Popular Science Monthly/Volume 16/December 1879/The Beginnings of Geographical Science
| THE BEGINNINGS OF GEOGRAPHICAL SCIENCE. |
By GEORGE A. JACKSON.
NO other science has to-day so distinguished a patronage as that of geography. In September, 1877, there convened at Brussels, in a palace of the King of the Belgians, and at his invitation, a Congress made up of the presidents of the leading geographical societies, and the most distinguished geographical writers, and explorers, and patrons of explorations, in the world. At that Congress was formed an association, under the presidency of King Leopold II., which has for its object the exploring, and opening up to science and civilization, of the whole unknown territory of Central Africa. Branches of this organization are formed in nearly all the nations of Europe, and are, as a rule, under the direction of the royal houses. Mr. Stanley also, in his "Dark Continent," makes hearty acknowledgment of encouragements and rewards received at royal hands. And as in these last days, so in the first days of its history, royal patronage did much to promote geographical science. The very earliest knowledge of geography was doubtless gained in a blind way, as men went to neighboring countries in the pursuit of trade; but Herodotus tells us that so far back as 640 b. c. a voyage for geographical discovery was undertaken, under the patronage of a king, Pharaoh Necho of Egypt. This monarch engaged a company of Tyrians to circumnavigate Africa. Setting out by the Red Sea, these voyagers sailed southward until autumn, when they landed and sowed corn, and waited for it to ripen. Reaping their crop, they set sail again, and in this manner, having consumed two years, in the third year they turned the pillars of Hercules and came back to Egypt. They asserted, said Herodotus, that which he could not believe, though others might, that, in sailing around Libya, they had the sun on the right hand. The arguments for and against the actuality of this voyage need not here be given. Suffice it that it was not an impossible achievement for mariners of that age; and that Eratosthenes, one of the earliest geographers, represented Libya as circumnavigable.
Accustomed as we are to-day to think of all science as of modern development, most men are content to have read a summary of the "Erdkunde," to have followed Humboldt in his principal researches, and to have formed some acquaintance with Buffon, and Zimmermann, and Blumenbach. If, besides, they know something of Malte-Brun, they think they have compassed the history of the science. A hundred years ago there was no such feeling. The vast advances of this century had not been made. Scholars were not far enough removed from the Renaissance to have lost all reverence for the ancients; and, although they no longer turned to Ptolemy for information, they had a lingering affection for the work which had been the geographical authority down to two hundred years before their day. Elaborate works were written in exposition of the ancient systems, with a patience that would hardly be exercised to-day. The father of such study was D'Anville; but perhaps no single work upon the subject is of more value to us than that of M. Gosselin.[1] In our sketch we have made large use of this work.
Tradition takes us back to days when men thought of the earth as a flat disk, covered with the arching vault of the skies, whose edges rested upon far-off giant pillars; and even to the time when they believed that the earth rested upon elephants, who stood on the back of a tortoise, who in turn were encompassed in the folds of a serpent; but those were not the days of science. The first among the Greeks to teach the doctrine of the sphericity of the earth was Thales (b. c. 640). He held that the equator was cut obliquely by the ecliptic, and he divided the earth into five zones. His successor was Anaximander, who also taught that the earth was a sphere (Diogenes Laertius), though some said (Plutarch) that he called it a column. The latter statement could hardly be true, as he was sufficiently scientific to erect at Lacedæmon a gnomon for observing the solstices and equinoxes, He is even said to have been the inventor of this instrument—which was a simple column, the length of whose shadow determined the position of the sun—though more probably Thales had brought the knowledge of it from Egypt. To Anaximander is also assigned the honor of having made the first geographical chart known among the Greeks. He is even claimed to have made an artificial globe representing the earth, with divisions of land and water. He was not, however, the inventor of maps, since among the Egyptians Sesostris, long before his day, is said to have caused maps to be made. Passing over Anaximenes and Anaxagoras, the next name worthy of mention is that of Pythagoras (b. c. 570), who, like Thales, had traveled in Egypt, where he is said to have learned the obliquity of the ecliptic. But the great thing for which Pythagoras is remembered by scientists was his doctrine that the earth revolved about the sun—a truth, however, which he taught only esoterically, his open doctrine being the common one that the sun revolved about the earth. Herodotus (b. c. 484), notwithstanding his extensive travels, contributed nothing to mathematical geography, and had very incorrect ideas as to the several divisions of the world. "Europe," he said, "was as long as Asia and Africa together. The river Nile, before entering Egypt, flowed eastward from near the west coast of Africa." This opinion he formed partly from the account which he said had been given by certain youths who were taken prisoners and carried into the interior of Africa, to a city on the bank of a great river flowing eastward, in which were crocodiles. Another reason he had was that to the north of the Mediterranean Sea a great river, the Ister (Danube) was known to flow from the extreme west to the east of Europe; and so, "inferring the unknown from the known," he concluded that the Nile must flow through Africa in a similar way.
