nly twenty-one inches.

Again, you may sometimes descend from the Alps when the fall of rain
and snow is heavy and incessant, into Italy, and find the sky over the
plains of Lombardy blue and cloudless, the wind at the same time
_blowing over the plain towards the Alps_. Below the wind is hot
enough to keep its vapor in a perfectly transparent state; but it
meets the mountains, is tilted up, expanded, and chilled. The cold of
the higher summits also helps the chill. The consequence is that the
vapor is precipitated as rain or snow, thus producing bad weather upon
the heights, while the plains below, flooded with the same air, enjoy
the aspect of the unclouded summer sun. Clouds blowing _from_ the
Alps are also sometimes dissolved over the plains of Lombardy.

In connection with the formation of clouds by mountains, one
particularly instructive effect may be here noticed. You frequently
see a streamer of cloud many hundred yards in length drawn out from an
Alpine peak. Its steadiness appears perfect, though a strong wind may
be blowing at the same time over the mountain head. Why is the cloud
not blown away? It _is_ blown away; its permanence is only apparent.
At one end it is incessantly dissolved; at the other end it is
incessantly renewed: supply and consumption being thus equalized, the
cloud appears as changeless as the mountain to which it seems to
cling. When the red sun of the evening shines upon these
cloud-streamers they resemble vast torches with their flames blown
through the air.

Architecture of Snow.

We now resemble persons who have climbed a difficult peak, and thereby
earned the enjoyment of a wide prospect. Having made ourselves masters
of the conditions necessary to the production of mountain snow, we are
able to take a comprehensive and intelligent view of the phenomena of
glaciers.

[Illustration: SNOW CRYSTALS.]

A few words are still necessary as to the formation of snow. The
molecules and atoms of all substances, when allowed free play, build
themselves into definite and, for the most part, beautiful forms
called crystals. Iron, copper, gold, silver, lead, sulphur, when
melted and permitted to cool gradually, all show this crystallizing
power. The metal bismuth shows it in a particularly striking manner,
and when properly fused and solidified, self-built crystals of great
size and beauty are formed of this metal.

[Illustration: SNOW-STAR.]

[Illustration: SNOW-STAR.]

If you dissolv