Greek Texts & Translations

"Winds arise from time to time when foreign matter continually and gradually finds its way into the air ; also through the gathering of great store of water. The rest of the winds arise when a few of them fall into the many hollows and they are thus divided and multiplied.

"Hail is caused by the firmer congelation and complete transformation, and subsequent distribution into drops, of certain particles resembling wind : also by the slighter congelation of certain particles of moisture and the vicinity of certain particles of wind which at one and the same time forces them together and makes them burst, so that they become frozen in parts and in the whole mass. 10.1.107 The round shape of hailstones is not impossibly due to the extremities on all sides being melted and to the fact that, as explained, particles either of moisture or of wind surround them evenly on all sides and in every quarter, when they freeze.

"Snow may be formed when a fine rain issues from the clouds because the pores are symmetrical and because of the continuous and violent pressure of the winds upon clouds which are suitable ; and then this rain has been frozen on its way because of some violent change to coldness in the regions below the clouds. Or again, by congelation in clouds which have uniform density a fall of snow might occur through the clouds which contain moisture being densely packed in close proximity to each other ; and these clouds produce a sort of compression and cause hail, and this happens mostly in spring. 10.1.108 And when frozen clouds rub against each other, this accumulation of snow might be thrown off. And there are other ways in which snow might be formed.

"Dew is formed when such particles as are capable of producing this sort of moisture meet each other from the air : again by their rising from moist and damp places, the sort of place where dew is chiefly formed, and their subsequent coalescence, so as to create moisture and fall downwards, just as in several cases something similar is observed to take place under our eyes. 10.1.109 And the formation of hoar-frost is not different from that of dew, certain particles of such a nature becoming in some such way congealed owing to a certain condition of cold air. "Ice is formed by the expulsion from the water of the circular, and the compression of the scalene and acute-angled atoms contained in it ; further by the accretion of such atoms from without, which being driven together cause the water to solidify after the expulsion of a certain number of round atoms.

"The rainbow arises when the sun shines upon humid air ; or again by a certain peculiar blending of light with air, which will cause either all the distinctive qualities of these colours or else some of them belonging to a single kind, and from the reflection of this light the air all around will be coloured as we see it to be, as the sun shines upon its parts. 10.1.110 The circular shape which it assumes is due to the fact that the distance of every point is perceived by our sight to be equal ; or it may be because, the atoms in the air or in the clouds and deriving from the sun having been thus united, the aggregate of them presents a sort of roundness.

"A halo round the moon arises because the air on all sides extends to the moon ; or because it equably raises upwards the currents from the moon so high as to impress a circle upon the cloudy mass and not to separate it altogether ; or because it raises the air which immediately surrounds the moon symmetrically from all sides up to a circumference round her and there forms a thick ring. 10.1.111 And this happens at certain parts either because a current has forced its way in from without or because the heat has gained possession of certain passages in order to effect this.

"Comets arise either because fire is nourished in certain places at certain intervals in the heavens, if circumstances are favourable ; or because at times the heaven has a particular motion above us so that such stars appear ; or because the stars themselves are set in motion under certain conditions and come to our neighbourhood and show themselves. And their disappearance is due to the causes which are the opposite of these. 10.1.112 Certain stars may revolve without setting not only for the reason alleged by some, because this is the part of the world round which, itself unmoved, the rest revolves, but it may also be because a circular eddy of air surrounds this part, which prevents them from travelling out of sight like other stars ; or because there is a dearth of necessary fuel farther on, while there is abundance in that part where they are seen to be. Moreover there are several other ways in which this might be brought about, as may be seen by anyone capable of reasoning in accordance with the facts. The wanderings of certain stars, if such wandering is their actual motion, and the regular movement of certain other stars,