Physical Geography of the Sea and its Meteorology/Chapter 3
CHAPTER III.
§ 150-191.—INFLUENCE OF THE GULF STREAM UPON CLIMATE AND COMMERCE.
150. How the Washington Observatory is warmed.—Modern ingenuity has suggested a beautiful mode of warming houses in winter. It is done by means of hot water. The furnace and the caldron are sometimes placed at a distance from the apartments to be warmed. It is so at the Washington Observatory. In this case, pipes are used to conduct the heated water from the caldron under the superintendent's dwelling over into one of the basement rooms of the Observatory, a distance of one hundred feet. These pipes are then flared out so as to present a large cooling surface; after which they are united into one again, through which the water, being now cooled, returns of its own accord to the caldron. Thus cool water is returning all the time and flowing in at the bottom of the caldron, while hot water is continually flowing out at the top. The ventilation of the Observatory is so arranged that the circulation of the atmosphere through it is led from this basement room, where the pipes are, to all other parts of the building; and in the process of this circulation, the warmth conveyed by the water to the basement is taken thence by the air and distributed over all the rooms. Now, to compare small things with great, we have, in the warm waters which are contained in the Gulf of Mexico, just such a heating apparatus for Great Britain, the North Atlantic, and Western Europe.
151. An analogy showing how the Gulf Stream raises temperature in Europe.—The furnace is the torrid zone; the Mexican Gulf and Caribbean Sea are the caldrons; the Gulf Stream is the conducting pipe. From the Grand Banks of Newfoundland to the shores of Europe is the basement—the hot-air chamber—in which this pipe is flared out so as to present a large cooling surface. Here the circulation of the atmosphere is arranged by nature; it is from west to east; consequently it is such that the warmth thus conveyed into this warm-air chamber of mid-ocean is taken up by the genial west winds, and dispensed, in the most benign manner, throughout Great Britain and the west of Europe. The mean temperature of the water-heated air-chamber of the Observatory is about 90°. The maximum temperature of the Gulf Stream is 86°, or about 9° above the ocean temperature due the latitude. Increasing its latitude 10°, it loses but 2° of temperature; and, after having run three thousand miles towards the north, it still preserves, even in winter, the heat of summer. With this temperature it crosses the 40th degree of north latitude, and there, overflowing its liquid banks, it spreads itself out for thousands of square leagues over the cold waters around, covering the ocean with a mantle of warmth that serves so much to mitigate in Europe the rigours of winter. Moving now more slowly, but dispensing its genial influences more freely, it finally meets the British Islands. By these it is divided (Plate IX.), one part going into the polar basin of Spitzbergen, the other entering the Bay of Biscay, but each with a warmth considerably above the ocean temperature. Such an immense volume of heated water cannot fail to carry with it beyond the seas a mild and moist atmosphere. And this it is which so much softens climate there.
152. Depth and temperature.—We know not, except approximately in a few places, what the depth of the under temperature of the Gulf Stream may be; but assuming the temperature and velocity at the depth of two hundred fathoms to he those of the surface, and taking the well-known difference between the capacity of air and of water for specific heat as the argument, a simple calculation will show that the quantity of heat discharged over the Atlantic from the waters of the Gulf Stream in a winter's day would be sufficient to raise the whole column of atmosphere that rests upon France and the British Islands from the freezing point to summer heat.
153. Contrasts of climates in the same latitudes.—Every west wind that blows crosses this stream on its way to Europe, and carries with it a portion of this heat to temper there the northern winds of winter. It is the influence of this stream upon climate that makes Erin the "Emerald Isle of the Sea,"—that clothes the shores of Albion in evergreen robes; while in the same latitude, on this side, the coasts of Labrador are fast bound in fetters of ice. In a valuable paper on currents,[1] Mr. Redfield states, that in 1831 the harbour of St. John's, Newfoundland, was closed with ice as late as the month of June; yet who ever heard of the port of Liverpool, on the other side, though 2° farther north, being closed with ice, even in the dead of winter?
154. Mildness of an Orkney winter.—The Thermal Chart (Plate IV.) shows this. The isothermal lines of 60°, 50°, etc., starting off from the parallel of 40° near the coasts of the United States, run off in a north-eastwardly direction, showing the same oceanic temperature on the European side of the Atlantic in latitude 55° or 60° that we have on the western side in latitude 40°. Scott, in one of his beautiful novels, tells us that the ponds in the Orkneys (latitude near 60°) are not frozen in winter. The people there owe their soft climate to this grand heating apparatus, and to the latent heat of the vapours from it which is liberated during the precipitation of them upon the regions round about. Driftwood from the West Indies is occasionally cast upon the islands of the North Sea and Northern Ocean by the Gulf Stream.
155. Amount of heat daily escaping through the Gulf Stream.—Nor do the beneficial influences of this stream upon climate end here. The West Indian Archipelago is encompassed on one side by its chain of islands, and on the other by the Cordilleras of the Andes, contracting with the Isthmus of Darien, and stretching themselves out over the plains of Central America and Mexico. Beginning on the summit of this range, we leave the regions of perpetual snow, and descend first into the tierra templada, and then into the terra caliente, or burning land. Descending still lower, we reach both the level and the surface of the Mexican seas, where, were it not for this beautiful and benign system of aqueous circulation, the peculiar features of the surrounding country assure us we should have the hottest, if not most pestilential climate in the world. As the waters in these two caldrons become heated, they are borne off by the Gulf Stream, and are replaced by cooler currents through the Caribbean Sea; the surface water, as it enters here, being 3° or 4°, and that in depth even 40° cooler than when it escapes from the Gulf.[2] Taking only this difference in surface temperature as an index of the heat accumulated there, a simple calculation will show that the quantity of heat daily carried off by the Gulf Stream from those regions, and discharged over the Atlantic, is sufficient to raise mountains of iron from zero to the melting-point, and to keep in flow from them a molten stream of metal greater in volume than the waters daily discharged from the Mississippi River.
