Chapter I: The Magnitude of the Sea (3)

"Our negro guide now informed us that we must make haste to recross our narrow bridge, as the sea would get up as the tide rose. We lost no time and got back dry enough; and I was obliged to make my sketches from the mainland. In about three-quarters of an hour the sight was truly magnificent. I do not exaggerate in the least when I say that the waves rolled in, long and unbroken, full twenty-five feet high, till, meeting the headland, they broke clear over it, sending the spray flying over to the mainland; while from the centre of this mass of foam, the Souffleur shot up with a noise, which we afterwards heard distinctly between two and three miles. Standing on the main cliff, more than a hundred feet above the sea, we were quite wet. All we wanted to complete the picture was a large ship going ashore."

[Footnote G: Journal of the Royal Geographical Society of London, vol. iii. 1833.]

THE SOUFFLEUR.

This plate shows the sea beating against some hollow rocks on the
coast of the Mauritius, and producing the remarkable phenomenon called
"The Souffleur," or "The Blower," water-spouts issuing from the
wave-worn cavities of the cliff to a considerable height, and with a
noise distinctly audible at a distance of three miles.

A similar phenomenon, on a still more grand and majestic scale, occurs near Huatulco, a small Mexican village on the coast of the Pacific. On sailing into the bay one hears a distant noise, which might be taken for the spouting of a gigantic whale, or the dying groans of a bull struck by the sharp steel of the matador, or the rolling of thunder. Anxious to know the cause, "It is the Buffadero," answer the boatmen, pointing to a fantastically-shaped rock towards which they are rowing. On approaching, a truly magnificent spectacle reveals itself; for a colossal fountain springs from an aperture in the rock to a height of 150 feet, and after having dissolved in myriads of gems, returns to the foaming element which gave it birth. This beautiful sight renews itself as often as the breakers rush against the rock, and must be of unequalled splendour when a tornado sweeps across the ocean and rolls its giant billows into the hollowed bosom of the cliff.

CHAP. V.

OCEAN CURRENTS.

Causes of the Oceanic Currents.--The Equatorial Stream.--The
Gulf Stream.--Its Influence on the Climate of the West European
Coasts.--The Cold Peruvian Stream.--The Japanese Stream.

Perpetual motion and change is the grand law, to which the whole of the created universe is subject, and immutable stability is nowhere to be found, but in the Eternal mind that rules and governs all things. The stars, which were supposed to be _fixed_ to the canopy of heaven, are restless wanderers through the illimitable regions of space. The hardest rocks melt away under the corroding influence of time, for the elements never cease gnawing at their surface, and dislocating the atoms of which they are composed. Our body appears to us unchanged since yesterday, and yet how many of the particles which formed its substance, have within these few short hours, been cast off and replaced by others. We fancy ourselves at rest, and yet a torrent of blood, propelled by an indefatigable heart, is constantly flowing through all our arteries and veins.

A similar external appearance of tranquillity might deceive the superficial observer, when sailing over the vast expanse of ocean, at a time when the winds are asleep, and its surface is unruffled by a wave. But how great would be his error! For every atom of the boundless sea is constantly moving and changing its place; from the depth to the surface, or from the surface to the depth; from the frozen pole to the burning equator, or from the torrid zone to the arctic ocean; now rising in the air in the form of invisible vapours, and then again descending upon our fields in fertilising showers.

The waters are, in fact, the greatest travellers on earth; they know all the secrets of the submarine world; climb the peaks of inaccessible mountains, shame the flight of the condor as he towers over the summit of the Andes, and penetrate deeper into the bowels of the earth than the miner has ever sunk his shaft.

Leaving their wanderings through the regions of air to the next chapter, I shall now describe the principal ocean currents, the simple, but powerful agencies by which they are set in motion, their importance in the economy of nature, and their influence on the climate of different countries.

Even in the torrid zone, the waters of the ocean, like a false friend, are warm merely on the surface, and of an almost icy coldness at a considerable depth. This low temperature cannot be owing to any refrigerating influence at the bottom of the sea, as the internal warmth of the earth increases in proportion to its depth, and the waters of profound lakes, in a southern climate, never show the same degree of cold as those of the vast ocean.

The phenomenon can thus only arise from a constant submarine current of cold water from the poles to the line, and strange as it may seem, its primary cause is to be sought for in the _warming_ rays of the _sun_, which, as we all know, distributes heat in a very unequal manner over the surface of the globe.

Heat expands all liquid bodies, and renders them lighter; cold increases their weight by condensation. In consequence of this physical law, the waters of the tropical seas, rendered buoyant by the heat of a vertical sun, must necessarily rise and spread over the surface of the ocean to the north and south, whilst colder and heavier streams from the higher latitudes flow towards the equator along the bottom of the ocean, to replace them as they ascend.

In this manner, the unequal action of the sun calls forth a general and constant movement of the waters from the poles to the equator, and from the equator to the poles; and this perpetual migration is one of the chief causes by which their purity is maintained. These opposite currents would necessarily flow direct to the north or south, were they not deflected from their course by the rotation of the earth, which gradually gives them a westerly or easterly direction.

The unequal influence of the sun in different parts of the globe, and the rotation of the earth, are, however, not the only causes by which the course of ocean-currents is determined.

Violent storms move the waters to a considerable depth, and retard the flow of rivers, and thus it is to be expected that continuous winds, even of moderate strength, must have a tendency to impel the waters in the same direction.

