THE OCEAN WORLD.
LONDON: PRINTED BY WILLIAM CLOWES AND SONS, STAMFORD STREET AND CHARING
CROSS.
[Illustration: Plate I.--The Argonaut sailing in the open sea.]
THE
OCEAN WORLD:
BEING A DESCRIPTION OF
THE SEA AND ITS LIVING INHABITANTS.
BY
LOUIS FIGUIER.
THE CHAPTERS ON CONCHOLOGY REVISED AND ENLARGED
BY CHARLES O. GROOM-NAPIER, F.G.S., &c.
WITH 427 ILLUSTRATIONS.
LONDON:
CASSELL, PETTER, AND GALPIN;
AND 596, BROADWAY, NEW YORK.
PREFACE.
"Our Planet is surrounded by two great oceans," says Dr. Maury, the
eminent American _savant_: "the one visible, the other invisible; one is
under foot, the other over head. One entirely envelopes it, the other
covers about two-thirds of its surface." It is proposed in "THE OCEAN
WORLD" to give a brief record of the Natural History of one of those
great oceans and its living inhabitants, with as little of the
nomenclature of Science, and as few of the repulsive details of Anatomy,
as is consistent with clearness of expression; to describe the ocean in
its majestic calm and angry agitation; to delineate its inhabitants in
their many metamorphoses; the cunning with which they attack or evade
their enemies; their instructive industry; their quarrels, their
combats, and their loves.
The learned Schleiden eloquently paints the living wonders of the deep:
"If we dive into the liquid crystal of the Indian Ocean, the most
wondrous enchantments are opened to us, reminding us of the fairy tales
of childhood's dreams. The strangely-branching thickets bear living
flowers. Dense masses of _Meandrineas_ and _Astreas_ contrast with the
leafy, cup-shaped expansions of the _Explanarias_, and the
variously-branching _Madrepores_, now spread out like fingers, now
rising in trunk-like branches, and now displaying an elegant array of
interlacing tracery. The colouring surpasses everything; vivid greens
alternate with brown and yellow; rich tints, ranging from purple and
deepest blue to a pale reddish-brown. Brilliant rose, yellow, or
peach-coloured _Nullipores_ overgrow the decaying masses: they
themselves being interwoven with the pearl-coloured plates of the
_Retipores_, rivalling the most delicate ivory carvings. Close by wave
the yellow and lilac Sea-fans (_Gorgonia_), perforated like delicate
trellis-work. The bright sand of the bottom is covered with a thousand
strange forms of sea-urchins and star-fishes. The leaf-like _Flustræ_
and _Escharæ_ adhere like mosses and lichens to the branches of
coral--the yellow, green, and purple-striped limpets clinging to their
trunks. The sea-anemones expand their crowns of tentacula upon the
rugged rocks or on flat sands, looking like beds of variegated
ranunculuses, or sparkling like gigantic cactus blossoms, shining with
brightest colours.
"Around the branches of the coral shrubs play the humming-birds of the
ocean: little fishes sparkling with red or blue metallic glitter, or
gleaming in golden green or brightest silvery lustre; like spirits of
the deep, the delicate milk-white jelly-fishes float softly through the
charmed world. Here gleam the violet and gold-green Isabelle, and the
flaming yellow, black, and vermilion-striped Coquette, as they chase
their prey; there the band-fish shoots snake-like through the thicket,
resembling a silvery ribbon glittering with rose and azure hue. Then
come the fabulous cuttle-fishes, in all the diaphanous colours of the
rainbow, but with no definite outline.
"When day declines, with the shades of night this fantastic garden is
lighted up with renewed splendour. Millions of microscopic medusæ and
crustaceans, like so many glowing sparks, dance through the gloom. The
Sea-pen waves in a greenish phosphorescent light. Whatever is beautiful
or wondrous among _fishes_, _Echinoderms_, _jelly-fishes_ and _polypi_
and _molluscs_, is crowded into the warm and crystal waters of the
Tropical ocean."
It is stated on the Title-page that "THE OCEAN WORLD" is chiefly
translated from M. Louis Figuier's two most recent works. In justice to
that gentleman, we must explain this statement. The History of the Ocean
is to a large extent, but not wholly, compiled from "La Terre et les
Mers," one of the volumes of M. Figuier's "Tableau de la Nature;" but
the larger portion of the work is a free translation of that author's
latest work, "La Vie et les Moeurs des Animaux." Other chapters, such as
"Life in the Ocean," the chapter on Crustaceans, and some others, are
compiled from various sources; they will not be found in either of M.
Figuier's volumes; but in other respects his text has been pretty
closely followed.
* * * * *
M. Figuier's plan is to begin the study of animals with the less perfect
beings occupying the lower rounds of the Zoological ladder, his reason
for doing so being an impression that the presence of the gradually
perfecting animal structure, from the simplest organisms up to the more
perfect forms, was specially calculated to attract the reader. "What can
be more curious or more interesting to the mind," he asks, "than to
examine the successive links in the uninterrupted chain of living beings
which commence with the Infusoria and terminate in Man?"
The work, he hopes, is not without the impress of a true character of
novelty and originality; at least he knows no work in which the strange
habits and special interests of the Zoophytes and Molluscs can be
studied, nor any work in which an attempt is made to represent them by
means of designs at once scientifically correct and attractive from the
picturesque character of the illustrations, most of which have been made
from specimens selected by Monsieur Ch. Bévalet from the various museums
in Paris.
One of those charming plain-speaking children we sometimes meet with
lately said to M. Figuier, "They tell me thou art a vulgariser of
Science. What is that?"
He took the child in his arms, and carried it to the window, where there
was a beautiful rose-tree in blossom, and invited it to pull a rose. The
child gathered the perfumed flower, not without pricking itself cruelly
with the spines; then, with its little hands still bleeding, it went to
distribute roses to others in the room.
"Thou art now a vulgariser," said he to the child; "for thou takest to
thyself the thorns, and givest the flowers to others!"
The parallel, although exaggerated, is not without its basis of truth,
and was probably suggested by the criticism some of his works have met
with; the critics forgetting apparently that these works are an attempt
to render scientific subjects popular, and attractive to the general
reader.
* * * * *
In the present edition of "THE OCEAN WORLD" it is only necessary to add
to the above (dated January, 1868), that the work has been revised
throughout, and some not unimportant errors corrected. For several of
these I am indebted to Mr. C. O. G. Napier, who has rearranged the whole
of the Mollusca. Mr. David Grieve has kindly revised and added to the
Crustacea; and to the Messrs. Johnston of Montrose, and Dr. Wilson
Johnston of the Bengal service, I am indebted for some valuable
practical information respecting the salmon and the various modes of
taking it.
W. S. O.
_March 1, 1869._
CONTENTS.
CHAPTER I.
PAGE
THE OCEAN 1
Depth of the Sea 5
Colour of the Ocean 11
Phosphorescence 13
Saltness of the Sea 15
CHAPTER II.
CURRENTS OF THE OCEAN 27
Trade-winds 28
Gulf Stream 31
Storms 32
Tides 35
Polar Seas 43
Antarctic Seas 50
CHAPTER III.
LIFE IN THE OCEAN 60
CHAPTER IV.
ZOOPHYTES 68
Foraminifera 87
Infusoria 97
CHAPTER V.
POLYPIFERA 116
CHAPTER VI.
CORALLINES 119
Tubiporinæ 120
Gorgoniadæ 121
Isidians 124
CHAPTER VII.
