One of his first endeavours was, to verify the obliquity of the ecliptic, as settled by Eratosthenes: he next fixed, as accurately as possible, the latitude of Alexandria; but it would lead us far from the object of our work, if we were even briefly to mention his discoveries in the science of pure astronomy. We must confine ourselves to those parts of his discoveries which benefitted geography, either directly or indirectly. After having, as successfully as his means and the state of the science would permit him to do, fixed the position of the stars, he transferred the method which he had employed for this purpose to geography: he was the first who determined the situation of places on the earth, by their latitudes and longitudes, with any thing like accuracy. The latitude, indeed, of many places had been fixed before; and the means of doing it were sufficiently simple and obvious: but with respect to some general and safe mode of ascertaining the longitudes, the ancient philosophers before Hipparchus, were ignorant of it. He employed for this purpose the eclipses of the moon. After having ascertained the latitudes and longitudes of a great many places, he proposed to draw up a catalogue of terrestial latitudes and longitudes, but this he was not able to accomplish: he had set the example, however and it was followed by subsequent astronomers. He fixed on the Fortunate Islands, which are supposed to be the Canaries, for his first meridian. His principal works most probably were destroyed in the conflagration of the Alexandrian library. His catalogue of the stars is preserved in the Almagest of Ptolemy; and his commentary on Aratus and Eudoxus is still extant.