considerably larger than the moon? [Sidenote: B] At least mathematicians tell us so, calculating the magnitude of the obscuring body from what takes place in eclipses, and from the passages of the moon through the shadow. For the shadow of the earth is less as it extends, because the illuminating body is greater, and its upper extremity is fine and narrow, as even Homer,[310] they say, did not fail to notice. He called night “pointed” because of the sharpness of the shadow. Such, at any rate, is the body by which the moon is caught in her eclipses, and yet she barely gets clear by a passage equal to three of her own diameters.
Just consider how many moons go to make an earth, if the earth cast a shadow as broad, at its shortest, as three moons. Yet you have fears for the moon lest she should tumble, while as for our earth, Aeschylus[311] has perhaps satisfied you that Atlas [Sidenote: C] _Stands, and the pillar which parts Heaven and Earth His shoulders prop, no load for arms t’ embrace._ Then, you think that under the moon there runs light air, quite inadequate to support a solid mass, while the earth, in Pindar’s[312] words, is compassed “by pillars set on adamant”. And this is why Pharnaces has no fear on his own account of the earth’s falling, but pities those who lie under the orbit of the moon, Ethiopians, say, or Taprobanes, on whom so great a weight might fall! Yet the moon has that which helps her against falling, in her very speed and the swing of her passage round, as objects placed in slings are hindered from falling by the [Sidenote: D] whirl of the rotation. For everything is borne on in its own natural direction unless this is changed by some other force.
Therefore the moon is not drawn down by her weight, since that tendency is counteracted by her circular movement. Perhaps it would be more reasonable to wonder if she were entirely at rest as the earth is, and unmoved. As things are, the moon has a powerful cause to prevent her from being borne down upon us; but the earth, being destitute of any other movement, might naturally be moved[313] by its own weight; being heavier than the moon not merely in proportion to its greater bulk, [Sidenote: E] but because the moon has been rendered lighter by heat and conflagration. It would actually seem that the moon, if she is a fire, is in need of earth, a solid substance whereon she moves and to which she clings, so feeding and keeping up the force of her flame. For it is impossible to conceive fire as maintained without fuel. But you Stoics say that our earth stands firm without foundation or root.’ ‘Of course,’ said Pharnaces, ‘it keeps its proper and natural place, namely the essential middle point, that place around which all weights press and [Sidenote: F] bear, converging towards it from all sides. But all the upper region, even if it receive any earth-like body thrown up with force, immediately thrusts it out hitherward, or rather lets it go, to be borne down by its own momentum.’
VII. At this point, wishing Lucius to have time to refresh his memory, I called on Theon: ‘Theon, which of the tragic poets has said that physicians _Purge bitter bile with bitter remedies?_’ Theon answered that it was Sophocles.[314] ‘And physicians must be allowed to do so,’ I said, ‘we cannot help it. But philosophers must not be listened to, if they choose to meet paradoxes with paradoxes, and, when contending against strange views, to invent views which are more strange and wonderful still. [Sidenote: 924] Here are these Stoics with their “tendency towards the middle”! Is there any paradox which is not implicit there? That our earth, with all those depths and heights and inequalities, is a Sphere? That there are people at our antipodes who live like timber-worms or lizards, their lower limbs turned upper-most as they plant them on earth? That we ourselves do not keep perpendicular as we move, but remain on the slant, swerving like drunkards? That masses of a thousand talents’ weight, borne through the depth of the earth, stop when they reach the middle point, though nothing meets or resists them; or, if mere momentum carry them down beyond the middle point, they wheel round and turn back of themselves? That [Sidenote: B] segments of beams[315] sawn off at the surface of the earth on either side, do not move downwards all the way, but as they fall upon the surface receive equal thrusts from the outside inwards and are jammed around the middle? That water rushing violently downwards, if it should reach this middle point—an incorporeal point as they say—would stand balanced around it for a pivot, swinging with an oscillation which never stops and never can be stopped? Some of these a man could not force himself [Sidenote: C] to present to his intellect as possible, even if untrue! This is to make _Up down, down up, where Topsy-Turvy reigns_,[316] all from us to the centre down, and all below the centre becoming up in its turn! So that if a man, by the “sympathy” of earth, were to stand with the central point of his own body touching the centre, he would have his head up and his feet up too! And if he were to dig into the space beyond, the down part of his body would bend upwards, and the soil would be dug out from above to below; and if another man could be conceived meeting him, the feet of both would be said to be up, and would really become so!
