Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/105

Rh PTOLEMY 93 The great problem that had attracted the attention and exercised the ingenuity of all geographers from the time of Dicsearchus to that of Ptolemy was to determine the length and breadth of the Inhabited World, which they justly regarded as the chief subject of the geographer's consideration. This question had been very fully discussed by Marinus, who had arrived at conclusions widely dif- ferent from those of his predecessors. Towards the north indeed there was no great difference of opinion, the latitude of Thule being generally recognized as that of the highest northern land, and this was placed both by Marinus and Ptolemy in 63 lat, not very far beyond the true position of the Shetland Islands, which had come in their time to be generally identified with the mysterious Thule of Pytheas. The western extremity, as already mentioned, had been in like manner determined by the prime meridian drawn through the supposed position of the Fortunate Islands. But towards the south and east Marinus gave an enormous extension to the con- tinents of Africa and Asia, beyond what had been known to or suspected by the earlier geographers, and, though Ptolemy greatly reduced his calculations, he still retained a very exaggerated esti- mate of their results. The additions thus made to the estimated dimensions of the known world were indeed in both directions based upon a real exten- sion of knowledge, derived from recent information ; but unfortu- nately the original statements were so perverted by misinterpretation in applying them to the construction of a map as to give results differing widely from the truth. The southern limit of the world as known to Eratosthenes, and even to Strabo (who had in this respect no further knowledge than his predecessor more than two centuries before), had been fixed by them at the parallel which passed through the eastern extremity of Africa (Cape Guardafui), or the Land of Cinnamon as they termed it, and that of the Sembritse (corresponding to Sennaar) in the interior of the same continent. This parallel, which would correspond nearly to that of 10 of true latitude, they supposed to be situated at a distance of 3400 stadia (340 geographical miles) from that of Meroe (the position of which was accurately known), and 13,400 to the south of Alexandria ; while they conceived it as passing, when prolonged to the eastward, through the island of Taprobane (Ceylon), which was universally recognized as the southernmost land of Asia. Both these geo- graphers were wholly ignorant of the vast extension of Africa to the south of this line and even of the equator, and conceived it as trending away to the west from the Land of Cinnamon and then to the north-west to the Straits of Gibraltar. Marinus had, how- ever, learned from itineraries both by land and sea the fact of this great extension, of which he had indeed conceived so exaggerated an idea that even after Ptolemy had reduced it by more than a half it was still materially in excess of the truth. The eastern coast of Africa was indeed tolerably well known, being frequented by Greek and Roman traders, as far as a place called Rhapta, opposite to Zanzibar, and this is placed by Ptolemy not far from its true posi- tion in 7 S. lat. But he added to this a bay of great extent as far as a promontory called Prasum (perhaps Cape Delgado), which he placed in 15^ S. lat. At the same time he assumed the position in about the same parallel of a region called Agisymba, which was supposed to have been discovered by a Roman general, whose itinerary was employed by Marinus. Taking, therefore, this parallel as the limit of knowledge to the south, while he retained that of Thule to the north, he assigned to the inhabited world a breadth of nearly 80, instead of less than 60, which it had occupied on the maps of Eratosthenes and Strabo. It had been a fixed belief with all the Greek geographers from the earliest attempts at scientific geography not only that the length of the Inhabited World greatly exceeded its breadth, but that it was more than twice as great, a wholly unfounded assump- tion, but to which their successors seem to have felt themselves bound to conform. Thus Marinus, while giving an undue extension to Africa towards the south, fell into a similar error, but to a far greater degree, in regard to the extension of Asia towards the east. Here also he really possessed a great advance in knowledge over all his predecessors, the increased trade with China for silk having led to an acquaintance, though of course of a very vague and general kind, with the vast regions in Central Asia that lay to the east of the Pamir range, which had formed the limit of the Asiatic nations previously known to the Greeks. But Marinus had learned that traders proceeding eastward from the Stone Tower a station at the foot of this range to Sera, the capital city of the Seres, occupied seven months on the journey, and from thence he arrived at the enormous result that the distance between the two points was not less than 36,200 stadia, or 3620 geographical miles. Ptolemy, while he justly points out the absurdity of this conclusion and the errone- ous mode of computation on which it was founded, had no means of correcting it by any real authority, and hence reduced it summarily by one half. The effect of this was to place Sera, the easternmost point on his map of Asia, at a distance of 45^ from the Stone Tower, which again he fixed, on the authority of itineraries cited by Marinus, at 24,000 stadia or 60 of longitude from the Euphrates, reckoning in both cases