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, F.R.S.
WITH ILLUSTRATIONS.
NEW EDITION.
LONGMANS, GREEN, AND CO.
LONDON, NEW YORK, AND BOMBAY.
1896.
All rights reserved
TO
MICHAEL FARADAY,
THIS BOOK
IS AFFECTIONATELY INSCRIBED.
1860.
PREFACE.
In the following work I have not attempted to mix Narrative and Science, believing that the mind once interested in the one, cannot with satisfaction pass abruptly to the other. The book is therefore divided into Two Parts: the first chiefly narrative, and the second chiefly scientific.
In Part I. I have sought to convey some notion of the life of an Alpine explorer, and of the means by which his knowledge is acquired. In Part II. an attempt is made to classify such knowledge, and to refer the observed phenomena to their physical causes.
The Second Part of the work is written with a desire to interest intelligent persons who may not possess any special scientific culture. For their sakes I have dwelt more fully on principles than I should have done in presence of a purely scientific audience. The brief sketch of the nature of Light and Heat, with which Part II. is commenced, will not, I trust, prove uninteresting to the reader for whom it is more especially designed.
Should any obscurity exist as to the meaning of the terms Structure, Dirt-bands, Regelation, Interference, and others, which occur in Part I., it will entirely disappear in the perusal of Part II.
Two ascents of Mont Blanc and two of Monte Rosa are recorded; but the aspects of nature, and other circumstances which attracted my attention, were so different in the respective cases, that repetition was scarcely possible.
The numerous interesting articles on glaciers which have been published during the last eighteen months, and the various lively discussions to which the subject has given birth, have induced me to make myself better acquainted than I had previously been with the historic aspect of the question. In some important cases I have stated, with the utmost possible brevity, the results of my reading, and thus, I trust, contributed to the formation of a just estimate of men whose labours in this field were long anterior to my own.
J. T.
Royal Institution, June, 1860.
PREFATORY NOTE.
"Glaciers of the Alps" was published nearly six and thirty years ago, and has been long out of print, its teaching in a condensed form having been embodied in the little book called "Forms of Water." The two books are, however, distinct in character; each appears to me to supplement the other; and as the older work is still frequently asked for, I have, at the suggestion of my husband's Publishers, consented to the present reprint, which may be followed later on by a reprint of "Hours of Exercise."
Before reproducing a book written so long ago, I sought to assure myself that it contained nothing touching the views of others which my husband might have wished at the present time to alter or omit. With this object I asked Lord Kelvin to be good enough to read over for me the pages which deal with the history of the subject and with discussions in which he himself took an active part. In kind response he writes:—"... After carefully going through all the passages relating to those old differences I could not advise the omission of any of them from the reprint. There were, no doubt, some keen differences of opinion and judgement among us, and other friends now gone from us, but I think the statements on controversial points in this beautiful and interesting book of your husband's are all thoroughly courteous and considerate of feelings, and have been felt to be so by those whose views were contested or criticised in them."
The current spelling of Swiss names has changed considerably since "Glaciers of the Alps" was written, but, except in the very few cases where an obvious oversight called for correction, the text has been left unaltered. Only the Index has been made somewhat fuller than it was.
L. C. T.
January, 1896.
CONTENTS.
PART I.
Visit to Penrhyn; the Cleavage of Slate Rocks; Sedgwick's theory—its difficulties; Sharpe's observations; Sorby's experiments; Lecture at the Royal Institution; Glacier Lamination; arrangement of an expedition to Switzerland
[2.]—Expedition of 1856: the Oberland.[9]
Valley of Lauterbrunnen; Pliability of rocks; the Wengern Alp; the Jungfrau and Silberhorn; Ice avalanches; Glaciers formed from them; Scene from the Little Scheideck; the Lower Grindelwald Glacier; the Heisse Platte—its Avalanches; Ice Minarets and Blocks; Echoes of the Wetterhorn; analogy with the Reflection of Light from angular mirrors; the Reichenbach Cascade; Handeck Fall; the Grimsel; the Unteraar Glacier; hut of M. Dollfuss; Hôtel des Neufchâtelois; the Rhone glacier from the Mayenwand; expedition up the glacier; Coloured Rings round the sun; crevasses of the névé; extraordinary meteorological phenomenon; Spirit of the Brocken
Kaunserthal and the Gebatsch Alp; Senner or Cheesemakers; Gebatsch Glacier; a night in a cowshed; passage to Lantaufer; a chamois on the rocks; my Guide; the atmospheric snow-line; passage of the Stelvio; Colour of fresh snow; Bormio; the pass recrossed by night; aspect of the mountains; Meran to Unserfrau; passage of the Hochjoch to Fend; singular hailstorm; wild glacier region; hidden crevasses; First Paper presented to the Royal Society
[4.]—Expedition of 1857: the Lake of Geneva.[33]
Blueness of the water; the head of the Lake; appearance of the Rhone; subsidence of particles; Mirage
[5.]—Chamouni and the Montanvert.[37]
Arrival; Coloured Shadows on the snow; Source of the Arveiron; fall of the Vault; "Sunrise in the Valley of Chamouni;" Scratched Rocks; quarters at the Montanvert
Not a Sea but a River of ice; Wave-forms on its surface; their explanation; Structure and Strata; Glacier Tables; first view of the Dirt Bands; influence of Illumination in rendering them visible; the Eye incapable of detecting differences between intense lights
Measurements commenced; the "Cleft Station" at Trélaporte; Regelation of snow granules; two chamois; view of the Mer de Glace and its Tributaries; Séracs of the Col du Géant; Sliding and Viscous theories; Rending of the ice; Striæ on its surface; White Ice-seams
Alone upon the glacier; Lakes and Rivulets; parallel between Glacier and Geological disturbance; splendid rainbow; aspect of the glacier at the base of the Séracs; visit to the Chief Guide at Chamouni; Liberties granted
Glacier du Talèfre; Jardin divides the névé; Blue Veins near the summit; surrounding scene; Moraines and Avalanches; Cascade du Talèfre; dangers on approaching it from above
Lightning and Rain; Spherical hailstones; an evening among the crevasses; Dangerous Leap; ice-practice; preparations for an ascent of Mont Blanc
[11.]—First Ascent of Mont Blanc (1857).[68]
Across the mountain to the Glacier des Bossons; its crevasses; Ladder left behind; consequent difficulties; the Grands Mulets; Twinkling and change of Colour of the Stars; moonlight on the mountains; start with one guide; difficulties among the crevasses; the Petit Plateau; Séracs of the Dôme du Goûter; bad condition of snow; the Grand Plateau; Coloured Spectra round the sun; the lost Guides; the Route missed; dangerous ice-slope; Guide exhausted; cutting steps; cheerless prospect; the Corridor; the Mur de la Côte; the Petits Mulets; food and drink disappear; Physiological experiences on the Calotte; Summit attained; the Clouds and Mountains; experiment on Sound; colour of the snow; the descent; a solitary prisoner; second night at the Grands Mulets; Inflammation of eyes; a blind man among the crevasses; descent to Chamouni; thunder on Mont Blanc
Life at the Montanvert; glacier "Blower;" Cascade of the Talèfre; difficulties in setting out lines; departure from the Montanvert; my hosts; prospect from the Glacier des Bois; Edouard Simond
Origin and aim of the expedition; Laminated Structure of the ice
[14.]—Passage of the Strahleck.[93]
Unpromising weather; appearance of the glacier and of the adjacent mountains; Transverse Protuberances; Dirt Bands; Structure; a Slip on a snow slope; the Finsteraarhorn; the Schreckhorn; extraordinary Atmospheric Effects; Summit of the Strahleck; Grand Amphitheatre; mutations of the clouds; descent of the rocks; a Bergschrund; fog in the valley; descent to the Grimsel
Ancient Glaciers in the valley of Hasli; Rounded, Polished, and Striated Rocks; level of the ancient ice; Groovings on the Grimsel Pass; glacier of the Rhone; descent of the Rhone valley; the Æggischhorn; Cloud Iridescences; the Aletsch glacier; the Märjelen See; Icebergs; Tributaries of the Aletsch; Grand glacier-region; crevasses; a chamois deceived
[16.]—Ascent of the Finsteraarhorn.[104]
Character of my Guide; iridescent cloud; evening on the Faulberg; the Jungfrau and her neighbours; a Mountain Cave; the Jungfrau before dawn; contemplated visit; the Grünhorn Lücke; Magnificent Corridor; sunrise; névé of the Viesch glacier; halt at the base of the Finsteraarhorn; Spurs and Couloirs of the mountain; Pyramidal Crest; scene of Agassiz's observations; a hard climb; discipline of such an ascent; Boiling Point; Registering Thermometer, its fate; daring utterance; descent by glissades; the Viesch glacier; hidden crevasses; a brave and competent guide
Subsequent days at the Æggischhorn; Afloat on the Icebergs; Bedding and Structure; Ancient Moraines of the Aletsch; Scratched Rocks; passage of the mountains to the end of the glacier; a wild gorge; arrival at Zermatt; the Riffelberg
[18.]—First Ascent of Monte Rosa.[122]
The ascent new to myself and my guide; directions; Ulrich Lauener; Ominous Clouds; passage of the Görner Glacier; Roches Moutonnées; Avalanche from the Twins; gradual advance of clouds; bridged chasms; Scene from a cliff; apparent atmospheric struggle; Sound of the snow; Dangerous Edge; Overhanging Cornice; staff driven through it; increased obscurity; Rocky Crest; loss of pocket-book; Summit attained; Boiling Point; fall of snow; exquisite forms of the Snow Crystals; a shower of frozen blossoms; the descent; mode of attachment; Startling Avalanche; Blue Light emitted from the fissures of the fresh snow; Stifling Heat; return to the Riffel