VIII. ‘Such are the monstrous paradoxes which they shoulder and trail along, no mere wallet, Heaven help us! but [Sidenote: D] a conjurer’s stock-in-trade and show-booth; and then they call other men triflers, because they place the moon, being an earth, up above, and not where the middle point is. And yet if every weighty body converges to the same point with all its parts, the earth will claim the heavy objects, not so much because she is middle of the whole, as because they are parts of herself; and the inclination of falling bodies will testify, [Sidenote: E] not to any property of earth[317], as middle of the universe, but rather to a community and fellowship between earth and her own parts, once ejected, now borne back to her. For as the sun draws into himself the parts of which he has been composed, so earth receives the stone as belonging to her, and drawn down towards herself; and thus each of such objects becomes united with her in time and grows into herself. If there is any body neither assigned originally to the earth, nor torn away from it, [Sidenote: F] but having somehow a substance and nature of its own, such as they would describe the moon to be, what is there to prevent its existing separately, self-centred, pressed together and compacted by its own parts? For it is not proved that earth is the middle of the universe, and, further, the way in which bodies here are collected and drawn together towards the earth suggests the manner in which bodies which have fallen together on to the moon may reasonably be supposed to keep their place with reference to her. Why the man who forces all earth-like and heavy objects into one place, and makes them parts of one body, does not apply the same law of coercion to light bodies, I cannot see, instead of allowing all those fiery structures to exist apart; nor why he does not collect all the stars into the same place, and hold distinctly that there must be a body common to all upward-borne and fiery units.
[Sidenote: 925] IX. ‘But you and your friends, dear Apollonides, say that the sun is countless millions of stades distant from the highest circle, and that Phosphor next to him, and Stilbon, and the other planets, move in a region below the fixed stars and at great intervals from one another; and yet you think that the universe provides within itself no interval in space for heavy and earth-like bodies. You see that it is ridiculous to call the moon no earth because she stands apart from the region below, and then to call her a star while we see her thrust so many [Sidenote: B] myriads of stades away from the upper circle as though sunk into an abyss. She is lower than the stars by a distance which we cannot state in words, since numbers fail you mathematicians when you try to reckon it, but she touches the earth in a sense and revolves close to it, _Like to the nave of a wagon, she glances_, says Empedocles,[318] _which near the mid axle..._ For she often fails to clear even the shadow of earth, rising but little,[319] because the illuminating body is so vast. But so nearly does she seem to graze the earth and to be almost in its embrace as she circles round, that she is shut off from the sun by it unless [Sidenote: C] she rises enough to clear that shaded, terrestrial region, dark as night, which is the appanage of earth. Therefore I think we may say with confidence that the moon is within the precincts of earth when we see her blocked by earth’s extremities.
X. ‘Now leave the other fixed stars and planets, and consider the conclusion proved by Aristarchus in his _Magnitudes and Distances_;[320] that the distance of the sun is to the distance of the moon from us in a ratio greater than eighteen to one, [Sidenote: D] less than twenty to one. Yet the highest estimate of the distance of the moon from us makes it fifty-six times the earth’s radius, and that is, even on a moderate measurement, forty thousand stades. Upon this basis, the distance of the sun from the moon works out to more than forty million three hundred thousand stades. So far has she been settled from the sun because of her weight, and so nearly has she approached the earth, that, if we are to distribute estates according to localities, the “portion and inheritance of the earth” invites the moon to join her, and the moon has a next claim to chattels and persons [Sidenote: E] on earth, in right of kinship and vicinity. And I think that we are not doing wrong in this, that while we assign so great and profound an interval to what we call the upper bodies, we also leave to bodies below as much room for circulation as the breadth from earth to moon. For he who confines the word “upper” to the extreme circumference of heaven, and calls all the rest “lower”, goes too far, and on the other hand he who circumscribes “below” to earth, or rather to her centre, is preposterous. On this side and on that the necessary interval must be granted,[321] since the vastness of the universe permits. Against the claim that everything after we leave the earth is “up” and poised on high, sounds the counterclaim that everything [Sidenote: F] after we leave the circle of the fixed stars is “down”!
