THE PRIMITIVE OCEAN.
The Giant-Book of the Earth-rind.--The Sea of Fire.--Formation of
a solid Earth-crust by cooling.--The Primitive Waters.--First
awakening of Life in the Bosom of the Ocean.--The Reign of the
Saurians.--The future Ocean. 433
PART III.
THE PROGRESS OF MARITIME DISCOVERY.
CHAPTER XXIII.
Maritime Discoveries of the Phœnicians.--Expedition of Hanno.
--Circumnavigation of Africa under the Pharaoh Necho.--Colæus of
Samos.--Pytheas of Massilia.--Expedition of Nearchus.
--Circumnavigation of Hindostan under the Ptolemies.--Voyages of
Discovery of the Romans.--Consequences of the Fall of the Roman
Empire.--Amalfi.--Pisa.--Venice.--Genoa.--Resumption of Maritime
Intercourse between the Mediterranean and the Atlantic.--Discovery
of the Mariner's Compass.--Marco Polo 443
CHAPTER XXIV.
Prince Henry of Portugal.--Discovery of Porto Santo and Madeira.
--Doubling of Cape Bojador.--Discovery of the Cape Verde Islands.
--Bartholomew Diaz.--Vasco de Gama.--Columbus.--His Predecessors.
--Discovery of Greenland by Günnbjorn.--Bjorne Herjulfson.--Leif.
--John Vaz Cortereal.--John and Sebastian Cabot.--Retrospective
View of the Beginnings of English Navigation.--Ojeda and Amerigo
Vespucci.--Vincent Yañez Pinson.--Cortez.--Verazzani.--Cartier.
--The Portuguese in the Indian Ocean 454
CHAPTER XXV.
Vasco Nuñez de Balboa.--His Discovery of the Pacific, and subsequent
Fate.--Ferdinand Magellan.--Sebastian el Cano, the first
Circumnavigator of the Globe.--Discoveries of Pizarro and Cortez.
--Urdaneta.--Juan Fernandez.--Mendoza.--Drake.--Discoveries of the
Portuguese and Dutch in the Western Pacific.--Attempts of the Dutch
and English to discover North-East and North-West Passages to India.
--Sir Hugh Willoughby and Chancellor.--Frobisher.--Davis.--Barentz.
--His Wintering in Nova Zembla.--Quiros.--Torres.--Schouten.--Le
Maire.--Abel Tasman.--Hudson.--Baffin.--Dampier.--Anson.--Byron.
--Wallis and Carteret.--Bougainville 464
CHAPTER XXVI.
What had Cook's Predecessors left him to discover?--His first Voyage.
--Discovery of the Society Islands, and of the East Coast of New
Holland.--His second Voyage.--Discovery of the Hervey Group.
--Researches in the South Sea.--The New Hebrides.--Discovery of New
Caledonia and of South Georgia.--His third Voyage.--The Sandwich
Islands.--New Albion.--West Georgia.--Cook's Murder.--Vancouver.
--La Peyrouse 485
CHAPTER XXVII.
Scoresby.--The Arctic Navigators.--Ross.--Parry.--Sufferings of
Franklin and his Companions on his Overland Expedition in 1821.
--Parry's Sledge-journey to the North Pole.--Sir John Franklin.
--M'Clure.--Kane.--M'Clintock.--South Polar Expeditions.
--Bellinghausen.--Weddell.--Biscoe.--Balleny.--Dumont d'Urville.
--Wilkes.--Sir James Ross.--Recent Scientific Voyages of
Circumnavigation 496
Description of the Frontispiece.
ARCTIC SLEDGE-JOURNEY.
The sledge plays a very conspicuous part in the history of arctic
discovery, as it enables the bold investigators of the icy
wildernesses of the North to penetrate to many places, impervious to
navigation, to establish dépôts of provisions for future emergencies,
or even becomes the means of saving their lives when their ship has
been lost or hopelessly blocked up. Whenever dogs can be had, these
useful animals are made use of for the transport. Our plate represents
one of these sledging parties threading its way through blocks of ice,
and gives a good idea of the difficulties they have to encounter.
LIST OF ILLUSTRATIONS.
PLATES.
Arctic Sledge-Journey _Frontispiece._
FACING PAGE
The Souffleur Rock, Mauritius 52
Lighthouse and Waterspout 65
Australian Sea-Bears 117
The Boats of H.M.S. "Trent" attacked by Walruses 131
Penguins 142
Subaqueous Life--Sticklebacks and Nest 195
Russian Official collecting Algæ 392
MAP.
Map of the Globe, showing the direction of the Ocean Currents,
Cotidal Lines, &c. _facing page 3_.
WOODCUTS.
Annelidans:--
Aphrodita, or Sea-Mouse, 264
Nereis, 263
Serpula, attached to a Shell, 266
Beachy Head, 5
Bell Rock Lighthouse, 86
Birds:--
Albatross, Wandering, 163
Auk, 168
Great, 151
Avoset, 144
Barnacle Goose, 146
Cormorant, common, 155
Curlew, 143
Eider Duck, 146
Flamingo, 142
Gannet, common, 156
Great Crested Grebe, 150
Guillemot, Black, 165
(winter plumage), 167
Herring Gulls, 158
Hooded Merganser, 404
Pelican, 116, 154
Penguins, 152
Petrel, Broad-billed, 160
Fork-tailed, 160
Stormy, 162
Plover, 144
Puffins, 165, 167
Red-breasted Merganser, 149
Scissor-bill (Rhynchops nigra), 144
Sheldrake, 148
Skimmer, Black, 144
Snow Goose, 146
Speckled Diver, 145
Tailor-bird, 143
Birds of Passage, 171
Bones of the Anterior Fin of a Whale, 96
Cœlenterata:--
Alcyonidium elegans, 363
Astræa, 373
Caryophyllia, 370
Chrysaora hysoscella, 357
Coryniadæ, 358
Ctenophora, 360
Diphyes appendiculata, 353
Grey Sea-Pen, 365
Isis hippuris, 369
Jelly Fishes, 349, 350, 351
Lucernalia auricula, 352
Medusæ, 349, 350, 351
Physalia caravella, 355
Physophora Philippii, 356
Red Coral, 367
Sertularia tricuspidata, 347
Stone Corals, 373, 374
Tubipora Musica, 370
Velella, 354
Virgularia mirabilis, 365
Vogtia pentacantha, 353
Compound Foraminiferous Protozoon, magnified, 380
Crustaceans:--
American Sand-Crab, 252
Balanus ovularis, and group of, 244
Barnacle, 101, 244
Calling-Crab of Ceylon, 251
Chelura tenebrans, 247
Diogenes Hermit-Crab, 254
Dromia vulgaris, 249
Jamaica Land-Crab, 250
King Crab, 246
Large-clawed Calling-Crab, 250
Limnoria lignorum, 247
Metamorphosis of Carcinus Mœnas, 258
Pea-Crab, 253
Phyllosoma, 258
Pinna Augustana, 253
Sandhopper, 246
Seyllarus equinoxialis, 248
square facets of, 247
Spotted Fin-Crab, 252
Spotted Mantis-Crab, 256
Stenopus hispidus, 261
Whale-Louse, 101
Crustaceans and Oysters, 256
Dental Apparatus of the Sea-Urchin, viewed from above, 339
Ear, Human, 196
Ear of the Perch, 196
Echinodermata:--
Cross-Fish, common, 334
Eatable Trepang, 340
Goniaster, 336
Lily-Encrinite, 330
Sand-Star, 332
Sea-Urchin, 337
Edible, 338
Mammillated, 338
Warted Euryale, 333
Eddystone Lighthouse, 84
Esquimaux in his Kayak, 120
Fingal's Cave, 47
Fishes:--
Ammodyte, or Launce, 230
Anabas of the dry tanks, 192
Anchovy, 214
Angler, 203
Bonito, 223
Cod, 215
Conger Eel, 228
Diodon, 205
Dory, 242
Electric Eel, 202
European Sly, 203
Fierasfer, 340
File-Fish, 232
Flounder, 238
Flying Fish, 156, 206, 224
Frog-Fish, 192
Gar-Fish, 223
Globe-Fish, 232
Gurnard, 197, 414
Haddock, 215
Halibut, 236
Herring, 101, 208
Lamprey, 231
Ling, 215
Mackerel, 222
Mullet, Grey, 415
Red, 197, 415
Myxine, 231
Perch, internal ear of the, 196
Picked Dog-Fish, 200
Pilchard, 212
Pilot-Fish, 225
Plaice, 238
Porcupine-Fish, 232
Salmo Rossii, 220
Salmon, 415
Sand-Eel, 415
Saw-Fish, 201
Sea-Horse, 234, 344
Shark, Blue, 200
Hammer-headed, 199
White, 198
Short Sun-Fish, 232, 422
Sole, 237
portion of skin of, highly magnified, 190
Sturgeon, common, 217
Surgeon-Fish, 205
Swimming Pegasus, 207
Sword-Fish, 99, 201
Thornback, 240
Torpedo, 201
Toxotes Jaculator, 203
Trunk-Fish, 232
Tunny, 221
Turbot, 237
Wolf-Fish, 197
Foraminifera, various forms of, 381
Fossils:--
Ammonite, 437
Belemnite, 437
Ichthyosaurus communis, 172, 438
Pentacrinus Briareus, portion of, 330
Plesiosaurus, 438
Trilobite, 436
Hill at the Rapid on Bear Lake River
(North-West Territory, North America), 23
H.M.S. "Resolute" lying to in the North Atlantic, 24
Ice-Bear approaching the "Dorothea" and "Trent", 137
Japan Junks, 63
Licmophora flabellata, 403
Mammals:--
Dolphin, 107
Dugong, 117
female, of Ceylon, 119
Manatee, 117
Polar Bear (Ursus maritimus), 134
Porpoise, 108
Rorqual, 101
Sea-Otter, 140
Seal, 119, 123, 135
Greenland, 123
Walrus, 129, 135
Whale, common, 97
Whale, Spermaceti, 102, 115
Mollusks:--
Argonaut, 280
Ascidia mammillata, 322
Banded Dipper, 141
Bivalve deprived of its shell, to show its various openings, 300
Botryllus, 324
Bulla, 294
Calamary, 272
Carinaria, 287
Cellularia, 319
Chelyosoma Macleayanum, 323, 327
Chinese Wentle-trap (Scalaria pretiosa), 289
Chiton squamosus, 285
Clavellina producta, 322
Clio borealis, 98
Cockle, common, 303, 306
Cuttle-Fish (Sepia), 104, 275
Diazona violacea, 324
Donax, 301
Edible Mussel, 307
Edible Oyster, 308
Eolis, 284
Eschara cervicornis, 318
Gorgeous Doris, 235
Haliotis, 287
Harp-shell, 288
Hippopus maculatus, 315
Ianthina communis, 290
Leaf-like Sea-mat, 316, 317
Limpet and Shell, 286, 292, 411
Magilus antiquus, 291
Mitre-shells, 288
Murex haustellum, 291, 296
Oliva hispidula, 290
Onychoteuthis, 274
Orange Cone-shell, 288
Pearl-Oyster, 312
Pearly Nautilus, 280
Periwinkle, 411
Petunculus, 302
Pholas striata, 302
Pinna, 305
Poulp (Octopus), 272, 273
Pteroceras scorpio, 290
Retepora cellularis, 318
Salpa, 326
Scyllæa, 283
Sea-Hare, compound stomach of, 295
Sepia, 104, 275
Solen, or Razor-Shell, 304
Strombus pes pelicani, 290
Syllæa, gizzard of, 294
Tiara, 283
Tridacna gigas, 314
Whelk, 413
Worm-shell, 291
Muscles and Electric Batteries of the Torpedo, 202
Nervous Axis of an Annelidan, 262
Noctiluca miliaris, 419
Ova of the Cuttle-Fish, 278
Protozoa:--
Amœba, 379
Foraminifera, 381
Halina papillaris, 386
Infusoria, marine, 384
Nummulina discoidalis, 378
Polycistina, 383
Sponges, 385
Tethea, 385, 386
Reptiles:--
Alligator Lucius, 173
Tortoise, 174
Turtle, Green, 170
Hawk's Bill, 180
Loggerhead, 176
Water-Snake, 183
Rocky Mountains at the bend of the Bear Lake River, 79
Rotifera:--
Conochilus volvox, 268
Philodina roseola, 269
Ptygura melicerta, 267
Saw of the Saw-Fish, 100
Sea-Fowl Shooting, 168
Skeleton of the Dugong, 118
of the Perch, 188
of the Seal, 119
of the Tortoise, 174
Skerryvore Lighthouse, 89
Skull and Head of Walrus, 129
Skull of Whale, with the Baleen, 98
Sockets with teeth, of Echinus esculentus, 339
Surirella constricta, 402
Theoretic representation of the Circulation in Fishes, 192
Theoretic representation of the Circulation in Mammals
and Birds, 175
Theoretic representation of the Circulation in Reptiles, 175
Torso Rock, near Point Deas Thomson, in the Arctic Ocean, 9
Urticating organs of Cœlenterata, 346
Water-Sports, 69, 70
PART I.