The steady trade-winds of the tropical zone, and the prevailing westerly winds in higher latitudes, consequently unite their influence with that of the above mentioned causes, in driving the waters of the tropical seas to the west, and those of the temperate zones to the east.

The tides also, which on the high seas generally move from east to west, promote the flow of the ocean in the same direction, and thus contribute to the westerly current of the tropical seas.

Nor must we forget that the obstacles which the ocean-currents meet on their way; such as intervening lines of coast, sand banks, submarine ridges, or mountain chains, have a great influence upon their course, and may even give them a diametrically opposite direction to that which they would otherwise have followed.

Having thus briefly mentioned the origin and causes of the currents, which intersect the seas like huge rivers, I shall now describe such of them as are most important and interesting in a geographical point of view.

In the northern part of the Atlantic, between Europe, North Africa, and the New World, the waters are constantly performing a vast circular or rotatory movement. Under the tropics they proceed like the trade-winds from east to west, assisting the progress of the ships that sail from the Canaries to South America, and rendering navigation in a straight line from Carthagena de Indias to Cumana (stream upwards) next to impossible. This westerly current receives a considerable addition from the _Mozambique_ stream, which, flowing from north to south between Madagascar and the coast of Caffraria, proceeds round the southern extremity of Africa, and after rapidly advancing to the north, along the western coast of that continent, as far as the island of St. Thomas, unites its waters with those of the equatorial current, and continues its course right across the Atlantic. In this manner the combined tropical streams reach the eastern extremity of South America (Cape Roque), where they divide into two arms. The one flowing to the south follows the south-eastern coast, and gradually takes a south-easterly direction, between the tropic of Capricorn and the mouth of the La Plata river, beyond the limits of the trade-winds. Its traces show themselves to the south-east of the Cape of Good Hope, and are finally lost far in the Indian Ocean.

The northern arm of the equatorial stream flows along the north-eastern coast of South America; constantly raising its temperature under the influence of a tropical sun, and progressing with a rapidity of a hundred miles in twenty-four hours (six feet and a half in a second), after having been joined by the waters of the Amazon river. Thus it continues to flow to the east, until the continent of Central America opposes an invincible barrier to its farther progress in this direction, and compels it to follow the windings of the coast of Costa Rica, Mosquitos, Campeche, and Tabasco. It then performs a vast circuit along the shores of the Mexican Gulf, and finally emerges through the Straits of Bahama into the open ocean.

Here it assumes a new name, and forms what navigators call the _Gulf-stream_, a rapid current of tepid water, which, flowing in a diagonal direction, recedes farther and farther from the coast of North America as it advances to the north-east. Under the forty-first degree of latitude it suddenly bends to the east, gradually diminishing in swiftness, and at the same time increasing in width.

Thus it flows across the Atlantic, to the south of the great bank of Newfoundland, where Humboldt found the temperature of its stream several degrees higher than that of the neighbouring and tranquil waters, which form, as it were, the banks of the warm oceanic current. Ere it reaches the western Azores, it divides into two arms, one of which is driven, partly by the natural impulse of its stream, but principally by the prevailing westerly and north-westerly winds, towards the coasts of Europe; while the other, flowing towards the Canary Islands and the western coast of Africa, finally returns into the equatorial current.

In this manner the waters are brought back to the point from which they came, after having performed a vast circuit of 20,000 miles, which it took them nearly three years to accomplish. According to Humboldt's calculations, a boat left to the current, and moving along without any other assistance, would require about thirteen months to float from the Canary Islands to the Caribbean Sea as far as Caraccas. From Caraccas to the Straits of Florida, it would remain another ten months on the way, for though the direct distance is but short, the current has to perform an enormous circuit of 2500 miles, and flows but slowly in those confined seas. But the accumulated waters having now to force their passage through the narrow channel between Cuba and the Bahama Islands on one side, and Florida on the other, attain so considerable a velocity, that the whole distance from the Havannah to the Bank of Newfoundland, is traversed in forty days. During this passage the Gulf-stream particularly deserves its name, and is easily distinguished from the surrounding waters by its higher temperature and its vivid dark blue colour. Numerous marine animals of the tropical seas,--the flying fish, the neat velella, the purple ianthina, the crosier nautilus, accompany it to latitudes which otherwise would prove fatal to their existence; and, trusting its tepid stream, float or swim along to the north or the north-east.

At the extremity of the Bank of Newfoundland, it becomes broader, wavers more or less in its course, according to the prevailing winds, and at the same time decreases in rapidity, so that the boat would most likely still require from ten to eleven months for this last station of its journey, ere it once more reached the Canary Islands.

The direction of the Gulf-stream explains to us how the productions of tropical America are so frequently found on the shores of the Eastern Atlantic. Humboldt relates that the main-mast of the "Tilbury," a ship of the line, wrecked during the seven years' war on the coast of San Domingo, was carried by the Gulf-stream to the North of Scotland; and cites the still more remarkable fact, that casks of palm oil belonging to the cargo of an English vessel, which foundered on a rock near Cape Lopez, likewise found their way to Scotland, having thus twice traversed the wide Atlantic; first borne from east to west by the equatorial current, and then carried from west to east, between 45° and 55° N. latitude, by means of the Gulf-stream.

