24. The Sidonians are said by historians to excel in various kinds of art, as the words of Homer also imply.[608] Besides, they cultivate science and study astronomy and arithmetic, to which they were led by the application of numbers (in accounts) and night sailing, each of which (branches of knowledge) concerns the merchant and seaman; in the same manner the Egyptians were led to the invention of geometry by the mensuration of ground, which was required in consequence of the Nile confounding, by its overflow, the respective boundaries of the country. It is thought that geometry was introduced into Greece from Egypt, and astronomy and arithmetic from Phœnicia. At present the best opportunities are afforded in these cities of acquiring a knowledge of these, and of all other branches of philosophy. If we are to believe Poseidonius, the ancient opinion about atoms originated with Mochus, a native of Sidon, who lived before the Trojan times. Let us, however, dismiss subjects relating to antiquity. In my time there were distinguished philosophers, natives of Sidon, as Boethus, with whom I studied the philosophy of Aristotle,[609] and Diodotus his brother. Antipater was of Tyre, and a little before my time Apollonius, who published a table of the philosophers of the school of Zeno, and of their writings. Tyre is distant from Sidon not more than 200 stadia. Between the two is situated a small town, called Ornithopolis, (the city of birds); next a river[610] which empties itself near Tyre into the sea. Next after Tyre is Palæ-tyrus (ancient Tyre), at the distance of 30 stadia.[611] [CAS. 758] 25. Then follows Ptolemaïs, a large city, formerly called Ace.[612] It was the place of rendezvous for the Persians in their expeditions against Egypt. Between Ace and Tyre is a sandy beach, the sand of which is used in making glass. The sand, it is said, is not fused there, but carried to Sidon to undergo that process. Some say that the Sidonians have, in their own country, the vitrifiable sand; according to others, the sand of every place can be fused. I heard at Alexandria from the glass-workers, that there is in Egypt a kind of vitrifiable earth, without which expensive works in glass of various colours could not be executed, but in other countries other mixtures are required; and at Rome, it is reported, there have been many inventions both for producing various colours, and for facilitating the manufacture, as for example in glass wares, where a glass bowl may be purchased for a copper coin,[613] and glass is ordinarily used for drinking.