Fontenelle’s A Week’s Conversation on the Plurality of Worlds is popular science in dialogue form: a narrator spends several evenings at a country estate instructing a noblewoman in the new astronomy. Across their conversations the two move outward from the Earth and Moon to the planets, the fixed stars, and the comets, weighing the Copernican system against the older Ptolemaic one and asking at every stage whether other worlds might be inhabited. The English edition adds a preface by the translator and, at the end, Joseph Addison’s Oxford oration in defence of the new philosophy.

The book’s governing premise is stated plainly in its preface: the author means to discourse of philosophy “not directly in a philosophical manner,” raising the subject so that it is neither too dry for ordinary men nor too mean for scholars. He claims not to instruct the learned but to divert them, presenting in a gay dress what they have already seen in a graver habit, while those to whom the subject is new may be both diverted and instructed. The fiction of a lady to be taught things she never heard serves that design: it renders the book more acceptable and encourages gentlewomen by the example of one of their own sex who, without any tincture of learning, rightly apprehends what vortexes and other worlds are. The author insists he has built on true philosophical arguments rather than an airy system with no foundation, and that he has related nothing about the inhabitants of the several worlds that may seem fabulous or chimerical.

From the Earth’s Motion to the Sun at the Center

The Preface: Philosophy in a Gay Dress

Fontenelle opens by measuring himself against Cicero, who, when he undertook to write philosophy in Latin, was warned he would labour in vain: admirers of philosophy would go to the Greek authors rather than read Latin at second hand, and those with no relish for the science would trouble with neither. Cicero answered that the ease of reading Latin might tempt the unphilosophical to become philosophers, and that those already philosophers would gladly see the subject handled in their own tongue. The author grants Cicero had reason to answer so, given his genius and reputation, but claims no such grounds of confidence for himself. His aim is to discourse of philosophy without raising it so high that it grows too dry for men or too mean for scholars. Told, as Cicero was, that the learned will not be pleased because they cannot be taught, nor the illiterate because they have no mind to learn, he will not answer as Cicero did; to keep a medium betwixt extremes is so difficult he would never desire the like trouble a second time. To those knowledgeable in natural philosophy he pretends not to instruct but to divert them, presenting in a gay dress what they have seen in a graver habit; those to whom the subject is new may be both diverted and instructed. He has chosen that part of philosophy most likely to excite curiosity—enquiring how this world is made and whether other worlds like it are also inhabited—leaving everyone to run their disquisitions as far as they please. He introduces a Lady to be instructed in things she never heard, using the fiction to render the book more acceptable and to encourage gentlewomen by the example of one of their own sex who, without supernatural parts or tincture of learning, understands what is said to her and rightly apprehends what vortexes and other worlds are. Why, he asks, might there not be a woman like this imaginary Countess? He has not composed an airy system with no foundation, but used true philosophical arguments, as many as he thought necessary; physical ideas are in themselves very agreeable, convincing reason while presenting to the imagination a prospect made to please it. Digressions he has used as the nature of conversation allows, placing them where readers would be least acquainted with the principal ideas. Concerning the inhabitants of the several worlds he has related nothing fabulous or chimerical, but said whatever may be reasonably thought of them, mingling true and false so as to be easily distinguished. To scrupulous persons who imagine that placing inhabitants anywhere but on Earth is dangerous to religion, he answers that religion can receive no prejudice by his system, which fills an infinity of worlds with inhabitants, if a little error of the imagination be rectified. When it is said the Moon is inhabited, some fancy there are men like ourselves there, and priests think him an atheist who holds that opinion, objecting that none of Adam’s posterity ever travelled to the Moon nor were colonies planted there. He grants the men in the Moon are not the Sons of Adam, and says theology would be puzzled if there be men there who never descended from him; but perhaps there is no need of answering the objection, for it concerns nobody but the men in the Moon, and he never affirmed there are men there. Asked what the inhabitants are, he says he never saw them. He denies saying there are no men in the Moon purposely to avoid the objection, for it appears impossible there should be any, according to his idea of that infinite diversity and variety observed in the works of Nature, which idea runs through the whole book. He believes the objection will be started only by such as speak of these discourses without having read them. In this edition he has interspersed many improvements in the body of the work, added a conversation gathering reasonings omitted in the foregoing ones, and subjoined some late discoveries in the firmament, several never yet made public. The contents list seven items: that the Earth is a planet turning on itself and round the Sun; that the Moon is an inhabited world; particulars concerning the world in the Moon and proofs the other planets are likewise inhabited; particulars of the worlds of Venus and Mercury; that the fixed stars are so many suns, each giving light to a world; new observations confirming the preceding discourses and late discoveries in the heavens; and Mr. Addison’s Oration at Oxford in defence of the new philosophy.