Major Rennell ("Investigation of Currents") relates the peregrinations of a bottle, thrown overboard from the "Newcastle," on the 20th of January, 1819, in lat. 38° 52′, and long. 66° 20′, and ultimately found on the 2nd of June, 1820, on the shore of the Island of Arran.

On the 16th of April, 1853, another bottle cast into the waters in the vicinity of the Bank of Newfoundland, on the 15th of March, 1852, was found near Bayonne, not far from the mouth of the Adour.

On the coasts of Orcadia, a sort of fruit, commonly known by the name of _Molucca_, or Orkney beans, are found in large quantities, particularly after storms of westerly wind.

These beans are the produce of West Indian trees (_Anacardium occidentale_), and find their way from the woods of Cuba and Jamaica, to the Ultima Thule of the ancients, by means of the Gulf-stream.

Large quantities of American drift-wood are transported by the same current to the dreary shores of Iceland,--a welcome gift to the inhabitants of a region where the highest tree is but a dwarfish shrub, and cabbages of the size of an apple are raised, as a great rarity, in the governor's garden.

A short time before Humboldt visited the island of Teneriffe, the sea had thrown out the trunk of a North American cedar-tree (_Cedrela odorata_), covered with the mosses and lichens that had grown upon it in the virgin forest.

The Gulf-stream has even contributed to the discovery of America, for it is well known that Columbus was strengthened in his belief in the existence of a western continent, by the stranding on the Azores of bamboos of an enormous size, of artificially carved pieces of wood, of trunks of a species of Mexican pine, and of the dead bodies of two men, whose features, resembling neither those of the inhabitants of Europe nor of Africa, indicated a hitherto unknown race. But not only lifeless and inanimate objects find their way across the wide Atlantic by means of the Gulf-stream and its spreading waters; the living aborigines of the distant regions of America have also sometimes been driven towards the coasts of Europe by the combined action of the currents and the winds. Thus, James Wallace tells us that, in the year 1682, a Greenlander in his boat was seen by many people near the south point of the island of Eda, but escaped pursuit. In 1684 another Greenland fisherman appeared near the island of Wistram. An Esquimaux canoe, which the current and the storm had cast ashore, is still to be seen in the church of Burra. In Cardinal Bembo's "History of Venice," it is related that, in the year 1508, a small boat with seven strange-featured men, was captured by a French vessel in the North Sea. The description given of them corresponds exactly with the appearance of the Esquimaux; they were of a middle-size, of a dark colour, and had a broad face with spreading features, marked with a violet scar. No one understood their language. They were clothed in seal-skins. They ate raw flesh, and drank blood as we do wine. Six of these men died on the journey; the seventh, a youth, was presented to the King of France, who at that time was residing at Orleans.

The appearance of so-called Indians on the coast of the German Sea, under the Othos and Frederic Barbarossa, or even, as Cornelius Nepos, Pomponius Melas, and Pliny relate, at the time when Quintus Metellus Celer was proconsul in Gaul, may be explained by similar effects of the current and continuous north-easterly winds. A king of the Boians made a present of the stranded dark-coloured men to Metellus Celer. Gomara, in his "General History of the Indies," expresses a belief that these Indians were natives of Labrador, which would be doubly interesting as the first instance recorded in history of the natives of the Old and the New World having been brought into contact with each other. We can easily account for the appearance of Esquimaux on the North European coasts in former times; as during the eleventh and twelve centuries, their race was much more numerous than at present, and extended, as we know, from the researches of Rask and Finn Magnussen, from Labrador to the good Winland, or the shores of the present State of Massachusetts and Connecticut.

If we compare the climates on the opposite coasts of the Northern Atlantic, we find a remarkable difference in favour of the Old World. The frozen regions of Labrador, lie under the same degree of latitude as Plymouth, where the myrtle and laurel remain perpetually verdant in the open air. In New York, which has a more southern situation than Rome, the winter is colder than at Bergen in Norway, which lies 20° farther to the north. While on the northern coasts of the old continent, the waters remain open a great part of the year, even beyond the latitude of 80°, the ice never completely thaws on the opposite shores of Greenland. What a contrast between the Feroë islands, where the harbours are never frozen, where fertile meadows afford pasturage to numerous flocks of sheep, and even crops of barley reward the labours of the husbandman, and the frightful wildernesses on the shores of Hudson's Straits!--and yet both are situated under the same latitude of 62°.

The milder winter and earlier spring which characterise the north-west coast of Europe, are due, in some measure, to the prevailing westerly winds; but there can be no doubt that they are mainly owing to the influence of the Gulf-stream, which, as we have seen, conveys the heated waters of the Mexican Gulf far to the north-east, and thus imparts warmth to the climate of our native isle. In both seas, on the contrary, which bound the peninsula or island of Greenland, icy currents descend, and continue their course to the south, along the coasts of North America. Near Newfoundland their temperature, in May, is found to be 14° lower than that of the air, and even in spring and the early summer they carry along with them immense ice-blocks, which are frequently drifted as far south as the latitude of New York, and finally disappear in the Gulf-stream.

It is evident that the cold of winter must be increased, and the spring retarded along the North American coasts by these cold streams, just as the coasts of Europe are favoured by streams of a contrary nature; and thus the ocean-currents go a great way to explain the remarkable differences of climate between the opposite shores of the Northern Atlantic.

