to behold all nations co-operating to carry out,
according to the same plan, one system of
philosophical research with regard to anything.
Though they may be enemies in all else, here,
as to the oceans which connect them, they are
to be friends. Every ship that navigates the
high seas with these charts and blank abstract
logs on board may henceforth be regarded as
a floating observatory. The system costs nothing
additional. The instruments which these
observations at sea call for, are such as are already
in use on board of every well-conditioned ship;
and the observations that are required are
precisely those which are necessary for her safe and
proper navigation.

Captain Maury grasps his subject in the
boldest and most comprehensive manner. He
tells us that our planet is invested with two
great oceans of Air and Water, one visible, the
other invisible. One is underfoot, the other
overhead. All the water of the one weighs
about four hundred times as much as all the air
of the other. It is at the bottom of this lighter
ocean where the forces to be studied are brought
into play. This place of meeting is the battlefield
of nature, the dwelling-place of man; it is
the scene of the greatest conflicts which he is
permitted to witness; for here rage in their
utmost fury the powers of sea, earth, and air.
Therefore we must necessarily refer to the
phenomena which are displayed at the meeting of
these two oceans. Both are in a state of what
is called unstable equilibrium; hence the
currents of the one and the winds of the other,
which have existed from the beginning and will
exist unto the end.

It would be scarcely fanciful to carry the
remark further, and to regard the aërial and the
aqueous oceans as living entities. Unstable
equilibrium is life; stable equilibrium is death.
A man walking erect on the earth is in a state
of unstable equilibrium; a corpse lying in its
coffin is in a state of stable equilibrium,
temporarily only, for it decomposes, floating away in
gases and falling piecemeal into dust. There is
therefore no real death on earth, only change.

As to the depth of the upper and the under
oceans, we know very little more of the one
than of the other; but the conjecture that
the average depth of the sea does not much
exceed four miles is probably as near the truth
as is the commonly received opinion that the
height of the atmosphere does not exceed fifty
miles. If the air were, like water, non-elastic
and not more compressible than this non-elastic
fluid, we could sound the atmospherical ocean
with the barometer, and gauge it by its pressure.
But the air is elastic. That at the
bottom is pressed down by the superincumbent
air with the force of about fifteen pounds
to the square inch, while that at the top is
inconceivably light. If, for the sake of
explanation, we imagine the lightest down in
layers of equal weight and ten feet thick, to be
carded into a pit several miles deep, we can
readily perceive that the bottom layer, though
it might have been ten feet thick when it first
fell, would now, the pit being full, be
compressed into a layer of only a few inches in
thickness by the weight of the accumulated and
superincumbent mass, while the top layer of all,
being uncompressed, would be exceedingly light,
and still ten feet thick; so that a person
ascending from the bottom of the pit would find
the layers of equal weight thicker and thicker
until he reached the top. So it is with the
barometer and the atmosphere: when it is
carried up in the air through several strata of given
thickness, the observer does not find that it falls
in the same proportion as its elevation is
increased.

More than three-fourths of the matter
contained in the entire atmosphere lies below the
tops of the highest mountains; the other fourth
is rarefied and expanded in consequence of the
diminished pressure, until the height of many
miles be attained. From the reflection of the
sun's rays after he has set, or before he rises
above the horizon, it is calculated that this
upper fourth part must extend at least forty or
forty-five miles higher. Sir John Herschel
has shown that, at the height of eighty or
ninety miles, there is a vacuum far more
complete than any we can produce by any air-
pump. In 1783, a large meteor, computed
to be half a mile in diameter and fifty miles
from the earth, was heard to explode. As
sound cannot travel through vacuum, it was
inferred that the explosion took place within the
limits of the atmosphere. Herschel concludes
that the aërial ocean is at least fifty miles deep.

The average depth of the ocean has been
variously computed by astronomers, from such
data as lay within their reach, to be from eleven
to twenty-six miles. About ten years ago,
Captain Maury was permitted to organise in
the American navy a plan for " sounding out"
the ocean with the plummet. Other navies,
especially the English, have done not a little in
furtherance of that object. Within this brief
period, though not a tenth part of the
undertaking has been yet completed, more knowledge
has been gained concerning the depths and
bottom of the deep sea, than all the world had
before acquired in all previous time. The
result does not thus far authorise the conclusion
that the average depth of ocean water is
more than three or four miles, nor have any
reliable soundings yet been made in water over
five miles deep.

In very shallow pools, where the water is not
more than a few inches deep, the ripples or
waves, as all of us when children have observed,
are small; their motion also is slow. But when
the water is deep, the waves are larger and more
rapid in their progress, thus indicating the existence
of a numerical relation between the depth
of the water and the breadth, height, and velocity
of waves. If, therefore, we knew the size,
and velocity of certain waves, we could compute
the depth of the ocean. Such a computation
has been made; Mr. Airy, the Astronomer
Royal, has given us tables of the velocities with
which waves of given breadths will travel in