ZOANTHARIA 147
Madreporidæ 149
Porites 162
Actiniaria 181
Minyadinians 193
CHAPTER VIII.
ACALEPHÆ 195
Medusadæ 213
Rhizostoma 219
Vilelladæ 229
Ctenophora 254
CHAPTER IX.
ECHINODERMATA 259
Asterias 260
Crinoidea 270
Echinidæ 280
MOLLUSCA.
GENERAL DEFINITION 301
CHAPTER X.
MOLLUSCOIDA 303
Tunicata 309
Ascidians 309
CHAPTER XI.
ACEPHALOUS MOLLUSCA 316
CHAPTER XII.
ACEPHALOUS MOLLUSCA 344
Mytilidæ 344
CHAPTER XIII.
CEPHALOUS MOLLUSCA 391
Their Characteristics 391
CHAPTER XIV.
PULMONARY GASTEROPODS 396
Limnæidæ 397
Buccinidæ 428
Purpura 430
Pterocera 439
CHAPTER XV.
MOLLUSCOUS PTEROPODS 441
CHAPTER XVI.
CEPHALOPODOUS MOLLUSCA 445
Tentaculifera 445
Acetabula 448
CHAPTER XVII.
CRUSTACEANS 477
General Definition 477
Crabs and Crayfish 486
Lobsters 496
CHAPTER XVIII.
FISHES 502
CARTILAGINOUS FISHES 508
Cyclostomata 508
Selachia 510
Sturiona 524
CHAPTER XIX.
OSSEI, OR BONY FISHES 529
Plectognathi 529
Lophobranchii 534
Malacopterygii 536
Abdominales 560
Acanthopterygians 590
Pharyngeans 596
ILLUSTRATIONS.
PLATE PAGE
I. THE ARGONAUT SAILING BEFORE THE WIND (_Frontispiece_) 467
II. SPONGE FISHING ON THE COAST OF SYRIA 78
III. CORAL FISHING ON THE COAST OF SICILY 138
IV. CORAL ISLAND IN THE POMOTOUAN ARCHIPELAGO 169
V. SEA ANEMONES (I.) 187
VI. SEA ANEMONES (II.) 189
VII. AGALMA RUBRA 239
VIII. GALEOLARIA AURANTIACA 244
IX. SEA-URCHINS 290
X. FISHING FOR HOLOTHURIA 295
XI. SYNAPTA DUVERNAEA 299
XII. DREDGING FOR OYSTERS 374
XIII. OYSTER PARKS ON LAKE FUSARO 376
XIV. PECTINIDÆ 386
XV. SPONDYLUS 388
XVI. ANODONTA 340
XVII. TRIDACNA GIGANTEA 338
XVIII. VENUS AND CYTHEREA 336
XIX. SOLENIDÆ (_Razor-fish_) 333
XX. TEMPLE OF SERAPIS 330
XXI. CONUS 427
XXII. CYPRÆADÆ 421
XXIII. VOLUTA 426
XXIV. CAPTURE OF A GIGANTIC CUTTLE-FISH 462
XXV. SHARK FISHING 520
XXVI. STURGEON FISHING ON THE VOLGA 528
XXVII. FISHING FOR ELECTRICAL EELS 539
XXVIII. GREENLANDERS FISHING FOR HALIBUT 551
XXIX. THE HERRING FISHERY 580
XXX. A ROMAN FEAST 593
XXXI. FISHING FOR TUNNY IN PROVENCE 598
XXXII. FISHING FOR MACKEREL OFF THE CORNWALL COAST 601
THE OCEAN WORLD.
CHAPTER I.
THE OCEAN.
Ἄοιστον μὲν ὔδωρ--"The best of all things is
water."--PINDAR.
It is estimated that the sea covers nearly two-thirds of the surface of
the earth. The calculation, as given by astronomers, is as follows: The
surface of the earth is 31,625,625 ½ square miles, that portion
occupied by the waters being about 23,814,121 square miles, and that
consisting of continents, peninsulas, and islands, being 7,811,504
miles; whence it follows that the surface covered with water is to dry
land as 3·8 is to 1·2. The waters thus cover a little more than
seven-tenths of the whole surface. "On the surface of the globe,"
Michelet remarks, "water is the rule, dry land the exception."
Nevertheless, the immensity and depth of the seas are aids rather than
obstacles to the intercourse and commerce of nations; the maritime
routes are now traversed by ships and steamers conveying cargoes and
passengers equal in extent to the land routes. One of the features most
characteristic of the ocean is its continuity; for, with the exception
of inland seas, such as the Caspian, the Dead Sea, and some others, the
ocean is one and indivisible. As the poet says, "it embraces the whole
earth with an uninterrupted wave."
Περὶ πᾶσαν θ' εἱλισσομένου
χθόν' ἀκοιμἡτω ῥεύματι.
ÆSCHYLUS in _Prometheus Vinctus_.
The mean depth of the sea is not very exactly ascertained, but certain
phenomena observed in the movement of tides are supposed to be incapable
of explanation without admitting a mean depth of three thousand five
hundred fathoms. It is true that a great number of deep-sea soundings
fall short of that limit; but, on the other hand, many others reach
seven or eight thousand. Admitting that three thousand fathoms
represents the mean depth of the ocean, Sir John Herschel finds that the
volume of its waters would exceed three thousand two hundred and
seventy-nine million cubic yards.
This vast volume of water is divided by geographers into five great
oceans: the Arctic, the Atlantic, Indian, Pacific, and Antarctic Oceans.
The Arctic Ocean extends from the Pole to the Polar Circle; it is
situated between Asia, Europe, and America.
The Atlantic Ocean commences at the Polar Circle and reaches Cape Horn.
It is situated between America, Europe, and Africa, a length of about
nine thousand miles, with a mean breadth of two thousand seven hundred,
covering a surface of about twenty-five million square miles, placed
between the Old World and the New. Beyond the Cape of Storms, as Cape
Horn may be truly called, it is only separated by an imaginary line from
the vast seas of the south, in which the waves, which are the principal
source of _tides_, have their birth. Here, according to Maury, the young
tidal wave, rising in the circumpolar seas of the south, and obedient to
the sun and moon, rolls on to the Atlantic, and in twelve hours after
passing the parallel of Cape Horn is found pouring its flood into the
Bay of Fundy, whence it is projected in great waves across the Atlantic
and round the globe, sweeping along its shores and penetrating its gulfs
and estuaries, rising and falling in the open sea two or three feet, but
along the shore having a range of ten or twelve feet. Sometimes, as at
Fundy on the American coast; at Brest on the French coast; and Milford
Haven, and the mouth of the Severn in the Bristol Channel, rising and
falling thirty or forty feet, "impetuously rushing against the shores,
but gently stopping at a given line, and flowing back to its place when
the word goes forth, 'Thus far shalt thou go, and no farther.' That
which no human power can repel, returns at its appointed time so
regularly and surely, that the hour of its approach and the measure of
its mass may be predicted with unerring certainty centuries beforehand."
The Indian Ocean is bounded on the north by Asia, on the west by Africa,
on the east by the peninsula of Molucca, the Sunda Isles, and
Australia.
The Pacific, or Great Ocean, stretches from north to south, from the
Arctic to the Antarctic Circle, being bounded on one side by Asia, the
island of Sunda, and Australia; on the other by the west coast of
America. This ocean contrasts in a striking manner with the Atlantic:
the one has its greatest length from north to south, the other from east
to west; the currents of the Pacific are broad and slow, those of the
other narrow and rapid; the waves of this are low, those of the other
very high. If we represent the volume of water which falls into the
Pacific by one, that received by the Atlantic will be represented by the
figure 5. The Pacific is the calmest of seas, and the Atlantic Ocean is
the most stormy.