On this occasion I cannot omit directing the reader's attention to the influence which the far-distant barrier of Central America has upon the climate of Great Britain. Supposing yon narrow belt of land to be suddenly whelmed under the ocean, then instead of circuitously winding round the Gulf of Mexico, the heated waters of the equatorial current would naturally flow into the Pacific, and the Gulf-stream no longer exist. We should not only lose the benefit of its warm current, but cold polar streams, descending farther to the south would take its place, and be ultimately driven by the westerly winds against our coasts. Our climate would then resemble that of Newfoundland, and our ports be blocked up during many months, by enormous masses of ice. Under these altered circumstances, England would no longer be the grand emporium of trade and industry, and would finally dwindle down from her imperial station to an insignificant dependency of some other country more favoured by Nature.

On examining other coast-lands, in different parts of the globe, we shall everywhere find the influence of the reigning currents producing analogous effects to those I have already mentioned.

The Southern Atlantic is not warmed like the European seas by tepid streams, it is exposed on all sides to the free afflux of the cold waters of the Antarctic Ocean, and during the summer months to the influence of drift ice. Thus, the southern extremity of America, Terra del Fuego, the Falkland Islands, South Georgia, Sandwich Land, and other isles of the southern ocean, have a much colder climate than the European coasts and islands situated under the same latitude.

Let us for instance compare the temperature of the Falkland Islands and of Port Famine in the Straits of Magellan, with that of Dublin, which is situated at an equal distance from the line.

Mean Temperature.
Latitude. Winter. Summer. Annual.

Dublin 53° 21′ N. +4·0° R. 15·3° 9·6°
Port Famine 53° 38′ S. +0·6 10·0 5·3
Falkland Islands 52° 0′ S. 4·36 11·8 8·24
Feroë Islands 62° 2′ N. 3·9 11·6 7·1

Thus the climate of the Falkland Islands is, as we see, not very different from that of the Feroë Islands, although the latter lie ten degrees farther from the equator.

In the Pacific Ocean, as well as in the Atlantic, we find a westerly current filling the whole breadth of the tropical zone, from the coast of America to that of Australia and the Indian Archipelago. The best known of its affluxes is the cold Peruvian stream, which, emerging from the Polar Sea, flows with great rapidity along the shores of Chili and Peru, and does not take a westerly direction, before reaching the neighbourhood of the line. It has everywhere a remarkably low temperature, comparatively to the latitude, and this sufficiently accounts for the equal and temperate climate on the coasts of Chili and Peru. Thus, the mean temperature of Callao (12° S. lat.) is only 20° R. while in Rio Janeiro (23° S. lat.), though so much farther from the line, the annual warmth rises to 23·2° R.

In the beginning of November, Humboldt found at Callao the temperature of the sea within the current not higher than 15·5°, while outside the stream it rose to 26° or even 28·5° R.

Even in the vicinity of the equator, after the current has already assumed a westerly direction, its mean temperature does not exceed 20·5°. But as it advances towards the west, its temperature gradually rises to 27° or 28°.

On the western banks of the Pacific the equatorial stream divides into several branches. Part of its waters flow to the south, a greater quantity penetrates through the channels of the south Asiatic Archipelago into the Indian Ocean, the remainder turns to the north-east, on the confines of the Chinese Sea, leaves the eastern coast of the Japanese Islands, and then spreads its warm waters under the influence of north-westerly winds over the northern part of the Pacific. Thus the Japanese stream plays here the same part as the Gulf-stream in the Atlantic, and exerts a similar, though less mighty influence over the climate of the west coast of America, as it is neither so large nor so warm, and, having to traverse a wider ocean, in higher latitudes, naturally loses more of its heat during the passage.

It is owing to this stream that Sitcha enjoys a mean annual temperature of +7° R., while Nain in Labrador, situated under the same latitude, is indebted to the Greenland current for a summer of +7·8°, a winter of -18·5°, and a miserable annual temperature of -3·6°. On the west coast of North America the analogous trees grow 3° or 4° nearer to the pole, and the aboriginal tribes go naked as far to the north as 52°, a simplicity of toilet that would but ill suit the Esquimaux of Labrador.

Besides their beneficial influence on different climates the ocean-currents tend to equalise, or to maintain the equilibrium of the saline composition of sea-water, and thus secure the existence of numberless marine animals. Their movements also contribute to the formation of sand-banks, where at certain seasons legions of fishes deposit their spawn and invite the persecutions of man.

The rapidity of currents is very different, but always important enough to be taken into account by navigators. The well-informed seaman makes use of them to traverse wide spaces with greater rapidity, and, after an apparently circuitous course, arrives sooner and more safely at his journey's end than the ignorant steersman, who vainly endeavours to strive against their power.

LIGHTHOUSE AND WATER-SPOUTS.

A Lighthouse on a rocky shore is represented as just lighted, the
twilight having become darkened by a sudden storm, during which the
phenomena of "water-spouts" occur, which are represented to the left
of the Lighthouse.

CHAP. VI.

THE AËRIAL AND TERRESTRIAL MIGRATIONS OF THE WATERS.

Movements of the Waters through Evaporation.--Origin of
Winds.--Trade-Winds.--Calms.--Monsoons.--Typhoons.--Tornadoes.--
Water-Spouts.--The Formation of Atmospherical Precipitations.--Dew.--
Its Origin.--Fog.--Clouds.--Rain.--Snow.--Hail Sources.--The Quantities
of Water which the Rivers pour into the Ocean.--Glaciers and their
Progress.--Icebergs.--Erratic Blocks.--Influence of Forests on the
Formation and Retention of Atmospherical Precipitations.--Consequences
of their excessive Destruction.--The Power of Man over Climate.--How
has it been used as yet?