The Rothe Kumm; pleasant companions; difficult descent; temperatures of rock, air, and grass; Singular Cavern in the ice; Structure and Stratification
[20.]—The Görner Grat and the Riffelhorn; Magnetic Phenomena.[137]
Formation and Dissipation of clouds; Scene from the Görner Grat; Magnetism of the Rocks; the Compass and Sun at variance; ascent of the Riffelhorn; Magnetic effects; places of most intense action; Scratched and Polished Rocks; Exfoliation of crust produced by the sliding of ancient glaciers; Magnetic Polarity; Consequent Points; Bearings from the Riffelhorn; action on a Distant Needle
Fog on the Riffelberg; its dissipation; Sunset from the Görner Grat; Cloud-wreaths on the Matterhorn; Streamers of Flame; grand Interference Phenomenon; investigation of Structure; the Görnerhorn glacier; Western glacier of Monte Rosa; the Schwarze, Trifti, and Théodule glaciers; welding of the Tributaries to parallel Strips; Temptation
[22.]—Second Ascent of Monte Rosa (1858).[151]
A Light Scrip; my Guide lent; a substitute; a party on the mountain; across the glacier and up the rocks; the guide expostulates; among the crevasses; the guide halts; left alone; beauty of the mountain; splendid effects of Diffraction; Cheer from the summit; on the Kamm; climbers meet; among the rocks; Alone on the Summit; the Axe slips; the prospect; the descent; serious accident; a word on climbing alone
The Furgge glacier; thunder and lightning; the Weissthor given up; excursion by Stalden to Saas; Herr Imseng; the Mattmark See and Hotel; ascent of a boulder; Snow-storm; cold quarters; the Monte Moro; the Allalein glacier; a noble vault; Structure and Dirt-bands; stormy weather; Avalanches at Saas; the Fée glacier; Frozen dust on the Mischabelhörner; Snow, Vapour, and Cloud; curious effect on the hearing; "a Terrible Hole;" singular group; a Song from 'The Robbers'
Need of observations on Alpine Temperature; Balmat's intention; aid from the Royal Society; Difficulties at Chamouni in 1858; the Intendant memorialised; his response; the Séracs revisited; Crevasses and Crumples; bad weather; thermometers placed at the Jardin; Avalanches of the Talèfre; wondrous sky
[25.]—Second Ascent of Mont Blanc (1858).[177]
Shadows of the Aiguilles; Silver Trees at sunrise; M. Necker's letter; Birds as Sparks and Stars against the sky; crevasse bridged; ladder rejected; a hunt for a pont; crevasses crossed; Magnificent Sunset; illuminated clouds; Storm on the Grands Mulets; a Comet discovered; start by starlight; the Petit Plateau a reservoir for avalanches; Balmat's warning; the Grand Plateau at dawn; blue of the ice; Balmat in danger; Clouds upon the Calotte; the Summit; wind and snow-dust; Balmat frostbitten; halt on the Calotte; descent to Chamouni; good conduct of porters
Hostility of Chief Guide; Procès Verbal; the British Association; application to the Sardinian authorities; President's Letter; Royal Society; Testimonial to Balmat
[27.]—Winter Expedition to the Mer de Glace, 1859. [195]
First defeat and fresh attempt; Geneva to Chamouni; deep snow; Desolation; slow progress; a horse in the snow; a struggle; Chamouni on Christmas night; mountains hidden; Climb to the Montanvert; Snow on the Pines; débris of avalanches; Breaking of snow; Atmospheric Changes; the mountains concealed and revealed; colour of the snow; the Montanvert in Winter; footprints in the snow; wonderful frost figures; Crystal Curtain; the Mer de Glace in Winter; the first night; "a rose of dawn;" Crimson Banners of the Aiguilles; the stakes fixed; a Hurricane on the glacier; the second night; Wild Snow-storm; a man in a crevasse; calm; Magnificent Snow Crystals; Sound through the falling snow; swift descent; Source of the Arveiron; Crystal Cave; appearance of water; westward from the vault; Majestic Scene; Farewell
PART II.
What is Light?—notion of the ancients; requires Time to pass through Space; Römer, Bradley, Fizeau; Emission Theory supported by Newton, opposed by Huyghens; the Wave Theory established by Young and Fresnel; Theory explained; nature of Sound; of Music; of Pitch; nature of Light; of Colour; two sounds may produce silence; two rays of light may produce darkness; two rays of heat may produce cold; Length and Number of waves of light; Liquid Waves; Interference; Diffraction; Colours of Thin Plates; applications of the foregoing to cloud iridescences, luminous trees, twinkling of stars, the Spirit of the Brocken, &c.
The Sun emits a multitude of Non-luminous Rays; Rays of Heat differ from rays of Light as one colour differs from another; the same ray may produce the sensations of light and heat
Heat a kind of Motion; system of exchanges; Luminous and Obscure Heat; Absorption by Gases; gases may be transparent to light, but opaque to heat; Heat selected from luminous sources; the Atmosphere acts the part of a Ratchet-wheel; possible heat of a Distant Planet; causes of Cold in the upper strata of the Earth's Atmosphere
[4.]—Origin of Glaciers. [248]
Application of principles; the Snow-line; its meaning; waters piled annually in a solid form on the summits of the hills; the Glaciers furnish the chief means of escape; superior and inferior snow-line
Whiteness of snow; whiteness of ice; Round air-bubbles; melting and freezing; Conversion of snow into ice by Pressure
[6.]—Colour of Water and Ice.[253]
Waves of Ether not entangled; they are separated in the prism; they are differently absorbed; Colour due to this; Water and Ice blue; water and ice opaque to radiant heat; Long Waves shivered on the molecules; Experiment; Grotto of Capri; the Laugs of Iceland
[7.]—Colours of the Sky. [257]
Newton's idea; Goethe's Theory; Clausius and Brücke; Suspended Particles; singular effect on a painting explained by Goethe; Light separated without Absorption; Reflected and Transmitted light; blueness of milk and juices; the Sun through London smoke; Experiments; Blue of the Eye; Colours of Steam; the Lake of Geneva
Glacier loaded along its edges by the ruins of the mountains; Lateral Moraines; Medial Moraines; their number one less than the number of Tributaries; Moraines of the Mer de Glace; successive shrinkings; Glacier Tables explained; 'Dip' of stones upon the glacier enables us to draw the Meridian Line; type 'Table;' Sand Cones; moraines engulfed and disgorged; transparency of ice under the moraines
[9.]—Glacier Motion,—Preliminary. [269]
Névé and Glacier; First Measurements; Hugi and Agassiz; Escher's defeat on the Aletsch; Piles fixed across the Aar glacier by Agassiz in 1841; Professor Forbes invited by M. Agassiz; Forbes's first observations on the Mer de Glace in 1842; motion of Agassiz's piles measured by M. Wild; Centre of the glacier moves quickest; State of the Question
[10.]—Motion of the Mer de Glace.[275]
The Theodolite; mode of measurement; first line; Centre Point not the quickest; second line; former result confirmed; Law of Motion sought; the glacier moves through a Sinuous Valley; effect of Flexure; Western half of glacier moves quickest; Point of Maximum Motion crosses axis; Eastern half moves quickest; Locus of Point of Maximum Motion; New Law; Motion of the Géant; motion of the Léchaud; Squeezing of the Tributaries through the Neck of the valley at Trélaporte; the Léchaud a Driblet
[11.]—Ice Wall at the Tacul,—Velocities of Top and Bottom.[289]
First attempt by Mr. Hirst; second attempt, stakes fixed at Top, Bottom, and Centre; dense fog; the stakes lost; process repeated; Velocities determined
[12.]—Winter Motion of the Mer de Glace. [294]
First line, Above the Montanvert; second line, Below the Montanvert; Ratio of winter to summer motion
[13.]—Cause of Glacier Motion,—De Saussure's Theory. [296]
First attempt at a Theory by Scheuchzer in 1705; Charpentier's theory, or the Theory of Dilatation; Agassiz's theory; Altmann and Grüner; theory of De Saussure, or the Sliding Theory; in part true; strained interpretation of this theory
Character of Rendu; his Essay entitled 'Théorie des Glaciers de la Savoie;' extracts from the essay; he ascribes "circulation" to natural forces; classifies glaciers; assigns the cause of the conversion of snow into ice; notices Veined Structure; "time and affinity;" notices Regelation; diminution of glaciers réservoirs; Remarkable Passage; announces Swifter Motion of Centre; North British Review; Discrepancies explained by Rendu; Liquid Motion ascribed to glacier; all the phenomena of a River reproduced upon the Mer de Glace; Ratio of Side and Central velocities; Errors removed
Anticipations of Rendu confirmed by Agassiz and Forbes; analogies with Liquid Motion established by Forbes; his Measurements in 1842; measurements in 1844 and 1846; Measurements of Agassiz and Wild in 1842, 1843, 1844, and 1845; Agassiz notices the "migration" of the Point of Swiftest Motion; true meaning of this observation; Summary of contributions on this part of the question
Discussions as to its meaning; Facts and Principles; definition of theory; Some Experiments on the Mer de Glace to test the Viscosity of the Ice
Caused by the Motion; Ice Sculpture; Fantastic Figures; beauty of the crevasses of the highest glaciers; Birth of a crevasse; Mechanical Origin; line of greatest strain; Marginal Crevasses; Transverse Crevasses; Longitudinal Crevasses; Bergschrunds; Influence of Flexure; why the Convex Sides of glaciers are most crevassed
Further considerations on Viscosity; Numerical Test; formation of crevasses opposed to viscosity
Connexion of Natural Forces; Equivalence of Heat and Work; heat produced by Mechanical Action; heat consumed in producing work; Chemical Attractions; Attraction of Gravitation; amount of heat which would be produced by the stoppage of the Earth in its Orbit; amount produced by the falling of the Earth into the Sun; shifting of Atoms; heat consumed in Molecular Work; Specific Heat; Latent Heat; 'friability' of ice near its melting point; Rotten Ice and softened Wax