The Antarctic Ocean extends from the Antarctic Polar Circle to the South
Pole.
It is remarkable that one half of the globe should be entirely covered
with water, whilst the other contains less of water than dry land.
Moreover, the distribution of land and water, if, in considering the
germ of the oceanic basins, we compare the hemispheres separated by the
Equator and the northern and southern halves of the globe, is found to
be very unequal.
Oceans communicate with continents and islands by coasts, which are said
to be scarped when a rocky coast makes a steep and sudden descent to the
sea, as in Brittany, Norway, and the west coast of the British Islands.
In this kind of coast certain rocky indentations encircle it, sometimes
above, sometimes under water, forming a labyrinth of islands, as at the
Land's End, Cornwall, where the Scilly Islands form a compact group of
from one to two hundred rocky islets, rising out of a deep sea; or in
the case of the Channel, on the opposite coast of France, where the
coast makes a sudden descent, forming steep cliffs and leaving an open
sea. The coast is said to be flat when it consists of soft argillaceous
soil descending to the shore with a gentle slope. Of this description of
coast there are two, namely, sandy beaches, and hillocks or dunes.
* * * * *
What is the average depth of the sea? It is difficult to give an exact
answer to this question, because of the great difficulty met with in
taking soundings, caused chiefly by the deviations of submarine
currents. No reliable soundings have yet been made in water over five
miles in depth.
Laplace found, on astronomical consideration, that the mean depth of the
ocean could not be more than ten thousand feet. Alexander von Humboldt
adopts the same figures. Dr. Young attributes to the Atlantic a mean
depth of a thousand yards, and to the Pacific, four thousand. Mr. Airy,
the Astronomer Royal, has laid down a formula, that waves of a given
breadth will travel with certain velocities at a given depth, from which
it is estimated that the average depth of the North Pacific, between
Japan and California, is two thousand one hundred and forty-nine
fathoms, or two miles and a half. But these estimates fall far short of
the soundings reported by navigators, in which, as we shall see, there
are important and only recently discovered elements of error. Du Petit
Thouars, during his scientific voyage in the frigate _Venus_, took some
very remarkable soundings in the Southern Pacific Ocean: one, without
finding bottom at two thousand four hundred and eleven fathoms; another,
in the equinoctial region, indicated bottom at three thousand seven
hundred and ninety.
In his last expedition, in search of a north-west passage, Captain Ross
found soundings at five thousand fathoms. Lieutenant Walsh, of the
American Navy, reports a cast of the deep-sea lead, not far from the
American coast, at thirty-four thousand feet without bottom. Lieutenant
Berryman reported another unsuccessful attempt to fathom mid ocean with
a line thirty-nine thousand feet in length. Captain Denman, of H. M. S.
Herald, reported bottom in the South Atlantic at the depth of forty-six
thousand feet; and Lieutenant J. P. Parker, of the United States frigate
_Congress_, on attempting soundings near the same region, let go his
plummet, after it had run out a line fifty thousand feet long, as if the
bottom had not been reached. We have the authority of Lieutenant Maury
for saying, however, that "there are no such depths as these." The
under-currents of the deep sea have power to take the line out long
after the plummet has ceased to sink, and it was before this fact was
discovered that these great soundings were reported. It has also been
discovered that the line, once dragged down into the depths of the
ocean, runs out unceasingly. This difficulty was finally overcome by the
ingenuity of Midshipman Brooke. Under the judicious patronage of the
Secretary to the United States Navy, Mr. Brooke invented the simple and
ingenious apparatus (Fig. 1), by which soundings are now made, in a
manner which not only establishes the depth, but brings up specimens of
the bottom. The sounding-line in this apparatus is attached to a weighty
rod of iron, the lower extremity of which contains a hollow cup for the
reception of tallow or some other soft substance. This rod is passed
through a hole in a thirty-two pound spherical shot, being supported in
its position by slings A, which are hooked on to the line by the swivels
_a_. When the rod strikes the bottom, the tension on the line ceases,
the swivels are reversed, the slings B are thrown out of the hooks, the
ball falls to the ground, and the rod, released from its weight, is
easily drawn up, bringing with it portions of the bottom attached to the
greasy substance in the cup. By means of this apparatus, specimens of
the bottom have been brought up from the depth of four miles.
[Illustration: Fig. 1. Brooke's Sounding Apparatus.]
The greatest depth at which the bottom has been reached with this
plummet is in the North Atlantic between the parallels of thirty-five
and forty degrees north, and immediately south of the great bank of
rocks off Newfoundland. This does not appear to be more than twenty-five
thousand feet deep. "The basin of the Atlantic," says Maury, "according
to the deep-sea soundings in the accompanying diagram, is a long trough
separating the Old World from the New, and extending, probably, from
pole to pole. In breadth, it contrasts strongly with the Pacific Ocean.
From the top of Chimborazo to the bottom of the Atlantic, at the deepest
place yet reached by the plummet in that ocean, the distance in a
vertical line is nine miles."
"Could the waters of the Atlantic be drawn off, so as to expose to view
this great sea gash which separates continents, and extends from the
Arctic to the Antarctic Seas, it would present a scene the most rugged,
grand, and imposing; the very ribs of the solid earth with the
foundations of the sea would be brought to light, and we should have
presented to us in one view, in the empty cradle of the ocean, 'a
thousand fearful wrecks,' with the array of 'dead men's skulls, great
anchors, heaps of pearls, and inestimable stones,' which, in the poet's
eye, lie scattered on the bottom of the sea, making it hideous with the
sight of ugly death."
The depth of the Mediterranean is comparatively inconsiderable. Between
Gibraltar and Ceuta, Captain Smith estimates the depth at about five
thousand seven hundred feet, and from one to three thousand in the
narrower parts of the straits. Near Nice, Saussure found bottom at three
thousand two hundred and fifty. It is said that the bottom is shallower
in the Adriatic, and does not exceed a hundred and forty feet between
the coast of Dalmatia and the mouths of the Po.
The Baltic Sea is remarkable for its shallow waters, its maximum rarely
exceeding six hundred feet.
It thus appears that the sea has similar inequalities to those observed
on land; it has its mountains, valleys, hills, and plains.
The Deep-sea Sounding Apparatus of Lieutenant Brooke has already
furnished some very remarkable results. Aided by it, Dr. Maury has
constructed his fine orographic map of the basin of the Atlantic, which
is probably as exact as the maps which represent Africa or Australia.
Dr. Maury has also published many charts, giving the depths of the
ocean, the substance of which is given in the accompanying map, which
represents the configuration of the Atlantic up to the tenth degree of
south latitude, not in figures, as in Dr. Maury's charts, but in tints;
diagonal lines from right to left, representing the shores of both
hemispheres, indicate a depth of less than a thousand fathoms; from left
to right, indicate bottom at one thousand to two thousand; horizontal
lines, two to three thousand fathoms; cross lines show an average depth
of three to four thousand fathoms; finally, the perpendicular lines
indicate a depth of four thousand fathoms and upwards. Solid black
indicates continents and islands; waving lines, surrounding both
continents at a short distance from the shore, indicate the sands which
surround the coast line at a little distance from the shore.
[Illustration: Fig. 2. Chart of the Atlantic Ocean.]
