The Glaciers of the Alps / Being a narrative of excursions and ascents, an account of the origin and phenomena of glaciers and an exposition of the physical principles to which they are related

by John Tyndall

FOOTNOTES:

[A] In 1858 Mr. E. W. Cooke made a pencil-sketch of this splendid panorama, which is the best and truest that I have yet seen.

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THE GÖRNER GRAT AND THE RIFFELHORN. MAGNETIC PHENOMENA.
(20.)

At an early hour on Saturday, the 14th of August, I heard the servant exclaim, "Das Wetter ist wunderschön!" which good news caused me to spring from my bed and prepare to meet the morn. The range of summits at the opposite side of the valley of St. Nicholas was at first quite clear, but as the sun ascended light cumuli formed round them, increasing in density up to a certain point; below these clouds the air of the valley was transparent; above them the air of heaven was still more so; and thus they swung midway between heaven and earth, ranging themselves in a level line along the necks of the mountains.

GENERATION OF CLOUDS. 1858.

It might be supposed that the presence of the sun heating the air would tend to keep it more transparent, by increasing its capacity to dissolve all visible cloud; and this indeed is the true action of the sun. But it is not the only action. His rays, as he climbed the eastern heaven, shot more and more deeply into the valley of St. Nicholas, the moisture of which rose as invisible vapour, remaining unseen as long as the air possessed sufficient warmth to keep it in the vaporous state. High up, however, the cold crags which had lost their heat by radiation the night before, acted like condensers upon the ascending vapour, and caused it to curdle into visible fog. The current, however, continued ascensional, and the clouds were slowly lifted above the tallest peaks, where they arranged themselves in fantastic forms, shifting and changing shape as they gradually melted away. One peak stood like a field-officer with his cap raised above his head, others sent straggling cloud-balloons upwards; but on watching these outliers they were gradually seen to disappear. At first they shone like snow in the sunlight, but as they became more attenuated they changed colour, passing through a dull red to a dusky purple hue, until finally they left no trace of their existence.

THE ROCKS WARMED. 1858.

SCENE FROM THE GÖRNER GRAT. 1858.

As the day advanced, warming the rocks, the clouds wholly disappeared, and a hyaline air formed the setting of both glaciers and mountains. I climbed to the Görner Grat to obtain a general view of the surrounding scene. Looking towards the origin of the Görner glacier the view was bounded by a wide col, upon which stood two lovely rounded eminences enamelled with snow of perfect purity. They shone like burnished silver in the sunlight, as if their surfaces had been melted and recongealed to frosted mirrors from which the rays were flung. To the right of these were the bounding crags of Monte Rosa, and then the body of the mountain itself, with its crest of crag and coat of snows. To the right of Monte Rosa, and almost rivalling it in height, was the vast mass of the Lyskamm, a rough and craggy mountain, to whose ledges clings the snow which cannot grasp its steeper walls, sometimes leaning over them in impending precipices, which often break, and send wild avalanches into the space below. Between the Lyskamm and Monte Rosa lies a large wide valley into which both mountains pour their snows, forming there the Western glacier of Monte Rosa[A]—a noble ice stream, which from its magnitude and permanence deserves to impose its name upon the trunk glacier. It extends downwards from the col which unites the two mountains; riven and broken at some places, but at others stretching white and pure down to its snow-line, where the true glacier emerges from the névé. From the rounded shoulders of the Twin Castor a glacier descends, at first white and shining, then suddenly broken into faults, fissures, and precipices, which are afterwards repaired, and the glacier joins that of Monte Rosa before the junction of the latter with the trunk stream. Next came a boss of rock, with a secondary glacier clinging to it as if plastered over it, and after it the Schwarze glacier, bounded on one side by the Breithorn, and on the other by the Twin Pollux. This glacier is of considerable magnitude. Over its upper portion rise the Twin eminences, pure and white; then follows a smooth and undulating space, after passing which the névé is torn up into a collection of peaks and chasms; these, however, are mended lower down, and the glacier moves smoothly and calmly to meet its brothers in the main valley. Next comes the Trifti glacier,[B] embraced on all sides by the rocky arms of the Breithorn; its mass is not very great, but it descends in a graceful sweep, and exhibits towards its extremity a succession of beautiful bands. Afterwards we have the glacier of the Petit Mont Cervin and those of St. Théodule, which latter are the last that empty their frozen cargoes into the valley of the Görner. All the glaciers here mentioned are welded together to a common trunk which squeezes itself through the narrow defile at the base of the Riffelhorn. Soon afterwards the moraines become confused, the glacier drops steeply to its termination, and ploughs up the meadows in front of it with its irresistible share.