Neither storms nor ocean-currents, nor ebb and flood, however great their influence, cause such considerable movements of the waters, or force them to wander so restlessly from place to place as the silent and imperceptible action of the warming sunbeam. In every zone evaporation is constantly active in impregnating the atmosphere with moisture, but the chief seat of its power is evidently in the equatorial regions, where the vertical rays of the great parent of light and heat plunge, day after day, into the bosom of ocean, and perpetually saturate the burning air with aqueous vapours.

In this chapter I intend following these invisible agents of fertility and life, as they lightly ascend from the tropical seas, and accompanying them in their various transformations, until they once more return to the bosom of their great parent. A cursory view of the benefits they confer on the vegetable and animal world, as they wander over the surface of the land, will, I hope, agreeably occupy the reader, and serve to increase his admiration for that deep and dark blue ocean without which all organic life would soon be extinct upon earth.

I begin with a few words on the winged carriers of marine exhalations, the _winds_, which, although now and then detrimental or fatal to individuals by their violence, largely compensate for these local injuries, by the constant and inestimable benefits they confer on the whole body of mankind.

On taking a comprehensive view of their origin, we find that, like the oceanic currents, they are chiefly caused by the unequal influence of solar warmth upon the atmosphere under the line and at the poles. In the torrid zone, the air, rarefied by intense heat, ascends in perpendicular columns high above the surface of the earth, and there flows off towards the poles, in the same manner as in a vase filled with cold water and placed over the flame of a lamp, the warmed liquid rises from the bottom and spreads over the surface.

But cold air-currents must naturally come flowing in an opposite direction from the poles to the equator to fill up the void, as in the example I have cited, colder and consequently heavier water comes streaming down the sides of the vase to replace the liquid which is rising in the centre under the influence of heat.

Thus the unequal distribution of solar warmth over the surface of the earth evidently generates a constant circulation of air from the equator to the poles, and from the icy regions to the tropics, and by this means the purity of the atmosphere is chiefly maintained. The sun is not only the great fountain of warmth, he is also the universal ventilator; he not only calls forth animal life, but at the same time, by a simple and admirable mechanism, provides for its health by constantly renewing the air, which is essential to its existence.

If caloric were the sole agent which influences the direction of the winds, or if the earth were one uniform plain, the opposite air-currents I have mentioned would naturally flow straight to the north and south; but their course is modified or diverted in the same manner as that of the ocean-currents by the rotation of the globe. Thus, the cold air-current (polar-stream) which comes rushing upon us from the Arctic regions, is felt in our latitude as the biting east or north-east wind, so trying to our nerves and organs of respiration, while we enjoy the warm air-current from the tropics as the mild western or south-western breeze.

But besides the rotation of the earth, there are many other local influences by which the winds are deflected from their course, or by whose agency partial air-currents are called forth. Among these we particularly notice high chains of mountains, the unequal capacity of sea and land in absorbing and retaining heat, which gives rise to sea and land breezes; the increasing or diminishing power of the sun in different seasons by which the equilibrium of the air is modified in many countries, the difference of radiation from a sandy desert or a forest, electrical discharges from clouds, &c. &c.

Although subject to many of these local disturbances, the winds generally blow with an astonishing regularity in the tropical zone; while in our variable climate the polar and equatorial stream are engaged in a perpetual strife, now bringing us warmth and moisture from the south and west, now cold and dryness from the north and east.

Thus, in the Atlantic and Pacific Ocean we find the trade-winds perpetually blowing from the east, the north-east trade-wind between 9° and 27° N. lat., and the south-east trade-wind between 3° N. lat. and 25° S. lat. It was by their assistance that Columbus was enabled to discover America, and that the wretched barks of Magellan traversed the wide deserts of the Pacific from end to end.

Between these two regions of the trade-winds lies the dreaded zone or girdle of the equatorial calms (doldrums), where long calms alternate with dreadful storms, and the sultry air weighs heavily upon the spirits.

"Down dropt the breeze, the sails dropt down,
'Twas sad as sad could be;
And we did speak, only to break
The silence of the sea.

"Day after day, day after day,
We stuck, nor breath, nor motion,
As idle as a painted ship
Upon a painted ocean."

On their polar limits, the trade-wind zones are again girdled with calm belts, the _horse latitudes_, whose mean breadth is from ten to twelve degrees. The boundaries of these alternating regions of winds and calms are not invariably the same, on the contrary, they are perpetually moving to the north or south, according to the position of the sun.

From 40° N. lat. to the pole, westerly winds begin to be prevalent, and in the Atlantic Ocean their proportion to the easterly winds is as two to one.

In the Northern Indian Ocean and in the Chinese Sea we also find the trade-wind, which is there called the _north-east monsoon_; here, however, it only blows from October to April, as during the summer terrestrial influences prevail which completely divert it from its course.

From the wide plains of central Asia glowing with the rays of a perpetually unclouded sun, the rarefied air rises into the higher regions. Other columns of air rush from the equator to fill up the void, and cause the trade-wind to vary its course, and change into the _south-western monsoons_ of the Indian Ocean, which blow from May to September. The regularly alternating monsoons materially contributed to the early development of navigation in the Indian seas, and conducted the Greeks and Romans as far as Ceylon, Malacca, and the Gulf of Siam. Similar monsoons, or deflections from the ordinary course of the trade-winds, occur also in the Mexican Gulf, in the Gulf of Guinea, and in that part of the Pacific which borders on Central America, through the influence of the heated plains of Africa, Utah, Texas, and New Mexico.

