Conversations on the Plurality of Worlds

by M. de Fontenelle

[7] Perhaps in Ethiopia. Astronomy, Art. 260.

I am glad, said the Marchioness, you have given me this genealogy of the sciences; astronomy is the only one that will suit me: geometry, according to your account of it, requires a more selfish heart than mine; and I have not susceptibility enough to attempt poetry with success; I have, however, as much leisure as can be needful for the study of astronomy; it is another favourable circumstance that we are in the country, leading a pastoral life. Do not mistake madam, answered I, talking of planets and fixed stars is not all that constitutes a pastoral life. Was the conversation of the shepherds, in the golden age, confined to astronomy? Ah, said she, but it would be dangerous to conform one's mode of life to their's. No, that of the other shepherds you mention appears preferable to me; therefore let us converse, if you please, in the Chaldean style. After this disposition of the stars was remarked, what followed? The next thing, I replied, was to imagine the arrangement of the different parts of the universe; that is what the learned call making a system. But before I explain to you the first of these systems, give me leave to premise that we are all naturally disposed to the same sort of madness as a certain Athenian of whom you have heard, who had taken it in his head that every vessel which went into the port of Pyreum belonged to him. We chuse to believe that every thing in creation is destined to our service; and when we enquire of some philosophers the use of such a prodigious number of fixed stars, of which a smaller proportion would have been sufficient for all the offices they appear to perform; they coolly answer, they were made to gratify our sight. On this selfish principle it was for a long time supposed that the earth was motionless in the midst of the universe, whilst all the heavenly bodies were created for the sole purpose of journeying round, and distributing their light to her. Next to the earth they placed the moon, after the moon, Mercury, then Venus, the Sun, Mars, Jupiter, Saturn; beyond all these the firmament of fixed stars. It was imagined that the earth was stationed exactly in the middle of the circles described by these planets which extended in proportion to their distance from the earth, and that consequently the most remote planets required a longer time to perform their revolutions, which certainly is true. But, interrupted the Marchioness, I can't see why you should disapprove such an arrangement of the universe, it appears to me sufficiently commodious and intelligible, I really feel quite satisfied with it. I have taken pains, answered I, to represent this system in the most favourable point of view; if I were to explain it exactly as it was conceived by Ptolemy the author of it, and his disciples, you would be quite shocked. As the motions of the planets are irregular, being sometimes quicker, sometimes slower; going sometimes in one direction, sometimes in another; now nearer to the earth, then at a greater distance from it; the ancients figured to themselves an endless number of circles intersecting each other, by which they endeavoured to understand the great variety of movements. The confusion, however, caused by such an infinity of circles was so perplexing that, at the time no better system was known, one of the kings of Castile,[8] a profound mathematician, was daring enough to say, that if the supreme Being had consulted him when he created the world, he would have given him some good advice. We are filled with horror at the impiety of this expression, but it serves to shew us how absurd must have been the hypothesis which could prompt it. The advice this man wished to have given, undoubtedly regarded the suppression of so many circles, which did but prevent the planetary motions from being understood. Probably he would likewise have expunged from the system two or three superfluous firmaments, supposed to be above the fixed stars. The philosophers, to explain some particular motion of the heavenly bodies, placed, beyond the heaven that bounds our view, a sky of crystal, which communicated this motion to the lower sky. Was a new movement discovered? they had nothing to do but to form a second crystal firmament. In short skies of crystal were made without any trouble. Why did they always chuse crystal? enquired the Marchioness; would nothing else have answered the purpose as well? No, answered I, it was necessary to have a substance, at once transparent and solid, for it was Aristotle's opinion that solidity was essential to the dignity of their nature, and as this was believed by a great man, nobody thought of doubting it. But since that time comets have been seen which, being higher than was formerly imagined, must have broken all the crystal of these skies, in passing through them, and by that mean, thrown the universe into confusion; it was therefore found necessary to change the matter of which these firmaments were composed, into a fluid, such as air.

[8] Alphonsus, king of Castile died in 1284.

