Fig. 20.Fig. 20.—The Copernican System.
Copernicus dealt only with the six planets then known and the sun and moon. As to the stars, he had no idea that they were suns like our own, at immense and various distances from us. The knowledge of the magnitude of the siderealuniverse was reserved for our own century, when it was discovered by the method of parallaxes. We will give Copernicus's own sketch of the planetary system:—
"In the highest place is the sphere of the fixed stars, an immovable sphere, which surrounds the whole of the universe. Among the movable planets the first is Saturn, which requires thirty years to make its revolution. After it Jupiter accomplishes its journey in twelve years; Mars follows, requiring two years. In the fourth line come the earth and the moon which in the course of one year return to their original position. The fifth place is occupied by Venus, which requires nine months for its journey. Mercury occupies the sixth place, whose orbit is accomplished in eighty days. In the midst of all is the sun. What man is there, who in this majestic temple could choose another and better place for that brilliant lamp which illuminates all the planets with their satellites? It is not without reason that the sun is called the lantern of the world, the soul and thought of the universe. In placing it in the centre of the planets, as on a regal throne, we give it the government of the great family of celestial bodies."
The hypothesis of the motion of the earth in its orbit appeared simply to Copernicus as a good basis for the exact determination of the ratios of the distances of the several planets about the sun. But he did not give up the excentrics and epicycles for the explanation of the irregular motions ofthe planets, and certain imaginary variations in the precession of the equinoxes and the obliquity of the ecliptic. According to him the earth was endowed with three different motions, the first about its axis, the second along the ecliptic, and a third, which he called the declination, moving it backwards along the signs of the zodiac from east to west. This last motion was invented to explain the phenomena of the seasons. He thought, like many other ancient philosophers, that a body could not turn about another without being fixed in some way to it—by a crystal sphere, or something—and in this case that the same surface would each day be presented to the sun, and so it requires a third rotation, by which its axis may remain constantly parallel to itself. Galileo, however, afterwards demonstrated the independence of the two motions in question, and proved that the third was unnecessary.
Copernicus was born in the Polish village of Thorn, in 1473, and died in 1543, at Warmia, of which he was canon, and where he built an observatory. The voyages of his youth, his labours, adversities, and old age at last broke him down, and in the winter of 1542 he took to his bed, and was incapable of further work. His work, which was just finished printing at Nuremberg, was brought to him by his friends before he died. He soon after completely failed in strength, and passed away tranquilly on the 23rd of May, 1543.
Plate VIII.Plate VIII.—Death of Copernicus.
The Copernican system required, however, establishing in the minds of astronomers generally before it took the place it now holds, and this work was done by Galileo—a name as celebrated as that of Copernicus himself, if not more so. This perhaps is due not only to his demonstration of the motion of the earth, but to his introduction of experimental philosophy, and his observational method in astronomy.
The next advance was made by Kepler, who overthrew at one blow all the excentrics and epicycles of the ancients, when by his laborious calculations he proved the ellipticity of the orbit of Mars.
The Grecian hypotheses were the logical consequences of two propositions which were universally admitted as axioms in the early and middle ages. First, that the motions of the heavenly bodies were uniform; second, that their orbits were perfect circles. Nothing appeared more natural than this belief, though false. So then when Kepler, in 1609, recognised the fact, by incontestable geometrical measurements, that Mars described an oval orbit round the sun, in which its velocity varied periodically, he could not believe either his observation or his calculation, and he puzzled his brain to discover what secret principle it was that forced the planet to approach and depart from the sun by turns. Fortunately for him, in this inquietude he came across a treatise by Gilbert,De Magnate, which had been published in London nine years before. In this remarkable work Gilbertproved by experiment that the earth acts on magnetized needles and on bars of iron placed near its surface just as a magnet does—and by a conjectural extension of this fact, which was a vague presentiment of the truth, he supposed that the earth itself might be retained in its constant orbit round the sun by a magnetic attraction. This idea was a ray of light to Kepler. It led him to see the secret cause of the alternating motions that had troubled him so much, and in the joy of that discovery he said, "If we find it impossible to attribute the vibration to a magnetic power residing in the sun, acting on the planet without any material medium between, we must conclude that the planet is itself endowed with a kind of intelligent perception which gives it power to know at each instant the proper angles and distances for its motion." In the result Kepler was led to enunciate to the world his three celebrated laws:—
1st. That the planets move in ellipses, of which the sun is in one of the foci.
