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+The Project Gutenberg EBook of The Glaciers of the Alps, by John Tyndall
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever. You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: The Glaciers of the Alps
+ Being a narrative of excursions and ascents, etc.
+
+Author: John Tyndall
+
+Release Date: November 2, 2010 [EBook #34192]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK THE GLACIERS OF THE ALPS ***
+
+
+
+
+Produced by Karl Eichwalder, Stephen H. Sentoff and the
+Online Distributed Proofreading Team at https://www.pgdp.net
+(This file was produced from images generously made
+available by The Internet Archive/Canadian Libraries)
+
+
+
+
+
+
+
+[Illustration: THE MER DE GLACE
+Showing the Cleft Station at Trelaporte, les Echelets, the Tacul, the
+Periades and the Grande Jorasse.]
+
+
+
+
+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.
+
+ Page
+ 1.--Introductory. 1
+
+ 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; Hotel des Neufchatelois; the
+ Rhone glacier from the Mayenwand; expedition up the glacier;
+ Coloured Rings round the sun; crevasses of the _neve_;
+ extraordinary meteorological phenomenon; Spirit of the
+ Brocken
+
+ 3.--The Tyrol. 23
+
+ 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
+
+ 6.--The Mer de Glace. 42
+
+ 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
+
+ 7. 46
+
+ Measurements commenced; the "Cleft Station" at Trelaporte;
+ Regelation of snow granules; two chamois; view of the Mer de
+ Glace and its Tributaries; _Seracs_ of the Col du Geant;
+ Sliding and Viscous theories; Rending of the ice; Striae on
+ its surface; White Ice-seams
+
+ 8. 57
+
+ Alone upon the glacier; Lakes and Rivulets; parallel between
+ Glacier and Geological disturbance; splendid rainbow; aspect
+ of the glacier at the base of the Seracs; visit to the Chief
+ Guide at Chamouni; Liberties granted
+
+ 9.--The Jardin. 61
+
+ Glacier du Talefre; Jardin divides the neve; Blue Veins near
+ the summit; surrounding scene; Moraines and Avalanches;
+ Cascade du Talefre; dangers on approaching it from above
+
+ 10. 64
+
+ 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; Seracs
+ of the Dome du Gouter; 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 Cote; 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
+
+ 12. 86
+
+ Life at the Montanvert; glacier "Blower;" Cascade of the
+ Talefre; difficulties in setting out lines; departure from
+ the Montanvert; my hosts; prospect from the Glacier des
+ Bois; Edouard Simond
+
+ 13.--Expedition of 1858. 92
+
+ 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
+
+ 15. 99
+
+ 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 AEggischhorn; Cloud Iridescences; the Aletsch
+ glacier; the Maerjelen 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 Gruenhorn
+ Luecke; Magnificent Corridor; sunrise; neve 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
+
+ 17. 119
+
+ Subsequent days at the AEggischhorn; 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 Goerner Glacier;
+ Roches Moutonnees; 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
+
+ 19. 133
+
+ The Rothe Kumm; pleasant companions; difficult descent;
+ temperatures of rock, air, and grass; Singular Cavern in the
+ ice; Structure and Stratification
+
+ 20.--The Goerner Grat and the Riffelhorn; Magnetic Phenomena. 137
+
+ Formation and Dissipation of clouds; Scene from the Goerner
+ 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
+
+ 21. 145
+
+ Fog on the Riffelberg; its dissipation; Sunset from the
+ Goerner Grat; Cloud-wreaths on the Matterhorn; Streamers of
+ Flame; grand Interference Phenomenon; investigation of
+ Structure; the Goernerhorn glacier; Western glacier of Monte
+ Rosa; the Schwarze, Trifti, and Theodule 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
+
+ 23. 160
+
+ 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 Fee glacier; Frozen dust on the
+ Mischabelhoerner; Snow, Vapour, and Cloud; curious effect on
+ the hearing; "a Terrible Hole;" singular group; a Song from
+ 'The Robbers'
+
+ 24. 168
+
+ 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 Seracs revisited; Crevasses and Crumples; bad weather;
+ thermometers placed at the Jardin; Avalanches of the
+ Talefre; 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
+
+ 26. 192
+
+ Hostility of Chief Guide; Proces 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; debris 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.
+
+ 1.--Light and Heat. 223
+
+ What is Light?--notion of the ancients; requires Time to
+ pass through Space; Roemer, 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.
+
+ 2.--Radiant Heat. 239
+
+ 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
+
+ 3.--Qualities of Heat. 241
+
+ 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
+
+ 5. 249
+
+ 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 Bruecke;
+ 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
+
+ 8.--The Moraines. 263
+
+ 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
+
+ Neve 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 Geant; motion of the Lechaud;
+ Squeezing of the Tributaries through the Neck of the valley
+ at Trelaporte; the Lechaud 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 Gruener; theory of De Saussure, or the
+ Sliding Theory; in part true; strained interpretation of
+ this theory
+
+ 14.--Rendu's Theory. 299
+
+ Character of Rendu; his Essay entitled 'Theorie 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 reservoirs_; 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
+
+ 15. 308
+
+ 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
+
+ 16.--Forbes's Theory. 311
+
+ 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
+
+ 17.--The Crevasses. 315
+
+ 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
+
+ 18. 325
+
+ Further considerations on Viscosity; Numerical Test;
+ formation of crevasses opposed to viscosity
+
+ 19.--Heat and Work. 328
+
+ 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
+
+ 20. 334
+
+ Papers presented to the Royal Society by Professor Forbes in
+ 1846; Capillary Hypothesis of glacier motion; hypothesis
+ examined
+
+ 21.--Thomson's Theory. 340
+
+ Statement of theory; influence of Pressure on the Melting
+ Point of Ice; difficulties of theory; Calculation of
+ requisite Pressure; Actual pressure insufficient
+
+ 22.--Pressure Theory. 346
+
+ 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
+
+ 23.--Regelation. 351
+
+ Faraday's first experiments; Freezing together of pieces of
+ ice at 32 deg.; 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
+
+ 25.--The Moulins. 362
+
+ 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 Flegere; 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 Geant. 413
+
+ Aspect of Seams; they sweep across the glacier concentric
+ with Structure; Structure at the base of the Talefre
+ cascade; Crumples; Scaling off by pressure; Origin of seams
+ of White Ice
+
+ 33. 419
+
+ Glacier du Geant 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
+
+ Summary 422
+
+ Appendix 427
+
+ Index 441
+
+
+
+
+ILLUSTRATIONS.
+
+
+ The Mer de Glace.--Showing the Cleft Station at Trelaporte,
+ the Echelets, the Tacul, the Periades, 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 Diffraction _To 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 Flegere _To face_ 367
+ 36. Ditto, as seen from les Charmoz " 368
+ 37. Ditto, as seen from the Cleft Station, Trelaporte " 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 Geant 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.
+
+[Sidenote: 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.
+
+[Sidenote: 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 laminae. 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.
+
+[Sidenote: 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 debris 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.
+
+[Sidenote: 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]
+
+[Sidenote: 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]
+
+[Sidenote: 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.
+
+[Sidenote: 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.
+
+
+
+
+[Sidenote: 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.
+
+[Sidenote: 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.
+
+[Sidenote: 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 debris which fell at intervals from
+the melting ice.
+
+[Sidenote: 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.
+
+[Sidenote: 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 Viescherhoerner, and a vast snow slope, from which
+one branch of the glacier was fed. Near the base of this _neve_, 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.
+
+[Sidenote: ICE MINARET. 1856.]
+
+[Illustration: Fig. 1. Ice Minaret.]
+
+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.
+
+[Sidenote: 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 deg. 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.
+
+[Illustration: Fig. 2. Diagram of an angular reflector.]
+
+[Sidenote: 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.
+
+[Sidenote: 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 debris, 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.
+
+[Sidenote: 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.
+
+[Sidenote: HOTEL DES NEUFCHATELOIS. 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 metres, 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 _Hotel des Neufchatelois_. 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.
+
+[Sidenote: 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.
+
+[Sidenote: 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 _neve_ 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.
+
+[Sidenote: 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
+batons. 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.
+
+
+
+
+[Sidenote: 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 Englaender sind die
+kuehnsten 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.
+
+[Sidenote: 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.
+
+[Sidenote: 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.
+
+[Sidenote: 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.
+
+[Sidenote: 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 debris, 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.
+
+[Sidenote: 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 debris 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 baton, 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.
+
+[Sidenote: THE STELVIO. 1856.]
+
+[Sidenote: COLOUR OF FRESH SNOW. 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. 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.
+
+[Sidenote: 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]
+
+[Sidenote: 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 _neve_, 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.
+
+
+
+
+[Sidenote: 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.
+
+[Sidenote: 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.
+
+[Illustration: Fig. 3, 4. Boats' sails inverted by Atmospheric
+Refraction.]
+
+[Sidenote: 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.
+
+[Sidenote: 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 aerial
+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.
+
+
+
+
+[Sidenote: CHAMOUNI AND THE MONTANVERT. 1857.]
+
+CHAMOUNI AND THE MONTANVERT.
+
+(5.)
+
+
+On the evening of the 12th of July I reached Chamouni; the weather was
+not quite clear, but it was promising; white cumuli had floated round
+Mont Blanc during the day, but these diminished more and more, and the
+light of the setting sun was of that lingering rosy hue which bodes good
+weather. Two parallel beams of a purple tinge were drawn by the shadows
+of the adjacent peaks, straight across the Glacier des Bossons, and the
+Glacier des Pelerins was also steeped for a time in the same purple
+light. Once when the surrounding red illumination was strong, the
+shadows of the Grands Mulets falling upon the adjacent snow appeared of
+a vivid green.
+
+This green belonged to the class of _subjective_ colours, or colours
+produced by contrast, about which a volume might be written. The eye
+received the impression of green, but the colour was not external to the
+eye. Place a red wafer on white paper, and look at it intently, it will
+be surrounded in a little time by a green fringe: move the wafer bodily
+away, and the entire space which it occupied upon the paper will appear
+green. A body may have its proper colour entirely masked in this way.
+Let a red wafer be attached to a piece of red glass, and from a
+moderately illuminated position let the sky be regarded through the
+glass; the wafer will appear of a vivid green. If a strong beam of light
+be sent through a red glass and caused to fall upon a screen, which at
+the same time is moderately illuminated by a separate source of white
+light, an opaque body placed in the path of the beam will cast a green
+shadow upon the screen which may be seen by several hundred persons at
+once. If a blue glass be used, the shadow will be yellow, which is the
+complementary colour to blue.
+
+[Sidenote: COLOURED SHADOWS. 1857.]
+
+When we suddenly pass from open sunlight to a moderately illuminated
+room, it appears dark at first, but after a little time the eye regains
+the power of seeing objects distinctly. Thus one effect of light upon
+the eye is to render it less sensitive, and light of any particular
+colour falling upon the eye blunts its appreciation of that colour. Let
+us apply this to the shadow upon the screen. This shadow is moderately
+illuminated by a jet of white light; but the space surrounding it is
+red, the effect of which upon the eye is to blind it in some degree to
+the perception of red. Hence, when the feeble white light of the shadow
+reaches the eye, the red component of this light is, as it were,
+abstracted from it, and the eye sees the residual colour, which is
+green. A similar explanation applies to the shadows of the Grands
+Mulets.
+
+On the 13th of July I was joined by my friend Mr. Thomas Hirst, and on
+the 14th we examined together the end of the Mer de Glace. In former
+times the whole volume of the Arveiron escaped from beneath the ice at
+the end of the glacier, forming a fine arch at its place of issue. This
+year a fraction only of the water thus found egress; the greater portion
+of it escaping laterally from the glacier at the summit of the rocks
+called _Les Mottets_, down which it tumbled in a fine cascade. The vault
+at the end of the glacier was nevertheless respectable, and rather
+tempting to a traveller in search of information regarding the structure
+of the ice. Perhaps, however, Nature meant to give me a friendly warning
+at the outset, for, while speculating as to the wisdom of entering the
+cavern, it suddenly gave way, and, with a crash which rivalled thunder,
+the roof strewed itself in ruins upon the floor.
+
+[Sidenote: SUNRISE AT CHAMOUNI. 1857.]
+
+Many years ago I had read with delight Coleridge's poem entitled
+'Sunrise in the Valley of Chamouni,' and to witness in all perfection
+the scene described by the poet, I waited at Chamouni a day longer than
+was otherwise necessary. On the morning of Wednesday, the 15th of July,
+I rose before the sun; Mont Blanc and his wondrous staff of Aiguilles
+were without a cloud; eastward the sky was of a pale orange which
+gradually shaded off to a kind of rosy violet, and this again blended by
+imperceptible degrees with the deep zenithal blue. The morning star was
+still shining to the right, and the moon also turned a pale face towards
+the rising day. The valley was full of music; from the adjacent woods
+issued a gush of song, while the sound of the Arve formed a suitable
+bass to the shriller melody of the birds. The mountain rose for a time
+cold and grand, with no apparent stain upon his snows. Suddenly the
+sunbeams struck his crown and converted it into a boss of gold. For some
+time it remained the only gilded summit in view, holding communion with
+the dawn while all the others waited in silence. These, in the order of
+their heights, came afterwards, relaxing, as the sunbeams struck each in
+succession, into a blush and smile.
+
+[Sidenote: GLACIER DES BOIS. 1857.]
+
+On the same day we had our luggage transported to the Montanvert, while
+we clambered along the lateral moraine of the glacier to the Chapeau.
+The rocks alongside the glacier were beautifully scratched and polished,
+and I paid particular attention to them, for the purpose of furnishing
+myself with a key to ancient glacier action. The scene to my right was
+one of the most wonderful I had ever witnessed. Along the entire slope
+of the Glacier des Bois, the ice was cleft and riven into the most
+striking and fantastic forms. It had not yet suffered much from the
+wasting influence of the summer weather, but its towers and minarets
+sprang from the general mass with clean chiselled outlines. Some stood
+erect, others leaned, while the white debris, strewn here and there over
+the glacier, showed where the wintry edifices had fallen, breaking
+themselves to pieces, and grinding the masses on which they fell to
+powder. Some of them gave way during our inspection of the place, and
+shook the valley with the reverberated noise of their fall. I
+endeavoured to get near them, but failed; the chasms at the margin of
+the glacier were too dangerous, and the stones resting upon the heights
+too loosely poised to render persistence in the attempt excusable.
+
+We subsequently crossed the glacier to the Montanvert, and I formally
+took up my position there. The rooms of the hotel were separated from
+each other by wooden partitions merely, and thus the noise of early
+risers in one room was plainly heard in the next. For the sake of quiet,
+therefore, I had my bed placed in the _chateau_ next door,--a little
+octagonal building erected by some kind and sentimental Frenchman, and
+dedicated "_a la Nature_." My host at first demurred, thinking the place
+not "_propre_," but I insisted, and he acquiesced. True the stone floor
+was dark with moisture, and on the walls a glistening was here and there
+observable, which suggested rheumatism, and other penalties, but I had
+had no experience of rheumatism, and trusted to the strength which
+mountain air and exercise were sure to give me, for power to resist its
+attacks. Moreover, to dispel some of the humidity, it was agreed that a
+large pine fire should be made there on necessary occasions.
+
+[Sidenote: QUARTERS AT THE MONTANVERT. 1857.]
+
+Though singularly favoured on the whole, still our residence at the
+Montanvert was sufficiently long to give us specimens of all kinds of
+weather; and thus my chateau derived an interest from the mutations of
+external nature. Sometimes no breath disturbed the perfect serenity of
+the night, and the moon, set in a black-blue sky, turned a face of
+almost supernatural brightness to the mountains, while in her absence
+the thick-strewn stars alone flashed and twinkled through the
+transparent air. Sometimes dull dank fog choked the valley, and heavy
+rain plashed upon the stones outside. On two or three occasions we were
+favoured by a thunderstorm, every peal of which broke into a hundred
+echoes, while the seams of lightning which ran through the heavens
+produced a wonderful intermittence of gloom and glare. And as I sat
+within, musing on the experiences of the day, with my pine logs
+crackling, and the ruddy fire-light gleaming over the walls, and lending
+animation to the visages sketched upon them with charcoal by the guides,
+I felt that my position was in every way worthy of a student of nature.
+
+
+
+
+THE MER DE GLACE.
+
+(6.)
+
+
+[Sidenote: A RIVER OF ICE. 1857.]
+
+The name "Mer de Glace" has doubtless led many who have never seen this
+glacier to a totally erroneous conception of its character. Misled
+probably by this term, a distinguished writer, for example, defines a
+glacier to be a sheet of ice spread out upon the slope of a mountain;
+whereas the Mer de Glace is indeed a _river_, and not a _sea_ of ice.
+But certain forms upon its surface, often noticed and described, and
+which I saw for the first time from the window of our hotel on the
+morning of the 16th of July, suggest at once the origin of the name. The
+glacier here has the appearance of a sea which, after it had been tossed
+by a storm, had suddenly stiffened into rest. The ridges upon its
+surface accurately resemble waves in shape, and this singular appearance
+is produced in the following way:--
+
+Some distance above the Montanvert--opposite to the Echelets--the
+glacier, in passing down an incline, is rent by deep fissures, between
+each two of which a ridge of ice intervenes. At first the edges of these
+ridges are sharp and angular, but they are soon sculptured off by the
+action of the sun. The bearing of the Mer de Glace being approximately
+north and south, the sun at mid-day shines down the glacier, or rather
+very obliquely across it; and the consequence is, that the fronts of the
+ridges, which look downward, remain in shadow all the day, while the
+backs of the ridges, which look up the glacier, meet the direct stroke
+of the solar rays. The ridges thus acted upon have their hindmost angles
+wasted off and converted into slopes which represent the _back_ of a
+wave, while the opposite sides of the ridges, which are protected from
+the sun, preserve their steepness, and represent the _front_ of the
+wave. Fig. 5 will render my meaning at once plain.
+
+[Sidenote: FROZEN WAVES. 1857.]
+
+[Illustration: Fig. 5. Wave-like forms on the Mer de Glace.]
+
+The dotted lines are intended to represent three of the ridges into
+which the glacier is divided, with their interposed fissures; the dots
+representing the boundaries of the ridges when the glacier is first
+broken. The parallel shading lines represent the direction of the sun's
+rays, which, falling obliquely upon the ridges, waste away the
+right-hand corners, and finally produce wave-like forms.
+
+We spent a day or two in making the general acquaintance of the glacier.
+On the 16th we ascended till we came to the rim of the Talefre basin,
+from which we had a good view of the glacier system of the region. The
+laminated structure of the ice was a point which particularly interested
+me; and as I saw the exposed sections of the _neve_, counted the lines
+of stratification, and compared these with the lines upon the ends of
+the secondary glaciers, I felt the absolute necessity either of
+connecting the veined _structure_ with the _strata_ by a continuous
+chain of observations, or of proving by ocular evidence that they were
+totally distinct from each other. I was well acquainted with the
+literature of the subject, but nothing that I had read was sufficient to
+prove what I required. Strictly speaking, nothing that had been written
+upon the subject rose above the domain of _opinion_, while I felt that
+without absolute _demonstration_ the question would never be set at
+rest.
+
+[Illustration: Fig. 6. Glacier Table.]
+
+[Sidenote: GLACIER TABLES. 1857.]
+
+On this day we saw some fine glacier tables; flat masses of rock, raised
+high upon columns of ice: Fig. 6 is a sketch of one of the finest of
+them. Some of them fell from their pedestals while we were near them,
+and the clean ice-surfaces which they left behind sparkled with minute
+stars as the small bubbles of air ruptured the film of water by which
+they were overspread. I also noticed that "petit bruit de crepitation,"
+to which M. Agassiz alludes, and which he refers to the rupture of the
+ice by the expansion of the air-bubbles contained within it. When I
+first read Agassiz's account of it, I thought it might be produced by
+the rupture of the minute air-bubbles which incessantly escape from the
+glacier. This, doubtless, produces an effect, but there is something in
+the character of the sound to be referred, I think, to a less obvious
+cause, which I shall notice further on.
+
+[Sidenote: FIRST SIGHT OF THE DIRT-BANDS. 1857.]
+
+At six P.M. this day I reached the Montanvert; and the same evening,
+wrapping my plaid around me, I wandered up towards Charmoz, and from its
+heights observed, as they had been observed fifteen years previously by
+Professor Forbes, the _dirt-bands_ of the Mer de Glace. They were
+different from any I had previously seen, and I felt a strong desire to
+trace them to their origin. Content, however, with the performance of
+the day, and feeling healthily tired by it, I lay down upon the bilberry
+bushes and fell asleep. It was dark when I awoke, and I experienced some
+difficulty and risk in getting down from the petty eminence referred to.
+
+The illumination of the glacier, as remarked by Professor Forbes, has
+great influence upon the appearance of the bands; they are best seen in
+a subdued light, and I think for the following reasons:--
+
+The dirt-bands are seen simply because they send less light to the eye
+than the cleaner portions of the glacier which lie between them; two
+surfaces, differently illuminated, are presented to the eye, and it is
+found that this difference is more observable when the light is that of
+evening than when it is that of noon.
+
+It is only within certain limits that the eye is able to perceive
+differences of intensity in different lights; beyond a certain
+intensity, if I may use the expression, light ceases to be light, and
+becomes mere pain. The naked eye can detect no difference in brightness
+between the electric light and the lime light, although, when we come
+to strict measurement, the former may possess many times the intensity
+of the latter. It follows from this that we might reduce the ordinary
+electric light to a fraction of its intensity, without any perceptible
+change of brightness to the naked eye which looks at it. But if we
+reduce the lime light in the same proportion the effect would be very
+different. This light lies much nearer to the limit at which the eye can
+appreciate differences of brightness, and its reduction might bring it
+quite within this limit, and make it sensibly dimmer than before. Hence
+we see that when two sources of intense light are presented to the eye,
+by reducing both the lights in the same proportion, the _difference_
+between them may become more perceptible.
+
+[Sidenote: BANDS SEEN BEST BY TWILIGHT. 1857.]
+
+Now the dirt-bands and the spaces between them resemble, in some
+measure, the two lights above mentioned. By the full glare of noon both
+are so strongly illuminated that the difference which the eye perceives
+is very small; as the evening advances the light of both is lowered in
+the same proportion, but the differential effect upon the eye is thereby
+augmented, and the bands are consequently more clearly seen.
+
+
+
+
+(7.)
+
+
+On Friday, the 17th of July, we commenced our measurements. Through the
+kindness of Sir Roderick Murchison, I found myself in the possession of
+an excellent five-inch theodolite, an instrument with the use of which
+both my friend Hirst and myself were perfectly familiar. We worked in
+concert for a few days to familiarize our assistant with the mode of
+proceeding, but afterwards it was my custom to simply determine the
+position where a measurement was to be made, and to leave the execution
+of it entirely to Mr. Hirst and our guide.
+
+On the 20th of July I made a long excursion up the glacier, examining
+the moraines, the crevasses, the structure, the moulins, and the
+disintegration of the surface. I was accompanied by a boy named Edouard
+Balmat,[A] and found him so good an iceman that I was induced to take
+him with me on the following day also.
+
+[Sidenote: THE CLEFT STATION. 1857.]
+
+Looking upwards from the Montanvert to the left of the Aiguille de
+Charmoz, a singular gap is observed in the rocky mountain wall, in the
+centre of which stands a detached column of granite. Both cleft and
+pillar are shown in the frontispiece, to the right. The eminence to the
+left of this gap is signalised by Professor Forbes as one of the best
+stations from which to view the Mer de Glace, and this point, which I
+shall refer to hereafter as the _Cleft Station_, it was now my desire to
+attain. From the Montanvert side a steep gully leads to the cleft; up
+this couloir we proposed to try the ascent. At a considerable height
+above the Mer de Glace, and closely hugging the base of the Aiguille de
+Charmoz, is the small Glacier de Tendue, shown in the frontispiece, and
+from which a steep slope stretches down to the Mer de Glace. This Tendue
+is the most _talkative_ glacier I have ever known; the clatter of the
+small stones which fall from it is incessant. Huge masses of granite
+also frequently fall upon the glacier from the cliffs above it, and,
+being slowly borne downwards by the moving ice, are at length seen
+toppling above the terminal face of the glacier. The ice which supports
+them being gradually melted, they are at length undermined, and sent
+bounding down the slope with peal and rattle, according as the masses
+among which they move are large or small. The space beneath the glacier
+is cumbered with blocks thus sent down; some of them of enormous size.
+
+[Sidenote: ROUGH ASCENT. 1857.]
+
+The danger arising from this intermittent cannonade, though in reality
+small, has caused the guides to swerve from the path which formerly led
+across the slope to the promontory of Trelaporte. I say "small,"
+because, even should a rock choose the precise moment at which a
+traveller is passing to leap down, the boulders at hand are so large and
+so capable of bearing a shock that the least presence of mind would be
+sufficient to place him in safety. But presence of mind is not to be
+calculated on under such circumstances, and hence the guides were right
+to abandon the path.
+
+Reaching the mouth of our gully after a rough ascent, we took to the
+snow, instead of climbing the adjacent rocks. It was moist and soft, in
+fact in a condition altogether favourable for the "regelation" of its
+granules. As the foot pressed upon it the particles became cemented
+together. A portion of the pressure was transmitted laterally, which
+produced attachments beyond the boundary of the foot; thus as the latter
+sank, it pressed upon a surface which became continually wider and more
+rigid, and at length sufficiently strong to bear the entire weight of
+the body; the pressed snow formed in fact a virtual _camel's foot_,
+which soon placed a limit to the sinking. It is this same principle of
+regelation which enables men to cross snow bridges in safety. By gentle
+cautious pressure the loose granules of the substance are cemented into
+a continuous mass, all sudden shocks which might cause the frozen
+surfaces to snap asunder being avoided. In this way an arch of snow
+fifteen or twenty inches in thickness may be rendered so firm that a
+man will cross it, although it may span a chasm one hundred feet in
+depth.
+
+As we ascended, the incline became very steep, and once or twice we
+diverged from the snow to the adjacent rocks; these were disintegrated,
+and the slightest disturbance was sufficient to bring them down; some
+fell, and from one of them I found it a little difficult to escape; for
+it grazed my leg, inflicting a slight wound as it passed. Just before
+reaching the cleft at which we aimed, the snow for a short distance was
+exceedingly steep, but we surmounted it; and I sat for a time beside the
+granite pillar, pleased to find that I could permit my legs to dangle
+over a precipice without prejudice to my head.
+
+[Sidenote: CHAMOIS ON THE MOUNTAINS. 1857.]
+
+While we remained here a chamois made its appearance upon the rocks
+above us. Deeming itself too near, it climbed higher, and then turned
+round to watch us. It was soon joined by a second, and the two formed a
+very pretty picture: their attitudes frequently changed, but they were
+always graceful; with head erect and horns curved back, a light limb
+thrown forward upon a ledge of rock, looking towards us with wild and
+earnest gaze, each seemed a type of freedom and agility. Turning now to
+the left, we attacked the granite tower, from which we purposed to scan
+the glacier, and were soon upon its top. My companion was greatly
+pleased--he was "tres-content" to have reached the place--he felt
+assured that many old guides would have retreated from that ugly gully,
+with its shifting shingle and debris, and his elation reached its climax
+in the declaration that, if I resolved to ascend Mont Blanc without a
+guide, he was willing to accompany me.
+
+[Sidenote: SCENE FROM THE STATION. 1857.]
+
+From the position which we had attained, the prospect was exceedingly
+fine, both of the glaciers and of the mountains. Beside us was the
+Aiguille de Charmoz, piercing with its spikes of granite the clear air.
+To my mind it is one of the finest of the Aiguilles, noble in mass, with
+its summits singularly cleft and splintered. In some atmospheric
+colourings it has the exact appearance of a mountain of cast copper, and
+the manner in which some of its highest pinnacles are bent, suggesting
+the idea of ductility, gives strength to the illusion that the mass is
+metallic. At the opposite side of the glacier was the Aiguille Verte,
+with a cloud poised upon its point: it has long been the ambition of
+climbers to scale this peak, and on this day it was attempted by a young
+French count with a long retinue of guides. He had not fair play, for
+before we quitted our position we heard the rumble of thunder upon the
+mountain, which indicated the presence of a foe more terrible than the
+avalanches themselves. Higher to the right, and also at the opposite
+side of the glacier, rose the Aiguille du Moine; and beyond was the
+basin of the Talefre, the ice cascade issuing from which appeared, from
+our position, like the foam of a waterfall. Then came the Aiguille de
+Lechaud, the Petite Jorasse, the Grande Jorasse, and the Mont Tacul; all
+of which form a cradle for the Glacier de Lechaud. Mont Mallet, the
+Periades, and the Aiguille Noire, came next, and then the singular
+obelisk of the Aiguille du Geant, from which a serrated edge of cliff
+descends to the summit of the "Col."
+
+[Sidenote: SERACS OF THE COL DU GEANT. 1857.]
+
+Over the slopes of the Col du Geant was spread a coverlet of shining
+snow, at some places apparently as smooth as polished marble, at others
+broken so as to form precipices, on the pale blue faces of which the
+horizontal lines of bedding were beautifully drawn. As the eye
+approaches the line which stretches from the Rognon to the Aiguille
+Noire, the repose of the _neve_ becomes more and more disturbed. Vast
+chasms are formed, which however are still merely indicative of the
+trouble in advance. If the glacier were lifted off we should probably
+see that the line just referred to would lie along the summit of a
+steep gorge; over this summit the glacier is pushed, and has its back
+periodically broken, thus forming vast transverse ridges which follow
+each other in succession down the slope. At the summit these ridges are
+often cleft by fissures transverse to them, thus forming detached towers
+of ice of the most picturesque and imposing character.[B] These towers
+often fall; and while some are caught upon the platforms of the cascade,
+others struggle with the slow energy of a behemoth through the debris
+which opposes them, reach the edges of the precipices which rise in
+succession along the fall, leap over, and, amid ice-smoke and
+thunder-peals, fight their way downwards.
+
+[Sidenote: GLACIER MOTION. 1857.]
+
+A great number of secondary glaciers were in sight hanging on the steep
+slopes of the mountains, and from them streams sped downwards, falling
+over the rocks, and filling the valley with a low rich music. In front
+of me, for example, was the Glacier du Moine, and I could not help
+feeling as I looked at it, that the arguments drawn from the deportment
+of such glaciers against the "sliding theory," and which are still
+repeated in works upon the Alps, militate just as strongly against the
+"viscous theory." "How," demands the antagonist of the sliding theory,
+"can a secondary glacier exist upon so steep a slope? why does it not
+slide down as an avalanche?" "But how," the person addressed may retort,
+"can a mass which you assume to be viscous exist under similar
+conditions? If it be viscous, what prevents it from rolling down?" The
+sliding theory assumes the lubrication of the bed of the glacier, but on
+this cold height the quantity melted is too small to lubricate the bed,
+and hence the slow motion of these glaciers. Thus a sliding-theory man
+might reason, and, if the external deportment of secondary glaciers were
+to decide the question, De Saussure might perhaps have the best of the
+argument.
+
+And with regard to the current idea, originated by M. de Charpentier,
+and adopted by Professor Forbes, that if a glacier slides it must slide
+as an avalanche, it may be simply retorted that, in part, _it does so_;
+but if it be asserted that an _accelerated motion_ is the necessary
+motion of an avalanche, the statement needs qualification. An avalanche
+on passing through a rough couloir soon attains a uniform velocity--its
+motion being accelerated only up to the point when the sum of the
+resistances acting upon it is equal to the force drawing it downwards.
+These resistances are furnished by the numberless asperities which the
+mass encounters, and which incessantly check its descent, and render an
+accumulation of motion impossible. The motion of a man walking down
+stairs may be on the whole uniform, but it is really made up of an
+aggregate of small motions, each of which is accelerated; and it is easy
+to conceive how a glacier moving over an uneven bed, when released from
+one opposing obstacle will be checked by another, and its motion thus
+rendered sensibly uniform.
+
+[Sidenote: MORAINES. 1857.]
+
+[Sidenote: TRIBUTARIES OF THE MER DE GLACE. 1857.]
+
+[Illustration: Fig. 7. Tributaries of the Mer de Glace.]
+
+From the Aiguille du Geant and Les Periades a glacier descended, which
+was separated by the promontory of La Noire from the glacier proceeding
+from the Col du Geant. A small moraine was formed between them, which is
+marked _a_ upon the diagram, Fig. 7. The great mass of the glacier
+descending from the Col du Geant came next, and this was bounded on the
+side nearest to Trelaporte by a small moraine _b_, the origin of which I
+could not see, its upper portion being shut out by a mountain
+promontory. Between the moraine _b_ and the actual side of the valley
+was another little glacier, derived from some of the lateral
+tributaries. It was, however, between the moraines _a_ and _b_ that the
+great mass of the Glacier du Geant really lay. At the promontory of the
+Tacul the lateral moraines of the Glacier des Periades and of the
+Glacier de Lechaud united to form the medial moraine _c_ of the Mer de
+Glace. Carrying the eye across the Lechaud, we had the moraine _d_
+formed by the union of the lateral moraines of the Lechaud and Talefre;
+further to the left was the moraine _e_, which came from the Jardin, and
+beyond it was the second lateral moraine of the Talefre. The Mer de
+Glace is formed by the confluence of the whole of the glaciers here
+named; being forced at Trelaporte through a passage, the width of which
+appears considerably less than that of the single tributary, the Glacier
+du Geant.
+
+In the ice near Trelaporte the blue veins of the glacier are beautifully
+shown; but they vary in distinctness according to the manner in which
+they are looked at. When regarded obliquely their colour is not so
+pronounced as when the vision plunges deeply into them. The weathered
+ice of the surface near Trelaporte could be cloven with great facility;
+I could with ease obtain plates of it a quarter of an inch thick, and
+possessing two square feet of surface. On the 28th of July I followed
+the veins several times from side to side across the Geant portion of
+the Mer de Glace; starting from one side, and walking along the veins,
+my route was directed obliquely downwards towards the axis of the
+tributary. At the axis I was forced to turn, in order to keep along the
+veins, and now ascended along a line which formed nearly the same angle
+with the axis at the other side. Thus the veins led me as it were along
+the two sides of a triangle, the vertex of which was near the centre of
+the glacier. The vertex was, however, in reality rounded off, and the
+figure rather resembled a hyperbola, which tended to coincidence with
+its asymptotes. This observation corroborates those of Professor Forbes
+with regard to the position of the veins, and, like him, I found that at
+the centre the veining, whose normal direction would be transverse to
+the glacier, was contorted and confused.
+
+[Sidenote: WASTING OF ICE. 1857.]
+
+Near the side of the Glacier du Geant, above the promontory of
+Trelaporte, the ice is rent in a remarkable manner. Looking upwards from
+the lower portions of the glacier, a series of vertical walls, rising
+apparently one above the other, face the observer. I clambered up among
+these singular terraces, and now recognise, both from my sketch and
+memory, that their peculiar forms are due to the same action as that
+which has given their shape to the "billows" of the Mer de Glace. A
+series of profound crevasses is first formed. The Glacier du Geant
+deviates 14 deg. from the meridian line, and hence the sun shines nearly
+down it during the middle portion of each day. The backs of the ridges
+between the crevasses are thus rounded off, one boundary of each fissure
+is destroyed, or at least becomes a mere steep declivity, while the
+other boundary being shaded from the sun preserves its verticality; and
+thus a very curious series of precipices is formed.
+
+Through all this dislocation, the little moraine on which I have placed
+the letter _b_ in the sketch maintains its right to existence, and under
+it the laminated structure of this portion of the glacier appears to
+reach its most perfect development. The moraine was generally a mere
+dirt track, but one or two immense blocks of granite were perched upon
+it. I examined the ice underneath one of these, being desirous of seeing
+whether the pressure resulting from its enormous weight would produce a
+veining, but the result was not satisfactory. Veins were certainly to be
+seen in directions different from the normal ones, but whether they were
+due to the bending of the latter, or were directly owing to the pressure
+of the block, I could not say. The sides of a stream which had cut a
+deep gorge in the clean ice of the Glacier du Geant afforded a fine
+opportunity of observing the structure. It was very remarkable--highly
+significant indeed in a theoretic point of view. Two long and
+remarkably deep blue veins traversed the bottom of the stream, and
+bending upwards at a place where the rivulet curved, drew themselves
+like a pair of parallel lines upon the clean white ice. But the general
+structure was of a totally different character; it did not consist of
+long bars, but approximated to the lenticular form, and was, moreover,
+of a washy paleness, which scarcely exceeded in depth of colouring the
+whitish ice around.
+
+[Sidenote: GROOVES ON THE SURFACE. 1857.]
+
+To the investigator of the structure nothing can be finer than the
+appearance of the glacier from one of the ice terraces cut in the
+Glacier du Geant by its passage round Trelaporte. As far as the vision
+extended the dirt upon the surface of the ice was arranged in striae.
+These striae were not always straight lines, nor were they unbroken
+curves. Within slight limits the various parts into which a glacier is
+cut up by its crevasses enjoy a kind of independent motion. The grooves,
+for example, on two ridges which have been separated by a small fissure,
+may one day have their striae perfect continuations of each other, but in
+a short time this identity of direction may be destroyed by a difference
+of motion between the ridges. Thus it is that the grooves upon the
+surface above Trelaporte are bent hither and thither, a crack or seam
+always marking the point where their continuity is ruptured. This
+bending occurs, however, within limits sufficiently small to enable the
+striae to preserve the same general direction.
+
+[Sidenote: SEAMS OF WHITE ICE. 1857.]
+
+My attention had often been attracted this day by projecting masses of
+what at first appeared to be pure white snow, rising in seams above the
+general surface of the glacier. On examination, however, I found them to
+be compact ice, filled with innumerable air-cells, and so resistant as
+to maintain itself in some places at a height of four feet above the
+general level. When amongst the ridges they appeared discontinuous and
+confused, being scattered apparently at random over the glacier; but
+when viewed from a sufficient distance, the detached parts showed
+themselves to belong to a system of white seams which swept quite across
+the Glacier du Geant, in a direction concentric with the structure.
+Unable to account for these singular seams, I climbed up among the
+tributary glaciers on the Rognon side of the Glacier du Geant, and
+remained there until the sun sank behind the neighbouring peaks, and the
+fading light warned me that it was time to return.
+
+
+FOOTNOTES:
+
+[A] "Le petit Balmat" my host always called him.
+
+[B] To such towers the name _Seracs_ is applied. In the chalets of
+Savoy, after the richer curd has been precipitated by rennet, a stronger
+acid is used to throw down what remains; an inferior kind of cheese
+called _Serac_ is thus formed, the shape and colour of which have
+suggested the application of the term to the cubical masses of ice.
+
+
+
+
+(8.)
+
+
+Early on the following day I was again upon the ice. I first confined
+myself to the right side of the Glacier du Geant, and found that the
+veins of white ice which I had noticed on the previous day were
+exclusively confined to this glacier, or to the space between the
+moraines _a_ and _b_ (Fig. 7), bending up so that the moraine _a_
+between the Glacier du Geant and the Glacier des Periades was tangent to
+them. At a good distance up the glacier I encountered a considerable
+stream rushing across it almost from side to side. I followed the
+rivulet, examining the sections which it exposed. At a certain point
+three other streams united, and formed at their place of confluence a
+small green lake. From this a rivulet rushed, which was joined by the
+stream whose track I had pursued, and at this place of junction a second
+green lake was formed, from which flowed a stream equal in volume to the
+sum of all the tributaries. It entered a crevasse, and took the bottom
+of the fissure for its bed. Standing at the entrance of the chasm, a low
+muffled thunder resounding through the valley attracted my attention. I
+followed the crevasse, which deepened and narrowed, and, by the blue
+light of the ice, could see the stream gambolling along its bottom, and
+flashing as it jumped over the ledges which it encountered in its way.
+The fissure at length came to an end: placing a foot on each side of it,
+and withholding the stronger light from my eyes, I looked down between
+its shining walls, and saw the stream plunge into a shaft which carried
+it to the bottom of the glacier.
+
+Slowly, and in zigzag fashion, as the crevasses demanded, I continued to
+ascend, sometimes climbing vast humps of ice from which good views of
+the surrounding glacier were obtained; sometimes hidden in the hollows
+between the humps, in which also green glacier tarns were often formed,
+very lonely and very beautiful.
+
+[Sidenote: A LAKE SET FREE. 1857.]
+
+While standing beside one of these, and watching the moving clouds which
+it faithfully mirrored, I heard the sound of what appeared to be a
+descending avalanche, but the time of its continuance surprised me.
+Looking through my opera-glass in the direction of the sound, I saw
+issuing from the end of a secondary glacier on the Tacul side a torrent
+of what appeared to me to be stones and mud. I could see the stones and
+finer debris jumping down the declivities, and shaping themselves into
+singular cascades. The noise continued for a quarter of an hour, after
+which the torrent rapidly diminished, until, at length, the ordinary
+little stream due to the melting of the glacier alone remained. A
+subglacial lake had burst its boundary, and carried along with it in its
+rush downwards the debris which it met with in its course.
+
+[Sidenote: IMPRESSIVE SCENE. 1857.]
+
+In some places I found the crevasses difficult, the ice being split in a
+very singular manner. Vast plates of it not more than a foot in
+thickness were sometimes detached from the sides of the crevasses, and
+stood alone. I was now approaching the base of the _seracs_, and the
+glacier around me still retained a portion of the turbulence of the
+cascade. I halted at times amid the ruin and confusion, and examined
+with my glass the cascade itself. It was a wild and wonderful scene,
+suggesting throes of spasmodic energy, though, in reality, all its
+dislocation had been _slowly_ and _gradually_ produced. True, the
+stratified blocks which here and there cumbered the terraces suggested
+_debacles_, but these were local and partial, and did not affect
+the general question. There is scarcely a case of geological
+disturbance which could not be matched with its analogue upon the
+glaciers,--contortions, faults, fissures, joints, and dislocations,--but
+in the case of the ice we can prove the effects to be due to
+slowly-acting causes; how reasonable is it then to ascribe to the
+operation of similar causes, which have had an incomparably longer time
+to work, many geological effects which at first sight might suggest
+sudden convulsion!
+
+Wandering slowly upwards, successive points of attraction drawing me
+almost unconsciously on, I found myself as the day was declining deep in
+the entanglements of the ice. A shower commenced, and a splendid rainbow
+threw an oblique arch across the glacier. I was quite alone; the scene
+was exceedingly impressive, and the possibility of difficulties on which
+I had not calculated intervening between me and the lower glacier, gave
+a tinge of anxiety to my position. I turned towards home; crossed some
+bosses of ice and rounded others; I followed the tracks of streams which
+were very irregular on this portion of the glacier, bending hither and
+thither, rushing through deep-cut channels, falling in cascades and
+expanding here and there to deep green lakes; they often plunged into
+the depths of the ice, flowed under it with hollow gurgle, and
+reappeared at some distant point. I threaded my way cautiously amid
+systems of crevasses, scattering with my axe, to secure a footing, the
+rotten ice of the sharper crests, which fell with a ringing sound into
+the chasms at either side. Strange subglacial noises were sometimes
+heard, as if caverns existed underneath, into which blocks of ice fell
+at intervals, transmitting the shock of their fall with a dull boom to
+the surface of the glacier. By the steady surmounting of difficulties
+one after another, I at length placed them all behind me, and afterwards
+hastened swiftly along the glacier to my mountain home.
+
+[Sidenote: CHAMOUNI RULES. 1857.]
+
+On the 30th incessant rain confined us to indoor work; on the 31st we
+determined the velocity with which the glacier is forced through the
+entrance of the trunk valley at Trelaporte, and also the motion of the
+Grand Moulin. We also determined both the velocity and the width of the
+Glacier du Geant. The 1st of August was spent by me at the cascade of
+the Talefre, examining the structure, crumpling, and scaling off of the
+ice. Finding that the rules at Chamouni put an unpleasant limit to my
+demands on my guide Simond, I visited the Guide Chef on the 2nd of
+August, and explained to him the object of my expedition, pointing out
+the inconvenience which a rigid application of the rules made for
+tourists would impose upon me. He had then the good sense to acknowledge
+the reasonableness of my remarks, and to grant me the liberty I
+requested. The 3rd of August was employed in determining the velocity
+and width of the Glacier de Lechaud, and in observations on the
+lamination of the glacier.
+
+
+
+
+[Sidenote: THE JARDIN. 1857.]
+
+THE JARDIN.
+
+(9.)
+
+
+[Sidenote: A RESERVOIR OF ICE. 1857.]
+
+On the 4th of August, with a view of commencing a series of observations
+on the inclinations of the Mer de Glace and its tributaries, we had our
+theodolite transported to the _Jardin_, which, as is well known, lies
+like an island in the middle of the Glacier du Talefre. We reached the
+place by the usual route, and found some tourists reposing on the soft
+green sward which covers the lower portion, and to which, and the
+flowers which spangle it, the place owes its name. Towards the summit of
+the Jardin, a rock jutted forward, apparently the very apex of the
+place, or at least hiding by its prominence everything that might exist
+behind it; leaving our guide with the instrument, we aimed at this, and
+soon left the grass and flowers behind us. Stepping amid broken
+fragments of rock, along slopes of granite, with fat felspar crystals
+which gave the boots a hold, and crossing at intervals patches of snow,
+which continued still to challenge the summer heat, I at length found
+myself upon the peak referred to; and, although it was not the highest,
+the unimpeded view which it commanded induced me to get astride it. The
+Jardin was completely encircled by the ice of the glacier, and this was
+held in a mountain basin, which was bounded all round by a grand and
+cliffy rim. The outline of the dark brown crags--a deeply serrated and
+irregular line--was forcibly drawn against the blue heaven, and still
+more strongly against some white and fleecy clouds which lay here and
+there behind it; while detached spears and pillars of rock, sculptured
+by frost and lightning, stood like a kind of defaced statuary along the
+ridge. All round the basin the snow reared itself like a buttress
+against the precipitous cliffs, being streaked and fluted by the descent
+of blocks from the summits. This mighty tub is the collector of one of
+the tributaries of the Mer de Glace. According to Professor Forbes, its
+greatest diameter is 4200 yards, and out of it the half-formed ice is
+squeezed through a precipitous gorge about 700 yards wide, forming there
+the ice cascade of the Talefre. Bounded on one side by the Grande
+Jorasse, and on the other by Mont Mallet, the principal tributary of the
+Glacier de Lechaud lay white and pure upon the mountain slope. Round
+further to the right we had the vast plateau whence the Glacier du Geant
+is fed, fenced on the left by the Aiguille du Geant and the Aiguille
+Noire, and on the right by the Monts Maudits and Mont Blanc. The scene
+was a truly majestic one. The mighty Aiguilles piercing the sea of air,
+the soft white clouds floating here and there behind them; the shining
+snow with its striped faults and precipices; the deep blue firmament
+overhead; the peals of avalanches and the sound of water;--all conspired
+to render the scene glorious, and our enjoyment of it deep.
+
+A voice from above hailed me as I moved from my perch; it was my friend,
+who had found a lodgment upon the edge of a rock which was quite
+detached from the Jardin, being the first to lift its head in opposition
+to the descending _neve_. Making a detour round a steep concave slope of
+the glacier, I reached the flat summit of the rock. The end of a ridge
+of ice abutted against it, which was split and bent by the pressure so
+as to form a kind of arch. I cut steps in the ice, and ascended until I
+got beneath the azure roof. Innumerable little rills of pellucid water
+descended from it. Some came straight down, clear for a time, and
+apparently motionless, rapidly tapering at first, and more slowly
+afterwards, until, at the point of maximum contraction, they resolved
+themselves into strings of liquid pearls which pattered against the ice
+floor underneath. Others again, owing to the directions of the little
+streamlets of which they were constituted, formed spiral figures of
+great beauty: one liquid vein wound itself round another, forming a
+spiral protuberance, and owing to the centrifugal motion thus imparted,
+the vein, at its place of rupture, scattered itself laterally in little
+liquid spherules.[A] Even at this great elevation the structure of the
+ice was fairly developed, not with the sharpness to be observed lower
+down, but still perfectly decided. Blue bands crossed the ridge of ice
+to which I have referred, at right angles to the direction of the
+pressure.
+
+[Sidenote: MORAINES OF THE TALEFRE. 1857.]
+
+I descended, and found my friend beneath an overhanging rock.
+Immediately afterwards a peal like that of thunder shook the air, and
+right in front of us an avalanche darted down the brown cliffs, then
+along a steep slope of snow which reared itself against the mountain
+wall, carrying with it the debris of the rocks over which it passed,
+until it finally lay a mass of sullied rubbish at the base of the
+incline: the whole surface of the Talefre is thus soiled. Another peal
+was heard immediately afterwards, but the avalanche which caused it was
+hidden from us by a rocky promontory. From this same promontory the
+greater portion of the medial moraine which descends the cascade of the
+Talefre is derived, forming at first a gracefully winding curve, and
+afterwards stretching straight to the summit of the fall. In the chasms
+of the cascade its boulders are engulfed, but the lost moraine is
+restored below the fall, as if disgorged by the ice which had swallowed
+it. From the extremity of the Jardin itself a mere driblet of a moraine
+proceeds, running parallel to the former, and like it disappearing at
+the summit of the cascade.
+
+[Sidenote: AMONG THE CREVASSES. 1857.]
+
+We afterwards descended towards the cascade, but long before this is
+attained the most experienced iceman would find himself in difficulty.
+Transverse crevasses are formed, which follow each other so speedily as
+to leave between them mere narrow ridges of ice, along which we moved
+cautiously, jumping the adjacent fissures, or getting round them, as the
+case demanded. As we approached the jaws of the gorge, the ridges
+dwindled to mere plates and wedges, which being bent and broken by the
+lateral pressure, added to the confusion, and warned us not to advance.
+The position was in some measure an exciting one. Our guide had never
+been here before; we were far from the beaten track, and the riven
+glacier wore an aspect of treacherous hostility. As at the base of the
+_seracs_, a subterranean noise sometimes announced the falling of
+ice-blocks into hollows underneath, the existence of which the resonant
+concussion of the fallen mass alone revealed. There was thus a dash of
+awe mingled with our thoughts; a stirring up of the feelings which
+troubled the coolness of the intellect. We finally swerved to the right,
+and by a process the reverse of straightforward reached the Couvercle.
+Nightfall found us at the threshold of our hotel.
+
+
+FOOTNOTES:
+
+[A] The recent hydraulic researches of Professor Magnus furnish some
+beautiful illustrations of this action.
+
+
+
+
+(10.)
+
+
+[Sidenote: ROUND HAILSTONES. 1857.]
+
+[Sidenote: A DANGEROUS LEAP. 1857.]
+
+On the 5th we were engaged for some time in an important measurement at
+the Tacul. We afterwards ascended towards the _seracs_, and determined
+the inclinations of the Glacier du Geant downwards. Dense cloud-masses
+gathered round the points of the Aiguilles, and the thunder bellowed at
+intervals from the summit of Mont Blanc. As we descended the Mer de
+Glace the valley in front of us was filled with a cloud of pitchy
+darkness. Suddenly from side to side this field of gloom was riven by a
+bar of lightning of intolerable splendour; it was followed by a peal of
+commensurate grandeur, the echoes of which leaped from cliff to cliff
+long after the first sound had died away. The discharge seemed to unlock
+the clouds above us, for they showered their liquid spheres down upon us
+with a momentum like that of swan-shot: all the way home we were
+battered by this pellet-like rain. On the 6th the rain continued with
+scarcely any pause; on the 7th I was engaged all day upon the Glacier du
+Geant; on the morning of the 8th heavy hail had fallen there, the stones
+being perfect spheres; the rounded rain-drops had solidified during
+their descent without sensible change of form. When this hail was
+squeezed together, it exactly resembled a mass of oolitic limestone
+which I had picked up in 1853 near Blankenburg in the Hartz. Mr. Hirst
+and myself were engaged together this day taking the inclinations: he
+struck his theodolite at the Angle, and went home accompanied by Simond,
+and the evening being extremely serene, I pursued my way down the centre
+of the glacier towards the Echelets. The crevasses as I advanced became
+more deep and frequent, the ridges of ice between them becoming
+gradually narrower. They were very fine, their downward faces being
+clear cut, perfectly vertical, and in many cases beautifully veined.
+Vast plates of ice moreover often stood out midway between the walls of
+the chasms, as if cloven from the glacier and afterwards set on edge.
+The place was certainly one calculated to test the skill and nerve of an
+iceman; and as the day drooped, and the shadow in the valley deepened, a
+feeling approaching to awe took possession of me. My route was an
+exaggerated zigzag; right and left amid the chasms wherever a hope of
+progress opened; and here I made the experience which I have often
+repeated since, and laid to heart as regards intellectual work also,
+that enormous difficulties may be overcome when they are attacked in
+earnest. Sometimes I found myself so hedged in by fissures that escape
+seemed absolutely impossible; but close and resolute examination so
+often revealed a means of exit, that I felt in all its force the brave
+verity of the remark of Mirabeau, that the word "impossible" is a mere
+blockhead of a word. It finally became necessary to reach the shore, but
+I found this a work of extreme difficulty. At length, however, it became
+pretty evident that, if I could cross a certain crevasse, my retreat
+would be secured. The width of the fissure seemed to be fairly within
+jumping distance, and if I could have calculated on a safe purchase for
+my foot I should have thought little of the spring; but the ice on the
+edge from which I was to leap was loose and insecure, and hence a kind
+of nervous thrill shot through me as I made the bound. The opposite side
+was fairly reached, but an involuntary tremor shook me all over after I
+felt myself secure. I reached the edge of the glacier without further
+serious difficulty, and soon after found myself steeped in the creature
+comforts of our hotel.
+
+On Monday, August 10th, I had the great pleasure of being joined by my
+friend Huxley; and though the weather was very unpromising, we started
+together up the glacier, he being desirous to learn something of its
+general features, and, if possible, to reach the Jardin. We reached the
+Couvercle, and squeezed ourselves through the Egralets; but here the
+rain whizzed past us, and dense fog settled upon the cascade of the
+Talefre, obscuring all its parts. We met Mr. Galton, the African
+traveller, returning from an attempt upon the Jardin; and learning that
+his guides had lost their way in the fog, we deemed it prudent to
+return.
+
+The foregoing brief notes will have informed the reader that at the
+period of Mr. Huxley's arrival I was not without due training upon the
+ice; I may also remark, that on the 25th of July I reached the summit
+of the Col du Geant, accompanied by the boy Balmat, and returned to the
+Montanvert on the same day. My health was perfect, and incessant
+practice had taught me the art of dealing with the difficulties of the
+ice. From the time of my arrival at the Montanvert the thought of
+ascending Mont Blanc, and thus expanding my knowledge of the glaciers,
+had often occurred to me, and I think I was justified in feeling that
+the discipline which both my friend Hirst and myself had undergone ought
+to enable us to accomplish the journey in a much more modest way than
+ordinary. I thought a single guide sufficient for this purpose, and I
+was strengthened in this opinion by the fact that Simond, who was a man
+of the strictest prudence, and who at first declared four guides to be
+necessary, had lowered his demand first to two, and was now evidently
+willing to try the ascent with us alone.
+
+[Sidenote: PREPARATIONS FOR A CLIMB. 1857.]
+
+On mentioning the thing to Mr. Huxley he at once resolved to accompany
+us. On the 11th of August the weather was exceedingly fine, though the
+snow which had fallen during the previous days lay thick upon the
+glacier. At noon we were all together at the Tacul, and the subject of
+attempting Mont Blanc was mooted and discussed. My opinion was that it
+would be better to wait until the fresh snow which loaded the mountain
+had disappeared; but the weather was so exquisite that my friends
+thought it best to take advantage of it. We accordingly entered into an
+agreement with our guide, and immediately descended to make preparations
+for commencing the expedition on the following morning.
+
+
+
+
+FIRST ASCENT OF MONT BLANC, 1857.
+
+(11.)
+
+
+[Sidenote: SCENE FROM THE CHARMOZ. 1857.]
+
+On Wednesday, the 12th of August, we rose early, after a very brief rest
+on my part. Simond had proposed to go down to Chamouni, and commence the
+ascent in the usual way, but we preferred crossing the mountains from
+the Montanvert, straight to the Glacier des Bossons. At eight o'clock we
+started, accompanied by two porters who were to carry our provisions to
+the Grands Mulets. Slowly and silently we climbed the hill-side towards
+Charmoz. We soon passed the limits of grass and rhododendrons, and
+reached the slabs of gneiss which overspread the summit of the ridge,
+lying one upon the other like coin upon the table of a money-changer.
+From the highest-point I turned to have a last look at the Mer de Glace;
+and through a pair of very dark spectacles I could see with perfect
+distinctness the looped dirt-bands of the glacier, which to the naked
+eye are scarcely discernible except by twilight. Flanking our track to
+the left rose a series of mighty Aiguilles--the Aiguille de Charmoz,
+with its bent and rifted pinnacles; the Aiguille du Grepon, the Aiguille
+de Blaitiere, the Aiguille du Midi, all piercing the heavens with their
+sharp pyramidal summits. Far in front of us rose the grand snow-cone of
+the Dome du Gouter, while, through a forest of dark pines which gathered
+like a cloud at the foot of the mountain, gleamed the white minarets of
+the Glacier des Bossons. Below us lay the Valley of Chamouni, beyond
+which were the Brevent and the chain of the Aiguilles Rouges; behind us
+was the granite obelisk of the Aiguille du Dru, while close at hand
+science found a corporeal form in a pyramid of stones used as a
+trigonometrical station by Professor Forbes. Sound is known to travel
+better up hill than down, because the pulses transmitted from a denser
+medium to a rarer, suffer less loss of intensity than when the
+transmission is in the opposite direction; and now the mellow voice of
+the Arve came swinging upwards from the heavier air of the valley to the
+lighter air of the hills in rich deep cadences.
+
+[Sidenote: PASSAGE TO THE PIERRE A L'ECHELLE. 1857.]
+
+The way for a time was excessively rough, our route being overspread
+with the fragments of peaks which had once reared themselves to our
+left, but which frost and lightning had shaken to pieces, and poured in
+granite avalanches down the mountain. We were sometimes among huge
+angular boulders, and sometimes amid lighter shingle, which gave way at
+every step, thus forcing us to shift our footing incessantly. Escaping
+from these, we crossed the succession of secondary glaciers which lie at
+the feet of the Aiguilles, and having secured firewood found ourselves
+after some hours of hard work at the Pierre a l'Echelle. Here we were
+furnished with leggings of coarse woollen cloth to keep out the snow;
+they were tied under the knees and quite tightly again over the insteps,
+so that the legs were effectually protected. We had some refreshment,
+possessed ourselves of the ladder, and entered upon the glacier.
+
+[Sidenote: LADDER LEFT BEHIND. 1857.]
+
+[Sidenote: DIFFICULT CREVASSES. 1857.]
+
+The ice was excessively fissured: we crossed crevasses and crept round
+slippery ridges, cutting steps in the ice wherever climbing was
+necessary. This rendered our progress very slow. Once, with the
+intention of lending a helping hand, I stepped forward upon a block of
+granite which happened to be poised like a rocking stone upon the ice,
+though I did not know it; it treacherously turned under me; I fell, but
+my hands were in instant requisition, and I escaped with a bruise, from
+which, however, the blood oozed angrily. We found the ladder necessary
+in crossing some of the chasms, the iron spikes at its end being firmly
+driven into the ice at one side, while the other end rested on the
+opposite side of the fissure. The middle portion of the glacier was not
+difficult. Mounds of ice rose beside us right and left, which were
+sometimes split into high towers and gaunt-looking pyramids, while the
+space between was unbroken. Twenty minutes' walking brought us again to
+a fissured portion of the glacier, and here our porter left the ladder
+on the ice behind him. For some time I was not aware of this, but we
+were soon fronted by a chasm to pass which we were in consequence
+compelled to make a long and dangerous circuit amid crests of crumbling
+ice. This accomplished, we hoped that no repetition of the process would
+occur, but we speedily came to a second fissure, where it was necessary
+to step from a projecting end of ice to a mass of soft snow which
+overhung the opposite side. Simond could reach this snow with his
+long-handled axe; he beat it down to give it rigidity, but it was
+exceedingly tender, and as he worked at it he continued to express his
+fears that it would not bear us. I was the lightest of the party, and
+therefore tested the passage, first; being partially lifted by Simond on
+the end of his axe, I crossed the fissure, obtained some anchorage at
+the other side, and helped the others over. We afterwards ascended until
+another chasm, deeper and wider than any we had hitherto encountered,
+arrested us. We walked alongside of it in search of a snow bridge, which
+we at length found, but the keystone of the arch had unfortunately given
+way, leaving projecting eaves of snow at both sides, between which we
+could look into the gulf, till the gloom of its deeper portions cut the
+vision short. Both sides of the crevasse were sounded, but no sure
+footing was obtained; the snow was beaten and carefully trodden down as
+near to the edge as possible, but it finally broke away from the foot
+and fell into the chasm. One of our porters was short-legged and a bad
+iceman; the other was a daring fellow, and he now threw the knapsack
+from his shoulders, came to the edge of the crevasse, looked into it,
+but drew back again. After a pause he repeated the act, testing the snow
+with his feet and staff. I looked at the man as he stood beside the
+chasm manifestly undecided as to whether he should take the step upon
+which his life would hang, and thought it advisable to put a stop to
+such perilous play. I accordingly interposed, the man withdrew from the
+crevasse, and he and Simond descended to fetch the ladder. While they
+were away Huxley sat down upon the ice, with an expression of fatigue
+stamped upon his countenance: the spirit and the muscles were evidently
+at war, and the resolute will mixed itself strangely with the sense of
+peril and feeling of exhaustion. He had been only two days with us, and,
+though his strength is great, he had had no opportunity of hardening
+himself by previous exercise upon the ice for the task which he had
+undertaken. The ladder now arrived, and we crossed the crevasse. I was
+intentionally the last of the party, Huxley being immediately in front
+of me. The determination of the man disguised his real condition from
+everybody but myself, but I saw that the exhausting journey over the
+boulders and debris had been too much for his London limbs. Converting
+my waterproof haversack into a cushion, I made him sit down upon it at
+intervals, and by thus breaking the steep ascent into short stages we
+reached the cabin of the Grands Mulets together. Here I spread a rug on
+the boards, and placing my bag for a pillow, he lay down, and after an
+hour's profound sleep he rose refreshed and well; but still he thought
+it wise not to attempt the ascent farther. Our porters left us: a baton
+was stretched across the room over the stove, and our wet socks and
+leggings were thrown across it to dry; our boots were placed around the
+fire, and we set about preparing our evening meal. A pan was placed upon
+the fire, and filled with snow, which in due time melted and boiled; I
+ground some chocolate and placed it in the pan, and afterwards ladled
+the beverage into the vessels we possessed, which consisted of two
+earthen dishes and the metal cases of our brandy flasks. After supper
+Simond went out to inspect the glacier, and was observed by Huxley, as
+twilight fell, in a state of deep contemplation beside a crevasse.
+
+[Sidenote: STAR TWINKLING. 1857.]
+
+Gradually the stars appeared, but as yet no moon. Before lying down we
+went out to look at the firmament, and noticed, what I suppose has been
+observed to some extent by everybody, that the stars near the horizon
+twinkled busily, while those near the zenith shone with a steady light.
+One large star in particular excited our admiration; it flashed
+intensely, and changed colour incessantly, sometimes blushing like a
+ruby, and again gleaming like an emerald. A determinate colour would
+sometimes remain constant for a sensible time, but usually the flashes
+followed each other in very quick succession. Three planks were now
+placed across the room near the stove, and upon these, with their rugs
+folded round them, Huxley and Hirst stretched themselves, while I
+nestled on the boards at the most distant end of the room. We rose at
+eleven o'clock, renewed the fire and warmed ourselves, after which we
+lay down again. I at length observed a patch of pale light upon the
+wooden wall of the cabin, which had entered through a hole in the end of
+the edifice, and rising found that it was past one o'clock. The
+cloudless moon was shining over the wastes of snow, and the scene
+outside was at once wild, grand, and beautiful.
+
+[Sidenote: START FROM THE GRANDS MULETS. 1857.]
+
+Breakfast was soon prepared, though not without difficulty; we had no
+candles, they had been forgotten; but I fortunately possessed a box of
+wax matches, of which Huxley took charge, patiently igniting them in
+succession, and thus giving us a tolerably continuous light. We had
+some tea, which had been made at the Montanvert, and carried to the
+Grands Mulets in a bottle. My memory of that tea is not pleasant; it had
+been left a whole night in contact with its leaves, and smacked strongly
+of tannin. The snow-water, moreover, with which we diluted it was not
+pure, but left a black residuum at the bottom of the dishes in which the
+beverage was served. The few provisions deemed necessary being placed in
+Simond's knapsack, at twenty minutes past two o'clock we scrambled down
+the rocks, leaving Huxley behind us.
+
+The snow was hardened by the night's frost, and we were cheered by the
+hope of being able to accomplish the ascent with comparatively little
+labour. We were environed by an atmosphere of perfect purity; the larger
+stars hung like gems above us, and the moon, about half full, shone with
+wondrous radiance in the dark firmament. One star in particular, which
+lay eastward from the moon, suddenly made its appearance above one of
+the Aiguilles, and burned there with unspeakable splendour. We turned
+once towards the Mulets, and saw Huxley's form projected against the sky
+as he stood upon a pinnacle of rock; he gave us a last wave of the hand
+and descended, while we receded from him into the solitudes.
+
+The evening previous our guide had examined the glacier for some
+distance, his progress having been arrested by a crevasse. Beside this
+we soon halted: it was spanned at one place by a bridge of snow, which
+was of too light a structure to permit of Simond's testing it alone; we
+therefore paused while our guide uncoiled a rope and tied us all
+together. The moment was to me a peculiarly solemn one. Our little party
+seemed so lonely and so small amid the silence and the vastness of the
+surrounding scene. We were about to try our strength under unknown
+conditions, and as the various possibilities of the enterprise crowded
+on the imagination, a sense of responsibility for a moment oppressed
+me. But as I looked aloft and saw the glory of the heavens, my heart
+lightened, and I remarked cheerily to Hirst that Nature seemed to smile
+upon our work. "Yes," he replied, in a calm and earnest voice, "and, God
+willing, we shall accomplish it."
+
+[Sidenote: A WRONG TURN. 1857.]
+
+A pale light now overspread the eastern sky, which increased, as we
+ascended, to a daffodil tinge; this afterwards heightened to orange,
+deepening at one extremity into red, and fading at the other into a pure
+ethereal hue to which it would be difficult to assign a special name.
+Higher up the sky was violet, and this changed by insensible degrees
+into the darkling blue of the zenith, which had to thank the light of
+moon and stars alone for its existence. We wound steadily for a time
+through valleys of ice, climbed white and slippery slopes, crossed a
+number of crevasses, and after some time found ourselves beside a chasm
+of great depth and width, which extended right and left as far as we
+could see. We turned to the left, and marched along its edge in search
+of a _pont_; but matters became gradually worse: other crevasses joined
+on to the first one, and the further we proceeded the more riven and
+dislocated the ice became. At length we reached a place where further
+advance was impossible. Simond in his difficulty complained of the want
+of light, and wished us to wait for the advancing day; I, on the
+contrary, thought that we had light enough and ought to make use of it.
+Here the thought occurred to me that Simond, having been only once
+before to the top of the mountain, might not be quite clear about the
+route; the glacier, however, changes within certain limits from year to
+year, so that a general knowledge was all that could be expected, and we
+trusted to our own muscles to make good any mistake in the way of
+guidance. We now turned and retraced our steps along the edges of chasms
+where the ice was disintegrated and insecure, and succeeded at length
+in finding a bridge which bore us across the crevasse. This error caused
+us the loss of an hour, and after walking for this time we could cast a
+stone from the point we had attained to the place whence we had been
+compelled to return.
+
+[Sidenote: SERACS OF THE DOME DU GOUTER. 1857.]
+
+Our way now lay along the face of a steep incline of snow, which was cut
+by the fissure we had just passed, in a direction parallel to our route.
+On the heights to our right, loose ice-crags seemed to totter, and we
+passed two tracks over which the frozen blocks had rushed some short
+time previously. We were glad to get out of the range of these terrible
+projectiles, and still more so to escape the vicinity of that ugly
+crevasse. To be killed in the open air would be a luxury, compared with
+having the life squeezed out of one in the horrible gloom of these
+chasms. The blush of the coming day became more and more intense; still
+the sun himself did not appear, being hidden from us by the peaks of the
+Aiguille du Midi, which were drawn clear and sharp against the
+brightening sky. Right under this Aiguille were heaps of snow smoothly
+rounded and constituting a portion of the sources whence the Glacier du
+Geant is fed; these, as the day advanced, bloomed with a rosy light. We
+reached the Petit Plateau, which we found covered with the remains of
+ice avalanches; above us upon the crest of the mountain rose three
+mighty bastions, divided from each other by deep vertical rents, with
+clean smooth walls, across which the lines of annual bedding were drawn
+like courses of masonry. From these, which incessantly renew themselves,
+and from the loose and broken ice-crags near them, the boulders amid
+which we now threaded our way had been discharged. When they fall their
+descent must be sublime.
+
+[Sidenote: THE LOST GUIDES. 1857.]
+
+The snow had been gradually getting deeper, and the ascent more
+wearisome, but superadded to this at the Petit Plateau was the
+uncertainty of the footing between the blocks of ice. In many places
+the space was merely covered by a thin crust, which, when trod upon,
+instantly yielded, and we sank with a shock sometimes to the hips. Our
+way next lay up a steep incline to the Grand Plateau, the depth and
+tenderness of the snow augmenting as we ascended. We had not yet seen
+the sun, but, as we attained the brow which forms the entrance to the
+Grand Plateau, he hung his disk upon a spike of rock to our left, and,
+surrounded by a glory of interference spectra of the most gorgeous
+colours, blazed down upon us. On the Grand Plateau we halted and had our
+frugal refreshment. At some distance to our left was the crevasse into
+which Dr. Hamel's three guides were precipitated by an avalanche in
+1820; they are still entombed in the ice, and some future explorer may
+perhaps see them disgorged lower down, fresh and undecayed. They can
+hardly reach the surface until they pass the snow-line of the glacier,
+for above this line the quantity of snow that annually falls being in
+excess of the quantity melted, the tendency would be to make the
+ice-covering above them thicker. But it is also possible that the waste
+of the ice underneath may have brought the bodies to the bed of the
+glacier, where their very bones may have been ground to mud by an agency
+which the hardest rocks cannot withstand.
+
+[Sidenote: THE GUIDE TIRED. 1857.]
+
+[Sidenote: A PERILOUS SLOPE. 1857.]
+
+As the sun poured his light upon the Plateau the little snow-facets
+sparkled brilliantly, sometimes with a pure white light, and at others
+with prismatic colours. Contrasted with the white spaces above and
+around us were the dark mountains on the opposite side of the valley of
+Chamouni, around which fantastic masses of cloud were beginning to build
+themselves. Mont Buet, with its cone of snow, looked small, and the
+Brevent altogether mean; the limestone bastions of the Fys, however,
+still presented a front of gloom and grandeur. We traversed the Grand
+Plateau, and at length reached the base of an extremely steep incline
+which stretched upwards towards the Corridor. Here, as if produced by a
+fault, consequent upon the sinking of the ice in front, rose a vertical
+precipice, from the coping of which vast stalactites of ice depended.
+Previous to reaching this place I had noticed a haggard expression upon
+the countenance of our guide, which was now intensified by the prospect
+of the ascent before him. Hitherto he had always been in front, which
+was certainly the most fatiguing position. I felt that I must now take
+the lead, so I spoke cheerily to the man and placed him behind me.
+Marking a number of points upon the slope as resting places, I went
+swiftly from one to the other. The surface of the snow had been
+partially melted by the sun and then refrozen, thus forming a
+superficial crust, which bore the weight up to a certain point, and then
+suddenly gave way, permitting the leg to sink to above the knee. The
+shock consequent on this, and the subsequent effort necessary to
+extricate the leg, were extremely fatiguing. My motion was complained of
+as too quick, and my tracks as imperfect; I moderated the former, and,
+to render my footholes broad and sure, I stamped upon the frozen crust,
+and twisted my legs in the soft mass underneath,--a terribly exhausting
+process. I thus led the way to the base of the Rochers Rouges, up to
+which the fault already referred to had prolonged itself as a crevasse,
+which was roofed at one place by a most dangerous-looking snow-bridge.
+Simond came to the front; I drew his attention to the state of the snow,
+and proposed climbing the Rochers Rouges; but, with a promptness unusual
+with him, he replied that this was impossible; the bridge was our only
+means of passing, and we must try it. We grasped our ropes, and dug our
+feet firmly into the snow to check the man's descent if the _pont_ gave
+way, but to our astonishment it bore him, and bore us safely after him.
+The slope which we had now to ascend had the snow swept from its
+surface, and was therefore firm ice. It was most dangerously steep, and,
+its termination being the fretted coping of the precipice to which I
+have referred, if we slid downwards we should shoot over this and be
+dashed to pieces upon the ice below.[A] Simond, who had come to the
+front to cross the crevasse, was now engaged in cutting steps, which he
+made deep and large, so that they might serve us on our return. But the
+listless strokes of his axe proclaimed his exhaustion; so I took the
+implement out of his hands, and changed places with him. Step after step
+was hewn, but the top of the Corridor appeared ever to recede from us.
+Hirst was behind unoccupied, and could thus turn his thoughts to the
+peril of our position: he _felt_ the angle on which we hung, and saw the
+edge of the precipice, to which less than a quarter of a minute's slide
+would carry us, and for the first time during the journey he grew giddy.
+A cigar which he lighted for the purpose tranquilized him.
+
+[Sidenote: WILL AND MUSCLE. 1857.]
+
+I hewed sixty steps upon this slope, and each step had cost a minute, by
+Hirst's watch. The Mur de la Cote was still before us, and on this the
+guide-books informed us two or three hundred steps were sometimes found
+necessary. If sixty steps cost an hour, what would be the cost of two
+hundred? The question was disheartening in the extreme, for the time at
+which we had calculated on reaching the summit was already passed, while
+the chief difficulties remained unconquered. Having hewn our way along
+the harder ice we reached snow. I again resorted to stamping to secure a
+footing, and while thus engaged became, for the first time, aware of the
+drain of force to which I was subjecting myself. The thought of being
+absolutely exhausted had never occurred to me, and from first to last I
+had taken no care to husband my strength. I always calculated that the
+_will_ would serve me even should the muscles fail, but I now found that
+mechanical laws rule man in the long run; that no effort of will, no
+power of spirit, can draw beyond a certain limit upon muscular force.
+The soul, it is true, can stir the body to action, but its function is
+to excite and apply force, and not to create it.
+
+While stamping forward through the frozen crust I was compelled to pause
+at short intervals; then would set out again apparently fresh, to find,
+however, in a few minutes that my strength was gone, and that I required
+to rest once more. In this way I gained the summit of the Corridor, when
+Hirst came to the front, and I felt some relief in stepping slowly after
+him, making use of the holes into which his feet had sunk. He thus led
+the way to the base of the Mur de la Cote, the thought of which had so
+long cast a gloom upon us; here we left our rope behind us, and while
+pausing I asked Simond whether he did not feel a desire to go to the
+summit--"_Bien sur_," was his reply, "_mais!_" Our guide's mind was so
+constituted that the "_mais_" seemed essential to its peace. I stretched
+my hand towards him, and said, "Simond, we must do it." One thing alone
+I felt could defeat us: the usual time of the ascent had been more than
+doubled, the day was already far spent, and if the ascent would throw
+our subsequent descent into night it could not be contemplated.
+
+[Sidenote: A DOZE ON THE CALOTTE. 1857.]
+
+We now faced the Mur, which was by no means so bad as we had expected.
+Driving the iron claws of our boots into the scars made by the axe, and
+the spikes of our batons into the slope above our feet, we ascended
+steadily until the summit was attained, and the top of the mountain rose
+clearly above us. We congratulated ourselves upon this; but Simond,
+probably fearing that our joy might become too full, remarked, "_Mais le
+sommet est encore bien loin!_" It was, alas! too true. The snow became
+soft again, and our weary limbs sank in it as before. Our guide went on
+in front, audibly muttering his doubts as to our ability to reach the
+top, and at length he threw himself upon the snow, and exclaimed, "_Il
+faut y renoncer!_" Hirst now undertook the task of rekindling the
+guide's enthusiasm, after which Simond rose, exclaiming, "_Ah! comme ca
+me fait mal aux genoux_," and went forward. Two rocks break through the
+snow between the summit of the Mur and the top of the mountain; the
+first is called the Petits Mulets, and the highest the Derniers Rochers.
