The Penn's Grove record., 1908-09-25
Structure of HailstoneS.
By L Able.

There are three plausible hypothe.
ses as to the origin of the snowy ice
at the centre of a ha~ilstone.
(a) The hailstone may have be-
u with the formation of a ball of
snow, and the clear ice may be a
deposit of cold water, frozen a few
seconds later by the cold of the
surrounding atmosphere. In this
case the air that is mixed with the
snowy ice at the centre would be
compressed by the freezing of the
surrounding clear ice, and would be
liberated rs a bubble when the hail
stone is melted under water.
OBJ The nucleus of the hailstone
may have been at first a large drop
of water, containing dissolved air,
which is forced out by the process of
freezing, precisely like the bubbles
of air that are seen in cakes of arti-
fetal ice. Cold water can dissolve
an appreciate percentage of its vol
ume Of air, all Of which is extruded
when water freezes; a bubble of
highly compressed air might thus be
formed at the centre of the hailstone.
If such a hailstone be melted in cold
water slowly, all of this air will be
r~edissolyed, and nc bubble will be
seen to rise to the surface. If the
stone be dissolved in hot water rapid
ly, or especially if the stone be
crushed forcibly and quickly under
water, the air may escape as a bub-
BILE without having had time to be
r~edissolved.
Co A hailstone formed of pure
water that has had no opportunity
to absorb OF dissolve air can be re-
duced to a temperature far below
freezing, but will eventually turn to
ice, at which moment it's tempera-
ture will rise to thirty-two degrees
Fahrenheit, and it will assume a
crystalline structure, SO as to re-
semble snow. Such a hailstone has,
therefore, a snowy nucleus without
inclosed air, and on being melted
under water will, of course, show no
bubble. In fact, the central space
is occupied, not by air, but by the
vapor of water only, and as the
pressure is very small, we may liken
this to a partial vacuum.
All these three forms of h~ailstones
and other forms as yet unthought
of, are possible; and If we could in
vent methods of distinguishing be-
tween these three kinds of ha~ilstones
we should have a better knowledge
of what goes on in the upper air
during the formation of hail.
Those who have proper convent
ences will find that the study of hail
stones under polarized light gives
additional information as to their
crystalline structure, but has not as
yet told us much about the process
of formation.
AS ice is a poor conductor of heat,
it is worth while to make some effort
to determine the temperature of the
interior of a large hailstone. The
external surface may safely be as
s%sA@HtSIava-the temperature of
evaporation or the average wet
bulb temperature prevailing in the
lower thousand feet of air through
which the hail has rapidly fallen,
but the centre must be at a tempera-
ture more nearly corresponding to
that at which the nucleus was
formed. There is, therefore, a state
of strain that should be revealed by
polarized light. The average tenn
p~erature Of the whole hailstone may
be easily and directly determined by
allowing hail to melt within a
calorimeter, where the heat con-
sumed can be determined, and then
the temperature be computed
Monthly Review.