It is now discovered with certainty, by the researches of later ages, that Venus and Mercury turn round the Sun, and not round the earth, on this subject the ancient system is absolutely exploded. I will now acquaint you with another which provides for every difficulty, one that does not require any amendments of the king of Castile, for its simplicity is so charming that one cannot refuse to believe it. Yours, interrupted the Marchioness, seems a sort of bargaining philosophy; whoever offers a system that is effected at the least expense, has the preference. 'Tis true, said I; we have no other chance of understanding the plan by which the operations of nature are carried on. Nature is a wonderful economist; if a work is to be effected, and two ways are practicable, we may be sure she will adopt that which costs her the least, however trifling the difference. This economy is notwithstanding in every respect consistent with the surprising magnificence which appears in all her productions. Magnificence is employed in the design, and frugality in the execution of it. Nothing should excite our admiration so much as a stupendous project effected by simple means: but we are apt to cherish ideas of a very different kind. We place the frugality in the designs of nature, and her grandeur in the execution. We imagine her forming a contracted plan, and executing it with ten times the labour that is requisite: what can be so ridiculous? I hope, she replied, that the system you are going to explain will strictly imitate nature; the simplicity you so admire will spare me a great deal of trouble in comprehending your instructions. Your hope will be realized, said I, we have now no useless incumbrances. At the appearance of a certain German named Copernicus,[9] astronomy became simplified; he destroyed all the unnecessary circles, and crushed to pieces the crystalline firmaments.[10] Animated with philosophic enthusiasm, he dislodged the earth from the central situation which had been assigned it, and in its room placed the sun, who was more worthy of such a mark of distinction. The planets were no longer supposed to perform their revolutions round the earth, and enclose it in the centre of their orbits. If they afford us light it is as it were by chance, and in consequence of passing us in their course. They all turn around the sun; the earth itself not excepted; and as a punishment for the indolent repose it had been thought to enjoy, Copernicus made it take an ample share of the general activity: in short of all these celestial attendants, appointed for the service of our little globe, the moon alone is left to move round it. Stop a moment, said the Marchioness, your imagination is so elevated with your subject, you have explained it in such pompous language, that I believe I have scarcely understood you. The sun, you say, is immoveable in the centre of the universe; which of the planets is next in succession? 'Tis Mercury, I replied. Mercury goes regularly round the Sun in nearly a circular orbit, of which that luminary is the central point. Next to Mercury is Venus, which turns in the same manner round the Sun. Afterwards comes the Earth, and being higher than Mercury and Venus, describes a larger circle round the Sun than either of those planets. Then follow Mars, Jupiter and Saturn, in the order I have named them; thus you see the circle of Saturn must be the most extensive of all; it likewise requires a longer time than the other planets to perform its revolution. But, exclaimed she, you have forgotten the moon. I shall recollect it presently, said I; the moon never abandons the earth, but is constantly going round it; but as the earth is continually moving onwards in a circle round the sun, the moon at once follows its motion, and revolves round it; this attendant planet, therefore only goes round the sun in consequence of invariably continuing near to the earth.

[9] He was born in 1472, at Thorn, in Prussia Royal: he died in 1543.

[10] Several of the ancients were of opinion that we should admit the motion of the earth. Astron. Art. 1075.

I understand you, said she, and I love the moon for remaining attached to us when we were forsaken by all the other planets. Confess that if your German could have alienated that too, he would have done it without regret; for one may see, in every part of his hypothesis, that he was but little inclined to favour the earth. He did well, I replied, to humble the vanity of men who chuse to claim the best situation in the universe; 'tis with pleasure I consider the world mixing in the crowd of planets. Pshaw! cried the Marchioness; do you think vanity can have any thing to do with a system of astronomy? Do you suppose I feel humbler for knowing that the earth goes round the sun? I assure you I esteem myself just as highly as I did before. Certainly, madam, I answered, men would be less concerned about the rank they held in the universe than that they enjoyed amongst their associates; neither would the disputes of two planets, for precedence, be so important in their judgement as those of two ambassadors. Nevertheless, the same disposition which induces a man of the world to aspire after the most honourable place in a room, will make a philosopher desirous of placing the globe on which he lives in the most distinguished situation in the universe. He likes to consider every thing made for his use; he encourages, without being aware of his vanity, so flattering an opinion, and his heart becomes deeply engaged about an affair of mere speculation. Upon my word, she exclaimed, you are calumniating human nature—how happened it that the opinions of Copernicus were received, since they are so very humiliating? Copernicus, answered I, was himself very doubtful of the reception they would meet with: it was a long while before he could resolve to publish his system; at last, however, he yielded to the entreaty of several distinguished characters; but what do you think was the consequence?—on the day they took him the first printed copy of his book, he died: so he made use of the shortest way to escape from all the contradictions he had been anticipating.