The passage from one monsoon to the other is of course only gradual, since the land also is only gradually heated and cooled. Thus at the change of the monsoon, an atmospheric war of several weeks' continuance occurs, during which the trade-wind and the monsoon measure their strength, and calms alternate with dreadful storms (typhoons, cyclones, tornadoes).

According to the researches and observations of Franklin, Cooper, Redfield, Reid, &c. &c., these storms are great rotatory winds, that move along a curved line in increasing circles. In the northern hemisphere, the rotatory movement follows a direction contrary to that of the hands of a clock; while the opposite takes place in the southern hemisphere. The knowledge of the laws which regulate the movements of storms is of great importance to the mariner, since it points out to him the direction he has to give his ship to gain the external limits of the tornado, and thus to remove it from danger.

_Water-spouts_ are formed by two winds blowing in opposite directions, and raising or sucking up the water in their vortex. They generally form a double cone; the superior part with its apex downwards, consisting of a dense cloud, while the inferior cone, the apex of which is turned upwards, consists of water, which is thus sometimes raised to a height of several hundred feet.

Water-spouts seldom last longer than half-an-hour. Their course and movements are irregular; straight forwards; in zig-zag lines; alternately rising and falling; stationary; slow; or progressing with the rapidity of thirty miles an hour. The rotatory movement is also variable; its power is often very great, but sometimes water-spouts pass over small vessels without injuring them. They are more frequent near the coast than on the high seas; and are more commonly seen in warm climates. They seem to occur particularly in regions where calms frequently alternate with storms, which is not to be wondered at, since they owe their origin to miniature storms or whirlwinds.

How do the aqueous vapours with which evaporation impregnates the atmosphere, again descend upon the surface of the earth?

Everybody knows that when in summer a bottle filled with cold water is brought into the room, it soon gets covered with thick dew-drops, which presently trickle down its sides, although it was perfectly dry on entering. Whence does this moisture come from? Not from the inside of the bottle as ignorant people might imagine, but from the surrounding atmosphere; in consequence of the capacity of the air to absorb and retain moisture, increasing or diminishing, as its temperature grows warmer or colder.

Thus when the cold bottle is introduced into the room, the warm sheet of air, which is in immediate contact with its surface, immediately cools, and being no longer able to retain all the moisture with which it was impregnated, is obliged to deposit it on the sides of the vessel. This familiar example suffices to explain the formation of dew, rain, hail, snow, hoar-frost, and all other atmospherical precipitations. They all result from the influence of some refrigerating cause upon the air; such as the passage of a warm current into a cooler region; the influx of a cold wind; a cold-radiating chain of high mountains; a forest, and so forth.

The very name of dew is refreshing, and calls forth a host of pleasing ideas, associated as it is with the memory of serene skies and sunny mornings. How beautiful are its diamonds glittering in all the colours of the rainbow, on verdant meads, or on the blushing petals of the rose. How suggestive of all that is lovely, pure, and innocent!

Poetry is of older date than prose, and bards have sung long before philosophers inquired. Thus, although the children of song from Homer and Theocritus to Byron and Wordsworth so frequently mention dew in their immortal strains, it is only in our time that its formation has been fully explained by Dr. Wells, who in a very ingenious and masterly essay on this subject, first proved that it results from the ground radiating or projecting heat into free space, and consequently becoming colder than the neighbouring air. During calm and clear nights, the upper surfaces of grass-blades, for instance, radiate their caloric into the serene sky, from which they receive none in return. The lower parts of the plant, being slow conductors of heat, can only transmit to them a small portion of terrestrial warmth, and their temperature consequently falling below that of the circumambient atmosphere, they condense its aqueous vapours. Clouds on the contrary compensate for the loss of heat the grass sustains from radiation, by reflecting or throwing back again upon the terrestrial surface, the caloric which would else have been dissipated in a clear sky, and this is the reason why dew does not fall, or but slightly falls during clouded nights. It is easy to conceive why none is formed in windy weather, as then the air in contact with the ground is constantly removed ere it has time to cool so far as to compel it to part with its moisture. We can also understand why dew is more abundant in autumn and spring than at any other season; as then very cold nights frequently follow upon warm days; and why it is most copious in the torrid zone, as in those sultry regions the air is more saturated with moisture than anywhere else, and the comparatively cold nights are almost constantly serene and calm. Hoar-frost is nothing but congealed dew, and owes its formation to the same causes.

When warmer air-currents are cooled by being transported into colder regions, or from any other refrigerating cause, a great part of their moisture generally condenses into small vesicles, but very little heavier than the surrounding atmosphere, which then becomes visible under the form of clouds, those great beautifiers of our changing skies, that frequently trace such picturesque, gorgeous, or singular groups and landscapes in the aërial regions. The inhabitants of countries where the heavens are monotonously serene, may well envy us the charms of a phenomenon which in some measure affords us compensation for so many disagreeable vicissitudes of the weather. Who that has admired at sunset the light clouds so beautifully fringed with silver and gold, or glowing with the richest purple, and loves to follow them in all their wonderful and fantastic transformations, will deny that they are the poesy and life of the skies, the awakeners of pleasing fancies and delightful reveries?