156. Its benign influences.—Who, therefore, can calculate the benign influence of this wonderful current upon the climate of the South? In the pursuit of this subject, the mind is led from nature up to the great Architect of nature; and what mind will not the study of this subject fill with profitable emotions? Unchanged and unchanging alone, of all created things, the ocean is the great emblem of its everlasting Creator. "He treadeth upon the waves of the sea," and is seen in the wonders of the deep. Yea, "He calleth for its waters, and poureth them out upon the face of the earth." In obedience to this call, the aqueous portion of our planet preserves its beautiful system of circulation. By it heat and warmth are dispensed to the extra-tropical regions; clouds and rain are sent to refresh the dry land; and by it cooling streams are brought from Polar Seas to temper the heat of the torrid zone. At the depth of two hundred and forty fathoms the temperature of the currents setting into the Caribbean Sea has been found as low as 48°, while that of the surface was 85°. Another cast with three hundred and eighty-six fathoms gave 43° below against 83° at the surface. The hurricanes of those regions agitate the sea to great depths; that of 1780 tore rocks up from the bottom seven fathoms deep, and cast them ashore. They therefore cannot fail to bring to the surface portions of the cooler water below.
157. Cold water at the bottom of the Gulf Stream.—At the very bottom of the Gulf Stream, when its surface temperature was 80°, the deep-sea thermometer of the Coast Survey has recorded a temperature as low as 35° Fahrenheit. These cold waters doubtless come down from the north to replace the warm water sent through the Gulf Stream to moderate the cold of Spitzbergen; for within the Arctic Circle the temperature at corresponding depths off the shores of that island is said to be only one degree colder than in the Caribbean Sea, while on the shores of Labrador and in the Polar Seas the temperature of the water beneath the ice was invariably found by Lieutenant De Haven at 28°, or 4° below the melting-point of fresh-water ice. Captain Scoresby relates, that on the coast of Greenland, in latitude 72°, the temperature of the air was 42°; of the water, 34°; and 29° at the depth of one hundred and eighteen fathoms. He there found a surface current setting to the south, and bearing with it this extremely cold water, with vast numbers of icebergs, whose centers, perhaps, were far below zero. It would be curious to ascertain the routes of these under-currents on their way to the tropical regions, which they are intended to cool. One has been found at the equator (§ 97) two hundred miles broad and 23° colder than the surface water. Unless the land or shoals intervene, it no doubt comes down in a spiral curve (§ 96), approaching in its course the great circle route.
158. Fish and currents.—Perhaps the best indication as to these cold currents may be derived from the fish of the sea. The whales, by avoiding its warm waters, pointed out to the fisherman the existence of the Gulf Stream. Along our own coasts, all those delicate animals and marine productions which delight in warmer waters are wanting; thus indicating, by their absence, the prevalence of the cold current from the north now known to exist there. In the genial warmth of the sea about the Bermudas on one hand, and Africa on the other, we find, in great abundance. those delicate shell-fish and coral formations which are altogether wanting in the same latitudes along the shores of South Carolina. The same obtains in the west coast of South America; for there the immense flow of polar waters known as Humboldt's Current almost reaches the line before the first sprig of coral is found to grow. A few years ago, great numbers of bonita and albercore—tropical fish— following the Gulf Stream, entered the English Channel, and alarmed the fishermen of Cornwall and Devonshire by the havoc which they created among the pilchards. It may well be questioned if the Atlantic cities and towns of America do not owe their excellent fish-markets, and the watering-places their refreshing sea-bathing in summer, to this littoral stream of cold water. The temperature of the Mediterranean is 4° or 5° above the ocean temperature of the same latitude, and the fish there are, for the most part, very indifferent. On the other hand, the temperature along the American coast is several degrees below that of the ocean, and from Maine to Florida, tables are supplied with the most excellent of fish. The sheep's-head of this cold current, so much esteemed in Virginia and the Carolinas, loses its flavour, and is held in no esteem, when taken on the warm coral banks of the Bahamas. The same is the case with other fish: when taken in the cold water of that coast, they have a delicious flavour, and are highly esteemed; but when taken in the warm water on the other edge of the Gulf Stream, though but a few miles distant, their flesh is soft and unfit for the table. The temperature of the water at the Balize reaches 90°. The fish taken there are not to be compared with those of the same latitude in this cold stream. New Orleans, therefore, resorts to the cool waters on the Florida coasts for her choicest fish. The same is the case in the Pacific. A current of cold water (§ 398) from the south sweeps the shores of Chili, Peru, and Columbia, and reaches the Galapagos Islands under the equator. Throughout this whole distance, the world does not afford a more abundant or excellent supply of fish. Yet out in the Pacific, at the Society Islands, where coral abounds, and the water preserves a higher temperature, the fish, though they vie in gorgeousness of colouring with the birds, and plants, and insects of the tropics, are held in no esteem as an article of food. I have known sailors, even after long voyages, still to prefer their salt beef and pork to a mess of fish taken there. The few facts which we have bearing upon this subject seem to suggest it as a point of the inquiry to be made, whether the habitat of certain fish does not indicate the temperature of the water; and whether these cold and warm currents of the ocean do not constitute the great highway's through which migratory fishes travel from one region to another. Why should not fish be as much the creatures of climate as plants, or as birds and other animals of land, sea, and air? Indeed, we know that some kinds of fish are found only in certain climates. In other words, they live where the temperature of the water ranges between certain degrees.
