be frozen
into hail. Hail generally precedes storms of rain.

Change of wind and the action of opposite currents, so necessary for the
production of rain, are also frequent during hail-storms. While clouds
are agitated with the most rapid motions, rain generally falls in
greatest abundance; and if the agitation be very great it generally
hails. Before the descent of hail a noise is heard, a particular kind of
crackling, which has been compared to the emptying of a bag of walnuts.

The descent of hail in some countries appears to occur at particular
periods. In the central parts of France, Italy, and Spain, it usually
hails most abundantly during the warmest hours of the day in spring and
summer, and in Europe generally it falls principally during the day; but
there are examples recorded of great hail-storms which have taken place
during the night. Near the equator, it seldom hails in places situated
at a lower level than 350 fathoms, for, although the hail may be formed,
the warmth of the regions prevents it from falling in that state.

The appearance of hail clouds seems to be distinguished from other stormy
clouds by a very remarkable shadowing. Their edges present a multitude
of indentations, and their surfaces disclose here and there immense
irregular projections. Arago has seen hail-clouds cover with a thick
veil the whole extent of a valley, at a time when the neighbouring hills
enjoyed a fine sky and an agreeable temperature.

Hailstones of similar forms are produced at similar levels. They are
smaller on the tops of mountains than in the neighbouring plains. If the
temperature or the wind alter, the figures of the hailstones become
immediately changed. Hailstones of the form of a six-sided pyramid have
been known to change, on the wind changing to the north-east, to convex
lenses, so transparent and nicely formed, that they magnified objects
without distorting them. Some hailstones are globular, others elongated,
and others armed with different points.

In the centres of hailstones small flakes of spungy snow are frequently
found, and this usually is the only opaque point in them. Sometimes the
surface is covered with dust, like fine flour, and is something between
hail and snow. This never falls during summer in southerly countries.
In the Andes hailstones from five to seven lines in diameter are
sometimes formed of layers of different degrees of transparency, so as to
permit rings of ice to be