From the time of Hipparchus to that of Ptolemy the geographer, the Alexandrian school, though rich in philosophers, who devoted their studies and labour to other branches of physical and metaphysical science, did not produce one, who improved geography, or the sciences on which it depends, with the exception of Posidonius. This philosopher, who belonged to the sect of the Stoics, was born at Apamea in Syria: he usually resided at Rhodes, and was the friend of Pompey and Cicero. The former, on his return from Syria, came thither to attend his lectures. Arriving at his house, he forbad his lictor to knock, as was usual, at the door; and paid homage to philosophy, by lowering the fasces at the abode of Posidonius. Pompey, being informed that he was at that time ill of the gout, visited him in his confinement, and expressed himself very much disappointed that he could not have the benefit of his lectures. Posidonius, thus honoured and flattered, in spite of his pain, delivered a lecture in the presence of his noble visitor; the subject of which was to prove, that nothing is good which is not honourable. Cicero informs us, that he also attended his lectures; and according to Suidas Marcellus, brought him to Rome in the year of the city 702; in this, however, Suidas is not supported by other and contemporary writers. We are indebted to Cleomedes for most of what we know of his opinions and discoveries; with such as relate to morals or to pure astronomy, we have no concern. But he was of service also to geography. He measured an arc of the terrestrial meridian; but his operation, as far as we can judge by the details which have reached us, was far from exact, and of course his result could not be accurate; it would appear, however, that his object was rather to verify the ancient measures of the earth, particularly that of Eratosthenes, and that he found them to agree nearly with his own. He explained the ebbing and flowing of the sea, from the motion of the moon, and seems to have been the first who observed the law of this phenomenon. In order to represent the appearance of the heavens, Cicero informs us that he constructed a kind of planetarium, by means of which he exhibited the apparent motion of the sun, moon, and planets round the earth. It is on the authority of Posidonius, that Strabo relates the voyage of Eudoxus of Cyzicum from the Persian Gulf round Africa to Cadiz, which we have already mentioned.