THE STELLAR UNIVEESE. 



Now, as the most satisfactory evidence of the annual motion of 

 the earth would be the discovery of this displacement, and 

 successive changes of apparent position of all objects on the firma- 

 ment consequent on such motion, the absence of any such 

 phenomenon must be admitted to constitute, primd facie, a 

 formidable argument against the earth's motion. 



11. The effects of annual parallax are observable, and indeed 

 are of considerable amount, in the case of all the bodies com- 

 posing the solar system. .The apparent annual motion of the sun 

 is altogether due to parallax. The apparent motions of the 

 planets and other bodies composing the solar system are the effects 

 of parallax, combined with the real motions of these various bodies. 



Until the annual motion of the earth was admitted, these effects 

 of annual parallax on the apparent motions of the solar system were 

 ascribed to a very complicated system of real motions of these 

 bodies, of which the earth was assumed to be the stationary centre, 

 the sun revolving round it, while at the same time the planets 

 severally revolved round the sun as a moveable centre. This 

 hypothesis, proposed originally by Apollonius of Perga, a Grecian 

 astronomer, some centuries before the birth of Christ, received 

 the name of the PTOLEMAIC SYSTEM, having been developed and 

 explained by PTOLEMY, an Egyptian astronomer who flourished 

 in the second century, and whose work, entitled " Syn taxis," 

 obtained great celebrity, and for many centuries continued to be 

 received as the standard of astronomical science. 



Although Pythagoras had thrown out the idea that the annual 

 motion of the sun was merely apparent, and that it arose 

 from a real motion of the earth, the natural repugnancy of the 

 human mind to admit a supposition so contrary to received 

 notions prevented this happy anticipation of future and remote 

 discovery from receiving the attention it merited ; and Aristotle, 

 less sagacious than Pythagoras, lent the great weight of his 

 authority to the contrary hypothesis, which was accordingly 

 adopted universally by the learned world, and continued to pre- 

 vail, until it was overturned in the middle of the sixteenth 

 century by the celebrated Copernicus, who revived the Pytha- 

 gorean hypothesis of the stability of the sun and the motion of 

 the earth. w 



The hypothesis proposed by him in a work entitled "De Re- 

 volutionibus Orbium Ccelestium," published in 1543, at the 

 moment of his death, is that since known as the COPEBNICAN 

 SYSTEM, and, being now established upon evidence sufficiently 

 demonstrative to divest it of its hypothetical character, is ad- 

 mitted as the exposition of the actual movements by which that 

 part of the universe sailed the solar system is affected. 

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