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TEE POPULAR SCIENCE MONTELY.— SUPPLEMENT. 



who were also astrologers would have been equal- 

 ly disinterested if they had helped to revolution- 

 ize the science of the stars. However, there is 

 a strong intrinsic probability that the private 

 opinions of Novara were favorable to the theory 

 of the earth's motion, just then beginning to be 

 openly discussed in Italy ; and a sentence of 

 George Joachim RhaHieus, the devoted friend 

 and disciple of Copernicus in his later years, 

 stating that Novara was not only an able astrono- 

 mer, but also " followed the good method," gives 

 strength to that probability. 



It is, perhaps, the most singular phenomenon 

 in the history of science that a system founded 

 on such a total ignorance of natural forces, and 

 involving so much that is repugnant to common- 

 sense as the Ptolemaic cosmology, should have 

 been universally received; and not only received, 

 but studied, expounded, and developed, during at 

 least fourteen centuries. This anomaly becomes 

 somewhat less perplexing on a little consideration 

 of its origin and history. The temperament of 

 the Greeks did not incline them to prolonged as- 

 tronomical observations. As Diodorus remarks, 

 they had too many other interests to distract 

 their thoughts ; and they wanted that secular 

 patience, reaching from generation to generation, 

 which enabled the Chaldeans to establish their 

 great year of 600, and the Egyptians their Sothaic 

 period of 1,461 years. Thus, up to the time of 

 Hipparchus, the astronomy of the Greeks con- 

 sisted of some more or less ingenious theories, 

 founded on traditions imported by their philos- 

 ophers from the East — fragments, perhaps, of 

 an older and more perfect science, which, like the 

 submerged continent of Lemuria, survived as 

 broken islets of truth floating in a vast sea of 

 error. This was the opinion of Bailly ; and al- 

 though no longer in favor with savants, it receives 

 at least some countenance from the fact that, in 

 the Indian Tables certain of the recorded obser- 

 vations imply a more advanced state of knowledge 

 than the Brahmans have, within historical times, 

 attained; such as that of the slow shifting in 

 space of the perihelion of the earth's orbit, and 

 the nearly exact determination of the yearly 

 amount of precession. Anaximander, a disciple 

 of Thales of Miletus, was the first among the 

 Greeks to propound the theory of the earth's ro- 

 tation on its axis, and the Pythagoreans, as long 

 as they continued to have distinctive opinions, all 

 held more or less explicitly the same doctrine. 

 Heraclides, of Pontus, after the middle of the 

 fourth century b. c, made the first approach to 

 the heliocentric theory of the planetary move- 



ments by making Mercury and Venus revoNe 

 round the sun — retaining, however, the central 

 position of the earth with regard to the sun itself 

 as well as the remaining planets. This doctrine, 

 which Heraclides is supposed, on the authority 

 of a doubtful passage in Macrobius, to have de- 

 rived from the Egyptians, was carried out to its 

 logical conclusion early in the following century 

 by Aristarchus of Samos, to whom belongs the 

 glory of having assigned to the earth its move- 

 ment of translation as well as of rotation, and of 

 having thus anticipated, in both its parts, the 

 doctrine of Copernicus. This line of opinion, 

 however, from Anaximander to Aristarchus, was 

 but an isolated development of thought, unsup- 

 ported by scientific proof, and repugnant to the 

 prima facie evidence of the senses. The over- 

 whelming preponderance of ideas conformed it- 

 self to direct appearances. 



Opinions have been hitherto equally divided 

 as to which side of the question was reenforced 

 by the august name of Plato. The real state of 

 the case seems to be, as Signor Schiaparelli has 

 pointed out with much learning and acumen, that 

 the Platonic ideas on the subject were progressive ; 

 advancing from the mythological conception of a 

 universe whirling on the spindle of necessity, 1 to 

 a clear grasp of the Pythagorean doctrine of the 

 earth's rotation. 2 At an intermediate stage of 

 his long development, he proposed to geometers 

 the problem of accounting for the apparent mo- 

 tions of the heavenly bodies on the hypothesis of 

 uniform circular motion round the earth as a 

 centre. (It must be remembered that the Greeks 

 carefully separated astronomy from physics ; re- 

 garding the first as dealing only with mathemati- 

 cal possibilities, while physics took exclusive cog- 

 nizance of natural laws.) Plato's challenge pro- 

 duced the homocentric system, elaborated by the 

 mathematicians Eudoxus and Calippus, which 

 accounted for the apparent paths of the sun, 

 moon, and planets, supposing them to be pro- 

 pelled by a series of spheres revolving with dif- 

 ferent velocities round the earth as a common 

 centre. This hypothesis answered admirably for 

 Jupiter and Saturn, but failed to explain the 

 anomalies of Mars, Venus, and Mercury. It was 

 consequently abandoned in favor of the system 

 of eccentrics and epicycles, as developed mathe- 

 matically by Apollonius of Perge. Uniform cir- 

 cular motion, being presupposed as a necessary 

 postulate, the accelerations and retardations of the 

 celestial bodies were explained by supposing the 



i " Republic, 1 ' book x. 

 2 " Laws," book vii. 