XI. ‘Look at the question broadly. In what sense is the earth “middle”, and middle of what? For the Whole is infinite; now the Infinite has neither beginning nor limit, so it ought not to have a middle; for a middle is in a sense itself a limit, but infinity is a negation of limits. It is amusing to hear a man labour to prove that the earth is the middle of the universe, not of the Whole, forgetting that the universe itself lies under the same difficulties; for the Whole, in its [Sidenote: 926] turn, left no middle for the universe. “Hearthless and homeless”[322] it is borne over an infinite void towards nothing which it can call its own; or, if it find some other cause for remaining, it stands still, not because of the nature of the place. Much the same can be conjectured about the earth and the moon; if one stands here unshaken while the other moves, it is in virtue of a difference of soul rather than of place and of nature. Apart from all this, has not one important point escaped them? If anything, however great, which is outside the centre of the earth is “up”, then no part of the universe is “down”.
Earth is “up”, and so are the things on the earth, absolutely [Sidenote: B] every body lying or standing about the earth becomes “up”; one thing alone is “down”, that incorporeal point which has of necessity to resist the pressure of the whole universe, if “down” is naturally opposed to “up”. Nor is this absurdity the only one. Weights lose the cause of their downward tendency and motion here, since there is no body below towards which they move. That the incorporeal should have so great a force as to direct all things towards itself, or hold them together about itself, is not probable, nor do they mean this. No! it is found on all grounds[323] to be irrational, and against the facts, that “up” should be the whole universe, and “down” nothing but an incorporeal and indivisible limit. The other view is reasonable, which we state thus, that a large space, possessing breadth, is apportioned both to “the XII. ‘However, let us assume, if you choose, that it is [Sidenote: C] contrary to nature that earth-like bodies should have their motions in heaven; and now let us look quietly, with no heroics, at the inference, which is this, not that the moon is not an earth, but that she is an earth not in its natural place. So the fire of Aetna is fire underground, which is contrary to nature, yet is fire; and air enclosed in bladders is light and volatile by nature, but has come perforce into a place unnatural to it. And the soul, the soul itself,’ I went on, ‘has it not been imprisoned in the body contrary to nature, a swift, and, as you hold, a fiery soul in a slow, cold body, the invisible within the sensible? Are we therefore to say that soul in body is nothing, and not rather that Reason, that divine thing, has been made subject to weight and density, that one which ranges all heaven [Sidenote: D] and earth and sea in a moment’s flight has passed into flesh and sinews, marrow and humours, wherein is the origin of countless passions?[324] Your Lord Zeus, is he not, so long as he preserves his own nature, one great continuous fire? Yet we see him brought down, and bent, and fashioned, assuming, and ready to assume, any and every complexion of change. Look well to it, my friend, whether when you shift all things [Sidenote: E] about, and remove each to its “natural” place, you are not devising a system to dissolve the universe and introducing Empedoclean strife, or rather stirring up the old Titans against Nature, in your eagerness to see once more the dreadful disorder and dissonance of the myth? All that is heavy in a place by itself, and all that is light in another, _Where neither sun’s bright face is separate seen, Nor earth’s rough brood, nor ocean any more_, [Sidenote: F] as Empedocles says! Earth had nothing to do with heat, water with wind; nothing heavy was found above, nothing light below; without commixture, without affection were the principles of all things, mere units, each desiring no intercourse with each or partnership, performing their separate scornful motions in mutual flight and aversion, a state of things which must always be, as Plato[325] teaches, where God is absent, the state of bodies deserted by intelligence and soul. So it was until the day when Providence brought Desire into Nature, and [Sidenote: 927] Friendship was engendered there, and Aphrodite, and Eros, as Empedocles tells us and Parmenides too and Hesiod,[326] so that things might change their places, and receive faculties from one another in turn, and, from being bound under stress, and forced, some to be in motion some to rest, might all begin to give in to the Better, instead of the Natural, and shift their places and so produce harmony and communion of the Whole.