159. A shoal of sea-nettles.—Navigators have often met with vast numbers of young sea-nettles (medusœ) drifting along with the Gulf Stream. They are known to constitute the principal food for the whale; but whither bound by this route has caused much curious speculation, for it is well known that the habits of the right whale are averse to the warm waters of this stream. An intelligent sea-captain informs me that, several years ago, in the Gulf Stream off the coast of Florida, he fell in with such a "school of young sea-nettles as had never before been heard of." The sea was covered with them for many leagues. He likened them, as they appeared on near inspection in the water, to acorns floating on a stream; but they were so thick as completely to cover the sea, giving it the appearance, in the distance, of a boundless meadow in the yellow leaf. He was bound to England, and was five or six days in sailing through them. In about sixty days afterwards, on his return, he fell in with the same school off the Western Islands, and here he was three or four days in passing them again. He recognized them as the same, for he had never before seen any like them; and on both occasions he frequently hauled up buckets full and examined them.
160. Food for whales.—Now the Western Islands is the great place of resort for whales; and at first there is something curious to us in the idea that the Gulf of Mexico is the harvest field, and the Gulf Stream the gleaner which collects the fruitage planted there, and conveys it thousands of miles off to the hungry whale at sea. But how perfectly in unison is it with the kind and providential care of that great and good Being that caters for the sparrow, and feeds the young ravens when they cry!
161. Piazzi Smyth's description.—Piazzi Smyth, the Astronomer Royal of Edinburgh, when bound to Teneriffe on his celebrated astronomical expedition of 1856, fell in with the annual harvest of these creatures. They were in the form of hollow gelatinous lobes, arranged in groups of five or nine—each lobe having an orange vein down the centre. Thus each animal was formed of an aggregation of lobes, with an orange-coloured vein, or stomach, in every lobe. "Examining," says he, "in the microscope a portion of one of the orange veins, apparently the stomach of the creature, it was found to be extraordinarily rich in diatomes, and of the most bizarre forms, as stars, Maltese crosses, embossed circles, semicircles, and spirals. The whole stomach could hardly have contained less than seven hundred thousand; and when we multiply them by the number of lobes, and then by the number of groups, we shall have some idea of the countless millions of diatomes that go to make a feast for the medusæ—some of the softest things in the world thus confounding and devouring the hardest—the flinty-shelled diatomaceæ." Each of these "sea-nettles," as the sailors call them, had in his nine stomachs not less, according to this computation, than five or six millions of these mites of flinty shells, the materials of which their inhabitants had collected from the silicious matter which the rains washed out from the valleys, and which the rivers are continually rolling down to the sea.
162. The waters of the sea bring forth—oh how abundantly!—The medusæ have the power of sucking in the sea-water slowly, and of ejecting it again with more or less force. Thus they derive both food and the power of locomotion, for, in the passage of the water, they strain it and collect the little diatomes. Imagine, now, how many medusæ-mouthfuls of water there must be in the sea, which, though loaded with diatomes, are never filtered through the stomachs of these creatures; imagine how many medusæ the whale must gulp down with every mouthful; imagine how deep and thickly the bottom of the sea must, during the process of ages, have become covered with the flinty remains of these little organisms; now call to mind the command which was given to the waters of the sea on the fifth day of creation; and then the boasted powers of the imagination are silenced in their very impotency, and the emotions of wonder, love, and praise take their place.
163. Contrasts between the climates of land and sea.—The sea has its climates as well as the land. They both change with the latitude; but one varies with the elevation above, the other with the depression below the sea level. The climates in each are regulated by circulation; but the chief regulators are, on the one hand, winds; on the other, currents.
164. Order and design.—The inhabitants of the ocean are as much the creatures of climate as are those of the dry land; for the same Almighty hand which decked the lily and cares for the sparrow, fashioned also the pearl and feeds the great whale; He adapted each to the physical conditions by which his providence has surrounded it. Whether of the land or the sea, the inhabitants are all his creatures, subjects of his laws, and agents in his economy. The sea, therefore, we may safely infer, has its offices and duties to perform; so, may we infer, have its currents, and so, too, its inhabitants; consequently, he who undertakes to study its phenomena must cease to regard it as a waste of waters. He must look upon it as a part of that exquisite machinery by which the harmonies of nature are preserved, and then he will begin to perceive the developments of order and the evidences of design: viewed in this light, it becomes a vast field for study—a most beautiful and interesting subject for contemplation.
