Читать книгу Terrestrial & Celestial Globes - Edward Luther Stevenson - Страница 6

Table of Contents

The beginnings of astronomical and of geographical science.—Primitive attempts at map construction, as seen in the Babylonian plan of the world.—Anaximander probably the first scientific cartographer.—Statements of Herodotus.—The place of Hecataeus, Hipparchus, Marinus, Ptolemy.—The Romans as map makers.—The earliest beliefs in a globular earth.—Thales, the Pythagoreans, Aristotle.—Eratosthenes and his measurements of the earth.—Crates probably the first to construct a terrestrial globe.—Statements of Strabo.—Ptolemy’s statements concerning globes and globe construction.—The allusions of Pliny.

THE beginnings of the science of astronomy and of the science of geography are traceable to a remote antiquity. The earliest records which have come down to us out of the cradleland of civilization contain evidence that a lively interest in celestial and terrestrial phenomena was not wanting even in the day of history’s dawning. The primitive cultural folk of the Orient, dwellers in its great plateau regions, its fertile valleys, and its desert stretches were wont, as we are told, to watch the stars rise nightly in the east, sweep across the great vaulted space above, and set in the west as if controlled in their apparent movement by living spirits. To them this exhibition was one marvelous and awe-inspiring. In the somewhat strange grouping of the stars they early fancied they could see the forms of many of the objects about them, of many of their gods and heroes, and we find their successors outlining these forms in picture in their representations of the heavens on the material spheres which they constructed. Crude and simple, however, were their astronomical theories relative to the shape, the structure, and the magnitude of the great universe in which they found themselves placed.1

Then too, as stated, there was something of interest to the people of that early day in the simple problems of geography; problems suggested by the physical features of their immediate environment; problems arising as they journeyed for trade or traffic, or the love of adventure, to regions now near, now remote. Very ancient records tell us of the attempts they made, primitive indeed most of them were, to sketch in general outline small areas of the earth’s surface, usually at first the homeland of the map maker, but to which they added as their knowledge expanded. The early Egyptians, for example, as we long have known, made use of rough outline drawings (Fig. 1)2 to represent certain features of special sections of their country, and recently discovered tablets in the lower Mesopotamian valley (Fig. 2) interestingly show us how far advanced in the matter of map making the inhabitants of that land were two thousand years before the Christian era.3 We are likewise assured, through references in the literature of classical antiquity, that maps were made by the early Greeks and Romans, and perhaps in great numbers as their civilization advanced, though none of their productions have survived to our day. To the Greeks indeed belongs the credit of first reducing geography and map making to a real science.4 No recent discovery by archaeologist or by historian, interesting as many of their discoveries have been, seems to warrant an alteration of this statement, long accepted as fact.

Fig. 1. Fragment Map of Egyptian Gold Mines.

Fig. 2. Tablet Representing Babylonian World-Plan.

The credit of being the first scientific cartographer has been generally assigned to the Greek Anaximander of Miletus (610–547 BC).5 While there is not a detailed description extant of the maps he is reputed to have made, we know that he accepted the so-called Homeric idea, that the earth has the form of a circular disc,6 and is surrounded by the Ocean Stream, an idea generally approved by the Ionic School of Philosophers.7 It is not improbable that we have an allusion to the work of Anaximander in the History of Herodotus (484–400? BC), wherein we are told that Aristagoras, the tyrant of Miletus, when on a mission to Cleomenes, the King of Sparta, carried with him “a copper plate on which was engraved the whole circuit of the earth, and likewise all the Seas and Rivers.”8 In another passage, Herodotus takes occasion to criticise maps of this circular character. “I laugh,” he says, “when I see that, though many before this have drawn maps of the Earth, yet no one has set the matter forth in an intelligent way; seeing that they draw the Ocean flowing round the Earth, which is circular as if drawn with compasses, and they make Asia equal in size to Europe. In a few words I shall declare the size of each division and of what nature it is as regards outline.”9 It is, however, interesting to observe that the father of historical geography and of history nowhere records his idea of a properly constructed map, and further that the circular form, which he condemned, is one which found wide acceptance even to the close of the middle ages.