Of more value to science were the observations of Pytheas (about 320 b. c.), a Greek seaman of Massilia (Marseilles), who sailed far northward from the coasts of Britain, where he said the longest day was nineteen hours long, to what he called Thule (probably Iceland), where he said "the summer tropic served for the arctic circle." Notwithstanding certain wild statements of Pytheas, such as that at this place there was found neither earth, air, nor sea, but a mingling of them all; and that the days and nights there were six months in length, we can not help believing that he did reach the arctic circle, and observe the phenomenon of the sun remaining above, the horizon throughout the twenty-four hours. To Pytheas also is due the first suggestion of a computation of latitude. He recorded that the length of the gnomon at Marseilles, the day of the summer solstice, was to the length of the shadow as 120 to 41·8, which, reckoning the tropic at 23° 51' 15", where it was placed by Eratosthenes, would give a latitude of 43° 3' 35". If allowance be made for the penumbra, this reckoning will be found very nearly correct. Other names to be noticed are Eudemus, the first Greek to give the angle of the ecliptic—as subtended by the side of a pentadecagon, or equal to 24°—and Eudoxus, who wrote a work on the "Period or Circumference of the Earth."
This brings us down to the school of Alexandria. Alexander had founded near the Canopic mouth of the Nile a city which was destined long to perpetuate his name and glory. The glory was to come not so much from its commercial importance, though it rose to be the chief commercial city of the world, as from its intellectual supremacy. It was the ambition of the Ptolemies to make their capital the intellectual center of the world, and in this they were successful. The Attic and Ionian scholars gave place to the Alexandrian, not only in the department of letters, but also in the domain of science. One of the librarians of the great Alexandrian Library was Eratosthenes (b. c. 270), who may justly be called the Father of Geography. His work is in great part preserved to us in the pages of Strabo and Pliny. Having under his eye everything that had ever been written upon the subject, he first combined the whole into a complete system, which can to-day be restored. The map of the world which he prepared, if less perfect in some respects than Ptolemy's, was in other respects far more perfect; indeed, was the most correct which the world was to see down to the sixteenth century a. d. Besides other and doubtless very important data, of which we have no information, Eratosthenes must have had a record of an expedition undertaken in the fifth century b. c. by Hanno, under the direction of the Carthaginian Senate, in which he sailed down the west coast of Africa as far as to the Gulf of Benin; as well as an account of the observations made by the followers of Alexander during his march through Asia, and by his naval commander Nearchus, who conducted the fleet from the mouths of the Indus along the coast to the Euphrates.
After him came Hipparchus, who lived at Rhodes (b. c. 160-145). His great merit was in his use of astronomical observations to determine positions upon the earth, instead of depending upon itinerary distances from a few known points, as had been the method of Eratosthenes, But the age did not appreciate his work, and the science was not to realize the advance which was thus made possible; nearly three centuries must elapse before the fruit of his labors was to appear. Eratosthenes had been able to determine latitude by the heavenly bodies, but not longitude. Hipparchus showed how this also could be done, by observing the eclipses of the sun and moon. Again, he invented the method of projection in map-making, another most valuable contribution to the science which was to be despised until a coming age.
