BOOKS.
THE GLACIERS OF THE ALPS.* FROM the beginning of the last century to the present time, gla- cier-motion has been one of the scientific puzzles which have en- gaged the attention of the learned. Philosophers have disputed, —we had almost said—quarrelled over their rival theories, and at this moment, some of the most eminent interpreters of nature are at variance as to the peculiar character of ice, by virtue of which, it is enabled to wind its course through the Alpine valleys with the action and regularity of a river. It is true that a certain professor of Tubingen, after a visit to the glaciers of Switzerland, went home and wrote a book flatly denying the possibility of their motion, but facts have been too strong for the generality of Alpine explorers, and with them, the cause, not the existence of the mo- tion, has been the subject of inquiry. Our latest information on all that relates to the glacier world is contributed by Professor Tyndall, the well-known and popular teacher of Natural Philoso- phy at the Royal Institution. In the Glaciers of the Alpe—a single octavo volume—the Professor gives us an account of four excursions made by him to the mountainous districts around Cha- mouni and Monte Rosa, and explains in clear and forcible lan- guage the various phenomena observed in the formation, move- ments, and final disappearance of the glaciers. The book is con- veniently divided into two parts, the first being " chiefly narra- tive," and relating the principal incidents of the excursions ; the second part is " chiefly scientific," but, in spite of this formidable heading, as some of our readers may perhaps think it, we do not expect it will be lightly passed over, for we have rarely seen pure science treated so simply, or put into a form so interesting to the .
reading public. In t e autumn of 1856, the author started in company with Professor Huxley for the scene of his future ex- plorations. This first expedition served as a sort of apprenticeship in familiarizing him with the general character of glaciers, and fitting him for the laborious and dangerous examinations he made in the three following years. The 12th of July, 1857, found him once more on the ice, with a clear sky overhead and Mont Blanc • invitingly near. The ascent, however, was not attempted until a month later, the interval being employed in making careful mea- surements of the speed of the glacier, and testing the various theories for explaining its motion. We must pass over the author's account of the ascent to Mont Blanc, which he accom- plished in company with a single guide. Professor Tyndall was now an accomplished iceman, and soon satisfied his companions that he could take care of himself. He thus speaks of their re- turn from the Finsteraarhorn :-
" Our descent was rapid, apparently reckless, amid loose spikes, boulders, and vertical prisms of rock, where a false step would assuredly have been attended with broken bones ; but the consciousness of certainty in our movements never forsook us, and proved a source of keen enjoyment. The senses were all awake, the eye clear, the heart strong, the limbs steady, yet flexible, with power of recovery in store, And ready for instant action should the footing give way. Such is the discipline which a perilous ascent imposes."
The ascent of Monte Rosa, 'although not requiring such phy- sical exertion as in the case of some other mountains, and, there- fore causing no shortness of breath, heart-beat, or headache, yet. demands a strong head, and a firm step to ensure the safety of the traveller. On the author's second ascent of this mountain, he went up alone, and the consciousness of being the first man who had ever stood in solitude on that lofty peak raised emotions that for his safety he found desirable to quiet :-
"Once indeed an accident made me shudder. While taking the cork from a bottle which is deposited on the top, and which contains the names of those who have ascended the mountain, my axe slipped out of my hand, and slid some thirty feet away from me. The thought of losing it made my flesh creep, for without it descent would be utterly impossible. I regained it, and looked upon it with an affection which might be bestowed upon a living thing, for it was literally my staff of life under the circum- stances."
Part of the pathway (if such it can be called) up and down this mountain led along a sloping roof of solid ice, terminating at its lower edge in a " cornice " of frozen snow overhanging the valley. At this critical place an accident happened to one of a party that ascended shortly before the Professor. He thus relates it :—
" I have stated that a portion of the Kamm was solid ice. On descending this, Mr. F.'s footing gave way, and he slipped forward. Lauener he guide) was forced to accompany him, for the place was too steep and slip- peg to permit of their motion being checked. Both were on the point of going over the Lyskamm side of the mountain, where they would have in- dubitably been dashed to pieces. There was no escape there,' said Lane- ner, in describing the incident to me subsequently, But I saw a possible rescue at the other side, so I sprang to the right, forcibly swinging my com- panion round ; but in doing so, the baton tripped me up ; we both fell, and rolled rapidly over each other down the incline. I knew that some preci- pices were in advance of us, over which we should have gone, so releasing myself from my companion, ,I threw myself in front of him, stopped myself with my axe, and thus placed a barrier before him"' The author may well close this account with an earnest exhor- tation to his readers to believe that " the dangers of Mont Blanc, Monte Rosa, and other mountains, are real, and if not properly provided against, may be terrible ; " and " if climbing without guides were to become habitual, deplorable consequences would assuredly sooner or later ensue." The regulations in forae at Chamouni for securing the safety of ordinary tourists were a source-of considerable annoyance to. the Professor, visiting the glaciers, as he did, almost entirely for scientific purposes ; and it was only after a special application to • The Glaciers of the Alps. By John Tyndall, F.B.B. Published by Murray. • the Intendant of the province, that he was enabled to roam over the mountains without being. encumbered with a host of guides. Thus scantily attended, occasionally enlivened by the companion- ship of some scientific friend, and sometimes solely dependent on his own good nerves and trusty axe, he ascended far beyond the range of human habitation, and visited the summits of several of the loftiest peaks in the great Alpine chain. We must now take a glance at the scientific portion of the work,—the most important, and by no means the least interest- ing part of the volume. In order to give his readers a clear