Papers presented to the Royal Society by Professor Forbes in 1846; Capillary Hypothesis of glacier motion; hypothesis examined
Statement of theory; influence of Pressure on the Melting Point of Ice; difficulties of theory; Calculation of requisite Pressure; Actual pressure insufficient
Pressure and Tension; possible experiments; Ice may be moulded into Vases and Statuettes or coiled into Knots; this no proof of Viscosity; Actual Experiments; a sphere of ice moulded to a lens; a lens moulded to a cylinder; a lump of ice moulded to a cup; straight bars of ice bent; ice thus moulded incapable of being sensibly stretched; when Tension is substituted for Pressure, analogy with viscous body breaks down
Faraday's first experiments; Freezing together of pieces of ice at 32°; Freezing in Hot Water; Faraday's recent experiments; Regelation not due to Pressure nor to Capillary Attraction; it takes place in vacuo; fracture and regelation; no viscidity discovered
[24.]—Crystallization and Internal Liquefaction. [353]
How crystals are 'nursed;' Snow-Crystals; Crystal Stars formed in Water; Arrangement of Atoms of Lake Ice; dissection of ice by a sunbeam; Liquid Flowers formed in ice; associated Vacuous Spots; curious sounds; their explanation; Cohesion of water when free from air; liquid snaps like a broken spring; Ebullition converted into Explosion; noise of crepitation; Water-cells in glacier ice; Vacuous Spots mistaken for Bubbles; not Flattened by Pressure; experiments; Cause of Regelation
Their character; Depth of Moulin on Grindelwald Glacier; Explanation the Grand Moulin of the Mer de Glace; Motion of moulins
[26.]—Dirt-Bands of the Mer de Glace.[367]
Their discovery by Professor Forbes; view of Bands from a point near the Flégère; Bands as seen from Les Charmoz; Skew Surface of glacier; aspect of Bands from the Cleft Station; Origin of bands; tendency to become straight; differences between observers
[27.]—Veined Structure of Glaciers.[376]
General appearance; Grooves upon the glacier; first observations; description by M. Guyot; observations of Professor Forbes; Structure and Stratification; subject examined; Marginal Structure; Transverse Structure; Longitudinal Structure; experimental illustrations; the Structure Complementary to the Crevasses; glaciers of the Oberland, Valais, and Savoy examined with reference to this question
[28.]—The Veined Structure and Differential Motion.[395]
Marginal Structure Oblique to sides; Drag towards the centre; difficulties of theory which ascribes the structure to Differential Sliding; it persists across the lines of maximum sliding
[29.]—The Ripple Theory of the Veined Structure. [398]
Ripples in Water supposed to correspond to Glacier Structure; analysis of theory; observation of the MM. Weber; water dropping from an oar; stream cleft by an obstacle; Two Divergent lines of Ripple; Single Line produced by Lateral Obstacle; Direction of ripples compounded of River's motion and Wave motion; Structure and Ripples due to different causes; their positions also different
[30.]—The Veined Structure and Pressure. [404]
Supposed case of pressed prism of glass; Experiments of Nature; Quartz-pebbles flattened and indented; Pressure would produce Lamination; Tangential Action
[31.]—The Veined Structure and the Liquefaction of Ice by Pressure.[408]
Influence of pressure on Melting and Boiling points; some substances swell, others shrink in melting; effects of pressure different on the two classes of bodies; Theoretic Anticipation by Mr. James Thomson; Melting point of Ice lowered by pressure; Internal Liquefaction of a prism of solid ice by pressure; Liquefaction in Layers; application to the Veined Structure
[32.]—White Ice-Seams of the Glacier du Géant. [413]
Aspect of Seams; they sweep across the glacier concentric with Structure; Structure at the base of the Talèfre cascade; Crumples; Scaling off by pressure; Origin of seams of White Ice
Glacier du Géant in a state of Longitudinal Compression; Measurements which prove that its hinder parts are advancing upon those in front; Shortening of its Undulations; Squeezing of white Ice-seams; development of Veined Structure
ILLUSTRATIONS.
The Mer de Glace.—Showing the Cleft Station at Trélaporte, the Echelets, the Tacul, the Périades, and the Grand Jorasse.[Frontispiece]
Fig.Page
[1]. Ice Minaret[14]
[2]. Diagram of an angular reflector[16]
[3], [4]. Boats' sails inverted by Atmospheric Refraction[35]
[5]. Wave-like forms on the Mer de Glace[43]
[6]. Glacier Table[44]
[7]. Tributaries of the Mer de Glace[53]
[8]. Magnetic Boulder of the Riffelhorn[143]
[9], [10], [11], [12]. Luminous Trees projected against the sky at sunrise[180], [181]
[13]. Snow on the Pines[201]
[14], [15]. Snow Crystals[214]
[16]. Chasing produced by waves[233]
[17]. Diagram explanatory of Interference[234]
[18]. Interference Spectra, produced by DiffractionTo face [235]
[19]. Moraines of the Mer de Glace" [264]
[20]. Typical section of a glacier Table[266]
[21]. Locus of the Point of Maximum Motion[286]
[22]. Inclinations of ice cascade of the Glacier des Bois[313]
[23]. Inclinations of Mer de Glace above l'Angle[314]
[24]. Fantastic Mass of ice[316]
[25]. Diagram explanatory of the mechanical origin of Crevasses[318]
[26]. Diagram showing the line of Greatest Strain[319]
[27a, b]. Section and Plan of a portion of the Lower Grindelwald Glacier[322]
[28]. Diagram illustrating the crevassing of Convex Sides of glacier[323]
[29]. Diagram illustrating test of viscosity[326]
[30], [31], [32], [33]. Moulds used in experiments with ice[346]-[348]
[34]. Liquid Flowers in lake ice[355]
[35]. Dirt-bands of the Mer de Glace, as seen from a point near the FlégèreTo face [367]
[36]. Ditto, as seen from les Charmoz" [368]
[37]. Ditto, as seen from the Cleft Station, Trélaporte" [369]
[38]. Plan of Dirt-bands taken from Johnson's 'Physical Atlas'[374]
[39]. Veined Structure on the walls of crevasses[381]
[40]. Figure explanatory of the Marginal Structure[383]
[41]. Plan of part of ice-fall, and of glacier below it (Glacier of the Rhone)[386]
[42]. Section of ditto[386]
[43]. Figure explanatory of Longitudinal Structure[388]
[44]. Structure and bedding on the Great Aletsch Glacier[391]
[45], [46]. Structure and Stratification on the Furgge glacier[394]
[47]. Diagram illustrating Differential Motion[395]
[48], [49]. Diagrams explanatory of the formation of Ripples[400], [403]
[50], [51]. Appearance of a prism of ice partially liquefied by Pressure.[410]
[52], [53]. Figures illustrative of compression and liquefaction of ice.[411]
[54], [55]. Sections of White Ice-seams[414]
[56], [57]. Variations in the Dip of the Veined Structure[414], [415]
[58]. Section of three glacier Crumples[416]
[59]. Wall of a crevasse, with incipient crumpling[416]
[60]. Plan of a Stream on the Glacier du Géant[418]
[61]. Plan of a Seam of White Ice on ditto[418]
PART I.
CHIEFLY NARRATIVE.
Ages are your days,
Ye grand expressors of the present tense
And types of permanence;
Firm ensigns of the fatal Being
Amid these coward shapes of joy and grief
That will not bide the seeing.
Hither we bring
Our insect miseries to the rocks,
And the whole flight with pestering wing
Vanish and end their murmuring,
Vanish beside these dedicated blocks.
Emerson
GLACIERS OF THE ALPS.
INTRODUCTORY.
(1.)
In the autumn of 1854 I attended the meeting of the British Association at Liverpool; and, after it was over, availed myself of my position to make an excursion into North Wales. Guided by a friend who knew the country, I became acquainted with its chief beauties, and concluded the expedition by a visit to Bangor and the neighbouring slate quarries of Penrhyn.
From my boyhood I had been accustomed to handle slates; had seen them used as roofing materials, and had worked the usual amount of arithmetic upon them at school; but now, as I saw the rocks blasted, the broken masses removed to the sheds surrounding the quarry, and there cloven into thin plates, a new interest was excited, and I could not help asking after the cause of this extraordinary property of cleavage. It sufficed to strike the point of an iron instrument into the edge of a plate of rock to cause the mass to yield and open, as wood opens in advance of a wedge driven into it. I walked round the quarry and observed that the planes of cleavage were everywhere parallel; the rock was capable of being split in one direction only, and this direction remained perfectly constant throughout the entire quarry.
CLEAVAGE OF SLATE ROCKS.
I was puzzled, and, on expressing my perplexity to my companion, he suggested that the cleavage was nothing more than the layers in which the rock had been originally deposited, and which, by some subsequent disturbance, had been set on end, like the strata of the sandstone rocks and chalk cliffs of Alum Bay. But though I was too ignorant to combat this notion successfully, it by no means satisfied me. I did not know that at the time of my visit this very question of slaty cleavage was exciting the greatest attention among English geologists, and I quitted the place with that feeling of intellectual discontent which, however unpleasant it may be for a time, is very useful as a stimulant, and perhaps as necessary to the true appreciation of knowledge as a healthy appetite is to the enjoyment of food.
On inquiry I found that the subject had been treated by three English writers, Professor Sedgwick, Mr. Daniel Sharpe, and Mr. Sorby. From Professor Sedgwick I learned that cleavage and stratification were things totally distinct from each other; that in many cases the strata could be observed with the cleavage passing through them at a high angle; and that this was the case throughout vast areas in North Wales and Cumberland. I read the lucid and important memoir of this eminent geologist with great interest: it placed the data of the problem before me, as far as they were then known, and I found myself, to some extent at least, in a condition to appreciate the value of a theoretic explanation.