165. Terrestrial adaptations.—To one who has never studied the mechanism of a watch, its main-spring or the balance-wheel is a mere piece of metal. He may have looked at the face of the watch, and, while he admires the motion of its hands, and the time it keeps, or the tune it plays, he may have wondered in idle amazement as to the character of the machinery which is concealed within. Take it to pieces, and show him each part separately; he will recognize neither design, nor adaptation, nor relation between them; but put them together, set them to work, point out the offices of each spring, wheel, and cog, explain their movements, and then show him the result; now he perceives that it is all one design; that, notwithstanding the number of parts, their diverse forms and various offices, and the agents concerned, the whole piece is of one thought, the expression of one idea. He now rightly concludes that when the main-spring was fashioned and tempered, its relation to all the other parts must have been considered; that the cogs on this wheel are cut and regulated—adapted—to the ratchets on that, &c.; and his final conclusion will be, that such a piece of mechanism could not have been produced by chance; for the adaptation of the parts is such as to show it to be according to design, and obedient to the will of one intelligence. So, too, when one looks out upon the face of this beautiful world, he may admire its lovely scenery. but his admiration can never grow into adoration unless he will take the trouble to look behind and study, in some of its details at least, the exquisite system of machinery by which such beautiful results are brought about. To him who does this, the sea, with its physical geography, becomes as the main-spring of a watch; its wheels, and its currents, and its salt, and its inhabitants, with their adaptations, as balance-wheels, cogs, and pinions, and jewels in the terrestrial mechanism. Thus he perceives that they too are according to design—parts of the physical machinery that are the expression of One Thought,—a unity, with harmonies which One Intelligence, and One Intelligence alone, could utter. And when he has arrived at this point, then he feels that the study of the sea, in its physical aspects, is truly sublime. It elevates the mind and ennobles the man; for "His gentleness makes" it great. The Gulf Stream is now no longer, therefore, to be regarded by such a one merely as an immense current of warm water running across the ocean, but as a balance-wheel—a part of that grand machinery by which air and water are adapted to each other, and by which this earth itself is adapted to the well-being of its inhabitants— of the flora which deck, and the fauna which enliven its surface.
166. Meteorology of the sea: Gulf Stream the weather-breeder—its storms—the great hurricane of 1780.—Let us now consider the Influence of the Gulf Stream upon the Meteorology of the Ocean. To use a sailor's expression, the Gulf Stream is the great "weather-breeder" of the North Atlantic Ocean. The most furious gales of wind sweep along with it; and the fogs of Newfoundland, which so much endanger navigation in spring and summer, doubtless owe their existence to the presence, in that cold sea, of immense volumes of warm water brought by the Gulf Stream. Sir Philip Brooke found the temperature of the air on each side of it at the freezing-point, while that of its waters was 80°. "The heavy, warm, damp air over the current produced great irregularities in his chronometers." The excess of heat daily brought into such a region by the waters of the Gulf Stream would, if suddenly stricken from them, be sufficient to make the column of superincumbent atmosphere hotter than melted iron. With such an element of atmospherical disturbance in its bosom, we might expect storms of the most violent kind to accompany it in its course. Accordingly, the most terrific that rage on the ocean have been known to spend their fury within or near its borders. Of all storms, the hurricanes of the West Indies and the typhoons of the China seas cause the most ships to founder. The stoutest men-of-war go down before them, and seldom, indeed, is any one of the crew left to tell the tale. Of this the Hornet, the Albany, and the Grampus, armed cruisers in the American navy, all are memorable and melancholy examples. Our nautical works tell us of a West India hurricane so violent that it forced the Gulf Stream back to its sources, and piled up the water in the Gulf to the height of thirty feet. The Ledbury Snow attempted to ride it out. When it abated, she found herself high up on the dry land, and discovered that she had let go her anchor among the tree-tops on Elliott's Key. The Florida-Keys were inundated many feet, and, it is said, the scene presented in the Gulf Stream was never surpassed in awful sublimity on the ocean. The water thus dammed up rushed out with frightful velocity against the fury of the gale, producing a sea that beggared description. The "great hurricane" of 1780 commenced in Barbados. In it the bark was blown from the trees, and the fruits of the earth destroyed; the very bottom and depths of the sea were uprooted, and the waves rose to such a height that forts and castles were washed away, and their great guns carried about in the air like chaff; houses were razed; ships wrecked; and the bodies of men and beasts lifted up in the air and dashed to pieces in the storm. At the different islands, not less than twenty thousand persons lost their lives on shore, while farther to the north, the "Stirling Castle" and the "Dover Castle," British men-of-war, went down at sea, and fifty sail were driven on shore at the Bermudas.
167. Inquiries instituted by the Admiralty.—Several years ago the British Admiralty set on foot inquiries as to the cause of the storms in certain parts of the Atlantic, which so often rage with disastrous effects to navigation. The result may be summed up in the conclusion to which the investigation led: that they are occasioned by the irregularity between the temperature of the Gulf Stream and of the neighbouring regions, both in the air and water.
168. The most stormy sea.—The southern points of South America and Africa have won for themselves, among seamen, the name of "the stormy capes;" but investigations carried on in that mine of sea-lore contained in the log-books at the National Observatory at Washington, have shown that there is not a storm-find in the wide ocean can out-top that which rages along the Atlantic coasts of North America. The China seas and the North Pacific may vie in the fury of their gales with this part of the Atlantic, but Cape Horn and the Cape of Good Hope cannot equal them, certainly, in frequency, nor do I believe in fury.
169. Northern seas more boisterous than southern.—In the ex-tropical regions of the south we lack those contrasts which the mountains, the deserts, the plains, the continents, and the seas of the north afford for the production of atmospherical disturbances. Neither have we in the southern seas such contrasts of hot and cold currents. The flow of warm water towards the pole, and of polar water towards the equator, is as great—perhaps if measured according to volume, is greater in the southern hemisphere. But in the southern hemisphere the currents are broad and sluggish; in the northern, narrow, sharp, and strong. Then we have in the north other climatic contrasts for which we may search southern seas in vain. Hence, without further investigation, we may infer southern seas to be less boisterous than northern.
170. Storms in the North Atlantic and Pacific.—By a like reasoning we may judge the North Pacific to be less boisterous than the North Atlantic; for, though we have continental climates on either side of each, and a Gulf Stream in both, yet the Pacific is a very much wider sea, and its Gulf Stream is (§ 54) not so warm, nor so sharp, nor so rapid; therefore the broad Pacific does not, on the whole, present the elements of atmospherical disturbance in that compactness which is so striking in the narrow North Atlantic.
