THE BEGINXINGS OF GEOGRAPHICAL SCIENCE. 241 



to transform — geographical science. He carried out both Hipparchus's 

 plan of determining latitude and longitude by astronomical observa- 

 tions, and that of representing the earth by the modern method of pro- 

 jection — with the " curved meridians and parallels " which Strabo had 

 despised. We can see from the errors which he makes that he did not 

 fully understand Hipparchus's ideas, but he did measurably; and he 

 had the energy to stamp his knowledge upon the world, and thereby 

 became the master of geography. 



To examine now the work of the two greatest geographers of an- 

 tiquity, Eratosthenes the father, and Ptolemy the master. 



We have seen Eratosthenes in the library of Alexandria, surround, 

 ed by every existing appliance of learning. Besides the data to which 

 we have referred, he had before him what Hipparchus calls the " An- 

 cient Map," possibly that of Anaximander, which Hipparchus prefers 

 in some respects to the map of Eratosthenes. But, with all these appli- 

 ances, he had not the one great essential to their accurate combination 

 into a system of the world, viz., the length of the earth's circumfer- 

 ence. He had, however, made certain astronomical observations that 

 were to help him. By observing the difference of the shadows at the 

 summer and winter solstices, he had calculated the angle of the eclip- 

 tic. He had also learned that the city of Syene, in Upper Egypt, was 

 directly under the northern tropic, since there, at the summer solstice, 

 the rays of the sun illumined the bottom of a deep well. Ascertain- 

 ing by the gnomon, or by the armillary spheres, which he invented, 

 the latitude north of the tropic of Alexandria, which he considered to 

 be on the same meridian with Syene, he found the arc between Syene 

 and Alexandria to be one fiftieth part of the earth's circle. Learning 

 then from the itineraries that the distance between the cities was 5,000 

 stadia, he multiplied this by fifty and had his circumference, 250,000 

 stadia ; or, as he divided the circle into 300°, each of 700 stadia, he 

 called the circumference 252,000 stadia. Not knowing the precise 

 length of the stadium, we can not tell how exact this measurement was ; 

 but to have measui-ed the earth at all was surely a brilliant beginning 

 of Eratosthenes's geographical work. His method, it may be said, is 

 the same that is followed to-day in measuring the earth. Having, then, 

 a basis upon which he can convert degrees into stadia and stadia into 

 degrees, he proceeds to construct his map. He makes no recognition 

 of the lines so prominent in all our maps of the world, the equator and 

 the tropic, and polar circles ; but simply establishes a few parallels at 

 irregular distances, viz., of the limits of the inhabitable eai-th — Meroe, 

 Syene, Alexandria, Rhodes, the Hellespont, Byzantium, the mouth of 

 the Borysthenes, and Thule. Some of the distances between these 

 parallels were determined by itinerary measurements, some by astro- 

 nomical observations. For example, the distance from Alexandria to 

 Rhodes was determined by estimating the arc between the cities at the 

 rate of 700 stadia to the degree. Again, the latitude of the Borys- 



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