COMPOSITION OF THE SEA--ITS SALTS--POWER AND USES OF WATER--ADVANTAGE
AND DISADVANTAGE OF SALTS--ANECDOTE--DEEP-SEA SOUNDINGS--BROOKES
APPARATUS--IMPORTANCE OF THE SEARCH AFTER TRUTH--ILLUSTRATIONS--
DISCOVERIES RESULTING FROM DEEP-SEA SOUNDINGS.
Before proceeding to the consideration of the wonders connected with and
contained in the sea, we shall treat of the composition of the sea
itself and of its extent, depth, and bottom.
What is the sea made of? Salt water, is the ready reply that rises
naturally to every lip. But to this we add the question,--What is salt
water? or, as there are many kinds of salt water, of what sort of salt
water does the sea consist? To these queries we give the following
reply, which, we doubt not, will rather surprise some of our readers.
Fresh water, as most people are aware, is composed of two gases--oxygen
and hydrogen. Sea water is composed of the same gases, with the
addition of muriate of soda, magnesia, iron, lime, sulphur, copper,
silex, potash, chlorine, iodine, bromine, ammonia, and silver. What a
dose! Let bathers think of it next time they swallow a gulp of sea
water.
Most of these substances, however, exist in comparatively small quantity
in the sea, with the exception of muriate of soda, or common table salt;
of which, as all bathers know from bitter experience, there is a very
considerable quantity. The quantity of silver contained in sea water is
very small indeed. Nevertheless, small though it be, the ocean is so
immense, that, it has been calculated, if all the silver in it were
collected, it would form a mass that would weigh about two hundred
million tons!
The salt of the ocean varies considerably in different parts. Near the
equator, the great heat carries up a larger proportion of water by
evaporation than in the more temperate regions; and thus, as salt is not
removed by evaporation, the ocean in the torrid zone is salter than in
the temperate or frigid zones.
The salts of the sea, and other substances contained in it, are conveyed
thither by the fresh-water streams that pour into it from all the
continent of the world. Maury, in his delightful work, "The Physical
Geography of the Sea," tells us that "water is Nature's great carrier.
With its currents it conveys heat away from the torrid zone, and ice
from the frigid; or, bottling the caloric away in the vesicle of its
vapour, it first makes it impalpable, and then conveys it by unknown
paths to the most distant parts of the Earth. The materials of which
the coral builds the island, and the sea-conch its shell, are gathered
by this restless leveller from mountains, rocks, and valleys, in all
latitudes. Some it washes down from the Mountains of the Moon in
Africa, or out of the gold-fields of Australia, or from the mines of
Potosi; others from the battle-fields of Europe, or from the marble
quarries of ancient Greece and Rome. The materials thus collected, and
carried over falls and down rapids, are transported to the sea."
Here, as these substances cannot be evaporated, they would accumulate to
such a degree as to render the ocean uninhabitable by living creatures,
had not God provided against this by the most beautiful compensation.
He has filled the ocean with innumerable animals and marine plants,
whose special duty it is to seize and make use of the substances thus
swept from the land, and reconvert them into solids. We cannot form an
adequate conception of the extent of the great work carried on
continually in this way; but we see part of it in the chalk cliffs, the
marl beds of the sea shore, and the coral islands of the South Seas,--of
which last more particular notice shall be taken in a succeeding
chapter.
The operations of the ocean are manifold. Besides forming a great
reservoir, into which what may be termed the impurities of the land are
conveyed, it is, as has been shown, the great laboratory of Nature,
where these are reconverted, and the general balance restored. But we
cannot speak of these things without making passing reference to the
operations of water, as that wonder-working agent of which the ocean
constitutes but a part.
Nothing in this world is ever lost or annihilated. As the ocean
receives all the water that flows from the land, so it returns that
water, fresh and pure, in the shape of vapour, to the skies; where, in
the form of clouds, it is conveyed to those parts of the earth where its
presence is most needed, and precipitated in the form of rain and dew,
fertilising the soil, replenishing rivers and lakes, penetrating the
earth's deep caverns; whence it bubbles up in the shape of springs, and,
after having gladdened the heart of man by driving his mills and causing
his food to grow, it finds its way again into the sea: and thus the good
work goes on with ceaseless regularity.
Water beats upon the rocks of the sea-shore until it pounds them into
sand, or rolls them into pebbles and boulders. It also sweeps the rich
soil from the mountains into the valleys. In the form of snow it
clothes the surface of the temperate and frigid zones with a warm
mantle, which preserves vegetable life from the killing frosts of
winter. In the form of ice it splits asunder the granite hills; and in
the northern regions it forms great glaciers, or masses of solidified
snow, many miles in extent, and many hundred feet thick. These glaciers
descend by slow, imperceptible degrees, to the sea; their edges break
off and fall into it, and, floating southward, sometimes in great
mountainous masses, are seen by man in the shape of icebergs.
