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I should be somewhat too bold if I were to assure you as on oath that hail is formed in the sky much in the way ice is with us, only that in the former case a whole cloud is frozen. So I may regard myself as a witness only in the second degree—one of those who say not that they have actually seen but have been informed. Or, I may, for once, do as the chroniclers do. After lying at large to their heart’s content, they fix on some one point for which they refuse to vouch, adding: Evidence of this will be found in the authorities. So, if you do not believe me, Posidonius will vouchsafe to you his authority both for the statement I have made, and for one that I am going to make. He will assure you, as confidently as if he had witnessed the process of formation, that hail is formed from a cloud that is charged with rain, and has already turned into moisture. You can discover without a tutor why the hail is round if you observe that drops of all kinds tend to become globular. This is seen, for example, in looking-glasses, which gather moisture from the breath, as well as in cups, and any other smooth surface bedewed with it. So, too, in the leaves of grass or trees, any drops that adhere take a circular form.
What is harder than rock, what softer than water?
Yet the hard rock is hollowed by drops of the soft water;
or, as another poet tells us:
The drip by its fall hollows the stone:
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and this hollow is itself round. Whence it is evident that its shape resembles this drip which hollows it out, sculpturing the spot to its own form and character. Besides, the hail, even were it not of this shape, might be rounded in its fall, and worn equally on all sides into globular form as it is again and again whirled round in its descent through the space of thick air it traverses. Snow, on the contrary, cannot be affected thus, because it is not so solid, being indeed very much scattered, and falling from no great height. It has its source in the neighbourhood of the earth, and its descent is of no great distance through the air, but starts from a point quite close by. Why should I not allow myself the same licence as Anaxagoras in differing from my authorities? Nowhere can equality of rights be claimed with more propriety than among the philosophers. Hail is simply ice held suspended in mid-air; snow is a floating congealed mass of the nature of hoar-frost. I have already said that the difference between water and dew is reproduced in the difference of hoar-frost and ice, and, in like manner, in that between snow and hail.