ygen and nitrogen. Like the sea, the
atmosphere is an ocean which flows, not in chaotic confusion, but in
regular, appointed courses; acting in obedience to the fixed, unvarying
laws of the Almighty, and having currents, counter-currents, and eddies
also, just like the watery ocean, which exercise a specific and salutary
influence where they exist.

The offices of the atmosphere are thus quaintly enumerated by Maury:--

"The atmosphere is an envelope or covering for the distribution of light
and heat over the Earth; it is a sewer into which, with every breath we
draw, we cast vast quantities of dead animal matter; it is a laboratory
for purification, in which that matter is recompounded, and wrought
again into wholesome and healthful shapes; it is a machine for pumping
up all the rivers from the sea, and for conveying the water from the
ocean to their sources in the mountains. It is an inexhaustible
magazine, marvellously stored; and upon the proper working of this
machine depends the well-being of every plant and animal that inhabits
the Earth."

An element whose operations are so manifold and so important could not
fail to engage the study of philosophic men in all ages; but so
difficult has been that study that little progress was made until very
recently, when men, acting in unison in all parts of the world, have, by
collating their observations, become acquainted with some of those laws
which govern the atmosphere, and direct its courses and velocities.

In early ages very little indeed was known about the wind beyond the
palpable facts of its existence, its varied condition, and its
tremendous power; and men's observations in regard to it did not extend
much beyond the noting of those peculiar and obvious aspects of the sky
which experience taught them to regard as evidences of approaching
storm. But, although such aspects of the heavens were, and always will
be, pretty safe and correct indicators of the Weather, they are by no
means infallible; and in some regions and under certain conditions they
are wanting altogether.

When the sea captain observes a lowering aspect of the sky, with, it may
be, a dark line above the distant edge of the sea, he knows--however
calm and unruffled may be the ocean around him--that wind may be
expected; and, calling the crew, he orders sail to be taken in, and
preparation made for the approaching breeze. But there are times when
no such warning is given, when the atmospher