The First Letter: A Promise of Philosophy

The first letter to Monsieur R* opens by promising a detail of time passed at the Countess of D**’s country seat, which would make a large volume of philosophy, whereas the recipient expects dancing, gaming, and hunting; instead he must take up with vortexes, planets, and new worlds. The writer says the recipient is a philosopher, so it will be no great disappointment, and that he has brought the Countess over to their party—youth and beauty being inestimable—asking whether Wisdom could appear more effectually than in the Countess’s person. It is impossible, he says, without her wit to express her sentiments as she delivered them, and she is very learned from her great disposition to learning, since it is not poring upon books that makes a scholar. He declines describing the situation and building of the Countess’s seat, saying he found no company with the lady, at which he was not displeased; the first two days drained him of news.

The Athenian and the Circles of the Ancients

The narrator compares human folly to an Athenian who fancied all ships entering the Pyræum Port belonged to him; likewise we believe all nature is designed for our use. Asked why so many fixed stars exist when fewer would serve, a philosopher coldly answers they were made to please our sight. On this principle people imagined the Earth rested in the center of the universe while all celestial bodies turned to give it light. They placed the Moon above the Earth, Mercury above the Moon, then Venus, the Sun, Mars, Jupiter, and Saturn, and above all these the heaven of fixed stars. The Earth sat in the middle of the circles containing the planets; the larger the circles, the farther from Earth, so the farthest planets took most time to finish their course—which is in effect true. The Countess interrupts, asking why he dislikes this system, which seems clear and intelligible. He replies he will make it plainer, for given as it came from Ptolomy its author, or others who studied it since, it would frighten rather than divert her.

Since the planets’ motions are not so regular but that they sometimes go faster, sometimes slower, sometimes nearer the Earth and sometimes farther, the Ancients invented many orbs or circles involved one within another to salve all objections. This confusion of circles was so great that a certain King of Aragon, a great mathematician but not much troubled with religion, said that had God consulted him when he made the world, he would have told him how to have framed it better. The saying was very atheistical; no doubt his instructions would have been suppressing those circles and taking away two or three superfluous heavens placed above the fixed stars. To explain celestial motion these philosophers had above the uppermost visible heaven another of crystal to influence the inferior heavens; and wherever they heard of another motion, they clapped up a heaven which cost them nothing. The Countess asks why the heaven must be of crystal. He answers nothing else would serve, for light was to come through them and yet they were to be solid; Aristotle would have it so, having found solidity one of their excellencies, and once he said it nobody would question it. But comets appeared much higher than the philosophers expected, which as they passed broke the crystal heavens and confounded the universe. To make the best of a bad market they melted down their broken glass and made the heavens fluid; and by observations of these latter ages it is now out of doubt that Venus and Mercury turn round the Sun, not round the Earth, according to the ancient system, now everywhere exploded, all authorities not worth a rush.

The Countess observes his philosophy is a kind of outcry where he that offers to do the work cheapest carries it. He agrees: Nature is a great huswife, always using what costs least; she is magnificent in the design but frugal in the execution.