2nd. The spaces described by the ideal radius which joins each planet to the sun are proportional to the times of their description. In other words, the nearer a planet is to the sun, the faster it moves.
3rd. The squares of the times of revolution are as the cubes of the major axes of the orbits.
Such were the laws of Kepler, the basis of modern astronomy, which led in the hands of Newton to the simpleexplanation by universal gravitation, which itself is now asking to be explained.
We are not to suppose that the system of Copernicus was universally accepted even by astronomers of note. By some an attempt was made to invent a system which should have all the advantages of this, and yet if possible save the immobility of the earth. Such was that of Tycho Brahe, who was born three years after the death of Copernicus, and died in 1601. He was one of the most laborious and painstaking observers of his time, although by the peculiarity of fate he is known generally only by his false system.
In 1577, Tycho Brahe wrote a little treatise,Tychonis Brahe, Dani, De Mundi Ætherei Recentioribus phenomenis, à proposof a comet that had lately appeared. He speaks at length of his system as follows:—"I have remarked that the ancient system of Ptolemy is not at all natural, and too complicated. But neither can I approve of the new one introduced by the great Copernicus after the example of Aristarchus of Samos. This heavy mass of earth, so little fit for motion, could not be displaced in this manner, and moved in three ways, like the celestial bodies, without a shock to the principles of physics. Besides, it is opposed to Scripture! I think then," he adds, "that we must decidedly and without doubt place the earth immovable in the centre of world, according to the belief of the ancients and the testimony of Scripture. In my opinion the celestial motions are arranged in such a
Fig. 21.Fig. 21.—Tycho Brahe's System.
way that the sun, the moon, and the sphere of the fixed stars, which incloses all, have the earth for their centre. The five planets turn about the sun as about their chief and king, the sun being constantly in the centre of their orbits, and accompany it in its annual motion round the earth." This system perfectly accounts for the apparent motions of the planets as seen from the earth, and is essentially a variation on the Copernican, rather than on the Ptolemaic system, but it lent itself less readily to future discoveries. It simply amounts, as far as the solar system is concerned, to impressing upon all the rest of it the motions of the earth, so as to leave the latter at rest; and were thesun only as large with respect to the earth as it seems, were the planets really smaller than the moon, and the stars only at a short distance, and smaller than the planets, it might seem more natural that they should move than the earth; but when all these suppositions were disproved, the very argument of Tycho Brahe for the stability of the earth turned the other way, and proved as incontestably that it moved. In the Copernican system, however, these questions are of no consequence; if the sun be at rest, this mass makes no difference; if the earth moves like the planets, their relative size does not alter anything; and if stars are immovable they may be at any distance and of any magnitude.
The objections of Tycho Brahe to the earth's motion were: First, that it was too heavy—we know now, however, that some other planets are heavier—and that the sun, which he would make move instead, is 340,000 times as heavy. Secondly, that if the earth moved, all loose things would be carried from east to west; but we have experience of many loose things being kept by friction on moving bodies, and can conceive how, all things may be kept by the attraction of the earth under the influence of its own motion. Thirdly, that he could not imagine that the earth was turned upside down every day, and that for twelve hours our heads are downwards.
But the existence of the antipodes overcomes this objection, and shows that there is no up and down in the universe, buteach man calls thatdownwhich is nearer to the centre of the earth than himself.
A variation on Tycho Brahe's system was attempted by one Longomontanus, who had lived with him for ten years. It consisted in admitting the diurnal rotation, but not the annual revolution, of the earth; but it made no progress, and was soon forgotten.
More remarkable than this was the attempt by Descartes in the same direction, namely, to hold the principles of Copernicus, and yet to teach the immobility of the earth. His idea of immobility was however very different from that of Tycho Brahe, or of any one else, and would only be called so by those who were bound to believe it at all costs.
His Theory of Vortices, as it is called, will be best given in his own words as contained in hisLes Principes de la Philosophie, third part, chap. xxvi., entitled, "That the earth is at rest in its heaven, which does not prevent its being carried along with it, and that it is the same with all the planets."
