24-2 THE POPULAR SCIENCE MONTHLY. 



thenes having been determined by itineraries, and the latitude of Thule 

 being known from Pytheas, as the same number of degrees from the 

 pole that the tropics were from the equator, this distance was determined. 

 The most important of these parallels was that of Rhodes, since upon 

 this he measured the entire length of the world. He reckoned his 

 measurements of longitude from Cape Sacrum in Iberia (now Cape St. 

 Vincent), this being considered on a parallel with the Straits of Gades 

 (Gibraltar), the Straits of Sicily, Rhodes, the Gulf of Issus (eastern 

 extremity of the Mediterranean), the Caspian Gates (mountain passes 

 south of the Caspian Sea), andThinse on the Eastern Ocean. Not hav- 

 ing here any astronomical data, his longitudes are less correct than his 

 latitudes. The principal points established are Carthage, the Straits of 

 Sicily, and Rome, which he erroneously places on the same meridian, 

 Alexandria and Rhodes, which he also places on the same meridian, 

 Issus, the Caspian Gates, the source of the Indus, and the mouth of 

 the Ganges. Though using a plane chart, he yet recognized the fact 

 that a degree of longitude on the parallel of Rhodes had not the same 

 value as at the equator, but was as 555 to 700, which is very nearly 

 correct. Dividing now the distances from Cape Sacrum, which he 

 gives us only in stadia, by 555, we find for Carthage a longitude of 

 21° 15' 40", which is only two degrees in excess of its true longitude ; 

 for Alexandria we have 45° 35' 8", which is an excess of between six 

 and seven degrees ; for Issus we have 54° 35' 40", making the Mediter- 

 ranean too long by between nine and ten degrees ; for the Indus the 

 longitude of 100° 10' 48" is between twenty-three and twenty-four 

 degrees too great ; while for the Ganges 126° 7' 34" is an excess of be- 

 tween forty-five and forty-six degrees. These excesses, it will be seen, 

 increase uniformly toward the east, as they would by using too short a 

 measure for the degree ; and since Eratosthenes expressly states that the 

 degree at Rhodes is only four fifths of that at the equator, it has been 

 conjectured that he has used stadia of different values. An argument in 

 favor of this is that, if we use a stadium of such value that there would 

 be 700 to a degree (as at the equator), the length of the Mediterra- 

 nean would be very nearly correct, nearer indeed than upon any subse- 

 quent map down to the eighteenth century a. d., while the mouth of 

 the Indus would be within three degrees of its true longitude. Know- 

 ing Eratosthenes's coi-rectness upon other points, one can hardly resist 

 the conviction that he did use stadia of different lengths, and that 

 Strabo and Pliny have failed to quote his statement and explanation 

 of the fact. "VYe are further confirmed in this opinion when we con- 

 sider that his age believed the inhabitable world to be very nearly 

 twice as long as it was broad, and that this estimate makes its length 

 to its breadth as 106 to 54. 



Nevertheless, we have given here a representation of his map, in 

 which 555 stadia, of the same length with the stadia of latitude, are 

 allowed to each degree of the parallel of Rhodes. 