Dawn, Rainbows, and the Moon’s Unmoderated Light

The conversation turns first to what the Moon’s inhabitants lack. Dawn and twilight, the narrator explains, are gifts Earth receives “over and above our due”—a gradual light that prepares us for the Sun and softens its departure. On the Moon, where the air is purer and less able to scatter the Sun’s beams, no such mercy exists. Day and night fall in an instant: eyes are dazzled by full light, then plunged into utter darkness, with no medium between the extremes. The rainbow, too, is unknown there, since it forms in the clouds that produce rain, and the Moon has none. The narrator jokes about what lovers in that world will do for similes now that such a magazine of comparisons is gone; the Countess answers that she will not grieve for the loss, since by the same reasoning the Moon has neither thunder nor lightning. She praises its glorious unbroken days and star-filled nights, free of storms and tempests, which look like plain effects of the wrath of Heaven.

The narrator calls her Moon an enchanted land, then asks whether it is pleasant to have a scorching Sun always overhead, with days fifteen times ours and not a cloud to temper the heat. He proposes that the great cavities visible through telescopes—not mountains but wells or vaults in the plains—are where the inhabitants retire from the broiling Sun, perhaps living nowhere else and building their cities there, as the underground part of Old Rome nearly matched the city above. He imagines passages connecting the wells. The Countess laughs; he retorts that the ridicule falls on her, since she assumes the Moon’s people must live on the surface because we do—when the contrary is true: as we dwell on the superficies of our planet, they cannot dwell on theirs.

Blessed Souls and the Moon’s Fixed Face

The Countess cannot bear to leave the Moon’s inhabitants in perpetual darkness. The narrator answers that she will be more concerned to hear of an ancient philosopher who made the Moon the residence of blessed souls, their happiness consisting in hearing the music of the spheres. When the Moon is eclipsed by Earth’s shadow, he claimed, they no longer hear the harmony but howl in anguish, so the Moon hastens back into the light. The Countess observes that we should now and then see some of these souls arrive here, and between the two planets sufficient provision is made for their felicity by transportation into a new world. The narrator confesses that such a voyage, though only in imagination, is delightful—far better than going to Japan, which is but crawling from one end of the globe to the other to see nothing but men.

He then completes the Moon’s description: her two movements being equal, she always wears the same face toward us, one half forever hidden. When it is night there—fifteen of our days—the Earth appears to her inhabitants first as a small spot, then larger, growing almost hourly until it covers the whole face of the Earth; whereas to us these changes come only from one night to another. He would give anything to divine the awkward reasonings of that world’s philosophers on our Earth appearing immoveable while all other bodies rise and set within fifteen days. Plainly they attribute this repose to her bigness, forty times the Moon’s, and their poets doubtless compare indolent princes to this majestic stillness. Yet one difficulty attends it: they must sensibly perceive our Earth turning on her center, Europe, Asia, and America presenting themselves in miniature one after another, almost as we see them on our maps.

The Sun, Mars, and the Vortex of Jupiter

The dialogue moves outward from the Sun. Once thought pure fire, the Sun was found to bear spots; some said these were new planets turning their dark halves toward us, but the narrator rejects this, noting the learned had courted princes by naming planets after them. The spots are now known to be clouds, streams, or dross rising and vanishing on the Sun’s surface, some as big as the Earth; others call them burning mountains, though some dismiss these as a fault in the spectacles. The Sun, he concludes, cannot be proper for habitation—its inhabitants would be stark blind, unable either to bear the light or, for want of distance, to receive it. Mars affords nothing curious: its day is barely an hour longer than ours, its year twice ours, and the Sun looks smaller there. Jupiter has four moons turning round it as ours does round us. The Countess thinks it more regular that all planets should circle the Sun; the narrator invokes Descartes’s vortices—masses of subtle matter whose parts share one general motion while each keeps its own, like a whirlwind. The great vortex bears the planets round the Sun; lesser planets falling into a greater’s vortex are forced to turn round it. Thus the Moon followed us because within reach of our vortex, and Jupiter, ninety times bigger than Earth, brought four little planets under subjection and would have swallowed us had we lain within his sphere. The Countess asks what assures we shall continue as we do; he answers that planets keep within their bounds, like the kings of China forbidden new conquests, each settling where the celestial matter’s strength sustains it.

