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The New Zealand Evangelist

The Glacier Theories

The Glacier Theories.

The following extract is made from one of a series of spirited papers, entitled “Wanderings Abroad,” that appeared some time ago in the Scottish Presbyterian:—

page 296

“There are many phenomena connected with the glaciers on which it might be instructive to dwell. Their transporting agency is astonishing. Geologists were long puzzled to explain how vast blocks of stone have been carried from the hills to which they belong. A block of mica lies on the Pentlands, while the Grampians afford the nearest rocks of the same formation from which it could have been detached. Granite of the Alps lies scattered on the surface of the Jurassic oolite. Speculations indescribably curious were once afloat in regard to the agencies that heaved them across the intervening distances. Fire was evoked in volcanic explosions from the depths of the earth to account for the mystery. Water was coaxed like another Samson to tell the secret of its strength, in order to explain the transportation of these stones, by a host of Delilahs in the shape of savans, fonder of prescribing what nature should do, than of observing what nature did. And yet, all the while among the Alps, every hour they might have witnessed in operation the very movements, the effects of which baffled their philosophy to explain. Stones of colossal size are hourly in motion, traversing great distances, and transported solely in their mystic journey by the agency of ice.

The ice moves the stone, but what moves the ice? The question conducts us at once to the great scientific problem of the day. Night and day, summer and winter, the glacier moves onward with a regularity scarcely affected by difference of temperature. That portion of its mass which once kissed the brow of Mount Blanc itself, winds its course amid the recesses of the valleys at its base, scooping into deeper hollows the grooves which the ice of preceding years had cut in the granite of its one bank and the lime of the other, tumbles over the slope where it first comes in sight of Chamouni, and descends till it rests on the soil of the valley, which it furrows like a ploughshare, and where the warmth of a milder region dissolves it into a river. Its page 297 motion is most distinctly ascertained: Professor Forbes could detect its advance in the brief space of an hour and a half. The glaciers differ in their rate of velocity: one has been shown to indicate a velocity in its centre of two hundred and sixty-nine feet in a year. The centre of a glacier moves fastest. The question recurs, what moves the ice?

Will gravitation serve to explain the mystery of its advance? Does it hasten downward by virtue of its own gravity, pressed by the incessant accumulation of ice and snow in its rear, and lubricated beneath by the water arising from the melting of the ice in immediate contact with the earth? But the glacier's rate of motion is greatest in the middle; it expands and contracts as the valley of its course widens or narrows, the average inclination of its bed is sometimes so low as three degrees only, while an inclination of thirty is required for the descent of a stone by its own weight. Many glaciers are frozen to the bottom, and indicate no water, by the help of which it is alleged they slide, and if these facts be duly pondered, the theory of Saussure, which accounts for their motion by the force of gravity alone, will be dissipated. The glacier still laughs our science to scorn, leaves us in a “fix” while it moves as much as ever, and poses us again with the riddle, What moves the ice?

“When the sun dips beyond the western horizon, and by its departure consigns the air to cold of a freezing temperature, a striking phenomenon occurs. —The rivulets that have flowed by the melting of the ice during the day, and by their lively echoes broken the silence of these bleak and wildered scenes, are arrested instantaneously in their course by an interdict which brooks no disobedience. The Mer de Glace is no Strathbogie. Frost asserts its sway. Congelation proceeds rapidly in the water lurking in the crevices of the glacier. Water expands when frozen, and the glacier, it is inferred, must expand too from the water so frozen in its thousand crevices,—To expand is to move. Such is page 298 the dilatation theory of Charpentier and Agassiz. This theory relied mainly for support on the fact, that the glacier moved fastest at the sides, where the fissures were most numerous, and when consequently the expansion would be greatest. But the glacier, by subsequent observations, has been proved to advance with the greatest volocity in the centre, and its motion is but little affected by the alterations of night and day or the vicissitudes of the seasons. Had it moved by dilatation, it should have advanced obviously with the greatest rapidity at night in summer, when the instantaneous congelation, which is assumed as the basis of the theory, takes place. The problem is as yet unsolved—the question is still without an answer, What moves the ice?

We are not tasking the credulity of our readers, when at length we announce what is declared to be the true answer. The ice moves itself! Should they wish the answer in a scientific form, we quote for their consideration the words of Professor Forbes, to whose researches we are indebted for it:— “A glacier is an imperfect fluid, or a viscous body, which is urged down slopes of a certain inclination by the mutual pressure of its parts.” What, ice a fluid! The solid, which the steel of our skates could hardly penetrate; which has groaned sonorously under the rumble of the Scottish bonspiel; which has bridged boisterous floods for the passage of armies, only a fluid! A discovery with a witness! A goodly quarto, crowded with facts, bristling with scientific demonstrations, beautified with maps, and hailed with acclamations by the scientific world, has been published by professor Forbes, in elucidation and support of this theory. The same laws are proved to be applicable to the glacier as to fluids. As a river is checked in its flow towards its sides, by the friction of its banks, so the glacier moves with least velocity at its sides and bottom. As a river adjusts itself to the inequalities of its channel, narrowing where it narrows, and widening where it widens, so the glaciers can escape from some gorge in the valley page 299 of its course, by a reduction of its size in proportion to the diminution of its channel. As viscosity dissolves under heat, and as a viscous flood quickens its motion under increase of temperature, so a glacier moves, on the whole, faster in summer, and in proportion to its inclination. The internal structure of the ice, too, yields still stronger evidence in favour of this theory. But we cannot dwell on these matters. We are describing a tour—not discoursing on philosophy, and to soothe our readers if wearied with the dynamics of this question, we close the discussion with an extract from the work of Mr. Forbes. The Professor's fancy gives fertility to a glacier—cultivates and calls the flowers of genuine poetry on a soil which opens to no other seedling. It were well if every flower yielded fruit so precious as the moral, couched in language, with one exception, so felicitious as that which follows:—

“Poets and philosophers have delighted to compare the course of human life to that of a river: perhaps a still apter simile may be found in the history of a glacier. Heaven-descended in its origin, it yet takes its mould from the hidden womb of the mountain which brought it forth. At first soft and ductile, it acquires a character and firmness of its own, as an inevitable destiny urges it on its onward career. Jostled and constrained by the inequalities of its prescribed path, hedged in by impassable carriers, which fix limits to its movements, it yields groaning to its fate, and still travels forward, scarred with the scars of many a conflict with opposing obstacles. All this while, although wasting, it is renewed by an unseen power—it evaporates, but is not consumed. On the surface it bears the spoils which during the progress of its existence it has made its own; often weighty burdens devoid of beauty or value—at times precious masses, sparkling with gems or with ice. Having at length attained its greatest width and extension, commanding admiration by its beauty and power, waste predominates over supply: the vital springs begin to fail: it stoops into an attitude of decrepitude; it drops the burdens one by one which it had borne so prondly aloft—its dissolution is inevitable. But as it is lesolved into its elements, it takes all at once a new, and livelier, and disembarrassed form; the wreck of its members it arises ‘another yet the same'—a noble, full-bodied, arrowy stream, which leaps rejoicing over the obstacles which before had stayed its progress, and hastens through fertile valleys, towards a fuller existence, and a final union with the boundless and the infinite.