171. Storms along their western shores.—Nevertheless, though the North Pacific generally may not be so stormy as the North Atlantic, we have reason to believe that meteorological agents of nearly equal power are clustered along the western shores of each ocean. Though the Gulf Stream of the Pacific is not so hot, nor the cool littoral currents so cold, as those of our ocean are, yet they lave the shores of a broader continent, and hug them quite as closely as ours do. Moreover, the Japan Current, with its neighbouring seas, is some 500 miles nearer to the pole of maximum cold than the Gulf Stream of the Atlantic is. Great prominence in the brewing of storms is to be given to the latent heat which is set free in the air when vapour is condensed into rain. The North Pacific being broader than the North Atlantic, supplies its shores (§ 283) more abundantly with vapour than the North Atlantic does. This no doubt assists to make furious and more frequent the storms of the North Pacific.
172. Position of the poles of maximum cold, and their influence upon the meteorology of these two oceans.—Some philosophers hold that there are in the northern hemisphere two poles of maximum cold: the Asiatic, near the intersection of the parallel of 80° with the meridian of 120° E., and the American, near lat. 79° and long. 100° W. The Asiatic pole is the colder. The distance between it and the Japan Current is about 1500 miles; the distance between the other pole and the Gulf Stream is about 2000 miles. The bringing of the heat of summer, as these two streams do, in such close juxtaposition with the cold of winter, cannot fail to produce violent commotions in the atmosphere. These commotions, as indicated by the storms, are far more frequent and violent in winter, when the contrasts between the warm and cool places are greater, than they are in summer, when those contrasts are least. Moreover, each of those poles is to the north-west of its ocean, the quarter whence come the most terrific gales of winter. Whatever be the exact degree of influence which future research may show to be exercised by these cool places, and the heat dispensed so near them by these mighty streams of tepid water, there is reason to believe that they do act and react upon each other with no inconsiderable meteorological power. In winter the Gulf Stream carries the temperature of summer as far north as the Grand Banks of Newfoundland.
173. Climates of England and silver fogs of Newfoundland.—The habitual dampness of the climate of the British Islands, as well as the occasional dampness of that along the Atlantic coasts of the United States when easterly winds prevail, is attributable also to the Gulf Stream. These winds come to us loaded with vapours gathered from its warm and smoking waters. The Gulf Stream carries the temperature of summer, even in the dead of winter, as far north as the Grand Banks of Newfoundland, and there maintains it in the midst of the severest frosts. It is the presence of this warm water and a cold atmosphere in juxtaposition there which gives rise to the "silver fogs" of Newfoundland, one of the most beautiful phenomena to be seen anywhere among the treasures of the frost-king.
174. Influences upon storms.—The influence which the Gulf Stream exercises upon the storms of the North Atlantic, which take their rise within the tropics, is felt as far over even as the coast of Africa: it is also felt upon those which, though not intertropical in their origin, are known to visit the offings of the American coasts. These gales, in whatever part of the ocean east of the Gulf Stream they take their rise, march to the northwest until they join it, when they "recurvate," as the phrase is, and take up their line of march to the north-east along with it. Gales of wind have been traced from latitude 10°N. on the other side of the Atlantic to the Gulf Stream on this, and then with it back again to the other side, off the shores of Europe. By examining the log-books of ships, the tracks of storms have been traced out and followed for a week or ten days. Their path is marked by wreck and disaster. At a meeting of the American Association for the Advancement of Science, in 1854, Mr. Redfield mentioned one which he had traced out, and in which no less than seventy odd vessels had been wrecked, dismasted, or damaged.
175. More observations in and about the Gulf Stream a desideratum.—Now, what should attract these storms to the Gulf Stream, is a question which yet remains to be satisfactorily answered. A good series of simultaneous barometric observations within and on either side of the Gulf Stream is a great desideratum in the meteorology of the Atlantic. At the equator, where the trade-winds meet and ascend, where the air is loaded with moisture, and where the vapour from the warm waters below is condensed into the equatorial cloud-ring above, we have a low barometer.
176. Certain storms make for it and follow it.—How is it with the Gulf Stream when these storms from right and left burst in upon it, and, turning about, course along with it? Its waters are warm; they give off vapour rapidly; and, were this vapour visible to an observer in the moon, he no doubt would, on a winter's day especially, be able to trace out by the mist in the air the path of the Gulf Stream through the sea.
177. How aqueous vapour assists in producing winds.—Let us consider the effect of vapour upon winds, and then the importance of the observations proposed (§ 175) will perhaps be better appreciated. Aqueous vapour assists in at least five, perhaps six, ways to put air in motion and produce winds. (1.) By evaporation the air is cooled; by cooling its specific gravity is changed, and, consequently, here is one cause of movement in the air, as is manifest in the tendency of the cooled air to flow-off, and of warmer and lighter to take its place. (2.) Excepting hydrogen and ammonia, there is no gas so light as aqueous vapour, its weight being to common air in the proportion of nearly 5 to 8; consequently, as soon as it is formed it commences to rise; and, as each vesicle of vapour may be likened, in the movements which it produces in the air, to a balloon as it rises, it will be readily perceived how these vaporous particles, as they ascend, become entangled with those of the air, and so, carrying them along, upward currents are produced: thus the wind is called on to rush in below, that the supply for the upward movement may be kept up. (3.) The vapour, being lighter than air, presses it out, and, as it were, takes its place, causing the barometer to fall: thus again an in-rush of wind is called for below. (4.) Arrived in the cloud-region, this vapour, being condensed, liberates the latent heat which it borrowed from the air and water below; which heat, being now set free and made sensible, raises the temperature of the surrounding air, causing it to expand and ascend still higher; and so winds are again called for. Ever ready, they come; thus we have a fourth way. (5.) Innumerable rain-drops now begin to fall, and in their descent, as in a heavy shower, they displace and press the air out below with great force. To this cause Espy ascribes the gusts of wind which are often found to blow outward from the centre, as it were, of sudden and violent thunder-showers. (6.) Probably, and especially in thunder-storms, electricity may assist in creating movements in the atmosphere, and so make claim to be regarded as a wind-producing agent. But the winds are supposed to depend mainly on the power of agents (2), (3), and (4) for their violence.