XIII. ‘For if it be true that no other part of the universe departed from Nature, but that each rests in its natural place, not needing any transposition or rearrangement, and never from the first having needed any, I am at a loss to know what there is for Providence to do, or of what Zeus, “in art most excellent”,[327] is the maker and the artist-father. There would [Sidenote: B] be no need of tactics in an army if each soldier knew of himself how to take and keep place and post at the proper time; nor of gardeners or builders if the water of its own nature is to flow over the parts which need it, and moisten them, or if bricks and beams should of themselves adopt the movements and inclinations which are natural, and arrange themselves in their fitting places. If such a theory strike out Providence [Sidenote: C] altogether, and if it be God’s own attribute to order and discriminate things, what marvel is it that Nature has been so disposed and partitioned that fire is here and stars there, and again that earth is planted where it is and the moon above, each held by a firmer bond than that of Nature, the bond of Reason? Since, if all things are to observe natural tendencies, and to move each according to its nature, let the sun no longer go round in a circle, nor Phosphorus, nor any of the other stars, because it is the nature of light and fiery bodies to move upwards, not in a circle! But if Nature admits of such local variation as that fire, here seen to ascend, yet when it reaches heaven, joins in the general rotation, what marvel if heavy [Sidenote: D] and earthlike bodies too, when placed there, assume another kind of motion, mastered by the circumambient element? For it is not according to Nature that light things lose their upward tendency in heaven, and yet heaven cannot prevail over those which are heavy and incline downwards. No, heaven at some time had power to rearrange both these and those, and turned the nature of each to what was better.
XIV. ‘However, if we are at last to have done with notions enslaved to usage,[328] and to state fearlessly what appears to be true, it is probable that no part of a whole has any order, or position, or movement of its own which can be described in absolute terms as natural. But when each body places itself at the disposal of that on account of which it has come into being, [Sidenote: E] and in relation to which it naturally exists or has been created, to move as is useful and convenient to it, actively and passively and in all its own states conforming to the conservation, beauty, or power of that other, then, I hold, its place, movements and disposition are according to Nature. In man certainly, who has, if anything has, come into being according to Nature, [Sidenote: F] the heavy and earth-like parts are found above, mostly about the head, the hot and fiery in the middle regions; of the teeth one set grows from above, the other from below, yet neither contrary to Nature; nor can it be said of the fire in him that when it is above and flashes in his eyes it is natural, but when it is in stomach or heart, unnatural; each has been arranged as is proper and convenient.
_Mark well the tortoise and the trumpet-shell_, says Empedocles, and, we may add, the nature of every shell-fish, and _Earth uppermost, flesh under thou shalt see._ Yet the stony substance does not squeeze or crush the growth[329] [Sidenote: 928] within, nor again does the heat fly off and be lost because of its lightness; they are mingled and co-ordinated according to the nature of each.
XV. ‘And so it is probably with the universe, if it be indeed a living structure; in many places it contains earth, in many others fire, water, and wind, which are not forced out under stress, but arranged on a rational system. Take the eye; it is not where it is in the body owing to pressure acting on its light substance, nor has the heart fallen or slipped down [Sidenote: B] into the region of the chest because of its weight; each is arranged where it is because it was better so. Let us not then suppose that it is otherwise with the parts of the universe; that earth lies here where it has fallen of its own weight, that the sun, as Metrodorus of Chios used to think, has been pressed out into the upper region because of his lightness, like a bladder, or that the other stars have reached the places which they now hold as if they had been weighed in a balance and kicked the beam. No, the rational principle prevailed; and some, like eyes to give light, are inserted into the face of the Whole and revolve; the sun acts as a heart, and sheds and distributes out of himself heat and light, as it were blood and breath.