THE PHYSICAL GEOGRAPHY OF THE SEA.
[Illustration]
CHAPTER I.
THE MAGNITUDE OF THE SEA.
Extent of the Ocean.--Length of its Coast-Line.--Mural, Rocky,
and Flat Coasts.--How deep is the Sea?--Average Depth of the
Atlantic Ocean.--The Telegraphic Plateau between Newfoundland
and Ireland.--Measurement of Depth by the Rapidity of the
Tide-Wave.--Progressive Changes in the Limits of the Ocean.--Alluvial
Deposits.--Upheaving.--Subsidence.--Does the Level of the Sea
remain unchanged, and is it everywhere the same?--Composition and
Temperature of Sea-Water.--Its intrinsic Colour.--The Azure Grotto at
Capri.--Modification of Colour owing to Animals and Plants.--Submarine
Landscapes viewed through the Clear Waters.
Of all the gods that divide the empire of the earth, Neptune rules over
the widest realms. If a giant-hand were to uproot the Andes and cast them
into the sea, they would be engulphed in the abyss, and scarcely raise
the general level of the waters.
The South American Pampas, bounded on the north by tropical palm-trees,
and on the south by wintry firs, are no doubt of magnificent dimensions,
yet these vast deserts seem insignificant when compared with the
boundless plains of earth-encircling ocean. Nay! a whole continent, even
America or Asia, appears small against the immensity of the sea, which
covers with its rolling waves nearly three-fourths of the entire surface
of the globe.
A single glance over the map shows us at once how very unequally water
and land are distributed. In one part we see continents and islands
closely grouped together, while in another the sea widely spreads in
one unbroken plain; here vast peninsulas stretch far away into the
domains of ocean, while there immense gulfs plunge deeply into the bosom
of the land. At first sight it might appear as if blind chance had
presided over this distribution, but a nearer view convinces us that
providential laws have established the existing relations between the
solid and fluid surfaces of the earth. If the sea had been much smaller,
or if the greatest mass of land had been concentrated in the tropical
zone, all the meteorological phenomena on which the existence of actual
organic life depends would have been so different, that it is _doubtful_
whether man could then have existed, and _certain_ that, under those
altered circumstances, he never would have attained his present state of
civilisation. The dependence of our intellectual development upon the
existing configuration of the earth, convinces us that Divine wisdom and
not chaotic anarchy has from all eternity presided over the destinies of
our planet.
The length of all the coasts which form the boundary between sea and
land can only be roughly estimated, for who has accurately measured
the numberless windings of so many shores? The entire coast line of
deeply indented Europe and her larger isles measures about 21,600 miles,
equal to the circumference of the earth; while the shores of compact
Africa extend to a length of only 14,000 miles. I need hardly point out
how greatly Europe's irregular outlines have contributed to the early
development of her superior civilisation and political predominance. The
coasts of America measure about 45,000 miles, those of Asia 40,000, while
those of Australia and Polynesia may safely be estimated at 16,000. Thus
the entire coast-line of the globe amounts to about 136,000 miles, which
it would take the best pedestrian full twenty-five years to traverse from
end to end.
How different is the aspect of these shores along which the ever-restless
sea continually rises or falls! Here steep rock-walls tower up from the
deep, while there a low sandy beach extends its flat profile as far
as the eye can reach. While some coasts are scorched by the vertical
sunbeam, others are perpetually blocked up with ice. Here the safe
harbour bids welcome to the weather-beaten sailor, the lighthouse greets
him from afar with friendly ray; the experienced pilot hastens to guide
him to the port, and all along the smiling margin of the land rise the
peaceful dwellings of civilised man. There, on the contrary, the roaring
breakers burst upon the shore of some dreary wilderness, the domain of
the savage or the brute. What a wonderful variety of scenes unrolls
itself before our fancy as it roams along the coasts of ocean from zone
to zone! what changes, as it wanders from the palm-girt coral island
of the tropical seas to the melancholy strands where, verging towards
the poles, all vegetable life expires! and how magnificently grand does
the idea of ocean swell out in our imagination, when we consider that
its various shores witness at one and the same time the rising and the
setting of the sun, the darkness of night and the full blaze of day, the
rigour of winter and the smiling cheerfulness of spring!
[Illustration: Beachy Head.]
The different formation of sea-coasts has necessarily a great influence
on commercial intercourse. Bold mural coasts, rising precipitously from
the deep sea, generally possess the best harbours. Rocky shores also
afford many good ports, but most frequently only for smaller vessels, and
of difficult access, on account of the many isolated cliffs and reefs
which characterise this species of coast formation.
In places where high lands reach down to the coast, the immediate depth
of the sea is proportionably great; but wherever the surface rises gently
landwards, the sea-bed continues with a corresponding slope downwards. On
these flat coasts the tides roll over a sandy or shingly beach; and here
the aid of human industry is frequently required to create artificial
ports, or to prevent those already existing from being choked with sand.
On many flat coasts the drift-sand has raised _dunes_, wearying the eye
by their monotonous uniformity; on others, where these natural bulwarks
are wanting, artificial embankments, or dykes protect the lowlands
against the encroachments of the sea, or else the latter forms vast
salt-marshes and lagunes. On some coasts these submerged or half-drowned
lands have been transformed by the industry of man into fertile meadows
and fields, of which the Dutch Netherlands afford the most celebrated
example; while in other countries, such as Egypt, large tracts of land
once cultivated have been lost to the sea, in consequence of long misrule
and tyranny.
* * * * *
How deep is the sea? How is its bottom formed? Does life still exist in
its abyssal depths? These mysteries of ocean, which no doubt floated
indistinctly before the mind of many an inquisitive mariner and
philosopher of ancient times, have only recently been subjected to a more
accurate investigation. Their solution is of the highest importance,
both to the physical geographer, whose knowledge must necessarily
remain incomplete until he can fully trace the deep-sea path of oceanic
currents, and to the zoologist, to whom it affords a wider insight into
the laws which govern the development of the innumerable forms of life
with which our globe is peopled.
The ordinary system of sounding by means of a weight attached to a
graduated line, and "armed" at its lower end with a thick coating of soft
tallow, so as to bring up evidence of its having reached the bottom in a
sample of mud, shells, sand, gravel, or ooze, answers perfectly well for
comparatively shallow water, and for the ordinary purposes of navigation,
but it breaks down for depths much over 1000 fathoms. The weight is not
sufficient to carry the line rapidly and vertically to the bottom; and if
a heavier weight be used, ordinary sounding line is unable to draw up its
own weight along with that of the lead from great depths, and gives way,
so that by this means no information can be gained as to the nature of
the sea-bottom. To obviate this difficulty, several ingenious instruments
have been invented, such as the "Bull-dog" sounding machine, which is so
contrived that on touching the bottom the weight becomes detached, while
at the same time a pair of scoops, closing upon one another scissorwise
on a hinge, and permanently attached to the sounding-line, retain and
are able to bring up a sample of the bottom.
With the aid of steam, dredging has also been successfully carried down
to 2,435 fathoms, so that the ocean bed may become in time as well known
to us as the bed of the Mersey or the Thames.
Both sounding and dredging at great depths are, however, difficult and
laborious tasks, which can only be performed under very favourable
circumstances, and require a vessel specially fitted at considerable
expense.
Many of the early deep soundings in the Atlantic, which reported the
astonishing depths of 46,000 or even 50,000 feet, are now known to have
been greatly exaggerated. In some cases bights of the line seem to be
carried along by submarine currents, and in others it is found that the
line has been running out by its own weight only, and coiling itself in
a tangled mass directly over the lead. These sources of error vitiate
very deep soundings; and consequently, in the last chart of the North
Atlantic, published on the authority of Rear-Admiral Richards in November
1870, none are entered beyond 4000 fathoms, and very few beyond 3000.
