Page:Arrian's Voyage Round the Euxine Sea Translated.djvu/170

Rh that this tar was but jut viible in the horizon of Rhodes, and that at Alexandria its meridian height was a forty-eighth part of a great circle in the heavens, or 7° 30′; and inferred from thence, what part of a great circle on the earth this difference would amount to. The ditance between Rhodes and Alexandria he took for granted to be 5000 tadia; and of coure the circumference of the earth would be 240,000 tadia. Cleomedes was however doubtful of this meaurement; as he oberves, that a les um is to be taken, if the ditance between Rhodes and Alexandria hould be found to be les than 5000 tadia; which ditance, Mr. Cotard very properly oberves, from Strabo, was not obtained by any attempt at menuration, but only from the etimation of navigators. But when Poidonius heard that Eratothenes had, by gnomonic obervations, acertained the ditance between dria