178. A channel of rarefied air in the atmosphere and over the Gulf Stream.—These agents, singly and together, produce rarefaction, diminish pressure, and call for an inward rush of air from either side. Mr. Espy asserts, and quotes actual observation to sustain the assertion, that the storms of the United States, even those which arise in the Mississippi Valley, travel east, and often march out to sea, where they join the Gulf Stream in its course. That those which have their origin at sea, on the other side of the Gulf Stream, do (§ 174) often make right for it, is a fact well known to seamen. The Gulf Stream from Bimini to the Grand Banks is constantly sending up volumes of steam; this, being lighter than air, produces a channel way of rarefied air through the atmosphere, as it winds along the course of the stream. The latent heat of this vapour when it is set free produces a still greater rarefaction, so that we may imagine there is in the atmosphere a sort of cast of the Gulf Stream, in which the barometer often stands low, and into which, as into the equinoctial calm belt (§ 175), the wind often blows from both sides. In this fact is probably to be found an explanation of the phenomena alluded to above, viz.: that certain storms, both in the Atlantic and in the United States, invariably make for the Gulf Stream, and, reaching it, turn and follow it in its course sometimes entirely across the ocean. Hence, the interest that is attached to a proper series of observations on the meteorology of the Gulf Stream.
179. Storms of—dreaded by seamen.—Sailors dread its storms more than they do the storms in any other part of the ocean. It is not the fury of the storm alone that they dread, but it is the "ugly sea" which these storms raise. The current of the stream running in one direction, and the wind blowing in another, create a sea that is often frightful.
180. Routes formerly governed by the Gulf Stream.—The influence of the Stream upon commerce and navigation.—Formerly the Gulf Stream controlled commerce across the Atlantic by governing vessels in their routes through this ocean to a greater extent than it does now, and simply for the reason that ships are faster, nautical instruments better, and navigators are more skilful now than formerly they were.
181. Difficulties with early navigators.—Up to the close of the last century, the navigator guessed as much as he calculated the place of his ship; vessels from Europe to Boston frequently made New York, and thought the landfall by no means bad. Chronometers, now so accurate, were then an experiment. The Nautical Ephemeris itself was faulty, and gave tables which involved errors of thirty miles in the longitude. The instruments of navigation erred by degrees quite as much as they now do by minutes; for the rude "cross staff" and "back staff," the "sea-ring" and "mariner's bow," had not yet given place to the nicer sextant and circle of reflection of the present day. Instances are numerous of vessels navigating the Atlantic in those times being 6°, 8°, and even 10° of longitude out of their reckoning in as many days from port.
182. Finding longitude by the Gulf Stream.—Though navigators had been in the habit of crossing and recrossing the Gulf Stream almost daily for three centuries, it never occurred to them to make use of it as a means of giving them their longitude, and of warning them of their approach to the shores of this continent. Dr. Franklin was the first to suggest this use of it. The contrast afforded by the temperature of its waters and that of the sea between the Stream and the shores of America was striking. The dividing line between the warm and the cool waters was sharp (§ 70); and this dividing line, especially that on the western side of the stream, seldom changed its position as much in longitude as mariners often erred in their reckoning.
183. Folgers Chart.—When he was in London, in 1770, he happened to be consulted as to a memorial which the Board of Customs at Boston sent to the Lords of the Treasury, stating that the Falmouth Packets were generally a fortnight longer to Boston than common traders were from London to Providence, Rhode Island. They therefore asked that the Falmouth packets might be sent to Providence instead of to Boston. This appeared strange to the doctor, for London was much farther than Falmouth, and from Falmouth the routes were the same, and the difference should have been the other way. He, however, consulted Captain Folger, a Nantucket whaler, who chanced to be in London also; the old fisherman explained to the philosopher that the difference arose from the circumstance that the Rhode Island captains were acquainted with the Gulf Stream, while those of the English packets were not. The latter kept in it, and were set back sixty or seventy miles a day, while the former avoided it altogether. He had been made acquainted with it by the whales which were found on either side of it, but never in it (§ 158). At the request of the doctor, he there traced on a chart the course of this stream from the Straits of Florida. The doctor had it engraved at Tower Hill, and sent copies of it to the Falmouth captains, who paid no attention to it. The course of the Gulf Stream as laid down by that fisherman from his general recollection of it, has been retained and quoted on the charts for navigation, we may say, until the present day. But the investigations of which we are treating are beginning to throw more light upon this subject; they are giving us more correct knowledge in every respect with regard to it, and to many other new and striking features in the physical geography of the sea.