"The general result," says Professor Wyville Thomson,[A] "to which we
are led by the careful and systematic deep-sea soundings which have been
undertaken of late years is that the depth of the sea is not so great as
was at one time supposed, and does not appear to average more than 2000
fathoms (12,000 feet), about equal to the mean height of the elevated
table-lands of Asia.
[Footnote A: "The Depths of the Sea," p. 228.]
"The thin shell of water which covers so much of the face of the earth
occupies all the broad general depressions in its crust, and it is only
limited by the more abrupt prominences which project above its surface,
as masses of land with their crowning plateaux and mountain ranges. The
Atlantic Ocean covers 30,000,000 of square miles, and the Arctic Sea
3,000,000, and taken together they almost exactly equal the united areas
of Europe, Asia, and Africa--the whole of the Old World--and yet there
seem to be few depressions on its bed to a greater depth than 15,000 or
20,000 feet--a little more than the height of Mont Blanc; and, except in
the neighbourhood of the shores, there is only one very marked mass of
mountains, the volcanic group of the Açores."
Accurate soundings are as yet much too distant to justify a detailed
description of the bed of the Atlantic. I will merely state that after
sloping gradually to a depth of 500 fathoms to the westward of the coast
of Ireland, in lat. 52° N., the bottom suddenly dips to 1700 fathoms,
at the rate of from about 15 to 19 feet in the 100. From this point to
within about 200 miles of the coast of Newfoundland, where it begins
to shoal again, there is a vast undulating plain averaging about 2000
fathoms in depth below the surface--the "telegraph plateau" on which now
rest the cables through which the electric power transmits its marvellous
messages from one world to another.
Our information about the beds of the Indian, the Antarctic, and the
Pacific Oceans is still more incomplete, but the few trustworthy
observations which have hitherto been made seem to indicate that neither
the depth nor the nature of the bottom of these seas differs greatly from
what we find nearer home.
The inclosed and land-locked European seas are very shallow when compared
with the high ocean: the Mediterranean, however, has in some parts a
depth of more than 6000 feet; and even in the Black Sea, the plummet
sometimes descends to more than 3000 feet; while the waters of the
Adriatic everywhere roll over a shallow bed.
The researches of Mr. Russell on the swiftness of the tide-wave, showing
that the rapidity of its progress increases with the depth of the waters
over which it passes, afford us another means, besides the sounding
line, of determining approximately the distance of the sea-bottom from
its surface. According to this method, the depth of the Channel between
Plymouth and Boulogne has been calculated at 180 feet; and the enormous
rapidity of the flood wave over the great open seas (300 miles an hour
and more) gives us for the mean depth of the Atlantic 14,400 feet, and
for that of the Pacific 19,500.
Natural philosophers have endeavoured to calculate the quantity of the
waters contained within the vast bosom of the ocean; but as we are
still very far from accurately knowing the mean depth of the sea, such
estimates are evidently based upon a very unsubstantial foundation.
So much at least is certain, that the volume of the waters of the ocean
as much surpasses all conception, as the number of their inhabitants, or
of the sands that line their shores.
* * * * *
[Illustration: Torso Rock, near Point Deas Thomson, in the Arctic Ocean.]
The boundaries of the ocean are not invariable; while in some parts
it encroaches upon the land, in others it retreats from the expanding
coast. In many places we find the sea perpetually gnawing and undermining
cliffs and rocks; and sometimes swelling with sudden rage, it devours a
broad expanse of plain, and changes fertile meads into a dreary waste of
waters. The Goodwin Sands, notorious for the loss of many a noble vessel,
were once a large tract of low ground belonging to Earl Goodwin, father
of Harold, the last of our Saxon kings; and being afterwards enjoyed
by the monastery of St. Augustine at Canterbury, the whole surface was
drowned by the abbot's neglect to repair the wall which defended it from
the sea. In spite of the endeavours of the Dutch to protect their flat
land by dykes against the inundatory waters, the storm-flood has more
than once burst through these artificial boundaries, and converted large
districts into inland seas.
But the spaces which in this manner the dry land has gradually or
suddenly lost, or still loses, to the chafing ocean are largely
compensated for in other places, by the vast accumulations of mud
and sand, which so many rivers continually carry along with them into
the sea. Thus at the mouths of the Nile, of the Ganges, and of the
Mississippi, large alluvial plains have been deposited, which now form
some of the most fruitful portions of the globe. The whole Delta of
Egypt, Bengal, and Louisiana, have thus gradually emerged from the waters.
The volcanic powers, which once caused the highest mountain chains to
rise from the glowing bosom of the earth, are still uninterruptedly
active in changing its surface, and are gradually displacing the present
boundaries of sea and land, upheaving some parts and causing others to
subside.
On the coast of Sweden, it has been ascertained that iron rings fixed to
rocks which formerly served for the fastening of boats are at present
much too high. Flat cliffs on which, according to ancient documents,
seals used to be clubbed while enjoying the warm sunbeam, are now quite
out of the reach of these amphibious animals. In the years 1731, 1752,
and 1755, marks were hewn in some conspicuous rocks, which after the
lapse of half a century were found to have risen about two feet higher
above the level of the sea. This phenomenon is confined to part of the
coast, so that it is clearly the result of a local and slowly progressive
upheaving.
Whilst a great part of Scandinavia is thus slowly but steadily rising,
the shores of Chili have been found to rise convulsively under the
influence of mighty volcanic shocks. Thus after the great earthquake of
1822, the whole coast, for the length of a hundred miles, was found to
be three or four feet higher than before, and a further elevation was
observed after the earthquake of Feb. 21st, 1835.
While to the north of Wolstenholme Sound, Kane remarked signs of
elevation, a converse depression was observed as he proceeded southwards
along the coast of Greenland, Esquimaux huts being seen washed by the
sea. The axis of oscillation must be somewhere about 77° N. lat.
At Keeling Island, in the Indian Ocean, Mr. Darwin found evidence
of subsidence. On every side of the lagoon, in which the water is
as tranquil as in the most sheltered lake, old cocoa-nut trees were
undermined and falling. The foundation-posts of a store-house on the
beach, which the inhabitants had said stood seven years before just above
high-water mark, were now daily washed by the tide. Earthquakes had been
repeatedly remarked by the inhabitants, so that Darwin no longer doubted
concerning the cause which made the trees to fall, and the store-house to
be washed by the daily tide.
On the columns of the temple of Serapis, near Puzzuoli, the astonished
naturalist sees holes scooped out by Pholades and Lithodomas, twenty-four
feet above the present level of the sea. These animals are marine
testacea, that have the power of burying themselves in stone, and
cannot live beyond the reach of low-water. How then have they been able
to scoop out those hieroglyphic marks so far above the level of their
usual abodes? for surely marble originally defective was never used
for the construction of so proud an edifice. Alternate depressions and
elevations of the soil afford us the only key to the enigma. Earthquakes
and oscillations, so frequent in that volcanic region, must first
have lowered the temple into the sea, where it was acted upon by the
sacrilegious molluscs, and then again their upheaving powers must have
raised it to its present elevation. Thus, even the solid earth changes
its features, and reminds us of the mutability of all created things.
There can be no doubt that, in consequence of the perpetual increase of
alluvial deposits, and of the volcanic processes I have mentioned, the
present boundaries of ocean must undergo great alterations in the course
of centuries, and the general level of the sea must either rise or fall;
but the evidence of history proves to us that, for the last 2000 years at
least, there has been no notable change in this respect.
The baths hewn out in the rocks of Alexandria, and the stones of its
harbour, have remained unaltered ever since the foundation of the city
by the Macedonian conqueror; and the ancient port of Marseilles shows
no more signs of a change of level than the old sea-walls of Cadiz.
Thus, all the elevations and depressions that have occurred in the bed
of ocean, or along its margin, and all the mud and sand that thousands
of rivers continually carry along with them into the sea, have left its
general level unaltered, at least within the historic ages. However
great their effects may appear to the eye that confines itself to local
changes, their influence, as far as the evidence of history reaches, has
been but slight upon the immensity of the sea.
Geodesical operations have proved that the level of the ocean, with
the exception of certain enclosed seas of limited extent, is everywhere
the same. The accurate measurements of Corabœuf and Delcros show no
perceptible difference between the level of the Channel and that of the
Mediterranean. In the course of the operations for measuring the meridian
in France, M. Delambre calculated the height of Rodez above the level
of the Mediterranean at Barcelona, and its height above the ocean which
washes the foot of the tower of Dunkirk, and found the difference to be
equal to a fraction of a yard.
The measurements which, at Humboldt's suggestion, General Bolivar caused
to be executed by Messrs. Lloyd and Filmore, prove that the Pacific is,
at the utmost, only a few feet higher than the Caribbean Sea, and even
that the relative height of the two seas changes with the tides.
The long and narrow inlet of the Red Sea, which, according to former
measurements, was said to be twenty-four or thirty feet higher than the
Mediterranean seems, from more recent and accurate investigations, to be
of the same level, and thus to form no exception to the general rule.
* * * * *
The salts contained in sea water, and to which it owes its peculiar
bitter and unpleasant taste, form about three and a half per cent. of
its weight, and consist principally of common table salt (chloride of
sodium), and the sulphates and carbonates of magnesia and lime. But,
besides these chief ingredients, there is scarcely a single elementary
body of which traces are not to be found in that universal solvent.
Wilson has pointed out fluoric combinations in sea water, and Malaguti
and Durocher (Annales de Chimie, 1851) detected lead, copper, and silver
in its composition. Tons of this precious metal are dissolved in the vast
volume of the ocean, and it contains arsenic sufficient to poison every
living thing.
Animal mucus, the product of numberless creatures, is mixed up with the
sea water, and it constantly absorbs carbonic acid and atmospheric air,
which are as indispensable to the marine animals and plants as to the
denizens of the atmospheric ocean.
In inclosed seas, communicating with the ocean only by narrow straits,
the quantity of saline particles varies from that of the high seas. Thus
the Mediterranean, when evaporation is favoured by heat, contains about
one half per cent. more salt than the ocean; while the Baltic, which,
on account of its northern position, is not liable to so great a loss,
and receives vast volumes of fresh water from a number of considerable
rivers, is scarcely half so salt as the neighbouring North Sea.
In the open ocean, the perpetual circulation of the waters produces an
admirable equality of composition: yet Dr. Lenz, who accompanied Kotzebue
in his second voyage round the world, and devoted great attention to
the subject, found that the Atlantic, particularly in its western part,
contains a somewhat larger proportion of salts than the Pacific; and that
the Indian Ocean, which connects those vast volumes of water, is more
salt towards the former than towards the latter.
