INFLUENCE OF THE PTOLEMAIC EPOCH. 177 



tion of mathematical considerations on the articulation and 

 expansion of continents ; by geognostic conjectures regarding 

 the connection of mountain chains, the action of clouds, and 

 the former submersion of lands, which still bear all the traces 

 of having constituted a dried portion of the sea's bottom. Fa- 

 vorable to the oceanic sluice-theory of Strabo of Lampsacus, 

 the Alexandrian librarian was led, by the belief of the former 

 swelling of the Euxine, the penetration of the Dardanelles, 

 and the consequent opening of the Pillars of Hercules, to an 

 important investigation of the problem of the equal level of 

 the whole " external sea* surrounding all continents." An 

 additional proof of this philosopher's power of generalizing 

 views is afforded by his assertions that the whole continent 

 of Asia is traversed by a continually-connected mountain chain, 

 running from west to east in the parallel of Rhodes (in the 

 diaphragm of Dicaearchus).t 



An animated desire to arrive at a generalization of views — 

 the consequence of the intellectual movement of the age — 

 gave rise to the first Greek measurement of degrees between 

 Syene and Alexandria, and this experiment may be regarded 

 as an attempt on the part of Eratosthenes to arrive at an ap- 

 proximative determination of the circumference of the Earth. 

 In this case, it is not the result at which he arrived from the 

 imperfect premises afforded by the Bematists which excites 

 our interest, but rather the attempt to rise from the narrow 

 limits of one circumscribed land to a knowledge of the mag- 

 nitude of the whole earth. 



A similar tendency toward generalization may be traced in 

 the splendid progress made in the scientific knowledge of the 

 heavens in the epoch of the Ptolemies. I allude here to the 

 determination of the places of the fixed stars by the earliest 

 Alexandrian astronomers, Aristyllus and Timochares ; to Aris- 

 tarchus of Samos, the cotemporary of Cleanthes, who, conver- 

 sant with ancient Pythagorean views, ventured upon an in- 



* On the physical and geognostical opinions of Eratosthenes, see Stra 

 bo, Mb. i., p. 49-56 ; Hb. ii., p. 108. 



t Strabo, lib. xi., p. 519; Agathem, in Hudson, Geogr. Grcec. Min., 

 vol. ii., p. 4. On the accuracy of the grand orographic views of Eratos- 

 thenes, see my Asie Centrale, t. i., p. 104-150, 198, 208-227, 413-415 ; 

 t. ii., p. 367 and 414-435 ; and Examen Critique de VHist. de la G6ogr., 

 t. i., p. 152-154. I have purposely called the measurement of a degree 

 made by Eratosthenes as the first Hellenic one, since a very ancient 

 Chaldean determination of the magnitude of a degree in camels' paces 

 is not improbable. See Chasles, Recherches sur I' Astronomie Indiennt 

 et Chaldienne, in the Comptes Rendvs de V Acad, des Sciences, t. xxiii., 

 1846, p. 851. 



H 2 