+At the former of these we paused to rest, and finished our scanty store
+of wine and provisions. We had not a bit of bread nor a drop of wine
+left; our brandy flasks were also nearly exhausted, and thus we had to
+contemplate the journey to the summit, and the subsequent descent to the
+Grands Mulets, without the slightest prospect of physical refreshment.
+The almost total loss of two nights' sleep, with two days' toil
+superadded, made me long for a few minutes' doze, so I stretched myself
+upon a composite couch of snow and granite, and immediately fell asleep.
+My friend, however, soon aroused me. "You quite frighten me," he said;
+"I have listened for some minutes, and have not heard you breathe once."
+I had, in reality, been taking deep draughts of the mountain air, but so
+silently as not to be heard.
+
+I now filled our empty wine-bottle with snow and placed it in the
+sunshine, that we might have a little water on our return. We then rose;
+it was half-past two o'clock; we had been upwards of twelve hours
+climbing, and I calculated that, whether we reached the summit or not,
+we could at all events work _towards_ it for another hour. To the sense
+of fatigue previously experienced, a new phenomenon was now added--the
+beating of the heart. We were incessantly pulled up by this, which
+sometimes became so intense as to suggest danger. I counted the number
+of paces which we were able to accomplish without resting, and found
+that at the end of every twenty, sometimes at the end of fifteen, we
+were compelled to pause. At each pause my heart throbbed audibly, as I
+leaned upon my staff, and the subsidence of this action was always the
+signal for further advance. My breathing was quick, but light and
+unimpeded. I endeavoured to ascertain whether the hip-joint, on account
+of the diminished atmospheric pressure, became loosened, so as to throw
+the weight of the leg upon the surrounding ligaments, but could not be
+certain about it. I also sought a little aid and encouragement from
+philosophy, endeavouring to remember what great things had been done by
+the accumulation of small quantities, and I urged upon myself that the
+present was a case in point, and that the summation of distances twenty
+paces each must finally place us at the top. Still the question of time
+left the matter long in doubt, and until we had passed the Derniers
+Rochers we worked on with the stern indifference of men who were doing
+their duty, and did not look to consequences. Here, however, a gleam of
+hope began to brighten our souls; the summit became visibly nearer,
+Simond showed more alacrity; at length success became certain, and at
+half-past three P.M. my friend and I clasped hands upon the top.
+
+[Sidenote: THE SUMMIT ATTAINED. 1857.]
+
+The summit of the mountain is an elongated ridge, which has been
+compared to the back of an ass. It was perfectly manifest that we were
+dominant over all other mountains; as far as the eye could range Mont
+Blanc had no competitor. The summits which had looked down upon us in
+the morning were now far beneath us. The Dome du Gouter, which had held
+its threatening _seracs_ above us so long, was now at our feet. The
+Aiguille du Midi, Mont Blanc du Tacul, and the Monts Maudits, the
+Talefre with its surrounding peaks, the Grand Jorasse, Mont Mallet, and
+the Aiguille du Geant, with our own familiar glaciers, were all below
+us. And as our eye ranged over the broad shoulders of the mountain, over
+ice hills and valleys, plateaux and far-stretching slopes of snow, the
+conception of its magnitude grew upon us, and impressed us more and
+more.
+
+[Sidenote: CLOUDS FROM THE SUMMIT. 1857.]
+
+The clouds were very grand--grander indeed than anything I had ever
+before seen. Some of them seemed to hold thunder in their breasts, they
+were so dense and dark; others, with their faces turned sunward, shone
+with the dazzling whiteness of the mountain snow; while others again
+built themselves into forms resembling gigantic elm trees, loaded with
+foliage. Towards the horizon the luxury of colour added itself to the
+magnificent alternations of light and shade. Clear spaces of amber and
+ethereal green embraced the red and purple cumuli, and seemed to form
+the cradle in which they swung. Closer at hand squally mists, suddenly
+engendered, were driven hither and thither by local winds; while the
+clouds at a distance lay "like angels sleeping on the wing," with
+scarcely visible motion. Mingling with the clouds, and sometimes rising
+above them, were the highest mountain heads, and as our eyes wandered
+from peak to peak, onwards to the remote horizon, space itself seemed
+more vast from the manner in which the objects which it held were
+distributed.
+
+[Sidenote: INTENSITY OF SOUND. 1857.]
+
+I wished to repeat the remarkable experiment of De Saussure upon sound,
+and for this purpose had requested Simond to bring a pistol from
+Chamouni; but in the multitude of his cares he forgot it, and in lieu of
+it my host at the Montanvert had placed in two tin tubes, of the same
+size and shape, the same amount of gunpowder, securely closing the tubes
+afterwards, and furnishing each of them with a small lateral aperture.
+We now planted one of them upon the snow, and bringing a strip of amadou
+into communication with the touchhole, ignited its most distant end: it
+failed; we tried again, and were successful, the explosion tearing
+asunder the little case which contained the powder. The sound was
+certainly not so great as I should have expected from an equal quantity
+of powder at the sea level.[B]
+
+The snow upon the summit was indurated, but of an exceedingly fine
+grain, and the beautiful effect already referred to as noticed upon the
+Stelvio was strikingly manifest. The hole made by driving the baton into
+the snow was filled with a delicate blue light; and, by management, its
+complementary pinky yellow could also be produced. Even the iron spike
+at the end of the baton made a hole sufficiently deep to exhibit the
+blue colour, which certainly depends on the size and arrangement of the
+snow crystals. The firmament above us was without a cloud, and of a
+darkness almost equal to that which surrounded the moon at 2 A.M. Still,
+though the sun was shining, a breeze, whose tooth had been sharpened by
+its passage over the snow-fields, searched us through and through. The
+day was also waning, and, urged by the warnings of our ever prudent
+guide, we at length began the descent.
+
+[Sidenote: AN UNEXPECTED GLISSADE. 1857.]
+
+Gravity was now in our favour, but gravity could not entirely spare our
+wearied limbs, and where we sank in the snow we found our downward
+progress very trying. I suffered from thirst, but after we had divided
+the liquefied snow at the Petits Mulets amongst us we had nothing to
+drink. I crammed the clean snow into my mouth, but the process of
+melting was slow and tantalizing to a parched throat, while the chill
+was painful to the teeth. We marched along the Corridor, and crossed
+cautiously the perilous slope on which we had cut steps in the morning,
+breathing more freely after we had cleared the ice-precipice before
+described. Along the base of this precipice we now wound, diverging from
+our morning's track, in order to get surer footing in the snow; it was
+like flour, and while descending to the Grand Plateau we sometimes sank
+in it nearly to the waist. When I endeavoured to squeeze it, so as to
+fill my flask, it at first refused to cling together, behaving like so
+much salt; the heat of the hand, however, soon rendered it a little
+moist, and capable of being pressed into compact masses. The sun met us
+here with extraordinary power; the heat relaxed my muscles, but when
+fairly immersed in the shadow of the Dome du Gouter, the coolness
+restored my strength, which augmented as the evening advanced. Simond
+insisted on the necessity of haste, to save us from the perils of
+darkness. "_On peut perir_" was his repeated admonition, and he was
+quite right. We reached the region of _ponts_, more weary, but, in
+compensation, more callous, than we had been in the morning, and moved
+over the soft snow of the bridges as if we had been walking upon eggs.
+The valley of Chamouni was filled with brown-red clouds, which crept
+towards us up the mountain; the air around and above us was, however,
+clear, and the chastened light told us that day was departing. Once as
+we hung upon a steep slope, where the snow was exceedingly soft, Hirst
+omitted to make his footing sure; the soft mass gave way, and he fell,
+uttering a startled shout as he went down the declivity. I was attached
+to him, and, fixing my feet suddenly in the snow, endeavoured to check
+his fall, but I seemed a mere feather in opposition to the force with
+which he descended.[C] I fell, and went down after him; and we carried
+quite an avalanche of snow along with us, in which we were almost
+completely hidden at the bottom of the slope. All further dangers,
+however, were soon past, and we went at a headlong speed to the base of
+the Grands Mulets; the sound of our batons against the rocks calling
+Huxley forth. A position more desolate than his had been can hardly be
+imagined. For seventeen hours he had been there. He had expected us at
+two o'clock in the afternoon; the hours came and passed, and till seven
+in the evening he had looked for us. "To the end of my life," he said,
+"I shall never forget the sound of those batons." It was his turn now to
+nurse me, which he did, repaying my previous care of him with high
+interest. We were all soon stretched, and, in spite of cold and hard
+boards, I slept at intervals; but the night, on the whole, was a weary
+one, and we rose next morning with muscles more tired than when we lay
+down.
+
+[Sidenote: BLIND AMID THE CREVASSES. 1857.]
+
+_Friday, 14th August._--Hirst was almost blind this morning; and our
+guide's eyes were also greatly inflamed. We gathered our things
+together, and bade the Grands Mulets farewell. It had frozen hard during
+the night, and this, on the steeper slopes, rendered the footing very
+insecure. Simond, moreover, appeared to be a little bewildered, and I
+sometimes preceded him in cutting the steps, while Hirst moved among the
+crevasses like a blind man; one of us keeping near him, so that he might
+feel for the actual places where our feet had rested, and place his own
+in the same position. It cost us three hours to cross from the Grands
+Mulets to the Pierre a l'Echelle, where we discarded our leggings, had a
+mouthful of food, and a brief rest. Once upon the safe earth Simond's
+powers seemed to be restored, and he led us swiftly downwards to the
+little auberge beside the Cascade du Tard, where we had some excellent
+lemonade, equally choice cognac, fresh strawberries and cream. How sweet
+they were, and how beautiful we thought the peasant girl who served
+them! Our guide kept a little hotel, at which we halted, and found it
+clean and comfortable. We were, in fact, totally unfit to go elsewhere.
+My coat was torn, holes were kicked through my boots, and I was
+altogether ragged and shabby. A warm bath before dinner refreshed all
+mightily. Dense clouds now lowered upon Mont Blanc, and we had not been
+an hour at Chamouni when the breaking up of the weather was announced by
+a thunder-peal. We had accomplished our journey just in time.
+
+
+FOOTNOTES:
+
+[A] Those acquainted with the mountain will at once recognise the grave
+error here committed. In fact on starting from the Grands Mulets we had
+crossed the glacier too far, and throughout were much too close to the
+Dome du Gouter.
+
+[B] I fired the second case in a field in Hampshire, and, as far as my
+memory enabled me to make the comparison, found its sound considerably
+_denser_, if I may use the expression. In 1859 I had a pistol fired at
+the summit of Mont Blanc: its sound was sensibly feebler and _shorter_
+than in the valley; it resembled somewhat the discharge of a cork from a
+champagne bottle, though much louder, but it could not be at all
+compared to the sound of a common cracker.
+
+[C] I believe that I could stop him now (1860).
+
+
+
+
+(12.)
+
+
+[Sidenote: HAPPY EVENINGS. 1857.]
+
+After our return we spent every available hour upon the ice, working at
+questions which shall be treated under their proper heads, each day's
+work being wound up by an evening of perfect enjoyment. Roast mutton and
+fried potatoes were our incessant fare, for which, after a little
+longing for a change at first, we contracted a final and permanent love.
+As the year advanced, moreover, and the grass sprouted with augmented
+vigour on the slopes of the Montanvert, the mutton, as predicted by our
+host, became more tender and juicy. We had also some capital Sallenches
+beer, cold as the glacier water, but effervescent as champagne. Such
+were our food and drink. After dinner we gathered round the pine-fire,
+and I can hardly think it possible for three men to be more happy than
+we then were. It was not the goodness of the conversation, nor any high
+intellectual element, which gave the charm to our gatherings; the
+gladness grew naturally out of our own perfect health, and out of the
+circumstances of our position. Every fibre seemed a repository of latent
+joy, which the slightest stimulus sufficed to bring into conscious
+action.
+
+[Sidenote: A GLACIER "BLOWER." 1857.]
+
+On the 17th I penetrated with Simond through thick gloom to the Tacul;
+on the 18th we set stakes at the same place: on the same day, while
+crossing the medial moraine of the Talefre, a little below the cascade,
+a singular noise attracted my attention; it seemed at first as if a
+snake were hissing about my feet. On changing my position the sound
+suddenly ceased, but it soon recommenced. There was some snow upon the
+glacier, which I removed, and placed my ear close to the ice, but it was
+difficult to fix on the precise spot from which the sound issued. I cut
+away the disintegrated portion of the surface, and at length discovered
+a minute crack, from which a stream of air issued, which I could feel as
+a cold blast against my hand. While cutting away the surface further, I
+stopped the little "blower." A marmot screamed near me, and while I
+paused to look at the creature scampering up the crags, the sound
+commenced again, changing its note variously--hissing like a snake,
+singing like a kettle, and sometimes chirruping intermittently like a
+bird. On passing my fingers to and fro over the crack, I obtained a
+succession of audible puffs; the current was sufficiently strong to blow
+away the corner of a gauze veil held over the fissure. Still the crack
+was not wide enough to permit of the entrance of my finger nail; and to
+issue with such force from so minute a rent the air must have been under
+considerable pressure. The origin of the blower was in all probability
+the following:--When the ice is recompacted after having descended a
+cascade, it is next to certain that chambers of air will be here and
+there enclosed, which, being powerfully squeezed afterwards, will issue
+in the manner described whenever a crack in the ice furnishes it with a
+means of escape. In my experiments on flowing mud, for example, the air
+entrapped in the mass while descending from the sluice into the trough,
+bursts in bubbles from the surface at a short distance downwards.
+
+[Sidenote: A DIFFICULT LINE. 1857.]
+
+I afterwards examined the Talefre cascade from summit to base, with
+reference to the structure, until at the close of the day thickening
+clouds warned me off. I went down the glacier at a trot, guided by the
+boulders capped with little cairns which marked the route. The track
+which I had pursued for the last five weeks amid the crevasses near
+l'Angle was this day barely passable. The glacier had changed, my work
+was drawing to a close, and, as I looked at the objects which had now
+become so familiar to me, I felt that, though not viscous, the ice did
+not lack the quality of "adhesiveness," and I felt a little sad at the
+thought of bidding it so soon farewell.
+
+At some distance below the Montanvert the Mer de Glace is riven from
+side to side by transverse crevasses: these fissures indicate that the
+glacier where they occur is in a state of longitudinal strain which
+produces transverse fracture. I wished to ascertain the amount of
+stretching which the glacier here demanded, and which the ice was not
+able to give; and for this purpose desired to compare the velocity of a
+line set out across the fissured portion with that of a second line
+staked out across the ice before it had become thus fissured. A previous
+inspection of the glacier through the telescope of our theodolite
+induced us to fix on a place which, though much riven, still did not
+exclude the hope of our being able to reach the other side. Each of us
+was, as usual, armed with his own axe; and carrying with us suitable
+stakes, my guide and myself entered upon this portion of the glacier on
+the morning of the 19th of August.
+
+[Sidenote: "NOUS NOUS TROUVERONS PERDUS!" 1857.]
+
+I was surprised on entering to find some veins of white ice, which from
+their position and aspect appeared to be derived from the Glacier du
+Geant; but to these I shall subsequently refer. Our work was extremely
+difficult; we penetrated to some distance along one line, but were
+finally forced back, and compelled to try another. Right and left of us
+were profound fissures, and once a cone of ice forty feet high leaned
+quite over our track. In front of us was a second leaning mass borne by
+a mere stalk, and so topheavy that one wondered why the slight pedestal
+on which it rested did not suddenly crack across. We worked slowly
+forwards, and soon found ourselves in the shadow of the topheavy mass
+above referred to; and from which I escaped with a wounded hand, caused
+by over-haste. Simond surmounted the next ridge and exclaimed, "_Nous
+nous trouverons perdus!_" I reached his side, and on looking round the
+place saw that there was no footing for man. The glacier here, as shown
+in the frontispiece, was cut up into thin wedges, separated from each
+other by profound chasms, and the wedges were so broken across as to
+render creeping along their edges quite impossible. Thus brought to a
+stand, I fixed a stake at the point where we were forced to halt, and
+retreated along edges of detestable granular ice, which fell in showers
+into the crevasses when struck by the axe. At one place an exceedingly
+deep fissure was at our left, which was joined, at a sharp angle, by
+another at our right, and we were compelled to cross at the place of
+intersection: to do this we had to trust ourselves to a projecting knob
+of that vile rotten ice which I had learned to fear since my experience
+of it on the Col du Geant. We finally escaped, and set out our line at
+another place, where the glacier, though badly cut, was not impassable.
+
+[Sidenote: FAREWELL TO THE MONTANVERT. 1857.]
+
+On the 20th we made a series of final measurements at the Tacul, and
+determined the motion of two lines which we had set out the previous
+day. On the 21st we quitted the Montanvert; I had been there from the
+15th of July, and the longer I remained the better I liked the
+establishment and the people connected with it. It was then managed by
+Joseph Tairraz and Jules Charlet, both of whom showed us every
+attention. In 1858 and 1859 I had occasion to revisit the establishment,
+which was then managed by Jules and his brother, and found in it the
+same good qualities. During my winter expedition of 1859 I also found
+the same readiness to assist me in every possible way; honest Jules
+expressing his willingness to ascend through the snow to the auberge if
+I thought his presence would in any degree contribute to my comfort.
+
+We crossed the glacier, and descended by the Chapeau to the Cascade des
+Bois, the inclination of which and of the lower portion of the glacier
+we then determined. The day was magnificent. Looking upwards, the
+Aiguilles de Charmoz and du Dru rose right and left like sentinels of
+the valley, while in front of us the ice descended the steep, a
+bewildering mass of crags and chasms. At the other side was the
+pine-clad slope of the Montanvert. Further on the Aiguille du Midi threw
+its granite pyramid between us and Mont Blanc; on the Dome du Gouter the
+_seracs_ of the mountain were to be seen, while issuing as if from a
+cleft in the mountain side the Glacier des Bossons thrust through the
+black pines its snowy tongue. Below us was the beautiful valley of
+Chamouni itself, through which the Arve and Arveiron rushed like
+enlivening spirits. We finally examined a grand old moraine produced by
+a Mer de Glace of other ages, when the ice quite crossed the valley of
+Chamouni and abutted against the opposite mountain-wall.
+
+[Sidenote: EDOUARD SIMOND. 1857.]
+
+Simond had proved himself a very valuable assistant; he was intelligent
+and perfectly trustworthy; and though the peculiar nature of my work
+sometimes caused me to attempt things against which his prudence
+protested, he lacked neither strength nor courage. On reaching Chamouni
+and adding up our accounts, I found that I had not sufficient cash to
+pay him; money was waiting for me at the post-office in Geneva, and
+thither it was arranged that my friend Hirst should proceed next
+morning, while I was to await the arrival of the money at Chamouni. My
+guide heard of this arrangement, and divined its cause: he came to me,
+and in the most affectionate manner begged of me to accept from him the
+loan of 500 francs. Though I did not need the loan, the mode in which it
+was offered to me augmented the kindly feelings which I had long
+entertained towards Simond, and I may add that my intercourse with him
+since has served only to confirm my first estimate of his worthiness.
+
+
+
+
+EXPEDITION OF 1858.
+
+(13.)
+
+
+[Sidenote: DOUBTS REGARDING STRUCTURE. 1858.]
+
+I had confined myself during the summer of 1857 to the Mer de Glace and
+its tributaries, desirous to make my knowledge accurate rather than
+extensive. I had made the acquaintance of all accessible parts of the
+glacier, and spared no pains to master both the details and the meaning
+of the laminated structure of the ice, but I found no fact upon which I
+could take my stand and say to an advocate of an opposing theory, "This
+is unassailable." In experimental science we have usually the power of
+changing the conditions at pleasure; if Nature does not reply to a
+question we throw it into another form; a combining of conditions is, in
+fact, the essence of experiment. To meet the requirements of the present
+question, I could not twist the same glacier into various shapes, and
+throw it into different states of strain and pressure; but I might, by
+visiting many glaciers, find all needful conditions fulfilled in detail,
+and by observing these I hoped to confer upon the subject the character
+and precision of a true experimental inquiry.
+
+The summer of 1858 was accordingly devoted to this purpose, when I had
+the good fortune to be accompanied by Professor Ramsay, the author of
+some extremely interesting papers upon ancient glaciers. Taking Zuerich,
+Schaffhausen, and Lucerne in our way, we crossed the Bruenig on the 22nd
+of July, and met my guide, Christian Lauener, at Meyringen. On the 23rd
+we visited the glacier of Rosenlaui, and the glacier of the
+Schwartzwald, and reached Grindelwald in the evening of the same day. My
+expedition with Mr. Huxley had taught me that the Lower Grindelwald
+Glacier was extremely instructive, and I was anxious to see many parts
+of it once more; this I did, in company with Ramsay, and we also spent a
+day upon the upper glacier, after which our path lay over the Strahleck
+to the glaciers of the Aar and of the Rhone.
+
+
+
+
+PASSAGE OF THE STRAHLECK.
+
+(14.)
+
+
+[Sidenote: A GLOOMY PROSPECT. 1858.]
+
+On Monday, the 26th of July, we were called at 4 A.M., and found the
+weather very unpromising, but the two mornings which preceded it had
+also been threatening without any evil result. There was, it is true,
+something more than usually hostile in the aspect of the clouds which
+sailed sullenly from the west, and smeared the air and mountains as if
+with the dirty smoke of a manufacturing town. We despatched our coffee,
+went down to the bottom of the Grindelwald valley, up the opposite
+slope, and were soon amid the gloom of the pines which partially cover
+it. On emerging from these, a watery gleam on the mottled head of the
+Eiger was the only evidence of direct sunlight in that direction. To our
+left was the Wetterhorn surrounded by wild and disorderly clouds,
+through the fissures of which the morning light glared strangely. For a
+time the Heisse Platte was seen, a dark brown patch amid the ghastly
+blue which overspread the surrounding slopes of snow. The clouds once
+rolled up, and revealed for a moment the summits of the Viescherhoerner;
+but they immediately settled down again, and hid the mountains from top
+to base. Soon afterwards they drew themselves partially aside, and a
+patch of blue over the Strahleck gave us hope and pleasure. As we
+ascended, the prospect in front of us grew better, but that behind
+us--and the wind came from behind--grew worse. Slowly and stealthily the
+dense neutral-tint masses crept along the sides of the mountains, and
+seemed to dog us like spies; while over the glacier hung a thin veil of
+fog, through which gleamed the white minarets of the ice.
+
+[Sidenote: ICE CASCADE AND PROTUBERANCES. 1858.]
+
+[Sidenote: DIRT-BANDS OF THE STRAHLECK BRANCH. 1858.]
+
+When we first spoke of crossing the Strahleck, Lauener said it would be
+necessary to take two guides at least; but after a day's performance on
+the ice he thought we might manage very well by taking, in addition to
+himself, the herd of the alp, over the more difficult part of the pass.
+He had further experience of us on the second day, and now, as we
+approached the herd's hut, I was amused to hear him say that he thought
+any assistance beside his own unnecessary. Relying upon ourselves,
+therefore, we continued our route, and were soon upon the glacier, which
+had been rendered smooth and slippery through the removal of its
+disintegrated surface by the warm air. Crossing the Strahleck branch of
+the glacier to its left side, we climbed the rocks to the grass and
+flowers which clothe the slopes above them. Our way sometimes lay over
+these, sometimes along the beds of streams, across turbulent brooks, and
+once around the face of a cliff, which afforded us about an inch of
+ledge to stand upon, and some protruding splinters to lay hold of by the
+hands. Having reached a promontory which commanded a fine view of the
+glacier, and of the ice cascade by which it was fed, I halted, to check
+the observations already made from the side of the opposite mountain.
+Here, as there, cliffy ridges were seen crossing the cascade of the
+glacier, with interposed spaces of dirt and debris--the former being
+toned down, and the latter squeezed towards the base of the fall, until
+finally the ridges swept across the glacier, in gentle swellings, from
+side to side; while the valleys between them, holding the principal
+share of the superficial impurity, formed the cradles of the so-called
+Dirt-Bands. These swept concentric with the protuberances across the
+glacier, and remained upon its surface even after the swellings had
+disappeared. The swifter flow of the centre of the glacier tends of
+course incessantly to lengthen the loops of the bands, and to thrust the
+summits of the curves which they form more and more in advance of their
+lateral portions. The depressions between the protuberances appeared to
+be furrowed by minor wrinkles, as if the ice of the depressions had
+yielded more than that of the protuberances. This, I think, is extremely
+probable, though it has never yet been proved. Three stakes, placed, one
+on the summit, another on the frontal slope, and another at the base of
+a protuberance, would, I think, move with unequal velocities. They
+would, I think, show that, upon the large and general motion of the
+glacier, smaller motions are superposed, as minor oscillations are known
+to cover parasitically the large ones of a vibrating string. Possibly,
+also, the dirt-bands may owe something to the squeezing of impurities
+out of the glacier to its surface in the intervals between the
+swellings. From our present position we could also see the swellings on
+the Viescherhoerner branch of the glacier, in the valleys between which
+coarse shingle and debris were collected, which would form dirt-bands if
+they could. On neither branch, however, do the bands attain the
+definition and beauty which they possess upon the Mer de Glace.
+
+After an instructive lesson we faced our task once more, passing amid
+crags and boulders, and over steep moraines, from which the stones
+rolled down upon the slightest disturbance. While crossing a slope of
+snow with an inclination of 45 deg., my footing gave way, I fell, but
+turned promptly on my face, dug my staff deeply into the snow, and
+arrested the motion before I had slid a dozen yards. Ramsay was behind me,
+speculating whether he should be able to pass the same point without
+slipping; before he reached it, however, the snow yielded, he fell, and
+slid swiftly downwards. Lauener, whose attention had been aroused by my
+fall, chanced to be looking round when Ramsay's footing yielded. With
+the velocity of a projectile he threw himself upon my companion, seized
+him, and brought him to rest before he had reached the bottom of the
+slope. The act made a very favourable impression upon me, it was so
+prompt and instinctive. An eagle could not swoop upon its prey with more
+directness of aim and swiftness of execution.
+
+[Sidenote: ICE CLIFFS THROUGH THE FOG. 1858.]
+
+While this went on the clouds were playing hide and seek with the
+mountains. The ice-crags and pinnacles to our left, looming through the
+haze, seemed of gigantic proportions, reminding one of the Hades of
+Byron's 'Cain.'
+
+ "How sunless and how vast are these dim realms!"
+
+We climbed for some time along the moraine which flanks the cascade, and
+on reaching the level of the brow Lauener paused, cast off his knapsack,
+and declared for breakfast. While engaged with it the dense clouds which
+had crammed the gorge and obscured the mountains, all melted away, and a
+scene of indescribable magnificence was revealed. Overhead the sky
+suddenly deepened to dark blue, and against it the Finsteraarhorn
+projected his dark and mighty mass. Brown spurs jutted from the
+mountain, and between them were precipitous snow-slopes, fluted by the
+descent of rocks and avalanches, and broken into ice-precipices lower
+down. Right in front of us, and from its proximity more gigantic to the
+eye, was the Schreckhorn, while from couloirs and mountain-slopes the
+matter of glaciers yet to be was poured into the vast basin on the rim
+of which we now stood.
+
+[Sidenote: MUTATIONS OF THE CLOUDS. 1858.]
+
+This it was next our object to cross; our way lying in part through deep
+snow-slush, the scene changing perpetually from blue heaven to gray haze
+which massed itself at intervals in dense clouds about the mountains.
+After crossing the basin our way lay partly over slopes of snow, partly
+over loose shingle, and at one place along the edge of a formidable
+precipice of rock. We sat down sometimes to rest, and during these
+pauses, though they were very brief, the scene had time to go through
+several of its Protean mutations. At one moment all would be perfectly
+serene, no cloud in the transparent air to tell us that any portion of
+it was in motion, while the blue heaven threw its flattened arch over
+the magnificent amphitheatre. Then in an instant, from some local
+cauldron, the vapour would boil up suddenly, eddying wildly in the air,
+which a moment before seemed so still, and enveloping the entire scene.
+Thus the space enclosed by the Finsteraarhorn, the Viescherhoerner, and
+the Schreckhorn, would at one moment be filled with fog to the mountain
+heads, every trace of which a few minutes sufficed to sweep away,
+leaving the unstained blue of heaven behind it, and the mountains
+showing sharp and jagged outlines in the glassy air. One might be almost
+led to imagine that the vapour molecules endured a strain similar to
+that of water cooled below its freezing point, or heated beyond its
+boiling point; and that, on the strain being relieved by the sudden
+yielding of the opposing force, the particles rushed together, and thus
+filled in an instant the clear atmosphere with aqueous precipitation.
+
+I had no idea that the Strahleck was so fine a pass. Whether it is the
+quality of my mind to take in the glory of the present so intensely as
+to make me forgetful of the glory of the past, I know not, but it
+appeared to me that I had never seen anything finer than the scene from
+the summit. The amphitheatre formed by the mountains seemed to me of
+exceeding magnificence; nor do I think that my feeling was subjective
+merely; for the simple magnitude of the masses which built up the
+spectacle would be sufficient to declare its grandeur. Looking down
+towards the Glacier of the Aar, a scene of wild beauty and desolation
+presented itself. Not a trace of vegetation could be seen along the
+whole range of the bounding mountains; glaciers streamed from their
+shoulders into the valley beneath, where they welded themselves to form
+the Finsteraar affluent of the Unteraar glacier.
+
+[Sidenote: DESCENT OF THE CRAGS. 1858.]
+
+After a brief pause, Lauener again strapped on his knapsack, and
+tempered both will and muscles by the remark, that our worst piece of
+work was now before us. From the place where we sat, the mountain fell
+precipitously for several hundred feet; and down the weathered crags,
+and over the loose shingle which encumbered their ledges, our route now
+lay. Lauener was in front, cool and collected, lending at times a hand
+to Ramsay, and a word of encouragement to both of us, while I brought up
+the rear. I found my full haversack so inconvenient that I once or twice
+thought of sending it down the crags in advance of me, but Lauener
+assured me that it would be utterly destroyed before reaching the
+bottom. My complaint against it was, that at critical places it
+sometimes came between me and the face of the cliff, pushing me away
+from the latter so as to throw my centre of gravity almost beyond the
+base intended to support it. We came at length upon a snow-slope, which
+had for a time an inclination of 50 deg.; then once more to the rocks;
+again to the snow, which was both steep and deep. Our batons were at
+least six feet long: we drove them into the snow to secure an anchorage,
+but they sank to their very ends, and we merely retained a length of them
+sufficient for a grasp. This slope was intersected by a so-called
+Bergschrund, the lower portion of the slope being torn away from its
+upper portion so as to form a crevasse that extended quite round the
+head of the valley. We reached its upper edge; the chasm was partially
+filled with snow, which brought its edges so near that we cleared it by
+a jump. The rest of the slope was descended by a _glissade_. Each sat
+down upon the snow, and the motion, once commenced, swiftly augmented to
+the rate of an avalanche, and brought us pleasantly to the bottom.
+
+[Sidenote: THROUGH GLOOM TO THE GRIMSEL. 1858.]
+
+As we looked from the heights, we could see that the valley through
+which our route lay was filled with gray fog: into this we soon plunged,
+and through it we made our way towards the Abschwung. The inclination of
+the glacier was our only guide, for we could see nothing. Reaching the
+confluence of the Finsteraar and Lauteraar branches, we went downwards
+with long swinging strides, close alongside the medial moraine of the
+trunk glacier. The glory of the morning had its check in the dull gloom
+of the evening. Across streams, amid dirt-cones and glacier-tables, and
+over the long reach of shingle which covers the end of the glacier, we
+plodded doggedly, and reached the Grimsel at 7 P.M., the journey having
+cost a little more than 14 hours.
+
+
+
+
+(15.)
+
+
+[Sidenote: ANCIENT GLACIER ACTION. 1858.]
+
+We made the Grimsel our station for a day, which was spent in examining
+the evidences of ancient glacier action in the valley of Hasli. Near the
+Hospice, but at the opposite side of the Aar, rises a mountain-wall of
+hard granite, on which the flutings and groovings are magnificently
+preserved. After a little practice the eye can trace with the utmost
+precision the line which marks the level of the ancient ice: above this
+the crags are sharp and rugged; while below it the mighty grinder has
+rubbed off the pinnacles of the rocks and worn their edges away. The
+height to which this action extends must be nearly two thousand feet
+above the bed of the present valley. It is also easy to see the depth to
+which the river has worked its channel into the ancient rocks. In some
+cases the road from Guttanen to the Grimsel lay right over the polished
+rocks, asperities being supplied by the chisel of man in order to
+prevent travellers from slipping on their slopes. Here and there also
+huge protuberant crags were rounded into domes almost as perfect as if
+chiselled by art. To both my companion and myself this walk was full of
+instruction and delight.
+
+On the 28th of July we crossed the Grimsel pass, and traced the
+scratchings to the very top of it. Ramsay remarked that their direction
+changed high up the pass, as if a tributary from the summit had produced
+them, while lower down they merged into the general direction of the
+glacier which had filled the principal valley. From the summit of the
+Mayenwand we had a clear view of the glacier of the Rhone; and to see
+the lower portion of this glacier to advantage no better position can be
+chosen. The dislocation of its cascade, the spreading out of the ice
+below, its system of radial crevasses, and the transverse sweep of its
+structural groovings, may all be seen. A few hours afterwards we were
+among the wild chasms at the brow of the ice-fall, where we worked our
+way to the centre of the ice, but were unable to attain the opposite
+side.
+
+Having examined the glacier both above and below the cascade, we went
+down the valley to Viesch, and ascended thence, on the 30th of July, to
+the Hotel Jungfrau on the slopes of the AEggischhorn. On the following
+day we climbed to the summit of the mountain, and from a sheltered nook
+enjoyed the glorious prospect which it commands. The wind was strong,
+and fleecy clouds flew over the heavens; some of which, as they formed
+and dispersed themselves about the flanks of the Aletschhorn, showed
+extraordinary iridescences.
+
+[Sidenote: THE MAeRJELEN SEE. 1858.]
+
+The sunbeams called us early on the morning of the 1st of August. No
+cloud rested on the opposite range of the Valais mountains, but on
+looking towards the AEggischhorn we found a cap upon its crest; we looked
+again--the cap had disappeared and a serene heaven stretched overhead.
+As we breasted the alp the moon was still in the sky, paling more and
+more before the advancing day; a single hawk swung in the atmosphere
+above us; clear streams babbled from the hills, the louder sounds
+reposing on a base of music; while groups of cows with tinkling bells
+browsed upon the green alp. Here and there the grass was dispossessed,
+and the flanks of the mountain were covered by the blocks which had been
+cast down from the summit. On reaching the plateau at the base of the
+final pyramid, we rounded the mountain to the right and came over the
+lonely and beautiful Maerjelen See. No doubt the hollow which this lake
+fills had been scooped out in former ages by a branch of the Aletsch
+glacier; but long ago the blue ice gave place to blue water. The glacier
+bounds it at one side by a vertical wall of ice sixty feet in height:
+this is incessantly undermined, a roof of crystal being formed over the
+water, till at length the projecting mass, becoming too heavy for its
+own rigidity, breaks and tumbles into the lake. Here, attacked by sun
+and air, its blue surface is rendered dazzlingly white, and several
+icebergs of this kind now floated in the sunlight; the water was of a
+glassy smoothness, and in its blue depths each ice mass doubled itself
+by reflection.[A]
+
+[Sidenote: THE ALETSCH GLACIER. 1858.]
+
+The Aletsch is the grandest glacier in the Alps: over it we now stood,
+while the bounding mountains poured vast feeders into the noble stream.
+The Jungfrau was in front of us without a cloud, and apparently so near
+that I proposed to my guide to try it without further preparation. He
+was enthusiastic at first, but caution afterwards got the better of his
+courage. At some distance up the glacier the snow-line was distinctly
+drawn, and from its edge upwards the mighty shoulders of the hills were
+heavy laden with the still powdery material of the glacier.
+
+Amid blocks and debris we descended to the ice: the portion of it which
+bounded the lake had been sapped, and a space of a foot existed between
+ice and water: numerous chasms were formed here, the mass being thus
+broken, preparatory to being sent adrift upon the lake. We crossed the
+glacier to its centre, and looking down it the grand peaks of the
+Mischabel, the noble cone of the Weisshorn, and the dark and stern
+obelisk of the Matterhorn, formed a splendid picture. Looking upwards, a
+series of most singularly contorted dirt-bands revealed themselves upon
+the surface of the ice. I sought to trace them to their origin, but was
+frustrated by the snow which overspread the upper portion of the
+glacier. Along this we marched for three hours, and came at length to
+the junction of the four tributary valleys which pour their frozen
+streams into the great trunk valley. The glory of the day, and that joy
+of heart which perfect health confers, may have contributed to produce
+the impression, but I thought I had never seen anything to rival in
+magnificence the region in the heart of which we now found ourselves. We
+climbed the mountain on the right-hand side of the glacier, where,
+seated amid the riven and weather-worn crags, we fed our souls for hours
+on the transcendent beauty of the scene.
+
+[Sidenote: A CHAMOIS DECEIVED. 1858.]
+
+We afterwards redescended to the glacier, which at this place was
+intersected by large transverse crevasses, many of which were apparently
+filled with snow, while over others a thin and treacherous roof was
+thrown. In some cases the roof had broken away, and revealed rows of
+icicles of great length and transparency pendent from the edges. We at
+length turned our faces homewards, and looking down the glacier I saw
+at a great distance something moving on the ice. I first thought it was
+a man, though it seemed strange that a man should be there alone. On
+drawing my guide's attention to it he at once pronounced it to be a
+chamois, and I with my telescope immediately verified his statement. The
+creature bounded up the glacier at intervals, and sometimes the vigour
+of its spring showed that it had projected itself over a crevasse. It
+approached us sometimes at full gallop: then would stop, look toward us,
+pipe loudly, and commence its race once more. It evidently made the
+reciprocal mistake to my own, imagining us to be of its own kith and
+kin. We sat down upon the ice the better to conceal our forms, and to
+its whistle our guide whistled in reply. A joyous rush was the
+creature's first response to the signal; but it afterwards began to
+doubt, and its pauses became more frequent. Its form at times was
+extremely graceful, the head erect in the air, its apparent uprightness
+being augmented by the curvature which threw its horns back. I watched
+the animal through my glass until I could see the glistening of its
+eyes; but soon afterwards it made a final pause, assured itself of its
+error, and flew with the speed of the wind to its refuge in the
+mountains.
+
+
+FOOTNOTES:
+
+[A] A painting of this exquisite lake has been recently executed by Mr.
+George Barnard.
+
+
+
+
+ASCENT OF THE FINSTERAARHORN, 1858.
+
+(16.)
+
+
+[Sidenote: MY GUIDE. 1858.]
+
+Since my arrival at the hotel on the 30th of July I had once or twice
+spoken about ascending the Finsteraarhorn, and on the 2nd of August my
+host advised me to avail myself of the promising weather. A guide, named
+Bennen, was attached to the hotel, a remarkable-looking man, between 30
+and 40 years old, of middle stature, but very strongly built. His
+countenance was frank and firm, while a light of good-nature at times
+twinkled in his eye. Altogether the man gave me the impression of
+physical strength, combined with decision of character. The proprietor
+had spoken to me many times of the strength and courage of this man,
+winding up his praises of him by the assurance that if I were killed in
+Bennen's company there would be two lives lost, for that the guide would
+assuredly sacrifice himself in the effort to save his _Herr_.
+
+He was called, and I asked him whether he would accompany me alone to
+the top of the Finsteraarhorn. To this he at first objected, urging the
+possibility of his having to render me assistance, and the great amount
+of labour which this might entail upon him; but this was overruled by my
+engaging to follow where he led, without asking him to render me any
+help whatever. He then agreed to make the trial, stipulating, however,
+that he should not have much to carry to the cave of the Faulberg, where
+we were to spend the night. To this I cordially agreed, and sent on
+blankets, provisions, wood, and hay, by two porters.
+
+[Sidenote: IRIDESCENT CLOUD. 1858.]
+
+My desire, in part, was to make a series of observations at the summit
+of the mountain, while a similar series was made by Professor Ramsay in
+the valley of the Rhone, near Viesch, with a view to ascertaining the
+permeability of the lower strata of the atmosphere to the radiant heat
+of the sun. During the forenoon of the 2nd I occupied myself with my
+instruments, and made the proper arrangements with Ramsay. I tested a
+mountain-thermometer which Mr. Casella had kindly lent me, and found the
+boiling point of water on the dining-room table of the hotel to be
+199.29 deg. Fahrenheit. At about three o'clock in the afternoon we quitted
+the hotel, and proceeded leisurely with our two guides up the slope of
+the AEggischhorn. We once caught a sight of the topmost pinnacle of the
+Finsteraarhorn; beside it was the Rothhorn, and near this again the
+Oberaarhorn, with the Viescher glacier streaming from its shoulders. On
+the opposite side we could see, over an oblique buttress of the mountain
+on which we stood, the snowy summit of the Weisshorn; to the left of
+this was the ever grim and lonely Matterhorn; and farther to the left,
+with its numerous snow-cones, each with its attendant shadow, rose the
+mighty Mischabel. We descended, and crossed the stream which flows from
+the Maerjelen See, into which a large mass of the glacier had recently
+fallen, and was now afloat as an iceberg. We passed along the margin of
+the lake, and at the junction of water and ice I bade Ramsay good-bye.
+At the commencement of our journey upon the ice, whenever we crossed a
+crevasse, I noticed Bennen watching me; his vigilance, however, soon
+diminished, whence I gathered that he finally concluded that I was able
+to take care of myself. Clouds hovered in the atmosphere throughout the
+whole time of our ascent; one smoky-looking mass marred the glory of the
+sunset, but at some distance was another which exhibited colours almost
+as rich and varied as those of the solar spectrum. I took the glorious
+banner thus unfurled as a sign of hope, to check the despondency which
+its gloomy neighbour was calculated to produce.
+
+[Sidenote: EVENING NEAR THE JUNGFRAU. 1858.]
+
+Two hours' walking brought us near our place of rest; the porters had
+already reached it, and were now returning. We deviated to the right,
+and, having crossed some ice-ravines, reached the lateral moraine of the
+glacier, and picked our way between it and the adjacent mountain-wall.
+We then reached a kind of amphitheatre, crossed it, and climbing the
+opposite slope, came to a triple grotto formed by clefts in the
+mountain. In one of these a pine-fire was soon blazing briskly, and
+casting its red light upon the surrounding objects, though but half
+dispelling the gloom from the deeper portions of the cell. I left the
+grotto, and climbed the rocks above it to look at the heavens. The sun
+had quitted our firmament, but still tinted the clouds with red and
+purple; while one peak of snow in particular glowed like fire, so vivid
+was its illumination. During our journey upwards the Jungfrau never once
+showed her head, but, as if in ill temper, had wrapped her vapoury veil
+around her. She now looked more good-humoured, but still she did not
+quite remove her hood; though all the other summits, without a trace of
+cloud to mask their beautiful forms, pointed heavenward. The calmness
+was perfect; no sound of living creature, no whisper of a breeze, no
+gurgle of water, no rustle of debris, to break the deep and solemn
+silence. Surely, if beauty be an object of worship, those glorious
+mountains, with rounded shoulders of the purest white--snow-crested and
+star-gemmed--were well calculated to excite sentiments of adoration.
+
+[Sidenote: THE CAVE OF THE FAULBERG. 1858.]
+
+I returned to the grotto, where supper was prepared and waiting for me.
+The boiling point of water, at the level of the "kitchen" floor, I found
+to be 196 deg. Fahr. Nothing could be more picturesque than the aspect of
+the cave before we went to rest. The fire was gleaming ruddily. I sat
+upon a stone bench beside it, while Bennen was in front with the red
+light glimmering fitfully over him. My boiling-water apparatus, which
+had just been used, was in the foreground; and telescopes,
+opera-glasses, haversacks, wine-keg, bottles, and mattocks, lay
+confusedly around. The heavens continued to grow clearer, the thin
+clouds, which had partially overspread the sky, melting gradually away.
+The grotto was comfortable; the hay sufficient materially to modify the
+hardness of the rock, and my position at least sheltered and warm. One
+possibility remained that might prevent me from sleeping--the snoring of
+my companion; he assured me, however, that he did not snore, and we lay
+down side by side. The good fellow took care that I should not be
+chilled; he gave me the best place, by far the best part of the clothes,
+and may have suffered himself in consequence; but, happily for him, he
+was soon oblivious of this. Physiologists, I believe, have discovered
+that it is chiefly during sleep that the muscles are repaired; and ere
+long the sound I dreaded announced to me at once the repair of Bennen's
+muscles and the doom of my own. The hollow cave resounded to the
+deep-drawn snore. I once or twice stirred the sleeper, breaking thereby
+the continuity of the phenomenon; but it instantly pieced itself
+together again, and went on as before. I had not the heart to wake him,
+for I knew that upon him would devolve the chief labour of the coming
+day. At half-past one he rose and prepared coffee, and at two o'clock I
+was engaged upon the beverage. We afterwards packed up our provisions
+and instruments. Bennen bore the former, I the latter, and at three
+o'clock we set out.
+
+[Sidenote: "SHALL WE TRY THE JUNGFRAU?" 1858.]
+
+We first descended a steep slope to the glacier, along which we walked
+for a time. A spur of the Faulberg jutted out between us and the
+ice-laden valley through which we must pass; this we crossed in order to
+shorten our way and to avoid crevasses. Loose shingle and boulders
+overlaid the mountain; and here and there walls of rock opposed our
+progress, and rendered the route far from agreeable. We then descended
+to the Gruenhorn tributary, which joins the trunk glacier at nearly a
+right angle, being terminated by a saddle which stretches across from
+mountain to mountain, with a curvature as graceful and as perfect as if
+drawn by the instrument of a mathematician. The unclouded moon was
+shining, and the Jungfrau was before us so pure and beautiful, that the
+thought of visiting the "Maiden" without further preparation occurred to
+me. I turned to Bennen, and said, "Shall we try the Jungfrau?" I think
+he liked the idea well enough, though he cautiously avoided incurring
+any responsibility. "If you desire it, I am ready," was his reply. He
+had never made the ascent, and nobody knew anything of the state of the
+snow this year; but Lauener had examined it through a telescope on the
+previous day, and pronounced it dangerous. In every ascent of the
+mountain hitherto made, ladders had been found indispensable, but we had
+none. I questioned Bennen as to what he thought of the probabilities,
+and tried to extract some direct encouragement from him; but he said
+that the decision rested altogether with myself, and it was his business
+to endeavour to carry out that decision. "We will attempt it, then," I
+said, and for some time we actually walked towards the Jungfrau. A gray
+cloud drew itself across her summit, and clung there. I asked myself why
+I deviated from my original intention? The Finsteraarhorn was higher,
+and therefore better suited for the contemplated observations. I could
+in no wise justify the change, and finally expressed my scruples. A
+moment's further conversation caused us to "right about," and front the
+saddle of the Gruenhorn.
+
+[Sidenote: MAGNIFICENT SCENE. 1858.]
+
+The dawn advanced. The eastern sky became illuminated and warm, and high
+in the air across the ridge in front of us stretched a tongue of cloud
+like a red flame, and equally fervid in its hue. Looking across the
+trunk glacier, a valley which is terminated by the Loetsch saddle was
+seen in a straight line with our route, and I often turned to look along
+this magnificent corridor. The mightiest mountains in the Oberland form
+its sides; still, the impression which it makes is not that of vastness
+or sublimity, but of loveliness not to be described. The sun had not yet
+smitten the snows of the bounding mountains, but the saddle carved out a
+segment of the heavens which formed a background of unspeakable beauty.
+Over the rim of the saddle the sky was deep orange, passing upwards
+through amber, yellow, and vague ethereal green to the ordinary
+firmamental blue. Right above the snow-curve purple clouds hung
+perfectly motionless, giving depth to the spaces between them. There was
+something saintly in the scene. Anything more exquisite I had never
+beheld.
+
+We marched upwards over the smooth crisp snow to the crest of the
+saddle, and here I turned to take a last look along that grand corridor,
+and at that wonderful "daffodil sky." The sun's rays had already smitten
+the snows of the Aletschhorn; the radiance seemed to infuse a principle
+of life and activity into the mountains and glaciers, but still that
+holy light shone forth, and those motionless clouds floated beyond,
+reminding one of that eastern religion whose essence is the repression
+of all action and the substitution for it of immortal calm. The
+Finsteraarhorn now fronted us; but clouds turbaned the head of the
+giant, and hid it from our view. The wind, however, being north,
+inspired us with a strong hope that they would melt as the day advanced.
+I have hardly seen a finer ice-field than that which now lay before us.
+Considering the _neve_ which supplies it, it appeared to me that the
+Viescher glacier ought to discharge as much ice as the Aletsch; but this
+is an error due to the extent of _neve_ which is here at once visible:
+since a glance at the map of this portion of the Oberland shows at once
+the great superiority of the mountain treasury from which the Aletsch
+glacier draws support. Still, the ice-field before us was a most noble
+one. The surrounding mountains were of imposing magnitude, and loaded to
+their summits with snow. Down the sides of some of them the
+half-consolidated mass fell in a state of wild fracture and confusion.
+In some cases the riven masses were twisted and overturned, the ledges
+bent, and the detached blocks piled one upon another in heaps; while in
+other cases the smooth white mass descended from crown to base without a
+wrinkle. The valley now below us was gorged by the frozen material thus
+incessantly poured into it. We crossed it, and reached the base of the
+Finsteraarhorn, ascended the mountain a little way, and at six o'clock
+paused to lighten our burdens and to refresh ourselves.
+
+[Sidenote: THE MOUNTAIN ASSAILED. 1858.]
+
+The north wind had freshened, we were in the shade, and the cold was
+very keen. Placing a bottle of tea and a small quantity of provisions in
+the knapsack, and a few figs and dried prunes in our pockets, we
+commenced the ascent. The Finsteraarhorn sends down a number of cliffy
+buttresses, separated from each other by wide couloirs filled with ice
+and snow. We ascended one of these buttresses for a time, treading
+cautiously among the spiky rocks; afterwards we went along the snow at
+the edge of the spine, and then fairly parted company with the rock,
+abandoning ourselves to the _neve_ of the couloir. The latter was steep,
+and the snow was so firm that steps had to be cut in it. Once I paused
+upon a little ledge, which gave me a slight footing, and took the
+inclination. The slope formed an angle of 45 deg. with the horizon; and
+across it, at a little distance below me, a gloomy fissure opened its
+jaws. The sun now cleared the summits which had before cut off his rays,
+and burst upon us with great power, compelling us to resort to our
+veils and dark spectacles. Two years before, Bennen had been nearly
+blinded by inflammation brought on by the glare from the snow, and he
+now took unusual care in protecting his eyes. The rocks looking more
+practicable, we again made towards them, and clambered among them till a
+vertical precipice, which proved impossible of ascent, fronted us.
+Bennen scanned the obstacle closely as we slowly approached it, and
+finally descended to the snow, which wound at a steep angle round its
+base: on this the footing appeared to me to be singularly insecure, but
+I marched without hesitation or anxiety in the footsteps of my guide.
+
+[Sidenote: THE CREST OF ROCKS. 1858.]
+
+We ascended the rocks once more, continued along them for some time, and
+then deviated to the couloir on our left. This snow-slope is much
+dislocated at its lower portion, and above its precipices and crevasses
+our route now lay. The snow was smooth, and sufficiently firm and steep
+to render the cutting of steps necessary. Bennen took the lead: to make
+each step he swung his mattock once, and his hindmost foot rose exactly
+at the moment the mattock descended; there was thus a kind of rhythm in
+his motion, the raising of the foot keeping time to the swing of the
+implement. In this manner we proceeded till we reached the base of the
+rocky pyramid which caps the mountain.
+
+[Sidenote: THE SUMMIT GAINED. 1858.]
+
+One side of the pyramid had been sliced off, thus dropping down almost a
+sheer precipice for some thousands of feet to the Finsteraar glacier. A
+wall of rock, about 10 or 15 feet high, runs along the edge of the
+mountain, and this sheltered us from the north wind, which surged with
+the sound of waves against the tremendous barrier at the other side.
+"Our hardest work is now before us," said my guide. Our way lay up the
+steep and splintered rocks, among which we sought out the spikes which
+were closely enough wedged to bear our weight. Each had to trust to
+himself, and I fulfilled to the letter my engagement with Bennen to ask
+no help. My boiling-water apparatus and telescope were on my back, much
+to my annoyance, as the former was heavy, and sometimes swung awkwardly
+round as I twisted myself among the cliffs. Bennen offered to take it,
+but he had his own share to carry, and I was resolved to bear mine.
+Sometimes the rocks alternated with spaces of ice and snow, which we
+were at intervals compelled to cross; sometimes, when the slope was pure
+ice and very steep, we were compelled to retreat to the highest cliffs.
+The wall to which I have referred had given way in some places, and
+through the gaps thus formed the wind rushed with a loud, wild, wailing
+sound. Through these spaces I could see the entire field of Agassiz's
+observations; the junction of the Lauteraar and Finsteraar glaciers at
+the Abschwung, the medial moraine between them, on which stood the Hotel
+des Neufchatelois, and the pavilion built by M. Dollfuss, in which
+Huxley and myself had found shelter two years before. Bennen was
+evidently anxious to reach the summit, and recommended all observations
+to be postponed until after our success had been assured. I agreed to
+this, and kept close at his heels. Strong as he was, he sometimes
+paused, laid his head upon his mattock, and panted like a chased deer.
+He complained of fearful thirst, and to quench it we had only my bottle
+of tea: this we shared loyally, my guide praising its virtues, as well
+he might. Still the summit loomed above us; still the angry swell of the
+north wind, beating against the torn battlements of the mountain, made
+wild music. Upward, however, we strained; and at last, on gaining the
+crest of a rock, Bennen exclaimed, in a jubilant voice, "_Die hoechste
+Spitze!_"--the highest point. In a moment I was at his side, and saw the
+summit within a few paces of us. A minute or two placed us upon the
+topmost-pinnacle, with the blue dome of heaven above us, and a world of
+mountains, clouds, and glaciers beneath.
+
+A notion is entertained by many of the guides that if you go to sleep at
+the summit of any of the highest mountains, you will
+
+ "Sleep the sleep that knows no waking."
+
+[Sidenote: THERMOMETER PLACED. 1858.]
+
+Bennen did not appear to entertain this superstition; and before
+starting in the morning, I had stipulated for ten minutes' sleep on
+reaching the summit, as part compensation for the loss of the night's
+rest. My first act, after casting a glance over the glorious scene
+beneath us, was to take advantage of this agreement; so I lay down and
+had five minutes' sleep, from which I rose refreshed and brisk. The sun
+at first beat down upon us with intense force, and I exposed my
+thermometers; but thin veils of vapour soon drew themselves before the
+sun, and denser mists spread over the valley of the Rhone, thus
+destroying all possibility of concert between Ramsay and myself. I
+turned therefore to my boiling-water apparatus, filled it with snow,
+melted the first charge, put more in, and boiled it; ascertaining the
+boiling point to be 187 deg. Fahrenheit. On a sheltered ledge, about two or
+three yards south of the highest point, I placed a minimum-thermometer,
+in the hope that it would enable us in future years to record the lowest
+winter temperatures at the summit of the mountain.[A]
+
+[Sidenote: SCENE FROM THE SUMMIT. 1858.]
+
+It is difficult to convey any just impression of the scene from the
+summit of the Finsteraarhorn: one might, it is true, arrange the visible
+mountains in a list, stating their heights and distances, and leaving
+the imagination to furnish them with peaks and pinnacles, to build the
+precipices, polish the snow, rend the glaciers, and cap the highest
+summits with appropriate clouds. But if imagination did its best in this
+way, it would hardly exceed the reality, and would certainly omit many
+details which contribute to the grandeur of the scene itself. The
+various shapes of the mountains, some grand, some beautiful, bathed in
+yellow sunshine, or lying black and riven under the frown of impervious
+cumuli; the pure white peaks, cornices, bosses, and amphitheatres; the
+blue ice rifts, the stratified snow-precipices, the glaciers issuing
+from the hollows of the eternal hills, and stretching like frozen
+serpents through the sinuous valleys; the lower cloud field--itself an
+empire of vaporous hills--shining with dazzling whiteness, while here
+and there grim summits, brown by nature, and black by contrast, pierce
+through it like volcanic islands through a shining sea,--add to this the
+consciousness of one's position which clings to one _unconsciously_,
+that undercurrent of emotion which surrounds the question of one's
+personal safety, at a height of more than 14,000 feet above the sea, and
+which is increased by the weird strange sound of the wind surging with
+the full deep boom of the distant sea against the precipice behind, or
+rising to higher cadences as it forces itself through the crannies of
+the weatherworn rocks,--all conspire to render the scene from the
+Finsteraarhorn worthy of the monarch of the Bernese Alps.
+
+[Sidenote: "HAVE NO FEAR." 1858.]
+
+[Sidenote: DISCIPLINE. 1858.]
+
+My guide at length warned me that we must be moving; repeating the
+warning more impressively before I attended to it. We packed up, and as
+we stood beside each other ready to march he asked me whether we should
+tie ourselves together, at the same time expressing his belief that it
+was unnecessary. Up to this time we had been separate, and the thought
+of attaching ourselves had not occurred to me till he mentioned it. I
+thought it, however, prudent to accept the suggestion, and so we united
+our destinies by a strong rope. "Now," said Bennen, "have no fear; no
+matter how you throw yourself, I will hold you." Afterwards, on another
+perilous summit, I repeated this saying of Bennen's to a strong and
+active guide, but his observation was that it was a hardy untruth, for
+that in many places Bennen could not have held me. Nevertheless a daring
+word strengthens the heart, and, though I felt no trace of that
+sentiment which Bennen exhorted me to banish, and was determined, as far
+as in me lay, to give him no opportunity of trying his strength in
+saving me, I liked the fearless utterance of the man, and sprang
+cheerily after him. Our descent was rapid, apparently reckless, amid
+loose spikes, boulders, and vertical prisms of rock, where a false step
+would assuredly have been attended with broken bones; but the
+consciousness of certainty in our movements never forsook us, and proved
+a source of keen enjoyment. The senses were all awake, the eye clear,
+the heart strong, the limbs steady, yet flexible, with power of recovery
+in store, and ready for instant action should the footing give way. Such
+is the discipline which a perilous ascent imposes.
+
+[Sidenote: DESCENT BY GLISSADES. 1858.]
+
+We finally quitted the crest of rocks, and got fairly upon the snow once
+more. We first went downwards at a long swinging trot. The sun having
+melted the crust which we were compelled to cut through in the morning,
+the leg at each plunge sank deeply into the snow; but this sinking was
+partly in the direction of the slope of the mountain, and hence assisted
+our progress. Sometimes the crust was hard enough to enable us to glide
+upon it for long distances while standing erect; but the end of these
+_glissades_ was always a plunge and tumble in the deeper snow. Once upon
+a steep hard slope Bennen's footing gave way; he fell, and went down
+rapidly, pulling me after him. I fell also, but turning quickly, drove
+the spike of my hatchet into the ice, got good anchorage, and held both
+fast; my success assuring me that I had improved as a mountaineer since
+my ascent of Mont Blanc. We tumbled so often in the soft snow, and our
+clothes and boots were so full of it, that we thought we might as well
+try the sitting posture in gliding down. We did so, and descended with
+extraordinary velocity, being checked at intervals by a bodily immersion
+in the softer and deeper snow. I was usually in front of Bennen,
+shooting down with the speed of an arrow and feeling the check of the
+rope when the rapidity of my motion exceeded my guide's estimate of
+what was safe. Sometimes I was behind him, and darted at intervals with
+the swiftness of an avalanche right upon him; sometimes in the same
+transverse line with him, with the full length of the rope between us;
+and here I found its check unpleasant, as it tended to make me roll
+over. My feet were usually in the air, and it was only necessary to turn
+them right or left, like the helm of a boat, to change the direction of
+motion and avoid a difficulty, while a vigorous dig of leg and hatchet
+into the snow was sufficient to check the motion and bring us to rest.
+Swiftly, yet cautiously, we glided into the region of crevasses, where
+we at last rose, quite wet, and resumed our walking, until we reached
+the point where we had left our wine in the morning, and where I
+squeezed the water from my wet clothes, and partially dried them in the
+sun.
+
+[Sidenote: THE VIESCH GLACIER. 1858.]
+
+We had left some things at the cave of the Faulberg, and it was Bennen's
+first intention to return that way and take them home with him. Finding,
+however, that we could traverse the Viescher glacier almost to the
+AEggischhorn, I made this our highway homewards. At the place where we
+entered it, and for an hour or two afterwards, the glacier was cut by
+fissures, for the most part covered with snow. We had packed up our
+rope, and Bennen admonished me to tread in his steps. Three or four
+times he half disappeared in the concealed fissures, but by clutching
+the snow he rescued himself and went on as swiftly as before. Once my
+leg sank, and the ring of icicles some fifty feet below told me that I
+was in the jaws of a crevasse; my guide turned sharply--it was the only
+time that I had seen concern on his countenance:--
+
+"_Gott's Donner! Sie haben meine Tritte nicht gefolgt._"
+
+"_Doch!_" was my only reply, and we went on. He scarcely tried the snow
+that he crossed, as from its form and colour he could in most cases
+judge of its condition. For a long time we kept at the left-hand side of
+the glacier, avoiding the fissures which were now permanently open. We
+came upon the tracks of a herd of chamois, which had clambered from the
+glacier up the sides of the Oberaarhorn, and afterwards crossed the
+glacier to the right-hand side, my guide being perfect master of the
+ground. His eyes went in advance of his steps, and his judgment was
+formed before his legs moved. The glacier was deeply fissured, but there
+was no swerving, no retreating, no turning back to seek more practicable
+routes; each stride told, and every stroke of the axe was a profitable
+investment of labour.
+
+We left the glacier for a time, and proceeded along the mountain side,
+till we came near the end of the Trift glacier, where we let ourselves
+down an awkward face of rock along the track of a little cascade, and
+came upon the glacier once more. Here again I had occasion to admire the
+knowledge and promptness of my guide. The glacier, as is well known, is
+greatly dislocated, and has once or twice proved a prison to guides and
+travellers, but Bennen led me through the confusion without a pause. We
+were sometimes in the middle of the glacier, sometimes on the moraine,
+and sometimes on the side of the flanking mountain. Towards the end of
+the day we crossed what seemed to be the consolidated remains of a great
+avalanche; on this my foot slipped, there was a crevasse at hand, and a
+sudden effort was necessary to save me from falling into it. In making
+this effort the spike of my axe turned uppermost, and the palm of my
+hand came down upon it, thus receiving a very ugly wound. We were soon
+upon the green alp, having bidden a last farewell to the ice. Another
+hour's hard walking brought us to our hotel. No one seeing us crossing
+the alp would have supposed that we had laid such a day's work behind
+us; the proximity of home gave vigour to our strides, and our progress
+was much more speedy than it had been on starting in the morning. I was
+affectionately welcomed by Ramsay, had a warm bath, dined, went to bed,
+where I lay fast locked in sleep for eight hours, and rose next morning
+as fresh and vigorous as if I had never scaled the Finsteraarhorn.
+
+
+FOOTNOTES:
+
+[A] The following note describes the single observation made with this
+thermometer. Mr. B. informs me that on finding the instrument Bennen
+swung it in triumph round his head. I fear, therefore, that the
+observation gives us no certain information regarding the minimum
+winter-temperature.
+
+ "St. Nicholas, 1859, Aug. 25.
+
+"Sir,--On Tuesday last (the 23rd inst.) a party, consisting of Messrs.
+B., H., R. L., and myself, succeeded in reaching the summit of the
+Finsteraarhorn under the guidance of Bennen and Melchior Anderegg. We
+made it an especial object to observe and reset the minimum-thermometer
+which you left there last year. On reaching the summit, before I had
+time to stop him, Bennen produced the instrument, and it is just
+possible that in moving it he may have altered the position of the
+index. However, as he held the instrument horizontally, and did not, as
+far as I saw, give it any sensible jerk, I have great confidence that
+the index remained unmoved.
+
+"The reading of the index was -32 deg. Cent.
+
+"A portion of the spirit extending over about 10-1/2 deg. (and standing
+tween 33 deg. and 43-1/2 deg.) was separated from the rest, but there
+appeared to be no data for determining when the separation had taken place.
+As it appeared desirable to unite the two portions of spirit before again
+setting the index to record the cold of another winter, we endeavoured
+to effect this by heating the bulb, but unfortunately, just as we were
+expecting to see them coalesce, the bulb burst, and I have now to
+express my great regret that my clumsiness or ignorance of the proper
+mode of setting the instrument in order should have interfered with the
+continuance of observations of so much interest. The remains of the
+instrument, together with a note of the accident, I have left in the
+charge of Wellig, the landlord of the hotel on the AEggischhorn.
+
+"We reached the summit about 10.40 A.M. and remained there till noon;
+the reading of a pocket thermometer in the shade was 41 deg. F.
+
+"Should there be any further details connected with our ascent on which
+you would like to have information, I shall be happy to supply them to
+the best of my recollection. Meanwhile, with a farther apology for my
+clumsiness, I beg to subscribe myself yours respectfully,
+
+ "H."
+
+"Professor Tyndall."
+
+
+
+
+(17.)
+
+
+[Sidenote: A ROTATING ICEBERG. 1858.]
+
+On the 6th of August there was a long fight between mist and sunshine,
+each triumphing by turns, till at length the orb gained the victory and
+cleansed the mountains from every trace of fog. We descended to the
+Maerjelen See, and, wishing to try the floating power of its icebergs, at
+a place where masses sufficiently large approached near to the shore, I
+put aside a portion of my clothes, and retaining my boots stepped upon
+the floating ice. It bore me for a time, and I hoped eventually to be
+able to paddle myself over the water. On swerving a little, however,
+from the position in which I first stood, the mass turned over and let
+me into the lake. I tried a second one, which served me in the same
+manner; the water was too cold to continue the attempt, and there was
+also some risk of being unpleasantly ground between the opposing
+surfaces of the masses of ice. A very large iceberg which had been
+detached some short time previously from the glacier lay floating at
+some distance from us. Suddenly a sound like that of a waterfall drew
+our attention towards it. We saw it roll over with the utmost
+deliberation, while the water which it carried along with it rushed in
+cataracts down its sides. Its previous surface was white, its present
+one was of a lovely blue, the submerged crystal having now come to the
+air. The summerset of this iceberg produced a commotion all over the
+lake; the floating masses at its edge clashed together, and a mellow
+glucking sound, due to the lapping of the undulations against the frozen
+masses, continued long afterwards.
+
+We subsequently spent several hours upon the glacier; and on this day I
+noticed for the first time a contemporaneous exhibition of _bedding_ and
+_structure_ to which I shall refer at another place. We passed finally
+to the left bank of the glacier, at some distance below the base of the
+AEggischhorn, and traced its old moraines at intervals along the flanks
+of the bounding mountain. At the summit of the ridge we found several
+fine old _roches moutonnees_, on some of which the scratchings of a
+glacier long departed were well preserved; and from the direction of the
+scratchings it might be inferred that the ice moved down the mountain
+towards the valley of the Rhone. A plunge into a lonely mountain lake
+ended the day's excursion.
+
+[Sidenote: END OF THE ALETSCH GLACIER. 1858.]
+
+On the 7th of August we quitted this noble station. Sending our guide on
+to Viesch to take a conveyance and proceed with our luggage down the
+valley, Ramsay and myself crossed the mountains obliquely, desiring to
+trace the glacier to its termination. We had no path, but it was hardly
+possible to go astray. We crossed spurs, climbed and descended pleasant
+mounds, sometimes with the soft grass under our feet, and sometimes
+knee-deep in rhododendrons. It took us several hours to reach the end of
+the glacier, and we then looked down upon it merely. It lay couched like
+a reptile in a wild gorge, as if it had split the mountain by its frozen
+snout. We afterwards descended to Moerill, where we met our guide and
+driver; thence down the valley to Visp; and the following evening saw us
+lodged at the Monte Rosa hotel in Zermatt.
+
+The boiling point of water on the table of the _salle a manger_, I found
+to be 202.58 deg. Fahr.
+
+[Sidenote: MEADOWS INVADED BY ICE. 1858.]
+
+On the following morning I proceeded without my friend to the Goerner
+glacier. As is well known, the end of this glacier has been steadily
+advancing for several years, and when I saw it, the meadow in front of
+it was partly shrivelled up by its irresistible advance. I was informed
+by my host that within the last sixty years forty-four chalets had been
+overturned by the glacier, the ground on which they stood being occupied
+by the ice; at present there are others for which a similar fate seems
+imminent. In thus advancing the glacier merely takes up ground which
+belonged to it in former ages, for the rounded rocks which rise out of
+the adjacent meadow show that it once passed over them.
+
+I had arranged to meet Ramsay this morning on the road to the
+Riffelberg. The meeting took place, but I then learned that a minute or
+two after my departure he had received intelligence of the death of a
+near relative. Thus was our joint expedition terminated, for he resolved
+to return at once to England. At my solicitation he accompanied me to
+the Riffel hotel. We had planned an ascent of Monte Rosa together, but
+the arrangement thus broke down, and I was consequently thrown upon my
+own resources. Lauener had never made the ascent, but he nevertheless
+felt confident that we should accomplish it together.
+
+
+
+
+FIRST ASCENT OF MONTE ROSA, 1858.
+
+(18.)
+
+
+[Sidenote: THE RIFFELBERG. 1858.]
+
+[Sidenote: SOUNDS ON THE GLACIER. 1858.]
+
+On Monday, the 9th of August, we reached the Riffel, and, by good
+fortune, on the evening of the same day, my guide's brother, the
+well-known Ulrich Lauener, also arrived at the hotel on his return from
+Monte Rosa. From him we obtained all the information possible respecting
+the ascent, and he kindly agreed to accompany us a little way the next
+morning, to put us on the right track. At three A.M. the door of my
+bedroom opened, and Christian Lauener announced to me that the weather
+was sufficiently good to justify an attempt. The stars were shining
+overhead; but Ulrich afterwards drew our attention to some heavy clouds
+which clung to the mountains on the other side of the valley of the
+Visp; remarking that the weather _might_ continue fair throughout the
+day, but that these clouds were ominous. At four o'clock we were on our
+way, by which time a gray stratus cloud had drawn itself across the neck
+of the Matterhorn, and soon afterwards another of the same nature
+encircled his waist. We proceeded past the Riffelhorn to the ridge above
+the Goerner glacier, from which Monte Rosa was visible from top to
+bottom, and where an animated conversation in Swiss patois commenced.
+Ulrich described the slopes, passes, and precipices, which were to guide
+us; and Christian demanded explanations, until he was finally able to
+declare to me that his knowledge was sufficient. We then bade Ulrich
+good-bye, and went forward. All was clear about Monte Rosa, and the
+yellow morning light shone brightly upon its uppermost snows. Beside the
+Queen of the Alps was the huge mass of the Lyskamm, with a saddle
+stretching from the one to the other; next to the Lyskamm came two
+white rounded mounds, smooth and pure, the Twins Castor and Pollux, and
+further to the right again the broad brown flank of the Breithorn.
+Behind us Mont Cervin gathered the clouds more thickly round him, until
+finally his grand obelisk was totally hidden. We went along the
+mountain-side for a time, and then descended to the glacier. The surface
+was hard frozen, and the ice crunched loudly under our feet. There was a
+hollowness and volume in the sound which require explanation; and this,
+I think, is furnished by the remarks of Sir John Herschel on those
+hollow sounds at the Solfaterra, near Naples, from which travellers have
+inferred the existence of cavities within the mountain. At the place
+where these sounds are heard the earth is friable, and, when struck, the
+concussion is reinforced and lengthened by the partial echoes from the
+surfaces of the fragments. The conditions for a similar effect exist
+upon the glacier, for the ice is disintegrated to a certain depth, and
+from the innumerable places of rupture little reverberations are sent,
+which give a length and hollowness to the sound produced by the crushing
+of the fragments on the surface.
+
+We looked to the sky at intervals, and once a meteor slid across it,
+leaving a train of sparks behind. The blue firmament, from which the
+stars shone down so brightly when we rose, was more and more invaded by
+clouds, which advanced upon us from our rear, while before us the solemn
+heights of Monte Rosa were bathed in rich yellow sunlight. As the day
+advanced the radiance crept down towards the valleys; but still those
+stealthy clouds advanced like a besieging army, taking deliberate
+possession of the summits, one after the other, while gray skirmishers
+moved through the air above us. The play of light and shadow upon Monte
+Rosa was at times beautiful, bars of gloom and zones of glory shifting
+and alternating from top to bottom of the mountain.
+
+[Sidenote: ADVANCE OF THE CLOUDS. 1858.]
+
+At five o'clock a gray cloud alighted on the shoulder of the Lyskamm,
+which had hitherto been warmed by the lovely yellow light. Soon
+afterwards we reached the foot of Monte Rosa, and passed from the
+glacier to a slope of rocks, whose rounded forms and furrowed surfaces
+showed that the ice of former ages had moved over them; the granite was
+now coated with lichens, and between the bosses where mould could rest
+were patches of tender moss. As we ascended, a peal to the right
+announced the descent of an avalanche from the Twins; it came heralded
+by clouds of ice-dust, which resembled the sphered masses of condensed
+vapour which issue from a locomotive. A gentle snow-slope brought us to
+the base of a precipice of brown rocks, round which we wound; the snow
+was in excellent order, and the chasms were so firmly bridged by the
+frozen mass that no caution was necessary in crossing them. Surmounting
+a weathered cliff to our left, we paused upon the summit to look upon
+the scene around us. The snow gliding insensibly from the mountains, or
+discharged in avalanches from the precipices which it overhung, filled
+the higher valleys with pure white glaciers, which were rifted and
+broken here and there, exposing chasms and precipices from which gleamed
+the delicate blue of the half-formed ice. Sometimes, however, the
+_neves_ spread over wide spaces without a rupture or wrinkle to break
+the smoothness of the superficial snow. The sky was now for the most
+part overcast, but through the residual blue spaces the sun at intervals
+poured light over the rounded bosses of the mountain.
+
+[Sidenote: MONTE ROSA CAPPED. 1858.]
+
+At half-past seven o'clock we reached another precipice of rock, to the
+left of which our route lay, and here Lauener proposed to have some
+refreshment; after which we went on again. The clouds spread more and
+more, leaving at length mere specks and patches of blue between them.
+Passing some high peaks, formed by the dislocation of the ice, we came
+to a place where the _neve_ was rent by crevasses, on the walls of which
+the stratification due to successive snow-falls was shown with great
+beauty and definition. Between two of these fissures our way now lay:
+the wall of one of them was hollowed out longitudinally midway down,
+thus forming a roof above and a ledge below, and from roof to ledge
+stretched a railing of cylindrical icicles, as if intended to bolt them
+together. A cloud now for the first time touched the summit of Monte
+Rosa, and sought to cling to it, but in a minute it dispersed in
+shattered fragments, as if dashed to pieces for its presumption. The
+mountain remained for a time clear and triumphant, but the triumph was
+short-lived: like suitors that will not be repelled, the dusky vapours
+came; repulse after repulse took place, and the sunlight gushed down
+upon the heights, but it was manifest that the clouds gained ground in
+the conflict.
+
+Until about a quarter past nine o'clock our work was mere child's play,
+a pleasant morning stroll along the flanks of the mountain; but steeper
+slopes now rose above us, which called for more energy, and more care in
+the fixing of the feet. Looked at from below, some of these slopes
+appeared precipitous; but we were too well acquainted with the effect of
+fore-shortening to let this daunt us. At each step we dug our batons
+into the deep snow. When first driven in, the batons[A] _dipped_ from
+us, but were brought, as we walked forward, to the vertical, and finally
+beyond it at the other side. The snow was thus forced aside, a rubbing
+of the staff against it, and of the snow-particles against each other,
+being the consequence. We had thus perpetual rupture and regelation;
+while the little sounds consequent upon rupture, reinforced by the
+partial echoes from the surfaces of the granules, were blended together
+to a note resembling the lowing of cows. Hitherto I had paused at
+intervals to make notes, or to take an angle; but these operations now
+ceased, not from want of time, but from pure dislike; for when the eye
+has to act the part of a sentinel who feels that at any moment the enemy
+may be upon him; when the body must be balanced with precision, and legs
+and arms, besides performing actual labour, must be kept in readiness
+for possible contingencies; above all, when you feel that your safety
+depends upon yourself alone, and that, if your footing gives way, there
+is no strong arm behind ready to be thrown between you and destruction;
+under such circumstances the relish for writing ceases, and you are
+willing to hand over your impressions to the safe keeping of memory.
+
+[Sidenote: THE "COMB" OF THE MOUNTAIN. 1858.]
