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islands or continents, being again dissolved by the progress of the summer's heat, pours forth numerous rills and limpid streams, which collect along the indented shores, and in the deep bays enclosed by precipitous rocks. There, this clear and gelid was ter soon freezes, and every successive year supplies an additional investing crust, till, after the lapse perhaps of several centuries, the icy mass rises at last to the size and aspect of a mountain, commensurate with the elevation of the adjoining cliffs. The melting of the snow, which is afterwards deposited on such enormous blocks, likewise contributes to their growth; and, by filling up the accidental holes or crevices, it renders the whole structure compact and uniform. Meanwhile, the principle of destruction has already begun its operations. The ceaseless agitation of the sea gradually wears and undermines the base of the icy mountain, till, at length, by the action of its own accumulated weight, when it has perhaps attained an altitude of a thousand, or even two thousand feet, it is torn from its frozen chains, and precipitated, with tremendous plunge, into the abyss below. This mighty launch now floats like a lofty island on the ocean; till, driven southwards by winds and currents, it insensibly wastes and dissolves away in the wide Atlantic. .
Such, we conceive, to be the real origin of the icy-mountains or icebergs, entirely similar in their formation to the glaciers which occur on the flanks of the Alps and the Pyrennees. They consist of a clear, compact and solid ice, which has the fine green tint verging to blue, which ice or water, when very pure and of a sufficient depth, always assumes. From the cavities of these icebergs, the crews of the northern whalers are accustom, ed, by means of a hose, or flexible tube of canvas, to fill their casks easily with the finest and softest water. Of the same species of ice, the fragments which are picked up as they float on the surface of the ocean, yield the adventurous navigator the most refreshing beverage..
It was long disputed among the learned, whether the waters of the ocean are capable of being congealed; and many frivolous and absurd arguments, of course, were advanced to prove the impossibility of the fact. But the question is now completely resolved; and the freezing of sea water is established both by observation and experiment. The product, however, is an imperfect sort of ice, easily distinguishable from the result of a regular crystallization: It is porous, incompact, and imperfectly diaphanous. It consists of spicular shoots, or thin flakes, which detain within their interstices the stronger brine; and its granular spongy texture has, in fact, the appearance of congealed syrup, or what the confectioners call water-zee. This saline ice
can, therefore, never yield pure water; yet, if the strong brine, imprisoned in it, be first suffered to drain off slowly, the loose mass that remains will melt into a brackish liquid, which in some cases may be deemed potable.
To congeal sea-water of the ordinary saltness, or containing nearly the thirtieth part of its weight of saline matter, it requires not an extreme cold, this process taking effect about the 27th degree on Fahrenheit's scale, or only 5 degrees below the freezing point of fresh water. Within the Arctic circle, therefore, the surface of the ocean being never much warmer, is, in the decline of the summer, soon cooled down to the limit at which congelation commences. About the end of July, or the beginning of August, a sheet of ice in the space of a single night is formed, perhaps an inch thick. · The frost now maintains ascendency, and shoots its increasing energy in all directions, till it has covered the whole extent of those seas with a solid vault to the depth of several feet. But, on the return of spring, the penetrating rays of the sun gradually melt or soften that icy floor, and render its substance friable and easily disrupted. The first strong wind, creating a swell in the ocean, then breaks up the vast continent into large fields, which are afterwards shivered into fragments by their mutual collision. This generally happens early in the month of June; and a few weeks are commonly sufficient to disperse and dissolve the floating ice. The sea is at last open, for a short and dubious interval, to the pursuits of the adventurous mariner.
While icebergs are thus the slow growth of ages, the fields or shoals of saline ice are annually formed and destroyed. The ice generated from melted snow, is hard, pellucid, and often swells to enormous height and dimensions. But the concretion of salt-water wants solidity, clearness and strength, and never rises to any very considerable thickness. It seldom floats during more than part of the year; though, in some cold seasons, the scattered fragments may be surprised by the early frost, and preserved till the following summer. · The whale-fishers enumerate several varieties of the salt-water ice. A very wide expanse of it, they call a field, and one of smaller dimensions, a floe, When a field is dissevered by a subaqueous or grown swell, it breaks into numerous pieces, seldom exceeding forty or fifty yards in diameter, which, taken coli lectively, are termed a pack. This pack again, when of a broad shape, is called a patch; and, when much elongated, a stream. The packs of ice are crowded and heaped together by violent winds; but they again separate and spread asunder in calm weather. If a ship can sail freely through the floating pieces af
ice, it is called drift-ice; and the ice itself is said to be loose or open. When, from the effect of abrasion, the larger blocks of ice are crumbled into minute fragments, this collection is called brash-ice. A portion of ice rising above the common level, is termed a hummock, being produced by the 'squeezing of one piece over another. These hummocks or protuberances break the uniform surface of the ice, and give it a most diversified and fantastic appearance. They are numerous in the heavy packs, and along the edges of ice-fields, reaching to the height of thirty feet. The term sludge is applied by the sailors to the soft and incoherent crystals which the frost forms when it first attacks the ruffled surface of the ocean. As these increase, they have some effect, like oil, to still the secondary waves; but they are prevented from coalescing into a continuous sheet, by the agitation which still prevails; and they form small discs, rounded by coria tinual attrition, and scarcely three inches in diameter, called pancakes. Sometimes these again unite into circular pieces, perhaps a foot thick, and many yards in circumference.