* * * * *
As water is a bad conductor of caloric, the temperature of the seas is in
general more constant than that of the air.
The equinoctial ocean seldom attains the maximum warmth of 83°, and has
never been known to rise above 87°; while the surface of the land between
the tropics is frequently heated to 129°. In the neighbourhood of the
line, the temperature of the surface-water oscillates all the year round
only between 82° and 85°, and scarce any difference is perceptible at
different times of the day.
The wonderful sameness and equability of the temperature of the tropical
ocean over spaces covering thousands of square miles, particularly
between 10° N. and 10° S. lat., far from the coasts, and where it is
not intersected by pelagic streams, affords, according to Arago, the
best means of solving a very important, and as yet unanswered question,
concerning the physics of the globe. "Without troubling itself,"
says that great natural philosopher, "about mere local influences,
each century might leave to succeeding generations, by a few easy
thermometrical measurements, the means of ascertaining whether the sun,
at present almost the only source of warmth upon the surface of the
earth, changes his physical constitution, and varies in his splendour
like most stars, or whether he has attained a permanent condition. Great
and lasting revolutions in his shining orb would reflect themselves more
accurately in the altered mean temperature of those ocean plains than in
the changed medium warmth of the dry land."
The warmest part of the ocean does not coincide with the Equator, but
seems to form two not quite parallel bands to the north and south.
In the northern Atlantic, the line of greatest temperature (87° F.) which
on the African coast is found but a little to the north of the Equator,
rises on the north coast of South America as high as 12° N. lat., and
in the Gulf of Mexico ranges even beyond the tropic. The influence of
the warmth-radiating land on inclosed waters is still more remarkable in
the Mediterranean (between 30° and 44° N. lat.) where during the summer
months a temperature of 84° and 85° is found, three degrees higher than
the medium warmth of the open tropical seas.
While in the torrid zone the temperature of the ocean is generally
inferior to that of the atmosphere, the contrary takes place in the Polar
seas. Near Spitzbergen, even under 80° N. lat., Gaimard never found the
temperature of the water below +33°. Between Norway and Spitzbergen the
mean warmth of the water in summer was +39°, while that of the air only
attained +37°.
In the enclosed seas of the Arctic Ocean, the enormous accumulation of
ice, which the warmth of a short summer is unable totally to dissolve,
naturally produces a very low temperature of the waters. Thus, in
Baffin's Bay, Sir John Ross found during the summer months only
thirty-one days on which the temperature of the water rose above freezing
point.
In the depths of the sea, even in the tropical zone, the water is found
of a frigid temperature, and this circumstance first led to the knowledge
of the submarine polar ocean currents; "for without these, the deep sea
temperature in the tropics could never have been lower than the maximum
of cold, which the heat-radiating particles attain at the surface."[B]
[Footnote B: Humboldt's "Kosmos."]
It was formerly believed that while the surface temperature--which
depended upon direct solar radiation, the direction of currents, the
temperature of winds, and other temporary causes--might vary to any
amount, at a certain depth the temperature was permanent at 4° C., the
temperature of the greatest density of fresh water. Late investigations,
however, have led to the conclusion that instead of there being a
permanent deep layer of water at 4° C., the average temperature of the
deep sea in temperate and tropical regions is about 0° C., the freezing
point of fresh water.
In the atmospheric ocean, aëronauts not seldom meet with warm air
currents flowing above others of a colder temperature; while, according
to a general law, the warmth of the air constantly diminishes as its
elevation above the surface of the sea increases.
Similar exceptions to the general rule are met with in the ocean. In
moderate depths sometimes the whole mass of water from the surface to the
bottom is abnormally warm, owing to the movement in a certain direction
of a great body of warm water, as in the "warm area" to the north-west of
the Hebrides, where, at a depth of 500 fathoms, the minimum temperature
was found to be 6° C. On the other hand, the whole body of water is
sometimes abnormally cold, as in the "cold area," between Scotland and
Faeroe, where, at a depth of 500 fathoms, the bottom temperature is found
to average -1° C.[C] The only feasible explanation of these enormous
differences of temperature, amounting to nearly 13° F. in two areas
freely communicating with one another, and in close proximity, is that
in the area to the north-west of the Hebrides a body of water warmed
even above the normal temperature of the latitude flows northwards from
some southern source, and occupies the whole depth of that comparatively
shallow portion of the Atlantic, while an arctic stream of frigid water
creeps from the north-eastward into the trough between Faeroe and the
Shetland Islands, and fills its deeper part in consequence of its higher
specific gravity. There can be no doubt that similar phenomena occur
in various parts of the ocean, and that the deep seas are frequently
intersected by streams differing in temperature from the surrounding
waters.
[Footnote C: "The Depths of the Sea," by Professor Wyville Thomson, p.
307.]
In some places, owing to the conformation of the neighbouring land or
of the sea-bottom, superficial warm and cold currents are circumscribed
and localised, thereby occasioning the singular phenomenon of a patch
or stripe of warm and a patch of cold sea meeting in an invisible but
well-defined line.
The temperature of the sea apparently never sinks at any depth below
-3·5° C. This is about the temperature of the maximum density of sea
water, which contracts steadily till just above its freezing point
(-3·67° C.), when kept perfectly still.
If we include in the tropical seas all that part of the ocean where the
surface temperature never falls below 68° F., and where consequently
living coral reefs may occur, we find that it nearly equals in size the
temperate and cold ocean-regions added together. This distribution of
the waters over the surface of the globe is of the highest importance to
mankind; for the immense extent of the tropical ocean, where, of course,
the strongest evaporation takes place, furnishes our temperate zone with
the necessary quantity of rain, and tends by its cooling influence to
diminish the otherwise unbearable heat of the equatorial lands.
The circumstance of ice being lighter than water also contributes to the
habitability of our earth. Ice is a bad conductor of heat; consequently
it shields the subjacent waters from the influence of frost, and prevents
its penetrating to considerable depths. If ice had been heavier than
water, the sea-bottom, in higher latitudes, would have been covered
with solid crystal at the very beginning of the cold season; and during
the whole length of the polar winter, the perpetually consolidating
surface-waters would have been constantly precipitated, till finally the
whole sea, far within the present temperate zone, would have formed one
solid mass of ice. The sun would have been as powerless to melt this
prodigious body, as it is to dissolve the glaciers of the Alps, and the
cold radiating from its surface would have rendered all the neighbouring
lands uninhabitable.
* * * * *
The mixture of the water of rivers with that of the sea presents some
hydrostatic phenomena which it is curious enough to observe. Fresh water
being lighter, ought to keep at the surface, while the salt water, from
its weight, should form the deepest strata. This, in fact, is what Mr.
Stephenson observed in 1818 in the harbour of Aberdeen at the mouth of
the Dee, and also in the Thames near London and Woolwich. By taking up
water from different depths with an instrument invented for the purpose,
Mr. Stephenson found that at a certain distance from the mouth the water
is fresh in the whole depth, even during the flow of the tide, but that
a little nearer the sea fresh water is found on the surface, while the
lower strata consist of sea water. According to his observations it is
between London and Woolwich that the saltness of the bottom begins to be
perceptible. Thus, below Woolwich the Thames, instead of flowing over a
solid bed, in reality flows upon a liquid bottom formed by the water of
the sea, with which no doubt it is more or less mixed.
Mr. Stephenson is of opinion that, at the flow of the tide, the fresh
water is raised as it were in a single mass by the salt water which
flows in, and which ascends the bed of the river, while the fresh water
continues to flow towards the sea.
Where the Amazon, the La Plata, the Orinoco, and other giant streams pour
out their vast volumes of water into the ocean, the surface of the sea is
fresh for many miles from the shore; but this is only superficial, for
below, even in the bed of the rivers, the bitterness of salt water is
found.
It is a curious fact, that in many parts of the ocean, fresh-water
springs burst from the bottom of the sea. Thus, in the Gulf of Spezzia,
and in the port of Syracuse, large jets of fresh water mingle with the
brine; and Humboldt mentions a still more remarkable submarine fountain
on the southern coast of Cuba, in the Gulf of Xagua, a couple of sea
miles from the shore, which gushes through the salt water with such
vehemence, that boats approaching the spot are obliged to use great
caution. Trading vessels are said sometimes to visit this spring, in
order to provide themselves in the midst of the ocean with a supply of
fresh water.
* * * * *
The sea is not colourless; its crystal mirror not only reflects the
bright sky or the passing cloud, but naturally possesses a pure bluish
tint, which is only rendered visible to the eye when the light penetrates
through a stratum of water of considerable depth. This may be easily
ascertained by experiment. Take a glass tube, two inches wide and two
yards long, blacken it internally with lamp-black and wax to within half
an inch of the end, the latter being closed by a cork. Throw a few pieces
of white porcelain into this tube, which, after being filled with pure
sea-water, must be set vertically on a white plate, and then, looking
through the open end, you will see the white of the porcelain changed
into a light blue tint.
In the Gulf of Naples, we find the inherent colour of the water exhibited
to us by Nature on a most magnificent scale. The splendid "Azure cave,"
at Capri, might almost be said to have been created for the purpose.
For many centuries its beauties had been veiled from man, as the narrow
entrance is only a few feet above the level of the sea, and it was
only discovered in the year 1826, by two Prussian artists accidentally
swimming in the neighbourhood. Having passed the portal, the cave widens
to grand proportions, 125 feet long, and 145 feet broad, and except
a small landing place on a projecting rock at the farther end, its
precipitous walls are on all sides bathed by the influx of the waters,
which in that sea are most remarkably clear, so that the smallest objects
may be distinctly seen on the light bottom at a depth of several hundred
feet. All the light that enters the grotto must penetrate the whole depth
of the waters, probably several hundred feet, before it can be reflected
into the cave from the clear bottom, and it thus acquires so deep a tinge
from the vast body of water through which it has passed, that the dark
walls of the cavern are illumined by a radiance of the purest azure, and
the most differently coloured objects below the surface of the water are
made to appear bright blue. Had Byron known of the existence of this
magic cave, Childe Harold would surely have sung its beauties in some of
his most brilliant stanzas.
All profound and clear seas are more or less of a deep blue colour,
while, according to seamen, a green colour indicates soundings. The
bright blue of the Mediterranean, so often vaunted by poets, is found all
over the deep pure ocean, not only in the tropical and temperate zones,
but also in the regions of eternal frost. Scoresby speaks with enthusiasm
of the splendid blue of the Greenland seas, and all along the great
ice-barrier which under 77° S. lat. obstructed the progress of Sir James
Ross towards the pole, that illustrious navigator found the waters of as
deep a blue as in the classical Mediterranean. The North Sea is green,
partly from its water not being so clear, and partly from the reflection
of its sandy bottom mixing with the essentially blue tint of the water.
