and surpasses it. We immediately see the rise of the liquid column
in the glass tube, exactly as mercury rises in the tube of a warmed
thermometer.
306. Our glass tube is ten inches long, and at starting the water
stood in it at a height of five inches. We will apply the spirit-lamp
flame until the water rises quite to the top of the tube and trickles
over. This experiment suffices to show the expansion of the water by
heat.
307. We now take a common finger-glass and put into it a little
pounded ice and salt. On this we place the flask, and then build
round it the freezing mixture. The liquid column retreats down the
tube, proving the contraction of the liquid by cold. We allow the
shrinking to continue for some minutes, noticing that the downward
retreat of the liquid becomes gradually slower, and that it finally
ceases altogether.
308. Keep your eye upon the liquid column; it remains quiescent for
a fraction of a minute, and then moves once more. But its motion is
now _upwards_ instead of downwards. _The freezing mixture now acts
exactly like the flame._
309. It would not be difficult to pass a thermometer through the cork
into the flask, and it would tell us the exact temperature at which
the liquid ceased to contract and began to expand. At that moment we
should find the temperature of the liquid a shade over 39° Fahr.
310. At this temperature, then, water attains _its maximum density_.
311. Seven degrees below this temperature, or at 32° Fahr., the
liquid begins to turn into solid crystals of ice, which you know
swims upon water because it is bulkier for a given weight. In fact,
this halt of the approaching molecules at the temperature of 39°,
is but the preparation for the subsequent act of crystallisation,
in which the expansion by cold culminates. Up to the point of
solidification the increase of volume is slow and gradual; while in
the act of solidification it is sudden, and of overwhelming strength.
312. By this force of expansion the Florentine Academicians long
ago burst a sphere of copper nearly three quarters of an inch in
thickness. By the same force the celebrated astronomer Huyghens burst
in 1667 iron cannons a finger breadth thick. Such experiments have
been frequently made since. Major Williams during a severe Quebec
winter filled a mortar with water, and closed it by driving into
its muzzle a plug of wood. Exposed to a temperature 50° Fahr. below
the freezing point of water, the metal resisted the strain, but the
plug gave way, being projected to a distance of 400 feet. At Warsaw
howitzer shells have been thus exploded; and you and I have shivered
thick bombshells to fragments, by placing them for half an hour in a
freezing mixture.
313. The theory of the shafts and pits referred to at the beginning
of this section is this: The water at the surface of the shaft is
warmed by the sun, say to a temperature of 39° Fahr. The water at
the bottom, in contact with the ice, must be at 32° or near it. The
heavier water is therefore at the top; it will descend to the bottom,
melt the ice there, and thus deepen the shaft.
314. The circulation here referred to undoubtedly goes on, and
some curious effects are due to it; but not, I think, the one here
ascribed to it. The _deepening_ of a shaft implies a quicker melting
of its bottom than of the surface of the glacier. It is not easy to
see how the fact of the solar heat being first absorbed by water,
and then conveyed by it to the bottom of the shaft, should make the
melting of the bottom more rapid than that of the ice which receives
the direct impact of the solar rays. The surface of the glacier must
sink _at least_ as rapidly as the bottom of the pit, so that the
circulation, though actually existing, cannot produce the effect
ascribed to it.
§ 46. _Consequences flowing from the foregoing Properties of Water.
Correction of Errors._
315. I was not much above your age when the property of water ceasing
to contract by cold at a temperature of 39° Fahr. was made known to
me, and I still remember the impression it made upon me. For I was
asked to consider what would occur in case this solitary exception to
an otherwise universal law ceased to exist.
316. I was asked to reflect upon the condition of a lake stored with
fish and offering its surface to very cold air. It was made clear
to me that the water on being first chilled would shrink in volume
and become heavier, that it would therefore sink and have its place
supplied by the warmer and lighter water from the deeper portions of
the lake.
317. It was pointed out to me that without the law referred to
this process of circulation would go on until the whole water of
the lake had been lowered to the freezing temperature. Congelation
would then begin, and would continue as long as any water remained
to be solidified. One consequence of this would be to destroy every
living thing contained in the lake. Other calamities were added,
all of which were said to be prevented by the perfectly exceptional
arrangement, that after a certain time the _colder_ water becomes the
_lighter_, floats on the surface of the lake, is there congealed,
thus throwing a protecting roof over the life below.
318. Count Rumford, one of the most solid of scientific men, writes
in the following strain about this question:--"It does not appear to
me that there is anything which human sagacity can fathom, within the
wide-extended bounds of the visible creation, which affords a more
striking or more palpable proof of the wisdom of the Creator, and
of the special care He has taken in the general arrangement of the
universe, to preserve animal life, than this wonderful contrivance.
319. "Let me beg the attention of my readers while I endeavour to
investigate this most interesting subject; and let me at the same
time bespeak his candour and indulgence. I feel the danger to which a
mortal exposes himself who has the temerity to explain the designs
of Infinite Wisdom. The enterprise is adventurous, but it surely
cannot be improper.
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.
[Illustration]
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.)
[Illustration]
333. These are the _Dirt Bands_ of the Mer de Glace; they were first
observed by Professor Forbes in 1842.
[Illustration]
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.[E]
[E] 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.
344. From Baffin's Bay these mighty masses come sailing down through
Davis' Straits into the broad Atlantic. A vast amount of heat is
demanded for the simple liquefaction of ice (§ 48); and the melting
of icebergs is on this account so slow, that when large they
sometimes maintain themselves till they have been drifted 2000 miles
from their place of birth.
