The diminution in the quantity of air, and consequently of
oxygen, taken in at each breath is to a certain extent counterbalanced by
an increased frequency and depth of the respirations, and a greater
capacity of the chest. In this country, alterations in the barometric
pressure are chiefly valuable as indicating an approaching change in the
wind, and as well as of the amount of moisture in the air; hence the
instrument is often called "the weather glass." A sudden diminution in the
atmospheric pressure is likely to be attended with an escape of ground air
from the soil, and therefore to cause injury to health, especially among
the occupants of basement rooms, unless the whole interior of the building
be covered with concrete.
_Temperature._--Experience has shown that man can bear greater variations
of temperature than any other animal, as in the Arctic regions a
temperature of -70 degrees Fahrenheit, or more than 100 degrees below
freezing point, can be safely borne; that he can not only live but work,
and remain in good health, in these regions provided that he be supplied
with suitable clothing and plenty of proper food. On the other hand, man
has existed and taken exercise in the interior of Australia when the
thermometer showed a temperature of 120 degrees Fahrenheit, or nearly 90
degrees above freezing point, so that he can live and be in fairly good
health within a range of nearly 200 degrees Fahrenheit.
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