Page:Dictionary of Greek and Roman Biography and Mythology (1870) - Volume 3.djvu/589

Rh PTOLEMAEUS. would place hira in agreement, or what he took for agreement, with the authority whom in his own mind he could not disbelieve. (Ilalraa and De- lambre, opp. citt. ; Weidler, Hist. Astron. ; La- a.ndiQ,Bibliogr.Astron.; Hoffman, Z(?*jc. lilhlioyr. ; the editions named, except when otherwise stated ; Fabric. Bibl. Graec., &c.) [A. De M.] THE GEOGRAPHICAL SYSTEM OF PTOLEMY. The rewypo^t/CTj "f^rrfynffis of Ptolemy, in eight books, may be regarded as an exhibition of the final state of geographical knowledge among the ancients, in so far as geograpliy is the science of determining the positions of places on the earth's surface ; for of the other branch of the science, the description of the objects of interest connected with different countries and places, in which the work of Strabo is so rich, that of Ptolemy contains com- paratively nothing. With the exception of the introductory matter in the first book, and the latter part of the work, it is a mere catalogue of the names of places, with their longitudes and lati- tudes, and with a few incidental references to ob- jects of interest. It is clear that Ptolemy made a diligent use of all the information that he had access to ; and the materials thus collected he arranged according to the principles of mathemati- cal geography. His work was the last attempt made by the ancients to form a complete geogra- phical system ; it was accepted as the text-book of the science ; and it maintained that position during the middle ages, and until the fifteenth century, when the rapid progress of maritime dis- covery caused it to be superseded. The treatise of Ptolemy was based on an earlier work by Marinus of Tyre, of which we derive almost our whole knowledge from Ptolemy him- self (i. 6, &c.). He tells us that Marinus was a diligent inquirer, and well acquainted with all the facts of the science, which had been collected be- fore his time ; but that his system required cor- rection, both as to the method of delineating the sphere on a plane surface, and as to the compu- tation of distances: he also informs us that the data followed by Marinus had been, in many cases, superseded by the more accurate accounts of recent travellers. It is, in fact, as the corrector of those points in the work of Marinus which were erro- neous or defective, that Ptolemy introduces him- self to his readers ; and his discussion of the necessary corrections occupies fifteen chapters of his first book (cc. 6 — 20). The most important of the errors which he ascribes to Marinus, is that he assigned to the known part of the world too small a length from east to west, and too small a breadth from north to south. He himself has fallen into the opposite error. Before giving an account of the system of Pto- lemy, it is necessary to notice the theory of Breh- mer, in his Enldeckungen im Alterthum, that the work of Marinas of Tyie was based upon ancient charts and other records of the geographical re- searches of the Phoenicians. This theory finds now but few defenders. It rests almost entirely on the presumption that the widely extended com- merce of the Phoenicians would give birth to various geographical documents, to which Marinus, living at Tyre, would have access. But against this may be set the still stronger presumption, that a scientific Greek writer, whether at Tyre or else- VOL. ni. PTOLEMAEUS. 577 where, would avail himself of the rich materials collected by Greek investigators, especially from the time of Alexander ; and this presumption iti converted into a certainty by the information which Ptolemy gives us respecting the Greek itineraries and peripluses which Marinus had used as autho- rities. The whole question is thoroughly discussed by Heeren, in his Comme?italio de Fontibus Geo- graphicorum Ptolemaei, Tubularumque Us annex- arum. Getting. 1827, which is appended to the English translation of his Ideen {Asiatic Nations, vol. iii. Append. C). He shows that Brehmer has greatly overrated the geographical knowledge of the Phoenicians, and that his hypothesis is alto- gether groundless. In examining the geographical system of Pto- lemy, it is convenient to speak separately of its mathematical and historical portions ; that is, of his notions respecting the figure of the earth, and the mode of determining positions on its surface, and his knowledge, derived from positive information, of the form and extent of the different countries, and the actual positions and distances of the various places in the then known world. 1. T/ie Mathematical Geograpliy of Ptolemy. — Firstly, as to the figure of the earth. Ptolemy assumes, what in his mathematical works he under- takes to prove, that the earth is neither a plane surface, nor fan-shaped, nor quadrangular, nor pyramidal, but spherical. It does not belong to the present subject to follow him through the de- tail of his proofs. The mode of laying down positions on the sur- face of this sphere, by imagining great circles pass- ing through the poles, and called meridians, because it is mid-day at the same time to all places through which each of them passes ; and other circles, one of which was the great circle equidistant from the poles (the equinoctial line or the equator), and the other small circles parallel to that one ; and the method of fixing the positions of these several circles, by dividing each great circle of the sphere into 360 equal parts (now called degrees., but by the Greeks " parts of a great circle"), and imagining a meridian to be drawn through each division of the equator, and a parallel through each division of any meridian ; — all this had been settled from the time of Eratosthenes. What we owe to Ptolemy or to Marinus (for it cannot be said with certainty to which) is the introduction of the terms longitude (fjLrJKos) and latitude (irXaros), the former to de- scribe the position of any place with reference to the length of the known world, that is, its distance, in degrees, from a fixed meridian, measured along its own parallel ; and the latter to describe the position of a place with reference to the breadth of the known world, that is, its distance, in degrees, from the equator, measured along its own meri- dian. Having introduced these terms, Marinus and Ptolemy designated the positions of the places they mentioned, by stating the numbers which represent the longitudes and latitudes of each. The subdivision of the degree adopted by Ptolemy is into twelfths. Connected with these fixed lines, is the subject of climates, by which the ancients understood belts of the earth's surface, divided by lines parallel to the equator, those lines being determined according to the different lengths of the day (the longest day was the sUmdard) at different places, or, which is the same thing, by the different lengths, at different