345. What is their origin? The Arctic glaciers. From the mountains
in the interior the indurated snows slide into the valleys and fill
them with ice. The glaciers thus formed move like the Swiss ones,
incessantly downward. But the Arctic glaciers reach the sea, enter
it, often ploughing up its bottom into submarine moraines. Undermined
by the lapping of the waves, and unable to resist the strain imposed
by their own weight, they break across, and discharge vast masses
into the ocean. Some of these run aground on the adjacent shores,
and often maintain themselves for years. Others escape southward, to
be finally dissolved in the warm waters of the Atlantic. The first
engraving on the opposite page is copied from a photograph taken by
Mr. Bradford during a recent expedition to the Northern seas. The
second represents a mass of ice upon the Glacier des Bossons. Their
likeness suggests their common origin.
[Illustration]
[Illustration]
§ 50. _The Æggischhorn, the Märgelin See and its Icebergs._
346. I am, however, unwilling that you should quit Switzerland
without seeing such icebergs as it can show, and indeed there are
other still nobler glaciers than the Mer de Glace with which you
ought to be acquainted. In tracing the Rhone to its source, you have
already ascended the valley of the Rhone. Let us visit it again
together; halt at the little town of Viesch, and go from it straight
up to the excellent hostelry on the slope of the Æggischhorn. This
we shall make our head-quarters while we explore that monarch of
European ice-streams,--the great Aletsch glacier.
347. Including the longest of its branches, this noble ice-river is
about twenty miles long, while at the middle of its trunk it measures
nearly a mile and a quarter from side to side. The grandest mountains
of the Bernese Oberland, the Jungfrau, the Monch, the Trugberg, the
Aletschhorn, the Breithorn, the Gletscherhorn, and many another noble
peak and ridge, are the collectors of its névés. From three great
valleys formed in the heart of the mountains these névés are poured,
uniting together to form the trunk of the Aletsch at a place named
by a witty mountaineer, the "Place de la Concorde of Nature." If the
phrase be meant to convey the ideas of tranquil grandeur, beauty of
form, and purity of hue, it is well bestowed.
348. Our hotel is not upon the peak of the Æggischhorn, but a brisk
morning walk soon places us upon the top. Thence we see the glacier
like a broad river stretching upwards to the roots of the Jungfrau,
and downwards past the Bel Alp towards its end. Prolonging the vision
downwards, we strike the noblest mountain group in all the Alps,--the
Dom and its attendant peaks, the Matterhorn and the Weisshorn. The
scene indeed is one of impressive grandeur, a multitude of peaks and
crests here unnamed contributing to its glory.
349. But low down to our right, and surrounded by the sheltering
mountains, is an object the beauty of which startles those who are
unprepared for it. Yonder we see the naked side of the glacier,
exposing glistening ice-cliffs sixty or seventy feet high. It would
seem as if the Aletsch here were engaged in the vain attempt to
thrust an arm through a lateral valley. It once did so; but the arm
is now incessantly broken off close to the body of the glacier, a
great space formerly covered by the ice being occupied by its water
of liquefaction. A lake of the loveliest blue is thus formed, which
reaches quite to the base of the ice-cliffs, saps them, as the Arctic
waves sap the Greenland glaciers, and receives from them the broken
masses which it has undermined. As we look down upon the lake, small
icebergs sail over the tranquil surface, each resembling a snowy swan
accompanied by its shadow.
350. This is the beautiful little lake of Märgelin, or, as the Swiss
here call it, the Märgelin See. You see that splash, and immediately
afterwards hear the sound of the plunging ice. The glacier has broken
before our eyes, and dropped an iceberg into the lake. All over the
lake the water is set in commotion, thus illustrating on a small
scale the swamping waves produced by the descent of vast islands of
ice from the Arctic glaciers. Look to the end of the lake. It is
cumbered with the remnants of icebergs now aground, which have been
in part wafted thither by the wind, but in part slowly borne by the
water which moves gently in this direction.
351. Imagine us below upon the margin of the lake, as I happened to
be on one occasion. There is one large and lonely iceberg about the
middle. Suddenly a sound like that of a cataract is heard; we look
towards the iceberg and see water teeming from its sides. Whence
comes the water? the berg has become top-heavy through the melting
underneath; it is in the act of performing a somersault, and in
rolling over carries with it a vast quantity of water, which rushes
like a waterfall down its sides. And notice that the iceberg, which
a moment ago was snowy-white, now exhibits the delicate blue colour
characteristic of compact ice. It will soon, however, be rendered
white again by the action of the sun. The vaster icebergs of the
Northern seas sometimes roll over in the same fashion. A week may be
spent with delight and profit at the Æggischhorn.
§ 51. _The Bel Alp._
352. From the Æggischhorn I might lead you along the mountain ridge
by the Betten See, the fish of which we have already tasted, to the
Rieder Alp, and thence across the Aletsch to the Bel Alp. This is a
fine mountain ramble, but you and I prefer making the glacier our
highway downwards. Easy at some places, it is by no means child's
play at others to unravel its crevasses. But the steady constancy and
close observation which we have hitherto found availing in difficult
places do not forsake us here. We clear the fissures; and, after four
hours of exhilarating work, we find ourselves upon the slope leading
up to the Bel Alp hotel.