+
+[Sidenote: ASCENT ALONG A CORNICE. 1858.]
+
+From the vast boss which constitutes the lower portion of Monte Rosa
+cliffy edges run upwards to the summit. Were the snow removed from these
+we should, I doubt not, see them as toothed or serrated crags,
+justifying the term "_kamm_," or "comb," applied to such edges by the
+Germans. Our way now lay along such a kamm, the cliffs of which had,
+however, caught the snow, and been completely covered by it, forming an
+edge like the ridge of a house-roof, which sloped steeply upwards. On
+the Lyskamm side of the edge there was no footing, and, if a human body
+fell over here, it would probably pass through a vertical space of some
+thousands of feet, falling or rolling, before coming to rest. On the
+other side the snow-slope was less steep, but excessively
+perilous-looking, and intersected by precipices of ice. Dense clouds now
+enveloped us, and made our position far uglier than if it had been
+fairly illuminated. The valley below us was one vast cauldron, filled
+with precipitated vapour, which came seething at times up the sides of
+the mountain. Sometimes this fog would partially clear away, and the
+light would gleam upwards from the dislocated glaciers. My guide
+continually admonished me to make my footing sure, and to fix at each
+step my staff firmly in the consolidated snow. At one place, for a short
+steep ascent, the slope became hard ice, and our position a very
+ticklish one. We hewed our steps as we moved upwards, but were soon glad
+to deviate from the ice to a position scarcely less awkward. The wind
+had so acted upon the snow as to fold it over the edge of the kamm, thus
+causing it to form a kind of cornice, which overhung the precipice on
+the Lyskamm side of the mountain. This cornice now bore our weight: its
+snow had become somewhat firm, but it was yielding enough to permit the
+feet to sink in it a little way, and thus secure us at least against the
+danger of slipping. Here also at each step we drove our batons firmly
+into the snow, availing ourselves of whatever help they could render.
+Once, while thus securing my anchorage, the handle of my hatchet went
+right through the cornice on which we stood, and, on withdrawing it, I
+could see through the aperture into the cloud-crammed gulf below. We
+continued ascending until we reached a rock protruding from the snow,
+and here we halted for a few minutes. Lauener looked upwards through the
+fog. "According to all description," he observed, "this ought to be the
+last kamm of the mountain; but in this obscurity we can see nothing."
+Snow began to fall, and we recommenced our journey, quitting the rocks
+and climbing again along the edge. Another hour brought us to a crest of
+cliffs, at which, to our comfort, the kamm appeared to cease, and other
+climbing qualities were demanded of us.
+
+[Sidenote: "DIE HOeCHSTE SPITZE." 1858.]
+
+On the Lyskamm side, as I have said, rescue would be out of the
+question, should the climber go over the edge. On the other side of the
+edge rescue seemed possible, though the slope, as stated already, was
+most dangerously steep. I now asked Lauener what he would have done,
+supposing my footing to have failed on the latter slope. He did not
+seem to like the question, but said that he should have considered well
+for a moment and then have sprung after me; but he exhorted me to drive
+all such thoughts away. I laughed at him, and this did more to set his
+mind at rest than any formal profession of courage could have done. We
+were now among rocks: we climbed cliffs and descended them, and advanced
+sometimes with our feet on narrow ledges, holding tightly on to other
+ledges by our fingers; sometimes, cautiously balanced, we moved along
+edges of rock with precipices on both sides. Once, in getting round a
+crag, Lauener shook a book from his pocket; it was arrested by a rock
+about sixty or eighty feet below us. He wished to regain it, but I
+offered to supply its place, if he thought the descent too dangerous. He
+said he would make the trial, and parted from me. I thought it useless
+to remain idle. A cleft was before me, through which I must pass; so,
+pressing my knees and back against its opposite sides, I gradually
+worked myself to the top. I descended the other face of the rock, and
+then, through a second ragged fissure, to the summit of another
+pinnacle. The highest point of the mountain was now at hand, separated
+from me merely by a short saddle, carved by weathering out of the crest
+of the mountain. I could hear Lauener clattering after me, through the
+rocks behind. I dropped down upon the saddle, crossed it, climbed the
+opposite cliff, and "_die hoechste Spitze_" of Monte Rosa was won.
+
+[Sidenote: GLOOM ON THE SUMMIT. 1858.]
+
+Lauener joined me immediately, and we mutually congratulated each other
+on the success of the ascent. The residue of the bread and meat was
+produced, and a bottle of tea was also appealed to. Mixed with a little
+cognac, Lauener declared that he had never tasted anything like it. Snow
+fell thickly at intervals, and the obscurity was very great;
+occasionally this would lighten and permit the sun to shed a ghastly
+dilute light upon us through the gleaming vapour. I put my
+boiling-water apparatus in order, and fixed it in a corner behind a
+ledge; the shelter was, however, insufficient, so I placed my hat above
+the vessel. The boiling point was 184.92 deg. Fahr., the ledge on which the
+instrument stood being 5 feet below the highest point of the mountain.
+
+The ascent from the Riffel hotel occupied us about seven hours, nearly
+two of which were spent upon the kamm and crest. Neither of us felt in
+the least degree fatigued; I, indeed, felt so fresh, that had another
+Monte Rosa been planted on the first, I should have continued the climb
+without hesitation, and with strong hopes of reaching the top. I
+experienced no trace of mountain sickness, lassitude, shortness of
+breath, heart-beat, or headache; nevertheless the summit of Monte Rosa
+is 15,284 feet high, being less than 500 feet lower than Mont Blanc. It
+is, I think, perfectly certain, that the rarefaction of the air at this
+height is not sufficient of itself to produce the symptoms referred to;
+physical exertion must be superadded.
+
+[Sidenote: "FROZEN FLOWERS." 1858.]
+
+After a few fitful efforts to dispel the gloom, the sun resigned the
+dominion to the dense fog and the descending snow, which now prevented
+our seeing more than 15 or 20 paces in any direction. The temperature of
+the crags at the summit, which had been shone upon by the unclouded sun
+during the earlier portion of the day, was 60 deg. Fahr.; hence the snow
+melted instantly wherever it came in contact with the rock. But some of
+it fell upon my felt hat, which had been placed to shelter the
+boiling-water apparatus, and this presented the most remarkable and
+beautiful appearance. The fall of snow was in fact a shower of frozen
+flowers. All of them were six-leaved; some of the leaves threw out
+lateral ribs like ferns, some were rounded, others arrowy and serrated,
+some were close, others reticulated, but there was no deviation from the
+six-leaved type. Nature seemed determined to make us some compensation
+for the loss of all prospect, and thus showered down upon us those
+lovely blossoms of the frost; and had a spirit of the mountain inquired
+my choice, the view, or the frozen flowers, I should have hesitated
+before giving up that exquisite vegetation. It was wonderful to think
+of, as well as beautiful to behold. Let us imagine the eye gifted with a
+microscopic power sufficient to enable it to see the molecules which
+composed these starry crystals; to observe the solid nucleus formed and
+floating in the air; to see it drawing towards it its allied atoms, and
+these arranging themselves as if they moved to music, and ended by
+rendering that music concrete. Surely such an exhibition of power, such
+an apparent demonstration of a resident intelligence in what we are
+accustomed to call "brute matter," would appear perfectly miraculous.
+And yet the reality would, if we could see it, transcend the fancy. If
+the Houses of Parliament were built up by the forces resident in their
+own bricks and lithologic blocks, and without the aid of hodman or
+mason, there would be nothing intrinsically more wonderful in the
+process than in the molecular architecture which delighted us upon the
+summit of Monte Rosa.
+
+[Sidenote: STARTLING AVALANCHE. 1858.]
+
+Twice or thrice had my guide warned me that we must think of descending,
+for the snow continued to fall heavily, and the loss of our track would
+be attended with imminent peril. We therefore packed up, and clambered
+downward among the crags of the summit. We soon left these behind us,
+and as we stood once more upon the kamm, looking into the gloom beneath,
+an avalanche let loose from the side of an adjacent mountain shook the
+air with its thunder. We could not see it, could form no estimate of its
+distance, could only hear its roar, which coming to us through the
+darkness, had an undefinable element of horror in it. Lauener remarked,
+"I never hear those things without a shudder; the memory of my brother
+comes back to me at the same time." His brother, who was the best
+climber in the Oberland, had been literally broken to fragments by an
+avalanche on the slopes of the Jungfrau.
+
+We had been separate coming up, each having trusted to himself, but the
+descent was more perilous, because it is more difficult to fix the heel
+of the boot than the toe securely in the ice. Lauener was furnished with
+a rope, which he now tied round my waist, and forming a noose at the
+other end, he slipped it over his arm. This to me was a new mode of
+attachment. Hitherto my guides in dangerous places had tied the ropes
+round _their_ waists also. Simond had done it on Mont Blanc, and Bennen
+on the Finsteraarhorn, proving thus their willingness to share my fate
+whatever that might be. But here Lauener had the power of sending me
+adrift at any moment, should his own life be imperilled. I told him that
+his mode of attachment was new to me, but he assured me that it would
+give him more power in case of accident. I did not see this at the time;
+but neither did I insist on his attaching himself in the usual way. It
+could neither be called anger nor pride, but a warm flush ran through me
+as I remarked, that I should take good care not to test his power of
+holding me. I believe I wronged my guide by the supposition that he made
+the arrangement with reference to his own safety, for all I saw of him
+afterwards proved that he would at any time have risked his life to save
+mine. The flush however did me good, by displacing every trace of
+anxiety, and the rope, I confess, was also a source of some comfort to
+me. We descended the kamm, I going first. "Secure your footing before
+you move," was my guide's constant exhortation, "and make your staff
+firm at each step." We were sometimes quite close upon the rim of the
+kamm on the Lyskamm side, and we also followed the depressions which
+marked our track along the cornice. This I now tried intentionally, and
+drove the handle of my axe through it once or twice. At two places in
+descending we were upon the solid ice, and these were some of the
+steepest portions of the kamm. They were undoubtedly perilous, and the
+utmost caution was necessary in fixing the staff and securing the
+footing. These however once past, we felt that the chief danger was
+over. We reached the termination of the edge, and although the snow
+continued to fall heavily, and obscure everything, we knew that our
+progress afterwards was secure. There was pleasure in this feeling; it
+was an agreeable variation of that grim mental tension to which I had
+been previously wound up, but which in itself was by no means
+disagreeable.
+
+[Sidenote: SPLENDID BLUE OF THE SNOW. 1858.]
+
+[Sidenote: STIFLING HEAT. 1858.]
+
+I have already noticed the colour of the fresh snow upon the summit of
+the Stelvio pass. Since I observed it there it has been my custom to pay
+some attention to this point at all great elevations. This morning, as I
+ascended Monte Rosa, I often examined the holes made in the snow by our
+batons, but the light which issued from them was scarcely perceptibly
+blue. Now, however, a deep layer of fresh snow overspread the mountain,
+and the effect was magnificent. Along the kamm I was continually
+surprised and delighted by the blue gleams which issued from the broken
+or perforated stratum of new snow; each hole made by the staff was
+filled with a light as pure, and nearly as deep, as that of the
+unclouded firmament. When we reached the bottom of the kamm, Lauener
+came to the front, and tramped before me. As his feet rose out of the
+snow, and shook the latter off in fragments, sudden and wonderful gleams
+of blue light flashed from them. Doubtless the blue of the sky has much
+to do with mountain colouring, but in the present instance not only was
+there no blue sky, but the air was so thick with fog and descending
+snow-flakes, that we could not see twenty yards in advance of us. A
+thick fog, which wrapped the mountain quite closely, now added its gloom
+to the obscurity caused by the falling snow. Before we reached the base
+of the mountain the fog became thin, and the sun shone through it. There
+was not a breath of air stirring, and, though we stood ankle-deep in
+snow, the heat surpassed anything of the kind I had ever felt: it was
+the dead suffocating warmth of the interior of an oven, which
+encompassed us on all sides, and from which there seemed no escape. Our
+own motion through the air, however, cooled us considerably. We found
+the snow-bridges softer than in the morning, and consequently needing
+more caution; but we encountered no real difficulty among them. Indeed
+it is amusing to observe the indifference with which a snow-roof is
+often broken through, and a traveller immersed to the waist in the jaws
+of a fissure. The effort at recovery is instantaneous; half
+instinctively hands and knees are driven into the snow, and rescue is
+immediate. Fair glacier work was now before us; after which we reached
+the opposite mountain-slope, which we ascended, and then went down the
+flank of the Riffelberg to our hotel. The excursion occupied us eleven
+and a half hours.
+
+
+FOOTNOTES:
+
+[A] My staff was always the handle of an axe an inch or two longer than
+an ordinary walking-stick.
+
+
+
+
+(19.)
+
+
+On the afternoon of the 11th I made an attempt alone to ascend the
+Riffelhorn, and attained a considerable height; but I attacked it from
+the wrong side, and the fading light forced me to retreat. I found some
+agreeable people at the hotel on my return. One clergyman especially,
+with a clear complexion, good digestion, and bad lungs--of free, hearty,
+and genial manner--made himself extremely pleasant to us all. He
+appeared to bubble over with enjoyment, and with him and others on the
+morning of the 13th I walked to the Goerner Grat, as it lay on the way to
+my work. We had a glorious prospect from the summit: indeed the
+assemblage of mountains, snow, and ice, here within view is perhaps
+without a rival in the world.[A] I shouldered my axe, and saying
+"good-bye" moved away from my companions.
+
+"Are you going?" exclaimed the clergyman. "Give me one grasp of your
+hand before we part."
+
+This was the signal for a grasp all round; and the hearty human kindness
+which thus showed itself contributed that day to make my work pleasant
+to me.
+
+[Sidenote: A DIFFICULT DESCENT. 1858.]
+
+We proceeded along the ridge of the Rothe Kumme to a point which
+commanded a fine view of the glacier. The ice had been over these
+heights in ages past, for, although lichens covered the surfaces of the
+old rocks, they did not disguise the grooves and scratchings. The
+surface of the glacier was now about a thousand feet below us, and this
+it was our desire to attain. To reach it we had to descend a succession
+of precipices, which in general were weathered and rugged, but here and
+there, where the rock was durable, were fluted and grooved. Once or
+twice indeed we had nothing to cling to but the little ridges thus
+formed. We had to squeeze ourselves through narrow fissures, and often
+to get round overhanging ledges, where our main trust was in our feet,
+but where these had only ledges an inch or so in width to rest upon.
+These cases were to me the most unpleasant of all, for they compelled
+the arms to take a position which, if the footing gave way, would
+necessitate a _wrench_, for which I entertain considerable abhorrence.
+We came at length to a gorge by which the mountain is rent from top to
+bottom, and into which we endeavoured to descend. We worked along its
+rim for a time, but found its smooth faces too deep. We retreated;
+Lauener struck into another track, and while he tested it I sat down
+near some grass tufts, which flourished on one of the ledges, and found
+the temperature to be as follows:--
+
+ Temperature of rock 42 deg. C.
+ Of air an inch above the rock 32
+ Of air a foot from rock 22
+ Of grass 25
+
+The first of these numbers does not fairly represent the temperature of
+the rock, as the thermometer could be in contact with it only at one
+side at a time. It was differences such as these between grass and
+stone, producing a mixed atmosphere of different densities, that
+weakened the sound of the falls of the Orinoco, as observed and
+explained by Humboldt.
+
+[Sidenote: SINGULAR ICE-CAVE. 1858.]
+
+By a process of "trial and error" we at length reached the ice, after
+two hours had been spent in the effort to disentangle ourselves from the
+crags. The glacier is forcibly thrust at this place against the
+projecting base of the mountain, and the structure of the ice
+correspondingly developed. Crevasses also intersect the ice, and the
+blue veins cross them at right angles. I ascended the glacier to a
+region where the ice was compressed and greatly contorted, and thought
+that in some cases I could see the veins crossing the lines of
+stratification. Once my guide drew my attention to what he called "_ein
+sonderbares Loch_." On one of the slopes an archway was formed which
+appeared to lead into the body of the glacier. We entered it, and
+explored the cavern to its end. The walls were of transparent blue ice,
+singularly free from air-bubbles; but where the roof of the cavern was
+thin enough to allow the sun to shine feebly through it, the transmitted
+light was of a pink colour. My guide expressed himself surprised at
+"_den roethlichen Schein_." At one place a plate of ice had been placed
+like a ceiling across the cavern; but owing to lateral squeezing it had
+been broken so as to form a V. I found some air-bubbles in this ice, and
+in all cases they were associated with blebs of water. A portion of the
+"ceiling," indeed, was very full of bubbles, and was at some places
+reduced, by internal liquefaction, to a mere skeleton of ice, with
+water-cells between its walls.
+
+[Sidenote: STRUCTURE AND STRATA. 1858.]
+
+High up the glacier (towards the old Weissthor) the horizontal
+stratification is everywhere beautifully shown. I drew my guide's
+attention to it, and he made the remark that the perfection of the lower
+ice was due to the pressure of the layers above it. "The snow by degrees
+compressed itself to glacier." As we approached one of the tributaries
+on the Monte Rosa side, where great pressure came into play, the
+stratification appeared to yield and the true structure to cross it at
+those places where it had yielded most. As the place of greatest
+pressure was approached, the bedding disappeared more and more, and a
+clear vertical structure was finally revealed.
+
+
+FOOTNOTES:
+
+[A] In 1858 Mr. E. W. Cooke made a pencil-sketch of this splendid
+panorama, which is the best and truest that I have yet seen.
+
+
+
+
+THE GOeRNER GRAT AND THE RIFFELHORN. MAGNETIC PHENOMENA.
+
+(20.)
+
+
+At an early hour on Saturday, the 14th of August, I heard the servant
+exclaim, "_Das Wetter ist wunderschoen!_" which good news caused me to
+spring from my bed and prepare to meet the morn. The range of summits at
+the opposite side of the valley of St. Nicholas was at first quite
+clear, but as the sun ascended light cumuli formed round them,
+increasing in density up to a certain point; below these clouds the air
+of the valley was transparent; above them the air of heaven was still
+more so; and thus they swung midway between heaven and earth, ranging
+themselves in a level line along the necks of the mountains.
+
+[Sidenote: GENERATION OF CLOUDS. 1858.]
+
+It might be supposed that the presence of the sun heating the air would
+tend to keep it more transparent, by increasing its capacity to dissolve
+all visible cloud; and this indeed is the true action of the sun. But it
+is not the only action. His rays, as he climbed the eastern heaven, shot
+more and more deeply into the valley of St. Nicholas, the moisture of
+which rose as invisible vapour, remaining unseen as long as the air
+possessed sufficient warmth to keep it in the vaporous state. High up,
+however, the cold crags which had lost their heat by radiation the night
+before, acted like condensers upon the ascending vapour, and caused it
+to curdle into visible fog. The current, however, continued ascensional,
+and the clouds were slowly lifted above the tallest peaks, where they
+arranged themselves in fantastic forms, shifting and changing shape as
+they gradually melted away. One peak stood like a field-officer with
+his cap raised above his head, others sent straggling cloud-balloons
+upwards; but on watching these outliers they were gradually seen to
+disappear. At first they shone like snow in the sunlight, but as they
+became more attenuated they changed colour, passing through a dull red
+to a dusky purple hue, until finally they left no trace of their
+existence.
+
+[Sidenote: THE ROCKS WARMED. 1858.]
+
+[Sidenote: SCENE FROM THE GOeRNER GRAT. 1858.]
+
+As the day advanced, warming the rocks, the clouds wholly disappeared,
+and a hyaline air formed the setting of both glaciers and mountains. I
+climbed to the Goerner Grat to obtain a general view of the surrounding
+scene. Looking towards the origin of the Goerner glacier the view was
+bounded by a wide col, upon which stood two lovely rounded eminences
+enamelled with snow of perfect purity. They shone like burnished silver
+in the sunlight, as if their surfaces had been melted and recongealed to
+frosted mirrors from which the rays were flung. To the right of these
+were the bounding crags of Monte Rosa, and then the body of the mountain
+itself, with its crest of crag and coat of snows. To the right of Monte
+Rosa, and almost rivalling it in height, was the vast mass of the
+Lyskamm, a rough and craggy mountain, to whose ledges clings the snow
+which cannot grasp its steeper walls, sometimes leaning over them in
+impending precipices, which often break, and send wild avalanches into
+the space below. Between the Lyskamm and Monte Rosa lies a large wide
+valley into which both mountains pour their snows, forming there the
+Western glacier of Monte Rosa[A]--a noble ice stream, which from its
+magnitude and permanence deserves to impose its name upon the trunk
+glacier. It extends downwards from the col which unites the two
+mountains; riven and broken at some places, but at others stretching
+white and pure down to its snow-line, where the true glacier emerges
+from the _neve_. From the rounded shoulders of the Twin Castor a glacier
+descends, at first white and shining, then suddenly broken into faults,
+fissures, and precipices, which are afterwards repaired, and the glacier
+joins that of Monte Rosa before the junction of the latter with the
+trunk stream. Next came a boss of rock, with a secondary glacier
+clinging to it as if plastered over it, and after it the Schwarze
+glacier, bounded on one side by the Breithorn, and on the other by the
+Twin Pollux. This glacier is of considerable magnitude. Over its upper
+portion rise the Twin eminences, pure and white; then follows a smooth
+and undulating space, after passing which the _neve_ is torn up into a
+collection of peaks and chasms; these, however, are mended lower down,
+and the glacier moves smoothly and calmly to meet its brothers in the
+main valley. Next comes the Trifti glacier,[B] embraced on all sides by
+the rocky arms of the Breithorn; its mass is not very great, but it
+descends in a graceful sweep, and exhibits towards its extremity a
+succession of beautiful bands. Afterwards we have the glacier of the
+Petit Mont Cervin and those of St. Theodule, which latter are the last
+that empty their frozen cargoes into the valley of the Goerner. All the
+glaciers here mentioned are welded together to a common trunk which
+squeezes itself through the narrow defile at the base of the Riffelhorn.
+Soon afterwards the moraines become confused, the glacier drops steeply
+to its termination, and ploughs up the meadows in front of it with its
+irresistible share.
+
+In a line with the Riffelhorn, and rising over the latter so high as to
+make it almost vanish by comparison, was the Titan obelisk of the
+Matterhorn, from the base of which the Furgge glacier struggles
+downwards. On the other side are the Zmutt glacier, the Schoenbuehl, and
+the Hochwang, from the Dent Blanche; the Gabelhorn and Trift glaciers,
+from the summits which bear those names. Then come the glaciers of the
+Weisshorn. Describing a curve still farther to the right we alight on
+the peaks of the Mischabel, dark and craggy precipices from this side,
+though from the AEggischhorn they appear as cones of snow. Sweeping by
+the Alphubel, the Allaleinhorn, the Rympfischorn, and Strahlhorn--all of
+them majestic--we reach the pass of the Weissthor, and the Cima di
+Jazzi. This completes the glorious circuit within the observer's view.
+
+[Sidenote: COMPASS AT FAULT. 1858.]
+
+I placed my compass upon a piece of rock to find the bearing of the
+Goerner glacier, and was startled at seeing the sun and it at direct
+variance. What the sun declared to be north, the needle affirmed to be
+south. I at first supposed that the maker had placed the S where the N
+ought to be, and _vice versa_. On shifting my position, however, the
+needle shifted also, and I saw immediately that the effect was due to
+the rock of the Grat. Sometimes one end of the needle _dipped_ forcibly,
+at other places it whirled suddenly round, indicating an entire change
+of polarity. The rock was evidently to be regarded as an assemblage of
+magnets, or as a single magnet full of "consequent points." A distance
+of transport not exceeding an inch was, in some cases, sufficient to
+reverse the position of the needle. I held the needle between the two
+sides of a long fissure a foot wide. The needle set _along_ the fissure
+at some places, while at others it set _across_ it. Sometimes a little
+jutting knob would attract the north end of the needle, while a closely
+adjacent little knob would forcibly repel it, and attract the south end.
+One extremity of a ledge three feet long was north magnetic, the other
+end was south magnetic, while a neutral point existed midway between the
+two, the ledge having therefore the exact polar arrangement of an
+ordinary bar-magnet. At the highest point of the rock the action
+appeared to be most intense, but I also found an energetic polarity in a
+mass at some distance below the summit.
+
+[Sidenote: MAGNETISM OF ROCKS. 1858.]
+
+Remembering that Professor Forbes had noticed some peculiar magnetic
+effect upon the Riffelhorn, I resolved to ascend it. Descending from the
+Grat we mounted the rocks which form the base of the horn; these are
+soft and soapy from the quantity of mica which they contain; the higher
+rocks of the horn are, however, very dense and hard. The ascent is a
+pleasant bit of mountain practice. We climbed the walls of rock, and
+wound round the ledges, seeking the assailable points. I tried the
+magnetic condition of the rocks as we ascended, and found it in general
+feeble. In other respects the Riffelhorn is a most remarkable mass. The
+ice of the Goerner glacier of former ages, which rose hundreds, perhaps
+thousands of feet above its present level, encountered the horn in its
+descent, and was split by the latter, a diversion of the ice along the
+sides of the peak being the consequence. Portions of the vertical walls
+of the horn are polished by this action as if they had come from the
+hands of a lapidary, and the scratchings are as sharp and definite as if
+drawn by points of steel. I never saw scratchings so perfectly
+preserved: the finest lines are as clear as the deepest, a consequence
+of the great density and durability of the rock. The latter evidently
+contains a good deal of iron, and its surface near the summit is of the
+rich brown red due to the peroxide of the metal. When we fairly got
+among the precipices we left our hatchets behind us, trusting
+subsequently to our hands and feet alone. Squeezing, creeping, clinging,
+and climbing, in due time we found ourselves upon the summit of the
+horn.
+
+[Sidenote: ASCENT OF THE RIFFELHORN. 1858.]
+
+A pile of stones had been erected near the point where we gained the
+top. I examined the stones of this pile, and found them strongly polar.
+The surrounding rocks also showed a violent action, the needle
+oscillating quickly, and sometimes twirling swiftly round upon a slight
+change of position. The fragments of rock scattered about were also
+polar. Long ledges showed north magnetism for a considerable length, and
+again for an equal length south magnetism. Two parallel masses separated
+from each other by a fissure, showed the same magnetic distribution.
+While I was engaged at one end of the horn, Lauener wandered to the
+other, on which stood two or three _hommes de pierres_. He was about
+disturbing some of the stones, when a yell from me surprised him. In
+fact, the thought had occurred to me that the magnetism of the horn had
+been developed by lightning striking upon it, and my desire was to
+examine those points which were most exposed to the discharge of the
+atmospheric electricity; hence my shout to my guide to let the stones
+alone. I worked towards the other end of the horn, examining the rocks
+in my way. Two weathered prominences, which seemed very likely
+recipients of the lightning, acted violently upon the needle. I
+sometimes descended a little way, and found that among the rocks below
+the summit the action was greatly enfeebled. On reaching another very
+prominent point, I found its extremity all north polar, but at a little
+distance was a cluster of consequent points, among which the transport
+of a few inches was sufficient to turn the needle round and round.
+
+[Sidenote: MAGNETISM OF THE HORN. 1858.]
+
+The piles of stone at the Zermatt end of the horn did not seem so
+strongly polar as the pile at the other end, which was higher; still a
+strong polar action was manifested at many points of the surrounding
+rocks. Having completed the examination of the summit, I descended the
+horn, and examined its magnetic condition as I went along. It seemed to
+me that the jutting prominences always exhibited the strongest action. I
+do not indeed remember any case in which a strong action did not
+exhibit itself at the ends of the terraces which constitute the horn. In
+all cases, however, the rock acted as a number of magnets huddled
+confusedly together, and not as if its entire mass was endowed with
+magnetism of one kind.
+
+[Illustration: Fig. 8. Magnetic Boulder of the Riffelhorn.]
+
+On the evening of the same day I examined the lower spur of the
+Riffelhorn. Amid its fissures and gullies one feels as if wandering
+through the ruins of a vast castle or fortification; the precipices are
+so like walls, and the scratching and polishing so like what might be
+done by the hands of man. I found evidences of strong polar action in
+some of the rocks low down. In the same continuous mass the action would
+sometimes exhibit itself over an area of small extent, while the
+remainder of the rock showed no appreciable action. Some of the boulders
+cast down from the summit exhibited a strong and varied polarity. Fig. 8
+is a sketch of one of these; the barbed end of each arrow represents the
+north end of the needle, which assumed the various positions shown in
+the figure. Midway down the spur I lighted upon a transverse wall of
+rock, which formed in earlier ages the boundary of a lateral outlet of
+the Goerner glacier. It was red and hard, weathered rough at some places,
+and polished smooth at others. The lines were drawn finely upon it, but
+its outer surface appeared to be peeling off like a crust; the polished
+layer rested upon the rock like a kind of enamel. The action of the
+glacier appeared to resemble that of the break of a locomotive upon
+rails, both being cases of exfoliation brought about by pressure and
+friction. This wall measured twenty-eight yards across, and one end of
+it, for a distance of ten or twelve yards, was all north polar; the
+other end for a similar distance was south polar, but there was a pair
+of consequent points at its centre.
+
+[Sidenote: THE MAGNETIC FORCE. 1868.]
+
+To meet the case of my young readers, I will here say a few words about
+the magnetic force. The common magnetic needle points nearly north and
+south; and if a bit of iron be brought near to either end of the needle,
+they will mutually attract each other. A piece of lead will not show
+this effect, nor will copper, gold, nor silver. Iron, in fact, is a
+magnetic metal, which the others are not. It is to be particularly
+observed, that the bit of iron attracts _both ends_ of the needle when
+it is presented to them in succession; and if a common steel sewing
+needle be substituted for the iron it will be seen that it also has the
+power of attracting both ends of the magnetic needle. But if the needle
+be rubbed once or twice along one end of a magnet, it will be found that
+one of its ends will afterwards _repel_ a certain end of the magnetic
+needle and attract the other. By rubbing the needle on the magnet, we
+thus develop both attraction and repulsion, and this double action of
+the magnetic force is called its _polarity_; thus the steel which was at
+first simply _magnetic_, is now magnetic and _polar_.
+
+It is the aim of persons making magnets, that each magnet should have
+but _two_ poles, at its two ends; it is, however, easy to develop in the
+same piece of steel several pairs or poles; and if the magnetization be
+irregular, this is sometimes done when we wish to avoid it. These
+irregular poles are called _consequent points_.
+
+Now I want my young reader to understand that it is not only because the
+rocks of the Goerner Grat and Riffelhorn contain iron, that they exhibit
+the action which I have described. They are not only magnetic, as common
+iron is, but, like the magnetized steel needle, they are magnetic and
+polar. And these poles are irregularly distributed like the "consequent
+points" to which I have referred, and this is the reason why I have used
+the term.
+
+[Sidenote: BEARINGS FROM THE RIFFELHORN. 1858.]
+
+Professor Forbes, as I have already stated, was the first to notice the
+effect of the Riffelhorn upon the magnetic needle, but he seems to have
+supposed that the entire mass of the mountain exercised "a local
+attraction" upon the needle; (upon which end he does not say). To enable
+future observers to allow for this attraction, he took the bearing of
+several of the surrounding mountains from the Riffelhorn; but it is very
+probable that had he changed his position a few inches, and perfectly
+certain had he changed it a few yards, he would have found a set of
+bearings totally different from those which he has recorded. The close
+proximity and irregular distribution of its consequent points would
+prevent the Riffelhorn from exerting any appreciable influence on _a
+distant needle_, as in this case the local poles would effectually
+neutralize each other.
+
+
+FOOTNOTES:
+
+[A] Now called, in the Federal map, the 'Grenz glacier.'--L. C. T.
+
+[B] I take this name from Studer's map. Sometimes, however, I have
+called it the "Breithorn glacier."
+
+
+
+
+(21.)
+
+
+[Sidenote: MONT CERVIN AS CLOUD-MAKER. 1858.]
+
+On the morning of the 15th the Riffelberg was swathed in a dense fog,
+through which heavy rain showered incessantly. Towards one o'clock the
+continuity of the gray mass was broken, and sky-gleams of the deepest
+blue were seen through its apertures; these would close up again, and
+others open elsewhere, as if the fog were fighting for existence with
+the sun behind it. The sun, however, triumphed, the mountains came more
+and more into view, and finally the entire air was swept clear. I went
+up to the Goerner Grat in the afternoon, and examined more closely the
+magnetism of its rocks; here, as on the Riffelhorn, I found it most
+pronounced at the jutting prominences of the Grat. Can it be that the
+superior exposure is more favourable to the formation of the magnetic
+oxide of iron? I secured a number of fragments, which I still possess,
+and which act forcibly upon a magnetic needle. The sun was near the
+western horizon, and I remained alone upon the Grat to see his last
+beams illuminate the mountains, which, with one exception, were without
+a trace of cloud. This exception was the Matterhorn, the appearance of
+which was extremely instructive. The obelisk appeared to be divided in
+two halves by a vertical line drawn from its summit half way down, to
+the windward of which we had the bare cliffs of the mountain; and to the
+left of it a cloud which appeared to cling tenaciously to the rocks. In
+reality, however, there was no clinging; the condensed vapour
+incessantly got away, but it was ever renewed, and thus a river of cloud
+had been sent from the mountain over the valley of Aosta. The wind in
+fact blew lightly up the valley of St. Nicholas charged with moisture,
+and when the air that held it rubbed against the cold cone of the
+Matterhorn the vapour was chilled and precipitated in his lee. The
+summit seemed to smoke sometimes like a burning mountain; for
+immediately after its generation, the fog was drawn away in long
+filaments by the wind. As the sun sank lower the ruddiness of his light
+augmented, until these filaments resembled streamers of flame. The sun
+sank deeper, the light was gradually withdrawn, and where it had
+entirely vanished it left the mountain like a desolate old man whose
+
+ "hoary hair
+ Stream'd like a meteor in the troubled air."
+
+For a moment after the sun had disappeared the scene was amazingly
+grand. The distant west was ruddy, copious gray smoke-wreaths were
+wafted from the mountains, while high overhead, in an atmospheric region
+which seemed perfectly motionless, floated a broad thin cloud, dyed with
+the richest iridescences. The colours were of the same character as
+those which I had seen upon the Aletschhorn, being due to interference,
+and in point of splendour and variety far exceeded anything ever
+produced by the mere coloured light of the setting sun.
+
+[Sidenote: CELLS IN THE ICE. 1858.]
+
+On the 16th I was early upon the glacier. It had frozen hard during the
+night, and the partially liberated streams flowed, in many cases, over
+their own ice. I took some clear plates from under the water, and found
+in them numerous liquid cells, each associated with an air-bubble or a
+vacuous spot. The most common shape of the cells was a regular hexagon,
+but there were all forms between the perfect hexagon and the perfect
+circle. Many cells had also crimped borders, intimating that their
+primitive form was that of a flower with six leaves. A plate taken from
+ice which was defended from the sunbeams by the shadow of a rock had no
+such cells; so that those that I observed were probably due to solar
+radiation.
+
+My first aim was to examine the structure of the Goernerhorn glacier,[A]
+which descends the breast of Monte Rosa until it is abruptly cut off by
+the great Western glacier of the mountain.[B] Between them is a moraine
+which is at once terminal as regards the former, and lateral as regards
+the latter. The ice is veined vertically along the moraine, the
+direction of the structure being parallel to the latter. I ascended the
+glacier, and found, as I retreated from the place where the thrust was
+most violent, that the structure became more feeble. From the glacier I
+passed to the rocks called "_auf der Platte_," so as to obtain a general
+view of its terminal portion. The gradual perfecting of the structure as
+the region of pressure was approached was very manifest: the ice at the
+end seemed to wrinkle up in obedience to the pressure, the structural
+furrows, from being scarcely visible, became more and more decided, and
+the lamination underneath correspondingly pronounced, until it finally
+attained a state of great perfection.
+
+[Sidenote: STRUCTURE OF THE ICE. 1858.]
+
+I now quitted the rocks and walked straight across the Western glacier
+of Monte Rosa to its centre, where I found the structure scarcely
+visible. I next faced the Goerner Grat, and walked down the glacier
+towards the moraine which divides it from the Goerner glacier. The
+mechanical conditions of the ice here are quite evident; each step
+brought me to a place of greater pressure, and also to a place of more
+highly developed structure, until finally near to the moraine itself,
+and running parallel to it, a magnificent lamination was developed. Here
+the superficial groovings could be traced to great distances, and beside
+the moraine were boulders poised on pedestals of ice through which the
+blue veins ran. At some places the ice had been weathered into laminae
+not more than a line in thickness.
+
+I now recrossed the Monte Rosa glacier to its junction with the
+Schwartze glacier, which descends between the Twins and Breithorn. The
+structure of the Monte Rosa glacier is here far less pronounced than at
+the other side, and the pressure which it endures is also manifestly
+less; the structure of the Schwartze glacier is fairly developed, being
+here parallel to its moraine. The cliffs of the Breithorn are much
+exposed to weathering action, and boulders are copiously showered down
+upon the adjacent ice. Between the Schwartze glacier and the glacier
+which descends from the breast of the Breithorn itself these blocks ride
+upon a spine of ice, and form a moraine of grand proportions. From it a
+fine view of the glacier is attainable, and the gradual development of
+its structure as the region of maximum pressure is approached is very
+plain. A number of gracefully curved undulations sweep across the
+Breithorn glacier, which are squeezed more closely together as the
+moraine is approached. All the glaciers that descend from the flanking
+mountains of the Goerner valley are suddenly turned aside where they meet
+the great trunk stream, and are reduced by the pressure to narrow
+stripes of ice separated from each other by parallel moraines.
+
+[Sidenote: TRIBUTARIES EXPLORED. 1858.]
+
+I ascended the Breithorn glacier to the base of an ice-fall, on one side
+of which I found large crumples produced by the pressure, the veined
+structure being developed at right angles to the direction of the
+latter. No such structure was visible above this place. The crumples
+were cut by fissures, perpendicular to which the blue veins ran. I now
+quitted the glacier, and clambered up the adjacent alp, from which a
+fine view of the general surface was attainable. As in the case of the
+Goernerhorn glacier, the gradual perfecting of the structure was very
+manifest; the dirt, which first irregularly scattered over the surface,
+gradually assumed a striated appearance, and became more and more
+decided as the moraine was approached. Descending from the alp, I
+endeavoured to measure some of the undulations; proceeding afterwards to
+the junction of the Breithorn glacier with that of St. Theodule. The end
+of the latter appears to be crumpled by its thrust against the former,
+and the moraine between them, instead of being raised, runs along a
+hollow which is flanked by the crumples on either side. The Breithorn
+glacier became more and more attenuated, until finally it actually
+vanished under its own moraines. On the sides of the crevasses, by which
+the Theodule glacier is here intersected, I thought I could plainly see
+two systems of veins cutting each other at an angle of fifteen or twenty
+degrees. Reaching the Goerner glacier, at a place where its dislocation
+was very great, I proceeded down it past the Riffelhorn, to a point
+where it seemed possible to scale the opposite mountain wall. Here I
+crossed the glacier, treading with the utmost caution along the combs of
+ice, and winding through the entanglement of crevasses until the spur of
+the Riffelhorn was reached; this I climbed to its summit, and afterwards
+crossed the green alp to our hotel.
+
+[Sidenote: TEMPTATION. 1858.]
+
+The foregoing good day's work was rewarded by a sound sleep at night.
+The tourists were called in succession next morning, but after each call
+I instantly subsided into deep slumber, and thus healthily spaced out
+the interval of darkness. Day at length dawned and gradually brightened.
+I looked at my watch and found it twenty minutes to six. My guide had
+been lent to a party of gentlemen who had started at three o'clock for
+the summit of Monte Rosa, and he had left with me a porter who undertook
+to conduct me to one of the adjacent glaciers. But as I looked from my
+window the unspeakable beauty of the morning filled me with a longing to
+see the world from the top of Monte Rosa. I was in exceedingly good
+condition--could I not reach the summit alone? Trained and indurated as
+I had been, I felt that the thing was possible; at all events I could
+try, without attempting anything which was not clearly within my power.
+
+
+FOOTNOTES:
+
+[A] Now called, in the Federal map, the "Monte Rosa glacier." Goernerhorn
+is an old local name for the central mass of Monte Rosa.--L. C. T.
+
+[B] _See_ p. 138, footnote.
+
+
+
+
+SECOND ASCENT OF MONTE ROSA, 1858.
+
+(22.)
+
+
+[Sidenote: A LIGHT SCRIP. 1858.]
+
+Whether my exercise be mental or bodily, I am always most vigorous when
+cool. During my student life in Germany, the friends who visited me
+always complained of the low temperature of my room, and here among the
+Alps it was no uncommon thing for me to wander over the glaciers from
+morning till evening in my shirt-sleeves. My object now was to go as
+light as possible, and hence I left my coat and neckcloth behind me,
+trusting to the sun and my own motion to make good the calorific waste.
+After breakfast I poured what remained of my tea into a small glass
+bottle, an ordinary demi-bouteille, in fact; the waiter then provided me
+with a ham sandwich, and, with my scrip thus frugally furnished, I
+thought the heights of Monte Rosa might be won. I had neither brandy nor
+wine, but I knew the immense amount of mechanical force represented by
+four ounces of bread and ham, and I therefore feared no failure from
+lack of nutriment. Indeed, I am inclined to think that both guides and
+travellers often impair their vigour and render themselves cowardly and
+apathetic by the incessant "refreshing" which they deem it necessary to
+indulge in on such occasions.
+
+[Sidenote: THE GUIDE EXPOSTULATES. 1858.]
+
+[Sidenote: THE GUIDE HALTS. 1858.]
+
+The guide whom Lauener intended for me was at the door; I passed him and
+desired him to follow me. This he at first refused to do, as he did not
+recognise me in my shirt-sleeves; but his companions set him right, and
+he ran after me. I transferred my scrip to his shoulders, and led the
+way upward. Once or twice he insinuated that that was not the way to the
+Schwarze-See, and was probably perplexed by my inattention. From the
+summit of the ridge which bounds the Goerner glacier the whole grand
+panorama revealed itself, and on the higher slopes of Monte Rosa--so
+high, indeed, as to put all hope of overtaking them, or even coming near
+them, out of the question--a row of black dots revealed the company
+which had started at three o'clock from the hotel. They had made
+remarkably good use of their time, and I was afterwards informed that
+the cause of this was the intense cold, which compelled them to keep up
+the proper supply of heat by increased exertion. I descended swiftly to
+the glacier, and made for the base of Monte Rosa, my guide following at
+some distance behind me. One of the streams, produced by superficial
+melting, had cut for itself a deep wide channel in the ice; it was not
+too wide for a spring, and with the aid of a run I cleared it and went
+on. Some minutes afterwards I could hear the voice of my companion
+exclaiming, in a tone of expostulation, "No, no, I won't follow you
+there." He however made a circuit, and crossed the stream; I waited for
+him at the place where the Monte Rosa glacier joins the rock, "_auf der
+Platte_," and helped him down the ice-slope. At the summit of these
+rocks I again waited for him. He approached me with some excitement of
+manner, and said that it now appeared plain to him that I intended to
+ascend Monte Rosa, but that he would not go with me. I asked him to
+accompany me to the summit of the next cliff, which he agreed to do; and
+I found him of some service to me. He discovered the faint traces of the
+party in advance, and, from his greater experience, could keep them
+better in view than I could. We lost them, however, near the base of the
+cliff at which we aimed, and I went on, choosing as nearly as I could
+remember the route followed by Lauener and myself a week previously,
+while my guide took another route, seeking for the traces. The glacier
+here is crevassed, and I was among the fissures some distance in advance
+of my companion. Fear was manifestly getting the better of him, and he
+finally stood still, exclaiming, "No man can pass there." At the same
+moment I discovered the trace, and drew his attention to it; he
+approached me submissively, said that I was quite right, and declared
+his willingness to go on. We climbed the cliff, and discovered the trace
+in the snow above it. Here I transferred the scrip and telescope to my
+own shoulders, and gave my companion a cheque for five francs. He
+returned, and I went on alone.
+
+The sun and heaven were glorious, but the cold was nevertheless intense,
+for it had frozen bitterly the night before. The mountain seemed more
+noble and lovely than when I had last ascended it; and as I climbed the
+slopes, crossed the shining cols, and rounded the vast snow-bosses of
+the mountain, the sense of being alone lent a new interest to the
+glorious scene. I followed the track of those who preceded me, which was
+that pursued by Lauener and myself a week previously. Once I deviated
+from it to obtain a glimpse of Italy over the saddle which stretches
+from Monte Rosa to the Lyskamm. Deep below me was the valley, with its
+huge and dislocated _neve_, and the slope on which I hung was just
+sufficiently steep to keep the attention aroused without creating
+anxiety. I prefer such a slope to one on which the thought of danger
+cannot be entertained. I become more weary upon a dead level, or in
+walking up such a valley as that which stretches between Visp and
+Zermatt, than on a steep mountain side. The sense of weariness is often
+no index to the expenditure of muscular force: the muscles may be
+charged with force, and, if the nervous excitant be feeble, the strength
+lies dormant, and we are tired without exertion. But the thought of
+peril keeps the mind awake, and spurs the muscles into action; they move
+with alacrity and freedom, and the time passes swiftly and pleasantly.
+
+[Sidenote: LEFT ALONE. 1858.]
+
+Occupied with my own thoughts as I ascended, I sometimes unconsciously
+went too quickly, and felt the effects of the exertion. I then slackened
+my pace, allowing each limb an instant of repose as I drew it out of the
+snow, and found that in this way walking became rest. This is an
+illustration of the principle which runs throughout nature--to
+accomplish physical changes, _time_ is necessary. Different positions of
+the limb require different molecular arrangements; and to pass from one
+to the other requires time. By lifting the leg slowly and allowing it to
+fall forward by its own gravity, a man may get on steadily for several
+hours, while a very slight addition to this pace may speedily exhaust
+him. Of course the normal pace differs in different persons, but in all
+the power of endurance may be vastly augmented by the prudent outlay of
+muscular force.
+
+The sun had long shone down upon me with intense fervour, but I now
+noticed a strange modification of the light upon the slopes of
+snow. I looked upwards, and saw a most gorgeous exhibition of
+interference-colours. A light veil of clouds had drawn itself between me
+and the sun, and this was flooded with the most brilliant dyes. Orange,
+red, green, blue--all the hues produced by diffraction were exhibited in
+the utmost splendour. There seemed a tendency to form circular zones of
+colour round the sun, but the clouds were not sufficiently uniform to
+permit of this, and they were consequently broken into spaces, each
+steeped with the colour due to the condition of the cloud at the place.
+Three times during my ascent similar veils drew themselves across the
+sun, and at each passage the splendid phenomena were renewed. As I
+reached the middle of the mountain an avalanche was let loose from the
+sides of the Lyskamm; the thunder drew my eyes to the place; I saw the
+ice move, but it was only the tail of the avalanche; still the volume of
+sound told me that it was a huge one. Suddenly the front of it appeared
+from behind a projecting rock, hurling its ice-masses with fury into the
+valley, and tossing its rounded clouds of ice-dust high into the
+atmosphere. A wild long-drawn sound, multiplied by echoes, now descended
+from the heights above me. It struck me at first as a note of
+lamentation, and I thought that possibly one of the party which was now
+near the summit had gone over the precipice. On listening more
+attentively I found that the sound shaped itself into an English
+"hurrah!" I was evidently nearing the party, and on looking upwards I
+could see them, but still at an immense height above me. The summit
+still rose before them, and I therefore thought the cheer premature. A
+precipice of ice was now in front of me, around which I wound to the
+right, and in a few minutes found myself fairly at the bottom of the
+Kamm.
+
+[Sidenote: GIDDINESS ON THE KAMM. 1858.]
+
+[Sidenote: SCRIP LEFT BEHIND. 1858.]
+
+I paused here for a moment, and reflected on the work before me. My head
+was clear, my muscles in perfect condition, and I felt just sufficient
+fear to render me careful. I faced the Kamm, and went up slowly but
+surely, and soon heard the cheer which announced the arrival of the
+party at the summit of the mountain. It was a wild, weird, intermittent
+sound, swelling or falling as the echoes reinforced or enfeebled it. In
+getting through the rocks which protrude from the snow at the base of
+the last spur of the mountain, I once had occasion to stoop my head,
+and, on suddenly raising it, my eyes swam as they rested on the unbroken
+slope of snow at my left. The sensation was akin to giddiness, but I
+believe it was chiefly due to the absence of any object upon the snow
+upon which I could converge the axes of my eyes. Up to this point I had
+eaten nothing. I now unloosed my scrip, and had two mouthfuls of
+sandwich and nearly the whole of the tea that remained. I found here
+that my load, light as it was, impeded me. When fine balancing is
+necessary, the presence of a very light load, to which one is
+unaccustomed, may introduce an element of danger, and for this reason I
+here left the residue of my tea and sandwich behind me. A long, long
+edge was now in front of me, sloping steeply upwards. As I commenced the
+ascent of this, the foremost of those whose cheer had reached me from
+the summit some time previously, appeared upon the top of the edge, and
+the whole party was seen immediately afterwards dangling on the Kamm. We
+mutually approached each other. Peter Bohren, a well-known Oberland
+guide, came first, and after him came the gentleman in his immediate
+charge. Then came other guides with other gentlemen, and last of all my
+guide, Lauener, with his strong right arm round the youngest of the
+party. We met where a rock protruded through the snow. The cold smote my
+naked throat bitterly, so to protect it I borrowed a handkerchief from
+Lauener, bade my new acquaintances good bye, and proceeded upwards. I
+was soon at the place where the snow-ridge joins the rocks which
+constitute the crest of the mountain; through these my way lay, every
+step I took augmenting my distance from all life, and increasing my
+sense of solitude. I went up and down the cliffs as before, round
+ledges, through fissures, along edges of rock, over the last deep and
+rugged indentation, and up the rocks at its opposite side, to the
+summit.
+
+[Sidenote: ALONE ON THE SUMMIT. 1858.]
+
+[Sidenote: THE AXE SLIPS. 1858.]
+
+A world of clouds and mountains lay beneath me. Switzerland, with its
+pomp of summits, was clear and grand; Italy was also grand, but more
+than half obscured. Dark cumulus and dark crag vied in savagery, while
+at other places white snows and white clouds held equal rivalry. The
+scooped valleys of Monte Rosa itself were magnificent, all gleaming in
+the bright sunlight--tossed and torn at intervals, and sending from
+their rents and walls the magical blue of the ice. Ponderous _neves_ lay
+upon the mountains, apparently motionless, but suggesting
+motion--sluggish, but indicating irresistible dynamic energy, which
+moved them slowly to their doom in the warmer valleys below. I thought
+of my position: it was the first time that a man had stood alone upon
+that wild peak, and were the imagination let loose amid the surrounding
+agencies, and permitted to dwell upon the perils which separated the
+climber from his kind, I dare say curious feelings might have been
+engendered. But I was prompt to quell all thoughts which might lessen my
+strength, or interfere with the calm application of it. Once indeed an
+accident made me shudder. While taking the cork from a bottle which is
+deposited on the top, and which contains the names of those who have
+ascended the mountain, my axe slipped out of my hand, and slid some
+thirty feet away from me. The thought of losing it made my flesh creep,
+for without it descent would be utterly impossible. I regained it, and
+looked upon it with an affection which might be bestowed upon a living
+thing, for it was literally my staff of life under the circumstances.
+One look more over the cloud-capped mountains of Italy, and I then
+turned my back upon them, and commenced the descent.
+
+The brown crags seemed to look at me with a kind of friendly
+recognition, and, with a surer and firmer feeling than I possessed on
+ascending, I swung myself from crag to crag and from ledge to ledge with
+a velocity which surprised myself. I reached the summit of the Kamm, and
+saw the party which I had passed an hour and a half before, emerging
+from one of the hollows of the mountain; they had escaped from the edge
+which now lay between them and me. The thought of the possible loss of
+my axe at the summit was here forcibly revived, for without it I dared
+not take a single step. My first care was to anchor it firmly in the
+snow, so as to enable it to bear at times nearly the whole weight of my
+body. In some places, however, the anchor had but a loose hold; the
+"cornice" to which I have already referred became granular, and the
+handle of the axe went through it up to the head, still, however,
+remaining loose. Some amount of trust had thus to be withdrawn from the
+staff and placed in the limbs. A curious mixture of carelessness and
+anxiety sometimes fills the mind on such occasions. I often caught
+myself humming a verse of a frivolous song, but this was mechanical, and
+the substratum of a man's feelings under such circumstances is real
+earnestness. The precipice to my left was a continual preacher of
+caution, and the slope to my right was hardly less impressive. I looked
+down the former but rarely, and sometimes descended for a considerable
+time without looking beyond my own footsteps. The power of a thought was
+illustrated on one of these occasions. I had descended with extreme
+slowness and caution for some time, when looking over the edge of the
+cornice I saw a row of pointed rocks at some distance below me. These I
+felt must receive me if I slipped over, and I thought how before
+reaching them I might so break my fall as to arrive at them unkilled.
+This thought enabled me to double my speed, and as long as the spiky
+barrier ran parallel to my track I held my staff in one hand, and
+contented myself with a slight pressure upon it.
+
+I came at length to a place where the edge was solid ice, which rose to
+the level of the cornice, the latter appearing as if merely stuck
+against it. A groove ran between the ice and snow, and along this groove
+I marched until the cornice became unsafe, and I had to betake myself to
+the ice. The place was really perilous, but, encouraging myself by the
+reflection that it would not last long, I carefully and deliberately
+hewed steps, causing them to dip a little inward, so as to afford a
+purchase for the heel of my boot, never forsaking one till the next was
+ready, and never wielding my hatchet until my balance was secured. I was
+soon at the bottom of the Kamm, fairly out of danger, and full of glad
+vigour I bore swiftly down upon the party in advance of me. It was an
+easy task to me to fuse myself amongst them as if I had been an old
+acquaintance, and we joyfully slid, galloped, and rolled together down
+the residue of the mountain.
+
+[Sidenote: ACCIDENT ON THE KAMM. 1858.]
+
+The only exception was the young gentleman in Lauener's care. A day or
+two previously he had, I believe, injured himself in crossing the Gemmi,
+and long before he reached the summit of Monte Rosa his knee swelled,
+and he walked with great difficulty. But he persisted in ascending, and
+Lauener, seeing his great courage, thought it a pity to leave him
+behind. I have stated that a portion of the Kamm was solid ice. On
+descending this, Mr. F.'s footing gave way, and he slipped forward.
+Lauener was forced to accompany him, for the place was too steep and
+slippery to permit of their motion being checked. Both were on the point
+of going over the Lyskamm side of the mountain, where they would have
+indubitably been dashed to pieces. "There was no escape there," said
+Lauener, in describing the incident to me subsequently, "but I saw a
+possible rescue at the other side, so I sprang to the right, forcibly
+swinging my companion round; but in doing so, the baton tripped me up;
+we both fell, and rolled rapidly over each other down the incline. I
+knew that some precipices were in advance of us, over which we should
+have gone, so, releasing myself from my companion, I threw myself in
+front of him, stopped myself with my axe, and thus placed a barrier
+before him." After some vain efforts at sliding down the slopes on a
+baton, in which practice I was fairly beaten by some of my new friends,
+I attached myself to the invalid, and walked with him and Lauener
+homewards. Had I gone forward with the foremost of the party, I should
+have completed the expedition to the summit and back in a little better
+than nine hours.
+
+[Sidenote: DANGER OF CLIMBING ALONE. 1858.]
+
+I think it right to say one earnest word in connexion with this ascent;
+and the more so as I believe a notion is growing prevalent that half
+what is said and written about the dangers of the Alps is mere humbug.
+No doubt exaggeration is not rare, but I would emphatically warn my
+readers against acting upon the supposition that it is general. The
+dangers of Mont Blanc, Monte Rosa, and other mountains, are real, and,
+if not properly provided against, may be terrible. I have been much
+accustomed to be alone upon the glaciers, but sometimes, even when a
+guide was in front of me, I have felt an extreme longing to have a
+second one behind me. Less than two good ones I think an arduous climber
+ought not to have; and if climbing without guides were to become
+habitual, deplorable consequences would assuredly sooner or later ensue.
+
+
+
+
+(23.)
+
+
+The 18th of August I spent upon the Furgge glacier at the base of Mont
+Cervin, and what it taught me shall be stated in another place. The
+evening of this day was signalised by the pleasant acquaintances which
+it gave me. It was my intention to cross the Weissthor on the morning of
+the 19th, but thunder, lightning, and heavy rain opposed the project,
+and with two friends I descended, amid pitiless rain, to Zermatt. Next
+day I walked by way of Stalden to Saas, where I made the acquaintance of
+Herr Imseng, the Cure, and on the 21st ascended to the Distel Alp. Near
+to this place the Allalein glacier pushes its huge terminus right across
+the valley and dams up the streams descending from the mountains higher
+up, thus giving birth to a dismal lake. At one end of this stands the
+Mattmark hotel, which was to be my headquarters for a few days.
+
+[Sidenote: ASCENT OF A BOULDER. 1858.]
+
+I reached the place in good company. Near to the hotel are two
+magnificent boulders of green serpentine, which have been lodged there
+by one of the lateral glaciers; and two of the ladies desiring to ascend
+one of these rocks, a friend and myself helped them to the top. The
+thing was accomplished in a very spirited way. Indeed the general
+contrast, in regard to energy, between the maidens of the British Isles
+and those of the Continent and of America is extraordinary. Surely those
+who talk of this country being in its old age overlook the physical
+vigour of its sons and daughters. They are strong, but from a
+combination of the greatest forces we may obtain a small resultant,
+because the forces may act in opposite directions and partly neutralize
+each other. Herein, in fact, lies Britain's weakness; it is strength
+ill-directed; and is indicative rather of the perversity of young blood
+than of the precision of mature years.
+
+[Sidenote: DISMAL QUARTERS. 1858.]
+
+Immediately after this achievement I was forsaken by my friends, and
+remained the only visitor in the hotel. A dense gray cloud gradually
+filled the entire atmosphere, from which the rain at length began to
+gush in torrents. The scene from the windows of the hotel was of the
+most dismal character; the rain also came through the roof, and dripped
+from the ceiling to the floor. I endeavoured to make a fire, but the air
+would not let the smoke of the pine-logs ascend, and the biting of the
+hydrocarbons was excruciating to the eyes. On the whole, the cold was
+preferable to the smoke. During the night the rain changed to snow, and
+on the morning of the 22nd all the mountains were thickly covered. The
+gray delta through which a river of many arms ran into the Mattmark See
+was hidden; against some of the windows of the _salle a manger_ the snow
+was also piled, obscuring more than half their light. I had sent my
+guide to Visp, and two women and myself were the only occupants of the
+place. It was extremely desolate--I felt, moreover, the chill of Monte
+Rosa in my throat, and the conditions were not favourable to the cure of
+a cold.
+
+On the 23rd the Allalein glacier was unfit for work; I therefore
+ascended to the summit of the Monte Moro, and found the Valaisian side
+of the pass in clear sunshine, while impenetrable fog met us on the
+Italian side. I examined the colour of the freshly fallen snow; it was
+not an ordinary blue, and was even more transparent than the blue of the
+firmament. When the snow was broken the light flashed forth; when the
+staff was dug into the snow and withdrawn, the blue gleam appeared; when
+the staff lay in a hole, although there might be a sufficient space all
+round it, the coloured light refused to show itself.
+
+My cough kept me awake on the night of the 23rd, and my cold was worse
+next day. I went upon the Allalein glacier, but found myself by no means
+so sure a climber as usual. The best guides find that their powers vary;
+they are not equally competent on all days. I have heard a celebrated
+Chamouni guide assert that a man's _morale_ is different on different
+days. The morale in my case had a physical basis, and it probably has so
+in all. The Allalein glacier, as I have said, crosses the valley and
+abuts against the opposite mountain; here it is forced to turn aside,
+and in consequence of the thrust and bending it is crumpled and
+crevassed. The wall of the Mattmark See is a fine glacier section:
+looked at from a distance, the ridges and fissures appear arranged like
+a fan. The structure of the crumpled ice varies from the vertical to the
+horizontal, and the ridges are sometimes split _along_ the planes of
+structure. The aspect of this portion of the glacier from some of the
+adjacent heights is exceedingly interesting.
+
+[Sidenote: THE VAULT OF THE ALLALEIN. 1858.]
+
+On the morning of the 25th I had two hours' clambering over the
+mountains before breakfast, and traced the action of ancient glaciers to
+a great height. The valley of Saas in this respect rivals that of Hasli;
+the flutings and polishings being on the grandest scale. After breakfast
+I went to the end of the Allalein glacier, where the Saas Visp river
+rushes from it: the vault was exceedingly fine, being composed of
+concentric arches of clear blue ice. I spent several hours here
+examining the intimate structure of the ice, and found the vacuum disks
+which I shall describe at another place, of the greatest service to me.
+As at Rosenlaui and elsewhere, they here taught me that the glacier was
+composed of an aggregate of small fragments, each of which had a
+definite plane of crystallization. Where the ice was partially weathered
+the surfaces of division between the fragments could be traced through
+the coherent mass, but on crossing these surfaces the direction of the
+vacuum disks changed, indicating a similar change of the planes of
+crystallization. The blue veins of the glacier went through its
+component fragments irrespective of these planes. Sometimes the vacuum
+disks were parallel to the veins, sometimes across them, sometimes
+oblique to them.
+
+Several fine masses of ice had fallen from the arch upon its floor, and
+these were disintegrated to the core. A kick, or a stroke of an axe,
+sufficed to shake masses almost a cubic yard in size into fragments
+varying not much on either side of a cubic inch. The veining was finely
+preserved on the concentric arches of the vault, and some of them
+apparently exhibited its abolition, or at least confusion, and fresh
+development by new conditions of pressure. The river being deep and
+turbulent this day, to reach its opposite side I had to climb the
+glacier and cross over the crown of its highest arch; this enabled me
+to get quite in front of the vault, to enter it, and closely inspect
+those portions where the structure appeared to change. I afterwards
+ascended the steep moraine which lies between the Allalein and the
+smaller glacier to the left of it; passing to the latter at intervals to
+examine its structure. I was at length stopped by the dislocated ice;
+and from the heights I could count a system of seven dirt-bands, formed
+by the undulations on the surface of the glacier. On my return to the
+hotel I found there a number of well-known Alpine men who intended to
+cross the Adler pass on the following day. Herr Imseng was there: he
+came to me full of enthusiasm, and asked me whether I would join him in
+an ascent of the Dom: we might immediately attack it; and he felt sure
+that we should succeed. The Dom is the highest of the Mischabel peaks,
+and is one of the grandest of the Alps. I agreed to join the Cure, and
+with this understanding we parted for the night.
+
+[Sidenote: AVALANCHE AT SAAS. 1858.]
+
+Thursday, 26th August.--A wild stormy morning after a wild and rainy
+night: the Adler pass being impassable, the mountaineers returned, and
+Imseng informed me that the Dom must be abandoned. He gave me the
+statistics of an avalanche which had fallen in the valley some years
+before. Within the memory of man Saas had never been touched by an
+avalanche, but a tradition existed that such a catastrophe had once
+occurred. On the 14th of March, 1848, at eight o'clock in the morning,
+the Cure was in his room; when he heard the cracking of pine-branches,
+and inferred from the sound that an avalanche was descending upon the
+village. It dashed in the windows of his house and filled his rooms with
+snow; the sound it produced being sufficient to mask the crashing of the
+timbers of an adjacent house. Three persons were killed. On the 3rd of
+April, 1849, heavy snow fell at Saas; the Cure waited until it had
+attained a depth of four feet, and then retreated to Fee. That night an
+avalanche descended, and in the line of its rush was a house in which
+five or six and twenty people had collected for safety: nineteen of them
+were killed. The Cure afterwards showed me the site of the house, and
+the direction of the avalanche. It passed through a pine wood; and on
+expressing my surprise that the trees did not arrest it, he replied that
+the snow was "quite like dust," and rushed among the trees like so much
+water. To return from Fee to Saas on the day following he found it
+necessary to carry two planks. Kneeling upon one of them, he pushed the
+other forward, and transferred his weight to it, drawing the other after
+him and repeating the same act. The snow was like flour, and would not
+otherwise bear his weight. Seeing no prospect of fine weather, I
+descended to Saas on the afternoon of the 26th. I was the only guest at
+the hotel; but during the evening I was gratified by the unexpected
+arrival of my friend Hirst, who was on his way over the Monte Moro to
+Italy.
+
+[Sidenote: THE FEE GLACIER. 1858.]
+
+[Sidenote: SNOW, VAPOUR AND CLOUD. 1858.]
+
+For the last five days it had been a struggle between the north wind and
+the south, each edging the other by turns out of its atmospheric bed,
+and producing copious precipitation; but now the conflict was
+decided--the north had prevailed, and an almost unclouded heaven
+overspread the Alps. The few white fleecy masses that remained were good
+indications of the swift march of the wind in the upper air. My friend
+and I resolved to have at least one day's excursion together, and we
+chose for it the glacier of the Fee. Ascending the mountain by a
+well-beaten path, we passed a number of "Calvaries" filled with tattered
+saints and Virgins, and soon came upon the rim of a flattened bowl quite
+clasped by the mountains. In its centre was the little hamlet of Fee,
+round which were fresh green pastures, and beyond it the perpetual ice
+and snow. It was exceedingly picturesque--a scene of human beauty and
+industry where savagery alone was to be expected. The basin had been
+scooped by glaciers, and as we paused at its entrance the rounded and
+fluted rocks were beneath our feet. The Alphubel and the Mischabel
+raised their crowns to heaven in front of us; the newly fallen snow
+clung where it could to the precipitous crags of the Mischabel, but on
+the summits it was the sport of the wind. Sometimes it was borne
+straight upwards in long vertical striae; sometimes the fibrous columns
+swayed to the right, sometimes to the left; sometimes the motion on one
+of the summits would quite subside; anon the white peak would appear
+suddenly to shake itself to dust, which it yielded freely to the wind. I
+could see the wafted snow gradually melt away, and again curdle up into
+true white cloud by precipitation; this in its turn would be pulled
+asunder like carded wool, and reduced a second time to transparent
+vapour.
+
+In the middle of the ice of the Fee stands a green alp, not unlike the
+Jardin; up this we climbed, halting at intervals upon its grassy knolls
+to inspect the glacier. I aimed at those places where on a priori
+grounds I should have thought the production of the veined structure
+most likely, and reached at length the base of a wall of rock from the
+edge of which long spears of ice depended. Here my friend halted, while
+Lauener and myself climbed the precipice, and ascended to the summit of
+the alp. The snow was deep at many places, and our immersions in unseen
+holes very frequent. From the peak of the Fee Alp a most glorious view
+is obtained; in point of grandeur it will bear comparison with any in
+the Alps, and its seclusion gives it an inexpressible charm. We remained
+for half an hour upon the warm rock, and then descended. It was our
+habit to jump from the higher ledges into the deep snow below them, in
+which we wallowed as if it were flour; but on one of these occasions I
+lighted on a stone, and the shock produced a curious effect upon my
+hearing. I appeared suddenly to lose the power of appreciating deep
+sounds, while the shriller ones were comparatively unimpaired. After I
+rejoined my friend it required attention on my part to hear him when he
+spoke to me. This continued until I approached the end of the glacier,
+when suddenly the babblement of streams, and a world of sounds to which
+I had been before quite deaf burst in upon me. The deafness was probably
+due to a strain of the tympanum, such as we can produce artificially,
+and thus quench low sounds, while shrill ones are scarcely affected.
+
+[Sidenote: "A TERRIBLE HOLE." 1858.]
+
+I was anxious to quit Saas early next morning, but the Cure expressed so
+strong a wish to show us what he called a _schauderhaftes Loch_--a
+terrible hole--which he had himself discovered, that I consented to
+accompany him. We were joined by his assistant and the priest of Fee.
+The stream from the Fee glacier has cut a deep channel through the
+rocks, and along the right-hand bank of the stream we ascended. It was
+very rough with fallen crags and fallen pines amid which we once or
+twice lost our way. At length we came to an aperture just sufficient to
+let a man's body through, and were informed by our conductor that our
+route lay along the little tunnel: he lay down upon his stomach and
+squeezed himself through it like a marmot. I followed him; a second
+tunnel, in which, however, we could stand upright, led into a spacious
+cavern, formed by the falling together of immense slabs of rock which
+abutted against each other so as to form a roof. It was the very type of
+a robber den; and when I remarked this, it was at once proposed to sing
+a verse from Schiller's play. The young priest had a powerful voice--he
+led and we all chimed in.
+
+[Sidenote: SONG OF THE ROBBERS. 1858.]
+
+ "Ein frohes Leben fuehren wir,
+ Ein Leben voller Wonne.
+ Der Wald ist unser Nachtquartier,
+ Bei Sturm und Wind hanthieren wir,
+ Der Mond ist unsre Sonne."
+
+Herr Imseng wore his black coat; the others had taken theirs off, but
+they wore their clerical hats, black breeches and stockings. We formed a
+singular group in a singular place, and the echoed voices mingled
+strangely with the gusts of the wind and the rush of the river.
+
+Soon afterwards I parted from my friend, and descended the valley to
+Visp, where I also parted with my guide. He had been with me from the
+22nd of July to the 29th of August, and did his duty entirely to my
+satisfaction. He is an excellent iceman, and is well acquainted both
+with the glaciers of the Oberland and of the Valais. He is strong and
+good-humoured, and were I to make another expedition of the kind I don't
+think that I should take any guide in the Oberland in preference to
+Christian Lauener.
+
+
+
+
+(24.)
+
+
+[Sidenote: CLIMBERS AND SCIENCE. 1858.]
+
+It is a singular fact that as yet we know absolutely nothing of the
+winter temperature of any one of the high Alpine summits. No doubt it is
+a sufficient justification of our Alpine men, as regards their climbing,
+_that they like it_. This plain reason is enough; and no man who ever
+ascended that "bad eminence" Primrose Hill, or climbed to Hampstead
+Heath for the sake of a freer horizon, can consistently ask a better. As
+regards physical science, however, the contributions of our mountaineers
+have as yet been _nil_, and hence, when we hear of the scientific value
+of their doings, it is simply amusing to the climbers themselves. I do
+not fear that I shall offend them in the least by my frankness in
+stating this. Their pleasure is that of overcoming acknowledged
+difficulties, and of witnessing natural grandeur. But I would venture to
+urge that our Alpine men will not find their pleasure lessened by
+embracing a scientific object in their doings. They have the strength,
+the intelligence, and let them add to these the accuracy which physical
+science now demands, and they may contribute work of enduring value. Mr.
+Casella will gladly teach them the use of his minimum-thermometers; and
+I trust that the next seven years will not pass without making us
+acquainted with the winter temperature of every mountain of note in
+Switzerland.[A]
+
+I had thought of this subject since I first read the conjectures of De
+Saussure on the temperature of Mont Blanc; but in 1857 I met Auguste
+Balmat at the Jardin, and there learned from him that he entertained the
+idea of placing a self-registering thermometer at the summit of the
+mountain. Balmat was personally a stranger to me at the time, but
+Professor Forbes's writings had inspired me with a respect for him,
+which this unprompted idea of his augmented. He had procured a
+thermometer, the graduation of which, however, he feared was not low
+enough. As an encouragement to Balmat, and with the view of making his
+laudable intentions known, I communicated them to the Royal Society, and
+obtained from the Council a small grant of money to purchase
+thermometers and to assist in the expenses of an ascent. I had now the
+thermometers in my possession; and having completed my work at Zermatt
+and Saas, my next desire was to reach Chamouni and place the instruments
+on the top of Mont Blanc. I accordingly descended the valley of the
+Rhone to Martigny, crossed the Tete Noire, and arrived at Chamouni on
+the 29th of August, 1858.
+
+[Sidenote: DIFFICULTIES AT CHAMOUNI. 1858.]
+
+Balmat was engaged at this time as the guide of Mr. Alfred Wills, who,
+however, kindly offered to place him at my disposal; and also expressed
+a desire to accompany me himself and assist me in my observations. I
+gladly accepted a proposal which gave me for companion so determined a
+climber and so estimable a man. But Chamouni was rife with difficulties.
+In 1857 the Guide Chef had the good sense to give me considerable
+liberty of action. Now his mood was entirely changed: he had been
+"molested" for giving me so much freedom. I wished to have a boy to
+carry a small instrument for me up the Mer de Glace--he would not allow
+it; I must take a guide. If I ascended Mont Blanc he declared that I
+must take four guides; that, in short, I must in all respects conform to
+the rules made for ordinary tourists. I endeavoured to explain to him
+the advantages which Chamouni had derived from the labours of men of
+science; it was such men who had discovered it when it was unknown, and
+it was by their writings that the attention of the general public had
+been called towards it. It was a bad recompense, I urged, to treat a man
+of science as he was treating me. This was urged in vain; he shrugged
+his shoulders, was very sorry, but the thing could not be changed. I
+then requested to know his superior, that I might apply to him; he
+informed me that there were a President and Commission of guides at
+Chamouni, who were the proper persons to decide the question, and he
+proposed to call them together on the 31st of August, at seven P.M., on
+condition that I was to be present to state my own case. To this I
+agreed.
+
+I spent that day quite alone upon the Mer de Glace, and climbed amid a
+heavy snow-storm to the Cleft station over Trelaporte. When I reached
+the Montanvert I was wet and weary, and would have spent the night there
+were it not for my engagement with the Guide Chef. I descended amid the
+rain, and at the appointed hour went to his bureau. He met me with a
+polite sympathetic shrug; explained to me that he had spoken to the
+Commission, but that it could not assemble _pour une chose comma ca_;
+that the rules were fixed, and I must abide by them. "Well," I
+responded, "you think you have done your duty; it is now my turn to
+perform mine. If no other means are available I will have this
+transaction communicated to the Sardinian Government, and I don't think
+that it will ratify what you have done." The Guide Chef evidently did
+not believe a word of it.
+
+Previous to taking any further step I thought it right to see the
+President of the Commission of Guides, who was also Syndic of the
+commune. I called upon him on the morning of the 1st of September, and,
+assuming that he knew all about the transaction, spoke to him
+accordingly. He listened to me for a time, but did not seem to
+understand me, which I ascribed partly to my defective French
+pronunciation. I expressed a hope that he did comprehend me; he said
+he understood my words very well, but did not know their purport. In
+fact he had not heard a single word about me or my request. He stated
+with some indignation that, so far from its being a subject on which the
+Commission could not assemble, it was one which it was their especial
+duty to take into consideration. Our conference ended with the
+arrangement that I was to write him an official letter stating the case,
+which he was to forward to the Intendant of the province of Faucigny
+resident at Bonneville. All this was done.
+
+[Sidenote: THE INTENDANT MEMORIALISED. 1858.]
+
+I subsequently memorialised the Intendant himself; and Balmat visited
+him to secure his permission to accompany me. I have to record, that
+from first to last the Intendant gave me his sympathy and support. He
+could not alter laws, but he deprecated a "judaical" interpretation of
+them. His final letter to myself was as follows:--
+
+[Sidenote: THE INTENDANT'S RESPONSE. 1858.]
+
+ "Intendance Royale de la Province de Faucigny,
+ "Bonneville, 11 Septembre, 1858.
+
+ "Monsieur,--
+
+ "J'apprends avec une veritable peine les difficultes que vous
+ rencontrez de la part de M. le Guide Chef pour l'effectuation
+ de votre perilleuse entreprise scientifique, mais je dois vous
+ dire aussi avec regret que ces difficultes resident dans un
+ reglement fait en vue de la securite des voyageurs, quel que
+ puisse etre le but de leurs excursions.
+
+ "Desireux neanmoins de vous etre utile, notamment en la
+ circonstance, j'invite aujourd'hui meme M. le Guide Chef a
+ avoir egard a votre projet, a faire en sa faveur une exception
+ au reglement ci-devant eu, tant qu'il n'y aura aucun danger
+ pour votre surete et celle des personnes qui vous
+ accompagneront, et enfin de se preter dans les limites de ses
+ moyens et attributions pour l'heureux succes de l'expedition,
+ dont les consequences et resultats n'interessent pas seulement
+ la science, mais encore la vallee de Chamounix en particulier.
+
+ "Agreez, Monsieur,
+ "l'assurance de ma consideration tres-distinguee.
+ "Pour l'Intendant en conge,
+ "Le Secretaire,
+ "DELEGLISE."
+
+While waiting for this permission I employed myself in various ways. On
+the 2nd of September I ascended the Brevent, from which Mont Blanc is
+seen to great advantage. From Chamouni its vast slopes are so
+foreshortened that one gets a very imperfect idea of the extent to be
+traversed to reach the summit. What, however, struck me most on the
+Brevent was the changed relation of the Aiguille du Dru and the Aiguille
+Verte. From Montanvert the former appears a most imposing mass, while
+the peak of the latter appears rather dwarfed behind it; but from the
+Brevent the Aiguille du Dru is a mere pinnacle stuck in the breast of
+the grander pyramid of the Aiguille Verte.
