edge 

 when she is gibbous, are always turned towards the sun. And this 

 explanation, once suggested, would be confirmed, the more it was ex- 

 amined. For instance, if there be near us a spherical stone, on which 

 the sun is shining, and if we place ourselves so that this stone and the 

 moon are seen in the same direction (the moon appearing just over 

 the top of the stone), we shall find that the visible part of the stone, 

 which is then illuminated by the sun, is exactly similar in form to the 

 moon, at whatever period of her changes she may be. The stone and 

 the moon being in the same position with respect to us, and both 

 being enlightened by the sun, the bright parts are the same in figure; 



51 Pliny, Sat. Hist. ii. LXT. 