* * * * *
The question may be asked, what useful purpose is served by taking
soundings at great depths? To this we may quote the answer of Franklin
to a question of similar tendency, addressed to aeronauts--"What purpose
is served by the birth of a child?" Every fact in physics is interesting
in itself; it forms a rallying point, round which, sooner or later,
others will meet, in order to establish some useful truth; and the
importance of making and recording deep-sea soundings is established by
the successful immersion of the transatlantic telegraph.
At the bottom of the Atlantic there exists a remarkable plateau,
extending from Cape Race in Newfoundland, to Cape Clear in Ireland, a
distance of over two thousand miles, with a breadth of four hundred and
seventy miles: its mean depth along the whole route is estimated at two
miles to two miles and a half. It is upon this telegraphic plateau, as
it has been called, that the attempt was made to lay down the cable in
1858, and it is on it that the enterprise has been so successfully
completed, during the year 1866. Tubular annelids, capable of boring
into all organic substances, are native to this plateau, and have
materially assisted in destroying the electric cable. The surface of the
plateau had been previously explored by means of Brooke's apparatus, and
the bottom was found to be composed chiefly of microscopic calcareous
shells (_Foraminifera_), and a few siliceous shells (_Diatomaceæ_).
These delicate and fragile shells, which seemed to strew the bottom of
the sea, in beds of great thickness, were brought up by the sounding-rod
in a state of perfect preservation, which proves that the water is
remarkably quiet in these depths,--an inference which is fully borne out
by the condition in which the cable of 1858 was found, when picked up in
1866.
[Illustration: Fig. 3. Section of the Atlantic, showing its depth and
the position of the Atlantic Telegraph.]
The first exploration of this plateau was undertaken by the American
brig _Dolphin_, which took a hundred soundings one hundred miles from
the coast of Scotland, afterwards taking the direction of the Azores, to
the north of which bottom was found, consisting of chalk and yellow
sand, at nine thousand six hundred feet. To the south of Newfoundland,
the depth was found to be sixteen thousand five hundred feet. In 1856,
Lieutenant Berryman, of the American steamer _Arctic_, completed a line
of soundings from St. John, Newfoundland, to Valentia, off the Irish
coast, and in 1857, Lieutenant Dayman, of the English steamship
_Cyclops_, repeated the same operation: this last line of soundings,
the result of which is represented in the accompanying section, differed
slightly from that followed by Lieutenant Berryman.
In the Gulf of Mexico, the depth does not seem to exceed seven thousand
feet; the Baltic does not in any place exceed eleven hundred. The depth
of the Mediterranean is, as we have said, very variable. At Nice,
according to Horace de Saussure, the average depth is three thousand
three hundred feet. Between the Dalmatian coast and the mouth of the Po,
bottom is found at a hundred and forty feet. Captain Smith found
soundings at from one thousand to nine thousand feet in the Straits of
Gibraltar, and at ten thousand feet between Gibraltar and Ceuta, where
the breadth exceeds sixteen miles. Between Rhodes and Alexandria, the
greatest depth is ten thousand feet. Between Alexandria and Candia it is
ten thousand three hundred. A hundred and twenty miles east of Malta it
is fifteen thousand. The peculiar form of the Mediterranean has led to
its being compared to a vast inverted tunnel.
The Arctic Ocean has, probably, no great depth. Hence salt water,
following the general law of contracting as it is cooled until it
freezes, no ice can be formed on its surface till the temperature has
fallen through its entire depth nearly to freezing point, when the
entire mass is consolidated into pack-ice. According to Baron Wrangel,
the bottom of the glacial sea, on the north coast of Siberia, forms a
gentle slope, and, at the distance of two hundred miles from the shore,
it is still only from ninety to a hundred feet. Nevertheless, in
Baffin's Bay, Dr. Kane made soundings at eleven thousand six hundred
feet.
The inequalities of the basin of the Pacific Ocean are, comparatively,
unknown to us. The greatest depth observed by Lieutenant Brooke in the
great ocean is two thousand seven hundred fathoms, which he found in
fifty-nine degrees north latitude and one hundred and sixty-six degrees
east longitude. Applying the theory of waves to the billows propelled
from the coast of Japan to California, during the earthquake of the 23rd
of December, 1854, Professor Bache calculated that the mean depth of
this part of the Pacific is fourteen thousand four hundred feet. In the
Pacific Ocean, latitude sixty degrees south and one hundred and sixty
degrees east longitude, he found soundings at fourteen thousand six
hundred feet--about two miles and a half. Another cast of the lead in
the Indian Ocean was made in seven thousand and forty fathoms, but
without bringing up any soil from the bottom. Among the fragments
brought up from the bottom of the Coral Sea, a remarkable absence of
calcareous shells was noted, whilst the siliceous fragments of sponges
were found in great quantities. Other soundings made in the Pacific, at
a depth of four or five miles, were examined by Ehrenberg, who found a
hundred and thirty-five different forms of infusoria represented, and
among them twenty-two species new to him. Generally speaking, the
composition of the infusoria of the Atlantic are calcareous; those of
the Pacific, siliceous. These animalcules draw from the sea the mineral
matter with which it is charged--that is, the lime or silica which form
their shell. These shells accumulate after the death of the animal, and
form the bottom of the ocean. The animals construct their habitations
near the surface; when they die, they fall into the depths of the ocean,
where they accumulate in myriads, forming mountains and plains in mid
ocean. In this manner, we may remark, _en passant_, many of the existing
continents had their birth in geological times. The horizontal beds of
marine deposits, which are called _sedimentary rocks_, and especially
the cretaceous rocks and calcareous beds of the Jurassic and Tertiary
periods, all result from such remains.[1]
The sea level is, in general, the same everywhere. It represents the
spherical form of our planet, and is the basis for calculating all
terrestrial heights; but many gulfs and inland seas open on the east are
supposed to be exceptions to this rule: the accumulation of waters,
pressed into these receptacles by the general movement of the sea from
east to west, it is alleged, may pile up the waters, in some cases, to a
greater height than the general level.
It had long been admitted, on the faith of inexact observation, that the
level of the Red Sea was higher than that of the Mediterranean. It has
also been said that the level of the Pacific Ocean at Panama is higher
by about forty inches than the mean level of the Atlantic at Chagres,
and that, at the moment of high water, this difference is increased to
about thirteen feet, while at low it is over six feet in the opposite
direction. This has been proved, so far as the evidence goes, to be
error in what concerns the difference in level of the Red Sea and
Mediterranean; and the opening of the Suez Canal, which is near at hand,
will probably furnish still more convincing proofs. Recent soundings
show that the mean level of the Pacific and Atlantic Oceans are
identical.
* * * * *
It has been calculated that all the waters of the several seas gathered
together would form a sphere of fifty or sixty leagues in diameter, and,
supposing the surface of the globe perfectly level, that these waters
would submerge it to the depth of more than six hundred feet. Again,
admitting the mean depth of the sea to be thirteen thousand feet, its
estimated contents ought to be nearly two thousand two hundred and fifty
millions of cubic miles of water; and, if the sea could be imagined to
be dried up, all the sewers of the earth would require to pour their
waters into it for forty thousand years, in order to fill the vast
basins anew.
* * * * *
If we could imagine the entire globe to be divided into one thousand
seven hundred and eighty-six parts by weight, we should find
approximately, according to Sir John Herschel, that the total weight of
the oceanic waters is equivalent to one of these parts.