Posidonius is a name to be remembered for an error which he introduced into the science, so successfully that it remained for many centuries. What it was we shall see under Ptolemy.
Strabo (54 b. c.), notwithstanding his voluminous work on geography, which, indeed, is of great value as a compilation of the facts then known about the different countries of the world, was not, like Eratosthenes, Hipparchus, and Ptolemy, a scientific geographer. He neglected mathematical and astronomical data, and, instead of following Hipparchus's method of projection, of which he knew, he expressly says that he describes the world as if it were spread out as a vast plain. Indeed, there is some reason to think that Strabo did not even prepare a map to accompany his work. From his descriptions, however, a map may be made, as was done by both D'Anville and Gosselin, and we find that it does not differ greatly from that of Eratosthenes. Almost the only improvements are in a better outline of the coasts of Iberia and Gaul, in a' truer longitude for the Sicilian Straits, and in a correct distance from these straits to Rhodes. On the other hand, Strabo loses sight of Thule, says that Africa is not circumnavigable, and makes greater errors in latitude and longitude than his distinguished predecessor.
The leading Roman writers on geography were Pomponius Mela, who wrote a treatise in three books, and Pliny, who devoted a part of his great work on natural history to geography.
Marin of Tyre deserves a glance. Phœnicia was the great commercial nation of the earlier ages. Her mariners brought tin from Britain and spices from the far East. She certainly had opportunities to surpass all other nations in geographical work. But we should almost infer that, when Cadmus brought letters from Phœnicia to Greece, as we learned in boyhood, he left no letters there; for, with all her wealth and opportunities, Phœnicia did little for literature or science. Wholly absorbed by the commercial spirit, she forgot all else. It is the same to-day. Commerce alone has never opened any great field to science. Arab traders have known the region about the sources of the Nile for centuries, but science was never the gainer. Some disinterested spirit must enter in. Patrons of science must send out explorers, or missionary workers must give their lives to opening up the dark places of the earth. In the last days of Tyre, however, one scientific name does appear—that of Marin. He collected some valuable information in regard to the east coast of Africa, of which Ptolemy made use. He also attempted in a crude way to use the method of projection in map-making.
Lastly appears the great name of Ptolemy (middle of the second century). As the scholars of Alexandria had the honor of collecting and carefully editing all the great literary works of antiquity, preparatory to the centuries of darkness through which the world was to pass, so, under the hand of Ptolemy, was put into compact and durable form what had then been gained of geographical science. If he is the great man who makes grand use of his knowledge, then was Ptolemy greater than Hipparchus; for, what Hipparchus had thought out three centuries before him, Ptolemy now used to reëstablish—almost to transform—geographical science. He carried out both Hipparchus's plan of determining latitude and longitude by astronomical observations, and that of representing the earth by the modern method of projection—with the "curved meridians and parallels" which Strabo had despised. We can see from the errors which he makes that he did not fully understand Hipparchus's ideas, but he did measurably; and he had the energy to stamp his knowledge upon the world, and thereby became the master of geography.
To examine now the work of the two greatest geographers of antiquity, Eratosthenes the father, and Ptolemy the master.
