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32 EVAPORATION OF ALPINE SNOW. 33
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d an tlj, is on the sunny side of the valley of
Chamouny. The oil extracted from it had
the smell of wax.
It has been sometimes supposed, that the
snow in th e higher Alps must be augmenting
every year, as it falls in the region
where intense frost for ever reigns. Such an
augmentation would indeed take place,
were it not for the operation of a cause, the
force and extent of which has been till
lately but imperfectly understood : — this
is evaporation. A series of experiments
were made by my ingenious friend, J.
Holdsworth, Esq., when surgeon to the
Hudson’s Bay company, on the evaporation
of ice and snow on the coast of Labrador,
and the result proved the rapidity with
which the bulk was lessened by this process.
It is well known, that when the
pressure of the atmosphere is diminished,
evaporation is greatly accelerated, and as
there is a great diminution of this pressure
at the altitude of the snowy region of the
Alps, the constant evaporation from the
surface of the snow, is sufficient to prevent
any accumulation in the average of a series
of years.
The experiments of Mr. Holdsworth
were made on the banks of Lake Winepie,
when the thermometer was below the freezing
point of Fahrenheit, and in a situation
sheltered from the sun’s rays. Snow enfolded
in crape, lost one-fifth of its weight
in twenty-six days ; and a slab of compact
ice from the lake, about two inches thick,
and weighing twenty pounds, lost one-fifth
of its weight, between the 28th of November
and the 31st of March. See Monthly
Magazine, April 1820.
Now there cannot be a doubt but that
the evaporation would have been far more
rapid at the elevation of 10,000 feet, and in
a situation freely exposed to great currents
o f wind, as on the summits of the Alps :
hence we may conclude that evaporation is
the main agent employed by nature, to
prevent the annual augmentation of snow
on lofty mountains. Other causes, such as
the constant ground-thaw observed by
Saussure, contribute, but in a minor degree,
to the same end. The thickness of the
snow on the summit of Mont Blanc was
estimated by Saussure at five hundred feet.
As the valley of Chamouny is the only
part of Savoy which is much frequented
by the English, the two inns here are morQ
VOL. II. D