"I adhere," he says, "to the hypothesis of Copernicus, because it seems to me the simplest and clearest. There is no vacuum anywhere in space.... The heavens are full of a universal liquid substance. This is an opinion now commonly received among astronomers, because they cannot see how the phenomena can be explained without it. The substance of the heavens has the common property of all liquids, that itsminutest particles are easily moved in any direction, and when it happens that they all move in one way, they necessarily carry with them all the bodies they surround, and which are not prevented from moving by any external cause. The matter of the heaven in which the planets are turns round continually like a vortex, which has the Sun for its centre. The parts that are nearest the Sun move faster than those that are at a greater distance; and all the planets, including the earth, remain always suspended in the same place in the matter of the heaven. And just as in the turns of rivers, when the water turns back on itself and twists round in circles, if any twig or light body floats on it, we see it carry them round, and make them move with it, and even among these twigs we may see some turning on their own centre, and those that are nearest to the middle of the vortex moving quicker than those on the outside; so we may easily imagine it to be with the planets, and this is all that is necessary to explain the phenomena. The matter that is round Saturn takes about thirty years to run its circle; that which surrounds Jupiter carries it and its satellites round in twelve years, and so on.... The satellites are carried round their primaries by smaller vortices.... The earth is not sustained by columns, nor suspended in the air by ropes, but it is environed on all sides by a very liquid heaven. It is at rest, and has no propulsion or motion, since we do not perceive any in it. This does not prevent it being carried round by its heaven, andfollowing its motion without moving itself, just as a vessel which is not moved by winds or oars, and is not retained by anchors, remains in repose in the middle of the sea, although the flood of the great mass of water carries it insensibly with it. Like the earth, the planets remain at rest in the region of heaven where each one is found. Copernicus made no difficulty in allowing that the earth moves. Tycho, to whom this opinion seemed absurd and unworthy of common sense, wished to correct him, but the earth has far more motion in his hypothesis than in that of Copernicus."
Fig. 22.Fig. 22.—Descartes' Theory of Vortices.
Such is the celebrated theory of vortices. The comparison of the rotation of the earth and planets and their revolution round the sun to the turning of small portions of a rapid stream, may contain an idea yet destined to be developed to account for these motions; but as used by Descartes it is a mere playing upon words admirably adapted to secure the concurrence of all parties; those who believed in the motion of the earth seeing that it did not interfere with their ideas in the least, and those who believed in its stability being gratified to find some way by which they might still cling to that belief and yet adopt the new ideas. This was its purpose, and that purpose it well served; but as a philosophical speculation it was worthless. When former astronomers declared that any planet moved, whether it were the earth or any other, they had no idea of attraction, but supposed the planet fixed to a sphere; this sphere moving and carrying the planet with it was what they meant by the planet moving: the theory of vortices merely substituted a liquid for a solid sphere, with this disadvantage, that if theplanet were fixed to a solid moving sphere, itmustmove; if only placed in a liquid one, that liquid might pass it if it did not have motion of its own.
Fig. 23.Fig. 23.—Vortices of the Stars.
A variation on Descartes' system of vortices was proposed in the eighteenth century, which supposed that the sun, instead of being fixed in the centre of the system, itselfcirculated round another centre, carrying Mercury with it. This motion of the sun was intented to explain the changes of magnitude of its disc as seen from the earth, and the diurnal and annual variations in its motion, without discarding its circular path.
Fig. 24.Fig. 24.—Variation of Descartes' Theory.
We have thus noticed all the chief astronomical systems that have at any time been entertained by astronomers. Theyone and all have given way before the universally acknowledged truth about which there is no longer any dispute. Systems are not now matters of opinion or theory. We speak of facts as certain as any that can be ascertained in any branch of knowledge. We have much to learn, but what we have settled as the basis of our knowledge will never more be altered as far as we can see.
Of course there have been always fantastic fancies put forth about the solar system, but they are more amusing than instructive. Some have said that there is no sun, moon, or stars, but that they are reflections from an immense light under the earth. Some savage races say that the moon when decreasing breaks up into stars, and is renewed each month by a creative act. The Indians used to say that it was full of nectar which the gods ate up when it waned, and which grew again when it waxed. The Brahmins placed the earth in the centre, and said that the stars moved like fishes in a sea of liquid. They counted nine planets, of which two are invisible dragons which cause eclipses; which, since they happen in various parts of the zodiac, show that these dragons revolve like the rest. They said the sun was nearer than the moon, perhaps because it is hotter and brighter. Berosus the Chaldean gave a very original explanation of the phases and eclipses of the moon. He said it had one side bright, and the other side just the colour of the sky, and in turning it represented the different colours to us.