in- sight into the working of some of the great natural agencies, the author commences by an inquiry into the nature of light and heat, explains the undulatory theory of light as now universally accepted, and shows how the brilliant coloured effects in cloud and sky are produced by diffraction and interference of the lumi- nous waves. Here, the Professor passes over well-trodden ground,—he is in his own domain, and, as many a tourist to the Royal Institution can testify, he is a safe and pleasant guide through the interesting region of Physics. Heat also receives considerable attention, and is defined as " a motion of the mole- cules or atoms of a body," but though the evidence in favour of this view is at present overwhelming, the author does not ask the reader to accept it as a certainty, if he feels sceptically disposed. He then turns to the question of glacier-motion, and glances at the various theories that have been proposed to account for it. A glacier, as we presume, is now pretty well known, begins in the accumulated snow of die mountain slopes, and is gradually forced downward in the direction of least resistance, until after con- tinued pressure it appears in the form of solid ice, and in this state,flows through the valleys until it reaches a temperature suf- ficiently high to melt it.: The motion of the glacier has long been known. As early as 1705, Seheuchzer suggested a theory for its explanation. "He supposed the motion to be caused by the conversion of water into ice within the glacier ; the known and almost irresistible expansion which takes place on freezing, furnishing the force which pushed the glacier downward." This was called the " dilatation theory," and was supported for a long time. but finally gave way. De Saussure believed the glacier slid over its bed, assisted by intervening currents of water. The truth appears to have been first brought to light by M. Rendu, Bishop of Annecy, whose essay on glaciers was published in 1841. Pressure was there stated to be the essential motive power, and the truth of M. Rendu's opinion has since been abundantly proved. But a great difficulty remained to be overcome. How could a solid mass of ice travel through a channel of varying breadth, and yet always occupy the entire space, winding round promontories and still retaining its continuity ? To explain this, Professor Forbes proposed his viscous theory," and, we believe, still adheres to it. The theory is thus given :—" A glacier is an imperfect fluid, or viscous body, which is urged down slopes of a certain inclination by the mutual pressure of its parts." Treacle, honey, and tar are mentioned as analogous bodies, such as, when subjected to tension, can be drawn out into filaments. This was a quality that was particularly investigated, or, we should rather say, looked for in the ice by Professor Tyndall during his recent excursions. It was found, however, that when a body of ice passed from a less to a greater incline, the mass was broken and fissured at the point where its inclination was changed. This should not
have happened if the ice had been of a viscous nature. But other observations were made also bearing on the subject. By planting rows of stakes across the glacier, Agassiz, many years ago, ascer- tained that its motion was greater in the centre than at the sides, the lateral friction retarding the ice at those points. There would consequently be a strain or drag of the ice from the sides towards the centre, and directed forward at an angle depending on the speed of the glacier. These lines of strain, then, would form a good test of the viscous nature of the ice.
Mr. Hopkins has proved what must be the result—fission of the ice across the line of strain. Such is found to be the case, and
the " marginal crevasses," as they are called, of a glacier, are exactly in the positions indicated by Mr. Hopkins—at right angles with the lines of greatest tension, and consequently running from the sides upwards towards the centre. These are awkward facts for the viscous theory to encounter.
Professor Tyndall passed much of his time whilst on the ice, in measuring the velocity of the glacier at different distances from the sides. By carrying on these measurements for some distance up and down the glacier, he ascertained a curious circumstance which was before unsuspected, and which strengthens the analogy between a glacier and a river. We will let the author tell us his thoughts when looking at a glacier winding through a sinuous
"•Talley :— Supposing a river, instead of a glacier, to sweep through this valley, its point of maximum motion would not always remain central, but would de- viate towards that aide of the valley to which the river turned its convex boundary. Indeed, the positions of towns along the banks of a navigable river, are mainly determined by this circumstance. They are, in most cases, situate on the convex sides of the bends, where the rush of water prevents silting up. Can it be, then, that the lee exhibits a similar deportment ? That the same principle which regulates the distribution of people along the banks of the Thames is also acting with silent energy amid the glaciers of the Alps ? If this be the case, the position of the point of maximum motion ought, of course, to shift with the bending of the glacier."
The conjecture was tested, and found to be true—the current of the great ice-river varied in its position, as in its course it wound through the valley, and foreshadowed in its action, the noble stream whose waters it would soon contribute to augment.
An interesting account of the plasticity of ice under severe and
gradual pressure, explains how any form may be produced by the regelation of the fractured particles, and thus the massive glacier is forced over the broken ground of the Alpine valleys—breaking into wide crevasses, again to unite, and moulding itself to the shape of its sinuous and rugged channel. The author paid his last visit to Chamouni in the winter of 1859, and saw that wild region under its dreariest aspect. The account of this visit is very interesting, and the results of the trip are of great scientific value. Professor Tyndall is not a man to be easily discouraged ; and we have shown by our extracts that he has been constantly in the habit of testing his own theories at the imminent risk of life and limb. The Professor's style is hardly a matter of criticism, as he is so well known as a lecturer, and he has already given us an example of what he can do with the pen in his excellent contribu- tions to the "Alpine Club" literature. Throughout the present volume, the author expresses himself with clearness and nrecision, and future travellers to Alpine regions will acknowledge the value of this last contribution to the history of the glacier world.
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