Book 42: on rains. The water that falls from the cloud sometimes resolves into such lightness, through the friction it has with the air, that it can no longer divide the air and seems to turn into that air. Sometimes in descending it multiplies, because it finds the minute particles of water which, by their lightness, were of slow descent, and it incorporates with them, and in every part of the descent it gains a quantity of water. Sometimes the winds bend the rain and make its descent oblique, whence for this cause the descent becomes slow and long, and often it turns into such minute particles that it cannot descend, and so it remains within the air.

Write how the clouds compose and dissolve themselves, and what cause raises the vapours of the water from the earth into the air, and the cause of mists and of the thickened air, and why it shows itself more blue and less blue at one time than another; and likewise write of the regions of the air and the cause of snows and of hailstones, and of the contracting of the water and its becoming hard in ice, and of the creating through the air of new figures of snow, and on the trees new figures of leaves in cold countries, and on the icy rocks, and of frost composing new figures of grass with various leaves, almost as if this frost were dew disposed to nourish and compose the said leaves.