+
+[Sidenote: THE "SERACS" REVISITED. 1858.]
+
+On the 4th I rose early, and, strapping on my telescope, ascended to the
+Montanvert, where I engaged a youth to accompany me up the glacier. The
+heavens were clear and beautiful:--blue over the Aiguille du Dru, blue
+over the Jorasse and Mont Mallet, deep blue over the pinnacles of
+Charmoz, and the same splendid tint stretched grandly over the Col du
+Geant and its Aiguille. No trace of condensation appeared till towards
+eleven o'clock, when a little black balloon of cloud swung itself over
+the Aiguilles Rouges. At one o'clock there were two large masses and a
+little one between them; while higher up a white veil, almost too thin
+to be visible, spread over a part of the heavens. At the zenith,
+however, and south, north, and west, the blue seemed to deepen as the
+day advanced. I visited the ice-wall at the Tacul, which seemed lower
+than it was last year; the cascade of le Geant appeared also far less
+imposing. Only in the early part of summer do we see the ice in its true
+grandeur: its edges and surfaces are then sharp and clear, but
+afterwards its nobler masses shrink under the influence of sun and air.
+The _seracs_ now appeared wasted and dirty, and not the sharp angular
+ice-castles which rose so grandly when I first saw them. Thirteen men
+had crossed the Col du Geant on the day previous, and left an ample
+trace behind them. This I followed nearly to the summit of the fall. The
+condition of the glacier was totally different from that of the opposite
+side on the previous year. The ice was riven, burrowed, and honeycombed,
+but the track amid all was easy: a vigorous English maiden might have
+ascended the fall without much difficulty. My object now was to examine
+the structure of the fall; but the ice was not in a good condition for
+such an examination: it was too much broken. Still a definite structure
+was in many places to be traced, and some of them apparently showed
+structure and bedding at a high angle to each other, but I could not be
+certain of it. I paused at every commanding point of view and examined
+the ice through my opera-glass; but the result was inconclusive. I
+observed that the terraces which compose the fall do not front the
+middle of the glacier, but turn their foreheads rather towards its
+eastern side, and the consequence is that the protuberances lower down,
+which are the remains of these terraces, are highest at the same side.
+Standing at the base of the Aiguille Noire, and looking downwards where
+the Glacier des Periades pushes itself against the Geant, a series of
+fine crumples is formed on the former, cut across by crevasses, on the
+walls of which a forward and backward dipping of the blue veins is
+exhibited. Huge crumples are also formed by the Glacier du Geant, which
+are well seen from a point nearly opposite the lowest lateral moraine of
+the Glacier des Periades. In some cases the upper portions of the
+crumples had scaled off so as to form arches of ice--a consequence
+doubtless of the pressure.
+
+[Sidenote: THERMOMETER AT THE JARDIN. 1858.]
+
+The beauty of some Alpine skies is treacherous; in fact the deepest blue
+often indicates an atmosphere charged almost to saturation with aqueous
+vapour. This was the case on the present occasion. Soon after reaching
+Chamouni in the evening, rain commenced and continued with scarcely any
+intermission until the afternoon of the 8th. I had given up all hopes of
+being able to ascend Mont Blanc; and hence resolved to place the
+thermometers in some more accessible position. On the 9th accordingly,
+accompanied by Mr. Wills, Balmat, and some other friends, I ascended to
+the summit of the Jardin, where we placed two thermometers: one in the
+ice, at a depth of three feet below the surface; another on a ledge of
+the highest rock.[B] The boiling point of water at this place was
+194.6 deg. Fahr.
+
+Deep snow was upon the Talefre, and the surrounding precipices were also
+heavily laden. Avalanches thundered incessantly from the Aiguille Verte
+and the other mountains. Scarcely five minutes on an average intervened
+between every two successive peals; and after the direct shock of each
+avalanche had died away the air of the basin continued to be shaken by
+the echoes reflected from its bounding walls.
+
+[Sidenote: EVENING RED. 1858.]
+
+The day was far spent before we had completed our work. All through the
+weather had been fine, and towards evening augmented to magnificence. As
+we descended the glacier from the Couvercle the sun was just
+disappearing, and the western heaven glowed with crimson, which crept
+gradually up the sky until finally it reached the zenith itself. Such
+intensity of colouring is exceedingly rare in the Alps; and this fact,
+together with the known variations in the intensity of the firmamental
+blue, justify the conclusion that the colouring must, in a great
+measure, be due to some _variable constituent_ of the atmosphere. If
+_the air_ were competent to produce these magnificent effects they would
+be the rule instead of the exception.
+
+[Sidenote: FINISHED WORK. 1858.]
+
+No sooner had the thermometers been thus disposed of than the weather
+appeared to undergo a permanent change. On the 10th it was perfectly
+fine--not the slightest mist upon Mont Blanc; on the 11th this was also
+the case. Balmat still had the old thermometer to which I have already
+referred; it might not do to show the minimum temperature of the air,
+but it might show the temperature at a certain depth below the surface.
+I find in my own case that the finishing of work has a great moral
+value: work completed is a safe fulcrum for the performance of other
+work; and even though in the course of our labours experience should
+show us a better means of accomplishing a given end, it is often far
+preferable to reach the end, even by defective means, than to swerve
+from our course. The habits which this conviction had superinduced no
+doubt influenced me when I decided on placing Balmat's thermometer on
+the summit of Mont Blanc.
+
+
+FOOTNOTES:
+
+[A] I find with pleasure that my friend Mr. John Ball is now exerting
+himself in this direction.
+
+[B] The minimum temperature of the subsequent winter, as shown by this
+thermometer, was -6 deg. Fahr., or 38 deg. below the freezing point. The
+instrument placed in the ice was broken.
+
+
+
+
+SECOND ASCENT OF MONT BLANC, 1858.
+
+(25.)
+
+
+[Sidenote: SHADOWS OF THE AIGUILLES. 1858.]
+
+On the 12th of September, at 5-1/2 A.M. the sunbeams had already fallen
+upon the mountain; but though the sky above him, and over the entire
+range of the Aiguilles, was without a cloud, the atmosphere presented an
+appearance of turbidity resembling that produced by the dust and thin
+smoke mechanically suspended in a London atmosphere on a dry summer's
+day. At 20 minutes past 7 we quitted Chamouni, bearing with us the good
+wishes of a portion of its inhabitants.
+
+[Sidenote: INTERFERENCE-SPECTRA. 1858.]
+
+A lady accompanied us on horseback to the point where the path to the
+Grands Mulets deviates from that to the Plan des Aiguilles; here she
+turned to the left, and we proceeded slowly upwards, through woods of
+pine, hung with fantastic lichens: escaping from the gloom of these, we
+emerged upon slopes of bosky underwood, green hazel, and green larch,
+with the red berries of the mountain-ash shining brightly between them.
+Through the air above us, like gnomons of a vast sundial, the Aiguilles
+cast their fanlike shadows, which moved round as the day advanced.
+Slopes of rhododendrons with withered flowers next succeeded, but the
+colouring of the bilberry-leaves was scarcely less exquisite than the
+freshest bloom of the Alpine rose. For a long time we were in the cool
+shadow of the mountain, catching, at intervals, through the twigs in
+front of us, glimpses of the sun surrounded by coloured spectra. On one
+occasion a brow rose in front of me; behind it was a lustrous space of
+heaven, adjacent to the sun, which, however, was hidden behind the brow;
+against this space the twigs and weeds upon the summit of the brow shone
+as if they were self-luminous, while some bits of thistle-down floating
+in the air appeared, where they crossed this portion of the heavens,
+like fragments of the sun himself. Once the orb appeared behind a
+rounded mass of snow which lay near the summit of the Aiguille du Midi.
+Looked at with the naked eyes, it seemed to possess a billowy motion,
+the light darting from it in dazzling curves,--a subjective effect
+produced by the abnormal action of the intense light upon the eye. As
+the sun's disk came more into view, its rays however still grazing the
+summit of the mountain, interference-spectra darted from it on all
+sides, and surrounded it with a glory of richly-coloured bars. Mingling
+however with the grandeur of nature, we had the anger and obstinacy of
+man. With a view to subsequent legal proceedings, the Guide Chef sent a
+spy after us, who, having satisfied himself of our delinquency, took his
+unpleasant presence from the splendid scene.
+
+Strange to say, though the luminous appearance of bodies projected
+against the sky adjacent to the rising sun is a most striking and
+beautiful phenomenon, it is hardly ever seen by either guides or
+travellers; probably because they avoid looking towards a sky the
+brightness of which is painful to the eyes. In 1859 Auguste Balmat had
+never seen the effect; and the only written description of it which we
+possess is one furnished by Professor Necker, in a letter to Sir David
+Brewster, which is so interesting that I do not hesitate to reproduce it
+here:--
+
+[Sidenote: PROFESSOR NECKER'S LETTER. 1858.]
+
+"I now come to the point," writes M. Necker, "which you particularly
+wished me to describe to you; I mean the luminous appearance of trees,
+shrubs, and birds, when seen from the foot of a mountain a little before
+sunrise. The wish I had to see again the phenomenon before attempting to
+describe it made me detain this letter a few days, till I had a fine day
+to go to see it at the Mont Saleve; so yesterday I went there, and
+studied the fact, and in elucidation of it I made a little drawing, of
+which I give you here a copy: it will, with the explanation and the
+annexed diagram (Fig. 9), impart to you, I hope, a correct idea of the
+phenomenon. You must conceive the observer placed at the foot of a hill
+interposed between him and the place where the sun is rising, and thus
+entirely in the shade; the upper margin of the mountain is covered with
+woods or detached trees and shrubs, which are projected as dark objects
+on a very bright and clear sky, except at the very place where the sun
+is just going to rise, for there all the trees and shrubs bordering the
+margin are entirely,--branches, leaves, stem and all,--of a pure and
+brilliant white, appearing extremely bright and luminous, although
+projected on a most brilliant and luminous sky, as that part of it which
+surrounds the sun always is. All the minutest details, leaves, twigs,
+&c., are most delicately preserved, and you would fancy you saw these
+trees and forests made of the purest silver, with all the skill of the
+most expert workman. The swallows and other birds flying in those
+particular spots appear like sparks of the most brilliant white.
+Unfortunately, all these details, which add so much to the beauty of
+this splendid phenomenon, cannot be represented in such small sketches.
+
+[Illustration: Fig. 9. Luminous Trees projected against the sky at
+sunrise.]
+
+"Neither the hour of the day nor the angle which the object makes with
+the observer appears to have any effect; for on some occasions I have
+seen the phenomenon take place at a very early hour in the morning.
+Yesterday it was 10 A.M., when I saw it as represented in Fig. 10. I saw
+it again on the same day at 5 P.M., at a different place of the same
+mountain, for which the sun was just setting. At one time the angle of
+elevation of the lighted white shrubs above the horizon of the spectator
+was about 20 deg., while at another place it was only 15 deg. But the
+extent of the field of illumination is variable, according to the distance
+at which the spectator is placed from it. When the object behind which the
+sun is just going to rise, or has just been setting, is very near, no
+such effect takes place. In the case represented in Fig. 9 the distance
+was about 194 metres, or 636 English feet, from the spectator in a
+direct line, the height above his level being 60 metres, or 197 English
+feet, and the horizontal line drawn from him to the horizontal
+projection of these points on the plane of his horizon being 160 metres,
+or 525 English feet, as will be seen in the following diagram, Fig. 10.
+
+[Sidenote: SILVER TREES AT SUNRISE. 1858.]
+
+[Illustration: Fig. 10. Luminous Trees projected against the sky at
+sunrise.]
+
+[Sidenote: BIRDS AS SPARKS OR STARS. 1858.]
+
+"In this case only small shrubs and the lower half of the stem of a tree
+are illuminated white, and the horizontal extent of this effect is also
+comparatively small; while at other places when I was near the edge
+behind which the sun was going to rise no such effect took place. But on
+the contrary, when I have witnessed the phenomenon at a greater distance
+and at a greater height, as I have seen it other times on the same and
+on other mountains of the Alps, large tracts of forests and immense
+spruce-firs were illuminated white throughout their whole length, as I
+have attempted to represent in Fig. 11, and the corresponding diagram,
+Fig. 12. Nothing can be finer than these silver-looking spruce-forests.
+At the same time, though at a distance of more than a thousand metres, a
+vast number of large swallows or swifts (_Cypselus alpinus_), which
+inhabit these high rocks, were seen as small brilliant stars or sparks
+moving rapidly in the air. From these facts it appears to me obvious
+that the extent of the illuminated spots varies in a direct ratio of
+their distance; but at the same time that there must be a constant
+angular space, corresponding probably to the zone, a few minutes of a
+degree wide, around the sun's disk, which is a limit to the occurrence
+of the appearance. This would explain how the real extent which it
+occupies on the earth's surface varies with the relative distance of the
+spot from the eye of the observer, and accounts also for the phenomenon
+being never seen in the low country, where I have often looked for it in
+vain. Now that you are acquainted with the circumstances of the fact, I
+have no doubt you will easily observe it in some part or other of your
+Scotch hills; it may be some long heather or furze will play the part
+of our Alpine forests, and I would advise you to try and place a
+bee-hive in the required position, and it would perfectly represent our
+swallows, sparks, and stars."
+
+[Illustration: Fig. 11. Luminous Trees projected against the sky at
+sunrise.]
+
+[Illustration: Fig. 12. Luminous Trees projected against the sky at
+sunrise.]
+
+[Sidenote: THE LADDER CONDEMNED. 1858.]
+
+Our porters, with one exception, reached the Pierre a l'Echelle as soon
+as ourselves; and here having refreshed themselves, and the due exchange
+of loads having been made, we advanced upon the glacier, which we
+crossed, until we came nearly opposite to the base of the Grands Mulets.
+The existence of one wide crevasse, which was deemed impassable, had
+this year introduced the practice of assailing the rocks at their base,
+and climbing them to the cabin, an operation which Balmat wished to
+avoid. At Chamouni, therefore, he had made inquiries regarding the width
+of the chasm, and acting on his advice I had had a ladder constructed in
+two pieces, which, united together by iron attachments, was supposed to
+be of sufficient length to span the fissure. On reaching the latter, the
+pieces were united, and the ladder thrown across, but the bridge was so
+frail and shaky at the place of junction, and the chasm so deep, that
+Balmat pronounced the passage impracticable.
+
+[Sidenote: CROSSING CREVASSES. 1858.]
+
+The porters were all grouped beside the crevasse when this announcement
+was made, and, like hounds in search of the scent, the group instantly
+broke up, seeking in all directions for a means of passage. The talk was
+incessant and animating; attention was now called in one direction, anon
+in another, the men meanwhile throwing themselves into the most
+picturesque groups and attitudes. All eyes at length were directed upon
+a fissure which was spanned at one point by an arch of snow, certainly
+under two feet deep at the crown. A stout rope was tied round the waist
+of one of our porters, and he was sent forward to test the bridge. He
+approached it cautiously, treading down the snow to give it compactness,
+and thus make his footing sure as he advanced; bringing regelation into
+play, he gave the mass the necessary continuity, and crossed in safety.
+The rope was subsequently stretched over the _pont_, and each of us
+causing his right hand to slide along it, followed without accident.
+Soon afterwards, however, we met with a second and very formidable
+crevasse, to cross which we had but half of our ladder, which was
+applied as follows:--The side of the fissure on which we stood was lower
+than the opposite one; over the edge of the latter projected a cornice
+of snow, and a ledge of the same material jutted from the wall of the
+crevasse, a little below us. The ladder was placed from ledge to
+cornice, both of its ends being supported by snow. I could hardly
+believe that so frail a bearing could possibly support a man's weight;
+but a porter was tied as before, and sent up the ladder, while we
+followed protected by the rope. We were afterwards tied together, and
+thus advanced in an orderly line to the Grands Mulets.
+
+[Sidenote: GORGEOUS SUNSET. 1858.]
+
+The cabin was wet and disagreeable, but the sunbeams fell upon the brown
+rocks outside, and thither Mr. Wills and myself repaired to watch the
+changes of the atmosphere. I took possession of the flat summit of a
+prism of rock, where, lying upon my back, I watched the clouds forming,
+and melting, and massing themselves together, and tearing themselves
+like wool asunder in the air above. It was nature's language addressed
+to the intellect; these clouds were visible symbols which enabled us to
+understand what was going on in the invisible air. Here unseen currents
+met, possessing different temperatures, mixing their contents both of
+humidity and motion, producing a mean temperature unable to hold their
+moisture in a state of vapour. The water-particles, obeying their mutual
+attractions, closed up, and a visible cloud suddenly shook itself out,
+where a moment before we had the pure blue of heaven. Some of the clouds
+were wafted by the air towards atmospheric regions already saturated
+with moisture, and along their frontal borders new cloudlets ever piled
+themselves, while the hinder portions, invaded by a drier or a warmer
+air, were dissipated; thus the cloud advanced, with gain in front and
+loss behind, its permanence depending on the balance between them. The
+day waned, and the sunbeams began to assume the colouring due to their
+passage through the horizontal air. The glorious light, ever deepening
+in colour, was poured bounteously over crags, and snows, and clouds, and
+suffused with gold and crimson the atmosphere itself. I had never seen
+anything grander than the sunset on that day. Clouds with their central
+portions densely black, denying all passage to the beams which smote
+them, floated westward, while the fiery fringes which bordered them were
+rendered doubly vivid by contrast with the adjacent gloom. The smaller
+and more attenuated clouds were intensely illuminated throughout. Across
+other inky masses were drawn zigzag bars of radiance which resembled
+streaks of lightning. The firmament between the clouds faded from a
+blood-red through orange and daffodil into an exquisite green, which
+spread like a sea of glory through which those magnificent argosies
+slowly sailed. Some of the clouds were drawn in straight chords across
+the arch of heaven, these being doubtless the sections of layers of
+cloud whose horizontal dimensions were hidden from us. The cumuli around
+and near the sun himself could not be gazed upon, until, as the day
+declined, they gradually lost their effulgence and became tolerable to
+the eyes. All was calm--but there was a wildness in the sky like that of
+anger, which boded evil passions on the part of the atmosphere. The sun
+at length sank behind the hills, but for some time afterwards carmine
+clouds swung themselves on high, and cast their ruddy hues upon the
+mountain snows. Duskier and colder waxed the west, colder and sharper
+the breeze of evening upon the Grands Mulets, and as twilight deepened
+towards night, and the stars commenced to twinkle through the chilled
+air, we retired from the scene.
+
+[Sidenote: STORM ON THE GRANDS MULETS. 1858.]
+
+The anticipated storm at length gave notice of its coming. The
+sea-waves, as observed by Aristotle, sometimes reach the shore before
+the wind which produces them is felt; and here the tempest sent out its
+precursors, which broke in detached shocks upon the cabin before the
+real storm arrived. Billows of air, in ever quicker succession, rolled
+over us with a long surging sound, rising and falling as crest succeeded
+trough and trough succeeded crest. And as the pulses of a vibrating
+body, when their succession is quick enough, blend to a continuous note,
+so these fitful gusts linked themselves finally to a storm which made
+its own wild music among the crags. Grandly it swelled, carrying the
+imagination out of doors, to the clouds and darkness, to the loosened
+avalanches and whirling snow upon the mountain heads. Moored to the rock
+on two sides, the cabin stood firm, and its manifest security allowed
+the mind the undisturbed enjoyment of the atmospheric war. We were
+powerfully shaken, but had no fear of being uprooted; and a certain
+grandeur of the heart rose responsive to the grandeur of the storm.
+Mounting higher and higher, it at length reached its maximum strength,
+from which it lowered fitfully, until at length, with a melancholy wail,
+it bade our rock farewell.
+
+A little before half-past one we issued from the cabin. The night being
+without a moon, we carried three lanterns. The heavens were crowded with
+stars, among which, however, angry masses of cloud here and there still
+wandered. The storm, too, had left a rear-guard behind it; and strong
+gusts rolled down upon us at intervals, at one time, indeed, so violent
+as to cause Balmat to express doubts of our being able to reach the
+summit. With a thick handkerchief bound around my hat and ears I enjoyed
+the onset of the wind. Once, turning my head to the left, I saw what
+appeared to me to be a huge mass of stratus cloud, at a great distance,
+with the stars shining over it. In another instant a precipice of _neve_
+loomed upon us; we were close to its base, and along its front the
+annual layers were separated from each other by broad dark bands.
+Through the gloom it appeared like a cloud, the lines of bedding giving
+to it the stratus character.
+
+[Sidenote: A COMET DISCOVERED. 1858.]
+
+Immediately before lying down on the previous evening I had opened the
+little window of the cabin to admit some air. In the sky in front of me
+shone a curious nodule of misty light with a pale train attached to it.
+In 1853, on the side of the Brocken, I had observed, without previous
+notice, a comet discovered a few days previously by a former fellow
+student, and here was another "discovery" of the same kind. I inspected
+the stranger with my telescope, and assured myself that it was a comet.
+Mr. Wills chanced to be outside at the time, and made the same
+observation independently. As we now advanced up the mountain its
+ominous light gleamed behind us, while high up in heaven to our left the
+planet Jupiter burned like a lamp of intense brightness. The Petit
+Plateau forms a kind of reservoir for the avalanches of the Dome du
+Gouter, and this year the accumulation of frozen debris upon it was
+enormous. We could see nothing but the ice-blocks on which the light of
+the lanterns immediately fell; we only knew that they had been
+discharged from the _seracs_, and that similar masses now rose
+threatening to our right, and might at any moment leap down upon us.
+Balmat commanded silence, and urged us to move across the plateau with
+all possible celerity. The warning of our guide, the wild and rakish
+appearance of the sky, the spent projectiles at our feet, and the comet
+with its "horrid hair" behind, formed a combination eminently calculated
+to excite the imagination.
+
+[Sidenote: DAWN ON THE GRAND PLATEAU. 1858.]
+
+And now the sky began to brighten towards dawn, with that deep and calm
+beauty which suggests the thought of adoration to the human mind. Helped
+by the contemplation of the brightening east, which seemed to lend
+lightness to our muscles, we cheerily breasted the steep slope up to the
+Grand Plateau. The snow here was deep, and each of our porters took the
+lead in turn. We paused upon the Grand Plateau and had breakfast;
+digging, while we halted, our feet deeply into the snow. Thence up to
+the corridor, by a totally different route from that pursued by Mr.
+Hirst and myself the year previously; the slope was steep, but it had
+not a precipice for its boundary. Deep steps were necessary for a time,
+but when we reached the summit our ascent became more gentle. The
+eastern sky continued to brighten, and by its illumination the Grand
+Plateau and its bounding heights were lovely beyond conception. The snow
+was of the purest white, and the glacier, as it pushed itself on all
+sides into the basin, was riven by fissures filled with a coerulean
+light, which deepened to inky gloom as the vision descended into them.
+The edges were overhung with fretted cornices, from which depended long
+clear icicles, tapering from their abutments like spears of crystal. The
+distant fissures, across which the vision ranged obliquely without
+descending into them, emitted that magical firmamental shimmer which,
+contrasted with the pure white of the snow, was inexpressibly lovely.
+Near to us also grand castles of ice reared themselves, some erect, some
+overturned, with clear cut sides, striped by the courses of the annual
+snows, while high above the _seracs_ of the plateau rose their still
+grander brothers of the Dome du Gouter. There was a nobility in this
+glacier scene which I think I have never seen surpassed;--a strength of
+nature, and yet a tenderness, which at once raised and purified the
+soul. The gush of the direct sunlight could add nothing to this heavenly
+beauty; indeed I thought its yellow beams a profanation as they crept
+down from the humps of the Dromedary, and invaded more and more the
+solemn purity of the realm below.
+
+[Sidenote: BALMAT IN DANGER. 1858.]
+
+Our way lay for a time amid fine fissures with blue walls, until at
+length we reached the edge of one which elicited other sentiments than
+those of admiration. It must be crossed. At the opposite side was a high
+and steep bank of ice which prolonged itself downwards, and ended in a
+dependent eave of snow which quite overhung the chasm, and reached to
+within about a yard of our edge of the crevasse. Balmat came forward
+with his axe, and tried to get a footing on the eave: he beat it gently,
+but the axe went through the snow, forming an aperture through which the
+darkness of the chasm was rendered visible. Our guide was quite free,
+without rope or any other means of security; he beat down the snow so as
+to form a kind of stirrup, and upon this he stepped. The stirrup gave
+way, it was right over the centre of the chasm, but with wonderful tact
+and coolness he contrived to get sufficient purchase from the yielding
+mass to toss himself back to the side of the chasm. The rope was now
+brought forward and tied round the waist of one of the porters; another
+step was cautiously made in the eave of snow, the man was helped across,
+and lessened his own weight by means of his hatchet. He gradually got
+footing on the face of the steep, which he mounted by escaliers; and on
+reaching a sufficient height he cut two large steps in which his feet
+might rest securely. Here he laid his breast against the sloping wall,
+and another person was sent forward, who drew himself up by the rope
+which was attached to the leader. Thus we all passed, each of us in turn
+bearing the strain of his successor upon the rope; it was our last
+difficulty, and we afterwards slowly plodded through the snow of the
+corridor towards the base of the Mur de la Cote.
+
+[Sidenote: STORM ON MONT BLANC. 1858.]
+
+[Sidenote: THERMOMETER BURIED. 1858.]
+
+Climbing zigzag, we soon reached the summit of the Mur, and immediately
+afterwards found ourselves in the midst of cold drifting clouds, which
+obscured everything. They dissolved for a moment and revealed to us the
+sunny valley of Chamouni; but they soon swept down again and completely
+enveloped us. Upon the Calotte, or last slope, I felt no trace of the
+exhaustion which I had experienced last year, but enjoyed free lungs and
+a quiet heart. The clouds now whirled wildly round us, and the fine
+snow, which was caught by the wind and spit bitterly against us, cut off
+all visible communication between us and the lower world. As we
+approached the summit the air thickened more and more, and the cold,
+resulting from the withdrawal of the sunbeams, became intense. We
+reached the top, however, in good condition, and found the new snow
+piled up into a sharp _arete_, and the summit of a form quite different
+from that of the _Dos d'un Ane_, which it had presented the previous
+year. Leaving Balmat to make a hole for the thermometer, I collected a
+number of batons, drove them into the snow, and, drawing my plaid round
+them, formed a kind of extempore tent to shelter my boiling-water
+apparatus. The covering was tightly held, but the snow was as fine and
+dry as dust, and penetrated everywhere: my lamp could not be secured
+from it, and half a box of matches was consumed in the effort to ignite
+it. At length it did flame up, and carried on a sputtering combustion.
+The cold of the snow-filled boiler condensing the vapour from the lamp
+gradually produced a drop, which, when heavy enough to detach itself
+from the vessel, fell upon the flame and put it out. It required much
+patience and the expenditure of many matches to relight it. Meanwhile
+the absence of muscular action caused the cold to affect our men
+severely. My beard and whiskers were a mass of clotted ice. The batons
+were coated with ice, and even the stem of my thermometer, the bulb of
+which was in hot water, was covered by a frozen enamel. The clouds
+whirled, and the little snow granules hit spitefully against the skin
+wherever it was exposed. The temperature of the air was 20 deg. Fahr. below
+the freezing point. I was too intent upon my work to heed the cold much,
+but I was numbed; one of my fingers had lost sensation, and my right
+heel was in pain: still I had no thought of forsaking my observation
+until Mr. Wills came to me and said that we must return speedily, for
+Balmat's hands were _gelees_. I did not comprehend the full significance
+of the word; but, looking at the porters, they presented such an aspect
+of suffering that I feared to detain them longer. They looked like worn
+old men, their hair and clothing white with snow, and their faces blue,
+withered, and anxious-looking. The hole being ready, I asked Balmat for
+the magnet to arrange the index of the thermometer: his hands seemed
+powerless. I struck my tent, deposited the instrument, and, as I watched
+the covering of it up, some of the party, among whom were Mr. Wills and
+Balmat, commenced the descent.[A]
+
+[Sidenote: BALMAT FROSTBITTEN. 1858.]
+
+I followed them speedily. Midway down the Calotte I saw Balmat, who was
+about a hundred yards in advance of me, suddenly pause and thrust his
+hands into the snow, and commence rubbing them vigorously. The
+suddenness of the act surprised me, but I had no idea at the time of its
+real significance: I soon came up to him; he seemed frightened, and
+continued to beat and rub his hands, plunging them, at quick intervals,
+into the snow. Still I thought the thing would speedily pass away, for
+I had too much faith in the man's experience to suppose that he would
+permit himself to be seriously injured. But it did not pass as I hoped
+it would, and the terrible possibility of his losing his hands presented
+itself to me. He at length became exhausted by his own efforts,
+staggered like a drunken man, and fell upon the snow. Mr. Wills and
+myself took each a hand, and continued the process of beating and
+rubbing. I feared that we should injure him by our blows, but he
+continued to exclaim, "N'ayez pas peur, frappez toujours, frappez
+fortement!" We did so, until Mr. Wills became exhausted, and a porter
+had to take his place. Meanwhile Balmat pinched and bit his fingers at
+intervals, to test their condition; but there was no sensation. He was
+evidently hopeless himself; and, seeing him thus, produced an effect
+upon me that I had not experienced since my boyhood--my heart swelled,
+and I could have wept like a child. The idea that I should be in some
+measure the cause of his losing his hands was horrible to me; schemes
+for his support rushed through my mind with the usual swiftness of such
+speculations, but no scheme could restore to him his lost hands. At
+length returning sensation in one hand announced itself by excruciating
+pain. "Je souffre!" he exclaimed at intervals--words which, from a man
+of his iron endurance, had a more than ordinary significance. But pain
+was better than death, and, under the circumstances, a sign of
+improvement. We resumed our descent, while he continued to rub his hands
+with snow and brandy, thrusting them at every few paces into the mass
+through which we marched. At Chamouni he had skilful medical advice, by
+adhering to which he escaped with the loss of six of his nails--his
+hands were saved.
+
+I cannot close this recital without expressing my admiration of the
+dauntless bearing of our porters, and of the cheerful and efficient
+manner in which they did their duty throughout the whole expedition.
+Their names are Edouard Bellin, Joseph Favret, Michel Payot, Joseph
+Folliguet, and Alexandre Balmat.
+
+
+FOOTNOTES:
+
+[A] In August, 1859, I found the temperature of water, boiling in an
+open vessel at the summit of Mont Blanc, to be 184.95 deg. Fahr. On that
+occasion also, though a laborious search was made for the thermometer,
+it could not be found.
+
+
+
+
+(26.)
+
+
+[Sidenote: PROCES-VERBAL. 1858.]
+
+The hostility of the chief guide to the expedition was not diminished by
+the letter of the Intendant; and he at once entered a _proces-verbal_
+against Balmat and his companions on their return to Chamouni. I felt
+that the power thus vested in an unlettered man to arrest the progress
+of scientific observations was so anomalous, that the enlightened and
+liberal Government of Sardinia would never tolerate such a state of
+things if properly represented to it. The British Association met at
+Leeds that year, and to it, as a guardian of science, my thoughts
+turned. I accordingly laid the case before the Association, and obtained
+its support: a resolution was unanimously passed "that application be
+made to the Sardinian authorities for increased facilities for making
+scientific observations in the Alps."
+
+Considering the arduous work which Balmat had performed in former years
+in connexion with the glaciers, and especially his zeal in determining,
+under the direction of Professor Forbes, their winter motion--for which,
+as in the case above recorded, he refused all personal remuneration--I
+thought such services worthy of some recognition on the part of the
+Royal Society. I suggested this to the Council, and was met by the same
+cordial spirit of co-operation which I had previously experienced at
+Leeds. A sum of five-and-twenty guineas was at once voted for the
+purchase of a suitable testimonial; and a committee, consisting of Sir
+Roderick Murchison, Professor Forbes, and myself, was appointed to
+carry the thing out. Balmat was consulted, and he chose a photographic
+apparatus, which, with a suitable inscription, was duly presented to
+him.
+
+[Sidenote: BRITISH ASSOCIATION. 1858.]
+
+Thus fortified, I drew up an account of what had occurred at Chamouni
+during my last visit, accompanied by a brief statement of the changes
+which seemed desirable. This was placed in the hands of the President of
+the British Association, to whose prompt and powerful co-operation in
+this matter every Alpine explorer who aspires to higher ground than
+ordinary is deeply indebted. The following letter assured me that the
+facility applied for by the British Association would be granted by the
+Sardinian Government, and that future men of science would find in the
+Alps a less embarrassed field of operations than had fallen to my lot in
+the summer of 1858.
+
+[Sidenote: THE PRESIDENT'S LETTER. 1858.]
+
+ "12, Hertford-street, Mayfair, W.,
+ "February 18th, 1859.
+
+ "My dear Sir,--
+
+ "Having, as I informed you in my last note, communicated with
+ the Sardinian Minister Plenipotentiary the day after receiving
+ your statement relative to the guides at Chamouni, I have been
+ favoured by replies from the Minister, of the 4th and 17th
+ February. In the first the Marquis d'Azeglio assures me that he
+ will bring the subject before the competent authorities at
+ Turin, accompanying the transmission 'd'une recommandation
+ toute speciale.' In the second letter the Marquis informs me
+ that 'the preparation of new regulations for the guides at
+ Chamouni had for some time occupied the attention of the
+ Minister of the Interior, and that these regulations will be in
+ rigorous operation, in all probability, at the commencement of
+ the approaching summer.' The Marquis adds that, 'as the
+ regulations will be based upon a principle of much greater
+ liberty, he has every reason to believe that they will satisfy
+ all the desires of travellers in the interests of science.'
+
+ "With much pleasure at the opportunity of having been in any
+ degree able to bring about the fulfilment of your wishes on the
+ subject,
+
+ "I remain, my dear Sir,
+ "Faithfully yours,
+ "RICHARD OWEN.
+ "Pres. Brit. Association.
+
+ "Prof. Tyndall, F.R.S."
+
+It ought to be stated that, previous to my arrival at Chamouni in 1858,
+an extremely cogent memorial drawn up by Mr. John Ball had been
+presented to the Marquis d'Azeglio by a deputation from the Alpine Club.
+It was probably this memorial which first directed the attention of the
+Sardinian Minister of the Interior to the subject.
+
+
+
+
+WINTER EXPEDITION TO THE MER DE GLACE, 1859.
+
+(27.)
+
+
+Having ten days at my disposal last Christmas, I was anxious to employ
+them in making myself acquainted with the winter aspects and phenomena
+of the Mer de Glace. On Wednesday, the 21st of December, I accordingly
+took my place to Paris, but on arriving at Folkestone found the sea so
+tempestuous that no boat would venture out.
+
+[Sidenote: FIRST DEFEAT, AND FRESH ATTEMPT. 1859.]
+
+The loss of a single day was more than I could afford, and this failure
+really involved the loss of two. Seeing, therefore, the prospect of any
+practical success so small, I returned to London, purposing to give the
+expedition up. On the following day, however, the weather lightened, and
+I started again, reaching Paris on Friday morning. On that day it was
+not possible to proceed beyond Macon, where, accordingly, I spent the
+night, and on the following day reached Geneva.
+
+Much snow had fallen; at Paris it still cumbered the streets, and round
+about Macon it lay thick, as if a more than usually heavy cloud had
+discharged itself on that portion of the country. Between Macon and
+Roussillon it was lighter, but from the latter station onwards the
+quantity upon the ground gradually increased.
+
+[Sidenote: GENEVA TO CHAMOUNI. 1859.]
+
+On Christmas morning, at 8 o'clock, I left Geneva by the diligence for
+Sallenches. The dawn was dull, but the sky cleared as the day advanced,
+and finally a dome of cloudless blue stretched overhead. The mountains
+were grand; their sunward portions of dazzling whiteness, while the
+shaded sides, in contrast with the blue sky behind them, presented a
+ruddy, subjective tint. The brightness of the day reached its maximum
+towards one o'clock, after which a milkiness slowly stole over the
+heavens, and increased in density until finally a drowsy turbidity
+filled the entire air. The distant peaks gradually blended with the
+white atmosphere above them and lost their definition. The black pine
+forests on the slopes of the mountains stood out in strong contrast to
+the snow; and, when looked at through the spaces enclosed by the tree
+branches at either side of the road, they appeared of a decided
+indigo-blue. It was only when thus detached by a vista in front that the
+blue colour was well seen, the air itself between the eye and the
+distant pines being the seat of the colour. Goethe would have regarded
+it as an excellent illustration of his 'Farbenlehre.'
+
+We reached Sallenches a little after 4 P.M., where I endeavoured to
+obtain a sledge to continue my journey. A fit one was not to be found,
+and a carriage was therefore the only resort. We started at five; it was
+very dark, but the feeble reflex of the snow on each side of the road
+was preferred by the postilion to the light of lamps. Unlike the
+enviable ostrich, I cannot shut my eyes to danger when it is near: and
+as the carriage swayed towards the precipitous road side, I could not
+fold myself up, as it was intended I should, but, quitting the interior
+and divesting my limbs of every encumbrance, I took my seat beside the
+driver, and kept myself in readiness for the spring, which in some cases
+appeared imminent. My companion however was young, strong, and
+keen-eyed; and though we often had occasion for the exercise of the
+quality last mentioned, we reached Servoz without accident.
+
+[Sidenote: DESOLATION. 1859.]
+
+[Sidenote: A HORSE IN THE SNOW. 1859.]
+
+Here we baited, and our progress afterwards was slow and difficult. The
+snow on the road was deep and hummocky, and the strain upon the horses
+very great. Having crossed the Arve at the Pont-Pelissier, we both
+alighted, and I went on in advance. The air was warm, and not a whisper
+disturbed its perfect repose. There was no moon, and the heavy clouds,
+which now quite overspread the heavens, cut off even the feeble light of
+the stars. The sound of the Arve, as it rushed through the deep valley
+to my left, came up to me through crags and trees with a sad murmur.
+Sometimes on passing an obstacle, the sound was entirely cut off, and
+the consequent silence was solemn in the extreme. It was a churchyard
+stillness, and the tall black pines, which at intervals cast their
+superadded gloom upon the road, seemed like the hearse-plumes of a dead
+world. I reached a wooden hut, where a lame man offers batons, minerals,
+and _eau de vie_, to travellers in summer. It was forsaken, and half
+buried in the snow. I leaned against the door, and enjoyed for a time
+the sternness of the surrounding scene. My conveyance was far behind,
+and the intermittent tinkle of the horses' bells, which augmented
+instead of diminishing the sense of solitude, informed me of the
+progress and the pauses of the vehicle. At the summit of the road I
+halted until my companion reached me; we then both remounted, and
+proceeded slowly towards Les Ouches. We passed some houses, the aspect
+of which was even more dismal than that of Nature; their roofs were
+loaded with snow, and white buttresses were reared against the walls.
+There was no sound, no light, no voice of joy to indicate that it was
+the pleasant Christmas time. We once met the pioneer of a party of four
+drunken peasants: he came right against us, and the coachman had to pull
+up. Planting his feet in the snow and propping himself against the
+leader's shoulder, the bacchanal exhorted the postilion to drive on; the
+latter took him at his word, and overturned him in the snow. After this
+we encountered no living thing. The horses seemed seized by a kind of
+torpor, and leaned listlessly against each other; vainly the postilion
+endeavoured to rouse them by word and whip; they sometimes essayed to
+trot down the slopes, but immediately subsided to their former
+monotonous crawl. As we ascended the valley, the stillness of the air
+was broken at intervals by wild storm-gusts, sent down against us from
+Mont Blanc himself. These chilled me, so I quitted the carriage, and
+walked on. Not far from Chamouni, the road, for some distance, had been
+exposed to the full action of the wind, and the snow had practically
+erased it. Its left wall was completely covered, while a few detached
+stones, rising here and there above the surface, were the only
+indications of the presence and direction of the right-hand wall. I
+could not see the state of the surface, but I learned by other means
+that the snow had been heaped in oblique ridges across my path. I
+staggered over four or five of these in succession, sinking knee-deep,
+and finally found myself immersed to the waist. This made me pause; I
+thought I must have lost the road, and vainly endeavoured to check
+myself by the positions of surrounding objects. I turned back and met
+the carriage: it had stuck in one of the ridges; one horse was down, his
+hind legs buried to the haunches, his left fore leg plunged to the
+shoulder in snow, and the right one thrown forward upon the surface.
+_C'est bien la route?_ demanded my companion. I went back exploring, and
+assured myself that we were over the road; but I recommended him to
+release the horses and leave the carriage to its fate. He, however,
+succeeding in extricating the leader, and while I went on in advance
+seeking out the firmer portions of the road, he followed, holding his
+horses by their heads; and half an hour's struggle of this kind brought
+us to Chamouni.
+
+[Sidenote: CHAMOUNI ON CHRISTMAS NIGHT. 1859.]
+
+It also was a little "city of the dead." There was no living thing in
+the streets, and neither sound nor light in the houses. The fountain
+made a melancholy gurgle, one or two loosened window-shutters creaked
+harshly in the wind, and banged against the objects which limited their
+oscillations. The Hotel de l'Union, so bright and gay in summer, was
+nailed up and forsaken; and the cross in front of it, stretching its
+snow-laden arms into the dim air, was the type of desolation. We rang
+the bell at the Hotel Royal, but the bay of a watch-dog resounding
+through the house was long our only reply. The bell appeared powerless
+to wake the sleepers, and its sound mingled dismally with that of the
+wind howling through the deserted passages. The noise of my boot-heel,
+exerted long on the front door, was at length effective; it was
+unbarred, and the physical heat of a good stove soon added itself to the
+warmth of the welcome with which my hostess greeted me.
+
+December 26th.--The snow fell heavily, at frequent intervals, throughout
+the entire day. Dense clouds draped all the mountains, and there was not
+the least prospect of my being able to see across the Mer de Glace. I
+walked out alone in the dim light, and afterwards traversed the streets
+before going to bed. They were quite forsaken. Cold and sullen the Arve
+rolled under its wooden bridge, while the snow fell at intervals with
+heavy shock from the roofs of the houses, the partial echoes from the
+surfaces of the granules combining to render the sound loud and hollow.
+Thus were the concerns of this little hamlet changed and fashioned by
+the obliquity of the earth's axis, the chain of dependence which runs
+throughout creation, linking the roll of a planet alike with the
+interests of marmots and of men.
+
+[Sidenote: ASCENT OF THE MOUNTAIN. 1859.]
+
+[Sidenote: SNOW ON THE PINES. 1859.]
+
+Tuesday, 27th December.--I rose at six o'clock, having arranged with my
+men to start at seven, if the weather at all permitted. Edouard Simond,
+my old assistant of 1857, and Joseph Tairraz were the guides of the
+party; the porters were Edouard Balmat, Joseph Simond (fils d'Auguste),
+Francois Ravanal, and another. They came at the time appointed; it was
+snowing heavily, and we agreed to wait till eight o'clock and then
+decide. They returned at eight, and finding them disposed to try the
+ascent to the Montanvert, it was not my place to baulk them. Through the
+valley the work was easy, as the snow had been partially beaten down,
+but we soon passed the habitable limits, and had to break ground for
+ourselves. Three of my men had tried to reach the Montanvert by _la
+Filia_ on the previous Thursday, but their experience of the route had
+been such as to deter them from trying it again. We now chose the
+ordinary route, breasting the slope until we reached the cluster of
+chalets, under the projecting eave of one of which the men halted and
+applied "pattens" to their feet. These consisted of planks about sixteen
+inches long and ten wide, which were firmly strapped to the feet. My
+first impression was that they were worse than useless, for though they
+sank less deeply than the unarmed feet, on being raised they carried
+with them a larger amount of snow, which, with the leverage of the leg,
+appeared to necessitate an enormous waste of force. I stated this
+emphatically, but the men adhered to their pattens, and before I reached
+the Montanvert I had reason to commend their practice as preferable to
+my theory. I was however guided by the latter, and wore no pattens. The
+general depth of the snow along the track was over three feet; the
+footmarks of the men were usually rigid enough to bear my weight, but in
+many cases I went through the crust which their pressure had produced,
+and sank suddenly in the mass. The snow became softer as we ascended,
+and my immersions more frequent, but the work was pure enjoyment, and
+the scene one of extreme beauty. The previous night's snow had descended
+through a perfectly still atmosphere, and had loaded all the branches of
+the pines; the long arms of the trees drooped under the weight, and
+presented at their extremities the appearance of enormous talons turned
+downwards. Some of the smaller and thicker trees were almost entirely
+covered, and assumed grotesque and beautiful forms; the upper part of
+one in particular resembled a huge white parrot with folded wings and
+drooping head, the slumber of the bird harmonizing with the torpor of
+surrounding nature. I have given a sketch of it in Fig. 13.
+
+[Illustration: Fig. 13. Snow on the Pines.]
+
+[Sidenote: SOUND OF BREAKING SNOW. 1859.]
+
+Previous to reaching the half-way spring, where the peasant girls offer
+strawberries to travellers in summer, we crossed two large couloirs
+filled with the debris of avalanches which had fallen the night before.
+Between these was a ridge forty or fifty yards wide on which the snow
+was very deep, the slope of the mountain also adding a component to the
+fair thickness of the snow. My shoulder grazed the top of the embankment
+to my right as I crossed the ridge, and once or twice I found myself
+waist deep in a vertical shaft from which it required a considerable
+effort to escape. Suddenly we heard a deep sound resembling the dull
+report of a distant gun, and at the same moment the snow above us broke
+across, forming a fissure parallel to our line of march. The layer of
+snow had been in a state of strain, which our crossing brought to a
+crisis: it gave way, but having thus relieved itself it did not descend.
+Several times during the ascent the same phenomenon occurred. Once,
+while engaged upon a very steep slope, one of the men cried out to the
+leader, "_Arretez!_" Immediately in front of the latter the snow had
+given way, forming a zigzag fissure across the slope. We all paused,
+expecting to see an avalanche descend. Tairraz was in front; he struck
+the snow with his baton to loosen it, but seeing it indisposed to
+descend he advanced cautiously across it, and was followed by the
+others. I brought up the rear. The steepness of the mountain side at
+this place, and the absence of any object to which one might cling,
+would have rendered a descent with the snow in the last degree perilous,
+and we all felt more at ease when a safe footing was secured at the
+further side of the incline.
+
+At the spring, which showed a little water, the men paused to have a
+morsel of bread. The wind had changed, the air was clearing, and our
+hopes brightening. As we ascended the atmosphere went through some
+extraordinary mutations. Clouds at first gathered round the Aiguille and
+Dome du Gouter, casting the lower slopes of the mountain into intense
+gloom. After a little time all this cleared away, and the beams of the
+sun striking detached pieces of the slopes and summits produced an
+extraordinary effect. The Aiguille and Dome were most singularly
+illumined, and to the extreme left rose the white conical hump of the
+Dromedary, from which a long streamer of snow-dust was carried southward
+by the wind. The Aiguille du Dru, which had been completely mantled
+during the earlier part of the day, now threw off its cloak of vapour
+and rose in most solemn majesty before us; half of its granite cone was
+warmly illuminated, and half in shadow. The wind was high in the upper
+regions, and, catching the dry snow which rested on the asperities and
+ledges of the Aiguille, shook it out like a vast banner in the air. The
+changes of the atmosphere, and the grandeur which they by turns revealed
+and concealed, deprived the ascent of all weariness. We were usually
+flanked right and left by pines, but once between the fountain and the
+Montanvert we had to cross a wide unsheltered portion of the mountain
+which was quite covered with the snow of recent avalanches. This was
+lumpy and far more coherent than the undisturbed snow. We took advantage
+of this, and climbed zigzag over the avalanches for three-quarters of an
+hour, thus reaching the opposite pines at a point considerably higher
+than the path. This, though not the least dangerous, was the least
+fatiguing part of the ascent.
+
+[Sidenote: COLOUR OF SNOW. 1859.]
+
+I frequently examined the colour of the snow: though fresh, its blue
+tint was by no means so pronounced as I have seen it on other occasions;
+still it was beautiful. The colour is, no doubt, due to the optical
+reverberations which occur within a fissure or cavity formed in the
+snow. The light is sent from side to side, each time plunging a little
+way into the mass; and being ejected from it by reflection, it thus
+undergoes a sifting process, and finally reaches the eye as blue light.
+The presence of any object which cuts off this cross-fire of the light
+destroys the colour. I made conical apertures in the snow, in some cases
+three feet deep, a foot wide at the mouth, and tapering down to the
+width of my baton. When the latter was placed along the axis of such a
+cone, the blue light which had previously filled the cavity disappeared;
+on the withdrawal of the baton it was followed by the light, and thus by
+moving the staff up and down its motions were followed by the alternate
+appearance and extinction of the light. I have said that the holes made
+in the snow seemed filled with a blue light, and it certainly appeared
+as if the air contained in the cavities had itself been coloured, and
+thereby rendered visible, the vision plunging into it as into a blue
+medium. Another fact is perhaps worth notice: snow rarely lies so smooth
+as not to present little asperities at its surface; little ridges or
+hillocks, with little hollows between them. Such small hollows resemble,
+in some degree, the cavities which I made in the snow, and from them, in
+the present instance, a delicate light was sent to the eye, faintly
+tinted with the pure blue of the snow-crystals. In comparison with the
+spots thus illuminated, the little protuberances were gray. The portions
+most exposed to the light seemed least illuminated, and their defect in
+this respect made them appear as if a light-brown dust had been strewn
+over them.
+
+[Sidenote: THE MONTANVERT IN WINTER. 1859.]
+
+After five hours and a half of hard work we reached the Montanvert. I
+had often seen it with pleasure. Often, having spent the day alone amid
+the _seracs_ of the Col du Geant, on turning the promontory of
+Trelaporte on my way home, the sight of the little mansion has gladdened
+me, and given me vigour to scamper down the glacier, knowing that
+pleasant faces and wholesome fare were awaiting me. This day, also, the
+sight of it was most welcome, despite its desolation. The wind had swept
+round the auberge, and carried away its snow-buttresses, piling the mass
+thus displaced against the adjacent sheds, to the roofs of which one
+might step from the surface of the snow. The floor of the little chateau
+in which I lodged in 1857 was covered with snow, and on it were the
+fresh footmarks of a little animal--a marmot might have made such marks,
+had not the marmots been all asleep--what the creature was I do not
+know.
+
+[Sidenote: CRYSTAL CURTAIN. 1859.]
+
+In the application of her own principles, Nature often transcends the
+human imagination; her acts are bolder than our predictions. It is thus
+with the motion of glaciers; it was thus at the Montanvert on the day
+now referred to. The floors, even where the windows appeared well
+closed, were covered with a thin layer of fine snow; and some of the
+mattresses in the bedrooms were coated to the depth of half an inch with
+this fine powder. Given a chink through which the finest dust can pass,
+dry snow appears competent to make its way through the same fissure. It
+had also been beaten against the windows, and clung there like a ribbed
+drapery. In one case an effect so singular was exhibited, that I doubted
+my eyes when I first saw it. In front of a large pane of glass, and
+quite detached from it, save at its upper edge, was a festooned curtain
+formed entirely of minute ice-crystals. It appeared to be as fine as
+muslin; the ease of its curves and the depth of its folds being such as
+could not be excelled by the intentional arrangement of ordinary gauze.
+The frost-figures on some of the window-panes were also of the most
+extraordinary character: in some cases they extended over large spaces,
+and presented the appearance which we often observe in London; but on
+other panes they occurred in detached clusters, or in single flowers,
+these grouping themselves together to form miniature bouquets of
+inimitable beauty. I placed my warm hand against a pane which was
+covered by the crystallization, and melted the frostwork which clung to
+it. I then withdrew my hand and looked at the film of liquid through a
+pocket-lens. The glass cooled by contact with the air, and after a time
+the film commenced to move at one of its edges; atom closed with atom,
+and the motion ran in living lines through the pellicle, until finally
+the entire film presented the beauty and delicacy of an organism. The
+connexion between such objects and what we are accustomed to call the
+feelings may not be manifest, but it is nevertheless true that, besides
+appealing to the pure intellect of man, these exquisite productions can
+also gladden his heart and moisten his eyes.
+
+[Sidenote: THE MER DE GLACE IN WINTER. 1859.]
+
+The glacier excited the admiration of us all: not as in summer, shrunk
+and sullied like a spent reptile, steaming under the influence of the
+sun; its frozen muscles were compact, strength and beauty were
+associated in its aspect. At some places it was pure and smooth; at
+others frozen fins arose from it, high, steep, and sharply crested. Down
+the opposite mountain side arrested streams set themselves erect in
+successive terraces, the fronts of which were fluted pillars of ice.
+There was no sound of water; even the Nant Blanc, which gushes from a
+spring, and which some describe as permanent throughout the winter,
+showed no trace of existence. From the Montanvert to Trelaporte the Mer
+de Glace was all in shadow; but the sunbeams pouring down the corridor
+of the Geant ruled a beam of light across the glacier at its upper
+portion, smote the base of the Aiguille du Moine, and flooded the
+mountain with glory to its crest. At the opposite side of the valley was
+the Aiguille du Dru, with a banneret of snow streaming from its mighty
+cone. The Grande Jorasse, and the range of summits between it and the
+Aiguille du Geant, were all in view, and the Charmoz raised its
+precipitous cliffs to the right, and pierced with its splinter-like
+pinnacles the clear cold air. As the night drew on, the mountains seemed
+to close in upon us; and on looking out before retiring to rest, a scene
+so solemn had never before presented itself to my eyes or affected my
+imagination.
+
+[Sidenote: THE FIRST NIGHT. 1859.]
+
+My men occupied the afternoon of the day of our arrival in making a
+preliminary essay upon the glacier while I prepared my instruments. To
+the person whom I intended to fix my stations, three others were
+attached by sound ropes of considerable length. Hidden crevasses we
+knew were to be encountered, and we had made due preparation for them.
+Throughout the afternoon the weather remained fine, and at night the
+stars shone out, but still with a feeble lustre. I could notice a
+turbidity gathering in the air over the range of the Brevent, which
+seemed disposed to extend itself towards us. At night I placed a chair
+in the middle of the snow, at some distance from the house, and laid on
+it a registering thermometer. A bountiful fire of pine logs was made in
+the _salle a manger_; a mattress was placed with its foot towards the
+fire, its middle line bisecting the right angle in which the fireplace
+stood; this being found by experiment to be the position in which the
+draughts from the door and from the windows most effectually neutralized
+each other. In this region of calms I lay down, and covering myself with
+blankets and duvets, listened to the crackling of the logs, and watched
+their ruddy flicker upon the walls, until I fell asleep.
+
+The wind rose during the night, and shook the windows: one pane in
+particular seemed set in unison to the gusts, and responded to them by a
+loud and melodious vibration. I rose and wedged it round with _sous_ and
+penny pieces, and thus quenched its untimely music.
+
+December 28th.--We were up before the dawn. Tairraz put my fire in
+order, and I then rose. The temperature of the room at a distance of
+eight feet from the fire was two degrees of Centigrade below zero; the
+lowest temperature outside was eleven degrees of Centigrade below
+zero,--not at all an excessive cold. The clouds indeed had, during the
+night, thrown vast diaphragms across the sky, and thus prevented the
+escape of the earth's heat into space.
+
+While my assistants were preparing breakfast I had time to inspect the
+glacier and its bounding heights. On looking up the Mer de Glace, the
+Grande Jorasse meets the view, rising in steep outline from the wall of
+cliffs which terminates the Glacier de Lechaud. Behind this steep
+ascending ridge, which is shown on the frontispiece, and upon it, a
+series of clouds had ranged themselves, stretching lightly along the
+ridge at some places, and at others collecting into ganglia. A string of
+rosettes was thus formed which were connected together by gauzy
+filaments. The portion of the heavens behind the ridge was near the
+domain of the rising sun, and when he cleared the horizon his red light
+fell upon the clouds, and ignited them to ruddy flames. Some of the
+lighter clouds doubled round the summit of the mountain, and swathed its
+black crags with a vestment of transparent red. The adjacent sky wore a
+strange and supernatural air; indeed there was something in the whole
+scene which baffled analysis, and the words of Tennyson rose to my lips
+as I gazed upon it:--
+
+[Sidenote: A "ROSE OF DAWN." 1859.]
+
+ "God made Himself an awful rose of dawn."
+
+I have spoken several times of the cloud-flag which the wind wafted from
+the summit of the Aiguille du Dru. On the present occasion this grand
+banner reached extraordinary dimensions. It was brindled in some places
+as if whipped into curds by the wind; but through these continuous
+streamers were drawn, which were bent into sinuosities resembling a
+waving flag at a mast-head. All this was now illuminated with the sun's
+red rays, which also fringed with fire the exposed edges and pinnacles
+both of the Aiguille du Dru and the Aiguille Verte. Thus rising out of
+the shade of the valley the mountains burned like a pair of torches, the
+flames of which were blown half a mile through the air. Soon afterwards
+the summits of the Aiguilles Rouges were illuminated, and day declared
+itself openly among the mountains.
+
+[Sidenote: THE STAKES FIXED. 1859.]
+
+But these red clouds of the morning, magnificent though they were,
+suggested thoughts which tended to qualify the pleasure which they gave:
+they did not indicate good weather. Sometimes, indeed, they had to fight
+with denser masses, which often prevailed, swathing the mountains in
+deep neutral tint, but which, again yielding, left the glory of the
+sunrise augmented by contrast with their gloom. Between eight and nine
+A.M. we commenced the setting out of our first line, one of whose
+termini was a point about a hundred yards higher up than the Montanvert
+hotel; a withered pine on the opposite mountain side marking the other
+terminus. The stakes made use of were four feet long. With the selfsame
+baton which I had employed upon the Mer de Glace in 1857, and which
+Simond had preserved, the worthy fellow now took up the line. At some
+places the snow was very deep, but its lower portions were sufficiently
+compact to allow of a stake being firmly fixed in it. At those places
+where the wind had removed the snow or rendered it thin, the ice was
+pierced with an auger and the stake driven into it. The greatest caution
+was of course necessary on the part of the men; they were in the midst
+of concealed crevasses, and sounding was essential at every step. By
+degrees they withdrew from me, and approached the eastern boundary of
+the glacier, where the ice was greatly dislocated, and the labour of
+wading through the snow enormous. Long detours were sometimes necessary
+to reach a required point; but they were all accomplished, and we at
+length succeeded in fixing eleven stakes along this line, the most
+distant of which was within about eighty yards of the opposite side of
+the glacier.
+
+[Sidenote: STORM ON THE GLACIER. 1859.]
+
+The men returned, and I consulted them as to the possibility of getting
+a line across at the _Ponts_; but this was judged to be impossible in
+the time. We thought, however, that a second line might be staked out at
+some distance below the Montanvert. I took the theodolite down the
+mountain-slope, wading at times breast-deep in snow, and having
+selected a line, the men tied themselves together as before, and
+commenced the staking out. The work was slowly but steadily and
+steadfastly done. The air darkened; angry clouds gathered around the
+mountains, and at times the glacier was swept by wild squalls. The men
+were sometimes hidden from me by the clouds of snow which enveloped
+them, but between those intermittent gusts there were intervals of
+repose, which enabled us to prosecute our work. This line was more
+difficult than the first one; the glacier was broken into sharp-edged
+chasms; the ridges to be climbed were steep, and the snow which filled
+the depressions profound. The oblique arrangement of the crevasses also
+magnified the labour by increasing the circuits. I saw the leader of the
+party often shoulder-deep in snow, treading the soft mass as a swimmer
+walks in water, and I felt a wish to be at his side to cheer him and to
+share his toil. Each man there, however, knew my willingness to do this
+if occasion required it, and wrought contented. At length the last stake
+being fixed, the faces of the men were turned homeward. The evening
+became wilder, and the storm rose at times to a hurricane. On the more
+level portions of the glacier the snow lay deep and unsheltered; among
+its frozen waves and upon its more dislocated portions it had been
+partially engulfed, and the residue was more or less in shelter. Over
+the former spaces dense clouds of snow rose, whirling in the air and
+cutting off all view of the glacier. The whole length of the Mer de
+Glace was thus divided into clear and cloudy segments, and presented an
+aspect of wild and wonderful turmoil. A large pine stood near me, with
+its lowest branch spread out upon the surface of the snow; on this
+branch I seated myself, and, sheltered by the trunk, waited until I saw
+my men in safety. The wind caught the branches of the trees, shook down
+their loads of snow, and tossed it wildly in the air. Every mountain
+gave a quota to the storm. The scene was one of most impressive
+grandeur, and the moan of the adjacent pines chimed in noble harmony
+with the picture which addressed the eyes.
+
+At length we all found ourselves in safety within doors. The windows
+shook violently. The tempest was however intermittent throughout, as if
+at each effort it had exhausted itself, and required time to recover its
+strength. As I heard its heralding roar in the gullies of the mountains,
+and its subsequent onset against our habitation, I thought wistfully of
+my stations, not knowing whether they would be able to retain their
+positions in the face of such a blast. That night however, as if the
+storm had sung our lullaby, we all slept profoundly, having arranged to
+commence our measurements as early as light permitted on the following
+day.
+
+[Sidenote: HEAVY SNOW. 1859.]
+
+Thursday, 29th December.--"Snow, heavy snow: it must have descended
+throughout the entire night; the quantity freshly fallen is so great;
+the atmosphere at seven o'clock is thick with the descending flakes." At
+eight o'clock it cleared up a little, and I proceeded to my station,
+while the men advanced upon the glacier; but I had scarcely fixed my
+theodolite when the storm recommenced. I had a man to clear away the
+snow and otherwise assist me; he procured an old door from the hotel,
+and by rearing it upon its end sheltered the object-glass of the
+instrument. Added to the flakes descending from the clouds was the
+spitting snow-dust raised by the wind, which for a time so blinded me
+that I was unable to see the glacier. The measurement of the first stake
+was very tedious, but practice afterwards enabled me to take advantage
+of the brief lulls and periods of partial clearness with which the storm
+was interfused.
+
+[Sidenote: A MAN IN A CREVASSE. 1859.]
+
+At nine o'clock my telescope happened to be directed upon the men as
+they struggled through the snow; all evidence of the deep track which
+they had formed yesterday having been swept away. I saw the leader sink
+and suddenly disappear. He had stood over a concealed fissure, the roof
+of which had given way and he had dropped in. I observed a rapid
+movement on the part of the remaining three men: they grouped themselves
+beside the fissure, and in a moment the missing man was drawn from
+between its jaws. His disappearance and reappearance were both
+extraordinary. We had, as I have stated, provided for contingencies of
+this kind, and the man's rescue was almost immediate.
+
+[Sidenote: SIX-RAYED CRYSTALS. 1859.]
+
+My attendant brought two poles from the hotel which we thrust obliquely
+into the snow, causing the free ends to cross each other; over these a
+blanket was thrown, behind which I sheltered myself from the storm as
+the men proceeded from stake to stake. At 9.30 the storm was so thick
+that I was unable to see the men at the stake which they had reached at
+the time; the flakes sped wildly in their oblique course across the
+field of the telescope. Some time afterwards the air became quite still,
+and the snow underwent a wonderful change. Frozen flowers similar to
+those I had observed on Monte Rosa fell in myriads. For a long time the
+flakes were wholly composed of these exquisite blossoms entangled
+together. On the surface of my woollen dress they were soft as down; the
+snow itself on which they fell seemed covered by a layer of down; while
+my coat was completely spangled with six-rayed stars. And thus prodigal
+Nature rained down beauty, and had done so here for ages unseen by man.
+And yet some flatter themselves with the idea that this world was
+planned with strict reference to human use; that the lilies of the field
+exist simply to appeal to the sense of the beautiful in man. True, this
+result is secured, but it is one of a thousand all equally important in
+the eyes of Nature. Whence those frozen blossoms? Why for aeons wasted?
+The question reminds one of the poet's answer when asked whence was the
+Rhodora:--
+
+ "Why wert thou there, O rival of the rose?
+ I never thought to ask, I never knew;
+ But in my simple ignorance suppose
+ The selfsame power that brought me there brought you!"[A]
+
+I sketched some of the crystals, but, instead of reproducing these
+sketches, which were rough and hasty, I have annexed two of the forms
+drawn with so much skill and patience by Mr. Glaisher.
+
+[Illustration: Fig. 14. Snow Crystals.]
+
+[Illustration: Fig. 15. Snow Crystals.]
+
+We completed the measurement of the first line before eleven o'clock,
+and I felt great satisfaction in the thought that I possessed something
+of which the weather could not deprive me. As I closed my note-book and
+shifted the instrument to the second station, I felt that my expedition
+was already a success.
+
+At a quarter past eleven I had my theodolite again fixed, and ranging
+the telescope along the line of pickets, I saw them all standing.
+Crossing the ice wilderness, and suggesting the operation of
+intelligence amid that scene of desolation, their appearance was
+pleasant to me. Just before I commenced, a solitary jay perched upon the
+summit of an adjacent pine and watched me. The air was still at the
+time, and the snow fell heavily. The flowers moreover were magnificent,
+varying from about the twentieth of an inch to two lines in diameter,
+while, falling through the quiet air, their forms were perfect. Adjacent
+to my theodolite was a stump of pine, from which I had the snow removed,
+in order to have something to kick my toes against when they became
+cold; and on the stump was placed a blanket to be used as a screen in
+case of need. While I remained at the station a layer of snow an inch
+thick fell upon this blanket, the whole layer being composed of these
+exquisite flowers. The atmosphere also was filled with them. From the
+clouds to the earth Nature was busy marshalling her atoms, and putting
+to shame by the beauty of her structures the comparative barbarities of
+Art.
+
+[Sidenote: SOUND THROUGH THE SNOW-STORM. 1859.]
+
+My men at length reached the first station, and the measurement
+commenced. The storm drifted up the valley, thickening all the air as it
+approached. Denser and denser the flakes fell; but still, with care and
+tact I was able to follow my party to a distance of 800 yards. I had not
+thought it possible to see so far through so dense a storm. At this
+distance also my voice could be heard, and my instructions understood;
+for once, as the man who took up the line stood behind his baton and
+prevented its projection against the white snow, I called out to him to
+stand aside, and he promptly did so. Throughout the entire measurement
+the snow never ceased falling, and some of the illusions which it
+produced were extremely singular. The distant boundary of the glacier
+appeared to rise to an extraordinary height, and the men wading through
+the snow appeared as if climbing up a wall. The labour along this line
+was still greater than on the former; on the steeper slopes especially
+the toil was great; for here the effort of the leader to lift his own
+body added itself to that of cutting his way through the snow. His
+footing I could see often yielded, and he slid back, checking his
+recession, however, by still plunging forward; thus, though the limbs
+were incessantly exerted, it was, for a time, a mere motion of vibration
+without any sensible translation. At the last stake the men shouted,
+"_Nous avons finis!_" and I distinctly heard them through the falling
+snow. By this time I was quite covered with the crystals which clung to
+my wrapper. They also formed a heap upon my theodolite, rising over the
+spirit-levels and embracing the lower portion of the vertical arc. The
+work was done; I struck my theodolite and ascended to the hotel; the
+greatest depth of snow through which I waded reaching, when I stood
+erect, to within three inches of my breast.
+
+[Sidenote: SWIFT DESCENT. 1859.]
+
+The men returned; dinner was prepared and consumed; the disorder which
+we had created made good; the rooms were swept, the mattresses replaced,
+and the shutters fastened, where this was possible. We locked up the
+house, and with light hearts and lithe limbs commenced the descent. My
+aim now was to reach the source of the Arveiron, to examine the water
+and inspect the vault. With this view we went straight down the
+mountain. The inclinations were often extremely steep, and down these we
+swept with an avalanche-velocity; indeed usually accompanied by an
+avalanche of our own creation. On one occasion Balmat was for a moment
+overwhelmed by the descending mass: the guides were startled, but he
+emerged instantly. Tairraz followed him, and I followed Tairraz, all of
+us rolling in the snow at the bottom of the slope as if it were so much
+flour. My practice on the Finsteraarhorn rendered me at home here. One
+of the porters could by no means be induced to try this flying mode of
+descent. Simond carried my theodolite box, tied upon a crotchet on his
+back; and once, while shooting down a slope, he incautiously allowed a
+foot to get entangled; his momentum rolled him over and over down the
+incline, the theodolite emerging periodically from the snow during his
+successive revolutions. A succession of _glissades_ brought us with
+amazing celerity to the bottom of the mountain, whence we picked our way
+amid the covered boulders and over the concealed arms of the stream to
+the source of the Arveiron.
+
+The quantity of water issuing from the vault was considerable, and its
+character that of true glacier water. It was turbid with suspended
+matter, though not so turbid as in summer; but the difference in force
+and quantity would, I think, be sufficient to account for the greater
+summer turbidity. This character of the water could only be due to the
+grinding motion of the glacier upon its bed; a motion which seems not to
+be suspended even in the depth of winter. The temperature of the water
+was the tenth of a degree Centigrade above zero; that of the ice was
+half a degree below zero: this was also the temperature of the air,
+while that of the snow, which in some places covered the ice-blocks, was
+a degree and a quarter below zero.
+
+[Sidenote: VAULT OF THE ARVEIRON. 1859.]
+
+The entrance to the vault was formed by an arch of ice which had
+detached itself from the general mass of the glacier behind: between
+them was a space through which we could look to the sky above. Beyond
+this the cave narrowed, and we found ourselves steeped in the blue light
+of the ice. The roof of the inner arch was perforated at one place by a
+shaft about a yard wide, which ran vertically to the surface of the
+glacier. Water had run down the sides of this shaft, and, being
+re-frozen below, formed a composite pillar of icicles at least twenty
+feet high and a yard thick, stretching quite from roof to floor. They
+were all united to a common surface at one side, but at the other they
+formed a series of flutings of exceeding beauty. This group of columns
+was bent at its base as if it had yielded to the forward motion of the
+glacier, or to the weight of the arch overhead. Passing over a number of
+large ice-blocks which partially filled the interior of the vault, we
+reached its extremity, and here found a sloping passage with a perfect
+arch of crystal overhead, and leading by a steep gradient to the air
+above. This singular gallery was about seventy feet long, and was
+floored with snow. We crept up it, and from the summit descended by a
+glissade to the frontal portion of the cavern. To me this crystal cave,
+with the blue light glistening from its walls, presented an aspect of
+magical beauty. My delight, however, was tame compared with that of my
+companions.
+
+[Sidenote: MAJESTIC SCENE. 1859.]
+
+Looking from the blue arch westwards, the heavens were seen filled by
+crimson clouds, with fiery outliers reaching up to the zenith. On
+quitting the vault I turned to have a last look at those noble sentinels
+of the Mer de Glace, the Aiguille du Dru, and the Aiguille Verte. The
+glacier below the mountains was in shadow, and its frozen precipices of
+a deep cold blue. From this, as from a basis, the mountain cones sprang
+steeply heavenward, meeting half way down the fiery light of the sinking
+sun. The right-hand slopes and edges of both pyramids burned in this
+light, while detached protuberant masses also caught the blaze, and
+mottled the mountains with effulgent spaces. A range of minor peaks ran
+slanting downwards from the summit of the Aiguille Verte; some of these
+were covered with snow, and shone as if illuminated with the deep
+crimson of a strontian flame. I was absolutely struck dumb by the
+extraordinary majesty of this scene, and watched it silently till the
+red light faded from the highest summits. Thus ended my winter
+expedition to the Mer de Glace.
+
+Next morning, starting at three o'clock, I was driven by my two guides
+in an open sledge to Sallenches. The rain was pitiless and the road
+abominable. The distance, I believe, is only six leagues, but it took us
+five hours to accomplish it. The leading mule was beyond the reach of
+Simond's whip, and proved a mere obstructive; during part of the way it
+was unloosed, tied to the sledge, and dragged after it. Simond
+afterwards mounted the hindmost beast and brought his whip to bear upon
+the leader, the jerking he endured for an hour and a half seemed almost
+sufficient to dislocate his bones. We reached Sallenches half an hour
+late, but the diligence was behind its time by this exact interval. We
+met it on the Pont St. Martin, and I transferred myself from the sledge
+to the interior. This was the morning of the 30th of December, and on
+the evening of the 1st of January I was in London.
+
+[Sidenote: MY ASSISTANTS. 1859.]
+
+I cannot finish this recital without saying one word about my men. Their
+behaviour was admirable throughout. The labour was enormous, but it was
+manfully and cheerfully done. I know Simond well; he is intelligent,
+truthful, and affectionate, and there is no guide of my acquaintance for
+whom I have a stronger regard. Joseph Tairraz is an extremely
+intelligent and able guide, and on this trying occasion proved himself
+worthy of my highest praise and commendation. Their two companions upon
+the glacier, Edouard Balmat (le Petit Balmat) and Joseph Simond (fils
+d'Auguste), acquitted themselves admirably; and it also gives me
+pleasure to bear testimony to the willing and efficient service of
+Francois Ravanal, who attended upon me during the observations.
+
+
+FOOTNOTES:
+
+[A] Emerson.
+
+
+
+
+PART II.
+
+CHIEFLY SCIENTIFIC.
+
+ Aber im stillen Gemach entwirft bedeutende Zirkel
+ Sinnend der Weise, beschleicht forschend den schaffenden Geist,
+ Prueft der Stoffe Gewalt, der Magnete Hassen und Lieben,
+ Folgt durch die Luefte dem Klang, folgt durch den Aether dem Strahl,
+ Sucht das vertraute Gesetz in des Zufalls grausenden Wundern,
+ Sucht den ruhenden Pol in der Erscheinungen Flucht.
+
+ Schiller.
+
+
+
+
+ON LIGHT AND HEAT.
+
+(1.)
+
+
+[Sidenote: THEORIES OF LIGHT.]
+
+What is Light? The ancients supposed it to be something emitted by the
+eyes, and for ages no notion was entertained that it required time to
+pass through space. In the year 1676 Roemer first proved that the light
+from Jupiter's satellites required a certain time to cross the earth's
+orbit. Bradley afterwards found that, owing to the velocity with which
+the earth flies through space, the rays of the stars are slightly
+inclined, just as rain-drops which descend vertically appear to meet us
+when we move swiftly through the shower. In Kew Gardens there is a
+sun-dial commemorative of this discovery, which is called the
+_aberration of light_. Knowing the velocity of the earth, and the
+inclination of the stellar rays, Bradley was able to calculate the
+velocity of light; and his result agrees closely with that of Roemer.
+Celestial distances were here involved, but a few years ago M. Fizeau,
+by an extremely ingenious contrivance, determined the time required by
+light to pass over a distance of about 9000 yards; and his experiment is
+quite in accordance with the results of his predecessors.
+
+But what is it which thus moves? Some, and among the number Newton,
+imagined light to consist of particles darted out from luminous bodies.
+This is the so-called Emission-Theory, which was held by some of the
+greatest men: Laplace, for example, accepted it; and M. Biot has
+developed it with a lucidity and power peculiar to himself. It was first
+opposed by the astronomer Huyghens, and afterwards by Euler, both of
+whom supposed light to be a kind of undulatory motion; but they were
+borne down by their great antagonists, and the emission-theory held its
+ground until the commencement of the present century, when Thomas Young,
+Professor of Natural Philosophy in the Royal Institution, reversed the
+scientific creed by placing the Theory of Undulation on firm
+foundations. He was followed by a young Frenchman of extraordinary
+genius, who, by the force of his logic and the conclusiveness of his
+experiments, left the Wave-Theory without a competitor. The name of this
+young Frenchman was Augustin Fresnel.
+
+Since his time some of the ablest minds in Europe have been applied to
+the investigation of this subject; and thus a mastery, almost
+miraculous, has been attained over the grandest and most subtle of
+natural phenomena. True knowledge is always fruitful, and a clear
+conception regarding any one natural agent leads infallibly to better
+notions regarding others. Thus it is that our knowledge of light has
+corrected and expanded our knowledge of _heat_, while the latter, in its
+turn, will assuredly lead us to clearer conceptions regarding the other
+forces of Nature.
+
+I think it will not be a useless labour if I here endeavour to state, in
+a simple manner, our present views of light and heat. Such knowledge is
+essential to the explanation of many of the phenomena referred to in the
+foregoing pages; and even to the full comprehension of the origin of the
+glaciers themselves. A few remarks on the nature of sound will form a
+fit introduction.
+
+[Sidenote: NATURE OF SOUND.]