Before concluding this chapter we may notice what information we possess as to the origin of the names by which the planets are known. These names have not always been given to them, and date only from the time when the poets began to associate the Grecian mythology with astronomy. The earlier names had reference rather to their several characters, although there appear to have been among every people two sets of names applied to them.
The earliest Greek names referred to their various degrees of brilliancy: thus Saturn, which is not easily distinguished, was called Phenon, orthat which appears; Jupiter was named Phaëton,the brilliant; Mars was Pysoïs, orflame-coloured; Mercury, Stilbon,the sparkling; Venus, Phosphorus; and Lucifer,the light-bearer. They called the latter also Calliste,the most beautiful. It was also known then as now under the appellations of the morning star and evening star, indicating its special position.
With the ancient Accadians, the planets had similar names, among others. Thus, "Mars was sometimes calledthe vanishing star, in allusion to its recession from the earth, and Jupiter theplanet of the ecliptic, from its neighbourhood to the latter" (Sayce). The name of Mars raises the interesting question as to whether they had noticed its phases as well as its movements—especially when, with reference to Venus, it is recorded in the "Observations of Bel," that "it rises, and in its orbit duly grows in size." They had also a rather confusingsystem of nomenclature by naming each planet after the star that it happened to be the nearest to at any point of its course round the ecliptic.
Among less cultivated nations also the same practice held, as with the natives of South America, whose name for the sun is a word meaningit brings the day; for the moon,it brings the night; and for Venus,it announces the day.
But even among the Eastern nations, from whom the Greeks and Romans borrowed their astronomical systems, it soon became a practice to associate these planets with the names of the several divinities they worshipped. This was perhaps natural from the adoration they paid to the celestial luminaries themselves on account of their real or supposed influence on terrestrial affairs; and, moreover, as time went on, and heroes had appeared, and they had to find them dwelling-places in the heavens, they would naturally associate them with one or other of the most brilliant and remarkable luminaries, to which they might suppose them translated. Beyond these general remarks, only conjectures can be made why any particular divinity should among the Greeks be connected with the several planets as we now know them. Such conjectures as the following we may make. Thus Jupiter, the largest, would take first rank, and be called after the name of the chief divinity. The soft and sympathising Venus—appearing at the twilight—would well denote the evening star. Mars would receive its name from its redappearance, naturally suggesting carnage and the god of war. Saturn, or Kronos, the god of time, is personified by the slow and almost imperceptible motion of that remote planet. While Mercury, the fiery and quick god of thieves and commerce, is well matched with the hide-and-seek planet which so seldom can be seen, and moves so rapidly.
These were the only planets known to the ancients, and were indeed all that could be discovered without a telescope. If the ancient Babylonians possessed telescopes, as has been conjectured from their speaking, as we have noticed above, of the increase of the size of Venus, and from the finding a crystal lens among the ruins of Nineveh, they did not use them for this purpose.
The other planets now known have a far shorter history. Uranus was discovered by Sir William Herschel on the 13th of March, 1781, and was at first taken for a comet. Herschel proposed to call it Georgium Sidus, after King George III. Lalande suggested it should be named Herschel, after its discoverer, and it bore this name for some time. Afterwards the names, Neptune, Astrœa, Cybele, and Uranus were successively proposed, and the latter, the suggestion of Bode, was ultimately adopted. It is the name of the most ancient of the gods, connected with the then most modern of planets in point of discovery, though also most ancient in formation, if recent theories be correct. Neptune, as everybody knows, was calculated into existence, if one may sospeak, by Adams and Leverrier independently, and was first seen, in the quarter indicated, by Dr. Galle at Berlin, in September, 1846, and by universal consent it received the name it now bears.
There are now also known a long series of what are called minor planets, all circulating between Mars and Jupiter, with their irregular orbits inextricably mingled together. Their discovery was led to in a remarkable manner. It was observed that the distances of the several planets might approximately be expressed by the terms of a certain mathematical series, if one term was supplied between Mars and Jupiter—a fact known by the name of Bode's law. When the new planet, Uranus, was found to obey this law, the feeling was so strong that there must be something to represent this missing term, that strong efforts were made to discover it, which led to success, and several, whose names are derived from the minor gods and goddesses, are now well known.