The specific weight of sea water is a little above that of fresh water,
the proportion being as a thousand to a thousand and twenty-seven. The
Dead Sea, which receives no fresh water into its bosom to maintain
itself at the same level as other seas, acquires a higher degree of
saltness, and is equal to a thousand and twenty-eight. The specific
gravity of sea water is about the same as the milk of a healthy woman.
* * * * *
The colour of the sea is continually varying, and is chiefly caused by
filtration of the solar rays. According to the testimony of the majority
of observers, the ocean, seen by reflection, presents a fine azure blue
or ultramarine (_cæruleum mare_). When the air is pure and the surface
calm this tint softens insensibly, until it is lost and blended with the
blue of the heavens. Near the shore it becomes more of a green or
glaucus, and more or less brilliant, according to circumstances. There
are some days when the ocean assumes a livid aspect, and others when it
becomes a very pure green; at other times, the green is sombre and sad.
When the sea is agitated, the green takes a brownish hue. At sunset, the
surface of the sea is illumined with tints of every hue of purple and
emerald. Placed in a vase, sea water appears perfectly transparent and
colourless. According to Scoresby, the Polar seas are of brilliant
ultramarine blue. Castaz says of the Mediterranean, that it is celestial
blue, and Tuckey describes the equinoctial Atlantic as being of a vivid
blue.
Many local causes influence the colours of marine waters, and give them
certain decided and constant shades. A bottom of white sand will
communicate a greyish or apple-green colour to the water, if not very
deep; when the sand is yellow, the green appears more sombre; the
presence of rocks is often announced by the deep colour which the sea
takes in their vicinity. In the Bay of Loango the waters appear of a
deep red, because the bottom is there naturally red. It appears white in
the Gulf of Guinea, yellow on the coast of Japan, green to the west of
the Canaries, and black round the Maldive group of islands. The
Mediterranean, towards the Archipelago, sometimes becomes more or less
red. The White and Black Seas appear to be named after the ice of the
one and the tempests to which the other is subject.
At other times, coloured animalcules give to the water a particular
tint. The Red Sea owes its colour to a delicate microscopic algæ
(_Trychodesmium erythræum_), which was subjected to the microscope by
Ehrenberg; but other causes of colouration are suggested. Some
microscopists maintain that it is imparted by the shells and other
remains of infusoria; others ascribe the colour to the evaporation which
goes on unceasingly in that riverless district, producing salt rocks on
a great scale all round its shores. In the same manner sea water,
concentrated by the action of the solar rays in the salt marshes of the
south of France, when they arrive at a certain stage of concentration
take a fine red colour, which is due to the presence of some red-shelled
animalcules which only appear in sea water of this strength. The saline
lakes on the Great Thibetian water sheds are due to this cause.
Strangely enough, these minute creatures die when the waters attain
greater density by further concentration, and also if it becomes weaker
from the effects of rain.
* * * * *
Navigators often traverse long patches of green, red, white, or yellow
coloured water, all of which are due to the presence of microscopic
crustaceans, medusæ, zoophytes, and marine plants; the Vermilion Sea on
the Californian coast is entirely due to the latter cause.
* * * * *
The phenomenon known as _Phosphorescence of the Sea_ is due to analogous
causes. This wonderful sight is observable in all seas, but is most
frequent in the Indian Ocean, the Arabian Gulf, and other tropical seas.
In the Indian Ocean, Captain Kingman, of the American ship _Shooting
Star_, traversed a zone twenty-three miles in length so filled with
phosphorescent animalcules that at seven hours forty-five minutes the
water was rapidly assuming a white, milky appearance, and during the
night it presented the appearance of a vast field of snow. "There was
scarcely a cloud in the heavens," he continues, "yet the sky, for about
ten degrees above the horizon, appeared as black as if a storm were
raging; stars of the first magnitude shone with a feeble light, and the
'Milky Way' of the heavens was almost entirely eclipsed by that through
which we were sailing." The animals which produced this appearance were
about six inches long, and formed of a gelatinous and translucent
matter. At times, the sea was one blaze of light, produced by countless
millions of minute globular creatures, called _Noctilucæ_. The motion of
a vessel or the plash of an oar will often excite their lucidity, and
sometimes, after the ebb of tide, the rocks and seaweed of the coast are
glowing with them. Various other tribes of animals there are which
contribute to this luminous appearance of the sea. M. Peron thus
describes the effect produced by _Pyrosoma Atlanticum_, on his voyage to
the Isle of France: "The wind was blowing with great violence, the night
was dark, and the vessel was making rapid way, when what appeared to be
a vast sheet of phosphorus presented itself floating on the waves, and
occupying a great space ahead of the ship. The vessel having passed
through this fiery mass, it was discovered that the light was occasioned
by animalcules swimming about in the sea at various depths round the
ship. Those which were deepest in the water looked like red-hot balls,
while those on the surface resembled cylinders of red-hot iron. Some of
the latter were caught: they were found to vary in size from three to
seven inches. All the exterior of the creatures bristled with long thick
tubercles, shining like so many diamonds, and these seemed to be the
principal seat of their luminosity. Inside also there appeared to be a
multitude of oblong narrow glands, exhibiting a high degree of
phosphoric power. The colour of these animals when in repose is an opal
yellow, mixed with green; but, on the slightest movement, the animal
exhibits a spontaneous contractile power, and assumes a luminous
brilliancy, passing through various shades of deep red, orange, green,
and azure blue."
The phosphorescence of the sea is a spectacle at once imposing and
magnificent. The ship, in plunging through the waves, seems to advance
through a sea of red and blue flame, which is thrown off by the keel
like so much lightning. Myriads of creatures float and play on the
surface of the waves, dividing, multiplying, and reuniting, so as to
form one vast field of fire. In stormy weather the luminous waves roll
and break in a silvery foam. Glittering bodies, which might be taken for
fire-fishes, seem to pursue and catch each other--lose their hold, and
dart after each other anew. From time immemorial, the phosphorescence of
the sea has been observed by navigators. The luminous appearance
presents itself on the crest of the waves, which in falling scatters it
in all directions. It attaches itself to the rudder and dashes against
the bows of the vessel. It plays round the reefs and rocks against which
the waves beat, and on silent nights, in the tropics, its effects are
truly magical. This phosphorescence is due chiefly to the presence of a
multitude of mollusks and zoophytes which seem to shine by their own
light; they emit a fluid so susceptible of expansion, that in the zigzag
movement pursued they leave a luminous train upon the water, which
spreads with immense rapidity. One of the most remarkable of these
minute mollusks is a species of _Pyrosoma_, a sort of mucous sac of an
inch long, which, thrown upon the deck of a ship, emits a light like a
rod of iron heated to a white heat. Sir John Herschel noted on the
surface of calm water a very curious form of this phosphorescence; it
was a polygon of rectilinear shape, covering many square feet of
surface, and it illuminated the whole region for some moments with a
vivid light, which traversed it with great rapidity.
The phosphorescence of the sea may also result from another cause. When
animal matter is decomposed, it becomes phosphorescent. The bodies of
certain fishes, when they become a prey to putrefaction, emit an intense
light. MM. Becquerel and Breschet have noted fine phosphorescent effects
from this cause in the waters of the Brenta at Venice. Animal matter in
a state of decomposition, proceeding from dead fish which floats on the
surface of ponds, is capable of producing large patches of oleaginous
matter, which, piled upon the water, communicates to a considerable
extent the phosphorescent aspect.