+
+It is known that sound is conveyed to our organs of hearing by the air:
+a bell struck in a vacuum emits no sound, and even when the air is thin
+the sound is enfeebled. Hawksbee proved this by the air-pump; De
+Saussure fired a pistol at the top of Mont Blanc,--I have repeated the
+experiment myself, and found, with him, that the sound is feebler than
+at the sea level. Sound is not produced by anything projected through
+the air. The explosion of a gun, for example, is sent forward by a
+motion of a totally different kind from that which animates the bullet
+projected from the gun: the latter is a motion of _translation_; the
+former, one of _vibration_. To use a rough comparison, sound is
+projected through the air as a push is through a crowd; it is the
+propagation of a _wave_ or _pulse_, each particle taking up the motion
+of its neighbour, and delivering it on to the next. These aerial waves
+enter the external ear, meet a membrane, the so-called tympanic
+membrane, which is drawn across the passage at a certain place, and
+break upon it as sea-waves do upon the shore. The membrane is shaken,
+its tremors are communicated to the auditory nerve, and transmitted by
+it to the brain, where they produce the impression to which we give the
+name of sound.
+
+[Sidenote: CAUSE OF MUSIC.]
+
+In the tumult of a city, pulses of different kinds strike irregularly
+upon the tympanum, and we call the effect _noise_; but when a succession
+of impulses reach the ear _at regular intervals_ we feel the effect as
+_music_. Thus, a vibrating string imparts a series of shocks to the air
+around it, which are transmitted with perfect regularity to the ear, and
+produce a _musical note_. When we hear the song of a soaring lark we may
+be sure that the entire atmosphere between us and the bird is filled
+with pulses, or undulations, or waves, as they are often called,
+produced by the little songster's organ of voice. This organ is a
+vibrating instrument, resembling, in principle, the reed of a clarionet.
+Let us suppose that we hear the song of a lark, elevated to a height of
+500 feet in the air. Before this is possible, the bird must have
+agitated a sphere of air 1000 feet in diameter; that is to say, it must
+have communicated to 17,888 tons of air a motion sufficiently intense to
+be appreciated by our organs of hearing.
+
+[Sidenote: CAUSE OF PITCH.]
+
+Musical sounds differ in _pitch_: some notes are high and shrill, others
+low and deep. Boys are chosen as choristers to produce the shrill
+notes; men are chosen to produce the bass notes. Now, the sole
+difference here is, that the boy's organ vibrates _more rapidly_ than
+the man's--it sends a greater number of impulses per second to the ear.
+In like manner, a short string emits a higher note than a long one,
+because it vibrates more quickly. The greater the number of vibrations
+which any instrument performs in a given time, the higher will be the
+pitch of the note produced. The reason why the hum of a gnat is shriller
+than that of a beetle is that the wings of the small insect vibrate more
+quickly than those of the larger one. We can, with suitable
+arrangements, make those sonorous vibrations visible to the eye;[A] and
+we also possess instruments which enable us to tell, with the utmost
+exactitude, the number of vibrations due to any particular note. By such
+instruments we learn that a gnat can execute many thousand flaps of its
+little wings in a second of time.
+
+[Sidenote: NATURE OF LIGHT.]
+
+In the study of nature the coarser phenomena, which come under the
+cognizance of the senses, often suggest to us the finer phenomena which
+come under the cognizance of the mind; and thus the vibrations which
+produce sound, and which, as has been stated, can be rendered visible to
+the eye by proper means, first suggested that _light_ might be due to a
+somewhat similar action. This is now the universal belief. A luminous
+body is supposed to have its atoms, or molecules, in a state of intense
+vibration. The motions of the atoms are supposed to be communicated to
+a medium suited to their transmission, as air is to the transmission of
+sound. This medium is called the _luminiferous ether_, and the little
+billows excited in it speed through it with amazing celerity, enter the
+pupil of the eye, pass through the humours, and break upon the retina or
+optic nerve, which is spread out at the back of the eye. Hence the
+tremors they produce are transmitted along the nerve to the brain, where
+they announce themselves as _light_. The swiftness with which the waves
+of light are propagated through the ether, is however enormously greater
+than that with which the waves of sound pass through the air. An aerial
+wave of sound travels at about the rate of 1100 feet in a second: a wave
+of light leaves 192,000 miles behind it in the same time.
+
+[Sidenote: CAUSE OF COLOUR.]
+
+Thus, then, in the case of sound, we have the sonorous body, the air,
+and the auditory nerve, concerned in the phenomenon; in the case of
+light, we have the luminous body, the ether, and the optic nerve. The
+fundamental analogy of sound and light is thus before us, and it is
+easily remembered. But we must push the analogy further. We know that
+the white light which comes to us from the sun is made up of an infinite
+number of coloured rays. By refraction with a prism we can separate
+those rays from each other, and arrange them in the series of colours
+which constitute the solar spectrum. The rainbow is an imperfect or
+_impure_ spectrum, produced by the drops of falling rain, but by prisms
+we can unravel the white light into pure red, orange, yellow, green,
+blue, indigo, and violet. Now, this spectrum is to the eye what the
+gamut is to the ear; each colour represents a note, and _the different
+colours represent notes of different pitch_. The vibrations which
+produce the impression of red are _slower_, and the waves which they
+produce are _longer_, than those to which we owe the sensation of
+violet; while the vibrations which excite the other colours are
+intermediate between these two extremes. This, then, is the second grand
+analogy between light and sound: _Colour answers to Pitch_. There is
+therefore truth in the figure when we say that the gentian of the Alps
+sings a shriller note than the wild rhododendron, and that the red glow
+of the mountains at sunset is of a lower pitch than the blue of the
+firmament at noon.
+
+[Sidenote: LENGTH OF ETHEREAL WAVES.]
+
+These are not fanciful analogies. To the mind of the philosopher these
+waves of ether are almost as palpable and certain as the waves of the
+sea, or the ripples on the surface of a lake. The length of the waves,
+both of sound and light, and the number of shocks which they
+respectively impart to the ear and eye, have been the subjects of the
+strictest measurement. Let us here go through a simple calculation. It
+has been found that 39,000 waves of red light placed end to end would
+make up an inch. How many inches are there in 192,000 miles? My youngest
+reader can make the calculation for himself, and find the answer to be
+12,165,120,000 inches. It is evident that, if we multiply this number by
+39,000, we shall obtain the number of waves of red light in 192,000
+miles; this number is 474,439,680,000,000. _All these waves enter the
+eye in one second_; thus the expression "I see red colour," strictly
+means, "My eye is now in receipt of four hundred and seventy-four
+millions of millions of impulses per second." To produce the impression
+of violet light a still greater number of impulses is necessary; the
+wave-length of violet is the 1/57500th part of an inch, and the number
+of shocks imparted in a second by waves of this length is, in round
+numbers, six hundred and ninety-nine millions of millions. The other
+colours of the spectrum, as already stated, rise gradually in pitch from
+the red to the violet.
+
+A very curious analogy between the eye and ear may here be noticed. The
+range of seeing is different in different persons--some see a longer
+spectrum than others; that is to say, rays which are obscure to some are
+luminous to others. Dr. Wollaston pointed out a similar fact as regards
+hearing; the range of which differs in different individuals. Savart has
+shown that a good ear can hear a musical note produced by 8 shocks in a
+second; it can also hear a note produced by 24,000 shocks in a second;
+but there are ears in which the range is much more limited. It is
+possible indeed to produce a sound which shall be painfully shrill to
+one person, while it is quite unheard by another. I once crossed a Swiss
+mountain in company with a friend; a donkey was in advance of us, and
+the dull tramp of the animal was plainly heard by my companion; but to
+me this sound was almost masked by the shrill chirruping of innumerable
+insects which thronged the adjacent grass; my friend heard nothing of
+this, it lay quite beyond his range of hearing.
+
+A third and most important analogy between sound and light is now to be
+noted; and it will be best understood by reference to something more
+tangible than either. When a stone is thrown into calm water a series of
+rings spread themselves around the centre of disturbance. If a second
+stone be thrown in at some distance from the first, the rings emanating
+from both centres will cross each other, and at those points where the
+ridge of one wave coincides with the ridge of another the water will be
+lifted to a greater height. At those points, on the contrary, where the
+ridge of one wave crosses the furrow of another, we have both
+obliterated, and the water restored to its ordinary level. Where two
+ridges or two furrows unite, we have a case of _coincidence_; but where
+a ridge and a furrow unite we have what is called _interference_. It is
+quite possible to send two systems of waves into the same channel, and
+to hold back one system a little, so that its ridges shall coincide
+with the furrows of the other system. The "interference" would be here
+complete, and the waves thus circumstanced would mutually destroy each
+other, smooth water being the result. In this way, by the addition of
+motion to motion, _rest_ may be produced.
+
+[Sidenote: LIGHT ADDED TO LIGHT MAKES DARKNESS.]
+
+In a precisely similar manner two systems of sonorous waves can be
+caused to interfere and mutually to destroy each other: thus, by adding
+sound to sound, _silence_ may be produced. Two beams of light also may
+be caused to interfere and effect their mutual extinction: thus, by
+adding light to light, we can produce _darkness_. Here indeed we have a
+critical analogy between sound and light--_the_ one, in fact, which
+compels the most profound thinkers of the present day to assume that
+light, like sound, is a case of undulatory motion.
+
+We see here the vision of the intellect prolonged beyond the boundaries
+of sense into the region of what might be considered mere imagination.
+But, unlike other imaginations, we can bring ours to the test of
+experiment; indeed, so great a mastery have we obtained over these
+waves, which eye has not seen, nor ear heard, that we can with
+mathematical certainty cause them to coincide or to interfere, to help
+each other or to destroy each other, at pleasure. It is perhaps possible
+to be a little more precise here. Let two stones--with a small distance
+between them--be dropped into water at the same moment; a system of
+circular waves will be formed round each stone. Let the distance from
+one little crest to the next following one be called _the length of the
+wave_, and now let us inquire what will take place at a point equally
+distant from the places where the two stones were dropped in. Fixing our
+attention upon the ridge of the first wave in each case, it is manifest
+that, as the water propagates both systems with the same velocity, the
+two foremost ridges will reach the point in question at the same
+moment; the ridge of one would therefore coincide with the ridge of the
+other, and the water at this point would be lifted to a height greater
+than that of either of the previous ridges.
+
+[Sidenote: COINCIDENCE AND INTERFERENCE.]
+
+Again, supposing that by any means we had it in our power to retard one
+system of waves so as to cause the first ridge of the one to be exactly
+one wave length behind the first ridge of the other, when they arrive at
+the point referred to. It is plain that the first ridge of the retarded
+system now falls in with the second ridge of the unretarded system, and
+we have another case of coincidence. A little reflection will show the
+same to be true when one system is retarded any number of _whole
+wave-lengths_; the first ridge of the retarded system will always, at
+the point referred to, coincide with a _ridge_ of the unretarded system.
+
+But now suppose the one system to be retarded only _half a wave-length_;
+it is perfectly clear that, in this case the first ridge of the retarded
+system would fall in with the first _furrow_ of the unretarded system,
+and instead of coincidence we should have interference. One system, in
+fact, would tend to make a hollow at the point referred to, the other
+would tend to make a hill, and thus the two systems would oppose and
+neutralize each other, so that neither the hollow nor the hill would be
+produced; the water would maintain its ordinary level. What is here said
+of a single half-wave-length of retardation, is also true if the
+retardation amount to any _odd_ number of half-wave-lengths. In all such
+cases we should have the ridge of the one system falling in with the
+furrow of the other; a mutual destruction of the waves of both systems
+being the consequence. The same remarks apply when the point, instead of
+being equally distant from both stones, is an even or an odd number of
+semi-undulations farther from the one than from the other. In the former
+case we should have coincidence, and in the latter case interference,
+at the point in question.
+
+[Sidenote: LIQUID WAVES.]
+
+To the eye of a person who understands these things, nothing can be more
+interesting than the rippling of water under certain circumstances. By
+the action of interference its surface is sometimes shivered into the
+most beautiful mosaic, shifting and trembling as if with a kind of
+visible music. When the tide advances over a sea-beach on a calm and
+sunny day, and its tiny ripples enter, at various points, the clear
+shallow pools which the preceding tide had left behind, the little
+wavelets run and climb and cross each other, and thus form a lovely
+_chasing_, which has its counterpart in the lines of light converged by
+the ripples upon the sand underneath. When waves are skilfully generated
+in a vessel of mercury, and a strong light reflected from the surface of
+the metal is received upon a screen, the most beautiful effects may be
+observed. The shape of the vessel determines, in part, the character of
+the figures produced; in a circular dish of mercury, for example, a
+disturbance at the centre propagates itself in circular waves, which
+after reflection again encircle the centre. If the point of disturbance
+be a little removed from the centre, the intersections of the direct and
+reflected waves produce the magnificent chasing shown in the annexed
+figure (16), which I have borrowed from the excellent work on Waves by
+the Messrs. Weber. The luminous figure reflected from such a surface is
+exceedingly beautiful. When the mercury is lightly struck by a glass
+point, in a direction concentric with the circumference of the vessel,
+the lines of light run round the vessel in mazy coils, interlacing and
+unravelling themselves in the most wonderful manner. If the vessel be
+square, a splendid mosaic is produced by the crossing of the direct and
+reflected waves. Description, however, can give but a feeble idea of
+these exquisite effects;--
+
+ "Thou canst not wave thy staff in the air,
+ Or dip thy paddle in the lake,
+ But it carves the brow of beauty there,
+ And the ripples in rhymes the oar forsake."
+
+[Sidenote: CHASING PRODUCED BY WAVES.]
+
+[Illustration: Fig. 16. Chasing produced by waves.]
+
+[Sidenote: EFFECT OF RETARDATION.]
+
+Now, all that we have said regarding the retardation of the waves of
+water, by a whole undulation and a semi-undulation, is perfectly
+applicable to the case of light. Two luminous points may be placed near
+to each other so as to resemble the two stones dropped into the water;
+and when the light of these is properly received upon a screen, or
+directly upon the retina, we find that at some places the action of the
+rays upon each other produces darkness, and at others augmented light.
+The former places are those where the rays emitted from one point are an
+_odd_ number of semi-undulations in advance of the rays sent from the
+other; the latter places are those where the difference of path
+described by the rays is either nothing, or an _even_ number of
+semi-undulations. Supposing _a_ and _b_ (Fig. 17) to be two such
+sources of light, and S R a screen on which the light falls; at a point
+_l_, equally distant from _a_ and _b_, we have _light_; at a point _d_,
+where _a d_ is half an undulation longer than _b d_, we have darkness;
+at _l'_, where _a l'_ is a whole wave-length, or two semi-undulations,
+longer than _b l'_, we again have light; and at a point _d'_, where the
+difference is three semi-undulations, we have darkness; and thus we
+obtain a series of bright and dark spaces as we recede laterally from
+the central point _l_.
+
+[Illustration: Fig. 17. Diagram explanatory of Interference.]
+
+Let a bit of tin foil be closely pasted upon a piece of glass, and the
+edge of a penknife drawn across the foil so as to produce a slit.
+Looking through this slit at a small and distant light, we find the
+light spread out in a direction at right angles to the slit, and if the
+light looked at be _monochromatic_, that is, composed of a single
+colour, we shall have a series of bright and dark bars corresponding to
+the points at which the rays from the different points of the slit
+alternately coincide and interfere upon the retina. By properly
+drawing a knife across a sheet of letter-paper a suitable slit may also
+be obtained; and those practised in such things can obtain the effect by
+looking through their fingers or their eyelashes.
+
+[Illustration: INTERFERENCE SPECTRA, PRODUCED BY DIFFRACTION.
+Fig. 18. _To face_ p. 235.]
+
+[Sidenote: CHROMATIC EFFECTS.]
+
+But if the light looked at be white, the light of a candle for example,
+or of a jet of gas, instead of having a series of bright and dark bars,
+we have the bars _coloured_. And see how beautifully this harmonizes
+with what has been already said regarding the different lengths of the
+waves which produce different colours. Looking again at Fig. 17 we see
+that a certain obliquity is necessary to cause one ray to be a whole
+undulation in advance of the other at the point _l'_; but it is
+perfectly manifest that the obliquity must depend upon the length of the
+undulation; a long undulation would require a greater obliquity than a
+short one; red light, for example, requires a greater obliquity than
+blue light; so that if the point _l'_ represents the place where the
+first bar of red light would be at its maximum strength, the maximum for
+blue would lie a little to the left of _l'_; the different colours are
+in this way separated from each other, and exhibit themselves as
+distinct fringes when a distant source of white light is regarded
+through a narrow slit.
+
+By varying the shape of the aperture we alter the form of the chromatic
+image. A circular aperture, for example, placed in front of a telescope
+through which a point of white light is regarded, is seen surrounded by
+a concentric system of coloured rings. If we multiply our slits or
+apertures the phenomena augment in complexity and splendour. To give
+some notion of this I have copied from the excellent work of M. Schwerd
+the annexed figure (Fig. 18) which represents the gorgeous effect
+observed when a distant point of light is looked at through two gratings
+with slits of different widths.[B] A bird's feather represents a
+peculiar system of slits, and the effect observed on properly looking
+through it is extremely interesting.
+
+[Sidenote: COLOURS OF THIN FILMS.]
+
+There are many ways by which the retardation necessary to the production
+of interference is effected. The splendid colours of a soap-bubble are
+entirely due to interference; the beam falling upon the transparent film
+is partially reflected at its outer surface, but a portion of it enters
+the film and is reflected at its _inner_ surface. The latter portion
+having crossed the film and returned, is retarded, in comparison with
+the former, and, if the film be of suitable thickness, these two beams
+will clash and extinguish each other, while another thickness will cause
+the beams to coincide and illuminate the film with a light of greater
+intensity. From what has been said it must be manifest that to make two
+red beams thus coincide a thicker film would be required than would be
+necessary for two blue or green beams; thus, when the thickness of the
+bubble is suitable for the development of red, it is not suitable for
+the development of green, blue, &c.; the consequence is that we have
+different colours at different parts of the bubble. Owing to its
+compactness and to its being shaded by a covering of debris from the
+direct heat of the sun, the ice underneath the moraines of glaciers
+appears sometimes of a pitchy blackness. While cutting such ice with my
+axe I have often been surprised and delighted by sudden flashes of
+coloured light which broke like fire from the mass. These flashes were
+due to internal rupture, by which fissures were produced as thin as the
+film of a soap-bubble; the colours being due to the interference of the
+light reflected from the opposite sides of the fissures.
+
+If spirit of turpentine, or olive oil, be thrown upon water, it speedily
+spreads in a thin film over the surface, and the most gorgeous
+chromatic phenomena may be thus produced. Oil of lemons is also
+peculiarly suited to this experiment. If water be placed in a tea-tray,
+and light of sufficient intensity be suffered to fall upon it, this
+light will be reflected from the upper and under surfaces of the film of
+oil, and the colours thus produced may be received upon a screen, and
+seen at once by many hundred persons. If the oil of cinnamon be used,
+fine colours are also obtained, and the breaking up of this film
+exhibits a most interesting case of molecular action. By using a kind of
+varnish, instead of oil, Mr. Delarue has imparted such tenacity to these
+films that they may be removed from the water on which they rest and
+preserved for any length of time. By such films the colours of certain
+beetles, and of the wings of certain insects, may be accurately
+imitated; and a rook's feather may be made to shine with magnificent
+iridescences. The colours of tempered metals, and the beautiful
+metallochrome of Nobili are also due to a similar cause.
+
+[Sidenote: DIFFRACTION.]
+
+These colours are called the colours of _thin plates_, and are
+distinguished in treatises on optics from the coloured bars and fringes
+above referred to, which are produced by _diffraction_, or the bending
+of the waves round the edge of an object. One result of this bending,
+which is of interest to us, was obtained by the celebrated Thomas Young.
+Permitting a beam of sunlight to enter a dark room through an aperture
+made with a fine needle, and placing in the path of the beam a bit of
+card one-thirtieth of an inch wide, he found the shadow of this card, or
+rather the line on which its shadow might be supposed to fall, always
+_bright_; and he proved the effect to be due to the bending of the waves
+of ether round the two edges of the card, and their coincidence at the
+other side. It has, indeed, been shown by M. Poisson, that the centre of
+the shadow of a small circular opaque disk which stands in the way of a
+beam diverging from a point is exactly as much illuminated as if the
+disk were absent. The singular effects described by M. Necker in the
+letter quoted at page 178 at once suggest themselves here; and we see
+how possible it is for the solar rays, in grazing a distant tree, so to
+bend round it as to produce upon the retina, where shadow might be
+expected, the impression of a tree of light.[C] Another effect of
+diffraction is especially interesting to us at present. Let the seed of
+lycopodium be scattered over a glass plate, or even like a cloud in the
+air, and let a distant point of light be regarded through it; the
+luminous point will appear surrounded by a series of coloured rings, and
+when the light is intense, like the electric or the Drummond light, the
+effect is exceedingly fine.
+
+[Sidenote: CLOUD IRIDESCENCE, ETC., EXPLAINED.]
+
+And now for the application of these experiments. I have already
+mentioned a series of coloured rings observed around the sun by Mr.
+Huxley and myself from the Rhone glacier; I have also referred to the
+cloud iridescences on the Aletschhorn; and to the colours observed
+during my second ascent of Monte Rosa, the magnificence of which is
+neither to be rendered by pigments nor described in words. All these
+splendid phenomena are, I believe, produced by diffraction, the vesicles
+or spherules of water in the case of the cloud acting the part of the
+sporules in the case of the lycopodium. The coloured fringe which
+surrounds the _Spirit of the Brocken_, and the spectra which I have
+spoken of as surrounding the sun, are also produced by diffraction. By
+the interference of their rays in the earth's atmosphere the stars can
+momentarily quench themselves; and probably to an intermittent action of
+this kind their twinkling, and the swift chromatic changes already
+mentioned, are due. Does not all this sound more like a fairy tale than
+the sober conclusions of science? What effort of the imagination could
+transcend the realities here presented to us? The ancients had their
+spheral melodies, but have not we ours, which only want a sense
+sufficiently refined to hear them? Immensity is filled with this music;
+wherever a star sheds its light its notes are heard. Our sun, for
+example, thrills concentric waves through space, and every luminous
+point that gems our skies is surrounded by a similar system. I have
+spoken of the rising, climbing and crossing of the tiny ripples of a
+calm tide upon a smooth strand; but what are they to those intersecting
+ripples of the "uncontinented deep" by which Infinity is engine-turned!
+Crossing solar and stellar distances, they bring us the light of sun and
+stars; thrilled back from our atmosphere, they give us the blue radiance
+of the sky; rounding liquid spherules, they clash at the other side, and
+the survivors of the tumult bear to our vision the wondrous cloud-dyes
+of Monte Rosa.
+
+
+FOOTNOTES:
+
+[A] The vibrations of the air of a room in which a musical instrument is
+sounded may be made manifest by the way in which fine sand arranges
+itself upon a thin stretched membrane over which it is strewn; and
+indeed Savart has thus rendered visible the vibrations of the tympanum
+itself. Every trace of sand was swept from a paper drum held in the
+clock-tower of Westminster when the Great Bell was sounded. Another way
+of showing the propagation of aerial pulses is to insert a small gas jet
+into a vertical glass tube about a foot in length, in which the flame
+may be caused to burn tranquilly. On pitching the voice to the note of
+an open tube a foot long, the little flame quivers, stretches itself,
+and responds by producing a clear melodious note of the same pitch as
+that which excited it. The flame will continue its song for hours
+without intermission.
+
+[B] I am not aware whether in his own country, or in any other, a
+recognition at all commensurate with the value of the performance has
+followed Schwerd's admirable essay entitled 'The Phenomena of
+Diffraction deduced from the Theory of Undulation.'
+
+[C] I think, however, that the strong irradiation from the glistening
+sides of the twigs and branches must also contribute to the result.
+
+
+
+
+[Sidenote: RADIANT HEAT.]
+
+(2.)
+
+
+Thus, then, we have been led from Sound to Light, and light now in its
+turn will lead us to _Radiant Heat_; for in the order in which they are
+here mentioned the conviction arose that they are all three different
+kinds of motion. It has been said that the beams of the sun consist of
+rays of different colours, but this is not a complete statement of the
+case. The sun emits a multitude of rays which are perfectly
+non-luminous; and the same is true, in a still greater degree, of our
+artificial sources of illumination. Measured by the quantity of heat
+which they produce, 90 per cent. of the rays emanating from a flame of
+oil are obscure; while 99 out of every 100 of those which emanate from
+an alcohol flame are of the same description.[A]
+
+[Sidenote: OBSCURE RAYS.]
+
+In fact, the visible solar spectrum simply embraces an interval of rays
+of which the eye is formed to take cognizance, but it by no means marks
+the limits of solar action. Beyond the violet end of the spectrum we
+have obscure rays capable of producing chemical changes, and beyond the
+red we have rays possessing a high heating power, but incapable of
+exciting the impression of light. This latter fact was first established
+by Sir William Herschel, and it has been amply corroborated since.
+
+The belief now universally prevalent is, that the rays of heat differ
+from the rays of light simply as one colour differs from another. As the
+waves which produce red are longer than those which produce yellow, so
+the waves which produce this obscure heat are longer than those which
+produce red. In fact, it may be shown that the longest waves never reach
+the retina at all; they are completely absorbed by the humours of the
+eye.
+
+What is true of the sun's obscure rays is also true of calorific rays
+emanating from any obscure source,--from our own bodies, for example, or
+from the surface of a vessel containing boiling water. We must, in fact,
+figure a warm body also as having its particles in a state of vibration.
+When these motions are communicated from particle to particle of the
+body the heat is said to be _conducted_; when, on the contrary, the
+particles transmit their vibrations through the surrounding ether, the
+heat is said to be _radiant_. This radiant heat, though obscure,
+exhibits a deportment exactly similar to light. It may be refracted and
+reflected, and collected in the focus of a mirror or of a suitable lens.
+The principle of interference also applies to it, so that by adding heat
+to heat we can produce _cold_. The identity indeed is complete
+throughout, and, recurring to the analogy of sound, we might define
+this radiant heat to be light of too low a pitch to be visible.
+
+I have thus far spoken of _obscure_ heat only; but the selfsame ray may
+excite both light and heat. The red rays of the spectrum possess a very
+high heating power. It was once supposed that the heat of the spectrum
+was an essence totally distinct from its light; but a profounder
+knowledge dispels this supposition, and leads us to infer that the
+selfsame ray, falling upon the nerves of feeling, excites heat, and
+falling upon the nerves of seeing, excites light. As the same electric
+current, if sent round a magnetic needle, along a wire, and across a
+conducting liquid, produces different physical effects, so also the same
+agent acting upon different organs of the body affects our consciousness
+differently.
+
+
+FOOTNOTES:
+
+[A] Melloni.
+
+
+
+
+(3.)
+
+
+[Sidenote: HEAT A KIND OF MOTION.]
+
+Heat has been defined in the foregoing section as a motion of the
+molecules or atoms of a body; but though the evidence in favour of this
+view is at present overwhelming, I do not ask the reader to accept it as
+a certainty, if he feels sceptically disposed. In this case, I would
+only ask him to accept it as a symbol. Regarded as a mere physical
+image, a kind of paper-currency of the mind, convertible, in due time,
+into the gold of truth, the hypothesis will be found exceedingly useful.
+
+All known bodies possess more or less of this molecular motion, and all
+bodies are communicating it to the ether in which they are immersed. Ice
+possesses it. Ice before it melts attains a temperature of 32 deg. Fahr.,
+but the substance in winter often possesses a temperature far below 32 deg.,
+so that in rising to 32 deg. it is _warmed_. In experimenting with ice I
+have often had occasion to cool it to 100 deg. and more below the freezing
+point, and to warm it afterwards up to 32 deg.
+
+If then we stand before a wall of ice, the wall radiates heat to us, and
+we also radiate heat to it; but the quantity which we radiate being
+greater than that which the ice radiates, we lose more than we gain, and
+are consequently chilled. If, on the contrary, we stand before a warm
+stove, a system of exchanges also takes place; but here the quantity we
+receive is in excess of the quantity lost, and we are warmed by the
+difference.
+
+In like manner the earth radiates heat by day and by night into space,
+and against the sun, moon, and stars. By day, however, the quantity
+received is greater than the quantity lost, and the earth is warmed; by
+night the conditions are reversed; the earth radiates more heat than is
+sent to her by the moon and stars, and she is consequently cooled.
+
+But here an important point is to be noted:--the earth receives the heat
+of the sun, moon, and stars, in great part as _luminous_ heat, but she
+gives it out as _obscure_ heat. I do not now speak of the heat reflected
+by the earth into space, as the light of the moon is to us; but of the
+heat which, after it has been absorbed by the earth, and has contributed
+to warm it, is radiated into space, as if the earth itself were its
+independent source. Thus we may properly say that the heat radiated from
+the earth is _different in quality_ from that which the earth has
+received from the sun.
+
+[Sidenote: QUALITIES OF HEAT.]
+
+In one particular especially does this difference of quality show
+itself; besides being non-luminous, the heat radiated from the earth is
+more easily intercepted and absorbed by almost all transparent
+substances. A vast portion of the sun's rays, for example, can pass
+instantaneously through a thick sheet of water; gunpowder could easily
+be fired by the heat of the sun's rays converged by passing through a
+thick water lens; the drops upon leaves in greenhouses often act as
+lenses, and cause the sun to burn the leaves upon which they rest. But
+with regard to the rays of heat emanating from an obscure source, they
+are all absorbed by a layer of water less than the 20th of an inch in
+thickness: water is opaque to such rays, and cuts them off almost as
+effectually as a metallic screen. The same is true of other liquids, and
+also of many transparent solids.
+
+[Sidenote: THE ATMOSPHERE LIKE A RATCHET.]
+
+Assuming the same to be true of gaseous bodies, that they also intercept
+the obscure rays much more readily than the luminous ones, it would
+follow that while the sun's rays penetrate our atmosphere with freedom,
+the change which they undergo in warming the earth deprives them in a
+measure of this penetrating power. They can reach the earth, but _they
+cannot get back_; thus the atmosphere acts the part of a ratchet-wheel
+in mechanics; it allows of motion in one direction, but prevents it in
+the other.
+
+De Saussure, Fourier, M. Pouillet, and Mr. Hopkins have developed this
+speculation, and drawn from it consequences of the utmost importance;
+but it nevertheless rested upon a basis of conjecture. Indeed some of
+the eminent men above-named deemed its truth beyond the possibility of
+experimental verification. Melloni showed that for a distance of 18 or
+20 feet the absorption of obscure rays by the atmosphere was absolutely
+inappreciable. Hence, the _total_ absorption being so small as to elude
+even Melloni's delicate tests, it was reasonable to infer that
+_differences_ of absorption, if such existed at all, must be far beyond
+the reach of the finest means which we could apply to detect them.
+
+[Sidenote: DIFFERENCES OF ABSORPTION BY GASES.]
+
+This exclusion of one of the three states of material aggregation from
+the region of experiment was, however, by no means satisfactory; for our
+right to infer, from the deportment of a solid or a liquid towards
+radiant heat, the deportment of a gas, is by no means evident. In both
+liquids and solids we have the molecules closely packed, and more or
+less chained by the force of cohesion; in gases, on the contrary, they
+are perfectly free, and widely separated. How do we know that the
+interception of radiant heat by liquids and solids may not be due to an
+arrangement and comparative rigidity of their parts, which gases do not
+at all share? The assumption which took no note of such a possibility
+seemed very insecure, and called for verification.
+
+My interest in this question was augmented by the fact, that the
+assumption referred to lies, as will be seen, at the root of the glacier
+question. I therefore endeavoured to fill the gap, and to do for gases
+and vapours what had been already so ably done for liquids and solids by
+Melloni. I tried the methods heretofore pursued, and found them
+unavailing; oxygen, hydrogen, nitrogen, and atmospheric air, examined by
+such methods, showed no action upon radiant heat. Nature was dumb, but
+the question occurred, "Had she been addressed in the proper language?"
+If the experimentalist is convinced of this, he will rest content even
+with a negative; but the absence of this conviction is always a source
+of discomfort, and a stimulus to try again.
+
+The principle of the method finally applied is all that can here be
+referred to; and it, I hope, will be quite intelligible. Two beams of
+heat, from two distinct sources, were allowed to fall upon the same
+instrument,[A] and to contend there for mastery. When both beams were
+perfectly equal, they completely neutralized each other's action; but
+when one of them was in any sensible degree stronger than the other, the
+predominance of the former was shown by the instrument. It was so
+arranged that one of the conflicting beams passed through a tube which
+could be exhausted of air, or filled with any gas; thus varying at
+pleasure the medium through which it passed. The question then was,
+supposing the two beams to be equal when the tube was filled with air,
+will the exhausting of the tube disturb the equality? The answer was
+affirmative; the instrument at once showed that a greater quantity of
+heat passed through the vacuum than through the air.
+
+The experiment was so arranged that the effect thus produced was very
+large as measured by the indications of the instrument. But the action
+of the simple gases, oxygen, hydrogen, and nitrogen, was incomparably
+less than that produced by some of the compound gases, while these
+latter again differed widely from each other. Vapours exhibited
+differences of equal magnitude. The experiments indeed proved that
+gaseous bodies varied among themselves, as to their power of
+transmitting radiant heat, just as much as liquids and solids. It was in
+the highest degree interesting to observe how a gas or vapour of perfect
+transparency, as regards light, acted like an opaque screen upon the
+heat. To the eye, the gas within the tube might be as invisible as the
+air itself, while to the radiant heat it behaved like a cloud which it
+was almost impossible to penetrate.
+
+[Sidenote: SELECTED HEAT.]
+
+Applying the same method, I have found that from the sun, from the
+electric light, or from the lime-light, a large amount of heat can be
+selected, which is unaffected not only by air, but by the most energetic
+gases that experiment has revealed to me; while this same heat, when it
+has its _quality_ changed by being rendered obscure, is powerfully
+intercepted. Thus the bold and beautiful speculation above referred to
+has been made an experimental fact; the radiant heat of the sun does
+certainly pass through the atmosphere to the earth with greater
+facility than the radiant heat of the earth can escape into space.
+
+[Sidenote: POSSIBLE HEAT OF NEPTUNE.]
+
+It is probable that, were the earth unfurnished with this atmospheric
+swathing, its conditions of temperature would be such as to render it
+uninhabitable by man; and it is also probable that a suitable atmosphere
+enveloping the most distant planet might render it, as regards
+temperature, perfectly habitable. If the planet Neptune, for example, be
+surrounded by an atmosphere which permits the solar and stellar rays to
+pass towards the planet, but cuts off the escape of the warmth which
+they excite, it is easy to see that such an accumulation of heat may at
+length take place as to render the planet a comfortable habitation for
+beings constituted like ourselves.[B]
+
+But let us not wander too far from our own concerns. Where radiant heat
+is allowed to fall upon an absorbing substance, a certain thickness of
+the latter is always necessary for the absorption. Supposing we place a
+thin film of glass before a source of heat, a certain percentage of the
+heat will pass through the glass, and the remainder will be absorbed.
+Let the transmitted portion fall upon a second film similar to the
+first, a smaller percentage than before will be absorbed. A third plate
+would absorb still less, a fourth still less; and, after having passed
+through a sufficient number of layers, the heat would be so _sifted_
+that all the rays capable of being absorbed by glass would be abstracted
+from it. Suppose all these films to be placed together so as to form a
+single thick plate of glass, it is evident that the plate must act upon
+the heat which falls upon it, in such a manner that the major portion is
+absorbed _near the surface at which the heat enters_. This has been
+completely verified by experiment.
+
+[Sidenote: COLD OF UPPER ATMOSPHERE.]
+
+Applying this to the heat radiated from the earth, it is manifest that
+the greatest quantity of this heat will be absorbed by the lowest
+atmospheric strata. And here we find ourselves brought, by
+considerations apparently remote, face to face with the fact upon which
+the existence of all glaciers depends, namely, the comparative coldness
+of the upper regions of the atmosphere. The sun's rays can pass in a
+great measure through these regions without heating them; and the
+earth's rays, which they might absorb, hardly reach them at all, but are
+intercepted by the lower portions of the atmosphere.[C]
+
+Another cause of the greater coldness of the higher atmosphere is the
+expansion of the denser air of the lower strata when it ascends. The
+dense air makes room for itself by pushing back the lighter and less
+elastic air which surrounds it: _it does work_, and, to perform this
+work, a certain amount of heat must be consumed. It is the consumption
+of this heat--its absolute annihilation as heat--that chills the
+expanded air, and to this action a share of the coldness of the higher
+atmosphere must undoubtedly be ascribed. A third cause of the difference
+of temperature is the large amount of heat communicated, _by way of
+contact_, to the air of the earth's surface; and a fourth and final
+cause is the loss endured by the highest strata through radiation into
+space.
+
+
+FOOTNOTES:
+
+[A] The opposite faces of a thermo-electric pile.
+
+[B] See a most interesting paper on this subject by Mr. Hopkins in the
+Cambridge 'Transactions,' May, 1856.
+
+[C] See M. Pouillet's important Memoir on Solar Radiation. Taylor's
+Scientific Memoirs, vol. iv. p. 44.
+
+
+
+
+ORIGIN OF GLACIERS.
+
+(4.)
+
+
+[Sidenote: THE SNOW-LINE.]
+
+Having thus accounted for the greater cold of the higher atmospheric
+regions, its consequences are next to be considered. One of these is,
+that clouds formed in the lower portions of the atmosphere, in warm and
+temperate latitudes, usually discharge themselves upon the earth as
+rain; while those formed in the higher regions discharge themselves upon
+the mountains as snow. The snow of the higher atmosphere is often melted
+to rain in passing through the warmer lower strata: nothing indeed is
+more common than to pass, in descending a mountain, from snow to rain;
+and I have already referred to a case of this kind. The appearance of
+the grassy and pine-clad alps, as seen from the valleys after a wet
+night, is often strikingly beautiful; the level at which the snow turned
+to rain being distinctly marked upon the slopes. Above this level the
+mountains are white, while below it they are green. The eye follows this
+_snow-line_ with ease along the mountains, and when a sufficient extent
+of country is commanded its regularity is surprising.
+
+The term "snow-line," however, which has been here applied to a local
+and temporary phenomenon, is commonly understood to mean something else.
+In the case just referred to it marked the place where the supply of
+solid matter from the upper atmospheric regions, during a single fall,
+was exactly equal to its consumption; but the term is usually understood
+to mean the line along which the quantity of snow which falls _annually_
+is melted, and no more. Below this line each year's snow is completely
+cleared away by the summer heat; above it a residual layer abides,
+which gradually augments in thickness from the snow-line upwards.
+
+[Sidenote: MOUNTAINS UNLOADED BY GLACIERS.]
+
+Here then we have a fresh layer laid on every year; and it is evident
+that, if this process continued without interruption, every mountain
+which rises above the snow-line must augment annually in height; the
+waters of the sea thus piled, in a solid form, upon the summits of the
+hills, would raise the latter to an indefinite elevation. But, as might
+be expected, the snow upon steep mountain-sides frequently slips and
+rolls down in avalanches into warmer regions, where it is reduced to
+water. A comparatively small quantity of the snow is, however, thus got
+rid of, and the great agent which Nature employs to relieve her
+overladen mountains is the glaciers.
+
+Let us here avoid an error which may readily arise out of the foregoing
+reflections. The principal region of clouds and rain and snow extends
+only to a limited distance upwards in the atmosphere; the highest
+regions contain very little moisture, and were our mountains
+sufficiently lofty to penetrate those regions, the quantity of snow
+falling upon their summits would be too trifling to resist the direct
+action of the solar rays. These would annually clear the summits to a
+certain level, and hence, were our mountains high enough, we should have
+a superior, as well as an inferior, snow-line; the region of perpetual
+snow would form a belt, below which, in summer, snowless valleys and
+plains would extend, and above which snowless summits would rise.
+
+
+
+
+(5.)
+
+
+[Sidenote: WHITE AND BLUE ICE.]
+
+At its origin then a glacier is snow--at its lower extremity it is ice.
+The blue blocks that arch the source of the Arveiron were once powdery
+snow upon the slopes of the Col du Geant. Could our vision penetrate
+into the body of the glacier, we should find that the change from white
+to blue essentially consists in the gradual expulsion of the air which
+was originally entangled in the meshes of the fallen snow. Whiteness
+always results from the intimate and irregular mixture of air and a
+transparent solid; a crushed diamond would resemble snow; if we pound
+the most transparent rock-salt into powder we have a substance as white
+as the whitest culinary salt; and the colourless glass vessel which
+holds the salt would also, if pounded, give a powder as white as the
+salt itself. It is a law of light that in passing from one substance to
+another possessing a different power of refraction, a portion of it is
+always reflected. Hence when light falls upon a transparent solid mixed
+with air, at each passage of the light from the air to the solid and
+from the solid to the air a portion of it is reflected; and, in the case
+of a powder, this reflection occurs so frequently that the passage of
+the light is practically cut off. Thus, from the mixture of two
+perfectly transparent substances, we obtain an opaque one; from the
+intimate mixture of air and water we obtain foam; clouds owe their
+opacity to the same principle; and the condensed steam of a locomotive
+casts a shadow upon the fields adjacent to the line, because the
+sunlight is wasted in echoes at the innumerable limiting surfaces of
+water and air.
+
+[Sidenote: AIR-BUBBLES IN ICE.]
+
+The snow which falls upon high mountain-eminences has often a
+temperature far below the freezing point of water. Such snow is _dry_,
+and if it always continued so the formation of a glacier from it would
+be impossible. The first action of the summer's sun is to raise the
+temperature of the superficial snow to 32 deg., and afterwards to melt it.
+The water thus formed percolates through the colder mass underneath, and
+this I take to be the first active agency in expelling the air
+entangled in the snow. But as the liquid trickles over the surfaces of
+granules colder than itself it is partially deposited in a solid form on
+these surfaces, thus augmenting the size of the granules, and cementing
+them together. When the mass thus formed is examined, the air within it
+is found as _round bubbles_. Now it is manifest that the air caught in
+the irregular interstices of the snow can have no tendency to assume
+this form so long as the snow remains solid; but the process to which I
+have referred--the saturation of the lower portions of the snow by the
+water produced by the melting of the superficial portions--enables the
+air to form itself into globules, and to give the ice of the _neve_ its
+peculiar character. Thus we see that, though the sun cannot get directly
+at the deeper portions of the snow, by liquefying the upper layer he
+charges it with heat, and makes it his messenger to the cold subjacent
+mass.
+
+The frost of the succeeding winter may, I think, or may not, according
+to circumstances, penetrate through this layer, and solidify the water
+which it still retains in its interstices. If the winter set in with
+clear frosty weather, the penetration will probably take place; but if
+heavy snow occur at the commencement of winter, thus throwing a
+protective covering over the _neve_, freezing to any great depth may be
+prevented. Mr. Huxley's idea seems to be quite within the range of
+possibility, that water-cells may be transmitted from the origin of the
+glacier to its end, retaining their contents always liquid.
+
+[Sidenote: SNOW PRESSED TO ICE.]
+
+It was formerly supposed, and is perhaps still supposed by many, that
+the snow of the mountains is converted into the ice of the glacier by
+the process of saturation and freezing just indicated. But the frozen
+layer would not yet resemble glacier ice; it is only at the deeper
+portions of the _neve_ that we find an approximation to the true ice of
+the glacier. This brings us to the second great agent in the process of
+glacification, namely, pressure. The ice of the _neve_ at 32 deg. may be
+squeezed or crushed with extreme facility; and if the force be applied
+slowly and with caution, the yielding of the mass may be made to
+resemble the yielding of a plastic body. In the depths of the _neve_,
+where each portion of the ice is surrounded by a resistant mass, rude
+crushing is of course out of the question. The layers underneath yield
+with extreme slowness to the pressure of the mass above them; they are
+squeezed, but not rudely fractured; and even should rude fracture occur,
+the ice, as shall subsequently be shown, possesses the power of
+restoring its own continuity. Thus, then, the lower portions of the
+_neve_ are removed by pressure more and more from the condition of snow,
+the air-bubbles which give to the _neve_-ice its whiteness are more and
+more expelled, and this process, continued throughout the entire
+glacier, finally brings the ice to that state of magnificent
+transparency which we find at the termination of the glacier of
+Rosenlaui and elsewhere. This is all capable of experimental proof. The
+Messrs. Schlagintweit compressed the snow of the _neve_ to compact ice;
+and I have myself frequently obtained slabs of ice from snow in London.
+
+
+
+
+COLOUR OF WATER AND ICE.
+
+(6.)
+
+
+The sun is continually sending forth waves of different lengths, all of
+which travel with the same velocity through the ether. When these waves
+enter a prism of glass they are retarded, but in different degrees. The
+shorter waves suffer the greatest retardation, and in consequence of
+this are most deflected from their straight course. It is this property
+which enables us to separate one from the other in the solar spectrum,
+and this separation proves that the waves are by no means inextricably
+entangled with each other, but that they travel independently through
+space.
+
+In consequence of this independence, the same body may intercept one
+system of waves while it allows another to pass: on this quality,
+indeed, depend all the phenomena of colour. A red glass, for example, is
+red because it is so constituted that it destroys the shorter waves
+which produce the other colours, and transmits only the waves which
+produce red. I may remark, however, that scarcely any glass is of a pure
+colour; along with the predominant waves, some of the other waves are
+permitted to pass. The colours of flowers are also very impure; in fact,
+to get pure colours we must resort to a delicate prismatic analysis of
+white light.
+
+[Sidenote: LONG WAVES MOST ABSORBED.]
+
+It has already been stated that a layer of water less than the twentieth
+of an inch in thickness suffices to stop and destroy all waves of
+radiant heat emanating from an obscure source. The longer waves of the
+obscure heat cannot get through water, and I find that all transparent
+compounds which contain _hydrogen_ are peculiarly hostile to the longer
+undulations. It is, I think, the presence of this element in the
+humours of the eye which prevents the extra red rays of the solar
+spectrum from reaching the retina. It is interesting to observe that
+while bisulphide of carbon, chloride of phosphorus, and other liquids
+which contain no hydrogen, permit a large portion of the rays emanating
+from an iron or copper ball, at a heat below redness, to pass through
+them with facility, the same thickness of substances equally
+transparent, but which contain hydrogen, such as ether, alcohol, water,
+or the vitreous humour of the eye of an ox, completely intercepts these
+obscure rays. The same is true of solid bodies; a very slight thickness
+of those which contain hydrogen offers an impassable barrier to all rays
+emanating from a non-luminous source.[A] But the heat thus intercepted
+is by no means lost; its _radiant form_ merely is destroyed. Its waves
+are shivered upon the particles of the body, but they impart warmth to
+it, while the heat which retains its radiant form contributes in no way
+to the warmth of the body through which it passes.
+
+[Sidenote: FINAL COLOUR OF ICE AND WATER BLUE.]
+
+Water then absorbs all the extra red rays of the sun, and if the layer
+be thick enough it invades the red rays themselves. Thus the greater the
+distance the solar beams travel through pure water the more are they
+deprived of those components which lie at the red end of the spectrum.
+The consequence is, that the light finally transmitted by the water, and
+which gives to it its colour, is _blue_.
+
+[Sidenote: EXPERIMENT.]
+
+I find the following mode of examining the colour of water both
+satisfactory and convenient:--A tin tube, fifteen feet long and three
+inches in diameter, has its two ends stopped securely by pieces of
+colourless plate glass. It is placed in a horizontal position, and pure
+water is poured into it through a small lateral pipe, until the liquid
+reaches half way up the glasses at the ends; the tube then holds a
+semi-cylinder of water and a semi-cylinder of air. A white plate, or a
+sheet of white paper, well illuminated, is then placed at a little
+distance from one end of the tube, and is looked at through the tube.
+Two semicircular spaces are then seen, one by the light which has passed
+through the air, the other by the light which has passed through the
+water; and their proximity furnishes a means of comparison, which is
+absolutely necessary in experiments of this kind. It is always found
+that, while the former semicircle remains white, the latter one is
+vividly coloured.[B]
+
+When the beam from an electric lamp is sent through this tube, and a
+convex lens is placed at a suitable distance from its most distant end,
+a magnified image of the coloured and uncoloured semicircles may be
+projected upon a screen. Tested thus, I have sometimes found, after
+rain, the ordinary pipe-water of the Royal Institution quite opaque;
+while, under other circumstances, I have found the water of a clear
+green. The pump-water of the Institution thus examined exhibits a rich
+sherry colour, while distilled water is blue-green.
+
+The blueness of the Grotto of Capri is due to the fact that the light
+which enters it has previously traversed a great depth of clear water.
+According to Bunsen's account, the _laugs_, or cisterns of hot water, in
+Iceland must be extremely beautiful. The water contains silica in
+solution, which, as the walls of the cistern arose, was deposited upon
+them in fantastic incrustations. These, though white, when looked at
+through the water appear of a lovely blue, which deepens in tint as the
+vision plunges deeper into the liquid.
+
+[Sidenote: ICE OPAQUE TO RADIANT HEAT.]
+
+Ice is a crystal formed from this blue liquid, the colour of which it
+retains. Ice is the most opaque of transparent solids to radiant heat,
+as water is the most opaque of liquids. According to Melloni, a plate of
+ice one twenty-fifth of an inch thick, which permits the rays of light
+to pass without sensible absorption, cuts off 94 per cent. of the rays
+of heat issuing from a powerful oil lamp, 99-1/2 per cent. of the rays
+issuing from incandescent platinum, and the whole of the rays issuing
+from an obscure source. The above numbers indicate how large a portion
+of the rays emitted by our artificial sources of light is obscure.
+
+When the rays of light pass through a sufficient thickness of ice the
+longer waves are, as in the case of water, more and more absorbed, and
+the final colour of the substance is therefore blue. But when the ice is
+filled with minute air-bubbles, though we should loosely call it
+_white_, it may exhibit, even in small pieces, a delicate blue tint.
+This, I think, is due to the frequent interior reflection which takes
+place at the surfaces of the air-cells; so that the light which reaches
+the eye from the interior may, in consequence of its having been
+reflected hither and thither, really have passed through a considerable
+thickness of ice. The same remark, as we have already seen, applies to
+the delicate colour of newly fallen snow.
+
+
+FOOTNOTES:
+
+[A] What is here stated regarding hydrogen is true of all the liquids
+and solids which have hitherto been examined,--but whether any
+exceptions occur, future experience must determine. It is only when in
+combination that it exhibits this impermeability to the obscure rays.
+
+[B] In my own experiments I have never yet been able to obtain a pure
+blue, the nearest approach to it being a blue-green.
+
+
+
+
+COLOURS OF THE SKY.
+
+(7.)
+
+
+[Sidenote: NEWTON'S HYPOTHESIS.]
+
+In treating of the Colours of Thin Plates we found that a certain
+thickness was necessary to produce blue, while a greater thickness was
+necessary for red. With that wonderful power of generalization which
+belonged to him, Newton thus applies this apparently remote fact to the
+blue of the sky:--"The blue of the first order, though very faint and
+little, may possibly be the colour of some substances, and particularly
+the azure colour of the skies seems to be of this order. For all
+vapours, when they begin to condense and coalesce into small parcels,
+become first of that bigness whereby such an azure is reflected, before
+they can constitute clouds of other colours. And so, this being the
+first colour which vapours begin to reflect, it ought to be the colour
+of the finest and most transparent skies, in which vapours are not
+arrived at that grossness requisite to reflect other colours, as we find
+it is by experience."
+
+M. Clausius has written a most interesting paper, which he endeavours to
+show that the minute particles of water which are supposed by Newton to
+reflect the light, cannot be little globes entirely composed of water,
+but bladders or hollow spheres; the vapour must be in what is generally
+termed the _vesicular_ state. He was followed by M. Bruecke, whose
+experiments prove that the suspended particles may be so small that the
+reasoning of M. Clausius may not apply to them.
+
+But why need we assume the existence of such particles at all?--why not
+assume that the colour of the air is blue, and renders the light of the
+sun blue, after the fashion of a blue glass or a solution of the
+sulphate of copper? I have already referred to the great variation which
+the colour of the firmament undergoes in the Alps, and have remarked
+that this seems to indicate that the blue depends upon some variable
+constituent of the atmosphere. Further, we find that the blue light of
+the sky is _reflected_ light; and there must be something in the
+atmosphere capable of producing this reflection; but this thing,
+whatever it is, produces another effect which the blue glass or liquid
+is unable to produce. These _transmit_ blue light, whereas, when the
+solar beams have traversed a great length of air, as in the morning or
+the evening, they are yellow, or orange, or even blood-red, according to
+the state of the atmosphere:--the transmitted light and the reflected
+light of the atmosphere are then totally different in colour.
+
+[Sidenote: GOETHE'S HYPOTHESIS.]
+
+Goethe, in his celebrated 'Farbenlehre,' gives a theory of the colour of
+the sky, and has illustrated it by a series of striking facts. He
+assumed two principles in the universe--Light and Darkness--and an
+intermediate stage of Turbidity. When the darkness is seen through a
+turbid medium on which the light falls, the medium appears blue; when
+the light itself is viewed through such a medium, it is yellow, or
+orange, or ruby-red. This he applies to the atmosphere, which sends us
+blue light, or red, according as the darkness of infinite space, or the
+bright surface of the sun, is regarded through it.
+
+As a theory of colours Goethe's work is of no value, but the facts which
+he has brought forward in illustration of the action of turbid media are
+in the highest degree interesting. He refers to the blueness of distant
+mountains, of smoke, of the lower part of the flame of a candle (which
+if looked at with a white surface behind it completely disappears), of
+soapy water, and of the precipitates of various resins in water. One of
+his anecdotes in connexion with this subject is extremely curious and
+instructive. The portrait of a very dignified theologian having suffered
+from dirt, it was given to a painter to be cleaned. The clergyman was
+drawn in a dress of black velvet, over which the painter, in the first
+place, passed his sponge. To his astonishment the black velvet changed
+to the colour of blue plush, and completely altered the aspect of its
+wearer. Goethe was informed of the fact; the experiment was repeated in
+his presence, and he at once solved it by reference to his theory. The
+varnish of the picture when mixed with the water formed a turbid medium,
+and the black coat seen through it appeared blue; when the water
+evaporated the coat resumed its original aspect.
+
+[Sidenote: SUSPENDED PARTICLES.]
+
+With regard to the real explanation of these effects, it may be shown,
+that, if a beam of white light be sent through a liquid which contains
+extremely minute particles in a state of suspension, the short waves are
+more copiously reflected by such particles than the long ones; blue, for
+example, is more copiously reflected than red. This may be shown by
+various fine precipitates, but the best is that of Bruecke. We know that
+mastic and various resins are soluble in alcohol, and are precipitated
+when the solution is poured into water: _Eau de Cologne_, for example,
+produces a white precipitate when poured into water. If however this
+precipitate be sufficiently diluted, it gives the liquid a bluish colour
+by reflected light. Even when the precipitate is very thick and gross,
+and floats upon the liquid like a kind of curd, its under portions often
+exhibit a fine blue. To obtain particles of a proper size, Bruecke
+recommends 1 gramme of colourless mastic to be dissolved in 87 grammes
+of alcohol, and dropped into a beaker of water, which is kept in a state
+of agitation. In this way a blue resembling that of the firmament may be
+produced. It is best seen when a black cloth is placed behind the glass;
+but in certain positions this blue liquid appears yellow; and these are
+the positions when the _transmitted_ light reaches the eye. It is
+evident that this change of colour must necessarily exist; for the blue
+being partially withdrawn by more copious reflection, the transmitted
+light must partake more or less of the character of the complementary
+colour; though it does not follow that they should be exactly
+complementary to each other.
+
+[Sidenote: THE SUN THROUGH LONDON SMOKE.]
+
+When a long tube is filled with clear water, the colour of the liquid,
+as before stated, shows itself by transmitted light. The effect is very
+interesting when a solution of mastic is permitted to drop into such a
+tube, and the fine precipitate to diffuse itself in the water. The
+blue-green of the liquid is first neutralized, and a yellow colour shows
+itself; on adding more of the solution the colour passes from yellow to
+orange, and from orange to blood-red. With a cell an inch and a half in
+width, containing water, into which the solution of mastic is suffered
+to drop, the same effect may be obtained. If the light of an electric
+lamp be caused to form a clear sunlike disk upon a white screen, the
+gradual change of this light by augmented precipitation into deep
+glowing red, resembling the colour of the sun when seen through fine
+London smoke, is exceedingly striking. Indeed the smoke acts, in some
+measure, the part of our finely-suspended matter.
+
+[Sidenote: MORNING AND EVENING RED.]
+
+By such means it is possible to imitate the phenomena of the firmament;
+we can produce its pure blue, and cause it to vary as in nature. The
+milkiness which steals over the heavens, and enables us to distinguish
+one cloudless day from another, can be produced with the greatest ease.
+The yellow, orange, and red light of the morning and evening can also be
+obtained: indeed the effects are so strikingly alike as to suggest a
+common origin--that the colours of the sky are due to minute particles
+diffused through the atmosphere. These particles are doubtless the
+condensed vapour of water, and its variation in quality and amount
+enables us to understand the variability of the firmamental blue, and of
+the morning and the evening red. Professor Forbes, moreover, has made
+the interesting observation that the steam of a locomotive, at a certain
+stage of its condensation, is blue or red according as it is viewed by
+reflected or transmitted light.
+
+These considerations enable us to account for a number of facts of
+common occurrence. Thin milk, when poured upon a black surface, appears
+bluish. The milk is colourless; that is, its blueness is not due to
+_absorption_, but to a _separation_ of the light by the particles
+suspended in the liquid. The juices of various plants owe their blueness
+to the same cause; but perhaps the most curious illustration is that
+presented by a blue eye. Here we have no true colouring matter, no
+proper absorption; but we look through a muddy medium at the black
+choroid coat within the eye, and the medium appears blue.[A]
+
+[Sidenote: COLOUR OF SWISS LAKES.]
+
+Is it not probable that this action of finely-divided matter may have
+some influence on the colour of some of the Swiss lakes--as that of
+Geneva for example? This lake is simply an expansion of the river Rhone,
+which rushes from the end of the Rhone glacier, as the Arveiron does
+from the end of the Mer de Glace. Numerous other streams join the Rhone
+right and left during its downward course; and these feeders, being
+almost wholly derived from glaciers, join the Rhone charged with the
+finer matter which these in their motion have ground from the rocks over
+which they have passed. But the glaciers must grind the mass beneath
+them to particles of all sizes, and I cannot help thinking that the
+finest of them must remain suspended in the lake throughout its entire
+length. Faraday has shown that a precipitate of gold may require months
+to sink to the bottom of a bottle not more than five inches high, and
+in all probability it would require _ages_ of calm subsidence to bring
+_all_ the particles which the Lake of Geneva contains to its bottom. It
+seems certainly worthy of examination whether such particles suspended
+in the water contribute to the production of that magnificent blue which
+has excited the admiration of all who have seen it under favourable
+circumstances.
+
+
+FOOTNOTES:
+
+[A] Helmholtz, 'Das Sehen des Menschen.'
+
+
+
+
+THE MORAINES.
+
+(8.)
+
+
+The surface of the glacier does not long retain the shining whiteness of
+the snow from which it is derived. It is flanked by mountains which are
+washed by rain, dislocated by frost, riven by lightning, traversed by
+avalanches, and swept by storms. The lighter debris is scattered by the
+winds far and wide over the glacier, sullying the purity of its surface.
+Loose shingle rattles at intervals down the sides of the mountains, and
+falls upon the ice where it touches the rocks. Large rocks are
+continually let loose, which come jumping from ledge to ledge, the
+cohesion of some being proof against the shocks which they experience;
+while others, when they hit the rocks, burst like bomb-shells, and
+shower their fragments upon the ice.
+
+[Sidenote: LATERAL MORAINES.]
+
+Thus the glacier is incessantly loaded along its borders with the ruins
+of the mountains which limit it; and it is evident that the quantity of
+rock and rubbish thus cast upon the glacier depends upon the character
+of the adjacent mountains. Where the summits are bare and friable, we
+may expect copious showers; where they are resistant, and particularly
+where they are protected by a covering of ice and snow, the quantity
+will be small. As the glacier moves downward, it carries with it the
+load deposited upon it. Long ridges of debris thus flank the glacier,
+and these ridges are called _lateral moraines_. Where two tributary
+glaciers join to form a trunk-glacier, their adjacent lateral moraines
+are laid side by side at the place of confluence, thus constituting a
+ridge which runs along the middle of the trunk-glacier, and which is
+called a _medial moraine_. The rocks and debris carried down by the
+glacier are finally deposited at its lower extremity, forming there a
+_terminal moraine_.
+
+[Sidenote: MEDIAL AND TERMINAL MORAINES.]
+
+It need hardly be stated that the number of medial moraines is only
+limited by the number of branch glaciers. If a glacier have but two
+branches, it will have only one medial moraine; if it have three
+branches, it will have two medial moraines; if _n_ branches, it will
+have _n_-1 medial moraines. The number of medial moraines, in short, is
+always _one less_ than the number of branches. A glance at the annexed
+figure will reveal the manner in which the lateral moraines of the Mer
+de Glace unite to form medial ones. (See Fig. 19.)
+
+[Illustration: MORAINES OF THE MER DE GLACE.
+Fig. 19. _To face p. 264_.]
+
+When a glacier diminishes in size it leaves its lateral moraines
+stranded on the flanks of the valleys. Successive shrinkings may thus
+occur, and _have_ occurred at intervals of centuries; and a succession
+of old lateral moraines, such as many glacier-valleys exhibit, is the
+consequence. The Mer de Glace, for example, has its old lateral
+moraines, which run parallel with its present ones. The glacier may also
+diminish _in length_ at distant intervals; the result being a succession
+of more or less concentric terminal moraines. In front of the
+Rhone-glacier we have six or seven such moraines, and the Mer de Glace
+also possesses a series of them.
+
+Let us now consider the effect produced by a block of stone upon the
+surface of a glacier. The ice around it receives the direct rays of the
+sun, and is acted on by the warm air; it is therefore constantly
+melting. The stone also receives the solar beams, is warmed, and
+transmits its heat, by conduction, to the ice beneath it. If the heat
+thus transmitted to the ice through the stone be less than an equal
+space of the surrounding ice receives, it is manifest that the ice
+around the stone will waste more quickly than that beneath it, and the
+consequence is, that, as the surface sinks, it leaves behind it a
+pillar of ice, on which the block is elevated. If the stone be wide and
+flat, it may rise to a considerable height, and in this position it
+constitutes what is called a glacier-_table_. (See Fig. 6.)
+
+[Sidenote: GLACIER TABLES ACCOUNTED FOR.]
+
+Almost all glaciers present examples of such tables; but no glacier with
+which I am acquainted exhibits them in greater number and perfection
+than the Unteraar glacier, near the Grimsel. Vast masses of granite are
+thus poised aloft on icy pedestals; but a limit is placed to their
+exaltation by the following circumstance. The sun plays obliquely upon
+the table all day; its southern extremity receives more heat than its
+northern, and the consequence is, that it _dips_ towards the south.
+Strictly speaking, the plane of the dip rotates a little during the day,
+being a little inclined towards the east in the morning, north and south
+a little after noon, and inclined towards the west in the evening; so
+that, theoretically speaking, the block is a sun-dial, showing by its
+position the hour of the day. This rotation is, however, too small to be
+sensible, and hence _the dip of the stones upon a glacier sufficiently
+exposed to the sunlight, enables us at any time to draw the meridian
+line along its surface_. The inclination finally becomes so great that
+the block slips off its pedestal, and begins to form another, while the
+one which it originally occupied speedily disappears, under the
+influence of sun and air. Fig. 20 represents a typical section of a
+glacier-table, the sun's rays being supposed to fall in the direction of
+the shading lines.
+
+[Sidenote: TYPE "TABLE."]
+
+[Illustration: Fig. 20. Typical section of a glacier Table.]
+
+Stones of a certain size are always lifted in the way described. A
+considerable portion of the heat which a large block receives is wasted
+by radiation, and by communication to the air, so that the quantity
+which reaches the ice beneath is trifling. Such a mass is, of course, a
+protector of the ice beneath it. But if the stone be small, and dark in
+colour, it absorbs the heat with avidity, communicates it quickly to
+the ice with which it is in contact, and consequently sinks in the ice.
+This is also the case with bits of dirt and the finer fragments of
+debris; they sink in the glacier. Sometimes, however, a pretty thick
+layer of sand is washed over the ice from the moraines, or from the
+mountain-sides; and such sand-layers give birth to ice-cones, which grow
+to peculiarly grand dimensions on the Lower Aar glacier. I say "grow,"
+but the truth, of course, is, that the surrounding ice wastes, while the
+portion underneath the sand is so protected that it remains as an
+eminence behind. At first sight, these sand-covered cones appear huge
+heaps of dirt, but on examination they are found to be cones of ice, and
+that the dirt constitutes merely a superficial covering.
+
+Turn we now to the moraines. Protecting, as they do, the ice from waste,
+they rise, as might be expected, in vast ridges above the general
+surface of the glacier. In some cases the surrounding mass has been so
+wasted as to leave the spines of ice which support the moraines forty or
+fifty feet above the general level of the glacier. I should think the
+moraines of the Mer de Glace about the Tacul rise to this height. But
+lower down, in the neighbourhood of the Echelets, these high ridges
+disappear, and nought remains to mark the huge moraine but a strip of
+dirt, and perhaps a slight longitudinal protuberance on the surface of
+the glacier. How have the blocks vanished that once loaded the moraines
+near the Tacul? They have been swallowed in the crevasses which
+intersect the moraines lower down; and if we could examine the ice at
+the Echelets we should find the engulfed rocks in the body of the
+glacier.
+
+[Sidenote: MORAINES ENGULFED AND DISGORGED.]
+
+Cases occur, wherein moraines, after having been engulfed, and hidden
+for a time, are again entirely disgorged by the glacier. Two moraines
+run along the basin of the Talefre, one from the Jardin, the other from
+an adjacent promontory, proceeding parallel to each other towards the
+summit of the great ice-fall. Here the ice is riven, and profound chasms
+are formed, in which the blocks and shingle of the moraines disappear.
+Throughout the entire ice-fall the only trace of the moraines is a broad
+dirt-streak, which the eye may follow along the centre of the fall, with
+perhaps here and there a stone which has managed to rise from its frozen
+sepulchre. But the ice wastes, and at the base of the fall large masses
+of stone begin to reappear; these become more numerous as we descend;
+the smaller debris also appears, and finally, at some distance below the
+fall, the moraine is completely restored, and begins to exercise its
+protecting influence; it rises upon its ridge of ice, and dominates as
+before over the surface of the glacier.
+
+[Sidenote: TRANSPARENCY OF ICE UNDER THE MORAINES.]
+
+The ice under the moraines and sand-cones is of a different appearance
+from that of the surrounding glacier, and the principles we have laid
+down enable us to explain the difference. The sun's rays, striking upon
+the unprotected surface of the glacier, enter the ice to a considerable
+depth; and the consequence is, that the ice near the surface of the
+glacier is always disintegrated, being cut up with minute fissures and
+cavities, filled with water and air, which, for reasons already
+assigned, cause the glacier, when it is clean, to appear white and
+opaque. The ice under the moraines, on the contrary, is usually dark and
+transparent; I have sometimes seen it as black as pitch, the blackness
+being a proof of its great transparency, which prevents the reflection
+of light from its interior.
+
+The ice under the moraines cannot be assailed in its depths by the solar
+heat, because this heat becomes _obscure_ before it reaches the ice, and
+as such it lacks the power of penetrating the substance. It is also
+communicated in great part by way of contact instead of by radiation. A
+thin film at the surface of the moraine-ice engages all the heat that
+acts upon it, its deeper portions remaining intact and transparent.
+
+
+
+
+GLACIER MOTION.
+
+PRELIMINARY.
+
+(9.)
+
+
+[Sidenote: NEVE AND GLACIER.]
+
+Though a glacier is really composed of two portions, one above and the
+other below the snow-line, the term glacier is usually restricted to the
+latter, while the French term _neve_ is applied to the former. It is
+manifest that the snow which falls upon the glacier proper can
+contribute nothing to its growth or permanence; for every summer is not
+only competent to abolish the accumulations of the foregoing winter, but
+to do a great deal more. During each summer indeed a considerable
+quantity of the ice below the snow-line is reduced to water; so that, if
+the waste were not in some way supplied, it is manifest that in a few
+years the lower portion of the glacier must entirely disappear. The end
+of the Mer de Glace, for example, could never year after year thrust
+itself into the valley of Chamouni, were there not some agency by which
+its manifest waste is made good. This agency is the motion of the
+glacier.
+
+To those unacquainted with the fact of their motion, but who have stood
+upon these vast accumulations of ice, and noticed their apparent fixity
+and rigidity, the assertion that a glacier moves must appear in the
+highest degree startling and incredible. They would naturally share the
+doubts of a certain professor of Tuebingen, who, after a visit to the
+glaciers of Switzerland, went home and wrote a book flatly denying the
+possibility of their motion. But reflection comes to the aid of sense,
+and qualifies first impressions. We ask ourselves how is the permanence
+of the glacier secured? How are the moraines to be accounted for?
+Whence come the blocks which we often find at the terminus of a glacier,
+and which we know belong to distant mountains? The necessity of motion
+to produce these results becomes more and more apparent, until at length
+we resort to actual experiment. We take two fixed points at opposite
+sides of the glacier, so that a block of stone which rests upon the ice
+may be in the straight line which unites the points; and we soon find
+that the block quits the line, and is borne downwards by the glacier. We
+may well realize the interest of the man who first engaged in this
+experiment, and the pleasure which he felt on finding that the block
+moved; for even now, after hundreds of observations on the motion of
+glaciers have been made, the actual observance of this motion for the
+first time is always accompanied by a thrill of delight. Such pleasure
+the direct perception of natural truth always imparts. Like Antaeus we
+touch our mother, and are refreshed by the contact.
+
+[Sidenote: HUGI'S MEASUREMENTS.]
+
+The fact of glacier-motion has been known for an indefinite time to the
+inhabitants of the mountains; but the first who made quantitative
+observations of the motion was Hugi. He found that from 1827 to 1830 his
+cabin upon the glacier of the Aar had moved 100 metres, or about 110
+yards, downwards; in 1836 it had moved 714 metres; and in 1841 M.
+Agassiz found it at a distance of 1,428 metres from its first position.
+This is equivalent in round numbers to an average velocity of 100 metres
+a year. In 1840 M. Agassiz fixed the position of the rock known as the
+Hotel des Neufchatelois; and on the 5th of September, 1841, he found
+that it had moved 213 feet downward. Between this date and September,
+1842, the rock moved 273 feet, thus accomplishing a distance of 486 feet
+in two years.
+
+But much uncertainty prevailed regarding the motion of the boulders, for
+they sometimes rolled upon the glacier, and hence it was resolved to
+use stakes of wood driven into the ice. In the month of July, 1841, M.
+Escher de la Linth fixed a system of stakes, every two of which were
+separated from each other by a distance of 100 metres, across the great
+Aletsch glacier. A considerable number of other stakes were fixed
+_along_ the glacier, the longitudinal separation being also 100 metres.
+On the 8th of July the stakes stood at a depth of about three feet in
+the ice. On the 16th of August he returned to the glacier. Almost all
+the stakes had fallen, and no trace, even of the holes in which they had
+been sunk, remained. M. Agassiz was equally unsuccessful on the glacier
+of the Aar. It must therefore be borne in mind, that, previous to the
+introduction of the facile modes of measurement which we now employ,
+severe labour and frequent disappointment had taught observers the true
+conditions of success.
+
+After his defeat upon the Aletsch, M. Escher joined MM. Agassiz and
+Desor on the Aar glacier, where, between the 31st of August and the 5th
+of September, they fixed in concert the positions of a series of blocks
+upon the ice, with the view of measuring their displacements the
+following year.
+
+[Sidenote: AGASSIZ'S MEASUREMENTS.]
+
+Another observation of great importance was also commenced in 1841.
+Warned by previous failures, M. Agassiz had iron boring-rods carried up
+the glacier, with which he pierced the ice at six places to a depth of
+ten feet, and at each place drove a wooden pile into the ice. These six
+stations were in the same straight line across the glacier; three of
+them standing upon the Finsteraar and three on the Lauteraar tributary.
+About this time also M. Agassiz conceived the idea of having the
+displacements measured the year following with precise instruments, and
+also of having constructed, by a professional engineer, a map of the
+entire glacier, on which all its visible "accidents" should be drawn
+according to scale. This excellent work was afterwards executed by M.
+Wild, now Professor of Geodesy and Topography in the Polytechnic School
+of Zuerich, and it is published as a separate atlas in connexion with M.
+Agassiz's 'Systeme Glaciaire.'
+
+[Sidenote: PROF. J. D. FORBES INVITED.]
+
+M. Agassiz is a naturalist, and he appears to have devoted but little
+attention to the study of physics. At all events, the physical portions
+of his writings appear to me to be very often defective. It was probably
+his own consciousness of this deficiency that led him to invoke the
+advice of Arago and others previous to setting out upon his excursions.
+It was also his desire "to see a philosopher so justly celebrated occupy
+himself with the subject," which induced him to invite Prof. J. D.
+Forbes of Edinburgh to be his guest upon the Aar glacier in 1841. On the
+8th of August they met at the Grimsel Hospice, and for three weeks
+afterwards they were engaged together daily upon the ice, sharing at
+night the shelter of the same rude roof. It is in reference to this
+visit that Prof. Forbes writes thus at page 38 of the 'Travels in the
+Alps':--"Far from being ready to admit, as my sanguine companions wished
+me to do in 1841, that the theory of glaciers was complete, and the
+cause of their motion certain, after patiently hearing all they had to
+say and reserving my opinion, I drew the conclusion that no theory which
+I had then heard of could account for the few facts admitted on all
+hands." In 1842 Prof. Forbes repaired, as early as the state of the snow
+permitted, to the Mer de Glace; he worked there, in the first instance,
+for a week, and afterwards crossed over to Courmayeur to witness a solar
+eclipse. The result of his week's observations was immediately
+communicated to Prof. Jameson, then editor of the 'Edinburgh New
+Philosophical Journal.'
+
+[Sidenote: CENTRE MOVES QUICKEST.]
+
+In that letter he announces the fact, but gives no details of the
+measurement, that "the central part of the glacier moves faster than the
+edges in a very considerable proportion; quite contrary to the opinion
+generally entertained." He also announced at the same time the
+continuous hourly advance of the glacier. This letter bears the date,
+"Courmayeur, Piedmont, 4th July," but it was not published until the
+month of October following.
+
+Meanwhile M. Agassiz, in company with M. Wild, returned to complete his
+experiment upon the glacier of the Aar. On the 20th of July, 1842, the
+displacements of the six piles which he had planted the year before were
+determined by means of a theodolite. Of the three upon the Finsteraar
+affluent, that nearest the side had moved 160 feet, the next 225 feet,
+while that nearest to the centre had moved 269 feet. Of those on the
+Lauteraar, that nearest the side had moved 125 feet, the next 210 feet,
+and that nearest the centre 246 feet. These observations were perfectly
+conclusive as to the quicker motion of the centre: they embrace a year's
+motion; and the magnitude of the displacements, causing errors of
+inches, which might seriously affect small displacements, to vanish,
+justifies us in ranking this experiment with the most satisfactory of
+the kind that have ever been made. The results were communicated to
+Arago in a letter dated from the glacier of the Aar, on the 1st of
+August, 1842; they were laid before the Academy of Sciences on the 29th
+of August, 1842, and are published in the 'Comptes Rendus' of the same
+date.
+
+The facts, then, so far as I have been able to collect them, are as
+follows:--M. Agassiz commenced his experiment about ten months before
+Professor Forbes, and the results of his measurements, with quantities
+stated, were communicated to the French Academy about two months prior
+to the publication of the letter of Professor Forbes in the 'Edinburgh
+Philosophical Journal.' But the latter communication, announcing in
+general terms the fact of the speedier central motion, was dated from
+Courmayeur twenty-seven days before the date of M. Agassiz's letter
+from the glacier of the Aar.
+
+[Sidenote: STATE OF THE QUESTION.]
+
+The speedier motion of the central portion of a glacier has been justly
+regarded as one of cardinal importance, and no other observation has
+been the subject of such frequent reference; but the general impression
+in England is that M. Agassiz had neither part nor lot in the
+establishment of the above fact; and in no English work with which I am
+acquainted can I find any reference to the above measurements. Relying
+indeed upon such sources for my information, I remained ignorant of the
+existence of the paper in the 'Comptes Rendus' until my attention was
+directed to it by Professor Wheatstone. In the next following chapters I
+shall have to state the results of some of my own measurements, and
+shall afterwards devote a little time to the consideration of the cause
+of glacier-motion. In treating a question on which so much has been
+written, it is of course impossible, as it would be undesirable, to
+avoid subjecting both my own views and those of others to a critical
+examination. But in so doing I hope that no expression shall escape me
+inconsistent with the courtesy which ought to be habitual among
+philosophers or with the frank recognition of the just claims of my
+predecessors.
