The smaller ice that almost fills the straits and bays, and cot crs many leagues up the ocean along the coast, is from four to ten fathoms thick, and chills the air to that degree, that there is a constant increase to the isle s by the sea's trashing against them, and the perpetual wet fogs, like small rain, freezing as they settle upon the ice ; and their being so deeply immersed under 'water, and such a small portion above, prevents the winds having much power to move them : for though z: blows from the north-west quarter near nine months in twelve, and consequently those isles are driven towards a warmer climate, yet the progressive motion is so slow, that it must take up many years before they can get 500 or 600 leagues to the southward ; I am of opinion some hundreds of years arc required; for they cannot, I think, dissolve before they come between the 50th and 40th degree of latitude, where the heat of the suming the upper parts, they lighten an ,vaste in time yet there is a perpetual supply 1.--oin the northern parts, which will so continue a3 tong as it pleases the Author of all beings to keep things in their present state." A new and ingenious theory of the formation of these huge masses of ie, has been recently given by Professor Leslie. A. Erns explanation is founded on the result of a ,..urious experiment, we shall make no apology for giving a full account of it in Mr Leslie's own words.
" When very feeble powers of refrigeration are em ployed, a most singular and beautiful appearance is in ourse of time slowly produced. If a pan of porous earthen-ware, from four to six inches wide, be filled to the utmost with common water till it rise above the lips, and now planted above a dish of ten or twelve inches di ameter, containing a body of sulphuric acid, and having a round broad receiver passed over it; on reducing the included air to some limit between the twentieth and the fifth part of its usual density, according to the coldness of the apartment, the liquid mass wilhin the space of an i hour or two, become entwined with icy shoots, which gradually enlarge and acquire more solidity, but always leave the fabric loose and unfrozen below. The icy crust which covers the rim, now receiving continual ac cessions from beneath, rises perpendicularly by insensible degrees. From each point on the rough surface of the vessel, filaments of ice, like bundles of spun-glass, are protruded, fed by the humidity conveyed through its substance, and forming, in their aggregation, a fine sil very surface, analogous to that of fibrous gypsum or sa tin-spar. At the same time, another similar growth, though of less extent, takes place on the under side of the pan, so that continuous icy threads might appear ver tically to transpierce the ware. The whole of the bot tom becomes likewise covered over with elegant icy fo liations. Twenty or thirty hours may be required to produce those singular effects; but the upper body of ice continues to rise for the space of several days, till it forms a circular wall of near three inches in height, leaving an interior grotto lined with fantastic groupcs of icicles. In the meanwhile, the exfoliations have dis appeared from the under side, and the outer incrustation is reduced, by the absorbing process, to a narrow ring. The icy wall now suffers a regular waste from external erosion, and its fibrous structure becomes rounded and less apparent. Of its altitude, however, it loses but little for sonic time ; and even a decomposition of congealed films along its coping or upper edge, seems to take place at a certain stage of the process. This curious effect is
owing to a circumstance, which, as it serves to explain some of the grand productions of nature, merits particu lar attention. The circular margin of the ice, being near er the action of the sulphuric acid than its inner cavi ty, must suffer, by direct evaporation, a greater loss of heat ; and consequently each portion of thin air that rises from the low cavity, being chilled in passing over the colder ledge, must deposit a minute corresponding share of its moisture, which instantly attaches itself and incrusts the ring. Whatever inequalities existed at first in the surface of the ice, will hence continually crease.
This explication seems to throw some light on the ori gin of those ast bodies of ice which occur within the Arc tic Circle, and which, towering like clustered peaks above the surface of the ocean, have received the name of icebergs. They frequently project above an hundred feet, and must therefore have ten times as much depth concealed under water. To suppose them to have been detached from a solid field of such tremendous thickness, would seem utterly improbable. It may indeed be doubt ed, whether any pact of the ocean be ever naturally fro• zen. The ice which I have formed from salt water by the frigorific process, was always incompaet, inclosing brine within its interstices, and resembling the aspect of what is called water-ice, or dilute syrup congealed. Per haps an extremely slow congelation, descending regular ly from the surface, may press down the saline particles, which are never absolutely detached from the water, and thus force them to combine more largely with the mass below. But even admitting this idea, it would be still required to account for the great elevation of those icy cliffs. The most satisfactory mode, probably, of ex plaining the phenomenon, is to refer it to the operation of a general principle, by which the inequalities on the surface of a field of ice must be constantly increased. The lower parts of the field, being nearer the tempered mass of the ocean, are not so cold as those which pro ject into the atmosphere, and consequently the air which ascends, becoming chilled in sweeping over the eminences, there deposits some of its moisture, forming an icy coat. But this continued incrustation, in the lapse of ages, produces a vast accumulation, till the shapeless mass is at length precipitated by its own weight.
Other natural phenomena will receive illustration from the facts disclosed by the refrigerating process. In the rigorous climes of the north, the alternations of the seasons are most rapid. On the approach of spring, the thick fields of lee which, in Russia or Canada, cover the Neva or the St Lawrence,break up with overwhelm ing fury, accompanied too by tremendous explosions. Nor is this noise to be ascribed to the mere crash of tho falling fragments. In those frightful climates, the win ter at once sets in with most intense frost, which proba bly envelops the globules of air separated from the wa ter in the act of congelation, and, invading them on all sides, reduces them to a state of high condensation. When the mild weather begins, therefore, to prevail, the body of ice, penetrated by the warmth, becomes soft and friable ; and the minute but numerously interspersed globules of imprisoned air, exerting together their con centrated elasticity, produce the most violent explosive disruptions." Sec :Mr Leslie's Short Account of Experiments and Instrument., depending on the relation of Air to Ilcat and Moisture, p. Edinburgh, 1813. (A)