Jupiter’s Moons and Tycho’s Folly

Jupiter turns on himself in ten hours, so his nights are five; under his poles lie six months of day and six of night, and his year is twelve of ours, hence four moons—finishing their courses in seventeen days, seven, three and a half, and two and forty hours—so that no more than twenty-one hours pass without one of them in view. Daily eclipses divert rather than frighten that world’s inhabitants. The Countess would have the moons’ people as colonies rendering homage; the narrator says they should send deputies with addresses. Jupiter’s power is imaginary, chiefly making them afraid: the nearest moon sees him three hundred and sixty times bigger than our Moon appears to us, hanging overhead, so its people may fear he will overwhelm them, as the Gauls feared the heavens would fall. The Countess notes everyone has a peculiar folly. The narrator recalls Tycho Brahe, who felt no dread at an eclipse when all others were in consternation, yet would shut himself up for a day if a hare crossed him or an old woman bolted upon him at his first coming out. The Countess answers that it would be unreasonable such a man could not redeem himself from fear of eclipses without falling into another whim as troublesome; that moon’s inhabitants shall come under the general rule and fall into another error.

Saturn, Mercury, and the Temperate Middle

The Countess asks, smiling, whether Saturn’s ring is a continual Moon and whether it too is inhabited. The narrator confesses he could almost send colonies everywhere, yet cannot well plant any there, it seems so irregular a habitation. The five little moons cannot but be inhabited; some think the ring is a circle of moons following close with equal motion, and that the five fell out of it. The people of Saturn live miserably: the Sun is but a pale star, and Greenland would be a perfect bagnio in comparison. The Countess shivers at Saturn and burns at Mercury; the narrator says the two extremities of the vortex must be opposite in all things. She concludes they must be very wise in Saturn, since he told her all were fools in Mercury. He says they have all the appearances of being phlegmatic—they know not what it is to laugh, take a day to answer the least question, and would think Cato a Merry-Andrew. She finds it odd that one world is all life and the other quite contrary, supposing it is because our Earth stands in the middle and partakes of both extremes. He approves: we are a mixture of the several kinds found in the rest of the planets, a fantastical assembly collected out of different worlds, so we need not travel to see the other worlds in epitome at home. She gives thanks that she is seated in the most temperate planet and region, and he replies she has more reason to thank Heaven that she is young, handsome, and a Frenchwoman.

The Countess Turns Demonstrator

The Countess, warming to the argument, asks to be taken for a Doctor and demands further proofs of the Earth’s motion. The narrator agrees with pleasure, confessing that the demonstration pleases him strangely—perhaps because he fancies it his own discovery, though it is so good and natural that he dare not claim to be its inventor. He notes that a learned man, pressed for objections, would be forced to hold forth at large, and that this is the surest way to confound him. The choice before them is stark: either all the celestial bodies circle the Earth every twenty-four hours, or the Earth turns on itself and imparts that apparent motion to them. That the heavens actually revolve around us in a day has the least appearance of truth in the world, though the absurdity is not immediately obvious.

The Order of the Heavens

Nature, the narrator observes, keeps a consistent order. All the planets make their great revolutions about the Sun in times proportioned to their distances, the most remote taking longest—an arrangement most agreeable to Nature. The same rule holds among the secondary planets: the four moons of Jupiter and the five of Saturn complete their circles in more or less time according to their remoteness. The planets also turn on their own centers at unequal rates, whether from their differing magnitudes or the differing swiftness of the vortices that enclose them, the inequality itself being beyond doubt. It is Nature’s general order that whatever is common to many things varies in some particulars.

The Impossible Equality

The Countess interrupts, saying she understands and agrees: if the planets turned about the Earth, they would do so in unequal times according to their distances, just as they do about the Sun. The narrator confirms it exactly, adding that their unequal distances from the Earth, their different magnitudes, and the differing rapidity of the vortices ought to produce differences in any pretended motion around us. The fixed stars, at prodigious distance and elevated above everything that could take a general motion around us, would show every appearance of not turning at all in twenty-four hours, as the near Moon does; and comets, strangers in our vortex running such differing courses with such unequal rapidity, should be excused from turning round us in the same space. Yet stars, comets, and all must turn round the Earth in twenty-four hours with the most exact equality—the only exact equality in the world, not one minute more or less allowed. The Countess, convinced this grand equality exists only in our imagination, is pleased that what is against the genius of Nature should fall on ourselves and that Nature stands discharged.