In the Bay of Loanga the sea has the colour of blood, and Captain Tuckey
discovered that this results from the reflection of the red ground-soil.
But the essential colour of the sea undergoes much more frequent changes
over large spaces, from enormous masses of minute _algæ_, and countless
hosts of small sea-worms, floating or swimming on its surface.
"A few days after leaving Bahia," says Mr. Darwin, "not far from the
Abrolhos islets, the whole surface of the water, as it appeared under a
weak lens, seemed as if covered by chipped bits of hay with their ends
jagged. Each bundle consisted of from twenty to sixty filaments, divided
at regular intervals by transverse septa, containing a brownish-green
flocculent matter. The ship passed several bands of them, one of which
was about ten yards wide, and, judging from the mud-like colour of the
water, at least two and a half miles long. Similar masses of floating
vegetable matter are a very common appearance near Australia. During two
days preceding our arrival at the Keeling Islands, I saw in many parts
masses of flocculent matter of a brownish green colour, floating in the
ocean. They were from half to three inches square, and consisted of two
kinds of microscopical confervæ. Minute cylindrical bodies, conical at
each extremity, were involved in large numbers in a mass of fine threads."
"On the coast of Chili," says the same author, "a few leagues north of
Conception, the 'Beagle' one day passed through great bands of muddy
water; and again, a degree south of Valparaiso, the same appearance
was still more extensive. Mr. Sulivan, having drawn up some water in a
glass, distinguished by the aid of a lens moving points. The water was
slightly stained, as if by red dust, and after leaving it for sometime
quiet, a cloud collected at the bottom. With a slightly magnifying lens,
small hyaline points could be seen darting about with great rapidity,
and frequently exploding. Examined with a much higher power, their shape
was found to be oval, and contracted by a ring round the middle, from
which line curved little setæ proceeded on all sides, and these were the
organs of motion. Their minuteness was such that they were individually
quite invisible to the naked eye, each covering a space equal only to
the one-thousandth of an inch, and their number was infinite, for the
smallest drop of water contained very many. In one day we passed through
two spaces of water thus stained, one of which alone must have extended
over several square miles. The colour of the water was like that of
a river which has flowed through a red clay district, and a strictly
defined line separated the red stream from the blue water."
In the neighbourhood of Callao, the Pacific has an olive-green colour,
owing to a greenish matter which is also found at the bottom of the sea,
in a depth of 800 feet. In its natural state it has no smell, but when
cast on the fire, it emits the odour of burnt animal substances.
Near Cape Palmas, on the coast of Guinea, Captain Tuckey's ship seemed to
sail through milk, a phenomenon which was owing to an immense number of
little white animals swimming on the surface, and concealing the natural
tint of the water.
The peculiar colouring of the Red Sea, from which it has derived its
name, is owing to the presence of a microscopic alga, _sui generis_,
floating at the surface of the sea and even less remarkable for its
beautiful red colour than for its prodigious fecundity.
I could add many more examples, where, either from minute algæ or from
small animals, the deep blue sea suddenly appeared in stripes of white,
yellow, green, brown, orange or red. For fear, however, of tiring the
reader's patience, I shall merely mention the _olive-green_ water, which
covers a considerable part of the Greenland seas. It is found between
74° and 80° N. lat., but its position varies with the currents, often
forming isolated stripes, and sometimes spreading over two or three
degrees of latitude. Small yellowish Medusæ, of from one-thirtieth to
one-twentieth of an inch in diameter are the principal agents that change
the pure ultramarine of the Arctic Ocean into a muddy green. According
to Scoresby, they are about one-fourth of an inch asunder, and in this
proportion a cubic inch of water must contain 64, a cubic foot 110,592,
a cubic fathom 23,887,872, and a cubic mile nearly twenty-four thousand
billions! From soundings made in the situation where these animals were
found, the sea is probably more than a mile deep; but whether these
substances occupy the whole depth is uncertain. Provided, however, the
depth to which they extend be about 250 fathoms, the immense number of
one species mentioned above may occur in a space of two miles square; and
what a stupendous idea must we form of the infinitude of marine life,
when we consider that those vast numbers, beyond all human conception,
occupy after all only a small part of the green-coloured ocean which
extends over twenty or thirty thousand square miles! It is here that the
giant whale of the north finds his richest pasture-grounds, which at
the same time invite man to follow on his track. A small red crustacean
(_Cetochilus australis_) which forms very extensive banks in the Pacific,
and in the middle of the Atlantic about 40° S. lat., affords a similar
supply of food to the whales frequenting those seas, and exposes them to
the same dangers.
When the sea is perfectly clear and transparent, it allows the eye to
distinguish objects at a very great depth. Near Mindora, in the Indian
Ocean, the spotted corals are plainly visible under twenty-five fathoms
of water. The crystalline clearness of the Caribbean sea excited the
admiration of Columbus, who in the pursuit of his great discoveries ever
retained an open eye for the beauties of nature. "In passing over these
splendidly adorned grounds," says Schöpf, "where marine life shows itself
in an endless variety of forms, the boat, suspended over the purest
crystal, seems to float in the air, so that a person unaccustomed to the
scene easily becomes giddy. On the clear sandy bottom appear thousands of
sea-stars, sea-urchins, molluscs, and fishes of a brilliancy of colour
unknown in our temperate seas. Fiery red, intense blue, lively green,
and golden yellow perpetually vary; the spectator floats over groves of
sea-plants, gorgonias, corals, alcyoniums, flabellums, and sponges, that
afford no less delight to the eye, and are no less gently agitated by the
heaving waters, than the most beautiful garden on earth when a gentle
breeze passes through the waving boughs."
With equal enthusiasm De Quatrefages expatiates on the beauties of the
submarine landscapes on the coast of Sicily. "The surface of the waters,
smooth and even like a mirror, enabled the eye to penetrate to an
incredible depth, and to recognise the smallest objects. Deceived by this
wonderful transparency, it often occurred during my first excursions,
that I wished to seize some annelide or medusa, which seemed to swim
but a few inches from the surface. Then the boatman smiled, took a net
fastened to a long pole, and, to my great astonishment, plunged it deep
into the water before it could attain the object which I had supposed
to be within my reach. The admirable clearness of the waters produced
another deception of a most agreeable kind. Leaning over the boat, we
glided over plains, dales, and hillocks, which, in some places naked
and in others carpeted with green or with brownish shrubbery, reminded
us of the prospects of the land. Our eye distinguished the smallest
inequalities of the piled-up rocks, plunged more than a hundred feet
deep into their cavernous hollows, and everywhere the undulations of
the sand, the abrupt edges of the stone-blocks, and the tufts of algæ
were so sharply defined, that the wonderful illusion made us forget
the reality of the scene. Between us and those lovely pictures we saw
no more the intervening waters that enveloped them as in an atmosphere
and carried our boat upon their bosom. It was as if we were hanging in
a vacant space, or looking down like birds hovering in the air upon a
charming prospect. Strangely formed animals peopled these submarine
regions, and lent them a peculiar character. Fishes, sometimes isolated
like the sparrows of our groves, or uniting in flocks like our pigeons
or swallows, roamed among the crags, wandered through the thickets
of the sea-plants, and shot away like arrows as our boat passed over
them. Caryophyllias, Gorgonias, and a thousand other zoophytes unfolded
their sensitive petals, and could hardly be distinguished from the
real plants with whose fronds their branches intertwined. Enormous
dark blue Holothurias crept along upon the sandy bottom, or slowly
climbed the rocks, on which crimson sea-stars spread out immoveably
their long radiating arms. Molluscs dragged themselves lazily along,
while crabs, resembling huge spiders, ran against them in their oblique
and rapid progress, or attacked them with their formidable claws.
Other crustaceans, analogous to our lobsters or shrimps, gambolled
among the fuci, sought for a moment the surface waters to enjoy the
light of heaven, and then by one mighty stroke of their muscular tail,
instantly disappeared again in the obscure recesses of the deep. Among
these animals whose shapes reminded us of familiar forms appeared other
species, belonging to types unknown in our colder latitudes: _Salpæ_,
strange molluscs of glassy transparency, that, linked together, form
swimming chains; great _Beroës_, similar to living enamel; _Diphyæ_
hardly to be distinguished from the pure element in which they move, and
finally, _Stephanomiæ_, animated garlands woven of crystal and flowers,
and which, still more delicate than the latter, disappear as they wither,
and do not even leave a cloud behind them in the vase, which a few
moments before their glassy bodies had nearly entirely filled."
[Illustration: Hill at the Rapid on Bear Lake River. (North-West
Territory, North America.)]
CHAP. II.
THE WAVES OF THE OCEAN.
Waves and the Mode of their Formation.--Height and Velocity of
Storm-Waves, on the High Seas, according to the Calculations of
Scoresby, Arago, Sir James Ross, and Wilkes.--Their Height and
Power on Coasts.--Their Destructive Effects along the British
Shore.--Dunwich.--Reculver.--Shakspeare's Cliff.
After having admired the sea in the grandeur of its expanse, and the
profundity of its depths, I shall, in this and the two following
chapters, examine in what manner the perpetual circulation of its waters
is maintained.
[Illustration: H.M.S. "Resolute" lying to in the North Atlantic.]
"The movements of the sea," says Humboldt, "are of a three-fold
description: partly irregular and transitory, depending upon the winds,
and occasioning waves; partly regular and periodical, resulting from
the attraction of the sun and the moon (ebb and flood); and partly
permanent, though of unequal strength and rapidity at different periods
(oceanic currents)."
Who has ever sojourned on the coast, or crossed the seas, and has not
been delighted by the aspect of the waves, so graceful when a light
breeze curls the surface of the waters, so sublime when a raging storm
disturbs the depths of the ocean?
But it is easier to admire the beauty of a wave than clearly to explain
its nature, so as to convey an accurate or sufficiently general
conception of its formation to the reader's mind. Those who are placed
for the first time on a stormy sea, discover with wonder that the large
waves which they see rushing along with a velocity of many miles an hour
do not carry the floating body along with them, but seem to pass under
the bottom of the ship with scarcely a perceptible effect in carrying the
vessel out of its course.
In like manner, the observer near the shore perceives that floating
pieces of wood are not carried towards the shore with the rapidity of
the waves, but are left nearly in the same place after the wave has
passed them as before. Nay, if the tide be ebbing, the waves may even be
observed rushing with great velocity towards the shore, while the body of
water is actually receding, and any object floating in it is carried in
the opposite direction to the waves out to sea.
