xvi INTRODUCTION 



under the vaulted heavens, but a globe. This 

 conclusion was accepted by many of the early 

 astronomers, and much speculation was pro- 

 voked by it as to the condition of the antip- 

 odes and the relation of the earth to the 

 heavenly bodies. In the system devised by 

 Ptolemy in the early part of our era, the earth 

 was placed at the center of things and the 

 heavenly bodies were supposed to move around 

 it. This geocentric theory was for a long time 

 the prevailing opinion of the structure of the 

 universe. It permeated much of the Middle 

 Ages and afforded the physical setting for 

 such great works of art as the Divine Comedy, 

 It was, however, eventually replaced by the 

 Copernican theory, according to which the 

 sun, not the earth, is the central body around 

 which the others move. So completely does 

 this heliocentric theory meet the facts of as- 

 tronomy that its truth is beyond dispute. But 

 in abandoning the old for the new, man was 

 obliged to give up his idea of a centrally lo- 

 cated habitation. In fact it may be said that 

 the Copernican theory removed the last physi- 

 cal vestige of the support for the anthropo- 

 centric conception and left this idea to survive 

 merely as a poetic figure. 



