ARCTIC SLEDGE-JOURNEY.
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THE SEA
AND
ITS LIVING WONDERS
A POPULAR ACCOUNT OF
THE MARVELS OF THE DEEP
AND OF THE
PROGRESS OF MARITIME DISCOVERY
FROM THE EARLIEST AGES TO THE PRESENT TIME

BY

DR. G. HARTWIG
AUTHOR OF "THE TROPICAL WORLD" "THE HARMONIES OF NATURE"
"THE POLAR WORLD" AND "THE SUBTERRANEAN WORLD"

SEVENTH EDITION

WITH NUMEROUS WOODCUTS AND PLATES

LONDON
LONGMANS, GREEN, AND CO.
AND NEW YORK: 15 EAST 16^th STREET
1892

[NOTICE]

The right of translation into French is reserved by the Author. All necessary steps for securing the Copyright have been taken.

PREFACE
TO
THE THIRD AND FOURTH EDITIONS.

Nothing can be more agreeable to an author anxious to merit the suffrages of the public, than the opportunity afforded him, by a new edition, of correcting past errors or adding improvements to his work. Should any one of my readers think it worth his while to compare 'The Sea,' such as it now is, with what it formerly was, I have no doubt he will do me the justice to say that I have conscientiously striven to deserve his approbation.

Two new chapters—one on Marine Constructions, the other on Marine Caves—have been added; those on the Molluscs and Cœlenterata (Jelly-fishes, Polyps) almost entirely re-written; and those on Fishes, Crustaceans, Microscopic Animals, the Geographical Distribution of Marine Life, and the Phosphorescence of the Sea, considerably enlarged; not to mention a number of minor improvements dispersed throughout the volume.

Great attention has also been paid to the Illustrations, many of questionable value having been omitted in the present edition, to make room for a number of others, which will be found of great use for the better understanding of the text.

In one word, I have done my best to raise my work to the standard of the actual state of science, and to render it, as far as my humble abilities go, a complete epitome of all that the general reader cares to know about the marvels of the deep.

G. Hartwig.

Salon Villas, Ludwigsburg:
June 30, 1873.

PREFACE
TO
THE FIRST TWO EDITIONS.

For years my daily walks have been upon the beach, and I have learnt to love the ocean as the Swiss mountaineer loves his native Alps, or the Highlander the heath-covered hills of Caledonia. May these feelings have imparted some warmth to the following pages, and serve to render the reader more indulgent to their faults!

G. Hartwig.

Göttingen: July 17, 1860.

[CONTENTS.]

[PART I.]
THE PHYSICAL GEOGRAPHY OF THE SEA.

[CHAPTER I.]
THE MAGNITUDE OF THE SEA.

[CHAPTER II.]
THE WAVES OF THE OCEAN.

[CHAPTER III.]
THE TIDES.

[CHAPTER IV.]
MARINE CAVES.

[CHAPTER V.]
OCEAN CURRENTS.

[CHAPTER VI.]
THE AËRIAL AND TERRESTRIAL MIGRATIONS OF THE WATERS.

[CHAPTER VII.]
MARINE CONSTRUCTIONS.

[PART II.]
THE INHABITANTS OF THE SEA.

[CHAPTER VIII.]
THE CETACEANS.

[CHAPTER IX.]
SEALS AND WALRUSES.

[CHAPTER X.]
SEA-BIRDS.

[CHAPTER XI.]
THE REPTILES OF THE OCEAN.

[CHAPTER XII.]
THE MARINE FISHES.

[CHAPTER XIII.]
CRUSTACEA.
CRABS—LOBSTERS.

[CHAPTER XIV.]
MARINE ANNELIDES.

[CHAPTER XV.]
MOLLUSCS.

[CHAPTER XVI.]
ECHINODERMATA.
STAR-FISHES, SEA-URCHINS, AND SEA-CUCUMBERS.

[CHAPTER XVII.]
CŒLENTERATA.
POLYPS AND JELLY-FISHES.

[CHAPTER XVIII.]
PROTOZOA.

[CHAPTER XIX.]
MARINE PLANTS.

[CHAPTER XX.]
THE GEOGRAPHICAL DISTRIBUTION OF MARINE LIFE.

[CHAPTER XXI.]
THE PHOSPHORESCENCE OF THE SEA.

[CHAPTER XXII.]
THE PRIMITIVE OCEAN.

[PART III.]
THE PROGRESS OF MARITIME DISCOVERY.

