Page:The geography of Strabo (1854) Volume 1.djvu/25

CHAP. i. 11. INTRODUCTION. 11 his track are also well known as great men and true philoso- phers. The two immediately succeeding Homer, according " At Syene in Upper Egypt, which is supposed to be the same as, or near to, the town of Assouan, (Lat. 24 10' N., Long. 32 59' E. of Greenwich,) Eratosthenes was told (that he observed is very doubtful) that deep w^ells were enlightened to the bottom on the day of the summer solstice, and that vertical objects cast no shadows. He concluded therefore, that Syehe was on the tropic, and its latitude equal to the obliquity of the ecliptic, which, as we have seen, he had determined : he presumed that it was in the same longitude as Alexandria, in which he was out about 3, which is not enough to produce what would at that time have been a sensible error. By observations made at Alexandria, he determined the zenith of that place to be distant by the fiftieth part of the circumference from the solstice, which was equivalent to saying that the arc of the meridian be- tween the two places is 7 12'. Cleomedes says that he used the (TKO^J/, or hemispherical dial of Berosus, in the determination of this latitude. Delambre rejects the idea with infinite scorn, and pronounces Cleomedes unworthy of credit ; and indeed it is not easy to see why Eratosthenes should have rejected the gnomon and the large circular instruments, un- less, perhaps, for the following reason. There is a sentiment of Cleomedes which seems to imply that the disappearance of the shadows at Syene on the day of the summer solstice was noticed to take place for 300 stadia every way round Syene. If Eratosthenes took his report about the phe- nomenon (and we have no evidence that he went to Syene himself) from those who could give no better account than this, we may easily under- stand why he would think the GKCL^I] quite accurate enough to observe with at his own end of the arc, since the other end of it was uncertain by as much as 300 stadia. He gives 500 stadia for the distance from Alex- andria to Syene, and this round number seems further to justify* us in concluding that he thought the process to be as rough as in truth it was. Martianus Capella states that he obtained this distance from the measures made by order of the Ptolemies (which had been commenced by Alex- ander) : this writer then implies that Eratosthenes did not go to Syene himself. " The result is 250,000 stadia for the circumference of the earth, which Eratosthenes altered into 252,000, that his result might give an exact number of stadia for the degree, namely, 700 ; this of course should have been 694|. Pliny calls this 31,500 Roman miles, and therefore supposes the stadium to be the eighth part of a Roman mile, or takes for granted that Eratosthenes used the Olympic stadium. It is likely enough that the Ptolemies naturalized this stadium in Egypt ; but never- theless, it is not unlikely that an Egyptian stadium was employed. If we assume the Olympic stadium, (202 yards,) the degree of Eratos- thenes is more than 79 miles, upwards of 10 miles too great. Nothing is known of any Egyptian stadium. Pliny asserts that Hipparchus, but for what reason he does not say, wanted to add 25,000 stadia to the cir- cumference as found by Eratosthenes. According to Plutarch, Eratos- thenes made the sun to be 804 millions of stadia from the earth, and the moon 780,000. According to Macrobius, he made the diameter of the sun to be 27 times that of the earth. With regard to the other merits of