* * * * *
Whatever may be the case elsewhere, there are local causes which affect
the colour of the waters in certain rivers, and even originate their
names. The Guaïnia, which with the Casiquaire forms the Rio Negro, is of
a deep brown, which scarcely interferes with the limpidity of its
waters. The waters of the Orinoco and the Casiquaire have also a
brownish colour. The Ganges is of a muddy brown, while the Djumna, which
it receives, is green or blue. The whitish colour belongs to the Rio
Bianco, or White River, and to many other rivers. The Ohio in America,
the Torgedale, the Goetha, the Traun at Ischl, and most of the Norwegian
rivers, are of a delicate limpid green. The Yellow River and the Blue
River in China are distinguished by the characteristic tint of their
waters. The Arkansas, the Red River, and the Lobregat in Catalonia, are
remarkable for their red colour, which, like the Dart and other English
rivers, they owe to the earth over which they flow, or which their
waters hold in suspension.
* * * * *
The water of the sea is essentially _salt_, of a peculiar flavour,
slightly acrid and bitter, and a little nauseous. It has an odour
perfectly _sui generis_, and is slightly viscous. In short, it includes
a great number of mineral salts and some other compounds, which give it
a very disagreeable taste, and render it unfit for domestic use. It
contains nearly all the soluble substances which exist on the globe, but
principally chloride of sodium, or marine salt, and sulphate of
magnesia, of potassium, and of lime.
Pure water is produced by a combination of one volume of oxygen and of
two volumes of hydrogen, or in weight, 100 oxygen and 12·50 hydrogen.
Sea water is composed of the same; but we find there, besides, other
elements, the presence of which chemistry reveals to us. In 1000 grains
of sea water the following ingredients are found:--
Water 962·0
Chloride of sodium 27·1
Chloride of magnesium 5·4
Chloride of potassium 0·4
Bromide of magnesia 0·1
Sulphate of magnesia 1·2
Sulphate of lime 0·8
Carbonate of lime 0·1
Leaving a residuum of 2·9
-----
1000
=====
consisting of sulphuretted hydrogen, hydrochlorate of ammonia, iodine
iron, copper, and even silver in various quantities and proportions,
according to the locality of the specimen. In examining the plates of
copper taken from the bottom of a ship at Valparaiso, which had been
long at sea, distinct traces of silver were found deposited by the sea.
Finally, we find dissolved in the ocean a peculiar mucus, which seems of
a mixed animal and vegetable nature, and is evidently organic matter
proceeding from the successive decomposition of the innumerable
generations of animals which have disappeared since the beginning of the
world. This matter has been described by the Count Marsigli, who
designates it sometimes under the name of _glu_, and sometimes as an
_unctuosity_. It is the "ooze" of marine surveyors, and consists chiefly
of carbonate of lime, ninety per cent. of which is formed of minute
animal organisms. Its mealy adhesiveness results from the pressure of
the superimposed water. The numerous salts which exist in the sea can
neither be deposited in its bed, nor exhaled with the vapour, to be
again poured upon the soil in showers of rain. Particular agents retain
these salts in solution, transform them, and prevent their accumulation.
Hence sea water always maintains a certain degree of saltness and
bitterness, and the ocean continues to present the chemical characters
which it has exhibited in all times, varying only in certain localities
where more or less fresh water is poured into the sea basin from rivers:
thus the saltness of the Mediterranean is greater than that of the
ocean, probably because it loses more water by evaporation than it
receives from its fresh-water affluents. For the opposite reason, the
Black and the Caspian Seas are less charged with these salts. The Dead
Sea is so strongly impregnated with salt that the body of a man floats
on its surface without sinking, like a piece of cork upon fresh water.
The supposed cause is excessive evaporation and the absence of rivers of
any importance.
The saltness of the sea seems to be generally less towards the poles
than the equator; but there are exceptions to this law. In the Irish
Channel, near the Cumberland coast, the water contains salt equal to the
fortieth of its weight; on the coast of France, it is equal to one
thirty-second; in the Baltic, it is equal to a thirtieth; at Teneriffe,
a twenty-eighth; and off the coast of Spain, to a sixteenth. Again, in
many places the sea is less salt at the surface than at the bottom. In
the Straits of the Dardanelles, at Constantinople, the proportion is as
seventy-two to sixty-two. In the Mediterranean, it is as thirty-two to
twenty-nine. It is also stated that as the salt increases at a certain
depth, the water becomes less bitter. At the mouth of the great rivers
it is scarcely necessary to add that the water is always less saline
than on shores which receive no supplies of fresh water; the same remark
applies to sea water in the vicinity of polar ice, the melting of which
is productive of much fresh water. A recent analysis of the water of the
Dead Sea by M. Roux gives about two pounds of salt to one gallon of
water. No mineral water, if we except that of the Salt Lake of Utah, is
so largely impregnated with saline substances; the quantity of bromide
of magnesia is 0·35 grammes to the litre. The water of the Dead Sea is,
according to these proportions, the richest natural depository of
bromide, which it might be made to furnish abundantly. The waters of the
great Lake of Utah and Lake Ourmiah in Persia are both highly saline. In
Lake Ourmiah, as in the Dead Sea, the proportion of salt is six times
greater than in the ocean. Many of our fresh-water lakes were probably
salt originally, but have by degrees lost their saline properties by the
mingling of their waters with those of the rivers which traverse or flow
into them. Among the lakes which appear to have been divested of their
saline properties may be mentioned the great lakes of Canada and the Sea
of Baikal, in all of which seals and other marine animals are still
found, which have become acclimatized as the water gradually became
fresh.
The saltness of sea water increases its density, and at the same time
its buoyancy, thus adapting it for bearing ships and other burdens on
its bosom; moreover, to abbreviate slightly Dr. Maury's remark, "the
brine of the ocean is the ley of the earth." From it the sea derives
dynamical power, and its currents their main strength. It is the salt of
the sea that imparts to its waters those curious anomalies in the laws
of freezing and of thermal dilatation, that assist the rays of heat to
penetrate its bosom; the salts of the sea invest it with adaptations
which fresh water could not possess. In the latter case, the maximum
density would be thirty-nine degrees two seconds F. instead of
twenty-seven degrees two seconds F., when the dynamical force of the sea
would be insufficient to put the Gulf Stream in motion. Nor could it
regulate those climates we call marine.
* * * * *
We have said that sea water contains nearly all the soluble substances
which exist in the globe. Nevertheless its exhalation is comparatively
pure. "The water which evaporates from the sea," says Youman, in his
"Chemistry," "is nearly pure, containing but very minute traces of
salts. Falling as rain upon the land, it washes the soil, percolates
through the rocky layers, and becomes charged with saline substances,
which are borne seaward by the returning currents. The ocean, therefore,
is the great depository of all substances that water can dissolve and
carry down from the surface of the continents; and, as there is no
channel for their escape, they would constantly accumulate, were it not
for the creatures which inhabit the seas, and utilize the material thus
brought within their reach." These substances are chloride of sodium or
marine salt, sulphates of magnesia, potassa, lime, and other substances
which the water of various seas is found to contain.
In the year 1847, I made an analysis of water taken a few leagues from
the coast at Havre, which gave the following result, from one litre (1
pint·760773):--[2]
Grammes.
Chloride of sodium 25·704
Chloride of magnesium 2·905
Sulphate of magnesia 2·462
Sulphate of lime 1·210
Sulphate of potassa 0·094
Carbonate of lime 0·132
Silicate of soda 0·017
Bromide of sodium 0·103
Bromide of magnesium 0·030
Oxide of iron, carbonate and phosphate of magnesia,} Only
and oxide of manganese } traces.
