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 continual 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 immense 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 latiB

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 considered 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 diminution 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 estimate, 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 ee has a variable thickness, yet seldom exceeding six feet. But

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, escaping 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 regions of the North. But, even were this ice once removed, a similar collection would soon succeed, since it is always the effect, and not the cause, of the disposition of the atmosphere, which it really serves to temper. We should be guilty of the

most vicious reasoning in a circle, if we maintained that ice first cooled the air, and that this cold air next increased the fields of ice.

But, whatever may be the vicissitudes of the Polar ice, they cannot, in any sensible manner, affect the climates of the lower latitudes. The whole circumjacent space where frost holds its reign, bears a very small proportion to the surface of the northern hemisphere. Reckoning even from the parallel of 60 degrees, it would not exceed the eighth part; but, since the gelid region hardly extends below the latitude of 75 degrees, it may be stated at the thirty-second part of the hemisphere. On the supposition, therefore, that the Arctic cold were all transferred and infused into the atmosphere of the South, it could yet produce no visible alteration of climate.

Even if we imagined, with Mr Scoresby, that during the years 1816 and 1817, two thousand square leagues of ice have disappeared in the Greenland seas, between the parallels of 74 and 80 degrees, this extent would still scarcely exceed half the surface of Ireland. It may be calculated, that the loss of heat on our globe, occasioned by a total eclipse of the sun, reckoning this only equivalent to a complete obscuration for the space of a single hour, is as much as would be absorbed by the thawing of a circle of ice 500 miles in diameter, and 150 feet thick. This quantity surpasses at least sixty times the ice-fields dispersed from Greenland, allowing them the mean thickness of 30 feet; and yet the temperature of the air is never depressed more than a degree or two during the continuance of any solar eclipse.

But the idea is quite chimerical, that any winds could ever transport the Polar influence to our shores. It may be shown, from the results of accurate experiment, that a current of air flowing over a warmer surface, whether of land or water, becomes, in the space of an hour, penetrated with the same temperature through a stratum of 80 feet; though the limit of actual contact, or of mutual attrition, is confined to a surface not exceeding the 500dth part of an inch in thickness. If we assign to it the height of a mile, which is a most ample allowance, it would lose all its sharpness, and acquire the standard heat in the course of 66 hours. Admitting this wind to travel at the rate even of 20 miles each hour, it would consequently spend all its frigorific action in a tract of 1320 miles. The gales from the remotest north must thus discharge their store of cold into the German sea or the Atlantic ocean. Nor could such impressions, though continued through a course of ages, have the smallest power to chill the superficial water; for the moment any portion of this

was cooled, it would, from its increased density, sink down inte the vast abyss. The surface would not be affected till after the cooling had, in its progress, pervaded the whole mass from the bottom upwards. According to the calculations of Laplace, founded on a comparison of the theory of tides with actual observation, the mean depth of the ocean exceeds ten English miles. Supposing, therefore, a wind blowing from some northerly point, and ten degrees colder than the water, were to sweep over the Atlantic six months every year, at the rate of fifteen miles an hour, it would take 220 years to cool that vast body of water only a single degree.

Some persons have imagined, that the mountains or islands of ice which are occasionally drifted into the Atlantic ocean must be sufficient, by their frigorific influence, to modify the character of our climate. One of the first who advanced that opinion, was the ingenious Richard Bradley, Fellow of the Royal Society, and Professor of Botany in the University of Cambridge. In A Survey of the Ancient Husbandry and Gardening, collected from the Greek and Roman writers, printed in octavo at London in 1725, he introduces the following remarkable passage.

"I the rather mention the Case of Winds becoming Cold, by mixing with the Effluvia of Snow or Ice; because I have made some Remarks upon the tempestuous Weather, which often happens about the End of May, or in June, which has in all my Observations been brought in by Westerly Winds; and again, I as surely find, that at such Times, large Islands of Ice and Snow are passing to the Southward in the Western Ocean, as I have been inform'd by several Captains of Ships that were then coming from our Plantations to England: Some of these Islands are so large, as to measure 60 Miles in Length, and yielding so great a Vapour, that for a Day's Voyage on one side of them, the Weather has been so hazy, that the Mariners could not discover what they were, and this was accompany'd with so much Cold, that they imagin'd they had mistaken in their Accounts, and got several Degrees too far towards the North; but a Day or two explain'd the Matter, and gave them an Opportunity of surveying what they had been so much surpriz'd at. Now considering the extraordinary Heat of the Sun, at the Season these appear, the Vapour must be very considerable that rises from them, and 'tis no Wonder then, that as it expands itself, it presses the Air with Violence enough to cause Tempests, and carry Cold along with it."

But a little reflection will convince us, that such remote influence on our climate must be quite insignificant. At a very wide estimation, the surface of ice exposed to the winds could never exceed the thousandth part of the whole expanse of the