In a line with the Riffelhorn, and rising over the latter so high as to make it almost vanish by comparison, was the Titan obelisk of the Matterhorn, from the base of which the Furgge glacier struggles downwards. On the other side are the Zmutt glacier, the Schönbühl, and the Hochwang, from the Dent Blanche; the Gabelhorn and Trift glaciers, from the summits which bear those names. Then come the glaciers of the Weisshorn. Describing a curve still farther to the right we alight on the peaks of the Mischabel, dark and craggy precipices from this side, though from the Æggischhorn they appear as cones of snow. Sweeping by the Alphubel, the Allaleinhorn, the Rympfischorn, and Strahlhorn—all of them majestic—we reach the pass of the Weissthor, and the Cima di Jazzi. This completes the glorious circuit within the observer's view.

COMPASS AT FAULT. 1858.

I placed my compass upon a piece of rock to find the bearing of the Görner glacier, and was startled at seeing the sun and it at direct variance. What the sun declared to be north, the needle affirmed to be south. I at first supposed that the maker had placed the S where the N ought to be, and vice versâ. On shifting my position, however, the needle shifted also, and I saw immediately that the effect was due to the rock of the Grat. Sometimes one end of the needle dipped forcibly, at other places it whirled suddenly round, indicating an entire change of polarity. The rock was evidently to be regarded as an assemblage of magnets, or as a single magnet full of "consequent points." A distance of transport not exceeding an inch was, in some cases, sufficient to reverse the position of the needle. I held the needle between the two sides of a long fissure a foot wide. The needle set along the fissure at some places, while at others it set across it. Sometimes a little jutting knob would attract the north end of the needle, while a closely adjacent little knob would forcibly repel it, and attract the south end. One extremity of a ledge three feet long was north magnetic, the other end was south magnetic, while a neutral point existed midway between the two, the ledge having therefore the exact polar arrangement of an ordinary bar-magnet. At the highest point of the rock the action appeared to be most intense, but I also found an energetic polarity in a mass at some distance below the summit.

MAGNETISM OF ROCKS. 1858.

Remembering that Professor Forbes had noticed some peculiar magnetic effect upon the Riffelhorn, I resolved to ascend it. Descending from the Grat we mounted the rocks which form the base of the horn; these are soft and soapy from the quantity of mica which they contain; the higher rocks of the horn are, however, very dense and hard. The ascent is a pleasant bit of mountain practice. We climbed the walls of rock, and wound round the ledges, seeking the assailable points. I tried the magnetic condition of the rocks as we ascended, and found it in general feeble. In other respects the Riffelhorn is a most remarkable mass. The ice of the Görner glacier of former ages, which rose hundreds, perhaps thousands of feet above its present level, encountered the horn in its descent, and was split by the latter, a diversion of the ice along the sides of the peak being the consequence. Portions of the vertical walls of the horn are polished by this action as if they had come from the hands of a lapidary, and the scratchings are as sharp and definite as if drawn by points of steel. I never saw scratchings so perfectly preserved: the finest lines are as clear as the deepest, a consequence of the great density and durability of the rock. The latter evidently contains a good deal of iron, and its surface near the summit is of the rich brown red due to the peroxide of the metal. When we fairly got among the precipices we left our hatchets behind us, trusting subsequently to our hands and feet alone. Squeezing, creeping, clinging, and climbing, in due time we found ourselves upon the summit of the horn.

ASCENT OF THE RIFFELHORN. 1858.

A pile of stones had been erected near the point where we gained the top. I examined the stones of this pile, and found them strongly polar. The surrounding rocks also showed a violent action, the needle oscillating quickly, and sometimes twirling swiftly round upon a slight change of position. The fragments of rock scattered about were also polar. Long ledges showed north magnetism for a considerable length, and again for an equal length south magnetism. Two parallel masses separated from each other by a fissure, showed the same magnetic distribution. While I was engaged at one end of the horn, Lauener wandered to the other, on which stood two or three hommes de pierres. He was about disturbing some of the stones, when a yell from me surprised him. In fact, the thought had occurred to me that the magnetism of the horn had been developed by lightning striking upon it, and my desire was to examine those points which were most exposed to the discharge of the atmospheric electricity; hence my shout to my guide to let the stones alone. I worked towards the other end of the horn, examining the rocks in my way. Two weathered prominences, which seemed very likely recipients of the lightning, acted violently upon the needle. I sometimes descended a little way, and found that among the rocks below the summit the action was greatly enfeebled. On reaching another very prominent point, I found its extremity all north polar, but at a little distance was a cluster of consequent points, among which the transport of a few inches was sufficient to turn the needle round and round.