What, then, is wave-motion as distinct from water-motion? The force of
the wind, pushing a given mass of water out of its place into another,
dislodges the original occupant, which is again pushed forward on the
occupant of the next place, and so on. As the water-particles crowd
upon one another, in the act of going out of their old places into the
new, the crowd forms a temporary heap visible on the surface of the
fluid, and as each successive mass is displacing the one before it, the
undulation or oscillatory movement spreads farther and farther over the
waters. Wave-motion is, in fact, the transference of motion without the
transference of matter: of form without the substance, of force without
the agent.
The strongest storm cannot suddenly raise high waves, they require
time for their development. Fancy the wind blowing over an even sea,
and it will set water-particles in motion all over the surface,
and thus give the first impulse to the formation of small waves.
Numberless oscillations unite their efforts, and create visible
elevations and depressions. Meanwhile, the wind is constantly setting
new particles in motion; long before the first oscillations have lost
their effect, countless others are perpetually arising, and thus the
sum of the propelling powers is constantly increasing, and gradually
raising mountain-waves, until their growth is finally limited by the
counterbalancing power of the earth's attraction.
As the strength of the waves only gradually rises, it also loses itself
only by degrees, and many hours after the tornado has ceased to rage,
mighty billows continue to remind the mariner of its extinguished fury.
The turmoil of waters awakened by the storm propagates itself hundreds
of miles beyond the space where its howling voice was heard, and often,
during the most tranquil weather, the agitated sea proclaims the distant
war of the elements.
The velocity of waves depends not only on the power of the impulse, but
also on the depth of the subjacent waters, as I have already mentioned in
the preceding chapter.
For this reason, as increased velocity augments the power of the impulse,
the waves in the Atlantic or Pacific, the mean depth of which may be
estimated at 12,000 or 18,000 feet, attain a much greater height than in
the comparatively shallow North Sea.
The breaking of the waves against the shore arises from their velocity
diminishing with their depth. As the small flat wave rolls up the beach,
its front part, retarded by the friction of the ground, is soon overtaken
by its back, moving in swifter progression, and thus arises its graceful
swelling, the toppling of its snow-white crest, and finally its pleasant
prattle among the shingles of the strand. This is one of those pictures
of nature which Homer describes with such inimitable truth in various
places of his immortal poems: he paints with admirable colours the slow
rising of the advancing wave, how it bends forward with a graceful curve,
and, crowning itself with a diadem of foam, spreads like a white veil
over the beach, leaving sea-weeds and shells behind, as it rustles back
again into the sea.
The height which waves may attain on the open sea has been accurately
investigated by the late Rev. Dr. Scoresby, during two passages across
the Atlantic in 1847 and 1848.
"In the afternoon of March 5th, 1848," says that eminent philosopher,
"I stood during a hard gale upon the cuddy-roof or saloon deck of the
'Hibernia:' a height, with the addition of that of the eye, of 23 feet
3 inches above the line of flotation (the ship's course being similar
to that of the waves). I am not aware that I ever saw the sea more
terribly magnificent; the great majority of the rolling masses of water
was more than 24 feet high, (including depression as well as altitude,
or reckoning above the mean-level, more than 12 feet). I then went to
the larboard paddle-box, about 7 feet higher (30 feet 2 inches up to the
eye), and found that one half of the waves rose above the level of the
view obtained.
"Frequently I observed long ranges (200 yards), which rose so high above
the visible horizon, as to form an angle estimated at two or three
degrees when the distance of the wave's summit was about 100 yards from
the observer. This would add near 13 feet to the level of the eye, and at
least one in half-a-dozen waves attained this altitude. Sometimes peaks
or crests of breaking seas would shoot upward, at least 10 or 15 feet
higher.
"The average wave was, I believe, fully equal to that of my sight on
the paddle-box, or more than 15 feet, and the _mean highest waves_, not
including the broken or acuminated crests, rose about 43 feet above
the level of the hollow occupied at the moment by the ship. It was a
grand storm-scene, and nothing could exceed the pictorial effect of the
partial sunbeams breaking through the heavy masses of clouds." From the
time taken by a regular wave to pass from stern to stem, Dr. Scoresby
calculated its velocity at 2875 feet in each minute, or 32·67 English
statute miles in an hour. The mean length of the wave-ridges, was from a
quarter to a third of a mile.
To those who might be inclined to doubt the accuracy of these
measurements, the remark may suffice that our celebrated countryman had
been for years engaged in the northern whale-fishery, where he had ample
opportunities for practising his eye in measuring distances. Besides,
the conclusions of many other trustworthy observers coincide with the
evaluations of Dr. Scoresby.
Thus Captain Wilkes, commander of the U. S. Exploring Expedition, found
the height of the waves near Orange Harbour, where they rose higher and
more regular than at any other time during the cruise, to be thirty-two
feet (depression and altitude), and their apparent progressive motion
about twenty-six and a half miles in an hour.
Sir James Ross calculated the height of the waves on a strongly agitated
sea at twenty-two feet, and, according to the French naturalists who
sailed in the frigate "La Venus," on her voyage round the world, the
highest waves they met with never exceeded that measure.
Thus, according to the joint testimony of the most eminent nautical
authorities, the waves in the open sea never attain the mountain-height
ascribed to them by the exuberant fancy of poets or exaggerating
travellers. But when the tempest surge beats against steep crags or rocky
coasts it rises to a much more considerable height. The lighthouse of
Bell Rock, though 112 feet high, is literally buried in foam and spray
to the very top during ground-swells, even when there is no wind. On the
20th November, 1827, the spray rose to the height of 117 feet above the
foundation or low-water mark, which, deducting eleven feet for the tide
that day, leaves 106 feet for the height of the wave. The strength of
that remarkable edifice may be estimated from the fact, that the power of
such a giant billow is equivalent to a pressure of three tons per square
foot.
In the Shetland Islands, which are continually exposed to the full fury
of the Atlantic surge (for no land intervenes between their western
shores and America), every year witnesses the removal of huge blocks
of stone from their native beds by the terrific action of the waves.
"In the winter of 1802," says Dr. Hibbert, in his description of that
northern archipelago, "a tabular-shaped mass, eight feet two inches by
seven feet, was dislodged from its bed and removed to a distance of from
eighty to ninety feet. I measured the recent bed from which a block had
been carried away the preceding winter (A.D. 1818), and found it to be
seventeen feet and a half by seven feet, and the depth two feet eight
inches. The removed mass had been borne to a distance of thirty feet,
when it was shivered into thirteen or more lesser fragments, some of
which were carried still farther from 30 to 120 feet. A block nine feet
two inches by six feet and a half, and four feet thick, was hurried up
the acclivity to a distance of 150 feet."
The great storm of 1824, which carried away part of the breakwater at
Plymouth, lifted huge masses of rock, from two to five tons in weight,
from the bottom of the weatherside and rolled them fairly to the top of
the pile. One block of limestone weighing seven tons was washed round
the western extremity of the breakwater, and swept to a distance of 150
feet. In 1807, during the erection of the Bell Rock lighthouse, six large
blocks of granite which had been landed on the reef were removed by the
force of the sea and thrown over a rising ledge to the distance of twelve
or fifteen paces, and an anchor weighing about twenty-two hundredweight
was cast upon the surface of the rock.
With such examples before our eyes, we cannot wonder that in the course
of centuries all shores exposed to the full shock of the waves, lashing
against them with every returning tide, should gradually be wasted and
worn away. One kind of stone stands the brunt of the elements longer than
another, but ultimately even the hardest rock must yield to the rage of
the billows, which when provoked by wintry gales, batter against them
with all the force of artillery.
Thus, all along our coasts we find innumerable instances of their
destructive power. Tynemouth Castle now overhangs the sea, although
formerly separated from it by a strip of land, and in the old maps of
Yorkshire we find spots, now sand-banks in the sea, marked as the ancient
sites of the towns and villages of Auburn, Hartburn, and Hyde. The cliffs
of Norfolk and Suffolk are subject to incessant and rapid decay. At
Sherringham, Sir Charles Lyell ascertained, in 1829, some facts which
throw light on the rate at which the sea gains upon the land. There was
then a depth of twenty feet (sufficient to float a frigate) at one point
in the harbour of that port, where only forty-eight years ago there
stood a cliff fifty feet high with houses upon it! "If once in half a
century," remarks the great geologist, "an equal amount of change were
produced suddenly by the momentary shock of an earthquake, history would
be filled with records of such wonderful revolutions of the earth's
surface; but if the conversion of high land into deep sea be gradual, it
excites only local attention." On the same coast, the ancient villages of
Shipden, Wimpwell, and Eccles have disappeared, several manors and large
portions of neighbouring parishes having gradually been swallowed up; nor
has there been any intermission, from time immemorial, in the ravages
of the sea along a line of coast twenty miles in length in which these
places stood. Dunwich, once the most considerable sea-port on the coast of
Suffolk, is now but a small village with about one hundred inhabitants.
From the time of Edward the Confessor, the ocean has devoured, piece
after piece, a monastery, seven churches, the high road, the town-hall,
the gaol, and many other buildings. In the sixteenth century not
one-fourth of the ancient town was left standing, yet, the inhabitants
retreating inland, the name has been preserved,--
"Stat magni nominis umbra,"--
as has been the case with many other ports, when their ancient site has
been blotted out.
The Isle of Sheppey is subject to such rapid decay, that the church at
Minster, now near the coast, is said to have been in the middle of the
island fifty years ago, and it has been conjectured that at the present
rate of destruction, the whole isle will be annihilated before the end of
the century.
Another remarkable instance of the destructive action of the tidal surge
is that of Reculver, on the Kentish coast, an important military station
in the time of the Romans, now nothing but a ruin and a name. So late
as the reign of Henry VIII., Reculver was still a mile distant from the
sea; but, in 1780, the encroaching waves had already reached the site
of the ancient camp, the walls of which, cemented as they were into one
solid mass by the unrivalled masonry of the Romans, continued for several
years after they were undermined to overhang the sea. In 1804, part of
the churchyard with the adjoining houses was washed away, and then the
ancient church with its two lofty spires, a well-known landmark, was
dismantled and abandoned as a place of worship.
Shakspeare's Cliff at Dover has also suffered greatly from the waves, and
continually diminishes in height, the slope of the hill being towards
the land. About the year 1810, there was an immense landslip from this
cliff, by which Dover was shaken as if by an earthquake, and a still
greater one in 1772.