+
+
+
+
+MOTION OF THE MER DE GLACE.
+
+(10.)
+
+
+[Sidenote: MY FIRST OBSERVATION.]
+
+On Tuesday, the 14th of July, 1857, I made my first observation on the
+motion of the Mer de Glace. Accompanied by Mr. Hirst I selected on the
+steep slope of the Glacier des Bois a straight pinnacle of ice, the
+front edge of which was perfectly vertical. In coincidence with this
+edge I fixed the vertical fibre of the theodolite, and permitted the
+instrument to stand for three hours. On looking through it at the end of
+this interval, the cross hairs were found projected against the white
+side of the pyramid; the whole mass having moved several inches
+downwards.
+
+The instrument here mentioned, which had long been in use among
+engineers and surveyors, was first applied to measure glacier-motion in
+1842; by Prof. Forbes on the Mer de Glace, and by M. Agassiz on the
+glacier of the Aar. The portion of the theodolite made use of is easily
+understood. The instrument is furnished with a telescope capable of
+turning up and down upon a pivot, without the slightest deviation right
+or left; and also capable of turning right or left without the slightest
+deviation up or down. Within the telescope two pieces of spider's
+thread, so fine as to be scarcely visible to the naked eye, are drawn
+across the tube and across each other. When we look through the
+telescope we see these fibres, their point of intersection being exactly
+in the centre of the tube; and the instrument is furnished with screws
+by means of which this point can be fixed upon any desired object with
+the utmost precision.
+
+[Sidenote: MODE OF MEASUREMENT.]
+
+In setting a straight row of stakes across the glacier, our mode of
+proceeding was in all cases this:--The theodolite was placed on the
+mountain-side flanking the glacier, quite clear of the ice; and having
+determined the direction of a line perpendicular to the axis of the
+glacier, a well-defined object was sought at the opposite side of the
+valley as close as possible to this direction; the object being, in some
+cases, the sharp edge of a cliff; in others, a projecting corner of
+rock; and, in others, a well-defined mark on the face of the rock. This
+object and those around it were carefully sketched, so that on returning
+to the place it could be instantly recognized. On commencing a line the
+point of intersection of the two spiders' threads within the telescope
+was first fixed accurately upon the point thus chosen, and an assistant
+carrying a straight baton was sent upon the ice. By rough signalling he
+first stood near the place where the first stake was to be driven in;
+and the object end of the telescope was then lowered until he came
+within the field of view. He held his staff upright upon the ice, and,
+in obedience to signals, moved upwards or downwards until the point of
+intersection of the spiders-threads exactly hit the bottom of the baton;
+a concerted signal was then made, the ice was pierced with an auger to a
+depth of about sixteen inches, and a stake about two feet long was
+firmly driven into it. The assistant then advanced for some distance
+across the glacier; the end of the telescope was now gently raised until
+he and his upright staff again appeared in the field of view. He then
+moved as before until the bottom of his staff was struck by the point of
+intersection, and here a second stake was fixed in the ice. In this way
+the process was continued until the line of stakes was completed.
+
+Before quitting the station, a plummet was suspended from a hook
+directly underneath the centre of the theodolite, and the place where
+the point touched the ground was distinctly marked. To measure the
+motion of the line of stakes, we returned to the place a day or two
+afterwards, and by means of the plummet were able to make the theodolite
+occupy the exact position which it occupied when the line was set out.
+The telescope being directed upon the point at the opposite side of the
+valley, and gradually lowered, it was found that no single stake along
+the line preserved its first position: they had all shifted downwards.
+The assistant was sent to the first stake; the point which it had first
+occupied was again determined, and its present distance from that point
+accurately measured. The same thing was done in the case of each stake,
+and thus the displacement of the whole row of stakes was ascertained.[A]
+The time at which the stake was fixed, and at which its displacement was
+measured, being carefully noted, a simple calculation determined _the
+daily motion_ of the stake.
+
+[Sidenote: THE FIRST LINE.]
+
+Thus, on the 17th of July, 1857, we set out our first line across the
+Mer de Glace, at some distance below the Montanvert; on the day
+following we measured the progress of the stakes. The observed
+displacements are set down in the following table:--
+
+First Line.--Daily Motion.
+
+ No. of stake. Inches.
+ West 1 moved 12-1/4
+ 2 " 16-3/4
+ 3 " 22-1/2
+ 4 " ...
+ 5 " 24-1/2
+ 6 moved ...
+ 7 " 26-1/4
+ 8 " ...
+ 9 " 28-3/4
+ 10 " 35-1/2 East.
+
+[Sidenote: THE CENTRE-POINT NOT THE QUICKEST.]
+
+The theodolite in this case stood on the Montanvert side of the valley,
+and the stakes are numbered from this side. We see that the motion
+gradually augments from the 1st stake onward--the 1st stake being held
+back by the friction of the ice against the flanking mountain-side. The
+stakes 4, 6, and 8 have no motion attached to them, as an accident
+rendered the measurement of their displacements uncertain. But one
+remarkable fact is exhibited by this line; the 7th stake stood upon the
+_middle_ of the glacier, and we see that its motion is by no means the
+quickest; it is exceeded in this respect by the stakes 9 and 10.
+
+The portion of the glacier on which the 10th stake stood was very much
+cut up by crevasses, and, while the assistant was boring it with his
+auger, the ice beneath him was observed, through the telescope, to slide
+suddenly forward for about 4 inches. The other stakes retained their
+positions, so that the movement was purely local. Deducting the 4 inches
+thus irregularly obtained, we should have a daily motion of 31-1/2
+inches for stake No. 10. The place was watched for some time, but the
+slipping was not repeated; and a second measurement on the succeeding
+day made the motion of the 10th stake 32 inches, whilst that of the
+centre of the glacier was only 27.
+
+Here, then, was a fact which needed explanation; but, before attempting
+this, I resolved, by repeated measurements in the same locality, to
+place the existence of the fact beyond doubt. We therefore ascended to a
+point upon the old and now motionless moraine, a little above the
+Montanvert Hotel; and choosing, as before, a well-defined object at the
+opposite side of the valley, we set between it and the theodolite a row
+of twenty stakes across the glacier. Their motions, measured on a
+subsequent day, and reduced to their daily rate, gave the results set
+down in the following table:--
+
+Second Line.--Daily Motion.
+
+ No. of stake. Inches.
+ West 1 moved 7-1/2
+ 2 " 10-3/4
+ 3 " 12-1/4
+ 4 " 14-1/2
+ 5 " 16
+ 6 " 16-3/4
+ 7 " 17-1/2
+ 8 " 19
+ 9 " 19-1/2
+ 10 " 21
+ 11 moved 21
+ 12 " 22-1/2
+ 13 " 21
+ 14 " 22-1/2
+ 15 " 20-1/2
+ 16 " 21-3/4
+ 17 " 22-1/4
+ 18 " 25-1/4
+ 19 " ...
+ 20 " 25-3/4 East.
+
+[Sidenote: CORROBORATIVE MEASUREMENTS.]
+
+As regards the retardation of the side, we observe here the same fact as
+that revealed by our first line--the motion gradually augments from the
+first stake to the last. The stake No. 20 stood upon the dirty portion
+of the ice, which was derived from the Talefre tributary of the Mer de
+Glace, and far beyond the middle of the glacier. These measurements,
+therefore, corroborate that made lower down, as regards the
+non-coincidence of the point of swiftest motion with the centre of the
+glacier.
+
+But it will be observed that the measurements do not show any
+retardation of the ice at the eastern extremity of the line of
+stakes--the motion goes on augmenting from the first stake to the last.
+The reason of this is, that in neither of the cases recorded were we
+able to get the line quite across the glacier; the crevasses and broken
+ice-ridges, which intercepted the vision, compelled us to halt before we
+came sufficiently close to the eastern side to make its retardation
+sensible. But on the 20th of July my friend Hirst sought out an elevated
+station on the Chapeau, or eastern side of the valley, whence he could
+command a view from side to side over all the humps and inequalities of
+the ice, the fixed point at the opposite side, upon which the telescope
+was directed, being the corner of a window of the Montanvert Hotel.
+Along this line were placed twelve stakes, the daily motions of which
+were found to be as follows:--
+
+Third Line.--Daily Motion.
+
+ No. of stake. Inches.
+ East 1 moved 19-1/2
+ 2 " 22-3/4
+ 3 " 28-3/4
+ 4 " 30-1/4
+ 5 " 33-3/4
+ 6 " 28-1/4
+ 7 moved 24-1/2
+ 8 " 25
+ 9 " 25
+ 10 " 18
+ 11 " ...
+ 12 " 8-1/2 West.
+
+The numbering of the stakes along this line commenced from the
+Chapeau-side of the glacier, and the retardation of that side is now
+manifest enough; the motion gradually augmenting from 19-1/2 to 33-1/2
+inches. But, comparing the velocity of the two extreme stakes, we find
+that the retardation of stake 12 is much greater than that of stake 1.
+Stake 5, moreover, which moved with the _maximum_ velocity, was not upon
+the centre of the glacier, but much nearer to the eastern than to the
+western side.
+
+[Sidenote: A NEW PECULIARITY OF GLACIER MOTION.]
+
+It was thus placed beyond doubt that the point of maximum motion of the
+Mer de Glace, at the place referred to, is not the centre of the
+glacier. But, to make assurance doubly sure, I examined the comparative
+motion along three other lines, and found in all the same undeviating
+result.
+
+This result is not only unexpected, but is quite at variance with the
+opinions hitherto held regarding the motion of the Mer de Glace. The
+reader knows that the trunk-stream is composed of three great
+tributaries from the Geant, the Lechaud, and the Talefre. The Glacier du
+Geant fills more than half of the trunk-valley, and the junction between
+it and its neighbours is plainly marked by the dirt upon the surface of
+the latter. In fact four medial moraines are crowded together on the
+eastern side of the glacier, and before reaching the Montanvert they
+have strewn their debris quite over the adjacent ice. A distinct limit
+is thus formed between the clean Glacier du Geant and the other dirty
+tributaries of the trunk-stream.
+
+Now the eastern side of the Mer de Glace is observed on the whole to be
+much more fiercely torn than the western side, and this excessive
+crevassing has been referred to _the swifter motion of the Glacier du
+Geant_. It has been thought that, like a powerful river, this glacier
+drags its more sluggish neighbours after it, and thus tears them in the
+manner observed. But the measurement of the foregoing three lines shows
+that this cannot be the true cause of the crevassing. In each case the
+stakes which moved quickest _lay upon the dirty portion of the
+trunk-stream_, far to the east of the line of junction of the Glacier du
+Geant, which in fact moved slowest of all.
+
+[Sidenote: LAW OF MOTION SOUGHT.]
+
+The general view of the glacier, and of the shape of the valley which it
+filled, suggested to me that the analogy with a river might perhaps make
+itself good beyond the limits hitherto contemplated. The valley was not
+straight, but sinuous. At the Montanvert the convex side of the glacier
+was turned eastward; at some distance higher up, near the passages
+called _Les Ponts_, it was turned westward; and higher up again it was
+turned once more, for a long stretch, eastward. Thus between Trelaporte
+and the Ponts we had what is called a point of contrary flexure, and
+between the Ponts and the Montanvert a second point of the same kind.
+
+[Sidenote: CONJECTURE REGARDING CHANGE OF FLEXURE.]
+
+Supposing a river, instead of the glacier, to sweep through this valley;
+_its_ point of maximum motion would not always remain central, but would
+deviate towards that side of the valley to which the river turned its
+convex boundary. Indeed the positions of towns along the banks of a
+navigable river are mainly determined by this circumstance. They are,
+in most cases, situate on the convex sides of the bends, where the rush
+of the water prevents silting up. Can it be then that the ice exhibits a
+similar deportment? that the same principle which regulates the
+distribution of people along the banks of the Thames is also acting with
+silent energy amid the glaciers of the Alps? If this be the case, the
+position of the point of maximum motion ought, of course, to shift with
+the bending of the glacier. Opposite the Ponts, for example, the point
+ought to be on the Glacier du Geant, and westward of the centre of the
+trunk-stream; while, higher up, we ought to have another change to the
+eastern side, in accordance with the change of flexure.
+
+On the 25th of July a line was set out across the glacier, one of its
+fixed termini being a mark upon the first of the three Ponts. The motion
+of this line, measured on a subsequent day, and reduced to its daily
+rate, was found to be as follows:--
+
+Fourth Line.--Daily Motion.
+
+ No. of stake. Inches.
+ East 1 moved 6-1/2
+ 2 " 8
+ 3 " 12-1/2
+ 4 " 15-1/4
+ 5 " 15-1/2
+ 6 " 18-3/4
+ 7 " 18-1/4
+ 8 " 18-3/4
+ 9 " 19-1/2
+ 10 moved 21
+ 11 " 20-1/2
+ 12 " 23-1/4
+ 13 " 23-1/4
+ 14 " 21
+ 15 " 22-1/4
+ 16 " 17-1/4
+ 17 " 15 West.
+
+This line, like the third, was set out and numbered from the eastern
+side of the glacier, the theodolite occupying a position on the heights
+of the Echelets. A moment's inspection of the table reveals a fact
+different from that observed on the third line; _there_ the most
+easterly stake moved with more than twice the velocity of the most
+westerly one; _here_, on the contrary, the most westerly stake moves
+with more than twice the velocity of the most easterly one.
+
+To enable me to compare the motion of the eastern and western halves of
+the glacier with greater strictness, my able and laborious companion
+undertook the task of measuring with a surveyor's chain the line just
+referred to; noting the pickets which had been fixed along the line, and
+the other remarkable objects which it intersected. The difficulty of
+thus directing a chain over crevasses and ridges can hardly be
+appreciated except by those who have tried it. Nevertheless, the task
+was accomplished, and the width of the Mer de Glace, at this portion of
+its course, was found to be 863 yards, or almost exactly half a mile.
+
+Referring to the last table, it will be seen that the two stakes
+numbered 12 and 13 moved with a common velocity of 23-1/4 inches per
+day, and that their motion is swifter than that of any of the others.
+The point of swiftest motion may be taken midway between them, and this
+point was found by measurement to lie 233 yards _west_ of the dirt which
+marked the junction of the Glacier du Geant with its fellow tributaries:
+whereas, in the former cases, it lay a considerable distance _east_ of
+this limit. Its distance from the eastern side of the glacier was 601
+yards, and from the western side 262 yards, being 170 yards west of the
+centre of the glacier.
+
+[Sidenote: CONJECTURE TESTED.]
+
+But the measurements enabled me to take the stakes in pairs, and to
+compare the velocity of a number of them which stood at certain
+distances from the eastern side of the valley, with an equal number
+which stood at the same distances from the western side. By thus
+arranging the points two by two, I was able to compare the motion of the
+entire body of the ice at the one side of the central line with that of
+the ice at the other side. Stake 17 stood about as far from the western
+side of the glacier as stake 3 did from its eastern side; 16 occupied
+the same relation to 4; 15, to 5; 13, to 7; and 12, to 9.
+
+Calling each pair of points which thus stand at equal distances from the
+opposite sides _corresponding points_, the following little table
+exhibits their comparative motions:--
+
+Numbers and Velocities of Corresponding Points on the Fourth Line.
+
+ No. Vel. No. Vel. No. Vel. No. Vel. No. Vel.
+ West 17 15 16 17-1/4 15 22-1/4 13 23-1/4 12 23-1/4
+ East 3 12-1/2 4 15-1/4 5 15-1/2 7 18-1/4 9 19-1/2
+
+[Sidenote: WESTERN HALF MOVES QUICKEST.]
+
+The table explains itself. We see that while stake 17, which stands
+_west_ of the centre, moves 15 inches, stake 3, which stands an equal
+distance _east_ of the centre, moves only 12-1/2 inches. Comparing every
+pair of the other points, we find the same to hold good; the western
+stake moves in each case faster than the corresponding eastern one.
+Hence, _the entire western half of the Mer de Glace, at the place
+crossed by our fourth line, moves more quickly than the eastern half of
+the glacier_.
+
+We next proceeded farther up, and tested the contrary curvature of the
+glacier, opposite to Trelaporte. The station chosen for this purpose was
+on a grassy platform of the promontory, whence, on the 28th of July, a
+row of stakes was fixed at right angles to the axis of the glacier.
+Their motions, measured on the 31st, gave the following results:--
+
+Fifth Line.[B]--Daily Motion.
+
+ No. of stake. Inches.
+ West 1 moved 11-1/4
+ 2 " 13-1/2
+ 3 " 12-3/4
+ 4 " 15
+ 5 " 15-1/4
+ 6 " 16
+ 7 " 17-1/4
+ 8 " 19-1/4
+ 9 moved 19-3/4
+ 10 " 19
+ 11 " 19-1/2
+ 12 " 17-1/2
+ 13 " 16
+ 14 " 14-3/4
+ 15 " 10 East.
+
+This line was set out and numbered from the Trelaporte side of the
+valley, and was also measured by Mr. Hirst, over boulders, ice-ridges,
+chasms, and moraines. The entire width of the glacier here was found to
+be 893 yards, or somewhat wider than it is at the Ponts. It will also be
+observed that its motion is somewhat slower.
+
+An inspection of the notes of this line showed me that stakes 3 and 14,
+4 and 12, 7 and 10, were "corresponding points;" the first of each pair
+standing as far from the western side, as the second stood from the
+eastern. In the following table these points and their velocities are
+arranged exactly as in the case of the fourth line.
+
+Numbers and Velocities of the Corresponding Points on the Fifth Line.
+
+ No. Vel. No. Vel. No. Vel.
+ West 3 12-3/4 4 15 7 17-1/4
+ East 14 14-3/4 12 17-1/2 10 19
+
+[Sidenote: EASTERN HALF MOVES QUICKEST.]
+
+In each case we find that the stake on the eastern side moves more
+quickly than the corresponding one upon the western side: so that where
+the fifth line crosses the glacier _the eastern half of the Mer de Glace
+moves more quickly than the western half_. This is the reverse of the
+result obtained at our fourth line, but it agrees with that obtained on
+our first three lines, where the curvature of the valley is similar. The
+analogy between a river and a glacier moving through a sinuous valley is
+therefore complete.
+
+Supposing the points of maximum motion to be determined for a great
+number of lines across the glacier, the line uniting all these points is
+what mathematicians would call the _locus_ of the point of maximum
+motion. At Trelaporte this line would lie east of the centre; at the
+Ponts it would lie west of the centre; hence, in passing from Trelaporte
+to the Ponts, it must cross the axis of the glacier. Again, at the
+Montanvert, it would lie east of the centre, and between the Ponts and
+the Montanvert the axis of the glacier would be crossed a second time.
+Supposing the dotted line in Fig. 21 to represent the middle line of the
+glacier, then the defined line would represent the locus of the point of
+maximum motion. _It is a curve more deeply sinuous than the valley
+itself, and it crosses the axis of the glacier at each point of contrary
+flexure._
+
+[Sidenote: LOCUS OF POINT OF SWIFTEST MOTION.]
+
+[Illustration: Fig. 21. Locus of the Point of Maximum Motion.]
+
+To complete our knowledge of the motion of the Mer de Glace, we
+afterwards determined the velocity of its two accessible
+tributaries--the Glacier du Geant, and the Glacier de Lechaud. On the
+29th of July, a line of stakes was set out across the former, a little
+above the Tacul, and their motion was subsequently found to be as
+follows:
+
+Sixth Line.--Daily Motion.
+
+ No. of stake. Inches.
+ 1 moved 11
+ 2 " 10
+ 3 " 12
+ 4 " 13
+ 5 " 12
+ 6 moved 12-3/4
+ 7 " 10-1/2
+ 8 " 10
+ 9 " 9
+ 10 " 5
+
+The width of the glacier at this place we found to be 1134 yards, and
+its maximum velocity, as shown by the foregoing table, 13 inches a day.
+
+On the 1st of August a line was set out across the Glacier de Lechaud,
+above its junction with the Talefre: it commenced beneath the block of
+stone known as the Pierre de Beranger. The displacements of the stakes,
+measured on the 3rd of August, gave the following results:--
+
+Seventh Line.--Daily Motion.
+
+ No. of stake. Inches.
+ 1 moved 4-1/2
+ 2 " 8-1/4
+ 3 " 9-1/2
+ 4 " 9
+ 5 " 8-1/2
+ 6 moved 7-1/2
+ 7 " 6-1/4
+ 8 " 8-1/2
+ 9 " 7
+ 10 " 5-1/2
+
+The width of the Glacier de Lechaud at this place was found to be 825
+yards; its maximum motion, as shown by the table, being 9-1/2 inches a
+day. This is the slowest rate which we observed upon either the Mer de
+Glace or its tributaries. The width of the Talefre-branch, as it
+descends the cascade, or, in other words, before it is influenced by the
+pressure of the Lechaud, was found approximately to be 638 yards.
+
+[Sidenote: SQUEEZING AT TRELAPORTE.]
+
+The widths of the tributaries were determined for the purpose of
+ascertaining the amount of lateral compression endured by the ice in its
+passage through the neck of the valley at Trelaporte. Adding all
+together we have--
+
+ Geant 1134 yards.
+ Lechaud 825 "
+ Talefre 638 "
+ Total 2597 yards.
+
+These three branches, as shown by the actual measurement of our 5th
+line, are forced at Trelaporte through a channel 893 yards wide; the
+width of the trunk stream is a little better than one-third of that of
+its tributaries, and it passes through this gorge at a velocity of
+nearly 20 inches a day.
+
+[Sidenote: THE LECHAUD A DRIBLET.]
+
+Limiting our view to one of the tributaries only, the result is still
+more impressive. Previous to its junction with the Talefre, the Glacier
+de Lechaud stretches before the observer as a broad river of ice,
+measuring 825 yards across: at Trelaporte it is squeezed, in a frozen
+vice, between the Talefre on one side and the Geant on the other, to a
+driblet, measuring 85 yards in width, or about one-tenth of its former
+transverse dimension. It will of course be understood that it is the
+_form_ and not the _volume_ of the glacier that is affected to this
+enormous extent by the pressure.
+
+Supposing no waste took place, the Glacier de Lechaud would force
+precisely the same amount of ice through the "narrows" at Trelaporte, in
+one day, as it sends past the Pierre de Beranger. At the latter place
+its velocity is about half of what it is at the former, but its width is
+more than nine times as great. Hence, if no waste took place, its
+_depth_, at Trelaporte, would be at _least_ 4-1/2 times its depth
+opposite the Pierre de Beranger. Superficial and subglacial melting
+greatly modify this result. Still I think it extremely probable that
+observations directed to this end would prove the comparative
+shallowness of the upper portions of the Glacier de Lechaud.
+
+
+FOOTNOTES:
+
+[A] Great care is necessary on the part of the man who measures the
+displacements. The staff ought to be placed along the original line, and
+the assistant ought to walk along it until the foot of a _perpendicular_
+from the stake is attained. When several days' motion is to be measured,
+this precaution is absolutely necessary; the eye being liable to be
+grossly deceived in _guessing_ the direction of a perpendicular.
+
+[B] The details of the measurement of the fourth and fifth lines are
+published in the 'Philosophical Transactions,' vol. cxlix., p. 261.
+
+
+
+
+ICE-WALL AT THE TACUL.
+
+VELOCITIES OF TOP AND BOTTOM.
+
+(11.)
+
+
+As regards the motion of the _surface_ of a glacier, two laws are to be
+borne in mind: 1st, that regarding the quicker movement of the centre;
+2nd, that regarding the locus of the point of maximum motion. Our next
+care must be to compare the motion of the surface of a glacier with the
+motion of those parts which lie near its bed. Rendu first surmised that
+the bottom of the glacier was retarded by friction, and both Professor
+Forbes[A] and M. Martins[B] have confirmed the conjecture. Theirs are
+the only observations which we possess upon the subject; and I was
+particularly desirous to instruct myself upon this important head by
+measurements of my own.
+
+[Sidenote: FIRST ATTEMPT AT MEASUREMENT.]
+
+During the summer of 1857 the eastern side of the Glacier du Geant, near
+the Tacul, exposed a nearly vertical precipice of ice, measuring 140
+feet from top to bottom. I requested Mr. Hirst to fix two stakes in the
+same vertical plane, one at the top of the precipice and one near the
+bottom. This he did upon the 3rd of August, and on the 5th I accompanied
+him to measure the progress of the stakes. On the summit of the
+precipice, and running along it, was the lateral moraine of the glacier.
+The day was warm and the ice liquefying rapidly, so that the boulders
+and debris, deprived incessantly of their support, came in frequent
+leaps and rushes down the precipice. Into this peril my guide was about
+to enter, to measure the displacement of the lower stake, while I was
+to watch, and call out the direction in which he was to run when a stone
+gave way. But I soon found that the initial motion was no sure index of
+the final motion. By striking the precipice, the stones were often
+deflected, and carried wide of their original direction. I therefore
+stopped the man, and sent him to the summit of the precipice to remove
+all the more dangerous blocks. This accomplished, he descended, and
+while I stood beside him, executed the required measurement. From the
+3rd to the 5th of August the upper stake had moved twelve inches, and
+the lower one six.
+
+Unfortunately some uncertainty attached itself to this result, due to
+the difficulty of fixing the lower stake. The guide's attention had been
+divided between his work and his safety, and he had to retreat more than
+a dozen times from the falling boulders and debris. I, on the other
+hand, was unwilling to accept an observation of such importance with a
+shade of doubt attached to it. Hence arose the desire to measure the
+motion myself. On the 11th of August I therefore reascended to the
+Tacul, and fixed a stake at the top of the precipice, and another at the
+bottom. While sitting on the old moraine looking at the two pickets, the
+importance of determining the motion of a point midway between the top
+and bottom forcibly occurred to me, but, on mentioning it to my guide,
+he promptly pronounced any attempt of the kind absurd.
+
+[Sidenote: STAKES FIXED AT TOP, BOTTOM, AND CENTRE.]
+
+On scanning the place carefully, however, the value of the observation
+appeared to me to outweigh the amount of danger. I therefore took my
+axe, placed a stake and an auger against my breast, buttoned my coat
+upon them, and cut an oblique staircase up the wall of ice, until I
+reached a height of forty feet from the bottom. Here the position of the
+stake being determined by Mr. Hirst, who was at the theodolite, I
+pierced the ice with the auger, drove in the stake, and descended
+without injury. During the whole operation however my guide growled
+audibly.
+
+On the following morning we commenced the ascent of Mont Blanc, a
+narrative of which is given in Part I. We calculated on an absence of
+three days, and estimated that the stakes which had just been fixed
+would be ready for measurement on our return; but we did not reach
+Chamouni until the afternoon of Friday, the 14th. Heavy clouds settled,
+during our descent, upon the summits behind us, and a thunder-peal from
+the Aiguilles soon heralded a fall of rain, which continued without
+intermission till the afternoon of the 16th, when the atmosphere
+cleared, and showed the mountains clothed to their girdles with snow.
+The Montanvert was thickly covered, and on our way to it we met the
+servants in charge of the cattle, which had been driven below the
+snow-line to obtain food.
+
+[Sidenote: THROUGH GLOOM TO THE TACUL.]
+
+On Monday morning, the 17th, a dense fog filled the valley of the Mer de
+Glace. I watched it anxiously. The stakes which we had set at the Tacul
+had been often in my thoughts, and I wished to make some effort to save
+the labour and peril incurred in setting them from being lost. I
+therefore set out, in one of the clear intervals, accompanied by my
+friend and Simond, determined to measure the motion of the stakes, if
+possible, or to fix them more firmly, if they still stood. As we passed,
+however, from l'Angle to the glacier, the fog became so dense and
+blinding that we halted. At my request Mr. Hirst returned to the
+Montanvert; and Simond, leaving the theodolite in the shelter of a rock,
+accompanied me through the obscurity to the Tacul. We found the topmost
+stake still stuck by its point in the ice; but the two others had
+disappeared, and we afterwards discovered their fragments in a
+snow-buttress, which reared itself against the base of the precipice.
+They had been hit by the falling stones, and crushed to pieces. Having
+thus learned the worst, we descended to the Montanvert amid drenching
+rain.
+
+[Sidenote: DESCENT OF BOULDERS.]
+
+On the morning of the 18th there was no cloud to be seen anywhere, and
+the sunlight glistened brightly on the surface of the ice. We ascended
+to the Tacul. The spontaneous falling of the stones appeared more
+frequent this morning than I had ever seen it. The sun shone with
+unmitigated power upon the ice, producing copious liquefaction. The
+rustle of falling debris was incessant, and at frequent intervals the
+boulders leaped down the precipice, and rattled with startling energy
+amid the rocks at its base. I sent Simond to the top to remove the
+looser stones; he soon appeared, and urged the moraine-shingle in
+showers down the precipice, upon a bevelled slope of which some blocks
+long continued to rest. They were out of the reach of the guide's baton,
+and he sought to dislodge them by sending other stones down upon them.
+Some of them soon gave way, drawing a train of smaller shingle after
+them; others required to be hit many times before they yielded, and
+others refused to be dislodged at all. I then cut my way up the
+precipice in the manner already described, fixed the stake, and
+descended as speedily as possible. We afterwards fixed the bottom stake,
+and on the 20th the displacements of all three were measured.[C] The
+spaces passed over by the respective stakes in 24 hours were found to be
+as follows:--
+
+ Inches.
+ Top stake 6.00
+ Middle stake 4.50
+ Bottom stake 2.56
+
+[Sidenote: MOTION OF STAKES.]
+
+The height of the precipice was 140.8 feet, but it sloped off at its
+upper portion. The height of the middle stake above the ground was 35
+feet, and of the bottom one 4 feet. It is therefore proved by these
+measurements that the bottom of the ice-wall at the Tacul moves with
+less than half the velocity of the top; while the displacement of the
+intermediate stake shows how the velocity gradually increases from the
+bottom upwards.
+
+
+FOOTNOTES:
+
+[A] 'Edinb. Phil. Journ.,' Oct. 1846, p. 417.
+
+[B] Agassiz, 'Systeme Glaciaire,' p. 522.
+
+[C] On this latter occasion my guide volunteered to cut the steps for me
+up to the pickets; and I permitted him to do so. In fact, he was at
+least as anxious as myself to see the measurement carried out.
+
+
+
+
+WINTER MOTION OF THE MER DE GLACE.
+
+(12.)
+
+
+The winter measurements were executed in the manner already described,
+on the 28th and 29th of December, 1859. The theodolite was placed on the
+mountain's side flanking the glacier, and a well-defined object was
+chosen at the opposite side of the valley, so that a straight line
+between this object and the theodolite was approximately perpendicular
+to the axis of the glacier. Fixing the telescope in the first instance
+with its cross hairs upon the object, its end was lowered until it
+struck the point upon the glacier at which a stake was to be fixed.
+Thanks to the intelligence of my assistants, after the fixing of the
+first stake they speedily took up the line at all other points,
+requiring very little correction to make their positions perfectly
+accurate. On the day following that on which the stakes were driven in,
+the theodolite was placed in the same position, and the distances to
+which the stakes had moved from their original positions were accurately
+determined. As already stated, the first line crossed the glacier about
+80 yards above the Montanvert Hotel.
+
+[Sidenote: HALF OF SUMMER MOTION.]
+
+Line No. I.--Winter Motion in Twenty-four Hours.
+
+ No. of stake. Inches.
+ West 1 7-1/4
+ 2 11
+ 3 13-1/2
+ 4 13
+ 5 13-3/4
+ 6 14-1/4
+ 7 15-3/4
+ 8 15-3/4
+ 9 12-1/4
+ 10 12
+ 11 6-1/2 East.
+
+[Sidenote: THE SAME LAW IN SUMMER AND WINTER.]
+
+The maximum here is fifteen and three-quarters inches; the maximum
+summer motion of the same portion of the glacier is about thirty
+inches. These measurements also show that in winter, as well as in
+summer, the side of the glacier opposite to the Montanvert moves quicker
+than that adjacent to it. The stake which moved with the maximum
+velocity was beyond the moraine of La Noire. The second line crossed the
+glacier about 130 yards below the Montanvert.
+
+Line No. II.--Winter Motion in Twenty-four Hours.
+
+ No. of stake. Inches.
+ 1 7-3/4
+ 2 9-1/2
+ 3 13-3/4
+ 4 16
+ 5 16
+ 6 15-3/4
+ 7 17-1/2
+ 8 16-1/2
+ 9 14-1/2
+ 10 14
+
+The maximum here is an inch and three-quarters greater than that of line
+No. 1. The summer maximum at this portion of the glacier also exceeds
+that of the part intersected by line No. 1. The surface of the glacier
+between the two lines is in a state of tension which relieves itself by
+a system of transverse fissures, and thus permits of the quicker advance
+of the forward portion.
+
+My desire, in making these measurements, was, in the first place, to
+raise the winter observations of the motion to the same degree of
+accuracy as that already possessed by the summer ones. Auguste Balmat
+had already made a series of winter observations on the Mer de Glace;
+but they were made in the way employed before the introduction of the
+theodolite by Agassiz and Forbes, and shared the unavoidable roughness
+of such a mode of measurement. They moreover gave us no information as
+to the motion of the different parts of the glacier along the same
+transverse line, and this, for reasons which will appear subsequently,
+was the point of chief interest to me.
+
+
+
+
+CAUSE OF GLACIER-MOTION.
+
+DE SAUSSURE'S THEORY.
+
+(13.)
+
+
+Perhaps the first attempt at forming a glacier-theory is that of
+Scheuchzer in 1705. He supposed the motion to be caused by the
+conversion of water into ice within the glacier; the known and almost
+irresistible expansion which takes place on freezing, furnishing the
+force which pushed the glacier downward. This idea was illustrated and
+developed with so much skill by M. de Charpentier, that his name has
+been associated with it; and it is commonly known as the Theory of
+Charpentier, or the Dilatation-Theory. M. Agassiz supported this theory
+for a time, but his own thermometric experiments show us that the body
+of the glacier is at a temperature of 32 deg. Fahr.; that consequently there
+is no interior magazine of cold to freeze the water with which the
+glacier is supposed to be incessantly saturated. So that these
+experiments alone, if no other grounds existed, would prove the
+insufficiency of the theory of dilatation. I may however add, that the
+arguments most frequently urged against this theory deal with an
+assumption, which I do not think its author ever intended to make.
+
+[Sidenote: THE GLACIER SLIDES.]
+
+Another early surmise was that of Altmann and Gruener (1760), both of
+whom conjectured that the glacier slid along its bed. This theory
+received distinct expression from De Saussure in 1799; and has since
+been associated with the name of that great alpine traveller, being
+usually called the 'Theory of Saussure,' and sometimes the 'Sliding
+Theory.' It is briefly stated in these words:--
+
+"Almost every glacier reposes upon an inclined bed, and those of any
+considerable size have beneath them, even in winter, currents of water
+which flow between the ice and the bed which supports it. It may
+therefore be understood that these frozen masses, drawn down the slope
+on which they repose, disengaged by the water from all adhesion to the
+bottom, sometimes even raised by this water, must glide by little and
+little, and descend, following the inclinations of the valleys, or of
+the slopes which they cover. It is this slow but continual sliding of
+the ice on its inclined base which carries it into the lower
+valleys."[A]
+
+[Sidenote: STRAINED INTERPRETATION.]
+
+De Saussure devoted but little time to the subject of glacier-motion;
+and the absence of completeness in the statement of his views, arising
+no doubt from this cause, has given subsequent writers occasion to affix
+what I cannot help thinking a strained interpretation to the sliding
+theory. It is alleged that he regarded a glacier as a perfectly rigid
+body; that he considered it to be "a mass of ice of small depth, and
+considerable but uniform breadth, sliding down a uniform valley, or
+pouring from a narrow valley into a wider one."[B] The introduction "of
+the smallest flexibility or plasticity" is moreover emphatically denied
+to him.[C]
+
+It is by no means probable that the great author of the 'Voyages' would
+have subscribed to this "rigid" annotation. His theory, be it
+remembered, is to some extent _true_: the glacier moves over its bed in
+the manner supposed, and the rocks of Britain bear to this day the
+traces of these mighty sliders. De Saussure probably contented himself
+with a general statement of what he believed to be the substantial
+cause of the motion. He visited the Jardin, and saw the tributaries of
+the Mer de Glace turning round corners, welding themselves together, and
+afterwards moving through a sinuous trunk-valley; and it is scarcely
+credible that in the presence of such facts he would have denied all
+flexibility to the glacier.
+
+The statement that he regarded a glacier to be a mass of ice of uniform
+width, is moreover plainly inconsistent with the following description
+of the glacier of Mont Dolent: "Its most elevated plateau is a great
+circus, surrounded by high cliffs of granite, of pyramidal forms; thence
+the glacier descends through a gorge, in which _it is narrowed_; but
+after having passed the gorge, it _enlarges again_, spreading out like a
+fan. Thus it has on the whole the form of a sheaf tied in the middle and
+dilated at its two extremities."[D]
+
+[Sidenote: GLACIER OF MONT DOLENT.]
+
+Curiously enough this very glacier, and these very words, are selected
+by M. Rendu as illustrative of the plasticity of glaciers. "Nothing," he
+says, "shows better the extent to which a glacier moulds itself to its
+locality than the form of the glacier of Mont Dolent in the Valley of
+Ferret;" and he adds, in connexion with the same passage, these
+remarkable words:--"There is a multitude of facts which would seem to
+necessitate the belief that the substance of glaciers enjoys a kind of
+ductility which permits it to mould itself to the locality which it
+occupies, to grow thin, to swell, and to narrow itself like a soft
+paste."[E]
+
+
+FOOTNOTES:
+
+[A] 'Voyages,' Sec. 535.
+
+[B] James D. Forbes, 'Occasional Papers on the Theory of Glaciers,'
+1859, p. 100.
+
+[C] "I adhere to the definition as excluding the introduction of the
+smallest flexibility or plasticity." 'Occ. Pap.,' p. 96.
+
+[D] 'Voyages,' tome ii. p. 290.
+
+[E] In connexion with this brief sketch of the 'Sliding Theory,' it
+ought to be stated, that Mr. Hopkins has proved experimentally, that ice
+may descend an incline at a sensibly uniform rate, and that the velocity
+is augmented by increasing the weight. In this remarkable experiment the
+motion was due to the slow disintegration of the lower surface of the
+ice. See 'Phil. Mag.,' 1845, vol. 26.
+
+
+
+
+RENDU'S THEORY.
+
+(14.)
+
+
+[Sidenote: RENDU'S CHARACTER.]
+
+M. Rendu, Bishop of Annecy, to whose writings I have just referred, died
+last autumn.[A] He was a man of great repute in his diocese, and we owe
+to him one of the most remarkable essays upon glaciers that have ever
+appeared. His knowledge was extensive, his reasoning close and accurate,
+and his faculty of observation extraordinary. With these were associated
+that intuitive power, that presentiment concerning things as yet
+untouched by experiment, which belong only to the higher class of minds.
+Throughout his essay a constant effort after quantitative accuracy
+reveals itself. He collects observations, makes experiments, and tries
+to obtain numerical results; always taking care, however, so to state
+his premises and qualify his conclusions that nobody shall be led to
+ascribe to his numbers a greater accuracy than they merit. It is
+impossible to read his work, and not feel that he was a man of
+essentially truthful mind, and that science missed an ornament when he
+was appropriated by the Church.
+
+The essay above referred to is printed in the tenth volume of the
+Memoirs of the Royal Academy of Sciences of Savoy, published in 1841,
+and is entitled, '_Theorie des Glaciers de la Savoie, par M. le Chanoine
+Rendu, Chevalier du Merite Civil et Secretaire perpetuel_.' The paper
+had been written for nearly two years, and might have remained
+unprinted, had not another publication on the same subject called it
+forth.
+
+I will place a few of the leading points of this remarkable production
+before the reader; commencing with a generalization which is highly
+suggestive of the character of the author's mind.
+
+[Sidenote: "THEORIE DES GLACIERS DE LA SAVOIE."]
+
+He reflects on the accumulation of the mountain-snows, each year adding
+fifty-eight inches of ice to a glacier. This would make Mont Blanc four
+hundred feet higher in a century, and four thousand feet higher in a
+thousand years. "It is evident," he says, "that nothing like this occurs
+in nature." The escape of the ice then leads him to make some general
+remarks on what he calls the "law of circulation." "The conserving will
+of the Creator has employed for the permanence of His work the great law
+of _circulation_, which, strictly examined, is found to reproduce itself
+in all parts of nature. The waters circulate from the ocean to the air,
+from the air to the earth, and from the earth to the ocean.... The
+elements of organic substances circulate, passing from the solid to the
+liquid or aeriform condition, and thence again to the state of solidity
+or of organisation. That universal agent which we designate by the names
+of fire, light, electricity, and magnetism, has probably also a
+_circulation_ as wide as the universe." The italics here are Rendu's
+own. This was published in 1841, but written, we are informed, nearly
+two years before. In 1842 Mr. Grove wrote thus:--"Light, heat,
+magnetism, motion, and chemical affinity, are all convertible material
+affections." More recently Helmholtz, speaking of the "circuit" formed
+by "heat, light, electricity, magnetism, and chemical affinity," writes
+thus:--"Starting from each of these different manifestations of natural
+forces, we can set every other in action." I quote these passages
+because they refer to the same agents as those named by M. Rendu, and to
+which he ascribes "_circulation_." Can it be doubted that this Savoyard
+priest had a premonition of the Conservation of Force? I do not want to
+lay more stress than it deserves upon a conjecture of this kind; but
+its harmony with an essay remarkable for its originality gives it a
+significance which, if isolated, it might not possess.
+
+[Sidenote: GLACIERS RIGHTLY DIVIDED.]
+
+With regard to the glaciers, Rendu commences by dividing them into two
+kinds, or rather the selfsame glacier into two parts, one of which he
+calls the "_glacier reservoir_," the other the "_glacier
+d'ecoulement_,"--two terms highly suggestive of the physical
+relationship of the _neve_ and the glacier proper. He feeds the
+reservoirs from three sources, the principal one of which is the snow,
+to which he adds the rain, and the vapours which are condensed upon the
+heights without passing into the state of either rain or snow. The
+conversion of the snow into ice he supposes to be effected by four
+different causes, the most efficacious of which is _pressure_.[B] It is
+needless to remark that this quite agrees with the views now generally
+entertained.
+
+In page 60 of the volume referred to there is a passage which shows that
+the "veined structure" of the glacier had not escaped him, though it
+would seem that he ascribed it to stratification. "When," he writes, "we
+perceive the profile of a glacier on the walls of a crevasse, we see
+different layers distinct in colour, but more particularly in density;
+some seem to have the hardness, as they have the greenish colour, of
+glass; others preserve the whiteness and porosity of the snow." There is
+also a very close resemblance between his views of the influence of
+"time and cohesion" and those of Prof. Forbes. "We may conclude," he
+writes, "that _time_, favouring the action of _affinity_, and the
+pressure of the layers one upon the other, causes the little crystals of
+which snow is composed to approach each other, bring them into contact,
+and convert them into ice."[C] Regelation also appears to have attracted
+his notice.[D] "When we fill an ice-house," he writes, "we break the ice
+into very small fragments; afterwards we wet it with water 8 or 10
+degrees above zero (Cent.) in temperature; but, notwithstanding this,
+the whole is converted into a compact mass of ice." He moreover
+maintains, in almost the same language as Prof. Forbes,[E] the opinion,
+that ice has always an inner temperature lower than zero (Cent.). He
+believed this to be a property "inherent to ice." "Never," he says, "can
+a calorific ray pass the first surface of ice to raise the temperature
+of the interior."[F]
+
+[Sidenote: OBSERVATIONS AND HYPOTHESES.]
+
+He notices the direction of the glacier as influencing the wasting of
+its ridges by the sun's heat; ascribing to it the effect to which I have
+referred in explaining the wave-like forms upon the surface of the Mer
+de Glace. His explanation of the Moulins, too, though insufficient,
+assigns a true cause, and is an excellent specimen of physical
+reasoning.
+
+With regard to the diminution of the _glaciers reservoirs_, or, in other
+words, to the manner in which the ice disappears, notwithstanding the
+continual additions made to it, we have the following remarkable
+passage:--"In seeking the cause of the diminution of glaciers, it has
+occurred to my mind that the ice, notwithstanding its hardness and its
+rigidity, can only support a given pressure without breaking or being
+squeezed out. According to this supposition, whenever the pressure
+exceeds that force, there will be rupture of the ice, and a flow in
+consequence. Let us take, at the summit of Mont Blanc, a column of ice
+reposing on a horizontal base. The ice which forms the first layer of
+that column is compressed by the weight of all the layers above it; but
+if the solidity of the said first layer can only support a weight equal
+to 100, when the weight exceeds this amount there will be rupture and
+spreading out of the ice of the base. Now, something very similar occurs
+in the immense crust of ice which covers the summits of Mont Blanc. This
+crust appears to augment at the upper surface and to diminish by the
+sides. To assure oneself that the movement is due to the force of
+pressure, it would be necessary to make a series of experiments upon the
+solidity of ice, such as have not yet been attempted."[G] I may remark
+that such experiments substantially verify M. Rendu's notion.
+
+But it is his observations and reasoning upon the _glaciers
+d'ecoulement_ that chiefly interest us. The passages in his writings
+where he insists upon the power of the glaciers to mould themselves to
+their localities, and compares them to a soft paste, to lava at once
+ductile and liquid, are well known from the frequent and flattering
+references of Professor Forbes; but there are others of much greater
+importance, which have hitherto remained unknown in this country.
+Regarding the motion of the Mer de Glace, Rendu writes as follows:--
+
+[Sidenote: MEASUREMENT OF MOTION.]
+
+[Sidenote: THE SIDES OF THE GLACIER RETARDED.]
+
+"I sought to appreciate the quantity of its motion; but I could only
+collect rather vague data. I questioned my guides regarding the position
+of an enormous rock at the edge of the glacier, but still upon the ice,
+and consequently partaking of its motion. The guides showed me the place
+where it stood the preceding year, and where it had stood two, three,
+four, and five years previously; they showed me the place where it would
+be found in a year, in two years, &c.; _so certain are they of the
+regularity of the motion_. Their reports, however, did not always agree
+precisely with each other, and their indications of time and distance
+lack the precision without which we proceed obscurely in the physical
+sciences. In reducing these different indications to a mean, I found the
+total advance of the glacier to be about 40 feet a year. During my last
+journey I obtained more certain data, which I have stated in the
+preceding chapter. _The enormous difference between the two results
+arises from the fact that the latter observations were made at the
+centre of the glacier_, WHICH MOVES MORE RAPIDLY, _while the former were
+made at the side, where the ice_ IS RETAINED BY THE FRICTION AGAINST ITS
+ROCKY WALLS."[H]
+
+An opinion, founded on a grave misapprehension which Rendu enables us to
+correct, is now prevalent in this country, not only among the general
+public, but also among those of the first rank in science. The nature of
+the mistake will be immediately apparent. At page 128 of the 'Travels in
+the Alps' its distinguished author gives a sketch of the state of our
+knowledge of glacier-motion previous to the commencement of his
+inquiries. He cites Ebel, Hugi, Agassiz, Bakewell, De la Beche,
+Shirwell, Rendu, and places them in open contradiction to each other.
+Rendu, he says, gives the motion of the Mer de Glace to be "242 feet per
+annum; 442 feet per annum; a foot a day; 400 feet per annum, and 40 feet
+per annum, or _one-tenth_ of the last!" ... and he adds, "I was not
+therefore wrong in supposing that the actual progress of a glacier was
+yet a new problem when I commenced my observations on the Mer de Glace
+in 1842."[I]
+
+In the 'North British Review' for August, 1859, a writer equally
+celebrated for the brilliancy of his discoveries and the vigour of his
+pen, collected the data furnished by the above paragraph into a table,
+which he introduced to his readers in the following words:--"It is to
+Professor Forbes alone that we owe the first and most correct researches
+respecting the motion of glaciers; and in proof of this, we have only to
+give the following list of observations which had been previously made.
+
+ Observers. Name of glacier. Annual rate of motion.
+
+ Ebel Chamouni 14 feet
+ Ebel Grindelwald 25 "
+ Hugi Aar 240 "
+ Agassiz Aar 200 "
+ Bakewell Mer de Glace 540 "
+ De la Beche Mer de Glace 600 "
+ Shirwell Mer de Glace 300 "
+ M. Rendu Mer de Glace 365 "
+ Saussure's Ladder Mer de Glace 375 "
+
+... Such was the state of our knowledge when Professor Forbes undertook
+the investigation of the subject."
+
+I am persuaded that the writer of this article will be the first to
+applaud any attempt to remove an error which, advanced on his great
+authority, must necessarily be widely disseminated. The numbers in the
+above table certainly differ widely, and it is perhaps natural to
+conclude that such discordant results can be of no value; but the fact
+really is that _every one of them may be perfectly correct_. This fact,
+though overlooked by Professor Forbes, was clearly seen by Rendu, who
+pointed out with perfect distinctness the sources from which the
+discrepancies were derived.
+
+[Sidenote: DISCREPANCIES EXPLAINED.]
+
+"It is easy," he says, "to comprehend that it is impossible to obtain a
+general measure,--that there ought to be one for each particular
+glacier. The nature of the slope, the number of changes to which it is
+subjected, the depth of the ice, the width of the couloir, the form of
+its sides, and a thousand other circumstances, must produce variations
+in the velocity of the glacier, and these circumstances cannot be
+everywhere absolutely the same. Much more, it is not easy to obtain this
+velocity for a single glacier, and for this reason. In those portions
+where the inclination is steep, the layer of ice is thin, and its
+velocity is great; in those where the slope is almost nothing, the
+glacier swells and accumulates; the mass in motion being double, triple,
+&c., the motion is only the half, the third, &c.
+
+[Sidenote: LIQUID MOTION ASCRIBED TO GLACIER.]
+
+"But this is not all," adds M. Rendu: "_Between the Mer de Glace and a
+river, there is a resemblance so complete that it is impossible to find
+in the latter a circumstance which does not exist in the former._ In
+currents of water the motion is not uniform, neither throughout their
+width nor throughout their depth; _the friction of the bottom, that of
+the sides_, the action of obstacles, cause the motion to vary, _and only
+towards the middle of the surface is this entire...._"[J]
+
+In 1845 Professor Forbes appears to have come to the same conclusion as
+M. Rendu; for after it had been proved that the centre of the Aar
+glacier moved quicker than the side in the ratio of fourteen to one, he
+accepted the result in these words:--"The movement of the centre of the
+glacier is to that of a point five metres from the edge as FOURTEEN to
+ONE: such is the effect of plasticity!"[K] Indeed, if the differences
+exhibited in the table were a proof of error, the observations of
+Professor Forbes himself would fare very ill. The measurements of
+glacier-motion made with his own hands vary from less than 42 feet a
+year to 848 feet a year, the minimum being less than _one-twentieth_ of
+the maximum; and if we include the observations made by Balmat, the
+fidelity of which has been certified by Professor Forbes, the minimum is
+only _one-thirty-seventh_ of the maximum.
+
+[Sidenote: NORTH BRITISH REVIEW.]
+
+There is another point connected with Rendu's theory which needs
+clearing up:--"The idea," writes the eminent reviewer, "that a glacier
+is a semifluid body is no doubt startling, especially to those who have
+seen the apparently rigid ice of which it is composed. M. Rendu himself
+shrank from the idea, and did not scruple to say that 'the rigidity of a
+mass of ice was in direct opposition to it;' and we think that Professor
+Forbes himself must have stood aghast when his fancy first associated
+the notion of imperfect fluidity with the solid or even the fissured ice
+of the glacier, and when he saw in his mind's eye the glaciers of the
+Alps flowing like a river along their rugged bed. A truth like this was
+above the comprehension and beyond the sympathy of the age; and it
+required a moral power of no common intensity to submit it to the ordeal
+of a shallow philosophy, and the sneers of a presumptuous criticism."
+
+These are strong words; but the fact is that, so far from "shrinking"
+from the idea, Rendu affirmed, with a clearness and an emphasis which
+have not been exceeded since, that all the phenomena of a river were
+reproduced upon the Mer de Glace; its deeps, its shallows, its
+widenings, its narrowings, its rapids, its places of slow motion, and
+the quicker flow of its centre than of its sides. He did not shrink from
+accepting a difference between the central and lateral motion amounting
+to a ratio of ten to one--a ratio so large that Professor Forbes at one
+time regarded the acceptance of it as a simple absurdity. In this he was
+perhaps justified; for his own first observations, which, however
+valuable, were hasty and incomplete, gave him a maximum ratio of about
+one and a half to one, while the ratio in some cases was nearly one of
+_equality_. The observations of Agassiz however show that the ratio,
+instead of being ten to one, may be _infinity_ to one; for the lateral
+ice may be so held back by a local obstacle that in the course of a year
+it shall make no sensible advance at all.
+
+[Sidenote: THE ICE AND THE GLACIER.]
+
+From one thing only did M. Rendu shrink; and it is _the_ thing regarding
+which we are still disunited. He shrank from stating the physical
+quality of the ice in virtue of which a glacier moved like a river. He
+demands experiments upon snow and ice to elucidate this subject. The
+very observations which Professor Forbes regards as proofs are those of
+which we require the physical explanation. It is not the viscous flow,
+if you please to call it such, of the glacier as a whole that here
+concerns us; but it is the quality of the _ice_ in virtue of which this
+kind of motion is accomplished. Professor Forbes sees this difference
+clearly enough: he speaks of "fissured ice" being "flexible" in hand
+specimens; he compares the glacier to a mixture of ice and sand; and
+finally, in a more matured paper, falls back for an explanation upon the
+observations of Agassiz regarding the capillaries of the glacier.[L]
+
+
+FOOTNOTES:
+
+[A] Expressions such as "last summer," "last autumn," "recently," will
+be taken throughout in the sense which they had in the early half of
+1860, when this book was first published.--L. C. T.
+
+[B] 'Memoir,' p. 77.
+
+[C] P. 75.
+
+[D] P. 71.
+
+[E] 'Philosophical Magazine,' 1859.
+
+[F] 'Memoir,' p. 69.
+
+[G] Page 80.
+
+[H] Page 95.
+
+[I] At page 38 of the 'Travels' the following passage also occurs:--"I
+believe that I may safely affirm that not one observation of the rate of
+motion of a glacier, either on the average or at any particular season
+of the year, existed when I commenced my experiments in 1842."
+
+[J] 'Theorie,' p. 96.
+
+[K] 'Occ. Pap.,' p. 74.
+
+[L] In all that has been written upon glaciers in this country the above
+passages from the writings of Rendu are unquoted; and many who mingled
+very warmly in the discussions of the subject were, until quite
+recently, ignorant of their existence. I was long in this condition
+myself, for I never supposed that passages which bear so directly upon a
+point so much discussed, and of such cardinal import, could have been
+overlooked; or that the task of calling attention to them should devolve
+upon myself nearly twenty years after their publication. Now that they
+are discovered, I conceive no difference of opinion can exist as to the
+propriety of placing them in their true position.
+
+
+
+
+(15.)
+
+
+The measurements of Agassiz and Forbes completely verify the
+anticipations of Rendu; but no writer with whom I am acquainted has
+added anything essential to the Bishop's statements as to the identity
+of glacier and liquid motion. He laid down the conditions of the problem
+with perfect clearness, and, as regards the distribution of merit, the
+point to be decided is the relative importance of his idea, and of the
+measurements which were subsequently made.
+
+[Sidenote: OBSERVATIONS OF FORBES.]
+
+The observations on which Professor Forbes based the analogy between a
+glacier and a river are the following:--In 1842 he fixed four marks upon
+the Mer de Glace a little below the Montanvert, the first of which was
+100 yards distant from the side of the glacier, while the last was at
+the centre "or a little beyond it." The relative velocity of these four
+points was found to be
+
+ 1.000 1.332 1.356 1.367.
+
+The first observations were made upon two of these points, two others
+being subsequently added. Professor Forbes also determined the velocity
+of two points on the Glacier du Geant, and found the ratio of motion, in
+the first instance, to be as 14 to 32. Subsequent measurements, however,
+showed the ratio to be as 14 to 18, the larger motion belonging to the
+station nearest to the centre of the glacier. These are the only
+measurements which I can find in his large work that establish the
+swifter motion of the centre of the glacier; and in these cases the
+velocity of the centre is compared with that of _one side_ only. In no
+instance that I am aware of, either in 1842 or subsequent years, did
+Professor Forbes extend his measurements quite across a glacier; and as
+regards completeness in this respect, no observations hitherto made can
+at all compare with those executed at the instance of Agassiz upon the
+glacier of the Aar.
+
+In 1844 Professor Forbes made a series of interesting experiments on a
+portion of the Mer de Glace near l'Angle. He divided a length of 90 feet
+into 45 equal spaces, and fixed pins at the end of each. His theodolite
+was placed upon the ice, and in seventeen days he found that the ice 90
+feet nearer the centre than the theodolite had moved 26 inches past the
+latter. These measurements were undertaken for a special object, and
+completely answered the end for which they were intended.
+
+In 1846 Professor Forbes made another important observation. Fixing
+three stakes at the heights of 8, 54, and 143 feet above the bed of the
+glacier, he found that in five days they moved respectively 2.87, 4.18,
+and 4.66 feet. The stake nearest the bed moved most slowly, thus
+showing that the ice is retarded by friction. This result was
+subsequently verified by the measurements of M. Martins, and by my own.
+
+If we add to the above an observation made during a short visit to the
+Aletsch glacier in 1844, which showed its lateral retardation, I believe
+we have before us the whole of the measurements executed by Professor
+Forbes, which show the analogy between the motion of a glacier and that
+of a viscous body.
+
+[Sidenote: MEASUREMENTS OF AGASSIZ.]
+
+Illustrative of the same point, we have the elaborate and extensive
+series of measurements executed by M. Wild under the direction of M.
+Agassiz upon the glacier of the Aar in 1842, 1843, 1844, and 1845, which
+exhibit on a grand scale, and in the most conclusive manner, the
+character of the motion of this glacier; and also show, on close
+examination, an analogy with fluid motion which neither M. Agassiz nor
+Professor Forbes suspected. The former philosopher publishes a section
+in his 'Systeme Glaciaire,' entitled 'Migrations of the Centre;' in
+which he shows that the middle of the glacier is not always the point of
+swiftest motion. The detection of this fact demonstrates the attention
+devoted by M. Agassiz to the discussion of his observations, but he
+gives no clue to the cause of the variation. On inspecting the shape of
+the valley through which the Aar glacier moves, I find that these
+"migrations" follow the law established in 1857 upon the Mer de Glace,
+and enunciated at page 286.
+
+To sum up this part of the question:--The _idea_ of semi-fluid motion
+belongs entirely to Rendu; the _proof_ of the quicker central flow
+belongs in part to Rendu, but almost wholly to Agassiz and Forbes; the
+proof of the retardation of the bed belongs to Forbes alone; while the
+discovery of the locus of the point of maximum motion belongs, I
+suppose, to me.
+
+
+
+
+FORBES'S THEORY.
+
+(16.)
+
+
+The formal statement of this theory is given in the following words:--"A
+glacier is an imperfect fluid, or viscous body, which is urged down
+slopes of a certain inclination by the mutual pressure of its parts."
+The consistency of the glacier is illustrated by reference to treacle,
+honey, and tar, and the theory thus enunciated and exemplified is called
+the 'Viscous Theory.'
+
+It has been the subject of much discussion, and great differences of
+opinion are still entertained regarding it. Able and sincere men take
+opposite sides; and the extraordinary number of Reviews which have
+appeared upon the subject during the last two years show the interest
+which the intellectual public of England take in the question. The chief
+differences of opinion turn upon the inquiry as to what Professor Forbes
+really meant when he propounded the viscous theory; some affirm one
+thing, some another, and, singularly enough, these differences continue,
+though the author of the theory has at various times published
+expositions of his views.
+
+[Sidenote: "FACTS AND PRINCIPLES."]
+
+The differences referred to arise from the circumstances that a
+sufficient distinction has not been observed between _facts_ and
+_principles_, and that the viscous theory has assumed various forms
+since its first promulgation. It has been stated to me that the theory
+of Professor Forbes is "the congeries of facts" which he has discovered.
+But it is quite evident that no recognition, however ample, of these
+facts would be altogether satisfactory to Professor Forbes himself. He
+claims recognition of his _theory_,[A] and no writer with whom I am
+acquainted makes such frequent use of the term. What then can the
+viscous theory mean apart from the facts? I interpret it as furnishing
+the principle from which the facts follow as physical consequences--that
+the glacier moves as a river because the ice is viscous. In this sense
+only can Professor Forbes's views be called a theory; in any other, his
+experiments are mere illustrations of the facts of glacier motion, which
+do not carry us a hair's breadth towards their physical cause.
+
+[Sidenote: VISCOUS THEORY;--WHAT IS IT?]
+
+What then is the meaning of viscosity or viscidity? I have heard it
+defined by men of high culture as "gluey tenacity;" and such tenacity
+they once supposed a glacier to possess. If we dip a spoon into treacle,
+honey, or tar, we can draw the substance out into filaments, and the
+same may be done with melted caoutchouc or lava. All these substances
+are viscous, and all of them have been chosen to illustrate the physical
+property in virtue of which a glacier moves. Viscosity then consists in
+the power of being drawn out when subjected to a force of tension, the
+substance, after stretching, being in a state of molecular equilibrium,
+or, in other words, devoid of that elasticity which would restore it to
+its original form. This certainly was the idea attached to Professor
+Forbes's words by some of his most strenuous supporters, and also by
+eminent men who have never taken part in any controversy on the subject.
+Mr. Darwin, for example, speaks of felspathic rocks being "stretched"
+while flowing slowly onwards in a pasty condition, in precisely the same
+manner as Professor Forbes believes that the ice of moving glaciers is
+stretched and fissured; and Professor Forbes himself quotes these words
+of Mr. Darwin as illustrative of his theory.[B]
+
+The question now before us is,--Does a glacier exhibit that power of
+yielding to a force of tension which would entitle its ice to be
+regarded as a viscous substance?
+
+[Sidenote: THEORY TESTED.]
+
+With a view to the solution of this question Mr. Hirst took for me the
+inclinations of the Mer de Glace and all its tributaries in 1857; the
+effect of a change of inclination being always noted. I will select from
+those measurements a few which bear more specially upon the subject now
+under consideration, commencing with the Glacier des Bois, down which
+the ice moves in that state of wild dislocation already described. The
+inclination of the glacier above this cascade is 5 deg. 10', and that of the
+cascade itself is 22 deg. 20', the change of inclination being therefore 17 deg.
+10'.
+
+[Illustration: Fig. 22. Inclinations of ice cascasde of the Glacier des
+Bois.]
+
+In Fig. 22 I have protracted the inclination of the cascade and of the
+glacier above it; the line A B representing the former and B C the
+latter. Now a stream of molten lava, of treacle, or tar, would, in
+virtue of its viscosity, be able to flow over the brow at B without
+breaking across; but this is not the case with the glacier; it is so
+smashed and riven in crossing this brow, that, to use the words of
+Professor Forbes himself, "it pours into the valley beneath in a cascade
+of icy fragments."
+
+[Sidenote: INCLINATIONS OF THE MER DE GLACE.]
+
+But this reasoning will appear much stronger when we revert to other
+slopes upon the Mer de Glace. For example, its inclination above l'Angle
+is 4 deg., and it afterwards descends a slope of 9 deg. 25', the change of
+inclination being 5 deg. 25'. If we protract these inclinations to scale, we
+have the line A B, Fig. 23, representing the steeper slope, and B C
+that of the glacier above it. One would surely think that a viscous body
+could cross the brow B without transverse fracture, but this the glacier
+cannot do, and Professor Forbes himself pronounces this portion of the
+Mer de Glace impassable. Indeed it was the profound crevasses here
+formed which placed me in a difficulty already referred to. Higher up
+again, the glacier is broken on passing from a slope of 3 deg. 10' to one of
+5 deg. Such observations show how differently constituted a glacier is from
+a stream of lava in a "pasty condition," or of treacle, honey, tar, or
+melted caoutchouc, to all which it has been compared. In the next
+section I shall endeavour to explain the origin of the crevasses, and
+shall afterwards make a few additional remarks on the alleged viscosity
+of ice.
+
+[Illustration: Fig. 23. Inclinations of Mer de Glace above l'Angle.]
+
+
+FOOTNOTES:
+
+[A] "Mr. Hopkins," writes Professor Forbes, "has done me the honour, in
+the memoirs before alluded to, to mention with approbation my
+observations and experiments on the subject of glaciers. He has been
+more sparing either in praise or criticism of the theory which I have
+founded upon them. Had Mr. Hopkins," &c.--_Eighth Letter_; 'Occ.
+Papers,' p. 66.
+
+[B] 'Occ. Papers,' p. 92.
+
+
+
+
+THE CREVASSES.
+
+(17.)
+
+
+[Sidenote: CREVASSES CAUSED BY THE MOTION.]
+
+Having made ourselves acquainted with the motion of the glacier, we are
+prepared to examine those rents, fissures, chasms, or, as they are most
+usually called, _Crevasses_, by which all glaciers are more or less
+intersected. They result from the motion of the glacier, and the laws of
+their formation are deduced immediately from those of the motion. The
+crevasses are sometimes very deep and numerous, and apparently without
+law or order in their distribution. They cut the ice into long ridges,
+and break these ridges transversely into prisms; these prisms gradually
+waste away, assuming, according to the accidents of their melting, the
+most fantastic forms. I have seen them like the mutilated statuary of an
+ancient temple, like the crescent moon, like huge birds with
+outstretched wings, like the claws of lobsters, and like antlered deer.
+Such fantastic sculpture is often to be found on the ice cascades, where
+the riven glacier has piled vast blocks on vaster pedestals, and
+presented them to the wasting action of sun and air. In Fig. 24 I have
+given a sketch of a mass of ice of this character, which stood in 1859
+on the dislocated slope of the Glacier des Bois.
+
+[Sidenote: FANTASTIC ICE-MASSES.]
+
+[Illustration: Fig. 24. Fantastic Mass of ice.]
+
+It is usual for visitors to the Montanvert to descend to the glacier,
+and to be led by their guides to the edges of the crevasses, where,
+being firmly held, they look down into them; but those who have only
+made their acquaintance in this way know but little of their magnitude
+and beauty in the more disturbed portions of glaciers. As might be
+expected, they have been the graves of many a mountaineer; and the
+skeletons found upon the glacier prove that even the chamois itself,
+with its elastic muscles and admirable sureness of foot, is not always
+safe among the crevasses. They are grandest in the higher ice-regions,
+where the snow hangs like a coping over their edges, and the water
+trickling from these into the gloom forms splendid icicles. The Goerner
+Glacier, as we ascend it towards the old Weissthor, presents many fine
+examples of such crevasses; the ice being often torn in a most curious
+and irregular manner. You enter a porch, pillared by icicles, and look
+into a cavern in the very body of the glacier, encumbered with vast
+frozen bosses which are fringed all round by dependent icicles. At the
+peril of your life from slipping, or from the yielding of the
+stalactites, you may enter these caverns, and find yourself steeped in
+the blue illumination of the place. Their beauty is beyond description;
+but you cannot deliver yourself up, heart and soul, to its enjoyment.
+There is a strangeness about the place which repels you, and not without
+anxiety do you look from your ledge into the darkness below, through
+which the sound of subglacial water sometimes rises like the tolling of
+distant bells. You feel that, however the cold splendours of the place
+might suit a purely spiritual essence, they are not congenial to flesh
+and blood, and you gladly escape from its magnificence to the sunshine
+of the world above.
+
+[Sidenote: BIRTH OF A CREVASSE.]
+
+From their numbers it might be inferred that the formation of crevasses
+is a thing of frequent occurrence and easy to observe; but in reality it
+is very rarely observed. Simond was a man of considerable experience
+upon the ice, but the first crevasse he ever saw formed was during the
+setting out of one of our lines, when a narrow rent opened beneath his
+feet, and propagated itself through the ice with loud cracking for a
+distance of 50 or 60 yards. Crevasses always commence in this way as
+mere narrow cracks, which open very slowly afterwards. I will here
+describe the only case of crevasse-forming which has come under my
+direct observation.
+
+On the 31st of July, 1857, Mr. Hirst and myself, having completed our
+day's work, were standing together upon the Glacier du Geant, when a
+loud dull sound, like that produced by a heavy blow, seemed to issue
+from the body of the ice underneath the spot on which we stood. This was
+succeeded by a series of sharp reports, which were heard sometimes above
+us, sometimes below us, sometimes apparently close under our feet, the
+intervals between the louder reports being filled by a low singing
+noise. We turned hither and thither as the direction of the sounds
+varied; for the glacier was evidently breaking beneath our feet, though
+we could discern no trace of rupture. For an hour the sounds continued
+without our being able to discover their source; this at length revealed
+itself by a rush of air-bubbles from one of the little pools upon the
+surface of the glacier, which was intersected by the newly-formed
+crevasse. We then traced it for some distance up and down, but hardly at
+any place was it sufficiently wide to permit the blade of my penknife to
+enter it. M. Agassiz has given an animated description of the terror of
+his guides upon a similar occasion, and there was an element of awe in
+our own feelings as we heard the evening stillness of the glacier thus
+disturbed.
+
+[Sidenote: MECHANICAL ORIGIN.]
+
+With regard to the mechanical origin of the crevasses the most vague and
+untenable notions had been entertained until Mr. Hopkins published his
+extremely valuable papers. To him, indeed, we are almost wholly indebted
+for our present knowledge of the subject, my own experiments upon this
+portion of the glacier-question being for the most part illustrations of
+the truth of his reasoning. To understand the fissures in their more
+complex aspects it is necessary that we should commence with their
+elements. I shall deal with the question in my own way, adhering,
+however, to the mechanical principles upon which Mr. Hopkins has based
+his exposition.
+
+[Illustration: Fig. 25. Diagram explanatory of the mechanical origin of
+Crevasses.]
+
+Let A B, C D, be the bounding sides of a glacier moving in the direction
+of the arrow; let _m_, _n_ be two points upon the ice, one, _m_, close
+to the retarding side of the valley, and the other, _n_, at some
+distance from it. After a certain time, the point _m_ will have moved
+downwards to _m'_, but in consequence of the swifter movement of the
+parts at a distance from the sides, _n_ will have moved in the same
+time to _n'_. Thus the line _m n_, instead of being at right angles to
+the glacier, takes up the oblique position _m' n'_; but to reach from
+_m'_ to _n'_ the line _m n_ would have to stretch itself considerably;
+every other line that we can draw upon the ice parallel to _m' n'_ is in
+a similar state of tension; or, in other words, the sides of the glacier
+are acted upon by an oblique pull towards the centre. Now, Mr. Hopkins
+has shown that the direction in which this oblique pull is strongest
+encloses an angle of 45 deg. with the side of the glacier.
+
+[Sidenote: LINE OF GREATEST STRAIN.]
+
+[Illustration: Fig. 26. Diagram showing the line of Greatest Strain.]
+
+What is the consequence of this? Let A B, C D, Fig. 26, represent, as
+before, the sides of the glacier, moving in the direction of the arrow;
+let the shading lines enclose an angle of 45 deg. with the sides. _Along_
+these lines the marginal ice suffers the greatest strain, and,
+consequently _across_ these lines and at right angles to them, the ice
+tends to break and to form _marginal crevasses_. The lines, _o p_, _o
+p_, mark the direction of these crevasses; they are at right angles to
+the line of greatest strain, and hence also enclose an angle of 45 deg. with
+the side of the valley, _being obliquely pointed upwards_.
+
+[Sidenote: MARGINAL AND TRANSVERSE CREVASSES.]
+
+This latter result is noteworthy; it follows from the mechanical data
+that the swifter motion of the centre tends to produce marginal
+crevasses which are inclined from the side of the glacier towards its
+source, and not towards its lower extremity. But when we look down upon
+a glacier thus crevassed, the first impression is that the sides have
+been dragged down, and have left the central portions behind them;
+indeed, it was this very appearance that led M. de Charpentier and M.
+Agassiz into the error of supposing that the sides of a glacier moved
+more quickly than its middle portions; and it was also the delusive
+aspect of the crevasses which led Professor Forbes to infer the slower
+motion of the eastern side of the Mer de Glace.
+
+The retardation of the ice is most evident near the sides; in most
+cases, the ice for a considerable distance right and left of the central
+line moves with a sensibly uniform velocity; there is no dragging of the
+particles asunder by a difference of motion, and, consequently, a
+compact centre is perfectly compatible with fissured sides. Nothing is
+more common than to see a glacier with its sides deeply cut, and its
+central portions compact; this, indeed, is always the case where the
+glacier moves down a bed of uniform inclination.
+
+But supposing that the bed is not uniform--that the valley through which
+the glacier moves changes its inclination abruptly, so as to compel the
+ice to pass over a brow; the glacier is then circumstanced like a stick
+which we try to break by holding its two ends and pressing it against
+the knee. The brow, where the bed changes its inclination, represents
+the knee in the case of the stick, while the weight of the glacier
+itself is the force that tends to break it. It breaks; and fissures are
+formed across the glacier, which are hence called _transverse
+crevasses_.
+
+[Sidenote: GRINDELWALD GLACIER.]
+
+No glacier with which I am acquainted illustrates the mechanical laws
+just developed more clearly and fully than the Lower glacier of
+Grindelwald. Proceeding along the ordinary track beside the glacier, at
+about an hour's distance from the village the traveller reaches a point
+whence a view of the glacier is obtained from the heights above it. The
+marginal fissures are very cleanly cut, and point nearly in the
+direction already indicated; the glacier also changes its inclination
+several times along the distance within the observer's view. On crossing
+each brow the glacier is broken across, and a series of transverse
+crevasses is formed, which follow each other down the slope. At the
+bottom of the slope tension gives place to pressure, the walls of the
+crevasses are squeezed together, and the chasms closed up. They remain
+closed along the comparatively level space which stretches between the
+base of one slope and the brow of the next; but here the glacier is
+again transversely broken, and continues so until the base of the second
+slope is reached, where longitudinal pressure instead of longitudinal
+strain begins to act, and the fissures are closed as before. In Fig. 27A
+I have given a sketchy section of a portion of the glacier, illustrating
+the formation of the crevasses at the top of a slope, and their
+subsequent obliteration at its base.
+
+[Sidenote: COMPRESSION AND TENSION.]
+
+[Illustration: Fig. 27A, B. Section and Plan of a portion of the Lower
+Grindelwald Glacier.]
+
+Another effect is here beautifully shown, namely, the union of the
+transverse and marginal crevasses to form continuous fissures which
+stretch quite across the glacier. Fig. 27B will illustrate my meaning,
+though very imperfectly; it represents a plan of a portion of the Lower
+Grindelwald glacier, with both marginal and transverse fissures drawn
+upon it. I have placed it under the section so that each part of it may
+show in plan the portion of the glacier which is shown in section
+immediately above it. It shows how the marginal crevasses remain after
+the compression of the centre has obliterated the transverse ones; and
+how the latter join on to the former, so as to form continuous fissures,
+which sweep across the glacier in vast curves, with their convexities
+turned upwards. The illusion before referred to is here strengthened;
+the crevasses turn, so to say, _against_ the direction of motion,
+instead of forming loops, with their convexities pointing downwards, and
+thus would impress a person unacquainted with the mechanical data with
+the idea that the glacier margins moved more quickly than the centre.
+The figures are intended to convey the idea merely; on the actual slopes
+of the glacier between twenty and thirty chasms may be counted: also the
+word "compression" ought to have been limited to the level portions of
+the sketch.
+
+[Sidenote: LONGITUDINAL CREVASSES.]
+
+Besides the two classes of fissures mentioned we often find others,
+which are neither marginal nor transverse. The terminal portions of many
+glaciers, for example, are in a state of compression; the snout of the
+glacier abuts against the ground, and having to bear the thrust of the
+mass behind it, if it have room to expand laterally, the ice will
+yield, and _longitudinal crevasses_ will be formed. They are of very
+common occurrence, but the finest example of the kind is perhaps
+exhibited by the glacier of the Rhone. After escaping from the steep
+gorge which holds the cascade, this glacier encounters the bottom of a
+comparatively wide and level valley; the resistance to its forward
+motion is augmented, while its ability to expand laterally is increased;
+it has to bear a longitudinal thrust, and it splits at right angles to
+the pressure [strain?]. A series of fissures is thus formed, the central
+ones of which are truly longitudinal; but on each side of the central
+line the crevasses diverge, and exhibit a fan-like arrangement. This
+disposition of the fissures is beautifully seen from the summit of the
+Mayenwand on the Grimsel Pass.