MAGNETISM OF THE HORN. 1858.

The piles of stone at the Zermatt end of the horn did not seem so strongly polar as the pile at the other end, which was higher; still a strong polar action was manifested at many points of the surrounding rocks. Having completed the examination of the summit, I descended the horn, and examined its magnetic condition as I went along. It seemed to me that the jutting prominences always exhibited the strongest action. I do not indeed remember any case in which a strong action did not exhibit itself at the ends of the terraces which constitute the horn. In all cases, however, the rock acted as a number of magnets huddled confusedly together, and not as if its entire mass was endowed with magnetism of one kind.

On the evening of the same day I examined the lower spur of the Riffelhorn. Amid its fissures and gullies one feels as if wandering through the ruins of a vast castle or fortification; the precipices are so like walls, and the scratching and polishing so like what might be done by the hands of man. I found evidences of strong polar action in some of the rocks low down. In the same continuous mass the action would sometimes exhibit itself over an area of small extent, while the remainder of the rock showed no appreciable action. Some of the boulders cast down from the summit exhibited a strong and varied polarity. [Fig. 8] is a sketch of one of these; the barbed end of each arrow represents the north end of the needle, which assumed the various positions shown in the figure. Midway down the spur I lighted upon a transverse wall of rock, which formed in earlier ages the boundary of a lateral outlet of the Görner glacier. It was red and hard, weathered rough at some places, and polished smooth at others. The lines were drawn finely upon it, but its outer surface appeared to be peeling off like a crust; the polished layer rested upon the rock like a kind of enamel. The action of the glacier appeared to resemble that of the break of a locomotive upon rails, both being cases of exfoliation brought about by pressure and friction. This wall measured twenty-eight yards across, and one end of it, for a distance of ten or twelve yards, was all north polar; the other end for a similar distance was south polar, but there was a pair of consequent points at its centre.

THE MAGNETIC FORCE. 1868.

To meet the case of my young readers, I will here say a few words about the magnetic force. The common magnetic needle points nearly north and south; and if a bit of iron be brought near to either end of the needle, they will mutually attract each other. A piece of lead will not show this effect, nor will copper, gold, nor silver. Iron, in fact, is a magnetic metal, which the others are not. It is to be particularly observed, that the bit of iron attracts both ends of the needle when it is presented to them in succession; and if a common steel sewing needle be substituted for the iron it will be seen that it also has the power of attracting both ends of the magnetic needle. But if the needle be rubbed once or twice along one end of a magnet, it will be found that one of its ends will afterwards repel a certain end of the magnetic needle and attract the other. By rubbing the needle on the magnet, we thus develop both attraction and repulsion, and this double action of the magnetic force is called its polarity; thus the steel which was at first simply magnetic, is now magnetic and polar.

It is the aim of persons making magnets, that each magnet should have but two poles, at its two ends; it is, however, easy to develop in the same piece of steel several pairs or poles; and if the magnetization be irregular, this is sometimes done when we wish to avoid it. These irregular poles are called consequent points.

Now I want my young reader to understand that it is not only because the rocks of the Görner Grat and Riffelhorn contain iron, that they exhibit the action which I have described. They are not only magnetic, as common iron is, but, like the magnetized steel needle, they are magnetic and polar. And these poles are irregularly distributed like the "consequent points" to which I have referred, and this is the reason why I have used the term.

BEARINGS FROM THE RIFFELHORN. 1858.

Professor Forbes, as I have already stated, was the first to notice the effect of the Riffelhorn upon the magnetic needle, but he seems to have supposed that the entire mass of the mountain exercised "a local attraction" upon the needle; (upon which end he does not say). To enable future observers to allow for this attraction, he took the bearing of several of the surrounding mountains from the Riffelhorn; but it is very probable that had he changed his position a few inches, and perfectly certain had he changed it a few yards, he would have found a set of bearings totally different from those which he has recorded. The close proximity and irregular distribution of its consequent points would prevent the Riffelhorn from exerting any appreciable influence on a distant needle, as in this case the local poles would effectually neutralize each other.