Thin wreaths of clouds have been observed, by travellers that have ascended the most elevated mountains, floating high above the peak of Chimborazo or Dhawalagiri, and thus shows us to what an amazing altitude the emanations of ocean are carried by the ascending air-current.

Sometimes when light clouds pass into a warmer atmosphere, they gradually dissolve and vanish; more frequently the accumulating moisture, too heavy to continue floating in the air, or condensed by electrical explosions, descends upon the earth in rain, which, with few exceptions, visits every part of the globe, either in its liquid form or congealed to snow or hail. But the quantity of rain which annually falls in different regions is very unequal, and strange to say, it is not most considerable in those countries whose climate enjoys an unenviable notoriety for its clouded atmosphere and the great number of its rainy days. In the tropical regions it is generally only about the time of the summer solstice that abundant showers of rain fall regularly every afternoon, while the rest of the year, the sky is uninterruptedly serene; but during the short period of the rainy season, a far greater quantity of water is precipitated upon the earth, than in the temperate zones.

While on the island of Guadaloupe, the annual quantity of rain amounts to 274·2 French inches, and to 283·3 at Mahabuleshwar, on the western declivity of the Ghauts, which, as far as has hitherto been ascertained, is the place where most rain descends; only from 35 to 40 inches fall on the western coast of England, where the skies are chronically weeping.

It is a remarkable circumstance that the annual quantity of rain which falls in the same place remains about the same from year to year; so that by an admirable balancing of conflicting influences, nature seems to have provided for stability in a province which of all others might be supposed most open to the caprices of chance.

Having thus followed the exhalations of ocean to the end of what may be called the first stage of their journey, and seen them descend in a condensed form upon the surface of the dry land, I will now accompany them in their ulterior progress to the bosom of the seas. A great part of them have many transformations and changes to undergo ere they can accomplish their return; repeatedly rising in vapours from the solid earth, and falling in showers upon its surface; or circulating through the tissues of organic life: but after all these intermediate stages and delays, they ultimately find their way into rivulets or streams, which after many a meander restore them to the vast reservoir from which they arose.

The waters that descend upon solid rocks, or fall in large quantities upon abrupt declivities, immediately flow into the brooks or rivers; but when they gently and gradually alight upon a porous soil, they are absorbed by the earth, and, displacing in virtue of capillary attraction, and of their superior weight, the air which fills the interstices between its solid particles, sink deeper and deeper until they meet with a solid and impenetrable stratum. If this forms a hollow basin, they naturally settle in the cavity; whence they are slowly displaced by fresh accessions and evaporation; but if its deepest declivity lies somewhere near the surface, they gradually gush forth under the form of sources or springs, having unequal distances to perform before they can reach the orifice. If no fresh supply of water falls, ere the most distant particles have reached their journey's end, the source dries up: but if new atmospheric precipitations continually take place, the source is perennial, although naturally of unequal strength at different times.

The temperature of springs varies from icy coldness to boiling heat. Cold springs arise when the waters, by which they are fed, descend from high mountains or do not penetrate a great way into the bowels of the earth; but if the filtering waters reach a depth which is constantly of a higher temperature, they then gush forth in the form of warm or even boiling springs.

A crowd of agreeable associations attaches itself to the idea of sources and springs, for they are generally both pleasing and useful to man. How we long in summer for the refreshing waters of the cool fountain issuing from the mountain side, and murmuring through the woods. The lover of nature spends hours near some solitary spring, and forgets the flow of time, as he observes the bubbling and listens to the sweet music of its crystal waters. A luxuriant vegetation marks their progress, though all around be burnt up by the scorching sun. Along their margin many a wild flower blooms, and herbs and shrubs and trees rejoice in a more vivid green, and statelier growth. There also congregate such members of the finny race, as delight in cooler streams of untainted purity, and birds love to build their nests among the sheltering foliage. Thus a little world forms around the gushing spring, and shows on a diminutive scale, how all that lives and breathes depends upon the liquid element for its existence.

While the waters filter through the earth they naturally dissolve a variety of substances, and all springs are more or less mixed with extraneous particles. But many of them, particularly such as are of a higher temperature and consequently arise from deeper strata, contain either a larger quantity or so peculiar a combination of mineral substances as to acquire medicinal virtues of the highest order, and to become objects of importance to a large portion of mankind. Numberless invalids annually flock to the hygeian fountains which nature unceasingly pours forth from her mysterious laboratory, and are by them restored to the enjoyments of a pleasurable existence.

How truly wonderful is the chain of processes which first raises vapours from the deep, and eventually causes them to gush forth from the entrails of the earth, laden with blessings and enriched with treasures more inestimable than those the miner toils for!

Although a river generally has its source in mountainous regions, it must be remembered that all the waters that descend upon the territory of which it forms the lowest level, gradually find their way into its current. Thus, the monarch of all streams, the Amazon River, is the natural drain of a territory thirty times larger than England. Thousands of rivulets and brooks, fed by the waters which descend from the slopes of thousands of glens and valleys, or filter through the vast forest-plains that rise but a few feet above their surface, all contribute to swell the majesty of its current. Its sources are in reality wherever, on that vast extent of land, water descends and drains into any one of its innumerable affluents. When we hear that on an average the river of the Amazons alone restores every minute half a million of tons of water to the ocean, and then consider the countless number of streams all alike active, that are scattered over the globe, we may form a faint idea of the vast quantity of vapours which are constantly rising from the deep, and of the magnitude of these silent operations of nature. Yet such is the immensity of ocean, that supposing all the waters it constantly loses, never to return again into its bosom, it would require thousands of years of evaporation to exhaust the immensity of its reservoirs!