All these planets, like the signs of the zodiac, are indicated by astronomers by certain symbols, which, as they derive their form from the names or nature of the planets, may properly here be explained. The sign of Neptune is♆, representing the trident of the sea; for Uranus♅, which is the first letter of Herschel with a little globe below;♄is the sickle of time, or Saturn;♃is the representation of the first letter of Zeus or Jupiter;♂is the lance and buckler of Mars;♀the mirror of Venus;☿the wand of Mercury;☉the sun's disc; and☽the crescent of the moon.
Plate IX.Plate IX.—The Solar System.
The more modern discoveries have, of course, been all made by means of the telescope, and a few words on the history of its discovery may fitly close this chapter.
According to Olbers, a concave and convex lens were first used in combination, to render objects less distant in appearance, in the year 1606. In that year the children of one Jean Lippershey, an optician of Middelburg, in Zealand, were playing with his lenses, and happened to hold one before the other to look at a distant clock. Their great surprise in seeing how near it seemed attracted their father's attention, and he made several experiments with them, at last fixing them as in the modern telescope—in draw tubes. On the 2nd of October, 1606, he made a petition to the States-General of Holland for a patent. The aldermen, however, saw no advantage in it, as you could only look with one eye instead of two. They refused the patent, and though the discovery was soon found of value, Lippershey reaped no benefit.
Galileo was the first to apply the telescope to astronomical observations. He did not have it made in Holland, but constructed it himself on Lippershey's principle. This was in 1609. Its magnifying power was at first 4, and he afterwards increased it to 7, and then to 30. With this he discovered the phases of Venus, the spots on the sun, the four satellites of Jupiter, and the mountains of the moon.
Plate X.Plate X.—The Discovery of the Telescope.
Kepler, in 1611, made the first astronomical telescope with two concave glasses.
Huyghens increased the magnifying power successively to 48, 50, and 92, and discovered Saturn's ring and his satellite No. 4.
Cassini, the first director of the Paris Observatory, brought it to 150, aided by Auzout Campani of Rome, and Rives of London. He observed the rotation of Jupiter (1665), that of Venus and Mars (1666), the fifth and third satellites of Saturn (1671), and afterwards the two nearer ones (1684); the other satellites of this planet were discovered, the sixth and seventh, by Sir William Herschel (1789), and the eighth by Bond and Lasel (1848).
We may add here that the satellites of Uranus were discovered, six by Herschel from 1790 to 1794, and two by Lassel in 1851, the latter also discovering Neptune's satellite in 1847.
The rotation of Saturn was discovered by Herschel in 1789, and that of Mercury by Schrœter in 1800.
The earliest telescopes which were reflectors were made by Gregory in 1663 and Newton in 1672. The greatest instruments of our century are that of Herschel, which magnifies 3,000 times, and Lord Rosse's, magnifying 6,000 times, the Foucault telescope at Marseilles, of 4,000, the reflector at Melbourne, of 7,000, and the Newall refractor.
Plate XI.Plate XI.—The Foundation of Paris Observatory.
The exact knowledge of the heavens, which makes so grand a feature in modern science, is due, however, not only to the existence of instruments, but also to the establishment of observatories especially devoted to their use. The first astronomical observatory that was constructed was that at Paris. In 1667 Colbert submitted the designs of it to Louis XIV., and four years afterwards it was completed. The Greenwich Observatory was established in 1676, that of Berlin in 1710, and that of St. Petersburg in 1725. Since then numerous others have been erected, private as well as public, in all parts of the world, and no night passes without numerous observations being taken as part of the ordinary duty of the astronomers attached to them.
With respect to the shape and position of the earth itself in the material universe, and the question of its motion or immobility, we cannot go so far back as in the case of the heavens, since it obviously requires more observation, and is not so pressing for an answer.
Amongst the Greeks several authors appear to have undertaken the subject, but only one complete work has come down to us which undertakes it directly. This is a work attributed to Aristotle,De Mundo. It is addressed to Alexander, and by some is considered to be spurious, because it lacks the majestic obscurity that in his acknowledged works repels the reader. Although, however, it is not as obscure as it might be, for the writer, it is quite bad enough, and its dryness and vagueness, its mixture of metaphysical and physical reasoning, logic and observation, and the change that has naturally passed over the meanings of many commonwords since they were written, render it very tedious and unpleasant reading.