184. Using the Gulf Stream in winter.—No part of the world affords a more difficult or dangerous navigation than the approaches of the South American coast in winter. Before the warmth of the Gulf Stream was known, a voyage at this season from Europe to New England, New York, and even to the Capes of the Delaware or Chesapeake, was many times more trying, difficult, and dangerous than it now is. In making this part of the coast, vessels are frequently met by snow-storms and gales which mock the seaman's strength and set at naught his skill. In a little while his bark becomes a mass of ice; with her crew frosted and helpless, she remains obedient only to her helm, and is kept away for the Gulf Stream. After a few hours' run, she reaches its edge, and almost at the next bound passes from the midst of winter into a sea at summer heat. Now the ice disappears from her apparel: the sailor bathes his stiffened limbs in tepid waters; feeling himself invigorated and refreshed with the genial warmth about him, he realizes, out there at sea, the fable of Antaeus and his mother Earth. He rises up, and attempts to make his port again, and is again, perhaps, as rudely met and beat back from the north-west; but each time that he is driven off from the contest, he comes forth from this stream, like the ancient son of Neptune, stronger and stronger, until, after many days, his freshened strength prevails, and he at last triumphs, and enters his haven in safety, though in this contest he sometimes falls to rise no more, for it is terrible. Many ships annually founder in these gales; and I might name instances, for they are not uncommon, in which vessels bound to Norfolk or Baltimore, with their crews enervated in tropical climates, have encountered, as far down as the Capes of Virginia, snow-storms that have driven them back into the Gulf Stream time and again, and have kept them out for forty, fifty, and even for sixty days, trying to make an anchorage.
185. Running south to spend the winter.—Nevertheless, the presence of the warm waters of the Gulf Stream, with their summer heat in mid-winter, off the shores of New England, is a great boon to navigation. At this season of the year especially, the number of wrecks and the loss of life along the Atlantic sea-front are frightful. The month's average of wrecks has been as high as three a day. How many escape by seeking refuge from the cold in the warm waters of the Gulf Stream is matter of conjecture. Suffice it to say, that before their temperature was known, vessels thus distressed knew of no place of refuge short of the West Indies; and the newspapers of that day—Franklin's Pennsylvania Gazette among them—inform us that it was no uncommon occurrence for vessels bound for the Capes of the Delaware in winter to be blown off and to go the West Indies, and there wait for the return of spring before they would attempt another approach to this part of the coast.
186. Thermal navigation.—Accordingly, Dr. Franklin's discovery with regard to the Gulf Stream temperature was looked upon as one of great importance, not only on account of its affording to the frosted mariner in winter a convenient refuge from the snow-storm, but because of its serving the navigator with an excellent land-mark or beacon for our coast in all weathers. And so viewing it, the doctor, through political considerations, concealed his discovery for a while. The prize of 20,000l., which had been offered, and partly paid, by the British government, to Harrison, the chronometer maker, for improving the means of finding longitude at sea, was fresh in the minds of navigators. And here it was thought a solution of the grand problem—for longitude at sea was a grand problem—had been stumbled upon by chance; for, on approaching the coast, the current of warm water in the Gulf Stream, and of cold water on this side of it, if tried with the thermometer, would enable the mariner to judge with great certainty, and in the worst of weather, as to his position. Jonathan Williams afterwards, in speaking of the importance which the thermal use of these warm and cold currents would prove to navigation, pertinently asked the question, "If these stripes of water had been distinguished by the colours of red, white, and blue, could they be more distinctly discovered than they are by the constant use of the thermometer?" And he might have added, could they have marked the position of the ship more clearly?
187. Commodore Truxton.—When his work on Thermometrical Navigation appeared, Commodore Truxton wrote to him: "Your publication will be of use to navigation by rendering sea-voyages secure far beyond what even you yourself will immediately calculate, for I have proved the utility of the thermometer very often since we sailed together. It will be found a most valuable instrument in the hands of mariners, and particularly as to those who are unacquainted with astronomical observations; * * * * these particularly stand in need of a simple method of ascertaining their approach to or distance from the coast, especially in the winter season; for it is then that passages are often prolonged, and ships blown off the coast by hard westerly winds, and vessels get into the Gulf Stream without its being known; on which account they are often hove to by the captains supposing themselves near the coast when they are very far off (having been drifted by the currents). On the other hand, ships are often cast on the coast by sailing in the eddy of the Stream, which causes them to outrun their common reckoning. Every year produces new proofs of these facts, and of the calamities incident thereto."
188. The discovery of the high temperature of the Gulf Stream followed by a decline in Southern commerce.—Though Dr. Franklin's discovery was made in 1775, yet, for political reasons, it was not generally made known till 1790. Its immediate effect in navigation was to make the ports of the Northern States as accessible in winter as in summer. What agency this circumstance had in the decline of the direct trade of the south, which followed this discovery, would be, at least to the political economist, a subject for much curious and interesting speculation. I have referred to the commercial tables of the time, and have compared the trade of Charleston with that of the northern cities for several years, both before and after the discovery of Dr. Franklin became generally known to navigators. The comparison shows an immediate decline in the southern trade and a wonderful increase in that of the north. But whether this discovery in navigation and this revolution in trade stand in the relation of cause and effect, or be merely a coincidence, let others judge.
189. Statistics.—In 1769 the commerce of the two Carolinas equalled that of all the New England States together; it was more than double that of New York, and exceeded that of Pennsylvania by one-third.[3] In 1792, the exports from New York amounted in value to two millions and a half; from Pennsylvania, to $3,820,000; and from Charleston alone, to $3,834,000. But in 1795—by which time the Gulf Stream began to be as well understood by navigators as it now is, and the average passages from Europe to the north were shortened nearly one-half, while those to the south remained about the same—the customs at Philadelphia alone amounted to $2,941,000, [4] or more than one-half of those collected in all the states together.