It might be supposed that the waters which congeal on the sides of mountains covered with perennial snow, or fill Alpine valleys in the form of glaciers, were eternally fixed on earth--but there also we are deceived by delusive appearances of immobility. Every year the glacier slowly but restlessly makes a step forwards into the valley, and while its lower end dissolves, new supplies of snow constantly feed it from above. It has been calculated by Agassiz that the ice masses of the Aar glacier require 133 years to perform their descent from its summit to its inferior extremity--a distance of ten miles--so that their sojourn in that chilled valley far surpasses that of the oldest patriarch of the mountains. How great must be their delight when they at last are liberated from the spell which so long enchained them, and freely bound along on their way to Ocean! How they must shudder at the idea of once more returning to their desolate prison, and long for the perpetual warmth of spicy groves and tropical gardens!

In the colder regions of the earth, in Greenland or Spitzbergen, immense glaciers frequently fill the valleys that open on the sea, descend even beyond the water's edge, and, as they move along, their overhanging masses separate from their base and plunge into the deep with a crash louder than thunder. The icebergs that drift about the Arctic seas, and are annually conveyed by the currents into lower latitudes, are formed in this manner. Huge blocks of granite, detached by atmospherical vicissitudes from the higher mountains and precipitated on the surface of the glaciers, frequently float on the broad back of an iceberg far away from the spot where they seemed rooted for eternity. As their crystal support melts away in its progress to warmer climes, these rocky fragments, which have been appropriately named _erratic blocks_, fall to the bottom of the sea hundreds or even thousands of miles from the starting point of their journey. Thus the great bank of Newfoundland is covered with stones from distant Greenland, raised high in the air by volcanic power myriads of years ago, and now condemned to an equally long repose below the surface of ocean. When will they rise again above the waters, and what further changes will they have to undergo ere their compacted atoms resolve themselves into dust and assume new forms? But, however remote their dissolution, it will inevitably come, for Time is all-powerful, and has an eternity to work out his changes.

The large blocks of stone that so wonderfully migrate on the wandering iceberg form but a small and insignificant portion of the terrestrial spoils which are transported to ocean by the returning waters. Every river is more or less laden with earthy particles which its current carries onwards to the sea and deposits at its mouth. In course of time their accumulation, as I have already mentioned, forms large tracts of fertile territory encroaching upon the maritime domains.

I shall end with a few words on the influence of forests in attracting or retaining the atmospherical moisture, as it is a subject of great importance in the economy of nations, and shows us how much it is in the power of man to improve or to defeat the provisions of nature in his favour.

Forests always cool the neighbouring atmosphere, for their foliage offers an immense warmth-radiating surface, so that the vapours readily condense above them and descend in frequent showers. At the same time their roots loosen the soil, and the successive falling of their leaves forms a thick layer of humus, which has an uncommon power in attracting and retaining moisture. Their thick canopy of verdure also prevents the rays of the sun from penetrating to the ground, and absorbing its humidity. Thus the soil on which forests stand is constantly saturated with water, and becomes the parent of perennial sources and rills, that spread fertility and plenty far from the spot where they originated.

The rain-attractive influence of forests did not escape the attention of Columbus, who ascribed the frequent showers which refreshed and cooled the air, as he sailed along the coasts of Jamaica, to the vast extent and density of the woods that covered the mountains of that island. On this occasion he mentions in his journal that formerly rain had been equally abundant on Madeira, the Canaries, and the Azores, before their shady forests were felled or burnt by the improvident settlers.

The wanton destruction of woods has entailed barrenness on countries renowned in former times for their fertility. The mountains of Greece were covered with trees during the great epoch of her history, and the well-watered land bore abundant fruits, and sustained a numerous population. But man recklessly laid waste the sources of his prosperity. Along with the woods, many brooks and rivulets disappeared, and ceased to water the parched plains. The rain gradually washed the vegetable earth from the sides of the naked hills, and condemned them to sterility. When the snow of the mountains began to thaw under the warm breath of spring, it was now no longer retained by the spongy soil of the forests, and gradually dissolved under their cover; but, rapidly melting, filled with its impetuous torrents the bed of the rivers, and overflowing their banks, spread ruin and devastation far around.

Unfortunately, forests when once destroyed are not so easily restored, and it requires many centuries ere the bared mountain side reassumes its pristine vesture of shady woods. First lichens, mosses, and other thrifty herbs, content to feed upon nothing, have to prepare a scanty humus for the reception of more pretentious guests. In course of time some small stunted shrub makes its appearance here and there in some peculiarly favoured spot, and after all requires vast powers of endurance to maintain itself on the niggard soil, exposed to the full enmity of wind and weather. This paves the way for a more vigorous and fortunate offspring; and as every year adds something to the vegetation on the mountain's side, and opposes increasing obstacles to the winds, the falling leaves and decaying herbage accumulate more and more, until dwarfish trees first find a sufficiency of soil to root upon, and finally, the proud monarch of the forest spreads out his powerful arms and raises his majestic summit to the skies.