The Earth’s Unequal Turns

The narrator declares himself such a foe to perfect equality that he cannot allow the Earth’s daily turns to be precisely twenty-four hours and always equal; he inclines to think there are variations. The Countess asks whether pendulums do not mark an entire equality. He objects to her pendulums: they cannot be altogether just, and when they show one circuit of twenty-four hours longer or shorter than another, we should rather believe them irregular than suspect the Earth. He would no more depend on the Earth than on a pendulum, though more time must be allowed the Earth than a pendulum to fall out of order. The Earth might draw nearer the Sun, where matter is more agitated and motion more rapid, completing her revolution in less time and shortening years and days—but imperceptibly, since we still divide years into 365 days and days into 24 hours; without living longer we should live more years, and withdrawing from the Sun we should live fewer years yet have lives of the same extent. The Countess observes that long successions of ages will make but little variation.

The Face in the Moon

The narrator agrees, praising Nature’s nice conduct and her method of bringing things about by insensible degrees. The Lady’s Face in the Moon, discovered with telescopes within twenty years, has grown considerably old—cheeks sunk, nose long, chin and forehead meeting, all graces vanished. The Countess asks what story he tells; he insists it is no imposition: a figure resembling a woman’s head jutting out of rocks was perceived, and changes have left three points serving for the forehead, nose, and chin of an old woman. The Countess asks if some Destiny is spiteful to Beauty. He suggests changes on our Earth may dress out some face seen by Lunar inhabitants, since everyone bestows on objects ideas of which they are full—astronomers see women’s faces, and ladies might discern fine men; he fancies her Ladyship’s charms there.

Hercules and the Mediterranean

Returning to the Earth’s changes, he recounts that old fables tell how Hercules split asunder with his hands the mountains Calpe and Abila between Africa and Spain, which had stopped the Ocean, so the sea rushed over the land and made the Mediterranean Gulf. This is not wholly fabulous but a history of remote times disguised by ignorance or love of the marvellous—the two most ancient frailties of mankind. That Hercules separated two mountains with his hands is incredible, but that in the time of one Hercules (of whom there were fifty) the Ocean forced down two mountains with an earthquake’s assistance and took its course between Europe and Africa is easy to believe. The Lunar inhabitants might suddenly discover a notable spot on our Earth, since seas are spots. It is commonly thought Sicily was separated from Italy and Cyprus from Syria; new islands form in seas; earthquakes have swallowed mountains. Philosophers apprehend that the kingdoms of Vaons and Sicily, seated on great subterranean vaults full of sulphur, will one day sink when the vaults can no longer resist the flames that exhale at Vesuvius and Aetna.

What the Heavens Are For

The argument that runs through every evening is a campaign against human vanity, and its instrument is scale. The narrator compares us to an Athenian who fancied that all the ships entering the Piraeus belonged to him; so we believe all nature is designed for our use, and a philosopher coldly answers that the fixed stars were made to please our sight. Once the Earth is stripped of its central place and set among the planets, the old astronomy collapses into a kind of economy: Nature is a great housewife, magnificent in the design but frugal in the execution, and the ancients who piled up crystal heavens and epicycles spent ten times the necessary charge. The Countess takes the point quickly and turns it back on the narrator—his philosophy is a kind of outcry where he that offers to do the work cheapest carries it. The joke is not idle. It names the standard by which the book asks to be judged: a system is to be preferred when it explains the same appearances with less machinery.

