THE TURNING OF THE EARTH 103 



contains little in the way of general considerations which had 

 not been eagerly discussed by the Greeks, that one especial 

 argument against the revolution of the fixed stars was the 

 frightful speed at which they would have to travel in order 

 to complete the circle of the heavens in twenty-four hours. 

 The sling in those days was a common weapon ; and they would 

 be led to consider that while it is easy to whirl an object about 

 on, say, a foot leash, at a high rate, this becomes increasingly 

 difficult as the leash is lengthened. So also with a little wheel 

 and a big one. 



If, therefore, it seemed preposterous that so great a thing as 

 the earth could turn, it was still more difficult to imagine the 

 flight through space of other large bodies, like the sun, in an 

 enormously larger orbit. This difficulty must have become 

 of increasing moment, as it became clear that the sun was 

 even larger than the earth, and hence almost inconceivably 

 distant. 



But if, as is abundantly attested by various fragments, there 

 were close reasoners like Philolaus of Crotona, Hicetas of 

 Syracuse, Heraclides of Pontus and others, who could maintain 

 the daily revolution of the earth, there were still difficulties 

 enough. The turning of the earth explained with exquisite 

 simplicity the apparent revolution of the heavens ; it did not 

 clear up the curious shift of the sun with the seasons. This 

 shift was double, first with reference to the circle the sun 

 describes in the heavens each day, with which the length of 

 the day seemed bound up ; and second, with reference to the 

 fixed stars. 



Why should the sun seem thus to wobble in the sky ? why 

 should the days be nearly twice as long as the nights in summer, 

 and in the winter hardly half ? If the earth be in reality 

 a revolving globe, a vast barrel-churn, one might go a step 

 further and suppose that, for some reason or other, it was 

 wobbling on its axis as well back and forth, swaying six months 

 one way and six months the other. This would explain the 

 change in the sun's apparent position, the change of days, and 

 of seasons too. But if it was a mental wrench to try to think 

 of a whirling earth, it was sheer deracination to propose an 

 earth that not only whirled, but in whirling swayed! The 

 mind grew vertiginous over the abyss of such a thought. Turn 

 it might, upon an axis that was fixed the idea was even 