Frequently huge rocks, that have fallen upon these glaciers from cliffs
in the arctic regions, are carried by them to other regions, and are
deposited on flat beaches, far from their native cliffs.
The saltness of the sea rendering it more dense, necessarily renders it
more buoyant, than fresh water. This is obviously a great advantage to
man in the matter of commerce. A ship does not sink so deep in the sea
as it does in a fresh-water lake; hence it can carry more cargo with
greater facility. It is easier to swim in salt than in fresh water.
The only disadvantage to commerce in the saltness of the sea is the
consequent unfitness of its water for drinking. Many and harrowing are
the accounts of instances in which sailors have been reduced to the most
terrible extremities for want of fresh water; and many a time, since
navigation began, have men been brought to feel the dread reality of
that condition which is so forcibly expressed in the poem of the
"Ancient Mariner":--
"Water, water everywhere,
And not a drop to drink."
Science, however, at length enabled us to overcome this disadvantage of
saltness. By the process of distillation, men soon managed to procure
enough water at least to save their lives. One captain of a ship, by
accident, lost all his fresh water; and, before he could put into port
to replenish, a gale of wind, which lasted three weeks, drove him far
out to sea. He had no distilling apparatus on board, and it seemed as
if all hope of the crew escaping the most horrible of deaths were
utterly taken away. In this extremity the captain's inventive genius
came to his aid. He happened to have on board an old iron pitch-pot,
with a wooden cover. Using this as a boiler, a pipe made of a pewter
plate, and a wooden cask as a receiver, he set to work, filled the pot
with sea water, put an ounce of soap therein to assist in purifying it,
and placed it on the fire. When the pot began to boil, the steam passed
through the pipe into the cask, where it was condensed into water, minus
the saline particles, which, not being evaporable, were left behind in
the pitch-pot. In less than an hour a quart of fresh water was thus
obtained; which, though not very palatable, was sufficiently good to
relieve the thirst of the ship's crew. Many ships are now regularly
supplied with apparatus for distilling sea water; and on the African
coasts and other unhealthy stations, where water is bad, the men of our
navy drink no other water than that which is distilled from the sea.
The salts of the ocean have something to do with the creating of oceanic
currents; which, in their turn, have a powerful influence on climates.
They also retard evaporation to some extent, and have some effect in
giving to the sea its beautiful blue colour.
The ocean covers about two-thirds of the entire surface of the Earth.
Its depth has never been certainly ascertained; but from the numberless
experiments and attempts that have been made, we are warranted in coming
to the conclusion that it nowhere exceeds five miles in depth, probably
does not quite equal that. Professor Wyville Thompson estimates the
average depth of the sea at about two miles.
Of the three great oceans into which the sea is naturally divided--the
Atlantic, the Pacific, and the Arctic--the Atlantic is supposed to be
the deepest. There are profundities in its bosom which have never yet
been sounded, and probably never will be.
The difficulty of sounding great depths arises from the fact that, after
a large quantity of line has been run out, the shock of the lead
striking the bottom cannot be felt. Moreover, there is sufficient force
in the deep-sea currents to sweep out the line after the lead has
reached the bottom so that, with the ordinary sounding-lines in use
among navigators, it is impossible to sound great depths. Scientific
men have, therefore, taxed their brains to invent instruments for
sounding the deep sea--for touching the bottom in what sailors call
"blue water." Some have tried it with a silk thread as a plumb-line,
some with spun-yarn threads, and various other materials and
contrivances. It has even been tried by exploding petards and ringing
bells in the deep sea, when it was supposed that an echo or
reverberation might be heard, and, from the known rate at which sound
travels through water, the depth might thus be ascertained. Deep-sea
leads have been constructed having a column of air in them, which, by
compression, would show the aqueous pressure to which they had been
subjected; but the trial proved to be more than the instrument could
stand.
Captain Maury, of the American Navy--whose interesting book has been
already referred to--invented an instrument for sounding the deep sea.
Here is his own description of it:--"To the lead was attached, upon the
principle of the screw-propeller, a small piece of clock-work for
registering the number of revolutions made by the little screw during
the descent; and it having been ascertained by experiment in shoal water
that the apparatus, in descending, would cause the propeller to make one
revolution for every fathom of perpendicular descent, hands provided
with the power of self-registering were attached to a dial, and the
instrument was complete. It worked beautifully in moderate depths, but
failed in blue water, from the difficulty of hauling it up if the line
used were small, and from the difficulty of getting it down if the line
used were large enough to give the requisite strength for hauling it
up." One eccentric old sea captain proposed to sound the sea with a
torpedo, or shell, which should explode the instant it touched the
bottom. Another gentleman proposed to try it by the magnetic telegraph,
and designed an instrument which should telegraph to the expectant
measurers above how it was getting on in the depths below. But all
these ingenious devices failed, and it is probable that the deepest
parts of the ocean-bed still remained untouched by man.