Everybody has heard of the force of gravitation, and of that of cohesion; but there is a more subtle play of forces exerted by the molecules of bodies upon each other when these molecules possess sufficient freedom of action. In virtue of such forces, the ultimate particles of matter are enabled to build themselves up into those wondrous edifices which we call crystals. A diamond is a crystal self-erected from atoms of carbon; an amethyst is a crystal built up from particles of silica; Iceland spar is a crystal built by particles of carbonate of lime. By artificial means we can allow the particles of bodies the free play necessary to their crystallization. Thus a solution of saltpetre exposed to slow evaporation produces crystals of saltpetre; alum crystals of great size and beauty may be obtained in a similar manner; and in the formation of a bit of common sugar-candy there are agencies at play, the contemplation of which, as mere objects of thought, is sufficient to make the wisest philosopher bow down in wonder, and confess himself a child.
CRYSTALLIZATION THEORY.
The particles of certain crystalline bodies are found to arrange themselves in layers, like courses of atomic masonry, and along these layers such crystals may be easily cloven into the thinnest laminæ. Some crystals possess one such direction in which they may be cloven, some several; some, on the other hand, may be split with different facility in different directions. Rock salt may be cloven with equal facility in three directions at right angles to each other; that is, it may be split into cubes; calcspar may be cloven in three directions oblique to each other; that is, into rhomboids. Heavy spar may also be cloven in three directions, but one cleavage is much more perfect, or more eminent as it is sometimes called, than the rest. Mica is a crystal which cleaves very readily in one direction, and it is sufficiently tough to furnish films of extreme tenuity: finally, any boy, with sufficient skill, who tries a good crystal of sugar-candy in various directions with the blade of his penknife, will find that it possesses one direction in particular, along which, if the blade of the knife be placed and struck, the crystal will split into plates possessing clean and shining surfaces of cleavage.
POLAR FORCES.
Professor Sedgwick was intimately acquainted with all these facts, and a great many more, when he investigated the cleavage of slate rocks; and seeing no other explanation open to him, he ascribed to slaty cleavage a crystalline origin. He supposed that the particles of slate rock were acted on, after their deposition, by "polar forces," which so arranged them as to produce the cleavage. According to this theory, therefore, Honister Crag and the cliffs of Penrhyn are to be regarded as portions of enormous crystals; a length of time commensurate with the vastness of the supposed action being assumed to have elapsed between the deposition of the rock and its final crystallization.
When, however, we look closely into this bold and beautiful hypothesis, we find that the only analogy which exists between the physical structure of slate rocks and of crystals is this single one of cleavage. Such a coincidence might fairly give rise to the conjecture that both were due to a common cause; but there is great difficulty in accepting this as a theoretic truth. When we examine the structure of a slate rock, we find that the substance is composed of the débris of former rocks; that it was once a fine mud, composed of particles of sensible magnitude. Is it meant that these particles, each taken as a whole, were re-arranged after deposition? If so, the force which effected such an arrangement must be wholly different from that of crystallization, for the latter is essentially molecular. What is this force? Nature, as far as we know, furnishes none competent, under the conditions, to produce the effect. Is it meant that the molecules composing these sensible particles have re-arranged themselves? We find no evidence of such an action in the individual fragments: the mica is still mica, and possesses all the properties of mica; and so of the other ingredients of which the rock is composed. Independent of this, that an aggregate of heterogeneous mineral fragments should, without any assignable external cause, so shift its molecules as to produce a plane of cleavage common to them all, is, in my opinion, an assumption too heavy for any theory to bear.
Nevertheless, the paper of Professor Sedgwick invested the subject of slaty cleavage with an interest not to be forgotten, and proved the stimulus to further inquiry. The structure of slate rocks was more closely examined; the fossils which they contained were subjected to rigid scrutiny, and their shapes compared with those of the same species taken from other rocks. Thus proceeding, the late Mr. Daniel Sharpe found that the fossils contained in slate rocks are distorted in shape, being uniformly flattened out in the direction of the planes of cleavage. Here, then, was a fact of capital importance,—the shells became the indicators of an action to which the mass containing them had been subjected; they demonstrated the operation of pressure acting at right angles to the planes of cleavage.
MECHANICAL THEORY.
The more the subject was investigated, the more clearly were the evidences of pressure made out. Subsequent to Mr. Sharpe, Mr. Sorby entered upon this field of inquiry. With great skill and patience he prepared sections of slate rock, which he submitted to microscopic examination, and his observations showed that the evidences of pressure could be plainly traced, even in his minute specimens. The subject has been since ably followed up by Professors Haughton, Harkness, and others; but to the two gentlemen first mentioned we are, I think, indebted for the prime facts on which rests the mechanical theory of slaty cleavage.[A]
LECTURE AT THE ROYAL INSTITUTION.
The observations just referred to showed the co-existence of the two phenomena, but they did not prove that pressure and cleavage stood to each other in the relation of cause and effect. "Can the pressure produce the cleavage?" was still an open question, and it was one which mere reasoning, unaided by experiment, was incompetent to answer. Sharpe despaired of an experimental solution, regarding our means as inadequate, and our time on earth too short to produce the result. Mr. Sorby was more hopeful. Submitting mixtures of gypsum and oxide of iron scales to pressure, he found that the scales set themselves approximately at right angles to the direction in which the pressure was applied. The position of the scales resembled that of the plates of mica which his researches had disclosed to him in slate rock, and he inferred that the presence of such plates, and of flat or elongated fragments generally, lying all in the same general direction, was the cause of slaty cleavage. At the meeting of the British Association at Glasgow, in 1855, I had the pleasure of seeing some of Mr. Sorby's specimens, and, though the cleavage they exhibited was very rough, still, the tendency to yield at right angles to the direction in which the pressure had been applied, appeared sufficiently manifest.
At the time now referred to I was engaged, and had been for a long time previously, in examining the effects of pressure upon the magnetic force, and, as far back as 1851, I had noticed that some of the bodies which I had subjected to pressure exhibited a cleavage of surpassing beauty and delicacy. The bearing of such facts upon the present question now forcibly occurred to me. I followed up the observations; visited slate yards and quarries, observed the exfoliation of rails, the fibres of iron, the structure of tiles, pottery, and cheese, and had several practical lessons in the manufacture of puff-paste and other laminated confectionery. My observations, I thought, pointed to a theory of slaty cleavage different from any previously given, and which, moreover, referred a great number of apparently unrelated phenomena to a common cause. On the 10th of June, 1856, I made them the subject of a Friday evening's discourse at the Royal Institution.[B]
ORIGIN OF RESEARCHES.
Such are the circumstances, apparently remote enough, under which my connexion with glaciers originated. My friend Professor Huxley was present at the lecture referred to: he was well acquainted with the work of Professor Forbes, entitled 'Travels in the Alps,' and he surmised that the question of slaty cleavage, in its new aspect, might have some bearing upon the laminated structure of glacier-ice discussed in the work referred to. He therefore urged me to read the 'Travels,' which I did with care, and the book made the same impression upon me that it had produced upon my friend. We were both going to Switzerland that year, and it required but a slight modification of our plans to arrange a joint excursion over some of the glaciers of the Oberland, and thus afford ourselves the means of observing together the veined structure of the ice.
Had the results of this arrangement been revealed to me beforehand, I should have paused before entering upon an investigation which required of me so long a renunciation of my old and more favourite pursuits. But no man knows when he commences the examination of a physical problem into what new and complicated mental alliances it may lead him. No fragment of nature can be studied alone; each part is related to every other part; and hence it is, that, following up the links of law which connect phenomena, the physical investigator often finds himself led far beyond the scope of his original intentions, the danger in this respect augmenting in direct proportion to the wish of the inquirer to render his knowledge solid and complete.
A BOY'S BOOK.
When the idea of writing this book first occurred to me, it was not my intention to confine myself to the glaciers alone, but to make the work a vehicle for the familiar explanation of such general physical phenomena as had come under my notice. Nor did I intend to address it to a cultured man of science, but to a youth of average intelligence, and furnished with the education which England now offers to the young. I wished indeed to make it a boy's class-book, which should reveal the mode of life, as well as the scientific objects, of an explorer of the Alps. The incidents of the past year have caused me to deviate, in some degree, from this intention, but its traces will be sufficiently manifest; and this reference to it will, I trust, excuse an occasional liberty of style and simplicity of treatment which would be out of place if intended for a reader of riper years.
FOOTNOTES:
[A] Mr. Sorby has drawn my attention to an able and interesting paper by M. Bauer, in Karsten's 'Archiv' for 1846; in which it is announced that cleavage is a tension of the mass produced by pressure. The author refers to the experiments of Mr. Hopkins as bearing upon the question.
[B] See [Appendix].
THE OBERLAND. 1856.
EXPEDITION OF 1856.
THE OBERLAND.
(2.)
On the 16th of August, 1856, I received my Alpenstock from the hands of Dr. Hooker, in the garden of the Pension Ober, at Interlaken. It bore my name, not marked, however, by the vulgar brands of the country, but by the solar beams which had been converged upon it by the pocket lens of my friend. I was the companion of Mr. Huxley, and our first aim was to cross the Wengern Alp. Light and shadow enriched the crags and green slopes as we advanced up the valley of Lauterbrunnen, and each occupied himself with that which most interested him. My companion examined the drift, I the cleavage, while both of us looked with interest at the contortions of the strata to our left, and at the shadowy, unsubstantial aspect of the pines, gleaming through the sunhaze to our right.
FOLDED ROCKS. 1856.
