HAIL, the aqueous vapor of the atmosphere
congealed in icy masses, called hailstones, and
precipitated upon the earth. Hailstones vary
in size and internal structure, from the
homogeneous masses one eighth of an inch in
diameter forming sleet, to the larger masses 3
in. in diameter, of beautiful crystalline structure, and to the still larger accretions of these masses sometimes a foot or more in diameter. The crystalline structure of most hailstones is remarkably distinct. The centre of the hail is a collection of semi-translucent granules or a spongy mass of snow and opaque ice; surrounding this nucleus is a more or less well defined radiated structure of crystals of ice; a large quantity of air is always enclosed within the interstices of the hailstone. Occasionally the stones are composed of concentric rings of ice and snow; when they consist of clear ice without the snowy nucleus, there is almost invariably found in the centre, in place of the nucleus, a cavity filled with condensed air; from experiments made in 1871 it has been shown that this bubble of enclosed air is
to a pressure of many atmospheres. Small bits of dust, leaves, and other foreign particles are occasionally found in the interior of the mass of a hailstone, and crystals of sulphur as well as ashes are particularly observed when the hail storm occurs in a volcanic region.
The small hailstones that fall in storms of sleet
are generally regarded as drops of water that
have been frozen in their downward passage
through layers of cold air; and their formation
is therefore believed to be a different process
from that attending the formation of larger
hailstones. These latter occur in connection
with a class of storms that are distinctively
known as hail storms. — The velocity with which
large hailstones fall to the ground is often so
great that, taken in connection with their mass, they cause very serious devastation; instances are recorded of animals being destroyed in large