SIO COSMOS. 



other, or, in other wtrds, to those in which thero etists a tend 

 ency of the komogcneous elementary substances to combine 

 together.* John PhiJoponus, the Alexandrian, a pupil of Am- 

 monias, the son of Hermias, who probably lived in the sixth 

 century, was the first who ascribed the movement of the heav- 

 enly bodies to a primitive impulse, connecting with this idea 

 that of the fall of bodies, or the tendency of all substances, 

 Vv'hether heavy or light, to reach the ground. t The idea con- 

 ceived by Copernicus, and more clearly expressed by Kepler, 

 :n his admirable work De Stella Martis, who even applied it 

 to the ebb and flow of the ocean, received in 1666 and 1674 

 a new impulse and a more extended application through the 

 sagacity of the ingenious Robert Hooke ;| Newton's theory oi 

 gravitation, which followed these earlier advances, presented 

 the grand means of converting the whole of physical astrono- 

 my into a true mecJicmisvi of the lieaven$,.\ 



Copernicus, as we find not only from his dedication to the 

 pope, but also from several passages in the work itself, had a 

 tolerable knowledge of the ideas entertained by the ancients 

 of the structure of the universe. He, however, only names in 

 the period anterior to Hipparchus, Hicetas (or, as he always 

 calls him, Nicetas) of Syracuse, Philolaiis the Pythagorean, 

 the TimsBus of Plato, Ecphantus, Heraclides of Pontus, and 

 the great geometrician Apollonius of Perga. Of the two 

 mathematicians, Aristarchus of Samos and Seleucus of Baby- 

 lon, whose systems came most nearly to his own, he mentions 

 only the first, making no reference to the second.il It has 



* See, regarding all that relates to the ideas of the ancients on at- 

 traction, gravity, and the fall of bodies, the passages collected with great 

 industry and discrimination, by Th. Henri Martin, Etudes sur le Tim6e 

 <Le Plaion, 1841, t. ii., p. 272-280, and 341. 



t Job. Philoponiis, De Creations Mundi, lib. i., cap. 12. 



t He subsequently relinquished the correct opinion (Brewster, Mar 

 tyrs of Science, 1846, p. 211) ; but the opinion that there dwells in the 

 centralbody of the planetary system — the sun — a power which governs 

 the movements of the planets, and that this solar force decreases either 

 as the squares of the distances or in direct ratio, was expressed by Kep- 

 ler in the Harmonices Mundi, completed in 1618. 



$ See Cosmos, vol. i., p. 48 and 63. 



II See op. cit., p. 177. The scattered passages to be found in the 

 work of Copernicus, relating to the ante-Hipparchian system of the 

 structure of the universe, are, exclusive of the dedication, the following : 

 lib. i., cap. 5 and 10; lib. v., cap. 1 and 3 (ed. pi'inc, 1543, p. 3, b. ; 

 7,b. ; 8, b. ; 133, b. ; 141 and 141, b. ; 179 and 181, b.). Everywhere 

 Copernicus shows a predilection for, and a very accurate acquaintance 

 with, the views of the Pythagoreans, or, to speak less definitely, with 

 those which were attriliuled to ilie most ancient among them. Thu3 