Nevertheless, as presenting us with the first recorded ideas on these questions of the nature and properties of the earth, it deserves attentive study. It is not a system of observations like those of Ptolemy and the Alexandrian School, but an entirely theoretical work. It is founded entirely on logic; but unfortunately, if the premisses are bad, the better the syllogism the more erroneous will be the conclusion; and it is just this which we find here. Thus if he be asked whether the earth turns or the heavens, he will reply that the earth isevidentlyin repose, and that this is the case not only because we observe it to be so, but because it is a necessity that it should be; because repose isnaturalto the earth, and it isnaturallyin equilibrium. This idea of "natural" leads very often astray. He is guided to his idea of what is natural by seeing what is, and then argues that what is, or appears to be, must be, because it is natural—thus arguing in a circle. Another example may be given in his answer to the question, Why must the stars move round the earth? He says it is natural, because a circle is a more perfect line, and must therefore be described by the perfect stars, and a circle is perfect because it has no ends! Unfortunately there are other curves that have no ends; but the circle was considered, without more reason, the most perfect curve, and therefore the planets must move in circles—an idea which had to waittill Kepler's time to be exploded. One more specimen of this style may be quoted, namely, his proof that every part of heaven must be eternally moving, while the earth must be in the centre and at rest. The proof is this. Everything which performs any act has been made for the purpose of that act. Now the work of God is immortality, from which it follows that all that is divine must have an eternal motion. But the heavens have a divine quality, and for this reason they have a spherical shape and move eternally in a circle. Now when a body has a circular motion, one part of it must remain at rest in its place, namely, that which is in the centre; the earth is in the centre—therefore it is at rest.
Aristotle says in this work that there are two kinds of simple motion, that in a circle and that in a straight line. The latter belongs to the elements, which either go up or down, and the former to the celestial bodies, whose nature is more divine, and which have never been known to change; and the earth and world must be the only bodies in existence, for if there were another, it must be the contrary to this, and there is no contrary to a circle; and again, if there were any other body, the earth would be attracted towards it, and move, which it does not. Such is the style of argument which was in those days thought conclusive, and which with a little development and inflation of language appeared intensely profound.
But what brings these speculations to the subject we havenow in hand is this: that when Aristotle thus proves the earth to be immovable in the centre of the universe, he is led on to inquire how it is possible for it to remain in one fixed place. He observed that even a small fragment of earth, when it is raised into the air and then let go, immediately falls without ever stopping in one place—falling, as he supposed, all the quicker according to its weight; and he was therefore puzzled to know why the whole mass of the earth, notwithstanding its weight, could be kept from falling.
Aristotle examines one by one the answers that have been given to this question. Thus Xenophanes gave to the earth infinitely extended roots, against which Empedocles uses such arguments as we should use now. Thales of Miletus makes the earth rest upon water, without finding anything on which the water itself can rest, or answering the question how it is that the heavier earth can be supported on the lighter water. Anaxemenes, Anaxagoras, and Democritus, who make the earth flat, consider it to be sustained by the air, which is accumulated below it, and also presses down upon it like a great coverlet. Aristotle himself says that he agrees with those philosophers who think that the earth is brought to the centre by the primitive rotation of things, and that we may compare it, as Empedocles does, to the water in glasses which are made to turn rapidly, and which does not fall out or move, even though upside down. He also quotes with approvalanother opinion somewhat similar to this, namely, that of Anaximander, which states that the earth is in repose, on account of its own equilibrium. Placed in the centre and at an equal distance from its extremities, there is no reason why it should move in one direction rather than the other, and rests immovable in the centre without being able to leave it.
The result of all is that Aristotle concludes that the earth is immovable, in the centre of the universe, and that it is not a star circulating in space like other stars, and that it does not rotate upon its axis; and he completes the system by stating that the earth is spherical, which is proved by the different aspects of the heavens to a voyager to the north or to the south.
Such was the Aristotelian system, containing far more error than truth, which was the first of any completeness. Scattered ideas, however, on the shape and method of support of the earth and the cause of various phenomena, such as the circulation of the stars, are met with besides in abundance.
The original ideas of the earth were naturally tinged by the prepossessions of each race, every one thinking his own country to be situated in the centre. Thus among the Hindoos, who lived near the equator, and among the Scandinavians, inhabiting regions nearer the pole, the same meaning attaches to the words by which they express their own country,medpiamaandmedgard, both meaning the central habitation. Olympus among the Greeks was made the centre of the earth, and afterwards the temple of Delphi. For the Egyptians the central point was Thebes; for the Assyrians it was Babylon; for the Indians it was the mountain Mero; for the Hebrews Jerusalem. The Chinese always called their country the central empire. It was then the custom to denote the world by a large disc, surrounded on all sides by a marvellous and inaccessible ocean. At the extremities of the earth were placed imaginary regions and fortunate isles, inhabited by giants or pigmies. The vault of the sky was supposed to be supported by enormous mountains and mysterious columns.
