is same
principle to the whole mountain side we can see that there will be,
during the day, a constant current of air flowing up the mountain. As
night comes on this upward movement will cease and there will be a
season of quiet until the earth has become colder than the air, and we
have a phenomenon of exactly the opposite kind, when the air contracts
instead of expands, which produces a downward current from the mountain
top.

These currents are as regular at certain seasons of the year as the land
and sea breeze. Of course, they may be obliterated for the time being,
by the presence of a stronger wind due to some other cause, such as
during the prevalence of a storm. In some of the regions of California
hottest during the day time, the nights are made endurable, and even
delightful, by the cool breezes that sweep down from the tops of the
mountains. It often happens that on the shady side of a high and steep
mountain where the sun's rays strike it so obliquely, if at all, that
the earth will be but little heated, there will be a vast mass of cold
air stored up. After the valley has become intensely heated by the sun
there is an ascending current of air which in turn causes a down rush
of the cold body of air from the mountain side. These local winds are
frequently very severe, only lasting, however, for a short time, until
an equilibrium of temperature and density has been established. A
wonderful exhibition of this sort of wind is said to occur at certain
times of the year on the coast at Tierra del Fuego, where a blast which
they call the "Williwaus," comes down from the mountain side, without
warning, with such tremendous force that no ship could stand the strain
if it should continue for any length of time. Fortunately the shock does
not last more than eight or ten seconds, when it is followed by a
perfect calm. It is as though a great volume of air had been fired from
some enormous cannon from the top of the mountain to the sea. The water
is pulverized into a spray that is driven in every direction.

Sometimes these violent blasts occur in the Alps, but from a very
different cause. Avalanches of great extent often take place on the
sides of the mountains, when a vast amount of material, equal to three
or four hundred million cubic feet of earth, will fall several thousand
feet. Often an avalanche of this kind will produce a wind, which is
confined, of course, to a restricted area, that is said to be so violent