Page:Ancient India as described by Ptolemy - John Watson McCrindle.djvu/6

 PREFACE. Ptolemy's *^ Treatise on Greography," likeliis famous work on astronomy to which it formed the seqael, was destined to govern the world's opinion on the subject of which it treated, from, the time of its publication until the dawn of the modern era, a period of about 1,300 years^ This treatise must have been composed in the interests of chartography rather than of geo» graphy, for the author's aim is not so much to describe the earth's surface as to lay down the principles on which maps should be con- structed, and to determine the latitude and longitude of places with a view to their being mapped in their proper positions. The principles he here laid down have proved of permanent validity, and are still practically applied in the art of map-construction, but his determinations of the position of places, owing to the paucity and imperfection of the astro- nomical observations on which, in combination with the existing measurements of terrestrial distances his conclusions were based, are all, with very few exceptions, incorrect. The work lost, of course, much of its old authority as soon as the discoveries of modern times had brought its grave and manifold errors to light. It did