We have seen Eratosthenes in the library of Alexandria, surrounded by every existing appliance of learning. Besides the data to which we have referred, he had before him what Hipparchus calls the "Ancient Map," possibly that of Anaximander, which Hipparchus prefers in some respects to the map of Eratosthenes. But, with all these appliances, he had not the one great essential to their accurate combination into a system of the world, viz., the length of the earth's circumference. He had, however, made certain astronomical observations that were to help him. By observing the difference of the shadows at the summer and winter solstices, he had calculated the angle of the ecliptic. He had also learned that the city of Syene, in Upper Egypt, was directly under the northern tropic, since there, at the summer solstice, the rays of the sun illumined the bottom of a deep well. Ascertaining by the gnomon, or by the armillary spheres, which he invented, the latitude north of the tropic of Alexandria, which he considered to be on the same meridian with Syene, he found the arc between Syene and Alexandria to be one fiftieth part of the earth's circle. Learning then from the itineraries that the distance between the cities was 5,000 stadia, he multiplied this by fifty and had his circumference, 250,000 stadia; or, as he divided the circle into 360°, each of 700 stadia, he called the circumference 252,000 stadia. Not knowing the precise length of the stadium, we can not tell how exact this measurement was; but to have measured the earth at all was surely a brilliant beginning of Eratosthenes's geographical work. His method, it may be said, is the same that is followed to-day in measuring the earth. Having, then, a basis upon which he can convert degrees into stadia and stadia into degrees, he proceeds to construct his map. He makes no recognition of the lines so prominent in all our maps of the world, the equator and the tropic, and polar circles; but simply establishes a few parallels at irregular distances, viz., of the limits of the inhabitable earth—Meroe, Syene, Alexandria, Rhodes, the Hellespont, Byzantium, the mouth of the Borysthenes, and Thule. Some of the distances between these parallels were determined by itinerary measurements, some by astronomical observations. For example, the distance from Alexandria to Rhodes was determined by estimating the arc between the cities at the rate of 700 stadia to the degree. Again, the latitude of the Borysthenes having been determined by itineraries, and the latitude of Thule being known from Pytheas, as the same number of degrees from the pole that the tropics were from the equator, this distance was determined. The most important of these parallels was that of Rhodes, since upon this he measured the entire length of the world. He reckoned his measurements of longitude from Cape Sacrum in Iberia (now Cape St. Vincent), this being considered on a parallel with the Straits of Gades (Gibraltar), the Straits of Sicily, Rhodes, the Gulf of Issus (eastern extremity of the Mediterranean), the Caspian Gates (mountain passes south of the Caspian Sea),and Thinæ on the Eastern Ocean. Not having here any astronomical data, his longitudes are less correct than his latitudes. The principal points established are Carthage, the Straits of Sicily, and Rome, which he erroneously places on the same meridian, Alexandria and Rhodes, which he also places on the same meridian, Issus, the Caspian Gates, the source of the Indus, and the mouth of the Ganges. Though using a plane chart, he yet recognized the fact that a degree of longitude on the parallel of Rhodes had not the same value as at the equator, but was as 555 to 700, which is very nearly correct. Dividing now the distances from Cape Sacrum, which he gives us only in stadia, by 555, we find for Carthage a longitude of 21° 15' 40", which is only two degrees in excess of its true longitude; for Alexandria we have 45° 35' 8", which is an excess of between six and seven degrees; for Issus we have 54° 35' 40", making the Mediterranean too long by between nine and ten degrees; for the Indus the longitude of 100° 10' 48" is between twenty-three and twenty-four degrees too great; while for the Ganges 126° 7' 34" is an excess of between forty-five and forty-six degrees. These excesses, it will be seen, increase uniformly toward the east, as they would by using too short a measure for the degree; and since Eratosthenes expressly states that the degree at Rhodes is only four fifths of that at the equator, it has been conjectured that he has used stadia of different values. An argument in favor of this is that, if we use a stadium of such value that there would be 700 to a degree (as at the equator), the length of the Mediterranean would be very nearly correct, nearer indeed than upon any subsequent map down to the eighteenth century a. d., while the mouth of the Indus would be within three degrees of its true longitude. Knowing Eratosthenes's correctness upon other points, one can hardly resist the conviction that he did use stadia of different lengths, and that Strabo and Pliny have failed to quote his statement and explanation of the fact. We are further confirmed in this opinion when we consider that his age believed the inhabitable world to be very nearly twice as long as it was broad, and that this estimate makes its length to its breadth as 106 to 54.
Nevertheless, we have given here a representation of his map, in which 555 stadia, of the same length with the stadia of latitude, are allowed to each degree of the parallel of Rhodes.