190. The shortening of voyages.—Nor did the effect of the doctor's discovery end here. Before it was made, the Gulf Stream was altogether insidious in its effects. By it, vessels were often drifted many miles out of their course without knowing it; and in bad and cloudy weather, when many days would intervene from one observation to another, the set of the current, though really felt but for a few hours during the interval, could only be proportioned out equally among the whole number of days. Therefore navigators could have only very vague ideas either as to the strength or the actual limits of the Gulf Stream, until they were marked out to the Nantucket fishermen by the whales, or made known by Captain Folger to Dr. Franklin. The discovery, therefore, of its high temperature assured the navigator of the presence of a current of surprising velocity, and which, now turned to certain account, would hasten, as it had retarded, his voyage in a wonderful degree. Such, at the present day, is the degree of perfection to which nautical tables and instruments have been brought, that the navigator may now detect, and with great certainty, every current that thwarts his way. He makes great use of them. General Sabine, in his passage, some years ago, from Sierra Leone to New York, was drifted one thousand six hundred miles of his way by the force of currents alone; and, since the application of the thermometer to the Gulf Stream, the average passage from England has been reduced from upwards of eight weeks to a little more than four. Some political economists of America have ascribed the great decline of southern commerce which followed the adoption of the Constitution of the United States to the protection given by federal legislation to northern interests. But I think these statements and figures show that this decline was in no small degree owing to the Gulf Stream, the water-thermometer, and the improvements in navigation; for they changed the relations of Charleston—the great southern emporium of the times—removing it from its position as a half-way house, and placing it in the category of an outside station.
191. The scope of these researches.—The plan of our work takes us necessarily into the air, for the sea derives from the winds some of the most striking features in its physical geography; and from the air all of its meteorology. "Without a knowledge of the winds, we can neither understand the navigation of the ocean, nor make ourselves intelligently acquainted with the great highways across it. As with the land, so with the sea; some parts of it are as untravelled and as unknown as the great Amazonian wilderness of Brazil, or the inland basins of Central Africa. To the south of a line extending from Cape Horn to the Cape of Good Hope (Plate VIII.) is an immense waste of waters. None of the commercial thoroughfares of the ocean lead through it; only the adventurous whale-man finds his way there now and then in pursuit of his game; but for all the purposes of science and navigation, it is a vast unknown region. Now, were the prevailing winds of the South Atlantic northerly or southerly instead of easterly or westerly, this unploughed sea would be an oft-used thoroughfare. Nay, more, the sea supplies the wind with food for the rain which these busy messengers convey away from the ocean to "the springs in the valleys which run among the hills." To the philosopher, the places which supply the vapours are as suggestive and as interesting for the instruction they afford, as the places are upon which the vapours are showered down. Therefore, as he who studies the physical geography of the land is expected to make himself acquainted with the regions of precipitation, so he who looks into the physical geography of the sea should search for the regions of evaporation, and for those springs in the ocean which supply the reservoirs among the mountains with water to feed the rivers; and, in order to conduct this search properly, he must consult the winds, and make himself acquainted with their circuits. Hence, in a work on the Physical Geography of the Sea and its Meteorology, we treat also of the Atmosphere.
- ↑ American Journal of Science, vol. xiv., p. 293.
- ↑ Temperature of the Caribbean Sea (from the journals of Mr. Dunsterville): Surface temperature: 83°, September; 84°, July; 83°-86½°, Mosquito Coast. Temperature in depth: 48° ,240 fathoms; 43°, 386 fathoms; 42°, 450 fathoms; 43°, 450 fathoms.
- ↑
From McPherson's Annals of Commerce.—Exports and Imports in 1769, valued in Sterling Money.
EXPORTS. To Great Britain. South of Europe West Indies. Africa. Total. £ s. d. £ s. d. £ s. d. £ s. d. New England 142,775 12 9 81,173 16 2 308,427 9 6 17,713 0 9 550,089 19 2 New York 113,382 8 8 50,885 13 0 66,324 17 5 1,313 2 6 231,906 1 7 Pennsylvania 28,112 6 9 203,762 11 11 178,331 7 8 560 9 9 410,756 16 1 North and South Carolina 405,014 13 1 76,119 12 10 87,758 19 3 691 12 1 569,584 17 3 IMPORTS. New England 223,695 11 6 25,408 17 9 314,749 14 5 180 0 0 564,034 3 8 New York 75,930 19 7 14,927 7 0 897,420 4 0 697 10 0 188,976 1 3 Pennsylvania 204,979 17 4 14,249 8 4 180,591 12 4 ... 399,830 18 1 North and South Carolina 327,084 8 6 7,009 5 10 76,269 17 11 137,620 10 9 535,714 2 3 - ↑
Value of Exports in Dollars. [fn 1]
1791. 1792. 1793. 1794. 1795. 1796. Massachusettts 2,519,651 2,888,104 3,755,347 5,292,441 7,117,907 9,949,345 New York 2,505,465 2,535,790 2,932,370 5,442,000 10,304,000 12,208,027 Pennsylvania 3,436,000 3,820,000 6,958,000 6,643,000 11,518,000 17,513,866 South Carolina 2,693,000 2,428,000 3,191,000 3,868,000 5,908,009 7,620,000 Duties on Imports in Dollars.
1791. 1792. 1793. 1794. 1795. 1796. 1833. Massachusetts. 1,006,000 723,000 1,044,000 1,121,000 1,520,000 1,460,000 3,055,000 New York 1,334,000 1,173,000 1,204,000 1,878,000 2,028,000 2,187,000 10,713,000 Pennsylvania 1,466,000 1,100,000 1,823,000 1,498,000 2,300,000 2,050,000 2,207,000 South Carolina 523,000 359,000 360,000 661,000 722,000 66,000 389,000
- ↑ Doc. No. 330, H. R., 2nd Session. 25th Congress. Some of its statements do not agree with those taken from M'Pherson, and previously quoted.