[Sidenote: C] Earth and sea are to the universe, according to Nature, what stomach and bladder are to the animal. The moon, lying between sun and earth, as the liver or some other soft organ between heart and stomach, distributes here the gentle warmth from above, while she returns to us, digested, purified, and refined in her own sphere, the exhalations of earth. Whether her earth-like solid substance contributes to any other useful purposes, we cannot say. We do know that universally the Better prevails over the law of Stress. How can the view of the Stoics lead us to any probable result? That view is, that the luminous and subtle part of the atmosphere has by its rarity formed the [Sidenote: D] sky, the dense and consolidated part stars, and that, of the stars, the moon is the dullest and the grossest. However, we may see with our eyes that the moon is not entirely separated from the atmosphere, but moves within a great belt of it, having beneath itself a wind-swept region, where bodies are whirled, and amongst them comets.
Thus these bodies have not been placed in the scales according to the weight or lightness of each, but have been arranged upon a different system.’
XVI. This said, as I was passing the turn to Lucius, the [Sidenote: E] argument now reaching the stage of demonstration, Aristotle said with a smile: ‘I protest that you have addressed your whole reply to those who assume that the moon herself is half fire, and who say of all bodies in common that they have an inclination of their own, some an upward one, some a downward. If there is a single person who holds that the stars move in a circle according to Nature, and are of a substance widely [Sidenote: F] different from the four elements, it has not occurred to our memory, even by accident; so that I am out of the discussion, and you also, Lucius.’ ‘No, no, good friend’, said Lucius. ‘As to the other stars, and the heaven in general, when your school asserts that they have a nature which is pure and transparent, and removed from all changes caused by passion, and when they introduce a circle of eternal[330] and never-ending revolution, perhaps no one would contradict you, at least for the present, although there are countless difficulties. But when the theory comes down and touches the moon, it no longer retains in her case the “freedom from passion” and the beauty of form of that body. Leaving out of account her other irregularities and points of difference, this very face which appears upon her has come there either from some passion proper to herself or by admixture of some other substance. [Sidenote: 929] Indeed, mixture implies some passion, since there is a loss of its own purity when a body is forcibly filled with what is inferior to itself. Consider her own torpor and dullness of speed, and her heat, so faint and ineffectual, wherein, as Ion[331] says— _The black grape ripens not_; to what are we to assign this, but to weakness in herself and passion, if passion can have place in an eternal and Olympian body? It comes to this, dear Aristotle; look on her as earth, and she appears a very beautiful object, venerable and highly adorned; but as star, or light, or any divine or heavenly body, I fear she may be found wanting in shapeliness and grace, and do no credit to her beautiful name, if out of all the multitude in heaven she alone goes round begging light of others, as Parmenides says, [Sidenote: B] _For ever peering toward the sun’s bright rays._ Now when our comrade, in his dissertation, was expounding the proposition of Anaxagoras, that “the sun places the brightness in the moon”, he was highly applauded. But I am not going to speak of things which I learned from you or with you, I will gladly pass on to the remaining points. It is then probable that the moon is illuminated not as glass or crystal by the sunlight shining in and through her, nor yet by way of accumulation of light and rays, as torches when they multiply their light. For then we should have full moon at the beginning of the month just as much as at the middle, if she does not conceal or block the sun, but allows him[332] to pass through [Sidenote: C] because of her rarity, or if he, by way of commixture, shines upon the light around her and helps to kindle it with his own. For it is not possible to allege any bending or swerving aside on her part at the time of her conjunction, as we can when she is at the half, or is gibbous or crescent. Being then “plumb opposite”, as Democritus puts it, to her illuminant, she receives and admits the sun, so that we should expect to see her shining herself and also allowing him to shine through her. Now she is very far from doing this; she is herself invisible at those times, and she often hides him out of our sight.
_So from above for men_, as Empedocles says, [Sidenote: D] _She quenched his beams, shrouding a slice of earth Wide as the compass of the glancing moon_; as though his light had fallen, not upon another star, but upon night and darkness.