What was the physical condition of the rock when it was thus bent and folded like a pliant mass? Was it necessarily softer than it is at present? I do not think so. The shock which would crush a railway carriage, if communicated to it at once, is harmless when distributed over the interval necessary for the pushing in of the buffer. By suddenly stopping a cock from which water flows you may burst the conveyance pipe, while a slow turning of the cock keeps all safe. Might not a solid rock by ages of pressure be folded as above? It is a physical axiom that no body is perfectly hard, none perfectly soft, none perfectly elastic. The hardest body subjected to pressure yields, however little, and the same body when the pressure is removed cannot return to its original form. If it did not yield in the slightest degree it would be perfectly hard; if it could completely return to its original shape it would be perfectly elastic.
Let a pound weight be placed upon a cube of granite; the cube is flattened, though in an infinitesimal degree. Let the weight be removed, the cube remains a little flattened; it cannot quite return to its primitive condition. Let us call the cube thus flattened No. 1. Starting with No. 1 as a new mass, let the pound weight be laid upon it; the mass yields, and on removing the weight it cannot return to the dimensions of No. 1; we have a more flattened mass, No. 2. Proceeding in this manner, it is manifest that by a repetition of the process we should produce a series of masses, each succeeding one more flattened than the former. This appears to be a necessary consequence of the physical axiom referred to above.
Now if, instead of removing and replacing the weight in the manner supposed, we cause it to rest continuously upon the cube, the flattening, which above was intermittent, will be continuous; no matter how hard the cube may be, there will be a gradual yielding of its mass under the pressure. Apply this to squeezed rocks—to those, for example, which form the base of an obelisk like the Matterhorn; that this base must yield, seems a certain consequence of the physical constitution of matter: the conclusion seems inevitable that the mountain is sinking by its own weight. Let two points be fixed, one near the summit, the other near the base of the obelisk; next year these points will have approached each other. Whether the amount of approach in a human lifetime be measureable we know not; but it seems certain that ages would leave their impress upon the mass, and render visible to the eye an action which at present is appreciable by the imagination only.
THE JUNGFRAU AND SILBERHORN. 1856.
We halted on the night of the 16th at the Jungfrau Hotel, and next morning we saw the beams of the rising sun fall upon the peaked snow of the Silberhorn. Slowly and solemnly the pure white cone appeared to rise higher and higher into the sunlight, being afterwards mottled with gold and gloom, as clouds drifted between it and the sun. I descended alone towards the base of the mountain, making my way through a rugged gorge, the sides of which were strewn with pine-trees, splintered, broken across, and torn up by the roots. I finally reached the end of a glacier, formed by the snow and shattered ice which fall from the shoulders of the Jungfrau. The view from this place had a savage magnificence such as I had not previously beheld, and it was not without some slight feeling of awe that I clambered up the end of the glacier. It was the first I had actually stood upon. The loneliness of the place was very impressive, the silence being only broken by fitful gusts of wind, or by the weird rattle of the débris which fell at intervals from the melting ice.
AVALANCHES. 1856.
Once I noticed what appeared to be the sudden and enormous augmentation of the waters of a cascade, but the sound soon informed me that the increase was due to an avalanche which had chosen the track of the cascade for its rush. Soon afterwards my eyes were fixed upon a white slope some thousands of feet above me; I saw the ice give way, and, after a sensible interval, the thunder of another avalanche reached me. A kind of zigzag channel had been worn on the side of the mountain, and through this the avalanche rushed, hidden at intervals, and anon shooting forth, and leaping like a cataract down the precipices. The sound was sometimes continuous, but sometimes broken into rounded explosions which seemed to assert a passionate predominance over the general level of the roar. These avalanches, when they first give way, usually consist of enormous blocks of ice, which are more and more shattered as they descend. Partly to the echoes of the first crash, but mainly, I think, to the shock of the harder masses which preserve their cohesion, the explosions which occur during the descent of the avalanche are to be ascribed. Much of the ice is crushed to powder; and thus, when an avalanche pours cataract-like over a ledge, the heavier masses, being less influenced by the atmospheric resistance, shoot forward like descending rockets, leaving the lighter powder in trains behind them. Such is the material of which a class of the smaller glaciers in the Alps is composed. They are the products of avalanches, the crushed ice being recompacted into a solid mass, which exhibits on a smaller scale most of the characteristics of the large glaciers.
After three hours' absence I reascended to the hotel, breakfasted, and afterwards returned with Mr. Huxley to the glacier. While we were engaged upon it the weather suddenly changed; lightning flashed about the summits of the Jungfrau, and thunder "leaped" among her crags. Heavy rain fell, but it cleared up afterwards with magical speed, and we returned to our hotel. Heedless of the forebodings of many prophets of evil weather we set out for Grindelwald. The scene from the summit of the Little Scheideck was exceedingly grand. The upper air exhibited a commotion which we did not experience; clouds were wildly driven against the flanks of the Eiger, the Jungfrau thundered behind, while in front of us a magnificent rainbow, fixing one of its arms in the valley of Grindelwald, and, throwing the other right over the crown of the Wetterhorn, clasped the mountain in its embrace. Through jagged apertures in the clouds floods of golden light were poured down the sides of the mountain. On the slopes were innumerable chalets, glistening in the sunbeams, herds browsing peacefully and shaking their mellow bells; while the blackness of the pine-trees, crowded into woods, or scattered in pleasant clusters over alp and valley, contrasted forcibly with the lively green of the fields.
THE HEISSE PLATTE. 1856.
At Grindelwald, on the 18th, we engaged a strong and competent guide, named Christian Kaufmann, and proceeded to the Lower Glacier. After a steep ascent, we gained a point from which we could look down upon the frozen mass. At first the ice presented an appearance of utter confusion, but we soon reached a position where the mechanical conditions of the glacier revealed themselves, and where we might learn, had we not known it before, that confusion is merely the unknown intermixture of laws, and becomes order and beauty when we rise to their comprehension. We reached the so-called Eismeer—Ice Sea. In front of us was the range of the Viescherhörner, and a vast snow slope, from which one branch of the glacier was fed. Near the base of this névé, and surrounded on all sides by ice, lay a brown rock, to which our attention was directed as a place noted for avalanches; on this rock snow or ice never rests, and it is hence called the Heisse Platte—the Hot Plate. At the base of the rock, and far below it, the glacier was covered with clean crushed ice, which had fallen from a crown of frozen cliffs encircling the brow of the rock. One obelisk in particular signalised itself from all others by its exceeding grace and beauty. Its general surface was dazzling white, but from its clefts and fissures issued a delicate blue light, which deepened in hue from the edges inwards. It stood upon a pedestal of its own substance, and seemed as accurately fixed as if rule and plummet had been employed in its erection. [Fig. 1] represents this beautiful minaret of ice.
ICE MINARET. 1856.
While we were in sight of the Heisse Platte, a dozen avalanches rushed downwards from its summit. In most cases we were informed of the descent of an avalanche by the sound, but sometimes the white mass was seen gliding down the rock, and scattering its smoke in the air, long before the sound reached us. It is difficult to reconcile the insignificant appearance presented by avalanches, when seen from a distance, with the volume of sound which they generate; but on this day we saw sufficient to account for the noise. One block of solid ice which we found below the Heisse Platte measured 7 feet 6 inches in length, 5 feet 8 inches in height, and 4 feet 6 inches in depth. A second mass was 10 feet long, 8 feet high, and 6 feet wide. It contained therefore 480 cubic feet of ice, which had been cast to a distance of nearly 1000 yards down the glacier. The shock of such hard and ponderous projectiles against rocks and ice, reinforced by the echoes from the surrounding mountains, will appear sufficient to account for the peals by which their descent is accompanied.
ECHOES OF THE WETTERHORN. 1856.
A second day, in company with Dr. Hooker, completed the examination of this glacier in 1856; after which I parted from my friends, Mr. Huxley intending to rejoin me at the Grimsel. On the morning of the 20th of August I strapped on my knapsack and ascended the green slopes from Grindelwald towards the Great Scheideck. Before reaching the summit I frequently heard the wonderful echoes of the Wetterhorn. Some travellers were in advance of me, and to amuse them an alpine horn was blown. The direct sound was cut off from me by a hill, but the echoes talked down to me from the mountain walls. The sonorous waves arrived after one, two, three, and more reflections, diminishing gradually in intensity, but increasing in softness, as if in its wanderings from crag to crag the sound had undergone a kind of sifting process, leaving all its grossness behind, and returning in delightful flute notes to the ear.
Let us investigate this point a little. If two looking-glasses be placed perfectly parallel to each other, with a lighted candle between them, an infinite series of images of the candle will be seen at both sides, the images diminishing in brightness the further they recede. But if the looking-glasses, instead of being parallel, enclose an angle, a limited number of images only will be seen. The smaller the angle which the reflectors make with each other, or, in other words, the nearer they approach parallelism, the greater will be the number of images observed.
To find the number of images the following is the rule:—Divide 360, or the number of degrees in a circle, by the number of degrees in the angle enclosed by the two mirrors, the quotient will be one more than the number of images; or, counting the object itself, the quotient is always equal to the number of images plus the object. In [Fig. 2] I have given the number and position of the images produced by two mirrors placed at an angle of 45°. a b and b c mark the edges of the mirrors, and 0 represents the candle, which, for the sake of simplicity, I have placed midway between them. Fix one point of a pair of compasses at B, and with the distance B 0 sweep a circle:—all the images will be ranged upon the circumference of this circle. The number of images found by the foregoing rule is 7, and their positions are marked in the figure by the numbers 1, 2, 3, &c.
ECHOES EXPLAINED. 1856.
Suppose the ear to occupy the place of the eye, and that a sounding body occupies the place of the luminous one, we should then have just as many echoes as we had images in the former case. These echoes would diminish in loudness just as the images of the candle diminish in brightness. At each reflection a portion both of sound and light is lost; hence the oftener light is reflected the dimmer it becomes, and the oftener sound is reflected the fainter it is.
