that it was a general treatise on the subject, like the comprehensive work of Strabo, but in reality it treats almost exclusively of Mathematical, or what may be called Cosmical, Geography. Ptolemy's object in composing it was not like that of the ordinary Geographer to describe places, but to correct and reform the map of the world in accordance with the increased knowledge which had been acquired of distant countries and with the improved state of science. He therefore limits his argument to an exposition of the geometrical principles on which Geography should be based, and to a determination of the position of places on the surface of the earth by their latitudes and longitudes. What he considered to be the proper method of determining geographical positions he states very clearly in the following passage: "The proper course," he says, "in drawing up a map of the world is to lay down as the basis of it those points that were determined by the most correct (astronomical) observations, and to fit into it those derived from other sources, so that their positions may suit as well as possible with the principal points thus laid down in the first instance."[1]
Unfortunately, as Bimbury remarks, it was impossible for him to carry out in practice—even approximately—the scheme that he had so well laid down in theory. The astronomical observations to which he could refer were but few—and they were withal either so defective or so inaccurate that he could not use them with con-
- ↑ Book I. cap. 4. The translation is Bunbury's.
