Conversations on the Plurality of Worlds

by M. de Fontenelle

The next morning as soon as the Marchioness was awake, I sent to enquire how she did, and whether she had been able to sleep whilst the globe was turning? I received for answer, that she already felt quite accustomed to the motion; and had slept as undisturbedly as Copernicus himself. Soon afterwards, some company came to spend the whole day with her; a tiresome custom which is always observed in the country; yet long as the visit was, we considered it a great kindness in the guests, not to prolong it to the next day; which I find is a common practice in this part of the world: however, as they had the civility to leave us, the Marchioness and I had the evening to ourselves. We immediately went to the park and resumed our astronomical conversation. She understood so perfectly all I had said on the former evening, that she disdained to hear any repetition of the subject, and desired me to enter on a new one.—Well then, said I, since the sun, which we concluded is immovable, can no longer be considered a planet; and the earth is proved to be one, and to move round the sun; you will be the less surprised to hear, that the moon is a world like ours; and to all appearance, inhabited.—I never heard speak of peopling the moon; she replied, but as a ridiculous, visionary hypothesis.—It may be so, answered I; I only adopt the interest of any party, in these cases, as people do in civil wars; in which the uncertainty of the event, induces them to hold a correspondence with opposite sides, and even, when possible, with their enemies. For my part, though I believe the moon is inhabited, I can be very civil to any one that disbelieves it; and I always retain the power of going over to their side without disgracing myself, if I found they had the advantage: but in the present state of the question I have the following reasons for thinking the moon is inhabited.

Let us suppose that no communication had ever been carried on between Paris and St. Dennis; and that a Parisian who had never gone out of his own city should stand on one of the towers of Notre-Dame, and at that distance view St. Dennis: were he asked if he believed that St. Dennis was inhabited like Paris, he would without hesitation answer, No; I see inhabitants in Paris, but I can discover none at St. Dennis, nor did I ever hear of any being there. Somebody standing by, might answer, that we certainly cannot see them from the towers of Notre-Dame, but that is, because we are at too great a distance; that from all we can discern of St. Dennis it is very much like Paris; that it has steeples, houses, walls; and therefore is very probably inhabited. All this makes no impression on our citizen; he insists upon it that St. Dennis is uninhabited because he does not see any body in it. The moon is our St. Dennis, and each of us is this Parisian who has never left the city in which he resides.

Oh! you wrong us, interrupted the Marchioness; we are not so stupid as your citizen; when he sees that St. Dennis is constructed exactly on the same plan as Paris, he must be out of his senses not to believe it inhabited: but the moon is very different from the earth. Be cautious, madam, said I; if the moon's resemblance to the earth prove it habitable, I shall force you to believe that it is inhabited. I confess, answered she, that if you can shew me the similarity, I cannot pretend to deny its being inhabited, and I see so much confidence in your looks that I am afraid you will be triumphant. The two different motions of the earth, which I never before knew any thing about, make me fearful of hastily rejecting any other opinion; but still, can it be possible that the earth is luminous like the moon?—that you know is essential to their similarity. Indeed, madam, I replied, the luminous quality of planets depends on less than you imagine. The sun alone is, in his nature, luminous; but the planets only reflect the light they receive from him. He enlightens the moon; the moon reflects his rays on the earth, and the earth is undoubtedly in the same manner a source of light to the moon; it is not farther from us to the moon, than from the moon to us.

But, enquired the Marchioness, is the earth equally capable of reflecting the sun's light? I see, answered I, you have an invincible partiality for the moon. Light is composed of globules which rebound from a solid substance, but pass through any thing in which they find interstices, such as air or glass: the moon, therefore, gives us light in consequence of being a hard, solid body, which sends back these globules. I suppose you will not dispute the hardness and solidity of the earth. See then the effect of an advantageous situation—because the moon is at a distance we only view her as a luminous body instead of a large mass of matter similar to the earth. Our globe, on the contrary, from having the ill luck to be more closely inspected, appears only a mass of dark soil, fit for nothing but to produce food for animals; we do not perceive the splendour of her light, because we cannot remove to a distance from her. So it is, answered the Marchioness, with the different ranks of society: we are dazzled with the grandeur of situations superior to our own, without considering how much every condition of human life resembles all the rest.