Thus the fame of the poet is likely to outlive for many centuries the
proud rock, the memory of which will always be entwined with his immortal
verse:--
"How fearful,
And dizzy 'tis to cast one's eyes so low!
The crows, and choughs, that wing the midway air,
Show scarce so gross as beetles: half way down
Hangs one that gathers samphire; dreadful trade!
Methinks, he seems no bigger than his head.
The fishermen, that walk upon the beach,
Appear like mice; and yon tall anchoring bark,
Diminish'd to her cock; her cock, a buoy
Almost too small for sight. The murmuring surge,
That on th' unnumber'd idle pebbles chafes,
Cannot be heard so high."
The peninsulas of Purbeck and Portland, the cliffs of Devonshire and
Cornwall, the coasts of Pembroke and Cardigan, the stormy Hebrides,
Shetland and Orcadia, all tell similar tales of destruction, a mere
summary of which would swell into a volume.
During the most violent gales the bottom of the sea is said by different
authors to be disturbed to a depth of 300, 350, or even 500 feet, and Sir
Henry de la Bêche remarks that when the depth is fifteen fathoms, the
water is very evidently discoloured by the action of the waves on the mud
and sand of the bottom. But in the deep caves of ocean all is tranquil,
all is still, and the most dreadful hurricanes that rage over the surface
leave those mysterious recesses undisturbed.
CHAP. III.
THE TIDES.
Description of the Phenomenon.--Devastations of Storm-Floods on Flat
Coasts.--What did the Ancients know of the Tides?--Their Fundamental
Causes revealed by Kepler and Newton.--Development of their Theory
by La Place, Euler, and Whewell.--Vortices caused by the Tides.--The
Maelstrom.--Charybdis.--The _Barre_ at the mouth of the Seine.--The
Euripus.
Living on the sea-coast would undoubtedly be deprived of one of its
greatest attractions, without the phenomenon of the tides, which,
although of daily recurrence, never loses the charm of novelty, and gives
constant occupation to the fancy by the life, movement, and perpetual
change it brings along with it. How wonderful to see the sandy plain on
which, but a few hours ago, we enjoyed a delightful walk, transformed
into a vast sheet of water through which large vessels plough their way!
How agreeable to trace the margin of the rising flood, and listen to its
murmurs! Those of the rustling grove or waving cornfield are not more
melodious. And then the variety of interesting objects which the reflux
of the tide leaves behind it on the beach--the elegantly formed shell,
the feathery sertularia, the delicate fucoid, and so many other strange
or beautiful marine productions, that may well challenge the attention of
the most listless lounger.
But the spectacle of the tides is not merely pleasing to the eye, or
attractive to the imagination; it serves also to rouse the spirit of
scientific inquiry. It is indeed hardly possible to witness their regular
succession without feeling curious to know by what causes they are
produced, and when we learn that they are governed by the attraction
of distant celestial bodies, and that their mysteries have been so
completely solved by man, that he is able to calculate their movements
for months and years to come, then indeed the pleasure and admiration
we feel at their aspect must increase, for we cannot walk upon the
beach without being constantly reminded that all the shining worlds that
stud the heavens are linked together by one Almighty power, and that
our spirit, which has been made capable of unveiling and comprehending
so many of the secrets of creation, must surely possess something of a
divine nature!
On all maritime coasts, except such as belong to mediterranean seas
not communicating freely with the ocean, the waters are observed to be
constantly changing their level. They regularly rise during about six
hours, remain stationary for a few minutes, and then again descend during
an equal period of time, when after having fallen to the lowest ebb, they
are shortly after seen to rise again, and so on in regular and endless
succession. In this manner twelve hours twenty-four minutes elapse on an
average from one flood to another, so that the sea twice rises and falls
in the course of a day, or rather twice during the time from one passage
of the moon through the meridian to the next, a period equivalent on an
average to 1-35/1000 day, or nearly twenty-five hours. Thus the tides
retard from one day to another; least at new and full moon, when our more
active satellite accomplishes her apparent diurnal motion round the earth
in twenty-four hours, thirty-seven minutes; and most at half-moon, when,
sailing more leisurely through the skies, she takes full twenty-five
hours and twenty-seven minutes to perform her daily journey.
As the retarding of the tides regularly corresponds with the retarding of
the moon, they always return at the same hour after the lapse of fourteen
days, so that at the end of each of her monthly revolutions, the moon
always finds them in the same position. The knowledge of this fact is
extremely useful to navigators, as it is easy to calculate the time of
any tide in a port by knowing when it is high-water on the days of new
and full moon.
The height of the tides in the same place is as unequal and changing as
the period of their intervals, and is equally dependent on the phases
of the moon, increasing with her growth, and diminishing with her
decrease. New and full moon always cause a higher rising of the flood
(spring-tide), followed by a deeper ebb, while at half-moon the change
of level is much less considerable (neap-tide). Thus in Plymouth, for
instance, the neap-tides are only twelve feet high, while the ordinary
spring-tides rise to more than twenty feet.
The highest tides take place during the equinoxes; and eclipses of the
sun and moon are also invariably accompanied by considerable floods,
a circumstance which cannot fail to add to the terror of the ignorant
and superstitious when a mysterious obscurity suddenly veils the great
luminaries of the sky. It has also been remarked that the tides are
stronger or weaker, according as the moon is at a greater or smaller
distance from the earth.
Thus as the height of the floods is always regulated by the relative
position of the sun and moon, and the movements of these heavenly bodies
can be calculated a long time beforehand, our nautical calendars are able
to tell us the days when the highest spring-tides may be expected.
This however can only be foretold to a certain extent, as the tidal
height not only depends upon the attraction of the heavenly bodies,
but also upon the casual influences of the wind, which defies all
calculation, and of the pressure of the air. Thus Mr. Walker observed
on the coasts of Cornwall and Devonshire that when the barometer falls
an inch, the level of the sea rises sixteen inches higher than would
otherwise have been the case.
When a strong and continuous wind blows in an opposite direction to
the tide-wave, and at the same time the barometer is high, the curious
spectators will therefore be deceived in their expectations, however
promising the position of the attracting luminaries may be; while an
ordinary spring-tide, favoured by a low state of the barometer and chased
by a violent storm against the coast, may attain more than double the
usual height. When all favourable circumstances combine, an event which
fortunately but rarely occurs, those dreadful _storm-tides_ take place,
as menacing to the flat coasts of the Netherlands as an eruption of Etna
to the towns and hamlets scattered along its base, for here also a vast
elementary power is let loose which bids defiance to human weakness. It
is then that the rebel sea affords a spectacle of appalling magnificence.
The whole surface seethes and boils in endless confusion. Gigantic waves
rear their monstrous heads like mighty Titans, and hurl their whole
colossal power against the dunes and dykes, as if, impelled by a wild
lust of conquest, they were burning to devour the rich alluvial plains
which once belonged to their domain. Far inland, the terrified peasant
hears the roar of the tumultuous waters, and well may he tremble when
the mountain-waves come thundering against the artificial barriers, that
separate his fields from the raging floods, for the annals of his country
relate many sad examples of their fury, and tell him that numerous
villages and extensive meads, once flourishing and fertile, now lie
buried fathom-deep under the waters of the sea.
Thus, on the first of November, 1170, the storm-flood, bursting through
the dykes, submerged all the land between the Texel, Medenblik, and
Stavoren, formed the island of Wieringen, and enlarged the openings by
which the Zuiderzee communicated with the ocean. The inundations of 1232
and 1242 caused, each of them, the death of more than 100,000 persons,
and that of 1287 swept away more than 80,000 victims in Friesland alone.
The irruption of 1395 considerably widened the channels between the Flie
and the Texel, and allowed large vessels to sail as far as Amsterdam
and Enkhuizen, which had not been the case before. Whilst reading these
accounts, we are led to compare the inhabitants of the Dutch lowlands
with those of the fertile fields and vineyards that clothe the sides of
Vesuvius: both exposed to sudden and irretrievable ruin from the rage
of two different elements, and yet both contented and careless of the
future; the first behind the dykes that have often given way to the
ocean, the latter on the very brink of a menacing volcano.
The tides which sometimes cause such dreadful devastations on the shores
of the North Sea are, as is well known, inconsiderable, or even hardly
perceptible in the Mediterranean, and thus many years passed ere the
Greeks and Romans first witnessed the grand phenomenon. The Phœnicians,
the merchant princes of antiquity, who at a very early period of history
visited the isolated Britons,--
"Penitus toto divisos orbe Britannos,"--
and sailed far away into the Indian Ocean, were of course well acquainted
with it; but it first became known to the Greeks through the voyage of
Colæus, a mariner of Samos, who, according to Herodotus, was driven by a
storm through the Straits of Hercules into the wide Atlantic 600 years
before Christ. About seventy years after this involuntary discovery,
the Phoceans of Massilia, or Marseilles, first ventured to follow on the
track of Colæus for the purpose of trading with Tartessus, the present
Cadiz; and from that time remained in constant commercial intercourse
with that ancient Phœnician colony.
With what eager attention may their countrymen have listened to the
wondrous tale of the alternate rising and sinking of the ocean! Such
must have been the astonishment of our forefathers when the first Arctic
voyagers told them of the floating icebergs, and of the perpetually
circling sun of the high northern summer.
Thus the tides became known to the Massilians about five centuries
before Christ, but in those times of limited international intercourse,
knowledge travelled but slowly from place to place; so that it was not
before the conquests of Alexander, which first opened the Red Sea and the
Persian Gulf to Grecian trade, that the great marine phenomenon began to
attract the general attention of philosophers and naturalists.
The flux and reflux of the sea is evidently so closely connected with the
movements and changes of the moon, that the intimate relations between
both could not possibly escape the penetrating sagacity of the Greeks.
Thus we read in Plutarch, that Pytheas of Marseilles, the great traveller
who sailed to the north as far as the Ultima Thule, and lived in the
times of Alexander the Great, ascribed to the moon an influence over the
tides. Aristotle expressed the same opinion, and Cæsar says positively
(Commentaries, _De Bel. Gal._ book iv. 29,) that the full-moon causes the
tides of the ocean to swell to their utmost height. Strabo distinguishes
a three-fold periodicity of the tides according to the daily, monthly,
and annual position of the moon, and Pliny expresses himself still more
to the point, by saying that the waters move as if obeying the thirsty
orb which causes them to follow its course.
