vi INQUIRY AND INTERPRETATION 143 



on which he subsisted was always in arrears ; and though the 

 three emperors, whose reigns he adorned, directed their ministers 

 to be more punctual in its payment, the disobedience of their 

 commands was a source of continual vexation to Kepler. When 

 he retired to Silesia, to spend the remainder of his days, his 

 pecuniary difficulties became still more harassing. Necessity 

 at length compelled him to apply personally for the arrears 

 which were due; and he accordingly set out in 1630, when 

 nearly sixty years of age, for Ratisbon ; but in consequence of 

 the great fatigue which so long a journey on horseback produced, 

 he was seized with a fever, which put an end to his life. Sir 

 David Brewster. 



The astronomical views of early Greek philosophers 

 were summed up by Aristotle in the fourth century B.C. 

 There were many speculations as to the form of the 

 earth and the nature of celestial phenomena, but few 

 have any scientific significance. " Some say," remarked 

 Aristotle in one of his works, " that the earth rests on 

 water. We have ascertained that the oldest statement 

 of this character is the one accredited to Thales the 

 Milesian [639-546 B.C.], to the effect that it rests on 

 water, floating like a piece of wood or something of that 

 sort." Aristotle himself stated plainly that the earth 

 is a round globe, and Pythagoras (566-470 B.C.) is believed 

 to have taught that the earth moves in the heavens, 

 but Aristarchus of Samos, in the third century B.C., 

 was the first philosopher to suggest that the sun is the 

 centre of our system and that the earth revolves around 

 it in a year. When, however, four hundred years later, 

 Ptolemy of Alexandria built up his system of astronomy, 

 he adopted the doctrine of an immovable earth in the 

 centre of the universe, and this was accepted as true until 

 the time of Copernicus. 



The earliest serious criticism of the views of Aristotle 

 and Ptolemy appear to have been made by Oresme, 

 who became Bishop of Lisieux, Normandy, in 1377, and 