The fields, and other collections of floating ice, are often discovered at a great distance, by that singular appearance on the verge of the horizon, which the Dutch seamen have termed ice-blink. It is a stratum of lucid whiteness, occasioned evidently by the glare of light reflected obliquely from the surface of the ice against the opposite atmosphere. This shining streak, which looks always brightest in clear weather, indicates, to the experienced navigator, 20 or 30 miles beyond the limit of direct vision, not only the extent and figure, but even the quality of the ice. The blink from packs of ice, appears of a pure white, while that which is occasioned by snow-fields has some tinge of yellow.
The mountains of hard and perfect ice, it has been shown, are the gradual production perhaps of many centuries. Along the western coast of Greenland, prolonged into Davis's Strait, they form an immensé rampart, which presents to the mariner a sublime spectacle, resembling, at a distance, whole groups of churches, mantling castles, or fleets under full sail. Every year, but especially in hot seasons, they are partially detached from their seats, and whelmed into the deep sea. In Davis's Strait, those icebergs appear the most frequent; and, about Disco Bay, where the soundings exceed 300 fathoms, masses of such enormous dimensions are met with, that the Dutch seamen compare them to cities, and often bestow on them the familiar names of Amsterdam or Haerlem. They are carried towards the Atlantic by the current, which generally flows from the northeast; and, after they reach the warmer water of the lower lati
VOL. XXX. No. 59,
tudes, they rapidly dissolve, and finally disappear, probably in the space of a few months.
The blocks of fresh-water ice appear black, as they swim in the sea; but show a fine emerald or beryl hue, when brought up on the deck. Though perfectly transparent, like crystal, they sometimes enclose threads, or streamlets, of air-bubbles, extricated in the act of congelation. This pure ice, being only a fifteenth part lighter than fresh water, must consequently project about one-tenth as it swims on the sea. An iceberg of 2000 feet in height would, therefore, after it floated, still rise 200 feet above the surface of the water. Such perhaps may be congidered as nearly the extreme dimensions. Those' mountains of ice may even acquire more elevation at a distance from land, both from the snow which falls on them, and from the copious vapours which precipitate and congeal on their surface. But, in general, they are carried forwards by the current which sets from the south-east into the Atlantic, where, bathed in a warmer fluid, they rapidly waste and dissolve. It may be shown, by experiment, that, if the water in which they float had only the temperature of 42°, the mass of ice would lose the thickness of an inch every hour, or two feet in a day. Supposing the surface of the sea to be at 52°, the daily dinrinution of thickness would be doubled, and would therefore amount to four feet. An iceberg, having 600 feet of total elevation, would hence, on this probable estimates require 150 days for its dissolution. But the melting of the ice would be greatly accelerated, if the mass were impelled through the water by the action of winds. A velocity of only a mile in an hour would triple the ordinary effect. Hence, though large bodies of ice are often found near the banks of Newfoundland, they seldom advance farther; or pass beyond the 48th degree of latitude. Within the Arctic regions, those stupendous blocks remain, by their mere inertia, so fixed on the water, as commonly to serve for the mooring of vessels employed in the whale fishery. In such cases, however, it is a necessary precaution, to lengthen out the cables, and ride at some distance from the frozen cliff; because the fragments of ice, which the seamen term calves, are frequently detached from the under part of the mass, and, darting upwards, acquire such a velocity in their ascent, that they would infallibly strike holes into the ship's bottom.
The ice produced from salt water is whitish, porous, and almost opaque. It is so dense, from the quantity of strong brine enclosed in its substance, that, when floating in the sea, it projects only one-fifth part above the surface. The porous saline ice how a variable thickness, yet seldom exceeding six feet But
sels employed inelas commonly tin, by their
we have already shown, that this saline ice which, during the greater part of the year, covers the Arctic Seas, is annually formed and destroyed; a small portion of it only, and at certain seasons, éscaping the general wreck. The thaw commonly lasts about three months; and, during that time, the heat of the solar rays, which, though oblique, yet act with unceasing energy, whether applied directly, or through the intervention of the air or the water, is adequate to the dissolution of all the ice produced in the course of the autumn, the winter, and the spring. It may be proved by experiment, that, under the Pole itself, the power of sun at the solstice could, in the space of a week, melt a stratum of five inches of ice. We may hence fairly compute the annual effect to be sufficient for thawing to the depth of forty inches. It should likewise be observed, that, owing to the prevailing haziness of the atmosphere in the northern latitudes, those singular cold emanations which are now found always to dart from an azure sky, and, in the more temperate climates, to diminish the calorific action of the sun often by one-fifth part, can scarcely exist. . On this account, perhaps the estimate of the annual destruction of Polar ice may be swelled to a thickness of four feet.
As heat is absorbed in the process of thawing, so it is again evolved in the act of congelation. The annual formation and destruction of ice within the Arctic Circle, is hence a beautiful provision of Nature, for mitigating the excessive inequality of temperature. Had only dry land been there opposed to the sun, it would have been absolutely scorched by his incessant beams in summer, and pinched in the darkness of winter by the most intense and penetrating cold. None of the animal or vegetable tribes could have at all supported such extremes. But, in the actual arrangement, the surplus heat of summer is spent in melting away the ice; and its deficiency in winter is partly supplied by the influence of the progress of congelation. As long as ice remains to thaw, or water to freeze, the temperature of the atmosphere can never vary beyond certain limits. Such is the harmony of the system; and all experience and observation forbid us to believe it to be subject to any radical change. Some years may chance to form more ice than others, or to melt more away; but it were idle to expect any thing like a general or permanent disruption of the glacial crust which binds the re-. gions of the North. But, even were this ice once removed, a similar collection would soon succeed, since it is always the effects and not the cause, of the disposition of the atmosphere, which it really serves to temper. We should be guilty of the