[CHAPTER XXIII.]

[CHAPTER XXIV.]

[CHAPTER XXV.]

[CHAPTER XXVI.]

[CHAPTER XXVII.]

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.

MAP.

Map of the Globe, showing the direction of the Ocean Currents, Cotidal Lines, &c. facing [page 3].

WOODCUTS.

PART I.
THE
PHYSICAL GEOGRAPHY OF THE SEA.

[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!

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.

[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.

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]

[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, aeronauts 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.

[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."

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.

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.

Sir Robert Sibbald describes a very remarkable marine whirlpool among the Orkney islands, which would prove dangerous to strangers, though it is of no consequence to the people who are used to it. It is not fixed to any particular place, but arises in various parts of the limits of the sea among these islands. Wherever it appears, it is very furious, and boats would inevitably be drawn in and perish with it, but the people who navigate them are prepared for it and always carry a bundle of straw or some such matter in the boat with them. This they fling into the vortex which immediately swallows it up, and, seemingly pleased with this propitiatory offering, subsides into smoothness, but soon after re-appears in another place.

A remarkable and sudden rising of the spring-tide takes place at the mouth of several rivers, for instance, the Indus (where the surprising phenomenon nearly caused the destruction of the fleet of Alexander the Great), the Hooghly, the Dordogne, &c. In the Seine it is observed on a scale of great magnitude. While the tide gradually rises near Havre and Harfleur, a giant wave is suddenly seen to surge near Quillebœuf, spanning the whole width of the river (from 30,000 to 36,000 feet). After this mighty billow has struck against the quay of Quillebœuf, it enters a more narrow bed and flows stream-upwards with the rapidity of a race horse, overflowing the banks on both sides, and not seldom causing considerable loss of property by its unexpected appearance. The astonishment it causes is increased when it takes place during serene weather, and without any signs of wind or storm. A deafening noise announces and accompanies this sudden swelling of the waters, which owes its first origin to the silent action of gravitation, and is the result of the diminishing velocity of the tide-wave over a shallow bottom.

While the tide-wave advances over the deep and open seas with an astonishing rapidity, its progress up the channel of a river is comparatively very slow, partly on account of the reason just mentioned, and partly from its meeting a current flowing in an opposite direction.

Thus, the tide takes no less than twelve hours for its progress from the mouth of the Thames to London, about the time it requires to travel all the way from Van Diemen's Land to the Cape of Good Hope. Consequently, when it is high-water at the mouth of the Thames at three o'clock in the afternoon, for instance, we have not high-water at London Bridge before three o'clock in the following morning, when it is again high water at the Nore. But, in the mean time, there has been low water at the Nore and high water about half-way to London, and while the high water is proceeding to London, it is ebbing at the intermediate places, and is low water there when it is high water at London and at the Nore. If the tide extended as far beyond London as London is from the Nore, we should have three high waters with two low waters interposed. The most remarkable instance of this kind is afforded by the gigantic river of the Amazons, as it appears by the observations of Condamine and others, that, between Para, at the mouth of the colossal stream, and the conflux of the Madera and Marañon, there are no less than seven simultaneous high waters with six low waters between them. Thus, four days after the tide-wave was first raised in the Southern Ocean, its last undulations expire deep in the bosom of the South American wilds.

The Mediterranean is generally supposed to be tideless, but this opinion is erroneous; and in the Adriatic, the flux of the sea is far from being inconsiderable, for, at Venice, the difference between high and low water is sometimes no less than six or even nine feet. Mr. W. Trevelyan, during a summer residence in the old port of Antium, on the Roman coast, found from a series of accurate observations, that the tides regularly succeed each other and attain a height of fourteen inches. In the eastern Mediterranean new measurements have proved that they are still more considerable, while in the western part of that inclosed sea they are almost imperceptible.

The differences of level caused by the Mediterranean tides, are indeed too inconsiderable to attract the general notice of the inhabitants on the coast, but in the famed Euripus, the narrow channel which separates the island of Eubœa or Negropont from continental Greece, the tide produces the striking phenomenon of very irregular fluctuations of the waters, from one end of the channel to the other.

This phenomenon was of course completely inexplicable to the ancient philosophers, and Aristotle is even said to have drowned himself in the Euripus in a fit of despair, since, with all his prodigious sagacity, he could not possibly solve the mystery. For us, who know that peculiar formations of the sea-bed and coasts are capable of considerably augmenting the force of the floods, and that tidal waves rushing into a narrow channel in opposite directions, and at different times, must necessarily produce irregular fluctuations of the waters, the phenomenon of the Euripus has ceased to be a mystery.

