Winds, temperature, and humidity all have a share in determining
atmospheric conditions, and no one of these plays a small part.
76. The Character of the Air. The atmosphere which envelops us at
all times extends more than fifty miles above us, its height being far
greater than the greatest depths of the sea. This atmosphere varies
from place to place; at the sea level it is heavy, on the mountain top
less heavy, and far above the earth it is so light that it does not
contain enough oxygen to permit man to live. Figure 40 illustrates by
a pile of pillows how the pressure of the air varies from level to
level.
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