246 THE POPULAR SCIENCE MONTHLY. 



the degree. With this distance, and with his own observed arc, he 

 made such a computation of the earth's circumference as gave him 500 

 stadia to the degree. But the absurdity of thus employing the 700- 

 stadium degree as an element in the computation, by which he obtained 

 the 500-stadium degree, did not prevent even Ptolemy from adopting 

 the latter estimate. A degree of 500 stadia at the equator gave him 

 one of 400 stadia on the parallel of Rhodes. On this basis, reckoning 

 from the Fortunate Isles (Ferro 18° 9' 45" west), he obtained the fol- 

 lowing longitude : Carthage 32° 20', Rhodes 56°, Issus 66° 30', Indus 

 122° 30', Ganges 146°, Thinae (conjectured to be Tenasserim, in farther 

 India) 177° 30' — errors respectively of about four, ten, twelve, thirty, 

 forty, and sixty-one degrees. These large errors he had no means of 

 recognizing, but when he came to his latitudes he did have a correc- 

 tive. Accepting, as he was disposed to do, Eratosthenes's distances, 

 all his own latitudes became too high. Pytheas's Thule, instead of 

 being at the arctic circle, would have been beyond the north pole. He 

 therefore did what is so often done, allowed one error to force him 

 into another, viz., the use of a degree of one length (500 stadia) for his 

 longitudes, and of another length (700 stadia) for his latitudes. Like 

 those of Eratosthenes, therefore, his latitudes are tolerably correct. 

 A few features of this map should be noticed in comparison with for- 

 mer maps. Thule, which was unnoticed by Strabo, reappears, though 

 it is not the Thule of Pytheas, but an island much nearer to Britain. 

 The Sicilian Straits are no longer on a parallel with the Columns of 

 Hercules, nor the straits and Rome on the same meridian. Alexan- 

 dria and Rhodes are on different meridians, as also the Hellespont and 

 Byzantium. The Caspian becomes again an inland sea. In the East, 

 the great peninsula of the Deccan disappears, the island of Taprobane 

 occupying its place. The Indian Ocean is an inland sea, Africa being 

 connected by unknown lands with the lands of the far East. 



In our map we have followed Gosselin's opinion that the Golden 

 Chersonese was the region about the mouths of the Irrawaddy River, 

 not the Malay Peninsula. But the most important of the minor fea- 

 tures of the map, with which we must close our sketch, is its repre- 

 sentation of the sources of the Nile. 



Nili caput qucarere was a work projDosed to itself by the ancient 

 as seriously as by the modern world. In the days of Herodotus the 

 source of the river was considered a question of antiquity. The an- 

 cient dynasties, the Persian conquerors, and later the Greeks and the 

 Romans, all made more or less of effort to solve the problem. We 

 have seen how Herodotus answered the question. In the days of Era- 

 tosthenes, opinions were far more correct. Speaking of the Astaboras 

 (Atbara), and the Astapus or the Astasobas (Blue Nile), he says, 

 " Certain authors pretend that this last name applies to another river, 

 which flovjs from lakes situated to the south, and forming the principal 

 affluent of the Nile." This is the first definite reference to the south- 