This vague notion of obedience or servitude was first raised by Kepler to
the clear and well defined idea of an attractive power. According to this
great and self-taught genius, all bodies strive to unite in proportion
to their masses. "The earth and moon would mutually approach and meet
together at a point, so much nearer to the earth as her mass is superior
to that of the moon, if their motion did not prevent it. The moon
attracts the ocean, and thus tides arise in the larger seas. If the earth
ceased to attract the waters, they would rise and flow up to the moon."
The general notion of a mutual attraction, however, did no more than
point out the way for the solution of the problem, and it was reserved
to our great Newton to accomplish the prophecy of his great predecessor,
"that the discovery of the true laws of gravitation would be accomplished
in a future generation, when it should please the Almighty Creator of
nature to reveal her mysteries to man."
Newton was the first who proved that the tide-generating power of a
celestial body arises from the difference of the attraction it exerts on
the centre and the surface of the earth. Thus it was at once made clear
how the water not only rises on the surface facing the moon, but also
on the opposite side of the earth, as in the latter case the moon acts
more strongly on the mass of the earth than on the waters which cover the
hemisphere most distant from her. The evident consequence is that the
earth _sinks_ (so to say), on the surface turned from the moon, whereby
a deepening of the waters, or, in other words, a rising of the tide, is
occasioned.
It now also became clear how the moon, whose attractive power upon the
earth is 160 times smaller than that of the sun, is yet able to occasion
a stronger tide, since, from her proximity to the earth, she attracts
the surface more forcibly than the centre with the thirtieth part of
her power, while the distant sun occasions a difference of attraction
on these two points equal only to one twelve-thousandth part of her
attractive force.
Now also a full explanation was first given why the highest tides take
place at new and full moon: that is, when the moon stands between the sun
and the earth; or the latter between the sun and the moon; as then the
two celestial bodies unite their powers; while at half-moon the solar
tide corresponding with the lunar ebb, or the lunar tide with the solar
ebb, counteract each other.
But even Newton explained the true theory of the tides only in its more
prominent and general features, and the labours of other mathematicians,
such as MacLaurin, Bernoulli, Euler, La Place, and Whewell, were required
for its further development, so as fully to explain all the particulars
of the sublime phenomenon.
The reproach has often been made to science, that she banishes poetry
from nature, and disenchants the forest and the field; but this surely
is not the case in the present instance, for what poetical fiction
can fill the soul with a grander image than that of the eternal
restlessly-progressing tide-wave, which, following the triumphant march
of the sun and moon, began as soon as the primeval ocean was formed, and
shall last uninterruptedly as long as our solar system exists!
Were the whole earth covered with one sea of equal depth, the tides would
regularly move onwards from east to west, and everywhere attain the same
height under the same latitude. But the direction and the force of the
tide-wave are modified by many obstacles on its way, such as coast-lines
and groups of islands, and it has to traverse seas of very unequal depth
and form. Flat coasts impede its current by friction, while it rolls
faster along deep mural coasts. From all these causes the strength of the
tides is very unequal in different places.
They are generally low on the wide and open ocean. Thus the highest tides
at Otaheiti do not exceed eleven inches, three feet at St. Helena, one
foot and a half at Porto Rico.
But when considerable obstructions oppose the progress of the tide-waves,
such as vast promontories, long and narrow channels, or bays of
diminishing width, and mouths of rivers directly facing its swell, it
rises to a very great height. Thus, at the bottom of Fundy Bay, which
stretches its long arm between Nova Scotia and New Brunswick, the
spring-tides rise to sixty, seventy, or even one hundred feet, while at
its entrance they do not exceed nine feet, and their swell is so rapid as
frequently to sweep away cattle feeding on the shore.
The Bristol Channel and the bay of St. Malo in Brittany, are also
renowned for their high tides. Near Chepstow, the flux is said sometimes
to reach the surprising height of seventy feet, and at St. Malo the
floods frequently rise to forty and fifty feet. When the water is low,
this small sea-port town appears surrounded on all sides by fantastically
shaped cliffs covered with sea-weeds and barnacles. Pools of salt water
interspersed here and there among the hollowed stones, or on the even
ground between them, and harbouring many curious varieties of marine
animals, are the only visible signs of the vicinity of the ocean, whose
hoarse murmurs are heard resounding from afar. But an astonishing change
takes place a few hours after, when the town, surrounded by the sea,
would be a complete island, but for a long, narrow causeway called "_the
Sillon_," which connects it with the mainland. On the side fronting
the open sea, the tide breaks with tremendous rage against the strong
buttresses that have been raised to oppose its fury, rises foamingly to
a height of thirty or forty feet, and threatens the tardy wanderer as he
loiters on the narrow causeway. The cliffs that erewhile were seen to
surround the town are now hidden under the waters, some few excepted,
that raise their rugged heads like minute islands above the circumambient
floods. The opposite side of the causeway is also washed by the sea: but
here its motions are less tumultuous, for after having broken against
numberless rocks and made a vast circuit, it scarce retains a vestige of
its primitive strength. On this side lies the vast, but deserted harbour
of St. Malo, completely dry at ebb-tide; a wide sea during the flood.
Two eminent French authors, Chateaubriand and Lamennais, were born at
St. Malo, and there can be no doubt that the imposing spectacle I have
briefly described must have greatly contributed to the widening of their
intellectual horizon. Daily witnesses from their early childhood of
one of the grandest phenomena of nature in all its wild sublimity, the
boundless and the infinite soon grew familiar to their mind, enriching it
with splendid imagery and bold conceptions.
Although the sun and the moon exert some attraction upon the smaller and
inclosed seas, yet the development of a powerful flood-wave necessarily
requires that the moon should act upon a sufficiently wide and deep
expanse of ocean. Even the Atlantic is not broad enough for this purpose,
as its equatorial width measures no more than one eighth of the earth's
circumference: and the Pacific itself, notwithstanding its vast area,
is so studded with islands and shallows, that it presents a much more
obstructed basin for the action of the tide-wave than might be expected,
from its apparent dimensions and equatorial position.
Thus it is in the Southern Ocean, where the greatest uninterrupted
surface of deep water is exposed to the influence of the moon, that we
must look for the "_chief cradle of the tides_." From this starting point
they flow on all sides to the northward, progressing like any other wave
that arises on a small scale in a pond from a gust of wind, the throwing
of a stone, or any other cause capable of producing an undulating
movement on the surface of the waters.
The tide-wave, which ultimately reaches our shores, arrives at the Cape
of Good Hope thirteen hours after it has left Van Diemen's Land, and
thence rolls onward in fourteen or fifteen hours to the coasts of Spain,
France, and Ireland. It penetrates into the North Sea by two different
ways. One of its ramifications turns round Scotland and thence flows
onwards to the south, taking nineteen or twenty hours for the passage
from Galway to the mouth of the Thames. A tide-wave, for instance, which
appears at five in the afternoon on the west coast of Ireland, arrives at
eight near the Shetland Islands, reaches Aberdeen at midnight, Hull at
five in the morning, and Margate at noon.
The other ramification of the same tide-wave, taking the shorter route
through the Channel, had meanwhile preceded it by twelve hours, having
reached Brest about five o'clock of the afternoon (at the same time that
the northern branch appeared at Galway), Cherbourg at seven, Brighton at
nine, Calais at eleven, and the mouth of the Thames at midnight.
Thus, in this southern corner of the North Sea, two tide-waves unite
that belong to two successive floods; the Scotch branch having started
twelve hours sooner from the great Southern Ocean than the Channel
branch, which thus results from the next following tide. The meeting of
the two branches naturally gives rise to a more considerable rising of
the waters, so that this circumstance, by allowing large ships to sail
up the Thames, may be considered as one of the fundamental causes of the
grandeur of London.
In other parts of the North Sea, where the two tide-waves appear at
different times, the contrary takes place, for the ebb of the one
coinciding with the rising of the other, they naturally weaken or
even neutralise each other. This occasions the low tides on the coast
of Jutland, in Denmark, where they are scarcely higher than in the
Mediterranean, and explains the otherwise startling fact of there being a
space in the North Sea where no periodical rise and fall of the waters
whatsoever takes place.
Thus we see that the relations of the tides in the North Sea, with regard
to height and time, are of a somewhat complicated nature, which could
only be explained after the numerous observations (amounting to more
than 40,000) made by order of the British Government in all parts of the
world, under the direction of Professor Whewell, had proved that all
the floods of the seas chiefly proceed from the great tide-wave of the
Southern Ocean, which, by its numerous ramifications in narrow seas or
through groups of islands and by the unequal rapidity of its progress,
according to the depth or shallowness of the waters it traverses,
occasions all the seeming anomalies which were quite inexplicable by the
simple Newtonian theory.
As every twelve hours a new tidal-wave originates in the Southern Ocean
which regularly follows in the same track as its predecessor, the tides
everywhere succeed each other in regular and equal periods, and can thus
everywhere be calculated beforehand.
In narrow straits or in the intricate channels which wind through
clusters of islands, different tidal-waves meeting from opposite
directions give rise to more or less dangerous whirlpools. One of the
most famous of these vortices, though inconsiderable in itself, is the
renowned Charybdis, which gave so much trouble to Ulysses on his passing
through the strait which separates Sicily from Italy, but is at present
an object of fear scarcely even to the poor fisherman's boat.
A much grander whirlpool, owing its celebrity, not to the fictions of
poetry, but to the magnificent scale on which it has been constructed by
nature, is the renowned Maelstrom, situated on the Norwegian coast in 68°
N. lat., and near the island of Moskoe, from whence it also takes the
name of Moskoestrom. It is four geographical miles in diameter, and in
tempestuous weather its roar, like that of Niagara, is said to be heard
several miles off. John Ramus gives us a terrible description of its
fury, and mentions that in the year 1645 it raged with such noise and
impetuosity, that on the island of Moskoe, the very stones of the houses
fell to the ground. He tells us also that whales frequently come too near
the stream, and, notwithstanding their giant strength, are overpowered by
its violence, but, unfortunately adds, that it is impossible to describe
their howlings and bellowings in their fruitless struggles to disengage
themselves--impossible, no doubt, as whales happen to have no voice at
all!
According to more modern travellers, such as the celebrated geologist
Leopold von Buch, the Maelstrom is far from being so terrible as depicted
by Ramus and other friends of the marvellous; so that, except during
storms and spring-tides, large ships may constantly cross it without
danger. The Norwegian fishermen are even said frequently to assemble on
the field of the Maelstrom on account of the great abundance of fishes
congregating in those troubled waters, and fearlessly to pursue their
avocations, while the whirlpool moves their boats in a circular direction.