Numerous variations have been suggested on the earliest supposed form of the earth, which was, as we have seen in a former chapter, originally supposed to be an immense flat of infinite depth, and giving support to the heavens.
As travels extended and geography began to be a science, it was remarked that an immense area of water circumscribed the solid earth by irregular boundaries—whence the idea of a universal ocean.
When, however, it was perceived that the horizon at sea was always circular, it was supposed that the ocean was bounded, and the whole earth came to be represented as contained in a circle, beneath which were roots reaching downwards without end, but with no imagined support.
Fig. 25.Fig. 25.—The Earth Floating.
Fig. 26.Fig. 26.—The Earth with Roots.
The Vedic priests asserted that the earth was supported on twelve columns, which they very ingeniously turned to their own account by asserting that these columns were supported by virtue of the sacrifices that were made to thegods, so that if these were not made the earth would collapse.
Fig. 27.Fig. 27.—The Earth of the Vedic Priests.
These pillars were invented in order to account for the passing of the sun beneath the earth after his setting, for which at first they were obliged to imagine a system of tunnels, which gradually became enlarged to the intervals between the pillars.
The Hindoos made the hemispherical earth to be supported upon four elephants, and the four elephants to stand on the back of an immense tortoise, which itself floated on the surface of a universal ocean. We are not however to laugh at this as intended to be literal; the elephants symbolised, it may be, the four elements, or the four directions of thecompass, and the tortoise was the symbol for strength and for eternity, which was also sometimes represented by a serpent.
Fig. 28.Fig. 28.—Hindoo Earth.
The floating of the earth on water or some other liquid long held ground. It was adopted by Thales, and six centuries later Seneca adopts the same opinion, saying that the humid element that supports the earth's disc like a vessel may be either the ocean or some liquid more simple than water.
Diodorus tells us that the Chaldeans considered the earth hollow and boat-shaped—perhaps turned upside down—and this doctrine was introduced into Greece by Heraclitus of Ephesus.
Fig. 29.Fig. 29.—The Earth of Anaximander.
Anaximander represents the earth as a cylinder, the upper face of which alone is inhabited. This cylinder, he states, is one-third as high as its diameter, and it floats freely in the centre of the celestial vault, because there is no reason why it should move to one side rather than the other. Leucippus, Democritus, Heraclitus, and Anaxagoras all adopted this purely imaginary form. Europe made the northern half, and Lybia (Africa) and Asia the southern, while Delphi was in the centre.
Anaximenes, without giving a precise opinion as to the form of the earth, made it out to be supported on compressed air, though he gave no idea as to how the air was to be compressed.
Plato thought to improve upon these ideas by making the earth cubical. The cube, which is bound by six equal faces, appeared to him the most perfect of solids, and thereforemost suitable for the earth, which was to stand in the centre of the universe.
Fig. 30.Fig. 30.—Plato's Cubical Earth.
Eudoxus, who in his long voyages throughout Greece and Egypt had seen new constellations appear as he went south, while others to the north disappeared, deduced the sphericity of the earth, in which opinion he was followed by Archimedes, and, as we have seen, by Aristotle.
According to Achilles Tatius, Xenophanes gave to the earth the shape of an immense inclined plane, which stretched out to infinity. He drew it in the form of a vast mountain. The summit only was inhabited by men, and round it circulated the stars, and the base was at an infinite depth. Hesiodhad before this obscurely said: "The abyss is surrounded by a brazen barrier; above it rest the roots of the earth." Epicurus and his school were well pleased with this representation. If such were the foundations of the earth, then it was impossible that the sun, and moon, and stars should complete their revolutions beneath it. A solid and indefinite support being once admitted, the Epicurean ideas about the stars were a necessary consequence; the stars must inevitably be put out each day in the west, since they are not seen to return to the place whence they started, and they must be rekindled some hours afterwards in the east. In the days of Augustus, Cleomedes still finds himself obliged to combat these Epicurean ideas about the setting and rising of the sun and stars. "These stupid ideas," he says, "have no other foundation than an old woman's story—that the Iberians hear each night the hissing noise made by the burning sun as it is extinguished, like a hot iron in the waters of the ocean." Modern travellers have shown us that similar ideas about the support of the earth have been entertained by more remote people. Thus, in the opinion of the Greenlanders, handed down from antiquity to our own days, the earth is supported on pillars, which are so consumed by time that they often crack, and were it not that they are supported by the incantations of the magicians, they would long since have broken down. This idea of the breaking of the pillars may possibly have originated in the known sinking of the landbeneath the sea, which is still going on even at the present day.
