THE PREDECESSORS OF COPERNICUS. 319 



in one lecture-room at the University of Padua in 1592, Galileo was 

 teaching the Euclid's Elements in another. It is easier to compre- 

 hend how students flocked to listen when a few years later Galileo 

 began his lectures upon astronomy, although by the conditions of his 

 professorship he was only permitted to expound the astronomy of 

 Sacro Bosco. 



Aristotle taught that the earth was spherical and gave reasons, good 

 and bad, for his belief. The distance of the sun was fixed by a most 

 ingenious method invented by Aristarchus of Samos (270 B. C.) who 

 concluded that the sun was about 19 times more distant than the moon 

 (it is, in fact, 390 times more distant). Hipparchus determined the 

 moon's distance for himself* and took the sun to be 19 times more 

 distant. He did not leave the earth in the central point of the sun's 

 orbit, but shifted that center towards the sixth degree of Gemini by 

 one twenty-fourth of the radius so as to account for observed inequali- 

 ties in the annual motion. Ptolemy adopted this result without ques- 

 tion, and it was accepted by astronomers for twelve centuries. It was 

 not until the time of Kepler that it was proved that the sun must be 

 at least fifty times as far away as the moon. This was one of the con- 

 sequences of Tycho's accurate observations. 



The Chaldeans and Egyptians held the earth to be a flat disc 

 canopied by the sky — the firmament — and this was the view of the 

 Hebrews. A distinctly Christian theory of the figure of the earth and 

 heavens, drawn from scripture, was formulated by the Egyptian monk 

 and traveler Cosmas Indicopleustes. According to this theory, the 

 earth was a flat parallelogram surrounded by the four seas. "We say, 

 therefore, with Isaiah, that the heaven embracing the universe is a 

 vault; with Job, that it is joined to the earth; and with Moses, that 

 the length of the earth is greater than its breadth. ' ' This explanation 

 of appearances was very generally accepted as orthodox, and was held 

 by the common people long after the learned had been convinced of the 

 earth's sphericity by the arguments of Ptolemy and Aristotle. Isidore 

 of Seville in the seventh century, and the Venerable Bede in the 

 eighth, declared for the opinion of Aristotle; Dante in the thirteenth 

 century supported it, and Columbus proved it in the fifteenth. In the 

 sixteenth, Magellan's voyage of circumnavigation settled the vexed 

 question once and for all. 



There is in the library of the University of Cambridge, so Dr. 

 Whewell reports, a French poem of the time of Edward the Second 

 (1307-27) illustrated with drawings that show men standing upright 

 on all parts of a spherical earth. By way of illustrating the tendency 



* He fixed the greatest distance of the moon at 78, the least at 67, semi- 

 diameters of the earth. The mean distance is, in fact, 60. The distance of the 

 sun, according to Hipparchus, was 1,300 semi-diameters. It is really about 

 23,000. 