We are not definitely informed as to just the course of improvement or advancement in early scientific map making among the Greeks, yet not a few names are known to us of those who made it a matter of special endeavor, as they specifically stated, to improve the work of their predecessors. We, for example, are told that Hecataeus (550–480 BC),10 likewise a native of Miletus, improved the maps of Anaximander, and that scientists of his day were astonished at his results; that Dicaearchus of Massina (350–290 BC)11 was the first to employ a central line of orientation on a map, one passing through the Mediterranean east and west, and that he represented on his map all the lands known since the expedition of Alexander the Great into the Far East; and further, that Eratosthenes, the librarian of Alexandria (276–196 BC),12 was the first to attempt a representation of the curved surface of the earth on a plane in accord with geometrical rules. The scientific cartographical ideas of Eratosthenes were further developed by Hipparchus (180–125 BC),13 who is generally referred to as the greatest astronomer of antiquity, and by Marinus of Tyre (fl. ca. 100 AD),14 who introduced the idea of inscribing lines of latitude and longitude on a map, crossing the same at right angles, which lines could be made to serve the useful purpose of orientation and be of assistance in giving proper location to all known places on the earth’s surface.

Map making in that early period reached its climax in the work of Claudius Ptolemy of Alexandria (ca. 87–150 AD).15 His ideas, however, seem not to have found general favor with his contemporaries, nor with the geographers of the middle ages. (Fig. 3.) It was not until the so-called period of great geographical discoveries and explorations in the fifteenth century that he became a real teacher within his chosen field.

Fig. 3. Ptolemy World Map.

Map making and the science of geography were continuously progressive among the Greeks. Imperial Rome witnessed little progress in either field. Among those who wrote in the Latin language, Pomponius Mela (fl. ca. 43 AD)16 and Pliny (ca. 23–79 AD)17 alone have rank of importance. In the matter of map construction the Romans held to many of the cruder methods and ideas of the Greeks, a fact which we learn from the fragmentary references in their literature, and from the itinerary or road maps (Fig. 4), of the period of the emperors, which have come down to us.18

Fig. 4. Sections of Peutinger Tables.

The idea of a globular earth was at first accepted by the geographers of antiquity with some hesitancy. That Thales (640–548 BC),19 one of the earliest astronomers and cosmographers, openly supported this theory, as is sometimes asserted, is hardly probable. It is rather to be assumed that according to his idea the earth has the form of a cylinder, and that it moves within a hollow sphere, an idea upheld by Anaximander, his disciple and successor, to whom reference has been made above. It was the Pythagorean philosophers who appear to have first transferred to the earth that which had already been accepted as a theory relative to the heavens, including the imaginary circles and the circular or spherical form, apparently arguing that the earth is a sphere because that is the most perfect form, that it is located in the center of the universe because that is the place of honor, and that it is at rest because rest is more dignified than motion.20 It however was Aristotle who undertook, in the manner of a philosopher, an elaborate defense of the Pythagorean doctrine of a globular earth, supporting his arguments, first, through a reference to such positive proof as may be found in gravitation or “the tendency of all particles of matter to form themselves about the middle and thus make a sphere,” and secondly, through a reference to the appearance of the earth’s shadow cast during an eclipse of the moon.21 A third proof, so familiar to us today, that distant objects as we approach them gradually reveal themselves above the horizon, seems not to have occurred to Aristotle, but was first employed by Strabo. “It is evident,” says the latter, “that, when persons on shipboard are unable to see at a distance lights which are on a level with the eye, the cause of this is the curvature of the sea; for if those lights are raised to a higher level, they become visible, even though the distance is increased; and in like manner, if the beholder attains a greater elevation he sees what was previously hidden. … Again, when men are approaching the land from the sea, the parts nearest the shore-line come more and more into view, and objects which at first appeared low attain a greater elevation.”22

After the attempt had been made to determine the circumference of the earth, as was done by Eratosthenes with more or less satisfactory results, the thought, very naturally, was suggested of making an artificial representation of the entire earth, so far as then understood, that is, of making a terrestrial globe. There is no intimation, however, in any early allusion to Eratosthenes that he was a globe maker, or that he knew anything about globe construction. We know that he thought of the earth as a sphere placed in the center of the universe, around which the celestial sphere revolves every twenty-four hours.23 Strabo, at a much later date, in referring to the geographical ideas of Eratosthenes, censured him for his unnecessarily elaborate proofs of the earth’s spherical character, apparently thinking the fact one too well known to require demonstration.

Fig. 5. Globe according to Crates.

