50 THE REALITIES OF MODERN SCIENCE 



a practical death or cessation in these centuries, how 

 between 1200 and 1600 they were revived, our histories 

 tell us. But to the scientist there may well be par- 

 ticular interest in the events by which science was 

 preserved and even fostered in its growth during these 

 centuries. 



In our Arabic numerals we have a trace and an ex- 

 ample of the contributions 1 of non-European races 

 during the medieval ages. Through their capture of 

 Alexandria in 641 A.D. the Arabs had become the 

 custodians of the records of Greek learning. This 

 city, founded at the mouth of the Nile by Alexander 

 the Great in about 330 B.C., was the home of many 

 famous scientists and mathematicians, whom it at- 

 tracted by its museum and its libraries. Here lived 

 Euclid (300 B.C.). Here also, about 150 A.D., the as- 

 tronomer Ptolemy taught his theory of a geocentric 

 celestial system, which was accepted until Copernicus 

 (1473-1543) demonstrated that the sun was the center. 

 About the same time Alexandria also produced the 

 noted inventor Hiero, whose steam engine is a sort 

 of anticipation of the modern steam turbine. To 

 the records of these and other achievements, as well 

 as to the entire field of Greek thought, the Arabs were 

 appreciative heirs, while Europe suffered a decay of 

 learning. 



In the meantime Christianity had spread widely 

 throughout Europe. The bishops of its various centers 

 had become responsible to the bishop at Rome, who 

 thus became the Pope. It had been accepted by the 



1 Algebra and trigonometry are of Arabic or at least of non-Eu- 

 ropean origin. 