Fig. 31.Fig. 31.—Egyptian Representation of the Earth.
An ancient Egyptian papyrus in the library of Paris gives a very curious hieroglyphical representation of the universe. The earth is here figured under the form of a reclining figure, and is covered with leaves. The heavens are personified by a goddess, which forms the vault by her star-bespangled body, which is elongated in a very peculiar manner. Two boats, carrying, one the rising sun, and the other the settingsun, are represented as moving along the heavens over the body of the goddess. In the centre of the picture is the god, Maon, a divine intelligence, which presides over the equilibrium of the universe.
We will now pass on from the early ideas of the general shape and situation of the world to inquire into the first outlines of geographical knowledge of details.
Of all the ancient writings which deal with such questions, the Hebrew Scriptures have the greatest antiquity, and in them are laid down many details of known countries, from which a fair map of the world as known to them might be made out. The prophet Esdras believed that six-sevenths of the earth was dry land—an idea which could not well be exploded till the great oceans had been traversed and America discovered.
More interesting, as being more complete, and written to a certain extent for the very purpose of relating what was known of the geography of the earth, are the writings of the oldest Grecian poets. The first elements of Grecian geography are contained in the two national and almost sacred poems, theIliadandOdyssey. So important have these writings been considered in regard to ancient geography, that for many centuries discussions have been carried on with regard to the details, though evidently fictitious, of the voyage of Ulysses, and twenty lines of theIliadhave furnished matter for a book of thirty volumes.
The shield of Achilles, forged by Vulcan and described in the eighteenth book of theIliad, gives us an authentic representation of the primitive cosmographical ideas of the age. The earth is there figured as a disc, surrounded on all sides by theRiver Ocean. However strange it may appear to us, to apply the termriverto the ocean, it occurs too often in Homer and the other ancient poets to admit of a doubt of its being literally understood by them. Hesiod even describes the sources of the ocean at the western extremity of the world, and the representation of these sources was preserved from age to age amongst authors posterior to Homer by nearly a thousand years. Herodotus says plainly that the geographers of his time drew their maps of the world according to the same ideas; the earth was figured with them as a round disc, and the ocean as a river, which washed it on all sides.
The earth's disc, theorbis terrarum, was covered according to Homer by a solid vault or firmament, beneath which the stars of the day and night were carried by chariots supported by the clouds. In the morning the sun rose from the eastern ocean, and in the evening it declined into the western; and a vessel of gold, the mysterious work of Vulcan, carried it quickly back by the north, to the east again. Beneath the earth Homer places, not the habitation of the dead, the caverns of Hades, but a vault called Tartarus, corresponding to the firmament. Here lived the Titans, the enemies of thegods, and no breath of wind, no ray of light, ever penetrated to this subterranean world. Writers subsequent to Homer by a century determined even the height of the firmament and the depth of Tartarus. An anvil, they said, would take nine days to fall from heaven to earth, and as many more to fall from earth to the bottom of Tartarus. This estimate of the height of heaven was of course far too small. If a body were to fall for nine days and nights, or 777,600 seconds under the attraction of the earth, it would only pass over 430,500 miles, that is not much more than half as far again as the moon. A ray of light would only take two seconds to pass over that distance, whereas it takes eight minutes to reach us from the sun, and four hours to come from Neptune—to say nothing of the distance of the stars.
The limits of the world in the Homeric cosmography were surrounded by obscurity. The columns of which Atlas was the guardian were supported on unknown foundations, and disappeared in the systems subsequent to Homer. Beyond the mysterious boundary where the earth ended and the heavens began an indefinite chaos spread out—a confused medley of life and inanity, a gulf where all the elements of heaven, Tartarus, and earth and sea are mixed together, a gulf of which the gods themselves are afraid.
Ideas such as these prevailed long after geometers and astronomers had proved the spherical form of the globe, and they were revived by the early Christian geographersand have left their trace even on the common language of to-day.