+
+[Illustration: Fig. 28. Diagram illustrating the crevassing of Convex
+Sides of glacier.]
+
+Here then we have the elements, so to speak, of glacier-crevassing, and
+through their separate or combined action the most fantastic cutting up
+of a glacier may be effected. And see how beautifully these simple
+principles enable us to account for the remarkable crevassing of the
+eastern side of the Mer de Glace. Let A B, C D, be the opposite sides of
+a portion of the glacier, near the Montanvert; C D being east, and A B
+west, the glacier moving in the direction of the arrow; let the points
+_m n_ represent the extremities of our line of stakes, and let us
+suppose an elastic string stretched across the glacier from one to the
+other. We have proved that the point of maximum motion here lies much
+nearer to the side C D than to A B. Let _o_ be this point, and, seizing
+the string at _o_, let it be drawn in the direction of motion until it
+assumes the position, _m_, _o'_, _n_. It is quite evident that _o' n_ is
+in a state greater tension than _o' m_, and the ice at the eastern side
+of the Mer de Glace is in a precisely similar mechanical condition. It
+suffers a greater strain than the ice at the opposite side of the
+valley, and hence is more fissured and broken. Thus we see that the
+crevassing of the eastern side of the glacier is a simple consequence of
+the quicker motion of that side, and does not, as hitherto supposed,
+demonstrate its slower motion. The reason why the eastern side of the
+glacier, as a whole, is much more fissured than the western side is,
+that there are two long segments which turn their convex curvature
+eastward, and only one segment of the glacier which turns its convexity
+westward.
+
+[Sidenote: CREVASSING OF CONVEX SIDE.]
+
+The lower portion of the Rhone glacier sweeps round the side of the
+valley next the Furca, and turns throughout a convex curve to this side:
+the crevasses here are wide and frequent, while they are almost totally
+absent at the opposite side of the glacier. The lower Grindelwald
+glacier turns at one place a convex curve towards the Eiger, and is much
+more fissured at that side than at the opposite one; indeed, the
+fantastic ice-splinters, columns, and minarets, which are so finely
+exhibited upon this glacier, are mainly due to the deep crevassing of
+the convex side. Numerous other illustrations of the law might, I doubt
+not, be discovered, and it would be a pleasant and useful occupation to
+one who takes an interest in the subject, to determine, by strict
+measurements upon other glaciers, the locus of the point of maximum
+motion, and to observe the associated mechanical effects.
+
+[Sidenote: BERGSCHRUNDS.]
+
+The appearance of crevasses is often determined by circumstances more
+local and limited than those above indicated; a boss of rock, a
+protuberance on the side of the flanking mountain, anything, in short,
+which checks the motion of one part of the ice and permits an adjacent
+portion to be pushed away from it, produces crevasses. Some valleys are
+terminated by a kind of mountain-circus with steep sides, against which
+the snow rises to a considerable height. As the mass is urged downwards,
+the lower portion of the snow-slope is often torn away from its higher
+portion, and a chasm is formed, which usually extends round the head of
+the valley. To such a crevasse the specific name _Bergschrund_ is
+applied in the Bernese Alps; I have referred to one of them in the
+account of the "Passage of the Strahleck."
+
+
+
+
+(18.)
+
+
+The phenomena described and accounted for in the last chapter have a
+direct bearing upon the question of viscosity. In virtue of the quicker
+central flow the lateral ice is subject to an oblique strain; but,
+instead of stretching, it breaks, and marginal crevasses are formed. We
+also see that a slight curvature in the valley, by throwing an
+additional strain upon one half of the glacier, produces an augmented
+crevassing of that side.
+
+But it is known that a substance confessedly viscous may be broken by a
+sudden shock or strain. Professor Forbes justly observes that
+sealing-wax at moderate temperatures will mould itself (with time) to
+the most delicate inequalities of the surface on which it rests, but may
+at the same time be shivered to atoms by the blow of a hammer. Hence, in
+order to estimate the weight of the objection that a glacier breaks when
+subjected to strain, we must know the conditions under which the force
+is applied.
+
+The Mer de Glace has been shown (p. 287) to move through the neck of the
+valley at Trelaporte at the rate of twenty inches a day. Let the sides
+of this page represent the boundaries of the glacier at Trelaporte, and
+any one of its lines of print a transverse slice of ice. Supposing the
+line to move down the page as the slice of ice moves down the valley,
+then the bending of the ice in twenty-four hours, shown on such a scale,
+would only be sufficient to push forward the centre in advance of the
+sides by a very small fraction of the width of the line of print. To
+such an extremely gradual strain the ice is unable to accommodate itself
+without fracture.
+
+[Sidenote: NUMERICAL TEST OF VISCOSITY.]
+
+Or, referring to actual numbers:--the stake No. 15 on our 5th line, page
+284, stood on the lateral moraine of the Mer de Glace; and between it
+and No. 14 a distance of 190 feet intervened. Let A B, Fig. 29, be the
+side of the glacier, moving in the direction of the arrow, and let _a b
+c d_ be a square upon the glacier with a side of 190 feet. The whole
+square moves with the ice, but the side _b d_ moves quickest; the point
+_a_ moving 10 inches, while _b_ moves 14.75 inches in 24 hours; the
+differential motion therefore amounts to an inch in five hours. Let _a
+b' d' c_ be the shape of the figure after five hours' motion; then the
+line _a b_ would be extended to _a b'_ and _c d_ to _c d'_.
+
+[Illustration: Fig. 29. Diagram illustrating test of viscosity.]
+
+The extension of _these_ lines does not however express the _maximum_
+strain to which the ice is subjected. Mr. Hopkins has shown that this
+takes place along the line _a d_; in five hours then this line, if
+capable of stretching, would be stretched to _a d'_. From the data given
+every boy who has mastered the 47th Proposition of the First Book of
+Euclid can find the length both of _a d_ and _a d'_; the former is
+3224.4 inches, and the latter is 3225.1, the difference between them
+being seven-tenths of an inch.
+
+This is the amount of yielding required from the ice in five hours, but
+it cannot grant this; the glacier breaks, and numerous marginal
+crevasses are formed. It must not be forgotten that the evidence here
+adduced merely shows what ice cannot do; what it _can_ do in the way of
+viscous yielding we do not know: there exists as yet no single
+experiment on great masses or small to show that ice possesses in any
+sensible degree that power of being drawn out which seems to be the very
+essence of viscosity.
+
+I have already stated that the crevasses, on their first formation, are
+exceedingly narrow rents, which widen very slowly. The new crevasse
+observed by our guide required several days to attain a width of three
+inches; while that observed by Mr. Hirst and myself did not widen a
+single inch in three days. This, I believe, is the general character of
+the crevasses; they form suddenly and open slowly. Both facts are at
+variance with the idea that ice is viscous; for were this substance
+capable of stretching at the slow rate at which the fissures widen,
+there would be no necessity for their formation.
+
+[Sidenote: STRETCHING OF ICE NOT PROVED.]
+
+It cannot be too clearly and emphatically stated that the _proved_ fact
+of a glacier conforming to the law of semi-fluid motion is a thing
+totally different from the _alleged_ fact of its being viscous. Nobody
+since its first enunciation disputed the former. I had no doubt of it
+when I repaired to the glaciers in 1856; and none of the eminent men who
+have discussed this question with Professor Forbes have thrown any doubt
+upon his measurements. It is the assertion that small pieces of ice are
+proved to be viscous[A] by the experiments made upon glaciers, and the
+consequent impression left upon the public mind--that ice possesses the
+"gluey tenacity" which the term viscous suggests--to which these
+observations are meant to apply.
+
+
+FOOTNOTES:
+
+[A] "The viscosity, though it cannot be traced in the parts _if very
+minute_ nevertheless _exists_ there, as unequivocally proved by
+experiments on the large scale."--Forbes in 'Phil. Mag.,' vol. x., p.
+301.
+
+
+
+
+HEAT AND WORK.
+
+(19.)
+
+
+[Sidenote: CONNEXION OF NATURAL FORCES.]
+
+Great scientific principles, though usually announced by individuals,
+are often merely the distinct expression of thoughts and convictions
+which had long been entertained by all advanced investigators. Thus the
+more profound philosophic thinkers had long suspected a certain
+equivalence and connexion between the various forces of nature;
+experiment had shown the direct connexion and mutual convertibility of
+many of them, and the spiritual insight, which, in the case of the true
+experimenter, always surrounds and often precedes the work of his hands,
+revealed more or less plainly that natural forces either had a common
+root, or that they formed a circle, whose links were so connected that
+by starting from any one of them we could go through the circuit, and
+arrive at the point from which we set out. For the last eighteen years
+this subject has occupied the attention of some of the ablest natural
+philosophers, both in this country and on the Continent. The connexion,
+however, which has most occupied their minds is that between _heat_ and
+_work_; the absolute numerical equivalence of the two having, I believe,
+been first announced by a German physician named Mayer, and
+experimentally proved in this country by Mr. Joule.
+
+[Sidenote: MECHANICAL EQUIVALENT OF HEAT.]
+
+A lead bullet may be made hot enough to burn the hand, by striking it
+with a hammer, or by rubbing it against a board; a clever blacksmith can
+make a nail red-hot by hammering it; Count Rumford boiled water by the
+heat developed in the boring of cannon, and inferred from the experiment
+that heat was not what it was generally supposed to be, an imponderable
+fluid, but a kind of motion generated by the friction. Now Mr. Joule's
+experiments enable us to state the exact amount of heat which a definite
+expenditure of mechanical force can originate. I say _originate_, not
+drag from any hiding-place in which it had concealed itself, but
+actually bring into existence, so that the total amount of heat in the
+universe is thereby augmented. If a mass of iron fall from a tower 770
+feet in height, we can state the precise amount of heat developed by its
+collision with the earth. Supposing all the heat thus generated to be
+concentrated in the iron itself, its temperature would thereby be raised
+nearly 10 deg. Fahr. Gravity in this case has expended a certain amount of
+force in pulling the iron to the earth, and this force is the
+_mechanical equivalent_ of the heat generated. Furthermore, if we had a
+machine so perfect as to enable us to apply all the heat thus produced
+to the raising of a weight, we should be able, by it, to lift the mass
+of iron to the precise point from which it fell.
+
+But the heat cannot lift the weight and still continue heat; this is the
+peculiarity of the modern view of the matter. The heat is consumed, used
+up, it is no longer heat; but instead of it we have a certain amount of
+gravitating force stored up, which is ready to act again, and to
+regenerate the heat when the weight is let loose. In fact, when the
+falling weight is stopped by the earth, the motion of its mass is
+converted into a motion of its molecules; when the weight is lifted by
+heat, molecular motion is converted into ordinary mechanical motion, but
+for every portion of either of them brought into existence an equivalent
+portion of the other must be consumed.
+
+What is true for masses is also true for atoms. As the earth and the
+piece of iron mutually attract each other, and produce heat by their
+collision, so the carbon of a burning candle and the oxygen of the
+surrounding air mutually attract each other; they rush together, and on
+collision the arrested motion becomes heat. In the former case we have
+the conversion of gravity into heat, in the latter the conversion of
+chemical affinity into heat; but in each case the process consists in
+the generation of motion by attraction, and the subsequent change of
+that motion into motion of another kind. Mechanically considered, the
+attraction of the atoms and its results is precisely the same as the
+attraction of the earth and weight and _its_ results.
+
+[Sidenote: HEAT PRODUCED IF THE EARTH STRUCK THE SUN.]
+
+But what is true for an atom is also true for a planet or a sun.
+Supposing our earth to be brought to rest in her orbit by a sudden
+shock, we are able to state the exact amount of heat which would be
+thereby generated. The consequence of the earth's being thus brought to
+rest would be that it would fall into the sun, and the amount of heat
+which would be generated by this second collision is also calculable.
+Helmholtz has calculated that in the former case the heat generated
+would be equal to that produced by the combustion of fourteen earths of
+solid coal, and in the latter case the amount would be 400 times
+greater.
+
+[Sidenote: SHIFTING OF ATOMS.]
+
+Whenever a weight is lifted by a steam-engine in opposition to the force
+of gravity an amount of heat is consumed equivalent to the work done;
+and whenever the molecules of a body are shifted in opposition to their
+mutual attractions work is also performed, and an equivalent amount of
+heat is consumed. Indeed the amount of work done in the shifting of the
+molecules of a body by heat, when expressed in ordinary mechanical work,
+is perfectly enormous. The lifting of a heavy weight to the height of
+1000 feet may be as nothing compared with the shifting of the atoms of a
+body by an amount so small that our finest means of measurement hardly
+enable us to determine it. Different bodies give heat different degrees
+of trouble, if I may use the term, in shifting their atoms and putting
+them in new places. Iron gives more trouble than lead; and water gives
+far more trouble than either. The heat expended in this molecular work
+is lost as heat; it does not show itself as temperature. Suppose the
+heat produced by the combustion of an ounce of candle to be concentrated
+in a pound of iron, a certain portion of that heat would go to perform
+the molecular work to which I have referred, and the remainder would be
+expended in raising the temperature of the body; and if the same amount
+of heat were communicated to a pound of iron and to a pound of lead, the
+balance in favour of temperature would be greater in the latter case
+than in the former, because the heat would have less molecular work to
+do; the lead would become more heated than the iron. To raise a pound of
+iron a certain number of degrees in temperature would, in fact, require
+more than three times the absolute quantity of heat which would be
+required to raise a pound of lead the same number of degrees.
+Conversely, if we place the pound of iron and the pound of lead, heated
+to the same temperature, into ice, we shall find that the quantity of
+ice melted by the iron will be more than three times that melted by the
+lead. In fact, the greater amount of molecular work invested in the iron
+now comes into play, the atoms again obey their own powerful forces, and
+an amount of heat corresponding to the energy of these forces is
+generated.
+
+This molecular work is that which has usually been called _specific
+heat_, or _capacity for heat_. According to the _materialistic_ view of
+heat, bodies are figured as sponges, and heat as a kind of fluid
+absorbed by them, different bodies possessing different powers of
+absorption. According to the _dynamic_ view, as already explained, heat
+is regarded as a motion, and capacity for heat indicates the quantity of
+that motion consumed in internal changes.
+
+The greatest of these changes occurs when a body passes from one state
+of aggregation to another, from the solid to the liquid, or from the
+liquid to the aeriform state; and the quantity of heat required for such
+changes is often enormous. To convert a pound of ice at 32 deg. Fahr. into
+water _at the same temperature_ would require an amount of heat
+competent, if applied as mechanical force, to lift the same pound of ice
+to a height of 110,000 feet; it would raise a ton of ice nearly 50 feet,
+or it would lift between 49 and 50 tons to a height of one foot above
+the earth's surface. To convert a pound of water at 212 deg. into a pound of
+steam at the same temperature would require an amount of heat which
+would perform nearly seven times the amount of mechanical work just
+mentioned.
+
+[Sidenote: HEAT CONSUMED IN MOLECULAR WORK.]
+
+This heat is entirely expended in _interior work_,[A] and does nothing
+towards augmenting the temperature; the water is at the temperature of
+the ice which produced it, both are 32 deg.; and the steam is at the
+temperature of the water which produced it, both are 212 deg. The whole of
+the heat is consumed in producing the change of aggregation; I say
+"_consumed_," not hidden or "latent" in either the water or the steam,
+but absolutely non-existent as heat. The molecular forces, however,
+which the heat has sacrificed itself to overcome are able to reproduce
+it; the water in freezing and the steam in condensing give out the exact
+amount of heat which they consumed when the change of aggregation was in
+the opposite direction.
+
+At a temperature of several degrees below its freezing point ice is much
+harder than at 32 deg. I have more than once cooled a sphere of the
+substance in a bath of solid carbonic acid and ether to a temperature of
+100 deg. below the freezing point. During the time of cooling the ice
+crackled audibly from its contraction, and afterwards it quite resisted
+the edge of a knife; while at 32 deg. it may be cut or crushed with extreme
+facility. The cold sphere was subjected to pressure; it broke with the
+detonation of a vitreous body, and was taken from the press a white
+opaque powder; which, on being subsequently raised to 32 deg. and again
+compressed, was converted into a pellucid slab of ice.
+
+[Sidenote: ICE NEAR THE MELTING POINT.]
+
+But before the temperature of 32 deg. is quite attained, ice gives evidence
+of a loosening of its crystalline texture. Indeed the unsoundness of ice
+at and near its melting point has been long known. Sir John Leslie, for
+example, states that ice at 32 deg. is _friable_; and every skater knows how
+rotten ice becomes before it thaws. M. Person has further shown that the
+latent heat of ice, that is to say, the quantity of heat necessary for
+its liquefaction, is not quite expressed by the quantity consumed in
+reducing ice at 32 deg. to the liquid state. The heat begins to be rendered
+latent, or in other words the change of aggregation commences, a little
+before the substance reaches 32 deg.,--a conclusion which is illustrated and
+confirmed by the deportment of melting ice under pressure.
+
+[Sidenote: ROTTEN ICE AND SOFTENED WAX.]
+
+In reference to the above result Professor Forbes writes as follows:--"I
+have now to refer to a fact ... established by a French experimenter, M.
+Person, who appears not to have had even remotely in his mind the theory
+of glaciers, when he announced the following facts, viz.--'That ice does
+not pass abruptly from the solid to the fluid state; that it begins to
+_soften_ at a temperature of 2 deg. Centigrade below its thawing point;
+that, consequently, between 28 deg. 4' and 32 deg. of Fahr. ice is actually
+passing through various degrees of plasticity within narrower limits,
+but in the same manner that wax, for example, softens before it melts.'"
+The "_softening_" here referred to is the "friability," of Sir J.
+Leslie, and what I have called a "loosening of the texture." Let us
+suppose the Serpentine covered by a sheet of pitch so smooth and hard as
+to enable a skater to glide over it; and which is afterwards gradually
+warmed until it begins to bend under his weight, and finally lets him
+through. A comparison of this deportment with that of a sheet of ice
+under the same circumstances enables us to decide whether ice "passes
+through various degrees of plasticity in the same manner as wax softens
+before it melts." M. Person concerned himself solely with the heat
+absorbed, and no doubt in both wax and ice that heat is expended in
+"interior work." In the one case, however, the body is so constituted
+that the absorbed heat is expended in rendering the substance viscous;
+and the question simply is, whether the heat absorbed by the ice gives
+its molecules a freedom of play which would entitle it also to be called
+viscous; whether, in short, "rotten ice" and softened wax present the
+same physical qualities?
+
+
+FOOTNOTES:
+
+[A] I borrow this term from Professor Clausius's excellent papers on the
+Dynamical Theory of Heat.
+
+
+
+
+(20.)
+
+
+There is one other point in connexion with the viscous theory which
+claims our attention. The announcement of that theory startled
+scientific men, and for two or three years after its first publication
+it formed the subject of keen discussion. This finally subsided, and
+afterwards Professor Forbes drew up an elaborate paper, which was
+presented in three parts to the Royal Society in 1845 and 1846, and
+subsequently published in the 'Philosophical Transactions.'
+
+In the concluding portion of Part III. Professor Forbes states and
+answers the question, "How far a glacier is to be regarded as a plastic
+mass?" in these words:--"Were a glacier composed of a solid crystalline
+cake of ice, fitted or moulded to the mountain bed which it occupies,
+like a lake tranquilly frozen, it would seem impossible to admit such a
+flexibility or yielding of parts as should permit any comparison to a
+fluid or semifluid body, transmitting pressure horizontally, and whose
+parts might change their mutual positions so that one part should be
+pushed out whilst another remained behind. But we know, in point of
+fact, that a glacier is a body very differently constituted. It is
+clearly proved by the experiments of Agassiz and others that the glacier
+is not a mass of ice, but of ice and water, the latter percolating
+freely through the crevices of the former to all depths of the glacier;
+and it is a matter of ocular demonstration that these crevices, though
+very minute, communicate freely with one another to great distances; the
+water with which they are filled communicates force also to great
+distances, and exercises a tremendous hydrostatic pressure to move
+onwards in the direction in which gravity urges it, the vast porous mass
+of seemingly rigid ice in which it is as it were bound up."
+
+[Sidenote: CAPILLARY HYPOTHESIS.]
+
+"Now the water in the crevices," continues Professor Forbes, "does not
+constitute the glacier, but only the principal vehicle of the force
+which acts on it, and the slow irresistible energy with which the icy
+mass moves onwards from hour to hour with a continuous march, bespeaks
+of itself the presence of a fluid pressure. But if the ice were not in
+some degree ductile or plastic, this pressure could never produce any
+the least forward motion of the mass. The pressure in the capillaries of
+the glacier can only tend to separate one particle from another, and
+thus produce tensions and compressions _within the body of the glacier
+itself_, which yields, owing to its slightly ductile nature, in the
+direction of least resistance, retaining its continuity, or recovering
+it by reattachment after its parts have suffered a bruise, according to
+the violence of the action to which it has been exposed."
+
+I will not pretend to say that I fully understand this passage, but,
+taking it and the former one together, I think it is clear that the
+water which is supposed to gorge the capillaries of the glacier is
+assumed to be essential to its motion. Indeed, an extreme degree of
+sensitiveness has been ascribed to the glacier as regards the changes of
+temperature by which the capillaries are affected. In three succeeding
+days, for example, Professor Forbes found the diurnal summer motion of a
+point upon the Mer de Glace to increase from 15.2 to 17.5 inches a day;
+a result which he says he is "persuaded" to be due to the increasing
+heat of the weather at the time. If, then, the glacier capillaries can
+be gorged so quickly as this experiment would indicate, it is fair to
+assume that they are emptied with corresponding speed when the supply is
+cut away.
+
+[Sidenote: TEMPERATURE AT CHAMOUNI; WINTER 1859.]
+
+The extraordinary coldness of the weather previous to the Christmas of
+1859 is in the recollection of everybody: this lowness of temperature
+also extended to the Mer de Glace and its environs. I had last summer
+left with Auguste Balmat and the Abbe Vueillet thermometers with which
+observations were made daily during the cold weather referred to. I take
+the following from Balmat's register.
+
+ Minimum
+ Date. temperature
+ Centigrade.
+ December 16 -15 deg.
+ " 17 -20
+ " 18 -16-1/2
+ " 19 -9
+ " 20 -13
+ " 21 -20-1/2
+ " 22 -4-1/4
+ December 23 -4-1/2 deg.
+ " 24 -6-1/2
+ " 25 -2
+ " 26 +2
+ " 27 -3
+ " 28 -10-1/2
+ " 29 -6
+
+The temperature at the Montanvert during the above period may be assumed
+as generally some degrees lower, so that for a considerable period,
+previous to my winter observations, the portion of the Mer de Glace near
+the Montanvert had been exposed to a very low temperature. I reached
+the place after the weather had become warm, but during my stay there
+the maximum temperature did not exceed -4-1/2 deg. C. Considering therefore
+the long drain to which the glacier had been subjected previous to the
+29th of December, it is not unreasonable to infer that the capillary
+supply assumed by Professor Forbes must by that time have been
+exhausted. Notwithstanding this, the motion of the glacier at the
+Montanvert amounted at the end of December to half its maximum summer
+motion.
+
+[Sidenote: BALMAT'S MEASUREMENTS.]
+
+The observations of Balmat which have been published by Professor
+Forbes[A] also militate, as far as they go, against the idea of
+proportionality between the capillary supply and the motion. If the
+temperatures recorded apply to the Mer de Glace during the periods of
+observation, it would follow that from the 19th of December 1846 to the
+12th of April 1847 the temperature of the air was constantly under zero
+Centigrade, and hence, during this time, the gorging of the capillaries,
+which is due to superficial melting, must have ceased. Still, throughout
+this entire period of depletion the motion of the glacier steadily
+increased from twenty-four inches to thirty-four and a half inches a
+day. What has been here said of the Montanvert, and of the points lower
+down where Balmat's measurements were made, of course applies with
+greater force to the higher portions of the glacier, which are withdrawn
+from the operation of superficial melting for a longer period, and
+which, nevertheless, if I understand Professor Forbes aright, have their
+motion _least affected_ in winter. He records, for example, an
+observation of Mr. Bakewell's, by which the Glacier des Bossons is shown
+to be stationary at its end, while its upper portions are moving at the
+rate of a foot a day. This surely indicates that, at those places where
+the glacier is longest cut off from superficial supply, the motion is
+least reduced, which would be a most strange result if the motion
+depended, as affirmed, upon the gorging of the capillaries.
+
+[Sidenote: BAKEWELL'S OBSERVATIONS.]
+
+The perusal of the conclusion of Professor Forbes's last volume shows me
+that a thought similar to that expressed above occurred to Mr. Bakewell
+also. Speaking of a shallow glacier which moved when the alleged
+temperature was so enormously below the freezing point that Professor
+Forbes regards the observation as open to question (in which I agree
+with him), Mr. Bakewell asks, "Is it possible that infiltrated water can
+have any action whatever under such circumstances?" The reply of
+Professor Forbes contains these words:--"I have nowhere affirmed the
+presence of liquid water to be a _sine qua non_ to the plastic motion of
+glaciers." This statement, I confess, took me by surprise, which was not
+diminished by further reading. Speaking of the influence of temperature
+on the motion of the Mer de Glace, Professor Forbes says, the glacier
+"took no real start until the frost had given way, and the tumultuous
+course of the Arveiron showed that its veins were again filled with the
+circulating medium to which the glacier, like the organic frame, owes
+its moving energy."[B] And again:--"It is this fragility precisely
+which, yielding to the hydrostatic pressure of the unfrozen water
+contained in the countless capillaries of the glacier, produces the
+crushing action which shoves the ice over its neighbour particles."[C]
+
+[Sidenote: HUXLEY'S OBSERVATIONS.]
+
+After the perusal of the foregoing paragraphs the reader will probably
+be less interested in the question as to whether the assumed capillaries
+exist at all in the glacier. According to Mr. Huxley's observations,
+they do not.[D] During the summer of 1857 he carefully experimented with
+coloured liquids on the Mer de Glace and its tributaries, and in no case
+was he able to discover these fissures in the sound unweathered ice. I
+have myself seen the red liquid resting in an auger-hole, where it had
+lain for an hour without diffusing itself in any sensible degree. This
+cavity intersected both the white ice and the blue veins of the glacier;
+and Mr. Huxley, in my presence, cut away the ice until the walls of the
+cavity became extremely thin, still no trace of liquid passed through
+them. Experiments were also made upon the higher portions of the Mer de
+Glace, and also on the Glacier du Geant, with the same result. Thus the
+very existence of these capillaries is rendered so questionable, that no
+theory of glacier-motion which invokes their aid could be considered
+satisfactory.
+
+
+FOOTNOTES:
+
+[A] 'Occ. Pap.,' p. 224.
+
+[B] 'Phil. Trans.,' 1846, p. 137, and 'Occ. Pap.,' p. 138.
+
+[C] 'Occ. Pap.,' p. 47.
+
+[D] 'Phil. Mag.,' 1857, vol. xiv., p. 241.
+
+
+
+
+THOMSON'S THEORY.
+
+(21.)
+
+
+In the 'Transactions' of the Royal Society of Edinburgh for 1849 is
+published a very interesting paper by Prof. James Thomson of Queen's
+College, Belfast, wherein he deduces, as a consequence of a principle
+announced by the French philosopher Carnot, that water, when subjected
+to pressure, requires a greater cold to freeze it than when the pressure
+is removed. He inferred that the lowering of the freezing point for
+every atmosphere of pressure amounted to .0075 of a degree Centigrade.
+This deduction was afterwards submitted to the test of experiment by his
+distinguished brother Prof. Wm. Thomson, and proved correct. On the fact
+thus established is founded Mr. James Thomson's theory of the
+"Plasticity of Ice as manifested in Glaciers."
+
+[Sidenote: STATEMENT OF THEORY.]
+
+The theory is this:--Certain portions of the glacier are supposed first
+to be subjected to pressure. This pressure liquefies the ice, the water
+thus produced being squeezed through the glacier in the direction in
+which it can most easily escape. But cold has been evolved by the act of
+liquefaction, and, when the water has been relieved from the pressure,
+it freezes in a new position. The pressure being thus abolished at the
+place where it was first applied, new portions of the ice are subjected
+to the force; these in their turn liquefy, the water is dispersed as
+before, and re-frozen in some other place. To the succession of
+processes here assumed Mr. Thomson ascribes the changes of form observed
+in glaciers.
+
+This theory was first communicated to the Royal Society through the
+author's brother, Prof. William Thomson, and is printed in the
+'Proceedings' of the Society for May, 1857. It was afterwards
+communicated to the British Association in Dublin, in whose 'Reports'
+it is further published; and again it was communicated to the Belfast
+Literary and Philosophical Society, in whose 'Proceedings' it also finds
+a place.
+
+On the 24th of November, 1859, Mr. James Thomson communicated to the
+Royal Society, through his brother, a second paper, in which he again
+draws attention to his theory. He offers it in substitution for my views
+as the best argument that he can adduce against them; he also
+controverts the explanations of regelation propounded by Prof. James D.
+Forbes and Prof. Faraday, believing that his own theory explains all the
+facts so well as to leave room for no other.
+
+[Sidenote: DIFFICULTIES OF THEORY.]
+
+But the passage in this paper which demands my chief attention is the
+following:--"Prof. Tyndall (writes Mr. Thomson), in papers and lectures
+subsequent to the publication of this theory, appears to adopt it to
+some extent, and to endeavour to make its principles co-operate with the
+views he had previously founded on Mr. Faraday's fact of regelation." I
+may say that Mr. Thomson's main thought was familiar to me long before
+his first communication on the plasticity of ice appeared; but it had
+little influence upon my convictions. Were the above passage correct, I
+should deserve censure for neglecting to express my obligations far more
+explicitly than I have hitherto done; but I confess that even now I do
+not understand the essential point of Mr. Thomson's theory,--that is to
+say, its application to the phenomena of glacier motion. Indeed, it was
+the obscurity in my mind in connexion with this point, and the hope that
+time might enable me to seize more clearly upon his meaning, which
+prevented me from giving that prominence to the theory of Mr. Thomson
+which, for aught I know, it may well deserve. I will here briefly state
+one or two of my difficulties, and shall feel very grateful to have them
+removed.
+
+[Sidenote: IMPROBABLE DEDUCTION.]
+
+Let us fix our attention on a vertical slice of ice transverse to the
+glacier, and to which the pressure is applied perpendicular to its
+surfaces. The ice liquefies, and, supposing the means of escape offered
+to the compressed water to be equal all round, it is plain that there
+will be as great a tendency to squeeze the water upwards as downwards;
+for the mere tendency to flow down by its own gravity becomes, in
+comparison to the forces here acting on the water, a vanishing quantity.
+But the fact is, that the ice above the slice is more permeable than
+that below it; for, as we descend a glacier, the ice becomes more
+compact. Hence the greater part of the dispersed water will be refrozen
+on that side of the slice which is turned towards the origin of the
+glacier; and the consequence is, that, according to Mr. Thomson's
+principle, the glacier ought to move up hill instead of down.
+
+I would invite Mr. Thomson to imagine himself and me together upon the
+ice, desirous of examining this question in a philosophic spirit; and
+that we have taken our places beside a stake driven into the ice, and
+descending with the glacier. We watch the ice surrounding the stake, and
+find that every speck of dirt upon it retains its position; there is no
+liquefaction of the ice that bears the dirt, and consequently it rests
+on the glacier undisturbed. After twelve hours we find the stake fifteen
+inches distant from its first position: I would ask Mr. Thomson how did
+it get there? Or let us fix our attention on those six stakes which M.
+Agassiz drove into the glacier of the Aar in 1841, and found erect in
+1842 at some hundreds of feet from their first position:--how did they
+get there? How, in fine, does the end of a glacier become its end? Has
+it been liquefied and re-frozen? If not, it must have been _pushed_ down
+by the very forces which Mr. Thomson invokes to produce his
+liquefaction. Both the liquefaction, as far as it exists, and the
+motion, are products of the same cause. In short, this theory, as it
+presents itself to my mind, is so powerless to account for the simplest
+fact of glacier-motion, that I feel disposed to continue to doubt my own
+competence to understand it rather than ascribe to Mr. Thomson an
+hypothesis apparently so irrelevant to the facts which it professes to
+explain.
+
+Another difficulty is the following:--Mr. Thomson will have seen that I
+have recorded certain winter measurements made on the Mer de Glace, and
+that these measurements show not only that the ice moves at that period
+of the year, but that it exhibits those characteristics of motion from
+which its plasticity has been inferred; the velocity of the central
+portions of the glacier being in round numbers double the velocity of
+those near the sides. Had there been any necessity for it, this ratio
+might have been augmented by placing the side-stakes closer to the walls
+of the glacier. Considering the extreme coldness of the weather which
+preceded these measurements, it is a moderate estimate to set down the
+temperature of the ice in which my stakes were fixed at 5 deg. Cent. below
+zero.
+
+[Sidenote: REQUISITE PRESSURE CALCULATED.]
+
+Let us now endeavour to estimate the pressure existing at the portion of
+the glacier where these measurements were made. The height of the
+Montanvert above the sea-level is, according to Prof. Forbes, 6300 feet;
+that of the Col du Geant, which is the summit of the principal tributary
+of the Mer de Glace, is 11,146 feet: deducting the former from the
+latter, we find the height of the Col du Geant above the Montanvert to
+be 4846 feet.
+
+Now, according to Mr. Thomson's theory and his brother's experiments,
+the melting point of ice is lowered .0075 deg. Centigrade for every
+atmosphere of pressure; and one atmosphere being equivalent to the
+pressure of about thirty-three feet of water, we shall not be over the
+truth if we take the height of an equivalent column of glacier-ice, of a
+compactness the mean of those which it exhibits upon the Col du Geant
+and at the Montanvert respectively, at forty feet. The compactness of
+glacier ice is, of course, affected by the air-bubbles contained within
+it.
+
+[Sidenote: ACTUAL PRESSURE INSUFFICIENT.]
+
+If, then, the pressure of forty feet of ice lower the melting point
+.0075 deg. Centigrade, it follows that the pressure of a column 4846 feet
+high will lower it nine-tenths of a degree Centigrade. Supposing, then,
+the _unimpeded thrust of the whole glacier, from the Col du Geant
+downwards_, to be exerted on the ice at the Montanvert; or, in other
+words, supposing the bed of the glacier to be absolutely smooth and
+every trace of friction abolished, the utmost the pressure thus obtained
+could perform would be to lower the melting point of the Montanvert ice
+by the quantity above mentioned. Taking into account the actual state of
+things, the friction of the glacier against its sides and bed, the
+opposition which the three tributaries encounter in the neck of the
+valley at Trelaporte, the resistance encountered in the sinuous valley
+through which it passes; and finally, bearing in mind the comparatively
+short length of the glacier, which has to bear the thrust, and oppose
+the latter by its own friction merely;--I think it will appear evident
+that the ice at the Montanvert cannot possibly have its melting point
+lowered by pressure more than a small fraction of a degree.
+
+The ice in which my stakes were fixed being -5 deg. Centigrade, according to
+Mr. Thomson's calculation and his brother's experiments, it would
+require 667 atmospheres of pressure to liquefy it; in other words, it
+would require the unimpeded pressure of a column of glacier-ice 26,680
+feet high. Did Mont Blanc rise to two and a half times its present
+height above the Montanvert, and were the latter place connected with
+the summit of the mountain by a continuous glacier with its bed
+absolutely smooth, the pressure at the Montanvert would be rather under
+that necessary to liquefy the ice on which my winter observations were
+made.
+
+[Sidenote: MEASUREMENTS APPLY TO SURFACE.]
+
+If it be urged that, though the temperature near the surface may be
+several degrees below the freezing point, the great body of the glacier
+does not share this temperature, but is, in all probability, near to
+32 deg., my reply is simple. I did not measure the motion of the ice in the
+body of the glacier; nobody ever did; my measurements refer to the ice
+at and near the surface, and it is this ice which showed the plastic
+deportment which the measurements reveal.
+
+Such, then, are some of the considerations which prevent me from
+accepting the theory of Mr. Thomson, and I trust they will acquit me of
+all desire, to make his theory co-operate with my views. I am, however,
+far from considering his deduction the less important because of its
+failing to account for the phenomena of glacier motion.
+
+
+
+
+THE PRESSURE-THEORY OF GLACIER-MOTION.
+
+(22.)
+
+
+[Sidenote: POSSIBLE MOULDING OF ICE.]
+
+Broadly considered, two classes of facts are presented to the
+glacier-observer; the one suggestive of viscosity, and the other of the
+reverse. The former are seen where _pressure_ comes into play, the
+latter where _tension_ is operative. By pressure ice can be moulded to
+any shape, while the same ice snaps sharply asunder if subjected to
+tension. Were the result worth the labour, ice might be moulded into
+vases or statuettes, bent into spiral bars, and, I doubt not, by the
+proper application of pressure, a _rope_ of ice might be formed and
+coiled into a _knot_. But not one of these experiments, though they
+might be a thousandfold more striking than any ever made upon a glacier,
+would in the least demonstrate that ice is really a viscous body.
+
+[Illustration: Fig. 30. Moulds used in experiments with ice.]
+
+I have here stated what I believe to be feasible. Let me now refer to
+the experiments which have been actually made in illustration of this
+point. Two pieces of seasoned box-wood had corresponding cavities
+hollowed in them, so that, when one was placed upon the other, a
+lenticular space was enclosed. A and B, Fig. 30, represent the pieces
+of box-wood with the cavities in plan: C represents their section when
+they are placed upon each other.
+
+[Sidenote: ACTUAL MOULDING OF ICE.]
+
+A _sphere_ of ice rather more than sufficient to fill the lenticular
+space was placed between the pieces of wood and subjected to the action
+of a small hydraulic press. The ice was crushed, but the crushed
+fragments soon reattached themselves, and, in a few seconds, a lens of
+compact ice was taken from the mould.
+
+[Illustration: Fig. 31. Moulds used in experiments with ice.]
+
+This lens was placed in a cylindrical cavity hollowed out in another
+piece of box-wood, and represented at C, Fig. 31; and a flat piece of
+the wood was placed over the lens as a cover, as at D. On subjecting the
+whole to pressure, the lens broke, as the sphere had done, but the
+crushed mass soon re-established its continuity, and in less than half a
+minute a compact cake of ice was taken from the mould.
+
+[Illustration: Fig. 32. Moulds used in experiments with ice.]
+
+In the following experiment the ice was subjected to a still severer
+test:--A hemispherical cavity was formed in one block of box-wood, and
+upon a second block a hemispherical protuberance was turned, smaller
+than the cavity, so that, when the latter was placed in the former, a
+space of a quarter of an inch existed between the two. Fig. 32
+represents a section of the two pieces of box-wood; the brass pins _a_,
+_b_, fixed in the slab G H, and entering suitable apertures in the mould
+I K, being intended to keep the two surfaces concentric. A lump of ice
+being placed in the cavity, the protuberance was brought down upon it,
+and the mould subjected to hydraulic pressure: after a short interval
+the ice was taken from the mould as a smooth compact _cup_, its crushed
+particles having reunited, and established their continuity.
+
+[Sidenote: ICE MOULDED TO CUPS AND RINGS.]
+
+[Illustration: Fig. 33. Moulds used in experiments with ice.]
+
+To make these results more applicable to the bending of glacier-ice, the
+following experiments were made:--A block of box-wood, M, Fig. 33, 4
+inches long, 3 wide, and 3 deep, had its upper surface slightly curved,
+and a groove an inch wide, and about an inch deep, worked into it. A
+corresponding plate was prepared, having its under surface part of a
+convex cylinder, of the same curvature as the concave surface of the
+former piece. When the one slab was placed upon the other, they
+presented the appearance represented in section at N. A straight prism
+of ice 4 inches long, an inch wide, and a little more than an inch in
+depth, was placed in the groove; the upper slab was placed upon it, and
+the whole was subjected to the hydraulic press. The prism broke, but,
+the quantity of ice being rather more than sufficient to fill the
+groove, the pressure soon brought the fragments together and
+re-established the continuity of the ice. After a few seconds it was
+taken from the mould a bent bar of ice. This bar was afterwards passed
+through three other moulds of gradually augmenting curvature, and was
+taken from the last of them a _semi-ring_ of compact ice.
+
+The ice, in changing its form from that of one mould to that of another,
+was in every instance broken and crushed by the pressure; but suppose
+that instead of three moulds three thousand had been used; or, better
+still, suppose the curvature of a single mould to change by extremely
+slow degrees; the ice would then so gradually change its form that no
+rude rupture would be apparent. Practically the ice would behave as a
+_plastic_ substance; and indeed this plasticity has been contended for
+by M. Agassiz, in opposition to the idea of viscosity. As already
+stated, the ice, bruised, and flattened, and bent in the above
+experiments, was incapable of being sensibly stretched; it was plastic
+to pressure but not to tension.
+
+A quantity of water was always squeezed out of the crushed ice in the
+above experiments, and the bruised fragments were intermixed with this
+and with air. Minute quantities of both remained in the moulded ice, and
+thus rendered it in some degree turbid. Its character, however, as to
+continuity may be inferred from the fact that the ice-cup, moulded as
+described, held water without the slightest visible leakage.
+
+[Sidenote: SOFTNESS OF ICE DEFINED.]
+
+[Sidenote: PRESSURE AND TENSION.]
+
+Ice at 32 deg. may, as already stated, be crushed with extreme facility, and
+glacier-ice with still more readiness than lake-ice: it may also be
+scraped with a knife with even greater facility than some kinds of
+chalk. In comparison with ice at 100 deg. below the freezing point, it might
+be popularly called _soft_. But its softness is not that of paste, or
+wax, or treacle, or lava, or honey, or tar. It is the softness of
+calcareous spar in comparison with that of rock-crystal; and although
+the latter is incomparably harder than the former, I think it will be
+conceded that the term viscous would be equally inapplicable to both. My
+object here is clearly to define terms, and not permit physical error to
+lurk beneath them. How far this ice, with a softness thus defined, when
+subjected to the gradual pressures exerted in a glacier, is bruised and
+broken, and how far the motion of its parts may approach to that of a
+truly viscous body under pressure, I do not know. The critical point
+here is that the ice changes its form, and preserves its continuity,
+during its motion, in virtue of _external_ force. It remains continuous
+whilst it moves, because its particles are kept in juxtaposition by
+pressure, and when this external prop is removed, and the ice, subjected
+to tension, has to depend solely upon the mobility of its own particles
+to preserve its continuity, the analogy with a viscous body instantly
+breaks down.[A]
+
+
+FOOTNOTES:
+
+[A] "Imagine," writes Professor Forbes, "a long narrow trough or canal,
+stopped at both ends and filled to a considerable depth with treacle,
+honey, tar, or any such viscid fluid. Imagine one end of the trough to
+give way, the bottom still remaining horizontal: if the friction of the
+fluid against the bottom be greater than the friction against its own
+particles, the upper strata will roll over the lower ones, and protrude
+in a convex slope, which will be propagated backwards towards the other
+or closed end of the trough. Had the matter been quite fluid the whole
+would have run out, and spread itself on a level: as it is, it assumes
+precisely the conditions which we suppose to exist in a glacier." This
+is perfectly definite, and my equally definite opinion is that no
+glacier ever exhibited the mechanical effects implied by this
+experiment.
+
+
+
+
+REGELATION.
+
+(23.)
+
+
+[Sidenote: FARADAY'S FIRST EXPERIMENT.]
+
+I was led to the foregoing results by reflecting on an experiment
+performed by Mr. Faraday, at a Friday evening meeting of the Royal
+Institution, on the 7th of June, 1850, and described in the 'Athenaeum'
+and 'Literary Gazette' for the same month. Mr. Faraday then showed that
+when two pieces of ice, with moistened surfaces, were placed in contact,
+they became cemented together by the freezing of the film of water
+between them, while, when the ice was below 32 deg. Fahr., and therefore
+_dry_, no effect of the kind could be produced. The freezing was also
+found to take place under water; and indeed it occurs even when the
+water in which the ice is plunged is as hot as the hand can bear.
+
+A generalisation from this interesting fact led me to conclude that a
+bruised mass of ice, if closely confined, must re-cement itself when its
+particles are brought into contact by pressure; in fact, the whole of
+the experiments above recorded immediately suggested themselves to my
+mind as natural deductions from the principle established by Faraday. A
+rough preliminary experiment assured me that the deductions would stand
+testing; and the construction of the box-wood moulds was the
+consequence. We could doubtless mould many solid substances to any
+extent by suitable pressure, breaking the attachment of their particles,
+and re-establishing a certain continuity by the mere force of cohesion.
+With such substances, to which we should never think of applying the
+term viscous, we might also imitate the changes of form to which
+glaciers are subject: but, superadded to the mere cohesion which here
+comes into play, we have, in the case of ice, the actual regelation of
+the severed surfaces, and consequently a more perfect solid. In the
+Introduction to this book I have referred to the production of slaty
+cleavage by pressure; and at a future page I hope to show that the
+lamination of the ice of glaciers is due to the same cause; but, as
+justly observed by Mr. John Ball, there is no tendency to cleave in the
+_sound_ ice of glaciers; in fact, this tendency is obliterated by the
+perfect regelation of the severed surfaces.
+
+[Sidenote: RECENT EXPERIMENTS OF FARADAY.]
+
+Mr. Faraday has recently placed pieces of ice, in water, under the
+strain of forces tending to pull them apart. When two such pieces touch
+at a single point they adhere and move together as a rigid piece; but a
+little lateral force carefully applied breaks up this union with a
+crackling noise, and a new adhesion occurs which holds the pieces
+together in opposition to the force which tends to divide them. Mr.
+James Thomson had referred regelation to the cold produced by the
+liquefaction of the pressed ice; but in the above experiment all
+pressure is not only taken away, but is replaced by tension. Mr. Thomson
+also conceives that, when pieces of ice are simply placed together
+without intentional pressure, the capillary attraction brings the
+pressure of the atmosphere into play; but Mr. Faraday finds that
+regelation takes place _in vacuo_. A true viscidity on the part of ice
+Mr. Faraday never has observed, and he considers that his recent
+experiments support the view originally propounded by himself, namely,
+that a particle of water on a surface of ice becomes solid when placed
+between two surfaces, because of the increased influence due to their
+joint action.
+
+
+
+
+CRYSTALLIZATION AND INTERNAL LIQUEFACTION.
+
+(24.)
+
+
+[Sidenote: HOW CRYSTALS ARE "NURSED."]
+
+In the Introduction to this book I have briefly referred to the force of
+crystallization. To permit this force to exercise its full influence, it
+must have free and unimpeded action; a crystal, for instance, to be
+properly built, ought to be suspended in the middle of the crystallizing
+solution, so that the little architects can work all round it; or if
+placed upon the bottom of a vessel, it ought to be frequently turned, so
+that all its facets may be successively subjected to the building
+process. In this way crystals can be _nursed_ to an enormous size. But
+where other forces mingle with that of crystallization, this harmony of
+action is destroyed; the figures, for example, that we see upon a glass
+window, on a frosty morning, are due to an action compounded of the pure
+crystalline force and the cohesion of the liquid to the window-pane. A
+more regular effect is obtained when the freezing particles are
+suspended in still air, and here they build themselves into those
+wonderful figures which Dr. Scoresby has observed in the Polar Regions,
+Mr. Glaisher at Greenwich, and I myself on the summit of Monte Rosa and
+elsewhere.
+
+Not only however in air, but in water also, figures of great beauty are
+sometimes formed. Harrison's excellent machine for the production of
+artificial ice is, I suppose, now well known; the freezing being
+effected by carrying brine, which had been cooled by the evaporation of
+ether, round a series of flat tin vessels containing water. The latter
+gradually freezes, and, on watching those vessels while the action was
+proceeding very slowly, I have seen little six-rayed stars of thin ice
+forming, and rising to the surface of the liquid. I believe the fact
+was never before observed, but it would be interesting to follow it up,
+and to develop experimentally this most interesting case of
+crystallization.
+
+[Sidenote: DISSECTION OF ICE BY SUNBEAM.]
+
+The surface of a freezing lake presents to the eye of the observer
+nothing which could lead him to suppose that a similar molecular
+architecture is going on there. Still the particles are undoubtedly
+related to each other in this way; they are arranged together on this
+starry type. And not only is this the case at the surface, but the
+largest blocks of ice which reach us from Norway and the Wenham Lake are
+wholly built up in this way. We can reveal the internal constitution of
+these masses by a reverse process to that which formed them; we can send
+an agent into the interior of a mass of ice which shall take down the
+atoms which the crystallizing forces had set up. This agent is a solar
+beam; with which it first occurred to me to make this simple experiment
+in the autumn of 1857. I placed a large converging lens in the sunbeams
+passing through a room, and observed the place where the rays were
+brought to a focus behind the lens; then shading the lens, I placed a
+clear cube of ice so that the point of convergence of the rays might
+fall within it. On removing the screen from the lens, a cone of sunlight
+went through the cube, and along the course of the cone the ice became
+studded with lustrous spots, evidently formed by the beam, as if minute
+reflectors had been suddenly established within the mass, from which the
+light flashed when it met them. On examining the cube afterwards I found
+that each of these spots was surrounded by a liquid flower of six
+petals; such flowers were distributed in hundreds through the ice, being
+usually clear and detached from each other, but sometimes crowded
+together into liquid bouquets, through which, however, the six-starred
+element could be plainly traced. At first the edges of the leaves were
+unbroken curves, but when the flowers expanded under a long-continued
+action, the edges became serrated. When the ice was held at a suitable
+angle to the solar beams, these liquid blossoms, with their central
+spots shining more intensely than burnished silver, presented an
+exhibition of beauty not easily described. I have given a sketch of
+their appearance in Fig. 34.
+
+[Sidenote: LIQUID FLOWERS IN ICE.]
+
+[Illustration: Fig. 34. Liquid Flowers in lake ice.]
+
+I have here to direct attention to an extremely curious fact. On sending
+the sunbeam through the transparent ice, I often noticed that the
+appearance of the lustrous spots was accompanied by an audible clink, as
+if the ice were ruptured inwardly. But there is no ground for assuming
+such rupture, and on the closest examination no flaw is exhibited by the
+ice. What then can be the cause of the noise? I believe the following
+considerations will answer the question:--
+
+Water always holds a quantity of air in solution, the diffusion of which
+through the liquid, as proved by M. Donny, has an immense effect in
+weakening the cohesion of its particles; recent experiments of my own
+show that this is also the case in an eminent degree with many volatile
+liquids. M. Donny has proved that, if water be thoroughly purged of its
+air, a long glass tube filled with this liquid may be inverted, while
+the tenacity with which the water clings to the tube, and with which its
+particles cling to each other, is so great that it will remain securely
+suspended, though no external hindrance be offered to its descent. Owing
+to the same cause, water deprived of its air will not boil at 212 deg.
+Fahr., and may be raised to a temperature of nearly 300 deg. without
+boiling; but when this occurs the particles break their cohesion
+suddenly, and ebullition is converted into explosion.
+
+Now, when ice is formed, every trace of the air which the water
+contained is squeezed out of it; the particles in crystallizing reject
+all extraneous matter, so that in ice we have a substance quite free
+from the air, which is never absent in the case of water; it therefore
+follows that if we could preserve the water derived from the melting of
+ice from contact with the atmosphere, we should have a liquid eminently
+calculated to show the effects described by M. Donny. Mr. Faraday has
+proved by actual experiment that this is the case.
+
+[Sidenote: WATER DEPRIVED OF AIR SNAPS ASUNDER.]
+
+Let us apply these facts to the explanation of the clink heard in my
+experiments. On sending a sunbeam through ice, liquid cavities are
+suddenly formed at various points within the mass, and these cavities
+are completely cut off from atmospheric contact. But the water formed by
+the melting ice is less in volume than the ice which produces it; the
+water of a cavity is not able to fill it, hence a vacuous space must be
+formed in the cell. I have no doubt that, for a time, the strong
+cohesion between the walls of the cell and the drop within it augments
+the volume of the latter a little, so as to compel it to fill the cell;
+but as the quantity of liquid becomes greater the shrinking force
+augments, until finally the particles snap asunder like a broken spring.
+At the same moment a lustrous spot appears, which is a vacuum, and
+simultaneously with the appearance of this vacuum the clink was always
+heard. Multitudes of such little explosions must be heard upon a glacier
+when the strong summer sun shines upon it, the aggregate of which must,
+I think, contribute to produce the "crepitation" noticed by M. Agassiz,
+and to which I have already referred.
+
+[Sidenote: FIGURES IN ICE; VACUOUS SPOTS.]
+
+In Plate VI. of the Atlas which accompanies the 'Systeme Glaciaire' of
+M. Agassiz, I notice drawings of figures like those I have described,
+which he has observed in glacier-ice, and which were doubtless produced
+by direct solar radiation. I have often myself observed figures of
+exquisite beauty formed in the ice on the surface of glacier-pools by
+the morning sun. In some cases the spaces between the leaves of the
+liquid flowers melt partially away, and leave the central spot
+surrounded by a crimped border; sometimes these spaces wholly disappear,
+and the entire space bounded by the lines drawn from point to point of
+the leaves becomes liquid, thus forming perfect hexagons. The crimped
+borders exhibit different degrees of serration, from the full leaves
+themselves to a gentle undulating line, which latter sometimes merges
+into a perfect circle. In the ice of glaciers, I have seen the internal
+liquefaction ramify itself like sprigs of myrtle; in the same ice, and
+particularly towards the extremities of the glacier, disks innumerable
+are also formed, consisting of flat round liquid spaces, a bright spot
+being usually associated with each. These spots have been hitherto
+mistaken for air-bubbles; but both they and the lustrous disks at the
+centres of the flowers are vacuous. I proved them to be so by plunging
+the ice containing them into hot water, and watching what occurred when
+the walls of the cells were dissolved, and a liquid connexion
+established between them and the atmosphere. In all cases they totally
+collapsed, and no trace of air rose to the surface of the warm water.
+
+No matter in what direction a solar beam is sent through lake-ice, the
+liquid flowers are all formed parallel to the surface of freezing. The
+beam may be sent parallel, perpendicular, or oblique to this surface;
+the flowers are always formed in the same planes. Every line
+perpendicular to the surface of a frozen lake is in fact an axis of
+symmetry, round which the molecules so arrange themselves, that, when
+taken down by the delicate fingers of the sunbeam, the six-leaved liquid
+flowers are the result.
+
+In the ice of glaciers we have no definite planes of freezing. It is
+first snow, which has been disturbed by winds while falling, and whirled
+and tossed about by the same agency after it has fallen, being often
+melted, saturated with its own water, and refrozen: it is cast in
+shattered fragments down cascades, and reconsolidated by pressure at the
+bottom. In ice so formed and subjected to such mutations, definite
+planes of freezing are, of course, out of the question.
+
+[Sidenote: CONSTITUTION OF GLACIER-ICE.]
+
+The flat round disks and vacuous spots to which I have referred come
+here to our aid, and furnish us with an entirely new means of analysing
+the internal constitution of a glacier. When we examine a mass of
+glacier-ice which contains these disks, we find them lying in all
+imaginable planes; not confusedly, however--closer examination shows us
+that the disks are arranged in groups, the members of each group being
+parallel to a common plane, but the parallelism ceases when different
+groups are compared. The effect is exactly what would be observed,
+supposing ordinary lake-ice to be broken up, shaken together, and the
+confused fragments regelated to a compact continuous mass. In such a
+jumble the original planes of freezing would lie in various directions;
+but no matter how compact or how transparent ice thus constituted might
+appear, a solar beam would at once reveal its internal constitution by
+developing the flowers parallel to the planes of freezing of the
+respective fragments. A sunbeam sent through glacier-ice always reveals
+the flowers in the planes of the disks, so that the latter alone at
+once informs us of its crystalline constitution.
+
+[Sidenote: VACUOUS CELLS MISTAKEN FOR AIR-CELLS.]
+
+Hitherto, as I have said, these disks have been mistaken for bubbles
+containing air, and their flattening has been ascribed to the pressure
+to which they have been subjected. M. Agassiz thus refers to them:--"The
+air-bubbles undergo no less curious modifications. In the neighbourhood
+of the _neve_, where they are most numerous, those which one sees on the
+surface are all spherical or ovoid, but by degrees they begin to be
+flattened, and near the end of the glacier there are some that are so
+flat _that they might be taken for fissures when seen in profile_. The
+drawing represents a piece of ice detached from the gallery of
+infiltration. All the bubbles are greatly flattened. But what is most
+extraordinary is, that, far from being uniform, _the flattening is
+different in each fragment_; so that the bubbles, according to the face
+which they offer, appear either very broad or very thin." This
+description of glacier-ice is correct: it agrees with the statements of
+all other observers. But there are two assumptions in the description
+which must henceforth be given up; first, the bubbles seen like fissures
+in profile are not air-bubbles at all, but vacuous spots, which the very
+constitution of ice renders a necessary concomitant of its inward
+melting; secondly, the assumption that the bubbles have been _flattened_
+by pressure must be abandoned; for they are found, and may be developed
+at will, in lake-ice on which no pressure has been exerted.
+
+[Sidenote: CELLS OF AIR AND WATER.]
+
+But these remarks dispose only of a certain class of cells contained in
+glacier-ice. Besides the liquid disks and vacuous spots, there are
+innumerable true bubbles entangled in the mass. These have also been
+observed and described by M. Agassiz; and Mr. Huxley has also given us
+an accurate account of them. M. Agassiz frequently found air and water
+associated in the same cell. Mr. Huxley found no exception to the rule:
+in each case the bubble of air was enclosed in a cell which was also
+partially filled with water. He supposes that the water may be that of
+the originally-melted snow which has been carried down from the _neve_
+unfrozen. This hypothesis is worthy of a great deal more consideration
+than I have had time to give to it, and I state it here in the hope that
+it will be duly examined.
+
+My own experience of these associated air and water cells is derived
+almost exclusively from lake-ice, in which I have often observed them in
+considerable numbers. In examining whether the liquid contents had ever
+been frozen or not, I was guided by the following considerations. If the
+air be that originally entangled in the solid, it will have the ordinary
+atmospheric density at least; but if it be due to the melting of the
+walls of the cell, then the water so formed being only eight-ninths of
+that of the ice which produced it, _the air of the bubble must be
+rarefied_. I suppose I have made a hundred different experiments upon
+these bubbles to determine whether the air was rarefied or not, and in
+every case found it so. Ice containing the bubbles was immersed in warm
+water, and always, when the rigid envelope surrounding a bubble was
+melted away, the air suddenly collapsed to a fraction of its original
+dimensions. I think I may safely affirm that, in some cases, the
+collapse reduced the bubbles to the thousandth part of their original
+volume. From these experiments I should undoubtedly infer, that in
+lake-ice at least, the liquid of the cells is produced by the melting of
+the ice surrounding the bubbles of air.
+
+But I have not subjected the bubbles of glacier-ice to the same
+searching examination. I have tried whether the insertion of a pin would
+produce the collapse of the bubbles, but it did not appear to do so. I
+also made a few experiments at Rosenlaui, with warm water, but the
+result was not satisfactory. That ice melts internally at the surfaces
+of the bubbles is, I think, rendered certain by my experiments, but
+whether the water-cells of glacier-ice are entirely due to such melting,
+subsequent observers will no doubt determine.
+
+[Sidenote: "LIQUID LIBERTY."]
+
+I have found these composite bubbles at all parts of glaciers; in the
+ice of the moraines, over which a protective covering had been thrown;
+in the ice of sand-cones, after the removal of the superincumbent
+debris; also in ice taken from the roofs of caverns formed in the
+glacier, and which the direct sunlight could hardly by any possibility
+attain. That ice should liquefy at the surface of a cavity is, I think,
+in conformity with all we know concerning the physical nature of heat.
+Regarding it as a motion of the particles, it is easy to see that this
+motion is less restrained at the surface of a cavity than in the solid
+itself, where the oscillation of each atom is controlled by the
+particles which surround it; hence _liquid liberty_, if I may use the
+term, is first attained at the surface. Indeed I have proved by
+experiment that ice may be melted internally by heat which has been
+conducted through its external portions without melting them. These
+facts are the exact complements of those of "regelation;" for here, two
+moist surfaces of ice being brought into close contact, their liquid
+liberty is destroyed and the surfaces freeze together.
+
+
+
+
+THE MOULINS.
+
+(25.)
+
+
+[Sidenote: MOULIN OF GRINDELWALD GLACIER.]
+
+[Sidenote: DEPTH OF THE SHAFT.]
+
+The first time I had an opportunity of seeing these remarkable
+glacier-chimneys was in the summer of 1856, upon the lower glacier of
+Grindelwald. Mr. Huxley was my companion at the time, and on crossing
+the so-called Eismeer we heard a sound resembling the rumble of distant
+thunder, which proceeded from a perpendicular shaft formed in the ice,
+and into which a resounding cataract discharged itself. The tube in fact
+resembled a vast organ-pipe, whose thunder-notes were awakened by the
+concussion of the falling water, instead of by the gentle flow of a
+current of air. Beside the shaft our guide hewed steps, on which we
+stood in succession, and looked into the tremendous hole. Near the first
+shaft was a second and smaller one, the significance of which I did not
+then understand; it was not more than 20 feet deep, but seemed filled
+with a liquid of exquisite blue, the colour being really due to the
+magical shimmer from the walls of the moulin, which was quite empty. As
+far as we could see, the large shaft was vertical, but on dropping a
+stone into it a shock was soon heard, and after a succession of bumps,
+which occupied in all seven seconds, we heard the stone no more. The
+depth of the moulin could not be thus ascertained, but we soon found a
+second and still larger one which gave us better data. A stone dropped
+into this descended without interruption for four seconds, when a
+concussion was heard; and three seconds afterwards the final shock was
+audible: there was thus but a single interruption in the descent.
+Supposing all the acquired velocity to have been destroyed by the shock,
+by adding the space passed over by the stone in four and in three
+seconds respectively, and making allowance for the time required by the
+sound to ascend from the bottom, we find the depth of the shaft to be
+about 345 feet. There is, however, no reason to suppose that this
+measures the depth of the glacier at the place referred to. These shafts
+are to be found in almost all great glaciers; they are very numerous in
+the Unteraar Glacier, numbers of them however being empty. On the Mer de
+Glace they are always to be found in the region of Trelaporte, one of
+the shafts there being, _par excellence_, called the Grand Moulin. Many
+of them also occur on the Glacier de Lechaud.
+
+As truly observed by M. Agassiz, these moulins occur only at those parts
+of the glacier which are not much rent by fissures, for only at such
+portions can the little rills produced by superficial melting collect to
+form streams of any magnitude. The valley of unbroken ice formed in the
+Mer de Glace near Trelaporte is peculiarly favourable for the collection
+of such streams; we see the little rills commencing, and enlarging by
+the contributions of others, the trunk-rill pouring its contents into a
+little stream which stretches out a hundred similar arms over the
+surface of the glacier. Several such streams join, and finally a
+considerable brook, which receives the superficial drainage of a large
+area, cuts its way through the ice.
+
+[Sidenote: MOULINS EXPLAINED.]
+
+But although this portion of the glacier is free from those
+long-continued and permanent strains which, having once rent the ice,
+tend subsequently to widen the rent and produce yawning crevasses, it is
+not free from local strains sufficient to produce _cracks_ which
+penetrate the glacier to a great depth. Imagine such a crack
+intersecting such a glacier-rivulet as we have described. The water
+rushes down it, and soon scoops a funnel large enough to engulf the
+entire stream. The moulin is thus formed, and, as the ice moves
+downward, the sides of the crack are squeezed together and regelated,
+the seam which marks the line of junction being in most cases distinctly
+visible. But as the motion continues, other portions of the glacier come
+into the same state of strain as that which produced the first crack; a
+second one is formed across the stream, the old shaft is forsaken, and a
+new one is hollowed out, in which for a season the cataract plays the
+thunderer. I have in some cases counted the forsaken shafts of six old
+moulins in advance of an active one. Not far from the Grand Moulin of
+the Mer de Glace in 1857 there was a second empty shaft, which evidently
+communicated by a subglacial duct with that into which the torrent was
+precipitated. Out of the old orifice issued a strong cold blast, the air
+being manifestly impelled through the duct by the falling water of the
+adjacent moulin.
+
+These shafts are always found in the same locality; the portion of the
+Mer de Glace to which I have referred is never without them. Some of the
+guides affirm that they are motionless; and a statement of Prof. Forbes
+has led to the belief that this was also his opinion.[A] M. Agassiz,
+however, observed the motion of some of these shafts upon the glacier of
+the Aar; and when on the spot in 1857, I was anxious to decide the point
+by accurate measurements with the theodolite.
+
+My friend Mr. Hirst took charge of the instrument, and on the 28th of
+July I fixed a single stake beside the Grand Moulin, in a straight line
+between a station at Trelaporte and a well-defined mark on the rock at
+the opposite side of the valley. On the 31st, the displacement of the
+stake amounted to 50 inches, and on the 1st of August it had moved
+74-1/2 inches--the moulin, to all appearance, occupying throughout the
+same position with regard to the stake. To render this certain,
+moreover we subsequently drove two additional stakes into the ice, thus
+enclosing the mouth of the shaft in a triangle. On the 8th of August the
+displacements were measured and gave the following results:--
+
+ Total Motion.
+ First (old) stake 198 inches.
+ Second (new) do. 123 "
+ Third 124 "
+
+[Sidenote: MOTION OF THE MOULINS.]
+
+The old stake had been fixed for 11 days, and its daily motion--_which
+was also that of the moulin_--averaged 18 inches a day. Hence the
+moulins share the general motion of the glacier, and their apparent
+permanence is not, as has been alleged, a proof of the semi-fluidity of
+the glacier, but is due to the breaking of the ice as it passes the
+place of local strain.
+
+[Sidenote: DEPTH OF "GRAND MOULIN" SOUGHT.]
+
+Wishing to obtain some estimate as to the depth of the ice, Mr. Hirst
+undertook the sounding of some of the moulins upon the Glacier de
+Lechaud, making use of a tin vessel filled with lumps of lead and iron
+as a weight. The cord gave way and he lost his plummet. To measure the
+depth of the Grand Moulin, we obtained fresh cord from Chamouni, to
+which we attached a four-pound weight. Into a cavity at the bottom of
+the weight we stuffed a quantity of butter, to indicate the nature of
+the bottom against which the weight might strike. The weight was dropped
+into the shaft, and the cord paid out until its slackening informed us
+that the weight had come to rest; by shaking the string, however, and
+walking round the edge of the shaft, the weight was liberated, and sank
+some distance further. The cord partially slackened a second time, but
+the strain still remaining was sufficient to render it doubtful whether
+it was the weight or the action of the falling water which produced it.
+We accordingly paid out the cord to the end, but, on withdrawing it,
+found that the greater part of it had been coiled and knotted up by the
+falling water. We uncoiled, and sounded again. At a depth of 132 feet
+the weight reached a ledge or protuberance of ice, and by shaking and
+lifting it, it was caused to descend 31 feet more. A depth of 163 feet
+was the utmost we could attain to. We sounded the old moulin to a depth
+of 90 feet; while a third little shaft, beside the large one, measured
+only 18 feet in depth. We could see the water escape from it through a
+lateral canal at its bottom, and doubtless the water of the Grand Moulin
+found a similar exit. There was no trace of dirt upon the butter, which
+might have indicated that we had reached the bed of the glacier.
+
+
+FOOTNOTES:
+
+[A] "Every year, and year after year, the watercourses follow the same
+lines of direction--their streams are precipitated into the heart of the
+glacier by vertical funnels, called 'moulins,' at the very same
+points."--Forbes's Fourth Letter upon Glaciers: 'Occ. Pap.,' p. 29.
+
+
+
+
+[Illustration: DIRT-BANDS OF THE MER DE GLACE, AS SEEN FROM A POINT
+NEAR THE FLEGERE.
+Fig. 35. _To face p. 367._]
+
+DIRT-BANDS OF THE MER DE GLACE.
+
+(26.)
+
+
+[Sidenote: DIRT-BANDS FROM THE FLEGERE.]
+
+These bands were first noticed by Prof. Forbes on the 24th of July,
+1842, and were described by him in the following words:--"My eye was
+caught by a very peculiar appearance of the surface of the ice, which I
+was certain that I now saw for the first time. It consisted of nearly
+hyperbolic brownish bands on the glacier, the curves pointing downwards,
+and the two branches mingling indiscriminately with the moraines,
+presenting an appearance of a succession of waves some hundred feet
+apart."[A] From no single point of view hitherto attained can all the
+Dirt-Bands of the Mer de Glace be seen at once. To see those on the
+terminal portion of the glacier, a station ought to be chosen on the
+opposite range of the Brevent, a few hundred yards beyond the Croix de
+la Flegere, where we stand exactly in front of the glacier as it issues
+into the valley of Chamouni. The appearance of the bands upon the
+portion here seen is represented in Fig. 35.
+
+It will be seen that the bands are confined to one side of the glacier,
+and either do not exist, or are obliterated by the debris, upon the
+other side. The cause of the accumulation of dirt on the right side of
+the glacier is, that no less than five moraines are crowded together at
+this side. In the upper portions of the Mer de Glace these moraines are
+distinct from each other; but in descending, the successive engulfments
+and disgorgings of the blocks and dirt have broken up the moraines; and
+at the place now before us the materials which composed them are strewn
+confusedly on the right side of the glacier. The portion of the ice on
+which the dirt-bands appear is derived from the Col du Geant. They do
+not quite extend to the end of the glacier, being obliterated by the
+dislocation of the ice upon the frozen cascade of Des Bois.
+
+[Sidenote: DIRT-BANDS FROM LES CHARMOZ.]
+
+Let us now proceed across the valley of Chamouni to the Montanvert;
+where, climbing the adjacent heights to an elevation of six or eight
+hundred feet above the hotel, we command a view of the Mer de Glace,
+from Trelaporte almost to the commencement of the Glacier des Bois. It
+was from this position that Professor Forbes first observed the bands.
+Fifteen, sixteen, and seventeen years later I observed them from the
+same position. The number of bands which Professor Forbes counted from
+this position was eighteen, with which my observations agree. The entire
+series of bands which I observed, with the exception of one or two, must
+have been the _successors_ of those observed by Professor Forbes; and my
+finding the same number after an interval of so many years proves that
+the bands must be due to some regularly recurrent cause. Fig. 36
+represents the bands as seen from the heights adjacent to the
+Montanvert.
+
+[Illustration: DIRT-BANDS OF THE MER DE GLACE, AS SEEN FROM LES CHARMOZ.
+Fig. 36. _To face p. 368._]
+
+I would here direct attention to an analogy between a glacier and a
+river, which may be observed from the heights above the Montanvert, but
+to which no reference, as far as I know, has hitherto been made. When a
+river meets the buttress of a bridge, the water rises against it, and,
+on sweeping round it, forms an elevated ridge, between which and the
+pier a depression occurs which varies in depth with the force of the
+current. This effect is shown by the Mer de Glace on an exaggerated
+scale. Sweeping round Trelaporte, the ice pushes itself beyond the
+promontory in an elevated ridge, from which it drops by a gradual slope
+to the adjacent wall of the valley, thus forming a depression typified
+by that already alluded to. A similar effect is observed at the opposite
+side of the glacier on turning round the Echelets; and both combine
+to form a kind of skew surface. A careful inspection of the
+frontispiece will detect this peculiarity in the shape of the glacier.
+
+[Sidenote: FROM THE CLEFT-STATION.]
+
+From neither of the stations referred to do we obtain any clue to the
+origin of the dirt-bands. A stiff but pleasant climb will place us in
+that singular cleft in the cliffy mountain-ridge which is seen to the
+right of the frontispiece; and from it we easily attain the high
+platform of rock immediately to the left of it. We stand here high above
+the promontory of Trelaporte, and occupy the finest station from which
+the Mer de Glace and its tributaries can be viewed. From this station we
+trace the dirt-bands over most of the ice that we have already scanned,
+and have the further advantage of being able to follow them to their
+very source.
+
+This source is the grand ice-cascade which descends in a succession of
+precipices from the plateau of the Col du Geant into the valley which
+the Glacier du Geant fills. We see from our present point of view that
+the bands _are confined to the portion of the glacier which has
+descended the cascade_. Fig. 37 represents the bands as seen from the
+Cleft-station above Trelaporte.
+
+[Illustration: DIRT-BANDS OF THE MER DE GLACE, AS SEEN FROM THE CLEFT
+STATION, TRELAPORTE.
+Fig. 37. _To face p. 369._]
+
+We are now however at such a height above the glacier and at such a
+distance from the base of the cascade, that we can form but an imperfect
+notion of the true contour of the surface. Let us therefore descend, and
+walk up the Glacier du Geant towards the cascade. At first our road is
+level, but we gradually find that at certain intervals we have to ascend
+slopes which follow each other in succession, each being separated from
+its neighbour by a space of comparatively level ice. The slopes increase
+in steepness as we ascend; they are steepest, moreover, on the
+right-hand side of the glacier, where it is bounded by that from the
+Periades, and at length we are unable to climb them without the aid of
+an axe. Soon afterwards the dislocation of the glacier becomes
+considerable; we are lost in the clefts and depressions of the ice, and
+are unable to obtain a view sufficiently commanding to subdue these
+local appearances and convey to us the general aspect. We have at all
+events satisfied ourselves as to the existence, on the upper portion of
+the glacier, of a succession of undulations which sweep transversely
+across it. The term "wrinkles," applied to them by Prof. Forbes, is
+highly suggestive of the appearance which they present.
+
+[Sidenote: SNOW-BANDS ON THE GLACIER DU GEANT.]
+
+From the Cleft-station bands of snow may also be seen partially crossing
+the glacier in correspondence with the undulations upon its surface. If
+the quantity deposited the winter previous be large, and the heat of
+summer not too great, these bands extend quite across the glacier. They
+were first observed by Professor Forbes in 1843. In his Fifth Letter is
+given an illustrative diagram, which, though erroneous as regards the
+position of the veined structure, is quite correct in limiting the
+snow-bands to the Glacier du Geant proper.
+
+At the place where the three welded tributaries of the Mer de Glace
+squeeze themselves through the strait of Trelaporte, the bands undergo a
+considerable modification in shape. Near their origin they sweep across
+the Glacier du Geant in gentle curves, with their convexities directed
+downwards; but at Trelaporte these curves, the chords of which a short
+time previous measured a thousand yards in length, have to squeeze
+themselves through a space of four hundred and ninety-five yards wide;
+and as might be expected, they are here suddenly sharpened. The apex of
+each being thrust forward, they take the form of sharp hyperbolas, and
+preserve this character throughout the entire length of the Mer de
+Glace.
+
+I would now conduct the reader to a point from which a good general view
+of the ice cascade of the Geant is attainable. From the old moraine near
+the lake of the Tacul we observe the ice, as it descends the fall, to
+be broken into a succession of precipices. It would appear as if the
+glacier had its back periodically broken at the summit of the fall, and
+formed a series of vast chasms separated from each other by cliffy
+ridges of corresponding size. These, as they approach the bottom of the
+fall, become more and more toned down by the action of sun and air, and
+at some distance below the base of the cascade they are subdued so as to
+form the transverse undulations already described. These undulations are
+more and more reduced as the glacier descends; and long before the Tacul
+is attained, every sensible trace of them has disappeared. The terraces
+of the ice-fall are referred to by Professor Forbes in his Thirteenth
+Letter, where he thus describes them:--"The ice-falls succeed one
+another at regulated intervals, which appear to correspond to the
+renewal of each summer's activity in those realms of almost perpetual
+frost, when a swifter motion occasions a more rapid and wholesale
+projection of the mass over the steep, thus forming curvilinear terraces
+like vast stairs, which appear afterwards by consolidation to form the
+remarkable protuberant wrinkles on the surface of the Glacier du Geant."
+
+[Sidenote: FORBES'S EXPLANATION.]
+
+With regard to the cause of the distribution of the dirt in bands,
+Professor Forbes writes thus in his Third Letter:--"I at length assured
+myself that it was entirely owing to the structure of the ice, which
+retains the dirt diffused by avalanches and the weather on those parts
+which are most porous, whilst the compacter portion is washed clean by
+the rain, so that those bands are nothing more than visible traces of
+the direction of the internal icy structure." Professor Forbes's theory,
+at that time, was that the glacier is composed throughout of a series of
+alternate segments of hard and porous ice, in the latter of which the
+dirt found a lodgment. I do not know whether he now retains his first
+opinion; but in his Fifteenth Letter he speaks of accounting for "the
+less compact structure of the ice beneath the dirt-band."