‘The view of Posidonius, that it is because of the depth of the moon’s body that the light of the sun is not passed through to us, is wrong on the face of it. For the air, which is unlimited, and has a depth many times that of the moon, is filled throughout with sunlight and brightness. There is left then that of Empedocles, that the illumination which we get from the moon [Sidenote: E] arises in some way from the reflexion of the sun as he falls upon her. Hence her light reaches us without heat or lustre, whereas we should expect both if there were a kindling by him or a commixture of lights. But as voices return an echo weaker than the original sound, and missiles which glance off strike with weaker impact, _E’en so the ray which smote the moon’s white orb_ reaches us in a feeble and exhausted stream, because the force is dispersed in the reflexion.’
XVII. Here Sylla broke in: ‘All these things no doubt [Sidenote: F] have their probabilities; but the strongest point on the other side was either explained away or it escaped our comrade’s attention; which was it?’
‘What do you mean?’ said Lucius. ‘The problem of the half-moon, I suppose?’
‘Precisely,’ said Sylla, ‘for as all reflexion takes place at equal angles, there is some reason in saying that when the moon is in mid-heaven at half-moon, the light is not carried from her on to the earth, but glances off beyond it; for the sun, being [Sidenote: 930] on the horizon, touches the moon with his rays, which will therefore, being reflected at equal angles, fall on the further side and beyond us, and will not send the light here; or else there will be a great distortion and variation in the angle, which is impossible.’
‘I assure you’, said Lucius, ‘that point was mentioned also;’ and here he glanced at Menelaus the mathematician, as he went on: ‘I am ashamed, dear Menelaus,’ he said, ‘in your presence to upset a mathematical assumption which is laid down as fundamental in all the Optics of Mirrors. But I feel obliged to say’, he continued, ‘that the law which requires reflexion in all cases to be at equal angles is neither self-evident [Sidenote: B] nor admitted. It is impugned in the instance of convex mirrors, when magnified images are reflected to the one point of sight. It is impugned also in that of double mirrors, when they are inclined towards one another so that there is an angle between them, and each surface returns a double image from one face, four images in all, two on the right, two on the left, two from the outer parts of the surfaces, two dimmer ones deep within the mirrors.[333] Plato[334] gives the cause why this takes place. He has told [Sidenote: C] us that if the mirrors be raised on either side, there is a gradual shifting of the visual reflexion as it passes from one side to the other. If then some images proceed directly to us, while others glance to the opposite side of the mirrors, and are returned thence to us, it is impossible that reflexion in all cases takes place at equal angles. They observe[335] that these images meet in one point, and further claim that the law of equal angles is disproved by the streams of light which actually proceed from the moon to the earth, holding the fact to be [Sidenote: D] far more convincing than the law. However, if we are so far to indulge the beloved geometry as to make her a present of this law, in the first place it may be expected to hold of mirrors which have been made accurately smooth. But the moon has many irregularities and rough parts, so that the rays proceeding from a large body, when they fall on considerable eminences, are exposed to counter-illuminations and reciprocal dispersion; the cross-light is reflected, involved, and accumulated as though it reached us from a number of mirrors. In the next place, even if we allow that the reflexions are produced at equal [Sidenote: E] angles upon the actual surface of the moon, yet, when the distance is so great, it is not impossible that the rays may be broken in their passage, or glance around, so that the light reaches us in one composite stream. Some go further, and show by a figure that many lights discharge their rays along a line inclined to the hypothenuse; but it was not possible to construct the diagram while speaking, especially before a large audience.