The same deflating logic governs the book’s treatment of light. The Moon shines because it is a solid body from which the particles of light rebound; the Earth must do the same, and the only reason we do not see it as a body of light is that we are too near it, just as the only reason we do not see the Moon as a great mass fit to furnish provisions for animals is that we are too far away. The Countess draws the moral: we are dazzled by the quality and fortune of those above us, when examined nicely we are all upon a level. The narrator agrees that we judge from the wrong places, too near to judge ourselves and too far off to know others. The true vantage, he says, is to stand between the Moon and the Earth, purely a spectator of this world and not an inhabitant.

The Inhabitants We Cannot See

Fontenelle’s most disarming move is to make the plurality of worlds a lesson in humility rather than a catalogue of marvels. The famous comparison of the Moon to St. Dennis and every man to a Parisian who has never left the city reduces the skeptic to a Cockney who denies that the suburb is inhabited because he cannot make out the people from the towers of Notre-Dame. The Countess protests that the comparison is too severe on his fellow citizens, since St. Dennis is just like Paris, whereas the Moon is not at all like the Earth—and the narrator answers that if the Moon resembles the Earth, she is under a necessity to believe it inhabited. The argument is circular on purpose, and the book knows it. What it offers instead of proof is a disciplined use of analogy, kept honest by the author’s repeated confession that he has never seen the inhabitants and never affirmed there are men in the Moon. The preface’s worry about theology—that no descendant of Adam ever travelled there, nor were colonies planted—is met not by refutation but by a change of subject: the objection, he says, concerns nobody but the men in the Moon.

The book’s most striking speculative passage extends the same humility to time. The narrator offers to justify a ridiculous thought, that one day there may be communication between Earth and Moon, and he does it by way of America. Its people, ignorant of navigation, could not have believed in ships that command the winds, yet the ships came. The art of flying is but newly invented, will improve by degrees, and in time grow perfect. The Countess calls this raving, and the narrator answers with the slow unfolding of the map: the Torrid and Frigid Zones once thought uninhabitable, the Antipodes once unthinkable, each in turn discovered. The World will unfold itself more hereafter. It is a plea against confidence, delivered by a man who cheerfully admits his own fancies.

Worlds That Are Born and Die

The later evenings turn from geography to mutability, and here the book’s tone darkens. The fixed stars are so many suns, each the center of a vortex; but stars seen for thousands of years are now no longer to be seen, and the inhabitants of a vortex whose sun is extinguished are left in eternal night. The narrator’s allegory of the roses makes the point with unusual force: if roses lasting but a day could write histories, the first rose would draw an exact picture of the gardener, and after fifteen thousand rose-ages his descendants, seeing no change, would conclude that the gardener is still the same and therefore certainly will die as they do. We whose lives are but a span ought not to make our continuance the measure of any other being’s duration. It is not easy, he observes, to be eternal. The Countess, who earlier trembled at the thought of a pale sun, finds the worlds far from immortality, like roses that blow one day and die the next.

Yet the book refuses to end in desolation. If old stars disappear, new ones come in their room, since every species must preserve itself; the narrator is inclined to believe that matter proper to make a sun gathers at long run into one place and lays the foundation of a new world. Nature, he is persuaded, can put the same secret in practice upon worlds that she practices upon herbs and plants. The Countess, who has followed him from the Earth’s two motions to the death of suns, comes to herself again at the thought that the heavens are as subject to change as the ground under her feet.

The Oration and the Book’s Afterlife

The volume closes not with the Countess but with Addison, whose Oxford oration in defence of the new philosophy is appended to the conversations. Its presence is a reminder that Fontenelle’s book travelled as a weapon in a controversy as well as a diversion for the curious: the translator’s preface and the added oration both frame the dialogues as an intervention on the side of the moderns. Within the dialogues themselves the same partisanship surfaces in small ways—the King of Aragon who told God how he might have framed the world better, the crystal heavens melted down like broken glass once comets broke through them, the authorities now “not worth a rush.” Fontenelle’s achievement is to have made that partisanship agreeable. He wrote philosophy as conversation, gave the argument to a woman who could not be fobbed off with easy answers, and trusted that a reader diverted would also be instructed. The book’s long life in translation, and the readiness of editors to add defences of the new astronomy to it, suggest the trust was not misplaced.