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But there are arguments on the other side. About mirrors there are two opinions; some people think that only phantoms are seen in them; in other words, the shape of our bodies, an emanation separated from our bodies. Others, however, affirm that images do not exist in the mirror, but that it is the very bodies that are seen, the eyesight being bent back and reflected on itself again. Now, the point is not how do we see whatever it is we see: the question is, how the image should resemble the original in the cloud as in a mirror.28 Could anything be more unlike than the sun and a rainbow in which neither the colour nor the shape nor the size of the sun is to be seen? A bow is far larger and, in the bright part, far redder than the sun: in the other colours, too, it is different from him. Besides, when you insist on comparing a mirror to the atmosphere (i.e. as embodied in a cloud), you must show me in the latter the same smoothness of texture, the same levelness of surface, the same brightness as in the former. But surely no clouds resemble mirrors to this extent. We often pass through the middle of clouds without seeing ourselves in them. People who climb to the tops of mountains look down on cloud, but cannot make out their reflection in it. True enough, but it is separate drops that are separate mirrors, says my opponent. Admitted. Still, I deny that a cloud consists of fully formed drops. It no doubt contains the elements from which the drops are formed, but not as drops. Clouds do not contain even water, but only the material to form water. Granting, for the sake of argument, that there are countless drops in the clouds and that they can reflect an object, yet they do not all produce one and the same reflection, but each its own. Further, you may join mirrors to one another, but they will not unite to form a single reflection: each portion will enclose a likeness of the object. Some mirrors are composed of a large number of very small parts. Set before them one man and a whole people is reflected, each portion producing an image of its own. The portions of the mirror thus united and placed side by side none the less keep their images separate, and out of one man make a crowd. But they do not blend in one that troop; they separate and distinguish the individual faces. Now, a rainbow is bounded by a single outline, the whole presents but one representation.
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Well, but, says our opponent, is not the water that is scattered from a burst pipe, or that is tossed up by the oar, wont to exhibit something similar to these colours that are seen in the bow? True, but not for the reason which you wish to bring out, to wit, that each single droplet receives an image of the sun. As a matter of fact, the drops fall too quickly to be able to form such an image. The medium must be stationary in order to receive the impression of what is to be reproduced.
How, then, it may be asked, does it come about? The drops, I reply, receive the colour, but not the image of the sun. Besides, as Nero Caesar says very elegantly:
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The neck of Venus’ dove glitters as the bird tosses its head, and so the neck of the peacock shines with varied colours as often as it is turned hither and thither. Are we, therefore, to say that feathers of this kind, whose every turn passes into new colours, are mirrors? Well, clouds differ in character from mirrors no less than the birds mentioned, and as chameleons and the other animals whose colour changes. In the latter case the cause is sometimes subjective: the creatures when inflamed with anger or passion vary their hue through the suffusion of moisture: at other times the position of the light, direct or slanting, gives the colour its particular hue. What resemblance, I say, is there between mirrors and clouds? Whereas those are not translucent, these transmit light. Those are dense and compact, these are rare. Mirrors are of uniform material throughout, clouds are made up of various elements brought together at random, and therefore are full of internal strife, and cannot long hold together. Consider further; at sunrise one sees a certain portion of the sky ruddy; at other times one sees clouds of fiery red. This particular colour is received by the clouds from encountering the sun: what, then, is there to prevent the many colours of the bow being derived by them in the same way from him, even though they do not possess the power of mirrors? A little ago, my opponent retorts, you advanced the argument that the rainbow is always produced opposite the sun, because an image could not be reflected from a mirror unless the object were in front of it. We agree in this point, he adds. Yes, for just as the object whose image is to be transferred to the mirror must be set opposite the mirror, in like manner, in order that the clouds may be tinged by the sun’s rays, the sun must occupy a suitable position. He does not produce the same effect if his light streams in on all sides; there must be a proper incidence of the rays to produce the effect. Such are the reasons alleged by those who will have it that the rainbow is a coloured cloud.
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Posidonius and those who are of opinion that the phenomenon is produced by reflection as from a mirror, answer their arguments thus: If there were any real colour in a bow, it would persist, and be seen more distinctly, the nearer it is. As it is, the image of the bow is clear only in the distance; it is lost as it begins to approach. I do not agree with this argument in refutation, though I approve the main sentiment which it supports. And I will tell you why. The cloud is coloured, but in such a way that the colour cannot be seen from every point. And no more can the cloud itself: for no one who is in it can see it. What wonder, then, if its colour cannot be seen by one to whom itself is not visible? And yet, although the cloud is not seen, it is there: and so is the colour. It is, therefore, no proof of the deceptiveness of the colour that it ceases to be manifest when one approaches it. For, I repeat, the same happens to the clouds themselves: they are not all a sham merely because under certain conditions they cease to be visible. Besides, when you are told that the cloud is dyed by the sun, it does not mean that that colour of his is mingled, as it were, with a hard, firm, durable body, but with a liquid unstable body that is incapable of more than a very brief impress. Let me add that there are certain artificial colours which display their virtue at a distance. The better and richer the Tyrian purple is, the higher up you must hold it to display its full blaze. It does not cease to possess its colour simply because it does not reveal its best shade in any and every position in which it is exhibited. I am of the same opinion as Posidonius in holding that the bow is formed in a cloud shaped like a hollow round mirror, whose form is that of a section through a ball. This cannot be proved without the aid of geometry: the mathematical proofs leave no doubt that the bow is an image of the sun, but one that does not resemble it. Nor, indeed, are all objects faithfully represented in mirrors. There are some mirrors one is terrified to let one’s eyes rest upon, such is the misshapen and distorted image they reproduce of those who gaze upon them. They deform the likeness they preserve withal. Some, again, there are, a glance at which causes great self-satisfaction in one’s strength: the arms are enormously increased, and the appearance of the whole body is enlarged to superhuman proportions. There are mirrors that turn faces to the right, and mirrors that turn them to the left, others twist and even invert them. What wonder, then, that a mirror of this kind should be formed in a cloud by which a defective appearance of the sun should be presented?