IV 



THE NEW COSMOLOGY COPERNICUS TO 

 KEPLER AND GALILEO 



WE have seen that the PtoleinakLastronomy, which 

 was the accepted doctrine throughout the Mid- 

 dle Ages, taught that the ^aj^h^is_round. Doubtless 

 there was a popular opinion ctiireiSrwhich regarded 

 the earth as flat, but it must be understood that this 

 opinion had no champions among men of science 

 during the Middle Ages. When, in the year 1492, 

 Columbus sailed out to the west on his memorable 

 voyage, his expectation of reaching India had full 

 scientific warrant, however much it may have been 

 scouted by certain ecclesiastics and by the average 

 man of the period. Nevertheless, we may well suppose 

 that the successful voyage of Columbus, and the still 

 more demonstrative one made about thirty years later 

 by Magellan, gave the theory of the earth's rotundity 

 a certainty it could never previously have had. Alex- 

 andrian geographers had measured the size of the earth, 

 and had not hesitated to assert that by sailing west- 

 ward one might reach India. But there is a wide 

 gap between theory and practice, and it required the 

 voyages of Columbus and his successors to bridge 

 that gap. 



After the companions of Magellan completed the 

 circumnavigation of the globe, the general shape of 



52 



