ALEXANDRIAN OR HELLENISTIC PERIOD 



but that their apparent motion is due to the actual 

 revolution of the earth? It is extremely difficult for 

 any one nowadays to put himself in a mental position 

 to answer this question. We are so accustomed to 

 conceive the solar system as we know it to be, that we 

 are wont to forget how very different it is from what it 

 seems. Yet one needs but to glance up at the sky, and 

 then to glance about one at the solid earth, to grant, 

 on a moment's reflection, that the geocentric idea is of 

 all others the most natural ; and that to conceive the 

 sun as the actual centre of the solar system is an idea 

 which must look for support to some other evidence 

 than that which ordinary observation can give. Such 

 was the view of most of the ancient philosophers, and 

 such continued to be the opinion of the majority of 

 mankind long after the time of Copernicus. We must 

 not forget that even so great an observing astronomer 

 as Tycho Brahe, so late as the seventeenth century, 

 declined to accept the heliocentric theory, though ad- 

 mitting that all the planets except the earth revolve 

 about the sun. We shall see that before the Alexan- 

 drian school lost its influence a geocentric scheme had 

 been evolved which fully explained all the apparent 

 motions of the heavenly bodies. All this, then, makes 

 us but wonder the more that the genius of an Aris- 

 tarchus could give precedence to scientific induction as 

 against the seemingly clear evidence of the senses. 



What, then, was the line of scientific induction that 

 led Aristarchus to this wonderful goal? Fortunate- 

 ly, we are able to answer that query, at least in 

 part. Aristarchus gained his evidence through some 

 wonderful measurements. First, he measured the 



217 



