* On each broad cloud. l. 15. The clouds consist of condensed vapour, the particles of which are too small separately to overcome the tenacity of the air, and which therefore do not descend. They are in such small spheres as to repel each other, that is, they are applied to each other by such very small surfaces, that the attraction of the particles of each drop to its own centre is greater than its attraction to the surface of the drop in its vicinity; every one has observed with what difficulty small spherules of quicksilver can be made to unite, owing to the same cause; and it is common to see on riding through shallow water on a clear day, numbers of very small spheres of water as they are thrown from the horses feet run along the surface for many yards before they again unite with it. In many cases these spherules of water, which compose clouds, are kept from uniting by a surplus of electric fluid; and fall in violent showers as soon as that is withdrawn from them, as in thunder storms. See note on Canto l. 1. 554.
If in this state a cloud becomes frozen, it is torn to pieces in its descent by the friction of the air, and falls in white flakes of snow. Or these flakes are rounded by being rubbed together by the winds, and by having their angles thawed off by the warmer air beneath as they descend; and part of the water produced by these angles thus dissolved is absorbed into the body of the hailstone, as may be seen by holding a lump of snow over a candle, and there becomes frozen into ice by the quantity of cold which the hailstone possesses beneath the freezing point, or which is produced by its quick evaporation in falling; and thus hailstones are often found of greater or less density according as they consist of a greater portion of snow or ice. If hailstones consisted of the large drops of showers frozen in their descent, they would consist of pure transparent ice.
As hail is only produced in summer, and is always attended with storms, some philo∣sophers have believed that the sudden departure of electriclty from a cloud may effect something yet unknown in this phenomenon; but it may happen in summer independent of electricity, because the aqueous vapour is then raised higher in the atmosphere, whence it has further to fall, and there is warmer air below for it to fall through.
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