Now the cliffs of the Wetterhorn are so many rough angular reflectors of the sound: some of them send it back directly to the listener, and we have a first echo; some of them send it on to others from which it is again reflected, forming a second echo. Thus, by repeated reflection, successive echoes are sent to the ear, until, at length, they become so faint as to be inaudible. The sound, as it diminishes in intensity, appears to come from greater and greater distances, as if it were receding into the mountain solitudes; the final echoes being inexpressibly soft and pure.
REICHENBACH AND HANDECK. 1856.
After crossing the Scheideck I descended to Meyringen, visiting the Reichenbach waterfall on my way. A peculiarity of the descending water here is, that it is broken up in one of the basins into nodular masses, each of which in falling leaves the light foaming mass which surrounds it as a train in the air behind; the effect exactly resembles that of the avalanches of the Jungfrau, in which the more solid blocks of ice shoot forward in advance of the lighter débris, which is held back by the friction of the air.
Next day I ascended the valley of Hasli, and observed upon the rocks and mountains the action of ancient glaciers which once filled the valley to the height of more than a thousand feet above its present level. I paused, of course, at the waterfall of Handeck, and stood for a time upon the wooden bridge which spans the river at its top. The Aar comes gambolling down to the bridge from its parent glacier, takes one short jump upon a projecting ledge, boils up into foam, and then leaps into a chasm, from the bottom of which its roar ascends through the gloom. A rivulet named the Aarlenbach joins the Aar from the left in the very jaws of the chasm: falling, at first, upon a projection at some depth below the edge, and, rebounding from this, it darts at the Aar, and both plunge together like a pair of fighting demons to the bottom of the gorge. The foam of the Aarlenbach is white, that of the Aar is yellow, and this enables the observer to trace the passage of the one cataract through the other. As I stood upon the bridge the sun shone brightly upon the spray and foam; my shadow was oblique to the river, and hence a symmetrical rainbow could not be formed in the spray, but one half of a lovely bow, with its base in the chasm, leaned over against the opposite rocks, the colours advancing and retreating as the spray shifted its position. I had been watching the water intently for some time, when a little Swiss boy, who stood beside me, observed, in his trenchant German, "There plunge stones ever downwards." The stones were palpable enough, carried down by the cataract, and sometimes completely breaking loose from it, but I did not see them until my attention was withdrawn from the water.
HUT OF M. DOLLFUSS. 1856.
On my arrival at the Grimsel I found Mr. Huxley already there, and, after a few minutes' conversation, we decided to spend a night in a hut built by M. Dollfuss in 1846, beside the Unteraar glacier, about 2000 feet above the Hospice. We hoped thus to be able to examine the glacier to its origin on the following day. Two days' food and some blankets were sent up from the Hospice, and, accompanied by our guide, we proceeded to the glacier.
HÔTEL DES NEUFCHÂTELOIS. 1856.
Having climbed a great terminal moraine, and tramped for a considerable time amid loose shingle and boulders, we came upon the ice. The finest specimens of "tables" which I have ever seen are to be found upon this glacier—huge masses of clean granite poised on pedestals of ice. Here are also "dirt-cones" of the largest size, and numerous shafts, the forsaken passages of ancient "moulins," some filled with water, others simply with deep blue light. I reserve the description and explanation of both cones and moulins for another place. The surfaces of some of the small pools were sprinkled lightly over with snow, which the water underneath was unable to melt; a coating of snow granules was thus formed, flexible as chain armour, but so close that the air could not escape through it. Some bubbles which had risen through the water had lifted the coating here and there into little rounded domes, which, by gentle pressure, could be shifted hither and thither, and several of them collected into one. We reached the hut, the floor of which appeared to be of the original mountain slab; there was a space for cooking walled off from the sleeping-room, half of which was raised above the floor, and contained a quantity of old hay. The number 2404 mètres, the height, I suppose, of the place above the sea, was painted on the door, behind which were also the names of several well-known observers—Agassiz, Forbes, Desor, Dollfuss, Ramsay, and others—cut in the wood. A loft contained a number of instruments for boring, a surveyor's chain, ropes, and other matters. After dinner I made my way alone towards the junction of the Finsteraar and Lauteraar glaciers, which unite at the Abschwung to form the trunk stream of the Unteraar glacier. Upon the great central moraine which runs between the branches were perched enormous masses of rock, and, under the overhanging ledge of one of these, M. Agassiz had his Hôtel des Neufchâtelois. The rock is still there, bearing traces of names now nearly obliterated by the weather, while the fragments around also bear inscriptions. There in the wilderness, in the gray light of evening, these blurred and faded evidences of human activity wore an aspect of sadness. It was a temple of science now in ruins, and I a solitary pilgrim to the desecrated blocks. As the day declined, rain began to fall, and I turned my face towards my new home; where in due time we betook ourselves to our hay, and waited hopefully for the morning.
But our hopes were doomed to disappointment. A vast quantity of snow fell during the night, and, when we arose, we found the glacier covered, and the air thick with the descending flakes. We waited, hoping that it might clear up, but noon arrived and passed without improvement; our fire-wood was exhausted, the weather intensely cold, and, according to the men's opinion, hopelessly bad; they opposed the idea of ascending further, and we had therefore no alternative but to pack up and move downwards. What was snow at the higher elevations changed to rain lower down, and drenched us completely before we reached the Grimsel. But though thus partially foiled in our design, this visit taught us much regarding the structure and general phenomena of the glacier.
THE RHONE GLACIER. 1856.
The morning of the 24th was clear and calm: we rose with the sun, refreshed and strong, and crossed the Grimsel pass at an early hour. The view from the summit of the pass was lovely in the extreme; the sky a deep blue, the surrounding summits all enamelled with the newly-fallen snow, which gleamed with dazzling whiteness in the sunlight. It was Sunday, and the scene was itself a Sabbath, with no sound to disturb its perfect rest. In a lake which we passed the mountains were mirrored without distortion, for there was no motion of the air to ruffle its surface. From the summit of the Mayenwand we looked down upon the Rhone glacier, and a noble object it seemed,—I hardly know a finer of its kind in the Alps. Forcing itself through the narrow gorge which holds the ice cascade in its jaws, and where it is greatly riven and dislocated, it spreads out in the valley below in such a manner as clearly to reveal to the mind's eye the nature of the forces to which it is subjected. Longfellow's figure is quite correct; the glacier resembles a vast gauntlet, of which the gorge represents the wrist; while the lower glacier, cleft by its fissures into finger-like ridges, is typified by the hand.
Furnishing ourselves with provisions at the adjacent inn, we devoted some hours to the examination of the lower portion of the glacier. The dirt upon its surface was arranged in grooves as fine as if produced by the passage of a rake, while the laminated structure of the deeper ice always corresponded to the superficial grooving. We found several shafts, some empty, some filled with water. At one place our attention was attracted by a singular noise, evidently produced by the forcing of air and water through passages in the body of the glacier; the sound rose and fell for several minutes, like a kind of intermittent snore, reminding one of Hugi's hypothesis that the glacier was alive.
RINGS AROUND THE SUN. 1856.
We afterwards climbed to a point from which the whole glacier was visible to us from its origin to its end. Adjacent to us rose the mighty mass of the Finsteraarhorn, the monarch of the Oberland. The Galenstock was also at hand, while round about the névé of the glacier a mountain wall projected its jagged outline against the sky. At a distance was the grand cone of the Weisshorn, then, and I believe still, unscaled;[A] further to the left the magnificent peaks of the Mischabel; while between them, in savage isolation, stood the obelisk of the Matterhorn. Near us was the chain of the Furca, all covered with shining snow, while overhead the dark blue of the firmament so influenced the general scene as to inspire a sentiment of wonder approaching to awe. We descended to the glacier, and proceeded towards its source. As we advanced an unusual light fell upon the mountains, and looking upwards we saw a series of coloured rings, drawn like a vivid circular rainbow quite round the sun. Between the orb and us spread a thin veil of cloud on which the circles were painted; the western side of the veil soon melted away, and with it the colours, but the eastern half remained a quarter of an hour longer, and then in its turn disappeared. The crevasses became more frequent and dangerous as we ascended. They were usually furnished with overhanging eaves of snow, from which long icicles depended, and to tread on which might be fatal. We were near the source of the glacier, but the time necessary to reach it was nevertheless indefinite, so great was the entanglement of fissures. We followed one huge chasm for some hundreds of yards, hoping to cross it; but after half an hour's fruitless effort we found ourselves baffled and forced to retrace our steps.
SPIRIT OF THE BROCKEN. 1856.
The sun was sloping to the west, and we thought it wise to return; so down the glacier we went, mingling our footsteps with the tracks of chamois, while the frightened marmots piped incessantly from the rocks. We reached the land once more, and halted for a time to look upon the scene within view. The marvellous blueness of the sky in the earlier part of the day indicated that the air was charged, almost to saturation, with transparent aqueous vapour. As the sun sank the shadow of the Finsteraarhorn was cast through the adjacent atmosphere, which, thus deprived of the direct rays, curdled up into visible fog. The condensed vapour moved slowly along the flanks of the mountain, and poured itself cataract-like into the valley of the Rhone. Here it met the sun again, which reduced it once more to the invisible state. Thus, though there was an incessant supply from the generator behind, the fog made no progress; as in the case of the moving glacier, the end of the cloud-river remained stationary where consumption was equal to supply. Proceeding along the mountain to the Furca, we found the valley at the further side of the pass also filled with fog, which rose, like a wall, high above the region of actual shadow. Once on turning a corner an exclamation of surprise burst simultaneously from my companion and myself. Before each of us and against the wall of fog, stood a spectral image of a man, of colossal dimensions; dark as a whole, but bounded by a coloured outline. We stretched forth our arms; the spectres did the same. We raised our alpenstocks; the spectres also flourished their bâtons. All our actions were imitated by these fringed and gigantic shades. We had, in fact, the Spirit of the Brocken before us in perfection.
