Part 20

320. "Had not Providence interfered on this occasion in a manner which may well be considered as miraculous, all the fresh water within the polar circle must inevitably have been frozen to a very great depth in winter, and every plant and tree destroyed."

321. Through many pages of his book Count Rumford continues in this strain to expound the ways and intentions of the Almighty, and he does not hesitate to apply very harsh words to those who cannot share his notions. He calls them hardened and degraded. We are here warned of the fact, which is too often forgotten, that the pleasure or comfort of a belief, or the warmth or exaltation of feeling which it produces, is no guarantee of its truth. For the whole of Count Rumford's delight and enthusiasm in connexion with this subject, and the whole of his ire against those who did not share his opinions, were founded upon an erroneous notion.

322. Water is not a solitary exception to an otherwise general law. There are other molecules than those of this liquid which require more room in the solid crystalline condition than in the adjacent molten condition. Iron is a case in point. Solid iron floats upon molten iron exactly as ice floats upon water. Bismuth is a still more impressive case, and we could shiver a bomb as certainly by the solidification of bismuth as by that of water. There is no fish, to be taken care of here, still the "contrivance" is the same.

323. I am reluctant to mention them in the same breath with Count Rumford, but I am told that in our own day there are people who profess to find the comforts of a religion in a superstition lower than any that has hitherto degraded the civilized human mind. So that the happiness of a faith and the truth of a faith are two totally different things.

324. Life and the conditions of life are in necessary harmony. This is a truism, for without the suitable conditions life could not exist. But both life and its conditions set forth the operations of inscrutable Power. We know not its origin; we know not its end. And the presumption, if not the degradation, rests with those who place upon the throne of the universe a magnified image of themselves, and make its doings a mere colossal imitation of their own.

§ 47. The Molecular Mechanism of Water-Congelation.

325. But let us return to our science. How are we to picture this act of expansion on the part of freezing water? By what operation do the molecules demand with such irresistible emphasis more room in the solid than in the adjacent liquid condition? In all cases of this kind we must derive our conceptions from the world of the senses, and transfer them afterwards to a world transcending the range of the senses.

326. You have not forgotten our conversation regarding "atomic poles" (§ 10), and how the notion of polar force came to be applied to crystals. With this fresh in your memory, you will have no great difficulty in understanding how expansion of volume may accompany the act of crystallisation.

327. I place a number of magnets before you. They, as matter, are affected by gravity, and, if perfectly free, they would move towards each other in obedience to the attraction of gravity.

328. But they are not only matter, but magnetic matter. They not only act upon each other by the simple force of gravity, but by the polar force of magnetism. Imagine them placed at a distance from each other, and perfectly free to move. Gravity first makes itself felt and draws them together. For a time the magnetic force issuing from the poles is insensible; but when a certain nearness is attained, the polar force comes into play. The mutually attracting points close up, the mutually repellent points retreat, and it is easy to see that this action may produce an arrangement of the magnets which requires more room. Suppose them surrounded by a box which exactly encloses them at the moment the polar force first comes into play. It is easy to see that in arranging themselves subsequently the repelled corners and ends of the magnets may be caused to press against the sides of the box, and even to burst it, if the forces be sufficiently strong.

329. Here then we have a conception which may be applied to the molecules of water. They, like the magnets, are acted upon by two distinct forces. For a time while the liquid is being cooled they approach each other, in obedience to their general attraction for each other. But at a certain point new forces, some attractive, some repulsive, emanating from special points of the molecules, come into play. The attracted points close up, the repelled points retreat. Thus the molecules turn and rearrange themselves, demanding, as they do so, more space, and overcoming all ordinary resistance by the energy of their demand. This, in general terms, is an explanation of the expansion of water in solidifying: it would be easy to construct an apparatus for its illustration.

§ 48. The Dirt Bands of the Mer de Glace.

330. Pass from bright sunshine into a moderately lighted room; for a time all appears so dark that the objects in the room are not to be clearly distinguished. Hit violently by the waves of light (§ 3) the optic nerve is numbed, and requires time to recover its sensitiveness.

331. It is for this reason that I choose the present hour for a special observation on the Mer de Glace. The sun has sunk behind the ridge of Charmoz, and the surface of the glacier is in sober shade. The main portion of our day's work is finished, but we have still sufficient energy to climb the slopes adjacent to the Montanvert to a height of a thousand feet or thereabouts above the ice.

