326 POPULAR SCIENCE MONTHLY 



in the original, and of comparing the opinions of learned critics, will 

 readily be directed to them by the special literature. 5 



Contenting ourselves with these brief literary indications, we may 

 pass on to the more intricate questions relating to the predecessors of 

 Aristarchus, and the influence of Pythagorean views upon later thinkers. 

 As has been previously remarked, Heraclides Ponticus acknowledged 

 that the heliocentric theory provided an adequate explanation of celes- 

 tial phenomena, and even approached so nearly to modern ideas as to 

 maintain the revolution of Mercury and Venus about the sun. This 

 we know from the testimony of numerous authors, chiefly Roman, 

 amongst whom Heraclides was held in high regard. Of interest is the 

 passage in Simplicius (' Commentary on Aristotle's de Ccelo/ Karsten's 

 edition, p. 232), which shows Heraclides' correct apprehension of the 

 causes determining the difference in length between the sidereal and 

 ordinary day of twenty-four hours. We are informed, however, by 

 Plutarch (Plac. Philos., III., 13) and later writers (e. g., Simplicius, 

 Hippolytus, Proclus, Chalcidius, and especially Vitruvius and Teren- 

 tius Varro) that although Heraclides of Pontus and Ecphantus the 

 Pythagorean believed the earth to turn upon its axis from west to east, 

 they distinctly denied to it a movement of translation through space. 

 It is clear also from Aristotle that it was no unheard-of thing to ex- 

 plain the apparent diurnal motion of the heavens upon the hypothesis 

 of the earth's rotation. Plato appears to have accepted this idea as the 

 starting-point of his system, complicated as it was with superadded 

 mechanism. But the great Athenian appears to have elaborated his 

 cosmical theory more as a speculative abstraction than as an orderly 

 induction from observed facts, and it was easy to explain the discrep- 

 ancy of the latter as due to false appearances. 



It has been claimed on the authority of Theophrastus, as reported 

 by Plutarch and Aristotle, that Plato repented in his old age at hav- 

 ing placed the earth at the center or ' altar ' of the universe, this being 

 deemed too sacred a position for it to occupy (Plutarch, Plat. Qucest., 

 VIII. 1; Aristotle, de Ccelo, II. 13, 3). But this is very far from 

 indicating that the heliocentric theory ever fully shaped itself in his 

 mind, although one sees that it required merely a combination of his 

 views and those of the Pythagorean school to arrive at a cosmical 



5 Besides the writings of Schiaparelli above mentioned, one should not 

 fail to consult H. Martin's works, especially his ' Etudes sur le Timee de 

 Platon,' Vol. II. (Paris, 1841), and Paul Tannery's ' Recherches sur l'Histoire 

 de l'Astroncmie ancienne ' (Paris, 1893). The fourth essay in Bergk's 

 ' Abhandlungen zur Geschichte der griechischen Philosophic und Astronomie ' 

 (Leipzig, 1883) is devoted to Aristarchus. The older work of Schaubach con- 

 tains some rather adverse estimates, no longer considered tenable. On 

 Pythagorean doctrines, one of the most critical essays in English is by George 

 Grote : ' Plato's Doctrine respecting the Rotation of the Earth, and Aristotle's 

 Comment upon that Doctrine' (London, 1860). 