At the time here referred to I had had but little experience of alpine phenomena. I had been through the Oberland in 1850, but was then too ignorant to learn much from my excursion. Hence the novelty of this day's experience may have rendered it impressive: still even now I think there was an intrinsic grandeur in its phenomena which entitles the day to rank with the most remarkable that I have spent among the Alps. At the Furca, to my great regret, the joint ramblings of my friend and myself ended; I parted from him on the mountain side, and watched him descending, till the gray of evening finally hid him from my view.
FOOTNOTES:
[A] The Weisshorn was first scaled, by Tyndall, in 1861.—L. C. T.
THE TYROL. 1856.
THE TYROL.
(3.)
My subsequent destination was Vienna; but I wished to associate with my journey thither a visit to some of the glaciers of the Tyrol. At Landeck, on the 29th of August, I learned that the nearest glacier was that adjacent to the Gebatsch Alp, at the head of the Kaunserthal; and on the following morning I was on my way towards this valley. I sought to obtain a guide at Kaltebrunnen, but failed; and afterwards walked to the little hamlet of Feuchten, where I put up at a very lonely inn. My host, I believe, had never seen an Englishman, but he had heard of such, and remarked to me in his patois with emphasis, "Die Engländer sind die kühnsten Leute in dieser Welt." Through his mediation I secured a chamois-hunter, named Johann Auer, to be my guide, and next morning I started with this man up the valley. The sun, as we ascended, smote the earth and us with great power; high mountains flanked us on either side, while in front of us, closing the view, was the mass of the Weisskugel, covered with snow. At three o'clock we came in sight of the glacier, and soon afterwards I made the acquaintance of the Senner or cheesemakers of the Gebatsch Alp.
THE GEBATSCH ALP. 1856.
The chief of these was a fine tall fellow, with free, frank countenance, which, however, had a dash of the mountain wildness in it. His feet were bare, he wore breeches, and fragments of stockings partially covered his legs, leaving a black zone between the upper rim of the sock and the breeches. His feet and face were of the same swarthy hue; still he was handsome, and in a measure pleasant to look upon. He asked me what he could cook for me, and I requested some bread and milk; the former was a month old, the latter was fresh and delicious, and on these I fared sumptuously. I went to the glacier afterwards with my guide, and remained upon the ice until twilight, when we returned, guided by no path, but passing amid crags grasped by the gnarled roots of the pine, through green dells, and over bilberry knolls of exquisite colouring. My guide kept in advance of me singing a Tyrolese melody, and his song and the surrounding scene revived and realised all the impressions of my boyhood regarding the Tyrol.
Milking was over when we returned to the chalet, which now contained four men exclusive of myself and my guide. A fire of pine logs was made upon a platform of stone, elevated three feet above the floor; there was no chimney, as the smoke found ample vent through the holes and fissures in the sides and roof. The men were all intensely sunburnt, the legitimate brown deepening into black with beard and dirt. The chief senner prepared supper, breaking eggs into a dish, and using his black fingers to empty the shell when the albumen was refractory. A fine erect figure he was as he stood in the glowing light of the fire. All the men were smoking, and now and then a brand was taken from the fire to light a renewed pipe, and a ruddy glare flung thereby over the wild countenance of the smoker. In one corner of the chalet, and raised high above the ground, was a large bed, covered with clothes of the most dubious black-brown hue; at one end was a little water-wheel turned by a brook, which communicated motion to a churndash which made the butter. The beams and rafters were covered with cheeses, drying in the warm smoke. The senner, at my request, showed me his storeroom, and explained to me the process of making cheese, its interest to me consisting in its bearing upon the question of slaty cleavage. Three gigantic masses of butter were in the room, and I amused my host by calling them butter-glaciers. Soon afterwards a bit of cotton was stuck in a lump of grease, which was placed in a lantern, and the wick ignited; the chamois-hunter took it, and led the way to our resting-place, I having previously declined a good-natured invitation to sleep in the big black bed already referred to.
AN ALPINE CHALET. 1856.
There was a cowhouse near the chalet, and above it, raised on pillars of pine, and approached by a ladder, was a loft, which contained a quantity of dry hay: this my guide shook to soften the lumps, and erected an eminence for my head. I lay down, drawing my plaid over me, but Auer affirmed that this would not be a sufficient protection against the cold; he therefore piled hay upon me to the shoulders, and proposed covering up my head also. This, however, I declined, though the biting coldness of the air, which sometimes blew in upon us, afterwards proved to me the wisdom of the suggestion. Having set me right, my chamois-hunter prepared a place for himself, and soon his heavy breathing informed me that he was in a state of bliss which I could only envy. One by one the stars crossed the apertures in the roof. Once the Pleiades hung above me like a cluster of gems; I tried to admire them, but there was no fervour in my admiration. Sometimes I dozed, but always as this was about to deepen into positive sleep it was rudely broken by the clamour of a group of pigs which occupied the ground-floor of our dwelling. The object of each individual of the group was to secure for himself the maximum amount of heat, and hence the outside members were incessantly trying to become inside ones. It was the struggle of radical and conservative among the pachyderms, the politics being determined by the accident of position.
THE GEBATSCH GLACIER. 1856.
I rose at five o'clock on the 1st of September, and after a breakfast of black bread and milk ascended the glacier as far as practicable. We once quitted it, crossed a promontory, and descended upon one of its branches, which was flanked by some fine old moraines. We here came upon a group of seven marmots, which with yells of terror scattered themselves among the rocks. The points of the glacier beyond my reach I examined through a telescope; along the faces of the sections the lines of stratification were clearly shown; and in many places where the mass showed manifest signs of lateral pressure, I thought I could observe the cleavage passing though the strata. The point, however, was too important to rest upon an observation made from such a distance, and I therefore abstained from mentioning it subsequently. I examined the fissures and the veining, and noticed how the latter became most perfect in places where the pressure was greatest. The effect of oblique pressure was also finely shown: at one place the thrust of the descending glacier was opposed by the resistance offered by the side of the valley, the direction of the force being oblique to the side; the consequence was a structure nearly parallel to the valley, and consequently oblique to the thrust which I believe to be its cause.
A CHAMOIS ON THE ROCKS. 1856.
After five hours' examination we returned to our chalet, where we refreshed ourselves, put our things in order, and faced a nameless "Joch," or pass; our aim being to cross the mountains into the valley of Lantaufer, and reach Graun that evening. After a rough ascent over the alp we came to the dead crag, where the weather had broken up the mountains into ruinous heaps of rock and shingle. We reached the end of a glacier, the ice of which was covered by sloppy snow, and at some distance up it came upon an islet of stones and débris, where we paused to rest ourselves. My guide, as usual, ranged over the summits with his telescope, and at length exclaimed, "I see a chamois." The creature stood upon a cliff some hundreds of yards to our left, and seemed to watch our movements. It was a most graceful animal, and its life and beauty stood out in forcible antithesis to the surrounding savagery and death.
On the steep slopes of the glacier I was assisted by the hand of my guide. In fact, on this day I deemed places dangerous, and dreaded them as such, which subsequent practice enabled me to regard with perfect indifference; so much does what we call courage depend upon habit, or on the fact of knowing that we have really nothing to fear. Doubtless there are times when a climber has to make up his mind for very unpleasant possibilities, and even gather calmness from the contemplation of the worst; but in most cases I should say that his courage is derived from the latent feeling that the chances of safety are immensely in his favour.
PASSAGE OF A JOCH. 1856.
After a tough struggle we reached the narrow row of crags which form the crest of the pass, and looked into the world of mountain and cloud on the other side. The scene was one of stern grandeur—the misty lights and deep cloud-glooms being so disposed as to augment the impression of vastness which the scene conveyed. The breeze at the summit was exceedingly keen, but it gave our muscles tone, and we sprang swiftly downward through the yielding débris which here overlies the mountain, and in which we sometimes sank to the knees. Lower down we came once more upon the ice. The glacier had at one place melted away from its bounding cliff, which rose vertically to our right, while a wall of ice 60 or 80 feet high was on our left. Between the two was a narrow passage, the floor of which was snow, which I knew to be hollow beneath: my companion, however, was in advance of me, and he being the heavier man, where he trod I followed without hesitation. On turning an angle of the rock I noticed an expression of concern upon his countenance, and he muttered audibly, "I did not expect this." The snow-floor had, in fact, given way, and exposed to view a clear green lake, one boundary of which was a sheer precipice of rock, and the other the aforesaid wall of ice; the latter, however, curved a little at its base, so as to form a short steep slope which overhung the water. My guide first tried the slope alone; biting the ice with his shoe-nails, and holding on by the spike of his bâton, he reached the other side. He then returned, and, divesting myself of all superfluous clothes, as a preparation for the plunge which I fully expected, I also passed in safety. Probably the consciousness that I had water to fall into instead of pure space, enabled me to get across without anxiety or mischance; but had I, like my guide, been unable to swim, my feelings would have been far different.
This accomplished, we went swiftly down the valley, and the more I saw of my guide the more I liked him. He might, if he wished, have made his day's journey shorter by stopping before he reached Graun, but he would not do so. Every word he said to me regarding distances was true, and there was not the slightest desire shown to magnify his own labour. I learnt by mere accident that the day's work had cut up his feet, but his cheerfulness and energy did not bate a jot till he had landed me in the Black Eagle at Graun. Next morning he came to my room, and said that he felt sufficiently refreshed to return home. I paid him what I owed him, when he took my hand, and, silently bending down his head, kissed it; then, standing erect, he stretched forth his right hand, which I grasped firmly in mine, and bade him farewell; and thus I parted from Johann Auer, my brave and truthful chamois-hunter.
On the following day I met Dr. Frankland in the Finstermuntz pass, and that night we bivouacked together at Mals. Heavy rain fell throughout the night, but it came from a region high above that of liquidity. It was first snow, which, as it descended through the warmer strata of the atmosphere, was reduced to water. Overhead, in the air, might be traced a surface, below which the precipitate was liquid, above which it was solid; and this surface, intersecting the mountains which surround Mals, marked upon them a beautifully-defined snow-line, below which the pines were dark and the pastures green, but above which pines and pastures and crags were covered with the freshly-fallen snow.
