488 THE POPULAR SCIENCE MONTHLY. 



men's tales. Having thus disposed of the anterior belief, he proceeds 

 to give his own idea of the earth, which he says no true Christian can 

 doubt. It was, that the earth was an oblong plain, inclosed at its 

 four extremities by huge walls of immense thickness, on which the 

 firmament or vault of the heavens rested ; and that near the north 

 pole there was a high mountain, around which the sun, the moon, and 

 the stars turned, the intervention of which mountain, at certain pe- 

 riods, caused eclipses.* 



We have now approached a period when Europe sank into the 

 deepest ignorance, communication between places was broken up 

 through the long continuance of wars ; roads were destroyed, there 

 was little or no commerce, for traveling was difiicult and dangerous, 

 and people in close proximity knew comparatively nothing of each 

 other. Fortunately, however, this was not the state of things through- 

 out the world. During the period that marks the rise, the maturity, 

 and decline of the empire of the Ai-abs, or from the ninth to the thir- 

 teenth century, geography was assiduously cultivated by them as a 

 science, especially in Bagdad, the capital of the Caliphs, and for a part 

 of that period in Sj)ain. It is to the Arabians that we owe the preser- 

 vation of the work of Ptolemy, which they translated into Arabic and 

 annotated. They determined the obliquity of the ecliptic, measured 

 two arcs of the meridian, ascertained more accurately the longitude of 

 places in Asia and about the Mediterranean, and enlarged descriptive 

 geography by an account of the countries in Asia over which they had 

 extended their conquests. As early as the ninth century they trafficked 

 in the ports of the Indian Ocean, and had intercourse also at that 

 time with China, through which probably the mariner's compass was 

 brought to the Mediterranean. I may also mention in this connection 

 that the Chinese, according to the statements of their own writers, had 

 maps from a very remote period. These are described as representing 

 the moimtains, seas, rivers, lakes, plains, and basins, and were com- 

 piled by order of the emperors. 



The Arabian geographers prepared an elaborate work (a. d. 830) 

 founded upon Ptolemy. It is lost, but, from the references to it by 

 Arab writers, we know that it gave a description of the habitable 

 earth, and indicated the prominent places in different countries by 

 their latitude and longitude, correcting, in the countries in which the 

 Arabs were well acquainted, the gross errors in longitude of Ptolemy. 

 It is from these tables of latitudes and longitudes that we know the 

 wide extent of the geographical knowledge of the Arabs. Their cor- 

 rections from west to east extended from Cadiz to the Indus, and they 

 restored to their true position the places in the countries watered by 

 the Euphrates and the Tigris. It is inferable, from statements of Arab 

 writers, that they had maps constructed upon a mathematical basis. 



* See "Popular Science Monthly," vol. x., March, 1877, article "How the Earth was 

 regarded in Old Times." 



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