Posidonius and those who are of opinion that the phenomenon is produced by reflection as from a mirror, answer their arguments thus: If there 10 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 11 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 12 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 13 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 14 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? VI Among the other arguments it must be mentioned that a rainbow never 1 is seen greater than a semicircle: the higher the sun is, too, the smaller is the bow. As our countryman Virgil says: