It was not to be expected, however, that Ptolemy could accurately fix the longitude and latitude of places in the remoter parts of the then known world; his latitudes and longitudes are accordingly frequently erroneous, but especially the latter. This arose partly from his taking five hundred stadia for a degree of a great circle, and partly from the vague method of calculating distances, by the estimate of travellers and merchants, and the number of days employed in their journies by land, and voyages by sea. As he took seven hundred stadia for a degree of latitude, his errors in latitude are not so important; and though the latitude he assigns to particular places is incorrect, yet the length of the globe, according to him, or the distance from the extreme points north and south, then known, is not far from the truth. Thus the latitude of Thule, according to Ptolemy, is 64 degrees north, and the parallel through the cinnamon country 16° 24' south, that is, 80° 24' on the whole, a difference from the truth of not more than six or seven degrees. It is remarked by D'Anville, and Dr. Vincent coincides in the justice of the remark, that the grandest mistake in the geography of Ptolemy has led to the greatest discovery of modern times. Strabo had affirmed, that nothing obstructed the passage from Spain to India by a westerly course, but the immensity of the Atlantic ocean; but, according to Ptolemy's errors in longitude, this ocean was lessened by sixty degrees; and as all the Portuguese navigators were acquainted with his work, as soon as it was resolved to attempt a passage to India, the difficulty was, in their idea, lessened by sixty degrees; and when Columbus sailed from Spain, he calculated on sixty degrees less than the real distance from that country to India. Thus, to repeat the observation of D'Anville, the greatest of his errors proved eventually the efficient cause of the greatest discovery of the moderns. Beside the peculiar merit of Ptolemy, which was perceived and acknowledged as soon as his work appeared, he possesses another excellence, which, as far as we know, was first pointed out and dwelt upon by Dr. Vincent. According to him, Ptolemy, in his description of India, serves as the point of connection between the Macedonian orthography and the Sanscrit, dispersing light on both sides, and showing himself like a luminary in the centre. He seems indeed to have obtained the native appellations of the places in India, in a wonderful manner; and thus, by recording names which cannot be mistaken, he affords the means of ascertaining the country, even though he gives no particulars regarding it. We have applied this remark to India exclusively, but it might be extended to almost all the names of places that occur in Ptolemy, though, as respects India, his obtaining the native appellations is more striking and useful.