THE STELVIO. 1856.
On the 2nd of September we crossed the Stelvio. The brown cone of the well-known Madatschspitze was clear, but the higher summits were clouded, and the fragments of sunshine which reached the lower world wandered like gleams of fluorescent light over the glaciers. COLOUR OF FRESH SNOW. 1856. Near the snow-line the partial melting of the snow had rendered it coarsely granular, but as we ascended it became finer, and the light emitted from its cracks and cavities a pure and deep blue. When a staff was driven into the snow low down the mountain, the colour of the light in the orifice was scarcely sensibly blue, but higher up this increased in a wonderful degree, and at the summit the effect was marvellous. I struck my staff into the snow, and turned it round and round; the surrounding snow cracked repeatedly, and flashes of blue light issued from the fissures. The fragments of snow that adhered to the staff were, by contrast, of a beautiful pink yellow, so that, on moving the staff with such fragments attached to it up and down, it was difficult to resist the impression that a pink flame was ascending and descending in the hole. As we went down the other side of the pass, the effect became more and more feeble, until, near the snow-line, it almost wholly disappeared.
We remained that night at the baths of Bormio, but the following afternoon being fine we wished to avail ourselves of the fair weather to witness the scene from the summit of the pass. Twilight came on before we reached Santa Maria, but a gorgeous orange overspread the western horizon, from which we hoped to derive sufficient light. It was a little too late when we reached the top, but still the scene was magnificent. A multitude of mountains raised their crowns towards heaven, while above all rose the snow-white cone of the Ortler. Far into the valley the giant stretched his granite limbs, until they were hid from us by darkness. As this deepened, the heavens became more and more crowded with stars, which blazed like gems over the heads of the mountains. At times the silence was perfect, unbroken save by the crackling of the frozen snow beneath our own feet; while at other times a breeze would swoop down upon us, keen and hostile, scattering the snow from the roofs of the wooden galleries in frozen powder over us. Long after night had set in, a ghastly gleam rested upon the summit of the Ortler, while the peaks in front deepened to a dusky neutral tint, the more distant ones being lost in gloom. We descended at a swift pace to Trafoi, which we reached before 11 p.m.
SINGULAR HAILSTORM. 1856.
Meran was our next resting-place, whence we turned through the Schnalzerthal to Unserfrau, and thence over the Hochjoch to Fend. From a religious procession we took a guide, who, though partly intoxicated, did his duty well. Before reaching the summit of the pass we were assailed by a violent hailstorm, each hailstone being a frozen cone with a rounded end. Had not their motion through the air something to do with the shape of these hailstones? The theory of meteorites now generally accepted is that they are small planetary bodies drawn to the earth by gravity, and brought to incandescence by friction against the earth's atmosphere. Such a body moving through the atmosphere must have condensed hot air in front of it, and rarefied cool air behind it; and the same is true to a small extent of a hailstone. This distribution of temperature must, I imagine, have some influence on the shape of the stone. Possibly also the stratified appearance of some hailstones may be connected with this action.[A]
THE HOCHJOCH AND FEND. 1856.
The hail ceased and the heights above us cleared as we ascended. At the top of the pass we found ourselves on the verge of a great névé, which lay between two ranges of summits, sloping down to the base of each range from a high and rounded centre: a wilder glacier scene I have scarcely witnessed. Wishing to obtain a more perfect view of the region, I diverged from the track followed by Dr. Frankland and the guide, and climbed a ridge of snow about half a mile to the right of them. A glorious expanse was before me, stretching itself in vast undulations, and heaping itself here and there into mountainous cones, white and pure, with the deep blue heaven behind them. Here I had my first experience of hidden crevasses, and to my extreme astonishment once found myself in the jaws of a fissure of whose existence I had not the slightest notice. Such accidents have often occurred to me since, but the impression made by the first is likely to remain the strongest. It was dark when we reached the wretched Wirthshaus at Fend, where, badly fed, badly lodged, and disturbed by the noise of innumerable rats, we spent the night. Thus ended my brief glacier expedition of 1856; and on the observations then made, and on subsequent experiments, was founded a paper presented to the Royal Society by Mr. Huxley and myself.[B]
FOOTNOTES:
[A] I take the following account of a grander storm of the above character from Hooker's 'Himalayan Journals,' vol. ii. p. 405.
"On the 20th (March, 1849) we had a change in the weather: a violent storm from the south-west occurred at noon, with hail of a strange form, the stones being sections of hollow spheres, half an inch across and upwards, formed of cones with truncated apices and convex bases: these cones were aggregated together with their bases outwards. The large masses were followed by a shower of the separate conical pieces, and that by heavy rain. On the mountains this storm was most severe: the stones lay at Darjeeling for seven days, congealed into masses of ice several feet long and a foot thick in sheltered places: at Purneah, fifty miles south, stones one and two inches across fell, probably as whole spheres."
[B] 'Phil. Trans.' 1857, pp. 327-346.—L. C. T.
THE LAKE OF GENEVA. 1857.
EXPEDITION OF 1857.
THE LAKE OF GENEVA.
(4.)
The time occupied in the observations of 1856 embraced about five whole days; and though these days were laborious and instructive, still so short a time proved to be wholly incommensurate with the claims of so wide a problem. During the subsequent experimental treatment of the subject, I had often occasion to feel the incompleteness of my knowledge, and hence arose the desire to make a second expedition to the Alps, for the purpose of expanding, fortifying, or, if necessary, correcting first impressions.
On Thursday, the 9th of July, 1857, I found myself upon the Lake of Geneva, proceeding towards Vevey. I had long wished to see the waters of this renowned inland sea, the colour of which is perhaps more interesting to the man of science than to the poets who have sung about it. Long ago its depth of blue excited attention, but no systematic examination of the subject has, so far as I know, been attempted. It may be that the lake simply exhibits the colour of pure water. Ice is blue, and it is reasonable to suppose that the liquid obtained from the fusion of ice is of the same colour; but still the question presses—"Is the blue of the Lake of Geneva to be entirely accounted for in this way?" The attempts which have been made to explain it otherwise show that at least a doubt exists as to the sufficiency of the above explanation.
BLUENESS OF THE WATER. 1857.
It is only in its deeper portions that the colour of the lake is properly seen. Where the bottom comes into view the pure effect of the water is disturbed; but where the water is deep the colour is deep: between Rolle and Nyon for example, the blue is superb. Where the blue was deepest, however, it gave me the impression of turbidity rather than of deep transparency. At the upper portion of the lake the water through which the steamer passed was of a blue green. Wishing to see the place where the Rhone enters the lake, I walked on the morning of the 10th from Villeneuve to Novelle, and thence through the woods to the river side. Proceeding along an embankment, raised to defend the adjacent land from the incursions of the river, an hour brought me to the place where it empties itself into the lake. The contrast between the two waters was very great: the river was almost white with the finely divided matter which it held in suspension; while the lake at some distance was of a deep ultramarine.
The lake in fact forms a reservoir where the particles held in suspension by the river have time to subside, and its waters to become pure. The subsidence of course takes place most copiously at the head of the lake; and here the deposit continues to form new land, adding year by year to the thousands of acres which it has already left behind it, and invading more and more the space occupied by the water. Innumerable plates of mica spangled the fine sand which the river brought down, and these, mixing with the water, and flashing like minute mirrors as the sun's rays fell upon them, gave the otherwise muddy stream a silvery appearance. Had I an opportunity I would make the following experiments:—
(a.) Compare the colour of the light transmitted by a column of the lake water fifteen feet long with that transmitted by a second column, of the same length, derived from the melting of freshly fallen mountain snow.
(b.) Compare in the same manner the colour of the ordinary water of the lake with that of the same water after careful distillation.
(c.) Strictly examine whether the light transmitted by the ordinary water contains an excess of red over that transmitted by the distilled water: this latter point, as will be seen farther on, is one of peculiar interest.
The length is fixed at fifteen feet, because I have found this length extremely efficient in similar experiments.
ATMOSPHERIC REFRACTION. 1857.
On returning to the pier at Villeneuve, a peculiar flickering motion was manifest upon the surface of the distant portions of the lake, and I soon noticed that the coast line was inverted by atmospheric refraction. It required a long distance to produce the effect: no trace of it was seen about the Castle of Chillon, but at Vevey and beyond it, the whole coast was clearly inverted; and the houses on the margin of the lake were also imaged to a certain height. Two boats at a considerable distance presented the appearance sketched in [Figs. 3 and 4]; the hull of each, except a small portion at the end, was invisible, but the sails seemed lifted up high in the air, with their inverted images below; as the boats drew nearer the hulls appeared inverted, the apparent height of the vessel above the surface of the lake being thereby nearly doubled, while the sails and higher objects, in these cases, were almost completely cut away. When viewed through a telescope the sensible horizon of the lake presented a billowy tumultuous appearance, fragments being incessantly detached from it and suspended in the air.
MIRAGE. 1857.
The explanation of this effect is the same as that of the mirage of the desert, which may be found in almost any book on physics, and which so tantalized the French soldiers in Egypt. They often mistook this aërial inversion for the reflection from a lake, and on trial found hot and sterile sand at the place where they expected refreshing waters. The effect was shown by Monge, one of the learned men who accompanied the expedition, to be due to the total reflection of very oblique rays at the upper surface of the layer of rarefied air which was nearest to the heated earth. A sandy plain, in the early part of the day, is peculiarly favourable for the production of such effects; and on the extensive flat strand which stretches between Mont St. Michel and the coast adjacent to Avranches in Normandy, I have noticed Mont Tombeline reflected as if glass instead of sand surrounded it and formed its mirror.