[336] XVIII. ‘Upon the whole question,’ he went on, ‘I am at a loss to see how they bring up the half-moon against us; the point fails equally upon her gibbous and crescent phases. For if the moon were a mass of air or fire which the sun illuminated, [Sidenote: F] he would not have left half her sphere always in shadow and darkness as seen by us; but even if he touched her in his circuit only in a small point, the proper consequence would follow, she would be affected all through, and her entire substance changed by the light penetrating everywhere with ease. When wine touches water on its extreme surface, or a drop of blood falls into liquid, the whole is discoloured at once, and turned to crimson. But the air itself, we are told, is not filled with sunshine by emanations or beams actually mingling with it, but by a change and alteration caused by something like a prick or touch. Now, how can they suppose that when star touches star or light light, it does not mingle with or alter the substance throughout, but only illuminates [Sidenote: 931] those points which it touches superficially? The circular orbit of the sun as he passes about the moon, which sometimes coincides with the line dividing her visible and invisible parts, and at other times rises to right angles with that line so as to cut those parts in two, and in turn be cut by her, produces her gibbous and crescent phases by the varying inclination and position of the bright part relatively to that in shadow. This proves beyond all question that the illumination is contact not commixture, not accumulation of light but its circumfusion. But the fact that she is not only illuminated herself but also sends [Sidenote: B] on the image of her brightness to us, allows us to insist the more confidently on our theory of her substance. For reflexions do not take place on a rarefied body, or one formed of subtle particles, nor is it easy to conceive light rebounding from light, or fire from fire; the body which is to produce recoil and reflexion must be heavy and dense, that there may be impact upon it and resilience from it. To the sun himself the air certainly allows a passage, offering no obstructions or resistance; whereas if timber, stones, or woven stuffs be placed to meet his light many cross rays are caused, and there is illumination all [Sidenote: C] round them. We see the same thing in the way his light reaches the earth. The earth does not pass his ray into a depth as water does, nor yet throughout her whole substance as air does. Just as his orbit passes round the moon, gradually cutting off a certain portion of her, so a similar orbit passes round the earth, illuminating a similar part of it and leaving another unilluminated, for the part of either body which receives light appears to be a little larger than a hemisphere. Allow me to speak geometrically in terms of proportion. Here are three bodies approached by the sun’s light, earth, moon, air; we see that the moon is illuminated like the earth, not like the air; but bodies naturally affected in the same way by the same must be themselves similar.’
XIX. When all had applauded Lucius, ‘Bravo!’ said I, [Sidenote: D] ‘a beautiful proportion fitted to a beautiful theory; for you must not be defrauded of your own.’ ‘In that case,’ he said, with a smile, ‘I must employ proportion a second time, in order that we may prove the moon like the earth, not only as being affected in the same way by the same body, but also as producing the same effect on the same. Grant me that no one of the phenomena relating to the sun is so like another as an eclipse to a sunset, remembering that recent concurrence[337] of sun and moon, which, beginning just after noon, showed us [Sidenote: E] plainly many stars in all parts of the heavens, and produced a chill in the temperature like that of twilight. If you have forgotten it, Theon here will bring up Mimnermus and Cydias, and Archilochus, and Stesichorus and Pindar[338] besides, all bewailing at eclipse time “the brightest star stolen from the sky” [Sidenote: F] and “night with us at midday”, speaking of the ray of the sun as “a track of darkness” and, besides all these, Homer[339] saying that the faces of men are “bound in night and gloom” and “the sun is perished out of the heaven”, i.e. around the moon, and how this occurs according to Nature, “when one moon perishes and one is born”. The remaining points have been reduced, I think, by the accuracy of mathematical methods to the one[340] certain principle that night is the shadow of earth, whereas an eclipse of the sun is the shadow of the moon when it falls within our vision. When the sun sets he is blocked from our sight by the earth; when he is eclipsed, by the moon. [Sidenote: 932] In both cases there is overshadowing; in his setting it is caused by the earth, in his eclipses by the moon, her shadow intercepting our vision. From all this it is easy to draw out a theory as to what happens. If the effect is similar, the agents are similar; for the same effects upon the same body must be due to the same agents. If the darkness of eclipses is not so profound, and does not affect the atmosphere so forcibly, let us not be surprised; the bodies which cause respectively night and eclipse are similar in nature, but unequal in size. The Egyptians, I believe, say that the moon’s bulk is one two-and-seventieth part of the earth’s, Anaxagoras made her as large as Peloponnesus; but [Sidenote: B] Aristarchus[341] proves that the