a degree of longitude as equivalent to 400 stadia, in accordance with his uniform system of allowing 500 stadia to 1 of latitude. Both distances were greatly in excess of the truth, independently of the error arising from this mistaken system of graduation. The distances west of the Euphrates were of course comparatively well known, nor did Ptolemy's calculation of the length of the Mediterranean differ very materially from those of previous Greek geographers, though still greatly exceeding the truth, after allowing for the permanent error of graduation. The effect of this last cause, it must be remembered, would unfortunately be cumulative, in consequence of the longitudes being computed from a fixed point in the west, instead of being reckoned east and west from Alexandria, which was undoubtedly the mode in which they were really calculated. The result of these combined causes of error was to lead him to assign no less than 180, or 12 hours, of longitude to the interval between the meridian of the Fortunate Islands and that of Sera, which really amounts to about 130. But in thus estimating the length and breadth of the known world Ptolemy attached a very different sense to these terms from that which they had generally borne with preceding writers. All former Greek geographers, with the single exception of Hipparchus, had agreed in supposing the Inhabited World to be surrounded on all sides by sea, and to form in fact a vast island in the midst of a circumfluous ocean. This notion, which was probably derived originally from the Homeric fiction of an ocean stream, and was certainly not based upon direct observation, was nevertheless of course in accordance with the truth, great as was the misconception it involved of the extent and magnitude of the continents included within this assumed boundary. Hence it was unfortunate that Ptolemy should in this respect have gone back to the views of Hipparchus, and have assumed that the land extended indefinitely to the north in the case of Europe and Scythia, to the east in that of Asia, and to the south in that of Africa. His boundary-line was in each of these cases an arbitrary limit, beyond which lay the Unknown Land, as he calls it. But in the last case he was not content with giving to Africa an indefinite extension to the south : he assumed the existence of a vast prolongation of the land to the east from its southernmost known point, so as to form a connexion with the south-eastern extremity of Asia, of the extent and position of which he had a wholly erroneous idea. In this last case Marinus had derived from the voyages of recent navigators in the Indian Seas a knowledge of the fact that there lay in that direction extensive lands which had been totally un- known to previous geographers, and Ptolemy had acquired still more extensive information in this quarter. But unfortunately he had formed a totally false conception of the bearings of the coasts thus made known, and consequently of the position of the lands to which they belonged, and, instead of carrying the line of coast northwards from the Golden Chersonese (the Malay Peninsula) to China or the land of the Sinse, he brought it down again towards the south after forming a great bay, so that he placed Cattigara the principal emporium in this part of Asia, and the farthest point known to him on a supposed line of coast, of unknown extent, but with a direction from north to south. The hypothesis that this land was continuous with the most southern part of Africa, so that the two enclosed one vast gulf, though a mere assumption, is stated by him as definitely as if it was based upon positive in- formation ; and it was long received by mediaeval geographers as an unquestioned fact. This circumstance undoubtedly contributed to perpetuate the error of supposing that Africa could not be cir- cumnavigated, in opposition to the more correct views of Strabo and other earlier geographers. On the other hand, there can be no doubt that the undue extension of Asia towards the east, so as to diminish by 50 of longitude the interval between that continent and the western coasts of Europe, had a material influence in foster- ing the belief of Columbus and others that it was possible to reach the Land of Spices (as the East Indian islands were then called) by direct navigation towards the west. It is not surprising that Ptolemy should have fallen into con- siderable errors respecting the more distant quarters of the world ; but even in regard to the Mediterranean and its dependencies, as well as the regions that surrounded them, with which he was in a certain sense well acquainted, the imperfection of his geographical knowledge is strikingly apparent. Here he had indeed some well-established data for his guidance, as far as latitudes were con- cerned. That of Massilia had been determined many years before by Pytheas within a few miles of its true position, and the latitude of Rome, as might be expected, was known with approximate accuracy. Those of Alexandria and Rhodes also were well known, having been the place of observation of distinguished astronomers, and the fortunate accident that the Island of Rhodes lay on the same parallel of latitude with the Straits of Gibraltar at the other end of the sea enabled him to connect the two by drawing the parallel direct from the one to the other. The importance attached to this line (36 N. lat.) by all preceding geographers has been already mentioned. Unfortunately Ptolemy, like his predecessors, supposed its course to lie almost uniformly through the open sea, wholly ignoring the great projection of the African coast towards