His great work, as it has reached us, consists almost
entirely of an elementary picture of the earth, (if it may be so called,)
in which its figure and size, and the position of places are determined.
There is only a short notice of the division of countries, and it is very
seldom that any historical notice is added. To this outline, it is supposed
that Ptolemy had added a detailed account of the countries then known,
which is lost.
His geography, such as we have described it, consists of eight books, and
is certainly much more scientific than any which had been previously
written on this science. In it there appears, for the first time, an
application of geometrical principles to the construction of maps: the
different projections of the sphere, and a distribution of the several
places on the earth, according to their latitude and longitude. Geography
was thus established on its proper principles, and intimately connected
with astronomical observations and mathematical science. The utility and
merit of Ptolemy's work seems to have been understood and acknowledged soon
after it appeared. Agathemidorus, who lived not long after him, praises him
for having reduced geography to a regular system; and adds, that he treats
of every thing relating to it, not carelessly, or merely according to the
ideas of his own, but to what had been delivered by more ancient authors,
adopting from them whatever he found consonant to truth.
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