------
32·657
======
The water of the Mediterranean contains more salts than that of the
ocean.
The following are, according to M. Usiglio, who was one of a commission
sent to examine the different kinds of salt water in the south of
France, the component parts of one hundred gallons of Mediterranean
water:--
lbs.
Chloride of sodium 29·524
Chloride of potassium 0·405
Chloride of magnesium 3·219
Sulphate of magnesia 2·477
Chloride of calcium 6·080
Sulphate of lime 1·557
Carbonate of lime 0·114
Bromide of sodium 0·356
Protoxide of iron 0·003
------
Total 43·735
======
We conclude, from the quantity of sea salt contained in the water of the
ocean, that, if it were spread over the surface of the globe, it would
form a layer of more than thirty feet in height.
The salt contained in sea water gives it a greater density than fresh
water; its average specific weight is 1.027. The density of the water of
the Mediterranean is, according to M. Usiglio, 1.025 when at the
temperature of seventy degrees. But the saltness of the sea varies very
much under the influence of a great many local circumstances, among
which we must count principally currents, winds favourable to
evaporation, rivers coming from the continents, &c.
It has been remarked that the sea is less salt towards the poles than at
the equator; that the saltness increases, in general, with the distance
from land, and the depth of the water; that the interior seas, such as
the Baltic, the Black Sea, the White Sea, the Sea of Marmora, and the
Yellow Sea, are less salt than the ocean. The Mediterranean is an
exception to this last rule; it is, as we have seen, salter than the
ocean. This difference is explained by the fact that the quantity of
fresh water brought into it by rivers is less than that lost by
evaporation. The Mediterranean must therefore grow salter with time,
unless its water is discharged into the ocean by a counter current,
which would run under the current coming from the Atlantic by the
Straits of Gibraltar.
The Black Sea, on the contrary, the water of which has a density of only
1.013, receives from rivers more fresh water than it loses by
evaporation. The saltness of this interior sea is only half as intense
as that of the ocean.
The Sea of Azov and the Caspian Sea are still less salt than the Black
Sea.
The following table shows the relative composition of the water in these
three interior seas:--
+--------------------------+--------------+--------------+--------------+
| | Black Sea. | Sea of Azov. | Caspian Sea. |
| In 100 Gallons of Water. | Density | Density | Density |
| | 1·013 | 1·009. | 1·005. |
+--------------------------+--------------+--------------+--------------+
| Chloride of sodium | 14·0195 | 9·6583 | 3·6731 |
| Chloride of potassium | 9·1892 | 0·1279 | 0·0761 |
| Chloride of magnesium | 1·3045 | 0·8870 | 0·6324 |
| Sulphate of magnesia | 1·4704 | 0·7642 | 1·2389 |
| Sulphate of lime | 0·1047 | 0·2879 | 0·4903 |
| Bicarbonate of magnesia | 0·2086 | 0·1286 | 0·0129 |
| Bicarbonate of lime | 0·3646 | 0·0221 | 0·1705 |
| Bromide of magnesium | 0·0052 | 0·0035 | traces |
| +--------------+--------------+--------------+
| | 17·6663 | 11·8795 | 6·2942 |
+--------------------------+--------------+--------------+--------------+
In lakes without any outlet, as the Dead Sea and the Lake of Ural, the
degree of saltness is considerably augmented. Numerous experiments have
proved that the water of the Dead Sea is six times salter than that of
the ocean. MM. Boutron and O'Henry analysed, in April, 1850, after the
rainy season, some water of the Dead Sea, taken at about two leagues
from the mouth of the Jordan; its density was then 1·10.
The saltness of sea water makes it more fitted to float ships, because
its density is increased by the salts which are dissolved in it. Besides
this, these salts contribute to prevent the water becoming contaminated
with decomposed organic matter.
By the table representing the composition of the water of the ocean and
of that of the Mediterranean, we see that salts of lime and potassium,
as well as iodine and silica, are only found in infinitely small
quantities. Nevertheless, the lime and silica contained in the sea water
are of very great importance; for these quantities, which appear to us
so small in the table of a chemical analysis, become enormous in the
entire extent of the ocean. The marine plants take in the lime, the
silica, the potassa, and the iodides which are dissolved in the sea
water; these mineral substances enter into their textures. It is from
the carbonate of lime and silica that the marine animals form their
solid covering, their shell or carapace. The infusoria make use of the
lime, silica, and potassa for the same purpose. It is by the life and
habits of the polypi that we explain those _Coral Islands_ found in the
sea, the existence of which has been a subject of much astonishment,
and ought, therefore, to find a place in this chapter.
The Pacific and Indian Oceans are studded with islands in a state of
formation, which owe their origin to the polypi and corallines. These
zoophytes extract from the sea water the lime and silicium which are
found there in the state of soluble salts. In order to grow and develop,
they must be continually under water. They are constantly producing
calcareous deposits; these deposits rise rapidly, and at last reach the
surface of the water. Then the seaweed and rubbish of all kinds that the
sea carries along with it, arrested by these emerged masses, cover them
with a layer of fertile soil; which is soon covered with vegetation, as
the birds and the waves bring seeds thither.
The Coral Islands of the Pacific, which are described in another
chapter, are formed in this manner.
Besides the substances named, sea water also contains, in
infinitesimally small quantities, metals, such as iron, copper, lead and
silver. The old copper collecting round the keels of ships sometimes so
much silver that it has been thought worth extracting! A curious
calculation has been attempted, based on the age of ships and the
distance they have gone during all their voyages, to show that the sea
contains in solution two million tons of silver.[3]
The question has often been asked, whence comes the salt and other
substances held in solution in sea water? If our readers will turn back
to the first few pages of "The World before the Deluge," they will
better understand the very simple geological explanation that we are
going to give of the origin of different substances dissolved in sea
water.
In the first stage of our planet, before the watery vapours contained in
the primitive atmosphere were condensed, and before they had begun to
fall on the earth in the form of boiling rain, the shell of the earth
contained an infinite variety of heterogeneous mineral substances, some
soluble in water, others not. When rain fell on the burning surface for
the first time, the waters became charged with all the soluble
substances, which were reunited and afterwards deposited, accumulating
in the large depressions of the soil. The seas of the primitive globe
were thus formed of rain water, holding in solution all that the earth
had given up, collected in large basins. Chloride of sodium, sulphates
of soda, magnesia, potassium, lime, and silica, in the form of soluble
silicate; in a word, every soluble matter that the primitive globe
contained formed part of the mineral contingent of this water. If we
reflect that through all time up to the present day none of the general
laws of nature have changed--if we consider that the soluble substances
contained in the water of the primitive seas have remained there, and
that the fresh water of the rivers constantly replaces the water which
disappears by evaporation--we have the true explanation of the saltness
of sea water. "It is a very simple theory, it is true," adds M. Figuier,
"but one that we have found nowhere, and the responsibility of which we
therefore claim. The chloride of sodium is by no means the only
substance dissolved in sea water. It contains, besides, many other
mineral substances: in short, every _soluble salt_ on the face of the
globe, and, along with them, portions of different metals in infinitely
small quantities."
