It does not appear on what grounds Ariſtotle[1], or rather the mathematicians of his age, eſtimated the circumference of the earth to be 400,000 ſtadia: but this is certain, that Eratoſthenes, did not borrow his calculations from them, but formed his opinion from obſervations of his own, which are yet preſerved. He attempted this arduous taſk by an actual meaſurement of a ſegment of a great circle on the globe, making his computation upon the whole by uniting obſervations made in the heavens with a correſponding diſtance, meaſured (as it was ſuppoſed to be) on a meridian of the earth.
The ſegment of the meridian, which he fixed on for this purpoſe,was that between Alexandria and Syene, the diſtance between which places he is ſaid to have meaſured, and found to be 5000 ſtadia. He alſo found that the angle of the meridian ſhadow upon the ſcaphia or ſun-dial at Alexandria was equal, at the ſmmer ſoſitice, to 150 part of the circle; and that there was no ſhadow foom the gnomon at Syene at the ſame period of time, and at the ſame inſtant of the day.
Suppoſing then Alexandria and Syene to lie under the ſame merichan, he concluded that the diſtance between them was 150 part of a great circle of the earth; and this diſtance being 'Will
ſuppoſed) by meaſure, 5000 ſtadia, the whole circumference of the earth muſt: be of courſe 250,000 ſtadia. But in the account of this proceſs, which is accurately detailed by Cleomedes, not a
- ↑ Dr. Blair ſuggeſts that this may be an objection to that work being written by Ariſtotle, as Eraſthenes was generally alllowed to be the firſt who attempted that menſuration. Blair's Hiſt of Geography.