It appears to have been the grammarian Crates of Mallos, a contemporary of Hipparchus, and a member of the Stoic School of Philosophers, who made the first attempt to construct a terrestrial globe (Fig. 5), and that he exhibited the same in Pergamum, not far from the year 150 BC24 It seems to have been Crates’ idea that the earth’s surface, when represented on a sphere, should appear as divided into four island-like habitable regions. On the one hemisphere, which is formed by a meridional plane cutting the sphere, lies our own oecumene or habitable world, and that of the Antoecians in corresponding longitude and in opposite latitude; on the other hemisphere lies the oecumene of the Perioecians in our latitude and in opposite longitude, and that of the Antipodes in latitude and longitude opposite to us.25 Through the formulation and expression of such a theory the idea of the existence of an antipodal people was put forth as a speculative problem, an idea frequently discussed in the middle ages, and settled only by the actual discovery of antipodal regions and antipodal peoples in the day of great transoceanic discoveries.26 That Strabo, at a later date, had this Pergamenian example in mind when stating certain rules to be observed in the construction of globes seems probable, since he makes mention of Crates’ globe. Strabo alone among ancient writers, so far as we at present know, treats of terrestrial globes, practically such as we find in use at the present day. He thought that a globe to be serviceable should be of large size, and his reasoning can readily be understood, for what at that time was really known of the earth’s surface was small indeed in comparison with what was unknown. Should one not make use of a sphere of large dimensions, the habitable regions (Fig. 6), in comparison with the earth’s entire surface, would occupy but small space. What Strabo states in his geography is interesting and may here well be cited. “Whoever would represent the real earth,” he says, “as near as possible by artificial means, should make a sphere like that of Crates, and upon this draw the quadrilateral within which his chart of geography is to be placed. For this purpose however a large globe is necessary since the section mentioned, though but a very small portion of the entire sphere, must be capable of containing properly all the regions of the habitable earth and of presenting an accurate view of them to those who wish to consult it. Any one who is able will certainly do well to obtain such a globe. But it should have a diameter of not less than ten feet; those who can not obtain a globe of this size, or one nearly as large, had better draw their charts on a plane surface of not less than seven feet. Draw straight lines for the parallels, and others at right angles to these. We can easily imagine how the eye can transfer the figure and extent (of these lines) from a plane surface to one that is spherical. The meridians of each country on the globe have a tendency to unite in a single point at the poles; nevertheless on the surface of a plane map there would be no advantage if the right lines alone which should represent the meridians were drawn slightly to converge.”27

Fig. 6. Globe according to Strabo.

It is not at all improbable that Strabo and Ptolemy made considerable advance in the practical construction of terrestrial globes, for it seems reasonable to conclude that they were in possession of such objects when writing, as they did, concerning them.

Ptolemy, we may note, expressly allowed that the size of a globe should be that which one might desire, and that it was not necessary it should be of large size. It was this great Alexandrian cosmographer who first demonstrated the scientific value of drawing on the surface of a globe or map the network of parallels and meridians, and of establishing by means of the two geographical coördinates the true geographical position of every known place. To the end of making globes more serviceable he suggested the use of a meridian circle, such as is today employed in globe construction, passing through both poles, within which circle the globe might be made to move freely on its axis. He, however, in this connection, did not give technical directions for the construction of terrestrial globes, but he says enough to assure us that the art of globe construction was measurably well understood in his day, and that the Greeks and the Romans considered them very useful instruments in the study of the heavens and the earth.28

The allusions of the naturalist Pliny (23–79 AD) to the spherical shape of the earth give us no particular intimation that he knew of the existence of terrestrial globes, but they are interesting as indicating a belief of his time in its spherical form, a belief, judging from the nature of the argument, apparently drawn from Aristotle. Referring to the shape of the earth, he observes that “everyone agrees it has the most perfect figure. We always speak of the ball of the earth, and we admit it to be a globe bounded by the poles. It has not indeed the form of an absolute sphere, from the number of lofty mountains and flat plains; but if the termination of the lines be bound by a curve, this would compose a perfect sphere. And this we learn from arguments drawn from the nature of things, although not from the same considerations which we have made use of with respect to the heavens. For in the heavens the hollow convexity everywhere bends on itself and leans upon the earth as a center, whereas the earth rises up solid and dense like something that swells up and is protruded outward. The heavens bend toward the center, while the earth goes out from the center, the continual rolling of the heavens about it forcing its immense mass into the form of a sphere.”29