The mean temperature of the surface of the sea is nearly the same as the
atmosphere, so long as no currents of heat or cold interpose their
perturbing influence. In the neighbourhood of the Tropics, it appears
that the surface of the water is slightly warmer than the ambient air,
but experiments on the temperature of the sea from the surface to the
bottom reveal, according to our author,[4] "some evidence which
establishes a curious law. In very deep water a perfectly uniform
temperature of four degrees below zero prevails, which corresponds, as
physics have established, to the maximum density of water. Under the
Equator this temperature exists at the depth of seven thousand feet. In
the Polar regions, where water is colder at the surface, this
temperature is maintained at four thousand six hundred feet. The
isothermal lines of four degrees form a line of demarcation between the
Zones, where the surface of the sea is colder, and those where it is
warmer than the bed of four degrees below zero." This is more clearly
shown in Fig. 4, which represents a section of the ocean, the curved
line which touches two points at the surface indicating the depths where
the temperature is constantly fixed at four degrees.
Dr. Maury's account of this phenomenon is asserted with less confidence.
The existence of an _isothermal floor_ of the ocean, as he calls it,
was first suggested by the observations of Kotzebue, Admiral Beechey,
and Sir James C. Ross. "Its temperature, according to Kotzebue, is
thirty-six degrees Fahr., or four degrees Cent.; the depth of this bed,
of invariable and uniform temperature, is twelve hundred fathoms at the
Equator; thence it gradually rises to the parallel of about fifty-six
degrees north and south, when it crops out, and there the temperature of
the sea from top to bottom is conjectured to be permanent at thirty-six
degrees. The place of this outcrop, no doubt, shifts with the seasons,
vibrating north and south, after the manner of the Calm belts.
Proceeding onwards to the Frigid zones, this aqueous stratum of an
unchanging temperature dips again, and continues to incline till it
reaches the Poles, at the depth of seven hundred and fifty fathoms; so
that on the equatorial side of the outcrop the water above the
isothermal floor is the warmer, but in Polar seas the supernatant water
is the colder."
[Illustration: Fig 4. Thermal Lines of equal Temperature.]
* * * * *
In the saline properties of sea water Maury discovers one of the
principal forces from which currents in the ocean proceed. "The brine of
the ocean is the ley of the earth," he says; "from it the sea derives
dynamical powers, and its currents their main strength. Hence, to
understand the dynamics of the ocean, it is necessary to study the
effects of their saltness upon the equilibrium of the waves. Why is the
sea made salt? It is the salts of the sea that impart to its waters
those curious anomalies in the laws of freezing and of thermal
dilatation. It is the salts of the sea that assist the rays of heat to
penetrate its bosom." The circulation of the ocean is indispensable to
the distribution of temperature--to the maintenance of the
meteorological and climatic conditions which rule the development of
life; and this circulation could not exist--at least, the character of
its waters would be completely changed--if they were fresh in place of
salt. "Let us imagine," says M. Julien, "that the sea, now entirely
composed of fresh water, of one uniform temperature from the Pole to the
Equator, and from the surface to its greatest depths; the solar heat
would penetrate the liquid beds nearest to the Equator; it would dilate
them, so as to raise them above their primitive level; by the single
effect of gravitation, they would glide on the surface towards the polar
zones. The absence of all solar radiation would tend, on the contrary,
to cool and contract them without this tendency. An exchange would be
established from the extremities towards the centre; in other words, a
counter current of cold and heavy water, calculated to replace the
losses occasioned by the action of solar radiation, would descend from
the Poles, but quite maintaining itself beneath the light and warm
current from the Equator."
In a like system of general circulation, the physical properties of pure
water, which attains its maximum of density seven degrees two seconds F.
below zero, would produce the most singular consequences. As its
temperature rose above that point, the water would become lighter,
having, consequently, a tendency to ascend towards the upper beds. After
this, the equatorial current, meeting in its progress towards the Poles
the cold water, would itself be cooled down; and when its temperature
had reached four degrees below zero, being now heavier than the polar
current, would change places with it, descending until it reached water
equally dense, while the polar current would ascend. Hence would arise a
sort of confusion of currents which would give to a fresh-water ocean
the strangest results, disarranging every instant the regular
circulation of its waters. It could not be so, however, in an ocean of
salt water, which attains its maximum specific gravity at four degrees
eight seconds F. below zero. By evaporation at the surface it is
concentrated and precipitated, and thus rendered denser than that
immediately below the surface. It consequently sinks, while the lower
beds come up to replace, in order to modify it, and in turn to be
precipitated in the same manner. "In this manner we find established a
continually ascending and descending movement, which carries down into
the depths of ocean the water warmed at the surface by the solar rays of
the Torrid zone. This double vertical current facilitates and prepares
the grand horizontal current which puts these submarine reservoirs of
heat in communication with the lower beds of the glacial sea. In the
Arctic basin the clouds, the melted snow, and the great rivers, which
have their mouths on the north of both continents, produce considerable
quantities of fresh water, which, mixing with the waves of the Polar
Sea, form a bed of mean density light enough to maintain itself and flow
off towards the Atlantic Ocean. These surface movements determine in the
lower regions certain contrary movements, whence originate the powerful
counter currents which ascend the Straits from Baffin's Bay and reappear
in the mysterious 'Polynia' of Kane, diffusing there its treasure of
heat brought from intertropical seas." Dr. Kane, in his interesting
Narrative, reports an open sea north of the parallel of eighty-two
degrees, which he and his party crossed a barrier of ice eighty miles
broad to reach, and before he reached it the thermometer marked sixty
degrees. Beyond this ice-bound region he found himself on the shores of
an iceless sea, extending in an unbroken sheet of water as far as the
eye could reach towards the Pole. Its waves were dashing on the beach
with the swell of a great ocean; the tides ebbed and flowed. Now the
question arises, Where did those tides have their origin? The tidal wave
of the Atlantic could not have passed under the icy barrier which De
Haven found so firm; therefore they must have been cradled in the cold
sea round the Pole; in which case it follows that most, if not all, the
unexplored regions about the Pole must be covered with deep water, the
only source of strong and regular tides. Seals were sporting and
waterfowl feeding in this open sea, as Dr. Kane tells us, and the
temperature of the water which rolled in and dashed at his feet with
measured beat was thirty-six degrees, while the bottom of the icy
barrier of eighty miles was probably hundreds of feet below the surface
level.
"The existence of these tides," says Maury, "with the immense flow and
drift which annually take place from the Polar Seas and the Atlantic,
suggests many conjectures as to the condition of these unexplored
regions. Whalemen have always been puzzled as to the breeding place of
the great whale. It is a cold-water animal, and, following up the train
of thought, the question arises, Is not the nursery for the great whale
in this Polar Sea, which is so set about and hemmed in by a hedge of
ice, that man may not trespass there?"
One or two points worthy of notice may be recorded here. Shallow water,
and water near the coast, or covering raised sand-banks, is colder than
water in the open sea. Alexander von Humboldt explains this phenomenon
by supposing that deep waters of higher temperature reascend from the
lowest depths and mingle with the upper beds. Fogs are frequently formed
over sand-banks, because the cold water which covers them produces a
local precipitation of atmospheric vapour. The contour of these fogs are
perfectly defined when seen from a distance: they reproduce the form and
accidents due to the submarine soil. Moreover, we often see clouds
arrested over these points, which look from afar like the peaks of
mountains.
FOOTNOTES:
[Footnote 1: "World before the Deluge." Second edition.]
[Footnote 2: Examen Comparatif des Principales eaux Minérales Salines de
France et d'Allemagne, par MM. L. Figuier et Mialhe. Read at the
Académie de Médecin, 23rd of May, 1848.]
[Footnote 3: Sir J. Herschel's "Physical Geography," p. 22, gives the
basis and details of this calculation.]
[Footnote 4: "La Terre et les Mers," p. 517. Troisième Ed.]