[CHAP. IV.]

MARINE CAVES.

Effects of the Sea on Rocky Shores.—Fingal's Cave.—Beautiful Lines of Sir Walter Scott.—The Antro di Nettuno.—The Cave of Hunga.—Legend of its Discovery.—Marine Fountains.—The Skerries.—The Souffleur in Mauritius.—The Buffadero on the Mexican Coast.

Whoever has only observed the swelling of the tide on the flat coasts of the North Sea, has but a faint idea of the Titanic power which it develops on the rocky shores of the wide ocean. Even in fair weather, the growing flood, oscillating over the boundless expanse of waters, rises in tremendous breakers, so that it is impossible to behold their fury without feeling a conviction that the hardest rock must ultimately be ground to atoms by such irresistible forces.

Day after day, year after year, they renew their fierce attacks, and as in the high Alpine valleys the tumultuous torrents rushing from the glaciers tear deep furrows in the flanks of the mountains, thus it is here the sea which stamps the seal of its might on the vanquished rocks, corrodes them into fantastic shapes, scoops out wide portals in their projecting promontories, and hollows out deep caverns in their bosoms.

Here, also, water appears as the beautifying element, decorating inanimate nature with picturesque forms, and the sea nowhere exhibits more romantic scenes than on the rocky shores against which her waves have been beating for many a millennium. How manifold the shapes into which the rocky shores are worn! how numberless the changes which each varying season, nay, every hour of the day with its constant alternations of ebb and flood, of cloud and sunshine, of storm or calm, produces in their physiognomy! Our coasts abound in beauties such as these; but pre-eminent above all other specimens of Ocean's fantastic architecture is Fingal's Cave, which may well challenge the world to show its equal.

From afar, the small island of Staffa, rising precipitously from the sea, seems destitute of all romantic interest, but on approaching, the traveller is struck with the remarkable basaltic columns of which it is chiefly composed. Most of them rest upon a substratum of solid shapeless rock, and generally form colonnades upwards of fifty feet high, following the contours of the inlets or promontories, and overtopped with smaller hillocks. Along the west coast of the island they are tolerably irregular, but on the south side Staffa appears as an immense Gothic edifice, or rather as a forest of gigantic pillars seemingly arranged with all the regularity of art. The admiration they cause is, however, soon effaced when the vast cave to which the remote islet owes its world-wide celebrity bursts upon the view. Fancy a grotto measuring 250 feet in length by 53 in width at the entrance, and spanned by an arch 117 feet high, which, though gradually sloping towards the interior, still maintains a height of 70 feet at the farthest end of the cavern! The walls consist of rows of huge hexagonal basaltic pillars, which seem regularly to diminish according to the rules of perspective. The roof of the vault is formed of the remnants of similar columns, whose shafts have beyond a doubt been torn away by the sea, which, destroying them one after the other, has gradually excavated this magnificent temple of Nature. All their interstices, like those of the pillars, are cemented with a kind of pale yellow spar, which brings out all the angles and sides of their surfaces, and forms a pleasing contrast with the dark purple colour of the basalt.

The whole floor of the cave is occupied by the sea, the depth of which, even at its farthest end, is above six feet, during ebb-tide; but it is only in perfectly calm weather that a boat is able to venture into the interior, for when the sea is any way turbulent (and this is generally the case among the stormy Hebrides) it is in danger of being hurled against the walls of the grot and dashed to pieces. Under these circumstances, the only access into the cave is by a narrow dyke or ledge running along its eastern wall, about fifteen feet above the water. It is formed of truncated basaltic pillars, over which it is necessary to clamber with great caution and dexterity, as they are always moist and slippery from the dashing spray. Frequently there is only room enough for one foot, and while the left hand grasps that of the guide, it is necessary to hold fast with the right to a pillar of the wall. As this difficult path is most dangerous in the darkest part of the cave, but few tourists are bold enough to trust themselves to it, for the least false step must infallibly precipitate the adventurous explorer into the seething caldron below. Sometimes a cormorant, fearless of any accident of this kind, has built his nest upon the top of one of the truncated pillars, which form the pavement of the pathway, and betrays by a peevish hissing his ill humour at being disturbed in his solitary retreat by the intrusion of man.

Fingal's Cave.