We call attention to only a few of its noticeable features. First of all, the accuracy of most of its latitudes is to be noted, some of them being more accurate than those given by Gosselin, less than a hundred
- Erratum—Parallel of Hellespont, marked Byzantium and vice versa.
years ago. Not only is the Mediterranean unduly elongated, but the placing of the Sicilian Straits and Carthage on the same meridian, and Alexandria and Rhodes on the same, necessitates much too great a distance between the straits and Rhodes. Since the length of the Macedonian coast was placed within its proper limits, no way remained to adjust the distances but to prolong the Thermaic Gulf to the westward, and make of Greece a long peninsula stretching from west to east. The Caspian Sea, owing to reports that had been brought by certain followers of Alexander, appears as an arm of the Northern Ocean. The most striking feature, however, is the representation of India as extending east instead of south, with the Ganges flowing into the Eastern Ocean. This would seem to have arisen in this way: The mouth of the Indus had been reported by Alexander's officers too far south. It was also well known that from the Indus to the island known as Taprobane (Ceylon) there was a long stretch of coast such as is given in the map. But, if this extended southward, it would carry India below what was considered to be the limit of the habitable world, seen in the map at latitude 11° 51' 26". So it was turned away to the eastward. The distance from the Indus to the mouth of the Ganges had been learned through the mission sent to India by Seleucus; and, since the latter river did not enter the sea on the southern coast, it must have an eastern embouchure. But as the traditional limit of the earth—a length twice its breadth—was now reached, it only remained to extend the coast-line to the northward to complete the map.
In accordance with the principles upon which his map was constructed, Eratosthenes said that India could be reached by sailing westward from Spain—a suggestion by which Columbus is said to have been influenced. Before leaving Eratosthenes it may be mentioned that Gosselin contends that this ancient geographer had been preceded by geographers far better informed and more skillful than himself, and that all the best features of his map are due to them. Indeed, he claims that there was a period long before Eratosthenes, when the geography of Europe was as well known as in his (Gosselin's) day, and he even intimates that projected maps, similar to our modern ones, had then been used. His arguments in support of this, however, will not bear scrutiny.
Ptolemy, we have said, prepared the science for the ages of darkness on which the world was soon to enter. In a sense, the first shadows of that darkness had already fallen. The science had gone backward perceptibly since the days of Eratosthenes. True, there was a larger fund of information in regard to the countries of the Roman Empire; but, as we see in Strabo, there was no scientific grasp of the world as a whole. Ptolemy was therefore almost as much of an exception to his age as Hipparchus had been to his. Still he had helps which none of his predecessors had had, such as the works of Strabo and Pliny, and Marin of Tyre, for statements of facts, and those of Eratosthenes, and, above all, Hipparchus for scientific statement. The work which he composed with these helps was to be the standard and
PTOLEMY’S MAP OF THE WORLD
only authority for more than thirteen centuries. Happily it has come down to us entire, though the different manuscript copies vary considerably among themselves. Through the generosity of the Emperor of Russia, facsimile copies have been made of the oldest extant Greek MS., written about the year 1200 a. d., and now at Mount Athos; and these copies are in the more important libraries of the world. The method of projection which Ptolemy used in his maps had been slow of practical realization. Hipparchus's work had not gained a circulation. Marin of Tyre had had but poor success in attempting it, so that Ptolemy's approach to success seems the more commendable. We present a map drawn upon his system. In it are to be noticed two great errors. We have spoken of Posidonius as the originator of an error. Dissatisfied with Eratosthenes's measurement of the earth, he had measured it anew. To do this he had observed by a star the arc between Alexandria and Rhodes, and had ascertained the distance as nearly as he could from the number of days' sail between the cities. But soon becoming dissatisfied in regard to the distance he had employed, he adopted Eratosthenes's distance, which the latter had obtained by computing the arc at 700 stadia to the degree. With