Listen to me, said the Marchioness: let us be just to every body: it certainly is difficult to imagine we turn round the sun, for we never change places; we rise in the morning where we went to rest at night——I see from your look that you are going to tell me, that as the earth moves altogether——. Assuredly, said I, it is the same thing as going to sleep in a boat which was sailing down a river; on waking, you would find yourself in the same boat, and in the same part of the boat. Yes, replied she, but here is a difference; when I awoke I should find an alteration in the shore, and that would prove that the boat had changed its place: it is not so with respect to the earth, I there find every thing as I left it. No, no, madam, you may observe an alteration in the shore, as you do in the boat: you will recollect that beyond all the planets are the fixed stars, these are what we must consider the objects on the shore. I am on the earth; the earth describes a large circle round the sun; when I look to the middle of this circle I find the sun, and were not its brightness so dazzling as to render the stars invisible, I should constantly see, by looking beyond the centre, some of the fixed stars opposite to the sun; by viewing them however at night, I can easily determine how they were situated in the day, which renders my observations equally accurate. If the earth remained in the same place I should always find the same fixed stars answering to the situation of the sun, but as the earth moves on in her orbit, I necessarily see other fixed stars at the point which I had before examined. Such is our shore, which is every day varying; and as the earth goes round the sun in a year, I observe the sun, during that space of time, successively answering to different fixed stars which compose a circle; this circle is called the Zodiac; shall I shew it you by tracing a figure on the earth? No, said she, I can dispense with that; it would give my park too learned an appearance. I think I have heard that a philosopher, shipwrecked on an island with which he was unacquainted, cried out to his companions on perceiving some lines and circles drawn on the sand; courage, my friends! the island is inhabited; here are the footsteps of men. You must consider that such footsteps ought not to be seen here.

It would certainly, I replied be more in character, to trace only the footsteps of lovers; that is to say, your name, engraved by your adorers on the bark of every tree. No more of adorers, cried she; let us talk of the sun. I understand perfectly why we imagined it performing the revolution which is merely effected by our own motion, but this circle requires a year; how, then, does the sun appear to go round us every day? You undoubtedly know, I replied, that if a ball were rolled along this walk it would have two sorts of motion; it would go towards the end of the walk, and at the same time turn several times on its own axis, so that the side of the ball which is at first uppermost will presently descend, and the other, of course, rise to the top. This is the case with the earth: whilst she is proceeding, through the year, in her orbit round the sun, she turns on her own axis every twenty-four hours: each part, therefore, of the earth loses, and recovers sight of the sun during that time. When in the morning we turn towards the sun, it seems to rise; and when, by continued rotation, we again are more distant from it, it appears to descend. That's curious enough, said she; the earth undertakes every thing, and the sun does nothing at all: and when the moon, the other planets, and the fixed stars appear to pass over us in four-and-twenty hours, it is merely imagination. Exactly so, I replied, and produced by the same cause. The planets perform their revolutions round the sun in unequal periods of time, in consequence of their different distances from it; and one which we see to day answer to a certain point in the zodiac, or circle of fixed stars, will to-morrow at the same hour answer to some other point: this is the effect both of the progress which the planet has made in its orbit and of that which we have made in ours. We move onward; the other planets do the same, but we do not continue all in a line: this occasions us to see them in such different situations, and renders their course apparently irregular. You now understand that such irregularity depends only on the different points from which we view them, and that, in reality all their movements are directed by the most exact order. It may be so, answered the Marchioness; but I should be glad if their order did not cost the earth so much: you seem to have very little consideration for it, and to require an astonishing agility in so large a body. But, said I, do you think it more reasonable for the sun, and all the other heavenly bodies, which are extremely large, to perform in four-and-twenty hours an immense journey round the earth? That the fixed stars, being in the largest circle, should travel, in the course of a day, more than twenty-seven thousand six hundred and sixty times two hundred millions of leagues?[11] All this must be if the earth does not turn on her axis every twenty-four hours. Surely there is much more rationality in supposing our globe to turn, which would give to each part but a journey of nine thousand leagues. Consider what a trifle are nine thousand in comparison of the terrific number I have just mentioned.

[11] According to later calculations, it would be a thousand millions of times a million of leagues; but a person who did not believe the motion of the earth would have no occasion to admit this prodigious distance.