332. We now look fairly down upon the glacier, and see it less foreshortened than from the Montanvert. We notice the diet overspreading its eastern side, due to the crowding together of its medial moraines. We see the comparatively clean surface of the Glacier du Géant; but we notice upon this surface an appearance which we have not hitherto seen. It is crossed by a series of grey bent bands, which follow each other in succession, from Trélaporte downwards. We count eighteen of these from our present position. (See sketch, page 128.)

333. These are the Dirt Bands of the Mer de Glace; they were first observed by Professor Forbes in 1842.

334. They extend down the glacier further than we can see; and if we cross the valley of Chamouni, and climb the mountains at the opposite side, to a point near the little auberge, called La Flégère, we shall command a view of the end of the glacier and observe the completion of the series of bands. We notice that they are confined throughout to the portion of the glacier derived from the Col du Géant. (See sketch, page 129.)

335. We must trace them to their source. You know how noble and complete a view is obtained of the glacier and Col du Géant from the Cleft Station above Trélaporte. Thither we must once more climb; and thence we can see the succession of bands stretching downwards to the Montanvert, and upwards to the base of the ice-cascade upon the Glacier du Géant. The cascade is evidently concerned in their formation. (See sketch opposite.)

336. And how? Simply enough. The glacier, as we know, is broken transversely at the summit of the ice-fall, and descends the declivity in a series of great transverse ridges. At the base of the fall, the chasms are closed, but the ridges in part remain forming protuberances, which run like vast wrinkles across the glacier. These protuberances are more and more bent because of the quicker motion of the centre, and the depressions between them form receptacles for the fine mud and débris washed by the little rills from the adjacent slopes.

337. The protuberances sink gradually through the wasting action of the sun, so that long before Trélaporte is reached they have wholly disappeared. Not so the dirt of which they were the collectors: it continues to occupy, in transverse bands, the flat surface of the glacier. At Trélaporte, moreover, where the valley becomes narrow, the bands are much sharpened, obtaining there the character which they afterwards preserve throughout the Mer de Glace. Other glaciers with cascades also exhibit similar bands.

§ 49. Sea Ice and Icebergs.

338. We are now equipped intellectually for a campaign into another territory. Water becomes heavier and more difficult to freeze when salt is dissolved in it. Sea water is therefore heavier than fresh, and the Greenland Ocean requires to freeze it a temperature 3½ degrees lower than fresh water. When concentrated till its specific gravity reaches 1.1045, sea water requires for its congelation a temperature 18⅓ degrees lower than the ordinary freezing-point.

Scoresby.

339. But even when the water is saturated with salt, the crystallising force studiously rejects the salt, and devotes itself to the congelation of the water alone. Hence the ice of sea water, when melted, produces fresh water. The only saline particles existing in such ice are those entangled 'mechanically in its pores. They have no part or lot in the structure of the crystal.

340. This exclusiveness, if I may use the term, of the water molecules; this entire rejection of all foreign elements from the edifices which they build, is enforced to a surprising degree. Sulphuric acid has so strong an affinity for water that it is one of the most powerful agents known to the chemist for the removal of humidity from air. Still, as shown by Faraday, when a mixture of sulphuric acid and water is frozen, the crystal formed is perfectly sweet and free from acidity. The water alone has lent itself to the crystallising force.

341. Every winter in the Arctic regions the sea freezes, roofing itself with ice of enormous thickness and vast extent. By the summer heat, and the tossing of the waves, this is broken up; the fragments are drifted by winds and borne by currents. They clash, they crush each other, they pile themselves into heaps, thus constituting the chief danger encountered by mariners in the polar seas.

342. But among the drifting masses of flat sea-ice, vaster masses sail, which spring from a totally different source. These are the Icebergs of the Arctic seas. They rise sometimes to an elevation of hundreds of feet above the water, while the weight of ice submerged is about seven times that seen above.

343. The first observers of striking natural phenomena generally allow wonder and imagination more than their due place. But to exclude all error arising from this cause, I will refer to the journal of a cool and intrepid Arctic navigator, Sir Leopold McClintock. He describes an iceberg 250 feet high, which was aground in 500 feet of water. This would make the entire height of the berg 750 feet, not an unusual altitude for the greater icebergs.