which causes a sudden rise in the
temperature near the surface of the earth. By taking advantage of this
principle of heat radiation from the earth's surface it is a very easy
matter to protect tender vegetation from even quite a severe frost, if
it occurs in the early fall, by a slight covering, such as thin paper.
The paper will act as a heat screen and in a measure prevent the heat
from radiating from the earth immediately under it. Frost--which of
course is but frozen dew--at this season of the year will form on a
still autumn night, although the atmosphere at some distance above the
ground is some degrees above the freezing point. The reason for this
will be obvious when we consider the facts that have been set forth
concerning the power of radiation to produce cold.

It has been estimated by meteorologists that the amount of water
condensed upon the surface of the earth in the form of dew amounts to as
much as five inches, or about one-seventh of the whole amount of
moisture that is evaporated into the air. It will thus be seen that dew
performs an important part in supporting vegetation.

The same operation in nature's great workshop that forms the dews of
summer creates the frosts of winter. The moisture in cold weather is
condensed the same as in warm. When it is condensed at the surface of
the earth we have the phenomenon of frost, but when condensed in the
upper regions of the atmosphere we have that of snow.

Heat radiation from the earth goes on in winter, which is evidenced by
the fact that a thick covering of snow is a great benefit to vegetation
as a protection against the injurious effects of frost. The writer has
seen flowers blooming abundantly at an altitude of 12,000 feet above the
sea-level, protected only by the friendly shelter of a snowbank. In some
cases the blooming flowers were in actual contact with the snow. By
experiment it has been determined that the earth under a thick coating
of snow is usually warmer by nine or ten degrees than the air
immediately above the snow covering.

CHAPTER XV.

HAILSTONES AND SNOW.

A hailstone is a curious formation of snow and ice, and most of the
large hailstones are conglomerate in their composition. They are usually
composed of a center of frozen snow, packed tightly and incased in a rim
of ice, and upon this rim are irregular crystalline formations jutting
out in points at irregular distances. Frequently, however, we find them
very symmetr