this distance, and with his own observed arc, he made such a computation of the earth's circumference as gave him 500 stadia to the degree. But the absurdity of thus employing the 700-stadium degree as an element in the computation, by which he obtained the 500-stadium degree, did not prevent even Ptolemy from adopting the latter estimate. A degree of 500 stadia at the equator gave him one of 400 stadia on the parallel of Rhodes. On this basis, reckoning from the Fortunate Isles (Ferro 18° 9' 45" west), he obtained the following longitude: Carthage 32° 20', Rhodes 56°, Issus 66° 30', Indus 122° 30', Ganges 146°, Thinæ (conjectured to be Tenasserim, in farther India) 177° 30'—errors respectively of about four, ten, twelve, thirty, forty, and sixty-one degrees. These large errors he had no means of recognizing, but when he came to his latitudes he did have a corrective. Accepting, as he was disposed to do, Eratosthenes's distances, all his own latitudes became too high. Pytheas's Thule, instead of being at the arctic circle, would have been beyond the north pole. He therefore did what is so often done, allowed one error to force him into another, viz., the use of a degree of one length (500 stadia) for his longitudes, and of another length (700 stadia) for his latitudes. Like those of Eratosthenes, therefore, his latitudes are tolerably correct. A few features of this map should be noticed in comparison with former maps. Thule, which was unnoticed by Strabo, reappears, though it is not the Thule of Pytheas, but an island much nearer to Britain. The Sicilian Straits are no longer on a parallel with the Columns of Hercules, nor the straits and Rome on the same meridian. Alexandria and Rhodes are on different meridians, as also the Hellespont and Byzantium. The Caspian becomes again an inland sea. In the East, the great peninsula of the Deccan disappears, the island of Taprobane occupying its place. The Indian Ocean is an inland sea, Africa being connected by unknown lands with the lands of the far East.
In our map we have followed Gosselin's opinion that the Golden Chersonese was the region about the mouths of the Irrawaddy River, not the Malay Peninsula. But the most important of the minor features of the map, with which we must close our sketch, is its representation of the sources of the Nile.
Nili caput quærere was a work proposed to itself by the ancient as seriously as by the modern world. In the days of Herodotus the source of the river was considered a question of antiquity. The ancient dynasties, the Persian conquerors, and later the Greeks and the Romans, all made more or less of effort to solve the problem. We have seen how Herodotus answered the question. In the days of Eratosthenes, opinions were far more correct. Speaking of the Astaboras (Atbara), and the Astapus or the Astasobas (Blue Nile), he says, "Certain authors pretend that this last name applies to another river, which flows from lakes situated to the south, and forming the principal affluent of the Nile." This is the first definite reference to the southern lakes, and how a knowledge of them had then been gained we do not know. It seems certain that no one in ancient times had ascended the river to them. Expeditions were repeatedly sent out with this object, notably one by Nero, which ascended higher than any other, but was finally stopped by impenetrable marshes, apparently in about 9° north latitude. But in ancient as in modern times the problem was finally approached in a different way. Marin of Tyre had furnished Ptolemy with information in regard to the east coast of Africa. Traders had gone as far south as the promontory of Prasum (Cape Delgado), and doubtless information gained there in regard to Madagascar had given rise to the conjecture of lands inclosing the Indian Ocean. But in trading along the coast these men had heard of two lakes in the interior, which were called the sources of the Nile. Ptolemy would seem to have made particular inquiries about these lakes, for he says that a Greek trader had told him that they were farther inland than he had supposed. He accordingly placed them, as seen in our map, in latitudes 6° and 7° south, and longitudes 57° and 65° east, or on either side of the meridian of Alexandria. Information like this was worthy of the greatest geographer of antiquity, and which should not so long have been despised; for it was only when modern explorers, following ancient traditions, went in from the coast of Zanzibar, that they—not solved but resolved the ancient problem of the sources of the Nile.
- ↑ Géographie des Grecs Analysée; ou Les Systêmes d'Eratosthenes, de Strabon, et de Ptolémée comparée entre eux et avec nos Connoissances modernes. M, Gosselin, à Paris, MDCCLXXXX.