'Tis precisely the same thing, I replied; we take upon us to decide on every thing, but we are never in a proper place for making our observations. We would form an opinion of ourselves, and we are too near; we would judge of others; they are too distant from our view. We should be placed between the earth and the moon to form a just comparison; a spectator, not an inhabitant of the world. I shall be inconsolable for the injustice we do our world, said she, and the partial regard we have for the moon, unless you can assure me that the inhabitants of that planet are as ignorant of their advantages, and consider our globe a luminous body, without knowing that from their own we derive so much light. I can make you easy on that head, answered I; we are certainly a luminary to them: they do not, it is true, see us describe a circle round them,[19] but that does not signify. The reason of our appearing to remain in the same place is this;—the side of the moon which was turned towards us at the creation, has always continued so; we always observe the same eyes, mouth, and other features of the face which, by the help of imagination, we have contrived out of the spots on her surface.[20] If the other half were presented to us, we should see spots arranged in a different form: this does not arise from the moon's not turning on her axis; she turns in the same time that is employed in going round the earth, that is, a month; but whilst she is performing part of her revolution on her axis, she at the same time performs an equal part of her circle round the earth, and thus, by putting herself in a new situation, continues to shew the same side: therefore although with regard to the sun and the rest of the heavenly bodies the moon evidently turns on her axis, yet when viewed from the earth she does not appear to do so. All the other luminaries seem to the moon to rise and set in the space of a fortnight, but she constantly sees our globe in the same part of the heavens.[21] This apparent immobility, were it invariable, would be thought inconsistent with the nature of a planet; but the moon has a sort of vibratory motion which sometimes conceals a small part of the face, and exhibits a part of the other side. Now, I can venture to say that the inhabitants attribute this motion to us, and imagine that we vibrate in the heavens, like a pendulum.

[19] This is an error, for if they consider the earth's situation relatively to the firmament, they must see that she performs a revolution in twenty-seven days: they certainly always find her answer to their zenith, or at the same distance from the zenith, but at the same time this zenith is continually answering to some new point in the heavens.

[20] When the moon is viewed through a telescope its spots bear no resemblance to the human face; but on contemplating it with the naked eye, it is easy to imagine that form; and it is become so common to talk of the face on the moon, that even an astronomer can hardly divest himself of the idea.

[21] The earth always answers to one side of the moon, but not the same point in the sky.

All the planets, said the Marchioness, are like us human beings, who always attribute to others what belongs to ourselves. The earth says; it is not I who turn, it is the sun. The moon says; it is not I who vibrate, but the earth: there is error throughout. I would not advise you to attempt making any reform, answered I; you had better consider the remaining proofs of the resemblance which the earth and moon bear to each other. Figure to yourself those two globes suspended in the heavens. You know the sun always enlightens one half of a circular body, whilst the other half remains in the shade. There is then one half of both the earth and the moon, which is enlightened by the sun, or in other words, in which it is day, and the other half in which it is night. Observe likewise that as a ball moves with less force and celerity after it has struck against a wall from which it flies off to an opposite place, so the light is weaker when reflected to us from a body that only receives it. The pale light of the moon is in reality the brilliancy of the sun, but as we receive it merely by reflection, in coming to us, it is deprived of its strength. Of course, it shines with much greater splendour on the moon, and for the same reason the dazzling light received by our globe, from the sun, must appear faint, when reflected back to the moon. That part of the moon which to us appears luminous during the night, is the side which has day-light; and the part of the earth which is illuminated by the day, when turned toward the dark side of the moon, affords equal light to her. All this depends on the mutual position of the earth and moon. During the first days of the month, when the moon is not discernible, she is placed between the sun and us, and proceeding in the day time with the sun: the luminous side is therefore necessarily turned to the sun, whilst the dark part is towards the earth. We are unable to see the unenlightened side of the moon, but this dark half viewing the part of our globe in which it is day, is assisted by our light, and though invisible to us, has the advantage of seeing the earth as a full moon: it is then to the lunar inhabitants full-earth, if I may so express myself.[22] After this, the moon advancing in her monthly round, and no longer between the sun and earth, turns towards us a small part of her enlightened half, and that we call the crescent. At the same time that part of the moon which is involved in the obscurity of night, ceases so see all the luminous side of the earth, and finds it continue to decrease.