At last an extremely simple and remarkably successful deep-sea sounding
apparatus was invented by Mr Brooke, an American officer. It consisted
of nothing more than thin twine for a sounding-line, and a cannon ball
for a sinker. The twine was made for the purpose, fine but very strong,
and was wound on a reel to the extent of ten thousand fathoms. The
cannon ball, which was from thirty-two to sixty-eight pounds' weight,
had a hole quite through it, into which was fixed a sliding rod, the end
of which, covered with grease, projected several inches beyond the ball.
By an ingenious and simple contrivance, the cannon ball was detached
when it reached the bottom of the sea, and the light rod was drawn up
with specimens of the bottom adhering to the grease.
With this instrument the Americans went to work with characteristic
energy, and, by always using a line of the same size and make, and a
sinker of the same shape and weight, they at last ascertained the law of
descent. This was an important achievement, because, having become
familiar with the precise rate of descent at all depths, they were
enabled to tell very nearly when the ball ceased to carry out the line,
and when it began to go out in obedience to the influence of deep-sea
currents. The greatest depth reached by Brooke's sounding-line is said
to have been a little under five miles in the North Atlantic.
The value of investigations of this kind does not appear at first sight,
to unscientific men. But those who have paid even a little attention to
the methods and processes by which grand discoveries have been made, and
useful inventions have been perfected, can scarcely have failed to come
to the conclusion that _the search after_ TRUTH, _pure and simple, of
any kind, and of every kind, either with or without reference to a
particular end_, is one of the most useful as well as elevating pursuits
in which man can engage.
_All_ truth is worth knowing and labouring after. No one can tell to
what useful results the discovery of even the smallest portion of truth
may lead. Some of the most serviceable and remarkable inventions of
modern times have been the result of discoveries of truths which at
first seemed to have no bearing whatever on those inventions. When
James Watt sat with busy reflective mind staring at a boiling kettle,
and discovered the expansive power of steam, no one could have for a
moment imagined that in the course of years the inventions founded on
the truth then discovered would result in the systematic driving of a
fleet of floating palaces all round the world at the rate of from twelve
to fifteen or twenty miles an hour! Instances of a similar kind might
be multiplied without end. In like manner, deep-sea sounding may lead
to great, as yet unimagined, results. Although yet in its infancy, it
has already resulted in the discovery of a comparatively shallow plateau
or ridge in the North Atlantic Ocean, rising between Ireland and
Newfoundland; a discovery which has been turned to practical account,
inasmuch as the plateau has been chosen to be the bed of our electric
telegraph between Europe and America. The first Atlantic cable was laid
on it; and although that cable suffered many vicissitudes at first, as
most contrivances do in their beginnings, communication between the two
continents was successfully established. Soundings taken elsewhere
showed that somewhat similar plateaus existed in other parts of the
Atlantic, and now the whole of Western Europe is being bound more
firmly, by additional cables, to the eastern seaboard of America.
This great and glorious achievement has been the result of the discovery
of two truths,--of a truth in science on the one hand, and a truth in
regard to the structure of the bed of the sea on the other. The study
of electricity and of deep-sea soundings was begun and carried on for
the sake of the discovery of _truth_ alone, and without the most distant
reference to the Atlantic Telegraph,--yet that telegraph has been one of
the results of that study. Who can tell how many more shall follow?
And even were no other result ever to follow, this one may prove to be
of the most stupendous importance to the human race.
Another discovery that has been made by deep-sea sounding is, that the
lowest depths of the ocean are always in a state of profound calm.
Oceanic storms do not extend to the bottom. When the tempest is lashing
the surface of the sea into a state of the most violent and tremendous
agitation, the caverns of the deep are wrapped in perfect repose. This
has been ascertained from the fact that in many places the bottom of the
sea, as shown by the specimens brought up by Brooke's apparatus, and
more recently by Professor Thompson's deep-sea dredge, is composed of
exceedingly minute shells of marine insects. These shells, when
examined by the microscope, are found to be unbroken and perfect, though
so fragile that they must certainly have been broken to pieces had they
ever been subjected to the influence of currents, or to the pulverising
violence of waves. Hence the conclusion that the bottom of the sea is
in a state of perpetual rest and placidity.
Indeed, when we think of it, we are led to conclude that this must
necessarily be the case. There are, as we shall presently show,
currents of vast size and enormous power constantly flowing through the
ocean; and when we think of the tremendous power of running water to cut
through the solid rock, as exemplified in the case of Niagara, and many
other rivers, what would be the result of the action of currents in the
sea, compared with which Niagara is but a tiny rivulet? Ocean currents,
then, flow on a bed of still water, that protects the bottom of the sea
from forces which, by calculation, we know would long ago have torn up
the foundations of the deep, and would probably have destroyed the whole
economy of nature, had not this beautiful arrangement been provided by
the all-wise Creator.