178 COSMOS. 



vestigatlon of the construction of the universe, and who was 

 the first to recomiize the immeasurable distance of the region 

 of fixed stars from our small planetary system ; nay, he even 

 conjectured the two-fold motion of the earth round its axis and 

 round the sun ; to Seleucus of Erythrsea (or of Babylon), =^ who, 

 a century subsequent to this period, endeavored to establish 

 the hypothesis of the Samian philosopher, which, resembling 

 the views of Copernicus, met with but little attention during 

 that age ; and, lastly, to Hipparchus, the founder of scientifi'^- 

 astronomy, and the greatest astronomical observer of antiquity. 

 Hipparchus was the actual originator of astronomical tables 

 among the Greeks,! and was also the discoverer of the pre- 

 cession of the equinoxes. On comparing his own observations 

 of fixed stars (made at Rhodes, and not at Alexandria) with 

 those made by Timochares and Aristyllus, he was led, proba- 

 bly without the apparition of a new star,$ to this great dis- 

 covery, to which, indeed, the earlier Egyptians might have 

 attained by a long-continued observation of the heliacal rising 

 of Sirius.^ 



A peculiar characteristic of the labors of Hipparchus is the 

 use he made of his observations of celestial phenomena for the 

 determination of geographical position. Such a connection 

 between the study of the earth and of the celestial regions, mu- 

 tually reflected on each other, animated through its uniting 

 influences the great idea of the Cosmos. In the new map of 

 the world constructed by Hipparchus, and founded upon that 

 of Eratosthenes, the geographical degrees of longitude and 

 latitude were based on lunar observations and on the measure- 

 ments of shadows, wherever such an application of astronom- 



* The latter appellation appears to me the more correct, since Strabo, 

 lib. xvi., p. 739, quotes, " Seleucus of Seleucia, among several very hon- 

 orable men, as a Chaldean, skilled iu the study of the heavenly bodies." 

 Seleucia, on the Tigris, a flourishing commercial city, is probably the 

 one meant. It is indeed singular that Strabo also speaks of a Seleucus, 

 an exact observer of the tides, and terms him, too, a Babylonian (lib. 

 i., p. 6), and subsequently (lib. iii., p. 174), perhaps from carelessness, 

 an Erythraean. (Compare Stobaeus, Eel. Phys., p. 440.) 



t Ideler, Handbuch der Chronologic, bd. i., s. 212 und 329. 



} Delambre, Histoire de V Astronomie Ancienne, t. i., p. 290. 



$ Bockh has entered into a discussion, in his Philolaos, s. 118, as to 

 whether the Pythagoreans were early acquainted, through Egyptian 

 sources, with the; precession, under the name of the motion of the heav- 

 ens of the fixed stars. Letronne {Observations sur les Reprisentationt 

 Zodiacales qui nous restent de V Antiquit6, 1824, p. 62) and Ideler (in his 

 Handbuch der Chronol., bd. i., s. 192) vindicate the exclusive claim of 

 Hipparchus to this discovery. 