+
+It appears to me that in the above explanation cause has been mistaken
+for effect. The ice on which the dirt-bands rest certainly appears to be
+of a spongier character than the cleaner intermediate ice; but instead
+of this being the cause of the dirt-bands, the latter, I imagine, by
+their more copious absorption of the sun's rays and the consequent
+greater disintegration of the ice, are the cause of the apparent
+porosity. I have not been able to detect any relative porosity in the
+"internal icy structure," nor am I able to find in the writings of
+Professor Forbes a description of the experiments whereby he satisfied
+himself that this assumed difference exists.
+
+[Sidenote: TRANSVERSE UNDULATIONS.]
+
+[Sidenote: INFLUENCE OF DIRECTION OF GLACIER.]
+
+Several days of the summer of 1857 were devoted by me to the examination
+of these bands. I then found the bases and the frontal slopes of the
+undulations to which I have referred covered with a fine brown mud.
+These slopes were also, in some cases, covered with snow which the great
+heat of the weather had not been able entirely to remove. At places
+where the residue of snow was small its surface was exceedingly
+dirty--so dirty indeed that it appeared as if peat-mould had been strewn
+over it; its edges particularly were of a black brown. It was perfectly
+manifest that this snow formed a receptacle for the fine dirt
+transported by the innumerable little rills which trickled over the
+glacier. The snow gradually wasted, but it left its sediment behind, and
+thus each of the snowy bands observed by Professor Forbes in 1843,
+contributed to produce an appearance perfectly antithetical to its own.
+I have said that the frontal slopes of the undulations were thus
+covered; and it was on these, and not in the depressions, that the snow
+principally rested. The reason of this is to be found in the _bearing_
+of the Glacier du Geant, which, looking downwards, is about fourteen
+degrees east of the meridian.[B] Hence the frontal slopes of the
+undulations have a _northern aspect_, and it is this circumstance which,
+in my opinion, causes the retention of the snow upon them. Irrespective
+of the snow, the mere tendency of the dirt to accumulate at the bases of
+the undulations would also produce bands, and indeed does so on many
+glaciers; but the precision and beauty of the dirt-bands of the Mer de
+Glace are, I think, to be mainly referred to the interception by the
+snow of the fine dark mud before referred to on the northern slopes of
+its undulations.
+
+[Sidenote: BANDS DO NOT CROSS MORAINES.]
+
+Were the statements of some writers upon this subject well founded, or
+were the dirt-bands as drawn upon the map of Professor Forbes correctly
+shown, this explanation could not stand a moment. It has been urged that
+the dirt-bands cannot thus belong to a single tributary of the Mer de
+Glace; for if they did, they would be confined to that tributary upon
+the trunk-glacier; whereas the fact is that they extend quite across the
+trunk, and intersect the moraines which divide the Glacier du Geant from
+its fellow-tributaries. From my first acquaintance with the Mer de Glace
+I had reason to believe that this statement was incorrect; but last year
+I climbed a third time to the Cleft-station for the purpose of once more
+inspecting the bands from this fine position. I was accompanied by Dr.
+Frankland and Auguste Balmat, and I drew the attention of both
+particularly to this point. Neither of them could discern, nor could I,
+the slightest trace of a dirt-band crossing any one of the moraines.
+Upon the trunk-stream they were just as much confined to the Glacier du
+Geant as ever. If the bands even existed east of the moraines, they
+could not be seen, the dirt on this part of the glacier being sufficient
+to mask them.
+
+The following interesting fact may perhaps have contributed to the
+production of the error referred to. Opposite to Trelaporte the eastern
+arms of the dirt-bands run so obliquely into the moraine of La Noire
+that the latter appears to be a tangent to them. But this moraine runs
+along the Mer de Glace, not far from its centre, and consequently the
+point of contact of each dirt-band with the moraine moves more quickly
+than the point of contact of the western arm of the same band with the
+side of the valley. Hence there is a tendency to _straighten_ the bands;
+and at some distance down the glacier the effect of this is seen in the
+bands abutting against the moraine of La Noire at a larger angle than
+before. The branches thus abutting have, I believe, been ideally
+prolonged across the moraines.
+
+[Illustration: Fig. 38. Plan of Dirt-bands taken from Johnson's
+'Physical Atlas.']
+
+On the map published by Prof. Forbes in 1843 the bands are shown
+crossing the medial moraines of the Mer de Glace; and they are also thus
+drawn on the map in Johnson's 'Physical Atlas' published in 1849. The
+text is also in accordance with the map:--"Opposite to the Montanvert,
+and beyond les Echelets, the curved loops (dirt-bands) extend _across
+the entire glacier_. They are single, and therefore _cut_ the medial
+moraine, though at a very slight angle."--'Travels,' p. 166. The italics
+here belong to Prof. Forbes. In order to help future observers to place
+this point beyond doubt, I annex, in Fig. 38, a portion of the map of
+the Mer de Glace taken from the Atlas referred to. If it be compared
+with Fig. 35 the difference between Prof. Forbes and myself will be
+clearly seen. The portion of the glacier represented in both diagrams
+may be viewed from the point near the Flegere already referred to.
+
+[Sidenote: ANNUAL "RINGS."]
+
+The explanation which I have given involves three considerations:--The
+transverse breaking of the glacier on the cascade, and the gradual
+accumulation of the dirt in the hollows between the ridges; the
+subsequent toning down of the ridges to gentle protuberances which sweep
+across the glacier; and the collection of the dirt upon the slopes and
+at the bases of these protuberances. Whether the periods of transverse
+fracture are annual or not--whether the "wrinkles" correspond to a
+yearly gush--and whether, consequently, the dirt-bands mark the growth
+of a glacier as the "annual rings" mark the growth of a tree, I do not
+know. It is a conjecture well worthy of consideration; but it is only a
+conjecture, which future observation may either ratify or refute.
+
+
+FOOTNOTES:
+
+[A] 'Travels,' page 162.
+
+[B] In the large map of Professor Forbes the bearing of the valley is
+nearly sixty degrees west of the meridian; but this is caused by the
+true north being drawn on the wrong side of the magnetic north; thus
+making the declination easterly instead of westerly. In the map in
+Johnson's 'Physical Atlas' this mistake is corrected.
+
+
+
+
+THE VEINED STRUCTURE OF GLACIERS.
+
+(27.)
+
+
+[Sidenote: GENERAL APPEARANCE.]
+
+The general appearance of the veined structure may be thus briefly
+described:--The ice of glaciers, especially midway between their
+mountain-sources and their inferior extremities, is of a whitish hue,
+caused by the number of small air-bubbles which it contains, and which,
+no doubt, constitute the residue of the air originally entrapped in the
+interstices of the snow from which it has been derived. Through the
+general whitish mass, at some places, innumerable parallel veins of
+clearer ice are drawn, which usually present a beautiful blue colour,
+and give the ice a laminated appearance. The cause of the blueness is,
+that the air-bubbles, distributed so plentifully through the general
+mass, do not exist in the veins, or only in comparatively small numbers.
+
+In different glaciers, and in different parts of the same glacier, these
+veins display various degrees of perfection. On the clean unweathered
+walls of some crevasses, and in the channels worn in the ice by
+glacier-streams, they are most distinctly seen, and are often
+exquisitely beautiful. They are not to be regarded as a partial
+phenomenon, or as affecting the constitution of glaciers to a small
+extent merely. A large portion of the ice of some glaciers is thus
+affected. The greater part, for example, of the Mer de Glace consists of
+this laminated ice; and the whole of the Glacier of the Rhone, from the
+base of the ice-cascade downwards, is composed of ice of the same
+description.
+
+[Sidenote: GROOVES ON THE SURFACE OF GLACIERS.]
+
+Those who have ascended Snowdon, or wandered among the hills of
+Cumberland, or even walked in the environs of Leeds, Blackburn, and
+other towns in Yorkshire and Lancashire, where the stratified sandstone
+of the district is used for building purposes, may have observed the
+weathered edges of the slate rocks or of the building-stone to be
+grooved and furrowed. Some laminae of such rocks withstand the action of
+the atmosphere better than others, and the more resistant ones stand out
+in ridges after the softer parts between them have been eaten away. An
+effect exactly similar is observed where the laminated ice of glaciers
+is exposed to the action of the sun and air. Little grooves and ridges
+are formed upon its surface, the more resistant plates protruding after
+the softer material between them has been melted away.
+
+One consequence of this furrowing is, that the light dirt scattered by
+the winds over the surface of the glacier is gradually washed into the
+little grooves, thus forming fine lines resembling those produced by the
+passage of a rake over a sanded walk. These lines are a valuable index
+to some of the phenomena of motion. From a position on the ice of the
+Glacier du Geant a little higher up than Trelaporte a fine view of these
+superficial groovings is obtained; but the dirt-lines are not always
+straight. A slight power of independent motion is enjoyed by the
+separate parts into which a glacier is divided by its crevasses and
+dislocations, and hence it is, that, at the place alluded to, the
+dirt-lines are bent hither and thither, though the ruptures of
+continuity are too small to affect materially the general direction of
+the structure. On the glacier of the Talefre I found these groovings
+useful as indicating the character of the forces to which the ice near
+the summit of the fall is subjected. The ridges between the chasms are
+in many cases violently bent and twisted, while the adjacent groovings
+enable us to see the normal position of the mass.
+
+[Sidenote: GUYOT'S OBSERVATIONS.]
+
+The veined structure has been observed by different travellers; but it
+was probably first referred to by Sir David Brewster, who noticed the
+veins of the Mer de Glace on the 10th of September, 1814. It was also
+observed by General Sabine,[A] by Rendu, by Agassiz, and no doubt by
+many others; but the first clear description of it was given by M.
+Guyot, in a communication presented to the Geological Society of France
+in 1838. I quote the following passage from this paper:--"I saw under my
+feet the surface of the entire glacier covered with regular furrows from
+one to two inches wide, hollowed out in a half snowy mass, and separated
+by protruding plates of harder and more transparent ice. It was evident
+that the mass of the glacier here was composed of two sorts of ice, one
+that of the furrows, snowy and more easily melted; the other that of the
+plates, more perfect, crystalline, glassy, and resistant; and that the
+unequal resistance which the two kinds of ice presented to the
+atmosphere was the cause of the furrows and ridges. After having
+followed them for several hundreds of yards, I reached a fissure twenty
+or thirty feet wide, which, as it cut the plates and furrows at right
+angles, exposed the interior of the glacier to a depth of thirty or
+forty feet, and gave a beautiful transverse section of the structure. As
+far as my vision could reach I saw the mass of the glacier composed of
+layers of snowy ice, each two of which were separated by one of the
+plates of which I have spoken, the whole forming a regularly laminated
+mass, which resembled certain calcareous slates."
+
+[Sidenote: FORBES'S RESEARCHES.]
+
+Previous observers had mistaken the lamination for stratification; but
+M. Guyot not only clearly saw that they were different, but in the
+comparison which he makes he touches, I believe, on the true cause of
+the glacier-structure. He did not hazard an explanation of the
+phenomenon, and I believe his memoir remained unprinted. In 1841 the
+structure was noticed by Professor Forbes during his visit to M. Agassiz
+on the lower Aar Glacier, and described in a communication presented by
+him to the Royal Society of Edinburgh. He subsequently devoted much time
+to the subject, and his great merit in connexion with it consists in the
+significance which he ascribed to the phenomenon when he first observed
+it, and in the fact of his having proved it to be a constitutional
+feature of glaciers in general.
+
+[Sidenote: FORBES'S THEORY.]
+
+The first explanation given of those veins by Professor Forbes was, that
+they were small fissures formed in the ice by its motion; that these
+were filled with the water of the melted ice in summer, which froze in
+winter so as to form the blue veins. This is the explanation given in
+his 'Travels,' page 377; and in a letter published in the 'Edinburgh New
+Philosophical Journal,' October, 1844, it is re-affirmed in these
+words:--"With the abundance of blue bands before us in the direction in
+which the differential motion must take place (in this case sensibly
+parallel to the sides of the glacier), it is impossible to doubt that
+these infiltrated crevices (for such they undoubtedly are) have this
+origin." This theory was examined by Mr. Huxley and myself in our joint
+paper; but it has been since alleged that ours was unnecessary labour,
+Prof. Forbes himself having in his Thirteenth Letter renounced the
+theory, and substituted another in its place. The latter theory differs,
+so far as I can understand it, from the former in this particular, that
+the _freezing of the water_ in the fissures is discarded, their sides
+being now supposed to be united "by the simple effects of time and
+cohesion."[B] For a statement of the change which his opinions have
+undergone, I would refer to the Prefatory Note which precedes the volume
+of 'Occasional Papers' recently published by Prof. Forbes; but it would
+have diminished my difficulty had the author given, in connexion with
+his new volume, a more distinct statement of his present views regarding
+the veined structure. With many of his observations and remarks I should
+agree; with many others I cannot say whether I agree or not; and there
+are others still with which I do not think I should agree: but in hardly
+any case am I certain of his precise views, excepting, indeed, the
+cardinal one, wherein he and others agree in ascribing to the structure
+a different origin from stratification. Thus circumstanced, my proper
+course, I think, will be to state what I believe to be the cause of the
+structure, and leave it to the reader to decide how far our views
+harmonize; or to what extent either of them is a true interpretation of
+nature.
+
+[Sidenote: USUAL ASPECT OF BLUE VEINS.]
+
+Most of the earlier observers considered the structure to be due to the
+stratification of the mountain-snows--a view which has received later
+development at the hands of Mr. John Ball; and the practical difficulty
+of distinguishing the undoubted effects of _stratification_ from the
+phenomena presented by _structure_, entitles this view to the fullest
+consideration. The blue veins of glaciers are, however, not always, nor
+even generally, such as we should expect to result from stratification.
+The latter would furnish us with distinct planes extending parallel to
+each other for considerable distances through the glacier; but this,
+though sometimes the case, is by no means the general character of the
+structure. We observe blue streaks, from a few inches to several feet in
+length, upon the walls of the same crevasse, and varying from the
+fraction of an inch to several inches in thickness. In some cases the
+streaks are definitely bounded, giving rise to an appearance resembling
+the section of a lens, and hence called the "lenticular structure" by
+Mr. Huxley and myself; but more usually they fade away in pale washy
+streaks through the general mass of the whitish ice. In Fig. 39 I have
+given a representation of the structure as it is very commonly exhibited
+on the walls of crevasses. Its aspect is not that which we should expect
+from the consolidation of successive beds of mountain snow.
+
+[Illustration: Fig. 39. Veined Structure of the walls of crevasses.]
+
+Further, at the bases of ice-cascades the structural laminae are usually
+_vertical_: below the cascade of the Talefre, of the Noire, of the
+Strahleck branch of the Lower Grindelwald Glacier, of the Rhone, and
+other ice-falls, this is the case; and it seems extremely difficult to
+conceive that a mass horizontally stratified at the summit of the fall,
+should, in its descent, contrive to turn its strata perfectly on end.
+
+Again, we often find a very feebly-developed structure at the central
+portions of a glacier, while the lateral portions are very decidedly
+laminated. This is the case where the inclination of the glacier is
+nearly uniform throughout; and where no medial moraines occur to
+complicate the phenomenon. But if the veins mark the bedding, there
+seems to be no sufficient reason for their appearance at the lateral
+portions of the glacier, and their absence from the centre.
+
+[Sidenote: ILLUSTRATIVE EXPERIMENTS.]
+
+This leads me to the point at which what I consider to be the true cause
+of the structure may be referred to. The theoretic researches of Mr.
+Hopkins have taught us a good deal regarding the pressures and tensions
+consequent upon glacier-motion. Aided by this knowledge, and also by a
+mode of experiment first introduced by Professor Forbes, I will now
+endeavour to explain the significance of the fact referred to in the
+last paragraph. If a plastic substance, such as mud, flow down a sloping
+canal, the lateral portions, being held back by friction, will be
+outstripped by the central ones. When the flow is so regulated that the
+velocity of a point at the centre shall not vary throughout the entire
+length of the canal, a coloured circle stamped upon the centre of the
+mud stream, near its origin, will move along with the mud, and still
+retain its circular form; for, inasmuch as the velocity of all points
+along the centre is the same, there can be no elongation of the circle
+longitudinally or transversely by either strain or pressure. A similar
+absence of longitudinal pressure may exist in a glacier, and, where it
+exists throughout, no central structure can, in my opinion, be
+developed.
+
+But let a circle be stamped upon the mud-stream near its side, then,
+when the mud flows, this circle will be distorted to an oval, with its
+major axis oblique to the direction of motion; the cause of this is that
+the portion of the circle farthest from the side of the canal moves
+more freely than that adjacent to the side. The mechanical effect of the
+slower lateral motion is to squeeze the circle in one direction, and
+draw it out in the perpendicular one.
+
+[Sidenote: MARGINAL STRUCTURE.]
+
+[Illustration: Fig. 40. Figure explanatory of the Marginal Structure.]
+
+A glance at Fig. 40 will render all that I have said intelligible. The
+three circles are first stamped on the mud in the same transverse line;
+but after they have moved downwards they will be in the same straight
+line no longer. The central one will be the foremost; while the lateral
+ones have their forms changed from circles to ovals. In a glacier of the
+shape of this canal exactly similar effects are produced. Now the
+shorter axis _m n_ of each oval is a line of squeezing or pressure; the
+longer axis is a line of strain or tension; and the associated
+glacier-phenomena are as follows:--Across the line _m n_, or
+perpendicular to the pressure, we have the _veined structure_ developed,
+while across the line of tension the glacier usually breaks and forms
+_marginal crevasses_. Mr. Hopkins has shown that the lines of greatest
+pressure and of greatest strain are at right angles to each other, and
+that in valleys of a uniform width they enclose an angle of forty-five
+degrees with the side of the glacier. To the structure thus formed I
+have applied the term _marginal structure_. Here, then, we see that
+there are mechanical agencies at work near the side of such a glacier
+which are absent from the centre, and we have effects developed--I
+believe _by the pressure_--in the lateral ice, which are not produced in
+the central.
+
+I have used the term "uniform inclination" in connexion with the
+marginal structure, and my reason for doing so will now appear. In many
+glaciers the structure, instead of being confined to the margins,
+sweeps quite across them. This is the case, for example, on the Glacier
+du Geant, the structure of which is prolonged into the Mer de Glace. In
+passing the strait at Trelaporte, however, the curves are squeezed and
+their apices bruised, so that the structure is thrown into a state of
+confusion; and thus upon the Mer de Glace we encounter difficulty in
+tracing it fairly from side to side. Now the key to this transverse
+structure I believe to be the following: Where the inclination of the
+glacier suddenly changes from a steep slope to a gentler, as at the
+bases of the "cascades,"--the ice to a certain depth must be thrown into
+a state of violent longitudinal compression; and along with this we have
+the resistance which the gentler slope throws athwart the ice descending
+from the steep one. At such places a structure is developed transverse
+to the axis of the glacier, and likewise transverse to the pressure. The
+quicker flow of the centre causes this structure to bend more and more,
+and after a time it sweeps in vast curves across the entire glacier.
+
+[Sidenote: STRUCTURE OF GRINDELWALD GLACIER.]
+
+In illustration of this point I will refer, in the first place, to that
+tributary of the Lower Glacier of Grindelwald which descends from the
+Strahleck. Walking up this tributary we come at length to the base of an
+ice-fall. Let the observer here leave the ice, and betake himself to
+either side of the flanking mountain. On attaining a point which
+commands a view both of the fall and of the glacier below it, an
+inspection of the glacier will, I imagine, solve to his satisfaction the
+case of structure now under consideration.
+
+It is indeed a grand experiment which Nature here submits to our
+inspection. The glacier descending from its _neve_ reaches the summit of
+the cascade, and is broken transversely as it crosses the brow; it
+afterwards descends the fall in a succession of cliffy ice-ridges with
+transverse hollows between them. In these latter the broken ice and
+debris collect, thus partially choking the fissures formed in the first
+instance. Carrying the eye downwards along the fall, we see, as we
+approach the base, these sharp ridges toned down; and a little below the
+base they dwindle into rounded protuberances which sweep in curves quite
+across the glacier. At the base of the fall the structure begins to
+appear, feebly at first, but becoming gradually more pronounced, until,
+at a short distance below the base of the fall, the eye can follow the
+fine superficial groovings from side to side; while at the same time the
+ice underneath the surface has become laminated in the most beautiful
+manner.
+
+It is difficult to convey by writing the force of the evidence which the
+actual observation of this natural experiment places before the mind.
+The ice at the base of the fall, retarded by the gentler inclination of
+the valley, has to bear the thrust of the descending mass, the sudden
+change of inclination producing powerful longitudinal compression. The
+protuberances are squeezed more closely together, the hollows between
+them appear to wrinkle up in submission to the pressure--in short, the
+entire aspect of the glacier suggests the powerful operations of the
+latter force. At the place where _it_ is exerted the veined structure
+makes its appearance; and being once formed, it moves downwards, and
+gives a character to other portions of the glacier which had no share in
+its formation.
+
+[Sidenote: BASE OF CASCADE A "STRUCTURE-MILL."]
+
+An illustration almost as good, and equally accessible, is furnished by
+the Glacier of the Rhone. I have examined the grand cascade of this
+glacier from both sides; and an ordinary mountaineer will find little
+difficulty in reaching a point from which the fall and the terminal
+portion of the glacier are both distinctly visible. Here also he will
+find the cliffy ridges separated from each other by transverse chasms,
+becoming more and more subdued at the bottom of the fall, and
+disappearing entirely lower down the glacier. As in the case of the
+Grindelwald Glacier the squeezing of the protuberances and of the spaces
+between them, is quite apparent, and where this squeezing commences the
+transverse structure makes its appearance. All the ice that forms the
+lower portion of this glacier has to pass through the _structure-mill_
+at the bottom of the fall, and the consequence is that _it is all
+laminated_.
+
+[Sidenote: STRUCTURE OF RHONE GLACIER.]
+
+[Illustration: Fig. 41. Plan of part of ice-fall, and of glacier below
+it (Glacier of the Rhone).]
+
+[Illustration: Fig. 42. Section of part of ice-fall, and of glacier
+below it (Glacier of the Rhone).]
+
+[Sidenote: TRANSVERSE STRUCTURE.]
+
+This case of structural development will be better appreciated on
+reference to Figs. 41 and 42, the former of which is a plan, and the
+latter a section, of a part of the ice-fall and of the glacier below it;
+_a b e f_ is the gorge of the fall, _f b_ being the base. The transverse
+cliffy ice-ridges are shown crossing the cascade, being subdued at the
+base to protuberances which gradually disappear as they advance
+downwards. The structure sweeps over the glacier in the direction of the
+fine curved lines; and I have also endeavoured to show the direction of
+the radial crevasses, which, in the centre at least, are at right angles
+to the veins. To the manifestation of structure here considered I have,
+for the sake of convenient reference, applied the term _transverse
+structure_.
+
+A third exhibition of the structure is now to be noticed. We sometimes
+find it in the _middle_ of a glacier and running _parallel_ to its
+length. On the centre of the ice-fall of the Talefre, for example, we
+have a structure of this kind which preserves itself parallel to the
+axis of the fall from top to bottom. But we discover its origin higher
+up. The structure here has been produced at the extremity of the Jardin,
+where the divided ice meets, and not only brings into partial
+parallelism the veins previously existing along the sides of the Jardin,
+but develops them still further by the mutual pressure of the portions
+of newly welded ice. Where two tributary glaciers unite, this is perhaps
+without exception the case. Underneath the moraine formed by the
+junction of the Talefre and Lechaud the structure is finely developed,
+and the veins run in the direction of the moraine. The same is true of
+the ice under the moraine formed by the junction of the Lechaud and
+Geant. These afterwards form the great medial moraines of the Mer de
+Glace, and hence the structure of the trunk-stream underneath these
+moraines is parallel to the direction of the glacier. This is also true
+of the system of moraines formed by the glaciers of Monte Rosa. It is
+true in an especial manner of the lower glacier of the Aar, whose
+medial moraine perhaps attains grander proportions than any other in the
+Alps, and underneath which the structure is finely developed.
+
+[Sidenote: LONGITUDINAL STRUCTURE.]
+
+[Illustration: Fig. 43. Figure explanatory of Longitudinal Structure.]
+
+The manner in which I have illustrated the production of this structure
+will be understood from Fig. 43. B B are two wooden boxes, communicating
+by sluice-fronts with two branch canals, which unite to a common trunk
+at G. They are intended to represent respectively the trunk and
+tributaries of the Unteraar Glacier, the part G being the Abschwung,
+where the Lauteraar and Finsteraar glaciers unite to form the Unteraar.
+The mud is first permitted to flow beneath the two sluices until it has
+covered the bottom of the trough for some distance, when it is arrested.
+The end of a glass tube is then dipped into a mixture of rouge and
+water, and small circles are stamped upon the mud. The two branches are
+thickly covered with these circles. The sluices being again raised, the
+mud in the branches moves downwards, carrying with it the circles
+stamped upon it; and the manner in which these circles are distorted
+enables us to infer the strains and pressures to which the mud is
+subjected during its descent. The figure represents approximately what
+takes place. The side-circles, as might be expected, are squeezed to
+oblique ovals, but it is at the junction of the branches that the chief
+effect of pressure is produced. Here, by the mutual thrust of the
+branches, the circles are not only changed to elongated ellipses, but
+even squeezed to straight lines. In the case of the glacier this is the
+region at which the structure receives its main development. To this
+manifestation of the veins I have applied the term _longitudinal
+structure_.
+
+The three main sources of the blue veins are, I think, here noted; but
+besides these there are many local causes which influence their
+production. I have seen them well formed where a glacier is opposed by
+the sudden bend of a valley, or by a local promontory which presents an
+obstacle sufficient to bring the requisite pressure into play. In the
+glaciers of the Tyrol and of the Oberland I have seen examples of this
+kind; but the three principal sources of the veins are, I think, those
+stated above.
+
+[Sidenote: EFFORTS TO SOLVE QUESTION.]
+
+It was long before I cleared my mind of doubt regarding the origin of
+the lamination. When on the Mer de Glace in 1857 I spared neither risk
+nor labour to instruct myself regarding it. I explored the Talefre
+basin, its cascade, and the ice beneath it. Several days were spent amid
+the ice humps and cliffs at the lower portion of the fall. I suppose I
+traversed the Glacier du Geant twenty times, and passed eight or ten
+days amid the confusion of its great cascade. I visited those places
+where, it had been affirmed, the veins were produced. I endeavoured to
+satisfy myself of the mutability which had been ascribed to them; but a
+close examination reduced the value of each particular case so much that
+I quitted the glacier that year with nothing more than an _opinion_ that
+the structure and the stratification were two different things. I,
+however, drew up a statement of the facts observed, with the view of
+presenting it to the Royal Society; but I afterwards felt that in thus
+acting I should merely swell the literature of the subject without
+adding anything certain. I therefore withheld the paper, and resolved
+to devote another year to a search among the chief glaciers of the
+Oberland, of the Canton Valais, and of Savoy, for proofs which should
+relieve my mind of all doubt upon the subject.
+
+[Sidenote: EXPEDITION FOR THIS PURPOSE.]
+
+Accordingly in 1858 I visited the glaciers of Rosenlaui, Schwartzwald,
+Grindelwald, the Aar, the Rhone, and the Aletsch, to the examination of
+which latter I devoted more than a week. I afterwards went to Zermatt,
+and, taking up my quarters at the Riffelberg, devoted eleven days to the
+examination of the great system of glaciers of Monte Rosa. I explored
+the Goerner Glacier up almost to the Cima de Jazzi; and believed that in
+it I could trace the structure from portions of the glacier where it
+vanished, through various stages of perfection, up to its full
+development. I believe this still; but yet it is nothing but a belief,
+which the utmost labour that I could bestow did not raise to a
+certainty. The Western glacier of Monte Rosa, the Schwartze Glacier, the
+Trifti Glacier, the glacier of the little Mont Cervin, and of St.
+Theodule, were all examined in connexion with the great trunk-stream of
+the Goerner, to which they weld themselves; and though the more I pursued
+the subject the stronger my conviction became that pressure was the
+cause of the structure, a crucial case was still wanting.
+
+In the phenomena of slaty cleavage, it is often, if not usually, found
+that the true cleavage _cuts_ the planes of stratification--sometimes at
+a very high angle. Had this not been proved by the observations of
+Sedgwick and others, geologists would not have been able to conclude
+that cleavage and bedding were two different things, and needed wholly
+different explanations. My aim, throughout the expedition of 1858, was
+to discover in the ice a parallel case to the above; to find a clear and
+undoubted instance where the veins and the stratification were
+simultaneously exhibited, cutting each other at an unmistakable angle.
+On the 6th of August, while engaged with Professor Ramsay upon the
+Great Aletsch Glacier, not far from its junction with the Middle
+Aletsch, I observed what appeared to me to be the lines of bedding
+running nearly horizontal along the wall of a great crevasse, while
+cutting them at a large angle was the true veined structure. I drew my
+friend's attention to the fact, and to him it appeared perfectly
+conclusive. It is from a sketch made by him at the place that Fig. 44
+has been taken.
+
+[Sidenote: CASE OF STRUCTURE ON THE ALETSCH.]
+
+[Illustration: Fig. 44. Structure and bedding on the Great Aletsch
+Glacier.]
+
+This was the only case of the kind which I observed upon the Aletsch
+Glacier; and as I afterwards spent day after day upon the Monte Rosa
+glaciers, vainly seeking a similar instance, the thought again haunted
+me that we might have been mistaken upon the Aletsch. In this state of
+mind I remained until the 18th of August, a day devoted to the
+examination of the Furgge Glacier, which lies at the base of the Mont
+Cervin.
+
+[Sidenote: STRUCTURE OF THE FURGGE GLACIER.]
+
+Crossing the valley of the Goerner Glacier, and taking a plunge as I
+passed into the Schwarze See, I reached, in good time, the object of my
+day's excursion. Walking up the glacier, I at length found myself
+opposed by a frozen cascade composed of four high terraces of ice. The
+highest of these was chiefly composed of ice-cliffs and _seracs_, many
+of which had fallen, and now stood like rocking-stones upon the edge of
+the second terrace. The glacier at the base of the cascade was strewn
+with broken ice, and some blocks two hundred cubic feet in volume had
+been cast to a considerable distance down the glacier.
+
+Upon the faces of the terraces the stratification of the _neve_ was most
+beautifully shown, running in parallel and horizontal lines along the
+weathered surface. The snow-field above the cascade is a frozen plain,
+smooth almost as a sheltered lake. The successive snow-falls deposit
+themselves with great regularity, and at the summit of the cascade the
+sections of the _neve_ are for the first time exposed. Hence their
+peculiar beauty and definition.
+
+[Sidenote: ICE TERRACE EXAMINED.]
+
+Indeed the figure of a lake pouring itself over a rocky barrier which
+curves convexly upwards, thus causing the water to fall down it, not
+only longitudinally over the vertex of the curve, but laterally over its
+two arms, will convey a tolerably correct conception of the shape of the
+fall. Towards the centre the ice was powerfully squeezed laterally, the
+beds were bent, and their continuity often broken by faults. On
+inspecting the ice from a distance with my opera glass, I thought I saw
+structural groovings cutting the strata at almost a right angle. Had the
+question been an undisputed one, I should perhaps have felt so sure of
+this as not to incur the danger of pushing the inquiry further; but,
+under the circumstances, danger was a secondary point. Resigning,
+therefore, my glass to my guide, who was to watch the tottering blocks
+overhead, and give me warning should they move, I advanced to the base
+of the fall, removed with my hatchet the weathered surface of the ice,
+and found underneath it the true veined structure, cutting, at nearly a
+right angle, the planes of stratification. The superficial groovings
+were not uniformly distributed over the fall, but appeared most decided
+at those places where the ice appeared to have been most squeezed. I
+examined three or four of these places, and in each case found the true
+veins nearly vertical, while the bedding was horizontal. Having
+perfectly satisfied myself of these facts, I made a speedy retreat, for
+the ice-blocks seemed most threatening, and the sunny hour was that at
+which they fall most frequently.
+
+I next tried the ascent of the glacier up a dislocated declivity to the
+right. The ice was much riven, but still practicable. My way for a time
+lay amid fissures which exposed magnificent sections, and every step I
+took added further demonstration to what I had observed below. The
+strata were perfectly distinct, the structure equally so, and one
+crossed the other at an angle of seventy or eighty degrees. Mr. Sorby
+has adduced a case of the crumpling of a bed of sandstone through which
+the cleavage passes: here on the glacier I had parallel cases; the beds
+were bent and crumpled, but the structure ran through the ice in sharp
+straight lines. This perhaps was the most pleasant day I ever spent upon
+the glaciers: my mind was relieved of a long brooding doubt, and the
+intellectual freedom thus obtained added a subjective grandeur to the
+noble scene before me. Climbing the cliffs near the base of the
+Matterhorn, I walked along the rocky spine which extends to the Hoernli,
+and afterwards descended by the valley of Zmutt to Zermatt.
+
+A year after my return to England a remark contained in Professor
+Mousson's interesting little work 'Die Gletscher der Jetzzeit' caused me
+to refer to the atlas of M. Agassiz's 'Systeme Glaciaire,' from which I
+learned that this indefatigable observer had figured a case of
+stratification and structure cutting each other. If, however, I had seen
+this figure beforehand, it would not have changed my movements; for the
+case, as sketched, would not have convinced me. I have now no doubt that
+M. Agassiz has preceded me in this observation, and hence my results
+are to be taken as mere confirmations of his.
+
+[Sidenote: LAMINATION AND STRATIFICATION.]
+
+Fig. 45 represents a crumpled portion of the ice with the lines of
+lamination passing through the strata. Fig. 46 represents a case where a
+fault had occurred, the veins at both sides of the line of dislocation
+being inclined towards each other.
+
+[Illustration: Fig. 45. Structure and Stratification on the Furgge
+glacier.]
+
+[Illustration: Fig. 46. Structure and Stratification on the Furgge
+glacier.]
+
+[Figs. 45 and 46 are from sketches made on the Furgge Glacier.--L. C.
+T.]
+
+
+FOOTNOTES:
+
+[A] In reply to a question in connexion with this subject, General
+Sabine has favoured me with the following note:--
+
+ "My dear Tyndall,
+
+ "It was in the summer of 1841, at the Lower Grindelwald
+ Glacier, that I first saw, and was greatly impressed and
+ interested by examining and endeavouring to understand (in
+ which I did not succeed), the veined structure of the ice. I do
+ not remember when I mentioned it to Forbes, but it must be
+ before 1843, because it is noticed in his book, p. 29. I had
+ never observed it in the glaciers of Spitzbergen or Baffin's
+ Bay, or in the icebergs of the shores and straits of Davis or
+ Barrow. I feel the more confident of this, because, when I
+ first saw the veined structure in Switzerland, my Arctic
+ experience was more fresh in my recollection, and I recollected
+ nothing like it.
+
+ "_Veins_ are indeed not uncommon in icebergs, but they quite
+ resemble veins in rocks, and are formed by water filling
+ fissures and freezing into blue ice, finely contrasted with the
+ white granular substance of the berg.
+
+ "The ice of the Grindelwald Glacier (where I examined the
+ veined structure) was broken up into very large masses, which
+ by pressure had been upturned, so that a very poor judgment
+ would be formed of the direction of the veins as they existed
+ in the glacier before it had broken up.
+
+ "Sincerely yours,
+ "EDWARD SABINE.
+
+ "_Feb. 20, 1860_."
+
+[B] In a letter to myself, published in the 17th volume of the
+'Philosophical Magazine,' Professor Forbes writes as follows:--"In 1846,
+then, I abandoned no part of the theory of the veined structure, on
+which as you say so much labour had been expended, except the admission,
+always yielded with reluctance, and got rid of with satisfaction, that
+the congelation of water in the crevices of the glacier may extend in
+winter to a great depth."
+
+
+
+
+THE VEINED STRUCTURE AND THE DIFFERENTIAL MOTION.
+
+(28.)
+
+
+[Sidenote: DIFFERENTIAL MOTION GREATEST AT EDGES.]
+
+I have now to examine briefly the explanation of the structure which
+refers it to differential motion--to a sliding of the particles of ice
+past each other, which leaves the traces of its existence in the blue
+veins. The fact is emphatically dwelt upon by those who hold this view,
+that the structure is best developed nearest to the sides of the
+glacier, where the differential motion is greatest. Why the differential
+motion is at its maximum near to the sides is easily understood. Let A
+B, C D, Fig. 47, represent the two sides of a glacier, moving in the
+direction of the arrow, and let _m a b c n_ be a straight line of stakes
+set out across the glacier to-day. Six months hence this line, by the
+motion of the ice downwards, will be bent to the form _m a' b' c' n_:
+this curve will not be circular, it will be flattened in the middle; the
+points _a_ and _c_, at some distance on each side of the centre _b_,
+move in fact with nearly the same velocity as the centre itself. Not so
+with the sides:--_a'_ and _c'_ have moved considerably in advance of _m_
+and _n_, and hence we say that the difference of motion, or the
+differential motion, of the particles of ice near to the side is a
+maximum.
+
+[Illustration: Fig. 47. Diagram illustrating Differential Motion.]
+
+During all this time the points _m a' b' c' n_ have been moving straight
+down the glacier; and hence it will be understood that the sliding of
+the parts past each other, or, in other words, the differential motion,
+_is parallel to the sides of the glacier_. This, indeed, is the only
+differential motion that experiment has ever established; and
+consequently, when we find the best blue veins referred to the sides of
+the glacier because the differential motion is there greatest, we
+naturally infer that the motion meant is parallel to the sides.
+
+[Sidenote: STRUCTURE OBLIQUE TO SIDES.]
+
+But the fact is, that this motion would not at all account for the blue
+veins, for they are not parallel to the sides, but _oblique_ to them.
+This difficulty revealed itself after a time to those who first
+propounded the theory of differential motion, and caused them to modify
+their explanation of the structure. Differential motion is still assumed
+to be the cause of the veins, but now a motion is meant oblique to the
+sides, and it is supposed to be obtained in the following way:--Through
+the quicker motion of the point _c'_ the ice between it and _n_ becomes
+distended; that is to say, the line _c' n_ is in a state of
+strain--there is a _drag_, it is said, oblique to the sides of the
+glacier; and it is therefore in this direction that the particles will
+be caused to slide past each other. Dr. Whewell, who advocates this
+view, thus expounds it. He supposes the case of an alpine valley filled
+with india-rubber which has been warmed until it has partially melted,
+or become viscous, and then asks, "What will now be the condition of the
+mass? The sides and bottom will still be held back by the friction; the
+middle and upper part will slide forwards, but not freely. This want of
+freedom in the motion (arising from the viscosity) will produce a drag
+towards the middle of the valley, where the motion is freest; hence the
+direction in which the filaments slide past each other will be obliquely
+directed towards the middle. The sliding will separate the mass
+according to such lines; and though new attachments will take place, the
+mass may be expected to retain the results of this separation in the
+traces of parallel fissures."[A] Nothing can be clearer than the image
+of the process thus placed before the mind's eye.
+
+One fact of especial importance is to be borne in mind: the sliding of
+filaments which is thus supposed to take place oblique to the glacier
+has never been proved; it is wholly assumed. A moraine, it is admitted,
+will run parallel to the side of a glacier, or a block will move in the
+same direction from beginning to end, without being sensibly drawn
+towards the centre, but still it is supposed that the sliding of parts
+exists, though of a character so small as to render it insensible to
+measurement.
+
+[Sidenote: STRUCTURE CROSSES LINES OF SLIDING.]
+
+My chief difficulty as regards this theory may be expressed in a very
+few words. If the structure be produced by differential motion, why is
+the large and _real_ differential motion which experiments have
+established incompetent to produce it? And how can the veins run, as
+they are admitted to do, _across the lines of maximum sliding_ from
+their origin throughout the glacier to its end?
+
+That a drag towards the centre of the glacier exists is undeniable, but
+that in consequence of the drag there is a sliding of filaments in this
+direction, is quite another thing. I have in another place[B]
+endeavoured to show experimentally that no such sliding takes place,
+that the drag on any point towards the centre expresses only half the
+conditions of the problem; being exactly neutralized by the thrust
+towards the sides. It has been, moreover, shown by Mr. Hopkins that the
+lines of maximum strain and of maximum sliding cannot coincide; indeed,
+if all the particles be urged by the same force, no matter how strong
+the pull may be, there will be no tendency of one to slide past the
+other.
+
+
+FOOTNOTES:
+
+[A] 'Philosophical Magazine,' Ser. III., vol. xxvi.
+
+[B] 'Proceedings of the Royal Institution,' vol. ii. p. 324.
+
+
+
+
+THE RIPPLE-THEORY OF THE VEINED STRUCTURE.
+
+(29.)
+
+
+[Sidenote: THEORY STATED.]
+
+[Sidenote: THEORY EXAMINED.]
+
+The assumption of oblique sliding, and the production thereby of the
+marginal structure, have, however, been fortified by considerations of
+an ingenious and very interesting kind. "How," I have asked, "can the
+oblique structure persist across the lines of greatest differential
+motion throughout the length of the glacier?" But here I am met by
+another question which at first sight might seem equally
+unanswerable--"How do ripple-marks on the surface of a flowing river,
+which are nothing else than lines of differential motion of a low order,
+cross the river from the sides obliquely, while the direction of
+greatest differential motion is parallel to the sides?" If I understand
+aright, this is the main argument of Professor Forbes in favour of his
+theory of the oblique marginal structure. It is first introduced in a
+note at page 378 of his 'Travels;' he alludes to it in a letter written
+the following year; in his paper in the 'Philosophical Transactions' he
+develops the theory. He there gives drawings of ripple-marks observed in
+smooth gutters after rain, and which he finds to be inclined to the
+course of the stream, exactly as the marginal structure is inclined to
+the side of the glacier. The explanation also embraces the case of an
+obstacle placed in the centre of a river. "A case," writes Professor
+Forbes, "parallel to the last mentioned, where a fixed obstacle cleaves
+a descending stream, and leaves its trace in a fan-shaped tail, is well
+known in several glaciers, as in that at Ferpecle, and the Glacier de
+Lys on the south side of Monte Rosa; particularly the last, where the
+veined structure follows the law just mentioned." In his Twelfth Letter
+he also refers to the ripples "as exactly corresponding to the position
+of the icy bands." In his letter to Dr. Whewell, published in the
+'Occasional Papers,' page 58, he writes as follows:--"The same is
+remarkably shown in the case of a stream of water, for instance a
+mill-race. Although the movement of the water, as shown by floating
+bodies, is exceedingly nearly (for small velocities sensibly) parallel
+to the sides, yet the variation of the speed from the side to the centre
+of the stream occasions a _ripple_, or molecular discontinuity, which
+inclines forwards from the sides to the centre of the stream at an angle
+with the axis depending on the ratio of the central and lateral
+velocity. The veined structure of the ice corresponds to the ripple of
+the water, a molecular discontinuity whose measure is not comparable to
+the actual velocity of the ice; and therefore the general movement of
+the glacier, as indicated by the moraines, remains sensibly parallel to
+the sides." This theory opens up to us a series of interesting and novel
+considerations which I think will repay the reader's attention. If the
+ripples in the water and the veins in the ice be due to the same
+mechanical cause, when we develop clearly the origin of the former we
+are led directly to the explanation of the latter. I shall now endeavour
+to reduce the ripples to their mechanical elements.
+
+The Messrs. Weber have described in their 'Wellenlehre' an effect of
+wave-motion which it is very easy to obtain. When a boat moves through
+perfectly smooth water, and the rower raises his oar out of the water,
+drops trickle from its blade, and each drop where it falls produces a
+system of concentric rings. The circular waves as they widen become
+depressed, and, if the drops succeed each other with sufficient speed,
+the rings cross each other at innumerable points. The effect of this is
+to blot out more or less completely all the circles, and to leave
+behind two straight divergent ripple-lines, which are tangents to all
+the external rings; being in fact formed by the intersections of the
+latter, as a caustic in optics is formed by the intersection of luminous
+rays. Fig. 48, which is virtually copied from M. Weber, will render this
+description at once intelligible. The boat is supposed to move in the
+direction of the arrow, and as it does so the rings which it leaves
+behind widen, and produce the divergence of the two straight resultant
+lines of ripple.
+
+[Sidenote: RIPPLES DEDUCED FROM RINGS.]
+
+[Illustration: Fig. 48. Diagram explanatory of the formation of
+Ripples.]
+
+The more quickly the drops succeed each other, the more frequent will be
+the intersections of the rings; but as the speed of succession augments
+we approach the case of _a continuous vein_ of liquid; and if we suppose
+the continuity to be perfectly established, the ripples will still be
+produced with a smooth space between them as before. This experiment may
+indeed be made with a well-wetted oar, which on its first emergence from
+the water sends into it a continuous liquid vein. The same effect is
+produced when we substitute for the stream of liquid a solid rod--a
+common walking-stick for example. A water-fowl swimming in calm water
+produces two divergent lines of ripples of a similar kind.
+
+We have here supposed the water of the lake to be at rest, and the
+liquid vein or the solid rod to move through it; but precisely the same
+effect is produced if we suppose the rod at rest and the liquid in
+motion. Let a post, for example, be fixed in the middle of a flowing
+river; diverging from that post right and left we shall have lines of
+ripples exactly as if the liquid were at rest and the post moved through
+it with the velocity of the river. If the same post be placed close to
+the bank, so that _one_ of its edges only shall act upon the water,
+diverging from that edge we shall have a _single_ line of ripples which
+will cross the river obliquely towards its centre. It is manifest that
+any other obstacle will produce the same effect as our hypothetical
+post. In the words of Professor Forbes, "the slightest prominence of any
+kind in the wall of such a conduit, a bit of wood or a tuft of grass, is
+sufficient to produce a well-marked ripple-streak from the side towards
+the centre."
+
+[Sidenote: MEASURE OF DIVERGENCE OF RIPPLES.]
+
+The foregoing considerations show that the divergence of the two lines
+of ripples from the central post, and of the single line in the case of
+the lateral post, have their mechanical element, if I may use the term,
+in the experiment of the Messrs. Weber. In the case of a swimming duck
+the connexion between the diverging lines of ripples and the propagation
+of rings round a disturbed point is often very prettily shown. When the
+creature swims with vigour the little foot with which it strikes the
+water often comes sufficiently near to the surface to produce an
+elevation,--sometimes indeed emerging from the water altogether. Round
+the point thus disturbed rings are immediately propagated, and the
+widening of those rings is _the exact measure of the divergence of the
+ripple lines_. The rings never cross the lines;--the lines never retreat
+from the rings.
+
+[Sidenote: RIPPLES AND VEINS DUE TO DIFFERENT CAUSES.]
+
+If we compare the mechanical actions here traced out with those which
+take place upon a glacier, I think it will be seen that the analogy
+between the ripples and the veined structure is entirely superficial.
+How the structure ascribed to the Glacier de Lys is to be explained I do
+not know, for I have never seen it; but it seems impossible that it
+could be produced, as ripples are, by a fixed obstacle which "cleaves a
+descending stream." No one surely will affirm that glacier-ice so
+closely resembles a fluid as to be capable of transmitting undulations,
+as water propagates rings round a disturbed point. The difficulty of
+such a supposition would be augmented by taking into account the motion
+of the _individual liquid particles_ which go to form a ripple; for the
+Messrs. Weber have shown that these move in closed curves, describing
+orbits more or less circular. Can it be supposed that the particles of
+ice execute a motion of this kind? If so, their orbital motions may be
+easily calculated, being deducible from the motion of the glacier
+compounded with the inclination of the veins. If so important a result
+could be established, all glacier theories would vanish in comparison
+with it.
+
+[Sidenote: POSITION OF RIPPLES NOT THAT OF STRUCTURE.]
+
+There is another interesting point involved in the passage above quoted.
+Professor Forbes considers that the ripple is occasioned by the
+variation of speed from the side to the centre of the stream, and that
+its _inclination_ depends on the ratio of the central and lateral
+velocity. If I am correct in the above analysis, this cannot be the
+case. The inclination of the ripple depends solely on the ratio of the
+river's translatory motion to the velocity of its wave-motion. Were the
+lateral and central velocities alike, a momentary disturbance at the
+side would produce a _straight_ ripple-mark, whose inclination would be
+compounded of the two elements just mentioned. If the motion of the
+water vary from side to centre, the velocity of wave-propagation
+remaining constant, the inclination of the ripple will also vary, that
+is to say, we shall have a _curved_ ripple instead of a straight one.
+This, of course, is the case which we find in Nature, but the curvature
+of such ripples is totally different from that of the veined structure.
+Owing to the quicker translatory movement, the ripples, as they approach
+the centre, tend more to parallelism with the direction of the river;
+and after having passed the centre, and reached the slower water near
+the opposite side, their inclination to the axis gradually augments.
+Thus the ripples from the two sides form a pair of symmetric curves,
+which cross each other at the centre, and possess the form _a o b_, _c o
+d_, shown in Fig. 49. A similar pair of curves would be produced by the
+reflection of these. Knowing the variation of motion from side to
+centre, any competent mathematician could find the equation of the
+ripple-curves; but it would be out of place for me to attempt it here.
+
+[Illustration: Fig. 49. Diagram explanatory of the formation of
+Ripples.]
+
+
+
+
+THE VEINED STRUCTURE AND PRESSURE.
+
+(30.)
+
+
+If a prism of glass be pressed by a sufficient weight, the particles in
+the line of pressure will be squeezed more closely together, while those
+at right angles to this line will be forced further apart. The existence
+of this state of strain may be demonstrated by the action of such
+squeezed glass upon polarised light. It gives rise to colours, and it is
+even possible to infer from the tint the precise amount of pressure to
+which the glass is subjected. M. Wertheim indeed has most ably applied
+these facts to the construction of a dynamometer, or instrument for
+measuring pressures, exceeding in accuracy any hitherto devised.
+
+When the pressure applied becomes too great for the glass to sustain, it
+flies to pieces. But let us suppose the sides of the prism defended by
+an extremely strong jacket, in which the prism rests like a
+closely-fitting plug, and which yields only when a pressure more than
+sufficient to crush the glass is applied. Let the pressure be gradually
+augmented until this point is attained; afterwards both the glass and
+its jacket will shorten and widen; the jacket will yield laterally,
+being pushed out with extreme slowness by the glass within.
+
+[Sidenote: POSSIBLE EXPERIMENT WITH GLASS PRISM.]
+
+Now I believe that it would be possible to make this experiment in such
+a manner that the glass should be _flattened_, partly through rupture,
+and partly through lateral molecular yielding; the prism would change
+its form, and yet present a firmly coherent mass when removed from its
+jacket. I have never made the experiment; nobody has, as far as I know;
+but experiments of this kind are often made by Nature. In the Museum of
+the Government School of Mines, for example, we have a collection of
+quartz stones placed there by Mr. Salter, and which have been subjected
+to enormous pressure in the neighbourhood of a fault. These rigid
+pebbles have, in some cases, been squeezed against each other so as to
+produce mutual flattening and indentation. Some of them have yielded
+along planes passing through them, as if one half had slidden over the
+other; but the reattachment is very strong. Some of the larger stones,
+moreover, which have endured pressure at a particular point, are
+fissured radially around this point. In short, the whole collection is a
+most instructive example of the manner and extent to which one of the
+most rigid substances in Nature can yield on the application of a
+sufficient force.
+
+[Sidenote: POSSIBLE EXPERIMENT WITH PRISM OF ICE.]
+
+Let a prism of ice at 32 deg. be placed in a similar jacket to that which we
+have supposed to envelop the glass prism. The ice yields to the pressure
+with incomparably greater ease than the glass; and if the force be
+slowly applied, the lateral yielding will far more closely resemble that
+of a truly plastic body. Supposing such a piece of ice to be filled with
+numerous small air-bubbles, the tendency of the pressure would be to
+flatten these bubbles, and to squeeze them out of the ice. Were the
+substance perfectly homogeneous, this flattening and expulsion would
+take place uniformly throughout its entire mass; but I believe there is
+no such homogeneous substance in nature;--the ice will yield at
+different places, leaving between them spaces which are comparatively
+unaffected by the pressure. From the former spaces the air-bubbles will
+be more effectually expelled; and I have no doubt that the result of
+such pressure acting upon ice so protected would be to produce a
+laminated structure somewhat similar to that which it produces in those
+bodies which exhibit slaty cleavage.
+
+[Sidenote: LAMINATION PRODUCED BY PRESSURE.]
+
+[Sidenote: NO SLIDING OF FILAMENTS.]
+
+I also think it certain that, in this lateral displacement of the
+particles, these must move past each other. This is an idea which I
+have long entertained, as the following passage taken from the paper
+published by Mr. Huxley and myself will prove:--"Three principal causes
+may operate in producing cleavage: first, the reducing of surfaces of
+weak cohesion to parallel planes; second, the flattening of minute
+cavities; and third, the weakening of cohesion by tangential action. The
+third action is exemplified by the state of the rails near a station
+where a break is habitually applied to a locomotive. In this case, while
+the weight of the train presses vertically, its motion tends to cause
+longitudinal sliding of the particles of the rail. Tangential action
+does not, however, necessarily imply a force of the latter kind. When a
+solid cylinder an inch in height is squeezed to a vertical cake a
+quarter of an inch in height, it is impossible, physically speaking,
+that the particles situated in the same vertical line shall move
+laterally with the same velocity; but if they do not, the cohesion
+between them will be weakened or ruptured. The pressure, however, will
+produce new contact; and if this have a cohesive value equal to that of
+the old contact, no cleavage from this cause can arise. The relative
+capacities of different substances for cleavage appear to depend in a
+great measure upon their different properties in this respect. In
+butter, for example, the new attachments are equal, or nearly so, to the
+old, and the cleavage is consequently indistinct; in wax this does not
+appear to be the case, and hence may arise in a great degree the
+perfection of its cleavage. The further examination of this subject
+promises interesting results." I would dwell upon this point the more
+distinctly as the advocates of differential motion may deem it to be in
+their favour; but it appears to me that the mechanical conceptions
+implied in the above passage are totally different from theirs. If they
+think otherwise, then it seems to me that they should change the
+expressions which refer the differential motion to a "drag" towards the
+centre, and the structure to the sliding of "filaments" past each other
+in consequence of this drag. Such filamentary sliding may take place in
+a truly viscous body, but it does not take place in ice.
+
+In one particular the ice resembles the butter referred to in the above
+quotation; for its new attachments appear to be equal to the old, and
+this, I think, is to be ascribed to its perfect regelation. As justly
+pointed out by Mr. John Ball, the veined ice of a glacier, if
+unweathered, shows no tendency to cleave; for though the expulsion of
+the air-bubbles has taken place, the reattachment of the particles is so
+firm as to abolish all evidence of cleavage. When the ice, on the
+contrary, is weathered, the plates become detached, and I have often
+been able to split such ice into thin tablets having an area of two or
+three square feet.
+
+In his Thirteenth Letter Professor Forbes throws out a new and possibly
+a pregnant thought in connexion with the veins. If I understand him
+aright--and I confess it is usually a matter of extreme difficulty with
+me to make sure of this--he there refers the veins, not to the expulsion
+of the air from the ice, but to its redistribution. The pressure
+produces "_lines of tearing_ in which the air is distributed in the form
+of regular globules." I do not know what might be made of this idea if
+it were developed, but at present I do not see how the supposed action
+could produce the blue bands; and I agree with Professor Wm. Thomson in
+regarding the explanation as improbable.[A]
+
+
+FOOTNOTES:
+
+[A] For an extremely ingenious view of the origin of the veined
+structure, I would refer to a paper by Professor Thomson, in the
+'Proceedings of the Royal Society,' April, 1858.
+
+
+
+
+THE VEINED STRUCTURE AND THE LIQUEFACTION OF ICE BY PRESSURE.
+
+(31.)
+
+
+I have already noticed an important fact for which we are indebted to
+Mr. James Thomson, and have referred to the original communications on
+the subject. I shall here place the physical circumstances connected
+with this fact before my reader in the manner which I deem most likely
+to interest him.
+
+[Sidenote: INFLUENCE OF PRESSURE ON BOILING POINT.]
+
+When a liquid is heated, the attraction of the molecules operates
+against the action of the heat, which tends to tear them asunder. At a
+certain point the force of heat triumphs, the cohesion is overcome, and
+the liquid boils. But supposing we assist the attraction of the
+molecules by applying an external pressure, the difficulty of tearing
+them asunder will be increased; more heat will be required for this
+purpose; and hence we say that the _boiling point_ of the liquid has
+been _elevated_ by the pressure.
+
+[Sidenote: INFLUENCE OF PRESSURE ON FUSING POINT.]
+
+If molten sulphur be poured into a bullet-mould, it will be found on
+cooling to contract, so as to leave a large hollow space in the middle
+of each sphere. Cast musket-bullets are thus always found to possess a
+small cavity within them produced by the contraction of the lead.
+Conceive the bullet placed within its mould and the latter heated; to
+produce fusion it is necessary that the sulphur or the lead should
+_swell_. Here, as in the case of the heated water, the tendency to
+expand is opposed by the attraction of the molecules; with a certain
+amount of heat however this attraction is overcome and the solid
+_melts_. But suppose we assist the molecular attraction by a suitable
+force applied externally, a greater amount of heat than before will be
+necessary to tear them asunder; and hence we say that the _fusing
+point_ has been _elevated_ by the pressure. This fact has been
+experimentally established by Messrs. Hopkins and Fairbairn, who applied
+to spermaceti and other substances pressures so great as to raise their
+points of fusion a considerable number of degrees.
+
+Let us now consider the case of the metal bismuth. If the molten metal
+be poured into a bullet-mould it will _expand_ on solidifying. I have
+myself filled a strong cast-iron bottle with the metal, and found its
+expansion on cooling sufficiently great to split the bottle from neck to
+bottom. Hence, in order to fuse the bismuth the substance must
+_contract_; and it is manifest that an external pressure which tends to
+squeeze the molecules more closely together here _assists_ the heat
+instead of opposing it. Hence, to fuse bismuth under great pressure, a
+less amount of heat will be required than when the pressure is removed;
+or, in other words, the fusing point of bismuth is _lowered_ by the
+pressure. Now, in passing from the solid to the liquid state, _ice_,
+like bismuth, contracts, and if the contraction be promoted by external
+pressure, as shown by the Messrs. Thomson, a less amount of heat
+suffices to liquefy it.
+
+[Sidenote: EXPERIMENTS.]
+
+These remarks will enable us to understand a singular effect first
+obtained by myself at the close of 1856 or in January 1857, noticed at
+the time in the 'Proceedings of the Royal Society,' and afterwards fully
+described in a paper presented to the Society in December of that year.
+A cylinder of clear ice two inches high and an inch in diameter was
+placed between two slabs of box-wood, and subjected to a gradual
+pressure. I watched the ice in a direction perpendicular to its length,
+and saw cloudy lines drawing themselves across it. As the pressure
+continued, these lines augmented in numbers, until finally the prism
+presented the appearance of a crystal of gypsum whose planes of cleavage
+had been forced out of optical contact. When looked at obliquely it was
+found that the lines were merely the sections of flat dim surfaces,
+which lay like laminae one over the other throughout the length of the
+prism. Fig. 50 represents the prism as it appeared when looked at in a
+direction perpendicular to its axis; Fig. 51 shows the appearance when
+viewed obliquely.[A]
+
+[Illustration: Fig. 50, 51. Appearance of a prism of ice partially
+liquefied by Pressure.]
+
+At first sight it might appear as if air had intruded itself between the
+separated surfaces of the ice, and to test this point I placed a
+cylinder two inches long and an inch wide upright in a copper vessel
+which was filled with ice-cold water. The ice cylinder rose about half
+an inch above the surface of the water. Placing the copper vessel on a
+slab of wood, and a second slab on the top of the cylinder of ice, the
+latter was subjected to the gradual action of a small hydraulic press.
+When the hazy surfaces were well developed in the portion of the ice
+above the water, the cylinder was removed and examined: the planes of
+rupture extended throughout the entire length of the cylinder, just as
+if it had been squeezed in air. I subsequently placed the ice in a stout
+vessel of glass, and squeezed it, as in the last experiment: the
+surfaces of discontinuity were seen forming _under the liquid_ quite as
+distinctly as in air.
+
+To prove that the surfaces were due to compression and not to any
+tearing asunder of the mass by tension, the following experiment was
+made:--A cylindrical piece of ice, one of whose ends, however, was not
+parallel to the other, was placed between the slabs of wood, and
+subjected to pressure. Fig. 52 shows the disposition of the experiment.
+The effect upon the ice cylinder was that shown in Fig. 53, the surfaces
+being developed along that side which had suffered the pressure. On
+examining the surfaces by a pocket lens they resembled the effect
+produced upon a smooth cold surface by breathing on it.
+
+[Illustration: Fig. 52, 53. Figures illustrative of compression and
+liquefaction of ice.]
+
+[Sidenote: LIQUID LAYERS PRODUCED BY PRESSURE.]
+
+The surfaces were always dim; and had the spaces been filled with air,
+or were they simply vacuous, the reflection of light from them would
+have been so copious as to render them much more brilliant than they
+were observed to be. To examine them more particularly I placed a
+concave mirror so as to throw the diffused daylight from a window full
+upon the cylinder. On applying the pressure dim spots were sometimes
+seen forming in the very middle of the ice, and these as they expanded
+laterally appeared to be in a state of intense motion, which followed
+closely the edge of each surface as it advanced through the solid ice.
+Once or twice I observed the hazy surfaces pioneered through the mass by
+dim offshoots, apparently liquid, and constituting a kind of
+decrystallisation. From the closest examination to which I was able to
+subject them, the surfaces appeared to me to be due to internal
+liquefaction; indeed, when the melting point of ice, having already a
+temperature of 32 deg., is lowered by pressure, its excess of heat must
+instantly be applied to produce this effect.
+
+[Sidenote: APPLICATION TO THE VEINED STRUCTURE.]
+
+I have already given a drawing (p. 386) showing the development of the
+veined structure at the base of the ice-cascade of the Rhone; and if we
+compare that diagram with Fig. 53 a striking similarity at once reveals
+itself. The ice of the glacier must undoubtedly be liquefied to some
+extent by the tremendous pressure to which it is here subjected.
+Surfaces of discontinuity will in all probability be formed, which
+facilitate the escape of the imprisoned air. The small quantity of water
+produced will be partly imbibed by the adjacent porous ice, and will be
+refrozen when relieved from the pressure. This action, associated with
+that ascribed to pressure in the last section, appears to me to furnish
+a complete physical explanation of the laminated structure of
+glacier-ice.
+
+
+FOOTNOTES:
+
+[A] This effect projected upon a screen is a most striking and
+instructive class experiment.
+
+
+
+
+WHITE ICE-SEAMS IN THE GLACIER DU GEANT.
+
+(32.)
+
+
+[Sidenote: GENERAL APPEARANCE OF WHITE ICE-SEAMS.]
+
+On the 28th of July, 1857, while engaged upon the Glacier du Geant, my
+attention was often attracted by protuberant ridges of what at first
+appeared to be pure white snow, but which on examination I found to be
+compact ice filled with innumerable round air-cells; and which, in
+virtue of its greater power of resistance to wasting, often rose to a
+height of three or four feet above the general level of the ice. As I
+stood amongst these ridges, they appeared detached and without order of
+arrangement, but looked at from a distance they were seen to sweep
+across the proper Glacier du Geant in a direction concentric with its
+dirt-bands and its veined structure. In some cases the seams were
+admirable indications of the relative displacement of two adjacent
+portions of the glacier, which were divided from each other by a
+crevasse. Usually the sections of a seam exposed on the opposite sides
+of a fissure accurately faced each other, and the direction of the seam
+on both sides was continuous; but at other places they demonstrated the
+existence of lateral faults, being shifted asunder laterally through
+spaces varying from a few inches to six or seven feet.
+
+On the following day I was again upon the same glacier, and noticed in
+many cases the white ice-seams exquisitely honeycombed. The case was
+illustrative of the great difference between the absorptive power of the
+ice itself and of the objects which lie upon its surface. Deep
+cylindrical cells were produced by spots of black dirt which had been
+scattered upon the surface of the white ice, and which sank to a depth
+of several inches into the mass. I examined several sections of the
+veins, and in general I found that their deeper portions blended
+gradually with the ice on either side of them. But higher up the glacier
+I found that the veins penetrated only to a limited depth, and did not
+therefore form an integrant portion of the glacier. Figs. 54 and 55 show
+the sections of two of the seams which were exposed on the wall of a
+crevasse at some distance below the great ice-fall of the Glacier du
+Geant.
+
+[Sidenote: SECTIONS OF SEAMS.]
+
+[Illustration: Fig. 54, 55. Sections of White Ice-seams.]
+
+[Illustration: Fig. 56. Variations in the Dip of the Veined Structure.]
+
+It was at the base of the Talefre cascade that the explanation of these
+curious seams presented itself to me. In one of my earliest visits to
+this portion of the glacier I was struck by a singular disposition of
+the blue veins on the vertical wall of a crevasse. Fig. 56 will
+illustrate what I saw. The veins, within a short distance, dipped
+_backward_ and _forward_, like the junctions of stones used to turn an
+arch. In some cases I found this variation of the structure so great as
+to pass in a short distance from the vertical to the horizontal, as
+shown in Fig. 57.
+
+[Sidenote: VARIATIONS IN "DIP" OF STRUCTURE.]
+
+[Illustration: Fig. 57. Variations in the Dip of the Veined Structure.]
+
+Further examination taught me that the glacier here is crumpled in a
+most singular manner; doubtless by the great pressure to which it is
+exposed. The following illustration will convey a notion of its aspect:
+Let one hand be laid flat upon a table, palm downwards, and let the
+fingers be bent until the space between the first joint and the ends of
+the fingers is vertical; one of the crumples to which I refer will then
+be represented. The ice seems bent like the fingers, and the crumples of
+the glacier are cut by crevasses, which are accurately typified by the
+spaces between the fingers. Let the second hand now be placed upon the
+first, as the latter is upon the table, so that the tops of the bent
+fingers of the second hand shall rest upon the roots of the first: two
+crumples would thus be formed; a series of such protuberances, with
+steep fronts, follow each other from the base of the Talefre cascade for
+some distance downwards.
+
+On Saturday the 1st of August I ascended these rounded terraces in
+succession, and observed among them an extremely remarkable disposition
+of the structure. Fig. 58 is a section of a series of three of the
+crumples, on which the shading lines represent the direction of the blue
+veins. At the base of each protuberance I found a seam of white ice
+wedged firmly into the glacier, and _each of the seams marked a place of
+dislocation of the veins_. The white seams thinned off gradually, and
+finally vanished where the violent crumpling of the ice disappeared. In
+Fig. 59 I have sketched the wall of a crevasse, which represents what
+may be regarded as the incipient crumpling. The undulating line shows
+the contour of the surface, and the shading lines the veins. It will be
+observed that the direction of the veins yields in conformity with the
+undulation of the surface; and an augmentation of the effect would
+evidently result in the crumples shown in Fig. 58. The appearance of the
+white seams at those places where a dislocation occurred was, as far as
+I could observe, invariable; but in a few instances the seams were
+observed upon the platforms of the terraces, and also upon their slopes.
+The width of a seam was very irregular, varying from a few inches at
+some places to three or four feet at others.
+
+[Sidenote: CRUMPLES OF THE TALEFRE.]
+
+[Illustration: Fig. 58. Section of three glacier Crumples.]
+
+[Illustration: Fig. 59. Wall of a crevasse, with incipient crumpling.]
+
+[Sidenote: MOULDS OF WHITE ICE-SEAMS.]
+
+On the 3rd of August I was again at the base of the Talefre cascade, and
+observed a fact the significance of which had previously escaped me. The
+rills which ran down the ice-slopes collected at the base of each
+protuberance into a stream, which, at the time of my visit, had hollowed
+out for itself a deep channel in the ice. At some places the stream
+widened, at others its banks of ice approached each other, and rapids
+were produced; in fact, _the channels of such streams appeared to be the
+exact moulds of the seams of white ice_.
+
+Instructed thus far, I ascended the Glacier du Geant on the 5th of
+August, and then observed on the wrinkles of this glacier the same
+leaning backwards and forwards of the blue veins as I had previously
+observed upon the Talefre. I also noticed on this day that a seam of
+white ice would sometimes open out into two branches, which, after
+remaining for some distance separate, would reunite and thus enclose a
+little glacier-island. At other places lateral branches were thrown off
+from the principal seam, thus suggesting the form of a glacier-rivulet
+which had been fed by tributary branches. On the 7th of August I hunted
+the seams still farther up the glacier; and found them at one place
+descending a steep ice-hill, being crossed by other similar bands, which
+however were far less white and compact. I followed these new bands to
+their origin, and found it to be a system of crevasses formed at the
+summit of the hill, some of which were filled with snow. Lower down the
+crevasses closed, and the snow thus jammed between their walls was
+converted into white ice. These seams, however, never attained the
+compactness and prominence of the larger ones which had their origin far
+higher up. I singled out one of the best of the latter, and traced it
+through all the dislocation and confusion of the ice, until I found it
+to terminate in a cavity filled with snow.
+
+This was near the base of the _seracs_, and the streams here were
+abundant. Comparing the shapes of some of them with that of the
+ice-bands lower down the glacier, a striking resemblance was observed.
+Fig. 60 is the plan of a deep-cut channel through which a stream flowed
+on the day to which I now refer. Fig. 61 is the plan of a seam of white
+ice sketched on the same day, low down upon the glacier. Instances of
+this kind might be multiplied; and the result, I think, renders it
+certain that the white ice-seams referred to are due to the filling up
+of the channels of glacier-streams by snow during winter, and the
+subsequent compression of the mass to ice during the descent of the
+glacier. I have found such seams at the bases of all cascades that I
+have visited; and in all cases they appear to be due to the same cause.
+The depth to which they penetrate the glacier must be profound, or the
+_ablation_ of the ice must be less than what is generally supposed; for
+the seams formed so high up on the Glacier du Geant may be traced low
+down upon the trunk-stream of the Mer de Glace.[A]
+
+[Sidenote: STREAMS AND SEAMS.]
+
+[Illustration: Fig. 60. Plan of a Stream on the Glacier du Geant.]
+
+[Illustration: Fig. 61. Plan of a Seam of White Ice on the Glacier du
+Geant.]
+
+[Sidenote: SCALING OFF BY PRESSURE.]
+
+These observations on the white ice-seams enable us to add an important
+supplement to what has been stated regarding the origin of the
+dirt-bands of the Mer de Glace; The protuberances at the base of the
+cascade are due not only to the toning down of the ridges produced by
+the transverse fracture of the glacier at the summit of the fall, but
+they undergo modifications by the pressure locally exerted at its base.
+The state of things represented in Fig. 57 is plainly due to the partial
+pushing of one crumple over that next in advance of it. There seems to
+be a differential motion of the parts of the glacier in the same
+longitudinal line; showing that upon the general motion of the glacier
+smaller local motions are superposed. The occurrence of the seams upon
+the faces of the slopes seems also to prove that the pressure is
+competent, in some cases, to cause the bases of the protuberances to
+swell, so that what was once the base of a crumple may subsequently form
+a portion of its slope. Another interesting fact is also observed where
+the pressure is violent: the crumples _scale off_, bows of ice being
+thus formed which usually span the crumples over their most violently
+compressed portions. I have found this scaling off at the bases of all
+the cascades which I have visited, and it is plainly due to the pressure
+exerted at such places upon the ice.
+
+
+FOOTNOTES:
+
+[A] The more permanent seams may possibly be due to the filling of the
+profound crevasses of the cascade.
+
+
+
+
+(33.)
+
+
+[Sidenote: COMPRESSION OF GLACIER DU GEANT.]
+
+Not only at the base of its great cascade, but throughout the greater
+part of its length, the Glacier du Geant is in a state of longitudinal
+compression. The meaning of this term will be readily understood: Let
+two points, for example, be marked upon the axis of the glacier; if
+these during its descent were drawn wider apart, it would show that the
+glacier was in a state of longitudinal strain or tension; if they
+remained at the same distance apart, it would indicate that neither
+strain nor pressure was exerted; whereas, if the two points approached
+each other, which could only be by the quicker motion of the hinder
+one, the existence of longitudinal compression would be thereby
+demonstrated.
+
+Taking "Le Petit Balmat" with me, to carry my theodolite, I ascended the
+Glacier du Geant until I came near the place where it is joined by the
+Glacier des Periades, and whence I observed a patch of fresh green grass
+upon the otherwise rocky mountain-side. To this point I climbed, and
+made it the station for my instrument. Choosing a well-defined object at
+the opposite side of the glacier, I set, on the 9th of August, in the
+line between this object and the theodolite, three stakes, one in the
+centre of the glacier, and the other two at opposite sides of the centre
+and about 100 yards from it. This done, I descended for a quarter of a
+mile, when I again climbed the flanking rocks, placing my theodolite in
+a couloir, down which stones are frequently discharged from the end of a
+secondary glacier which hangs upon the heights above. Here, as before, I
+fixed three stakes, chiselled a mark upon the granite, so as to enable
+me to find the place, and regained the ice without accident. A day or
+two previously we had set out a third line at some distance lower down,
+and I was thus furnished with a succession of points along the glacier,
+the relative motions of which would decide whether it was _pressed_ or
+_stretched_ in the direction of its length. On the 10th of August Mr.
+Huxley joined us; and on the following day we all set out for the
+Glacier du Geant, to measure the progress of the stakes which I had
+fixed there. Hirst remained upon the glacier to measure the
+displacements; I shouldered the theodolite; and Huxley was my guide to
+the mountain-side, sounding in advance of me the treacherous-looking
+snow over which we had to pass.
+
+Calling the central stake of the highest line No. 1, that of the middle
+line No. 2, and that of the line nearest the Tacul No. 3, the following
+are the spaces moved over by these three points in twenty-four hours:
+
+ Inches. Distances asunder.
+
+ No. 1 20.55
+ } 545 yards.
+ No. 2 15.43
+ } 487 yards.
+ No. 3 12.75
+
+Here we have the fact which the aspect of the glacier suggested. The
+first stake moves five inches a day more than the second, and the second
+nearly three inches a day more than the third. As surmised, therefore,
+the glacier is in a state of longitudinal compression, whereby a portion
+of it 1000 yards in length is shortened at the rate of eight inches a
+day.
+
+[Sidenote: STRUCTURE IN WHITE ICE-SEAMS.]
+
+In accordance with this result, the transverse undulations of the
+Glacier du Geant, described in the chapter upon Dirt-Bands, _shorten_ as
+they descend. A series of three of them measured along the axis of the
+glacier on the 6th of August, 1857, gave the following respective
+lengths:--955 links, 855 links, 770 links, the shortest undulation being
+the farthest from the origin of the undulations. This glacier then
+constitutes a vast ice-press, and enables us to test the explanation
+which refers the veined structure of the ice to pressure. The glacier
+itself is transversely laminated, as already stated; and in many cases a
+structure of extreme definition and beauty is developed in the
+compressed snow, which constitutes the seams of white ice. In 1857 I
+discovered a well-developed lenticular structure in some of these seams.
+In 1858 I again examined them. Clearing away the superficial portions
+with my axe, I found, drawn through the body of the seams, long lines of
+blue ice of exquisite definition; in fact, I had never seen the
+structure so delicately exhibited. The seams, moreover, were developed
+in portions of the white ice which were near the _centre_ of the
+glacier, and where consequently filamentous sliding was entirely out of
+the question.
+
+
+
+
+[Sidenote: PARTIAL SUMMARY.]
+
+PARTIAL SUMMARY.
+
+
+1. Glaciers are derived from mountain snow, which has been consolidated
+to ice by pressure.
+
+2. That pressure is competent to convert snow into ice has been proved
+by experiment.
+
+3. The power of yielding to pressure diminishes as the mass becomes more
+compact; but it does not cease even when the substance has attained the
+compactness which would entitle it to be called ice.
+
+4. When a sufficient depth of snow collects upon the earth's surface,
+the lower portions are squeezed out by the pressure of the
+superincumbent mass. If it rests upon a slope it will yield principally
+in the direction of the slope, and move downwards.
+
+5. In addition to this, the whole mass slides bodily along its inclined
+bed, and leaves the traces of its sliding on the rocks over which it
+passes, grinding off their asperities, and marking them with grooves and
+scratches in the direction of the motion.
+
+6. In this way the deposit of consolidated and unconsolidated snow which
+covers the higher portions of lofty mountains moves slowly down into an
+adjacent valley, through which it descends as a true glacier, partly by
+sliding and partly by the yielding of the mass itself.
+
+7. Several valleys thus filled may unite in a single valley, the
+tributary glaciers welding themselves together to form a trunk-glacier.
+
+8. Both the main valley and its tributaries are often sinuous, and the
+tributaries must change their direction to form the trunk; the width of
+the valley often varies. The glacier is forced through narrow gorges,
+widening after it has passed them; the centre of the glacier moves more
+quickly than the sides, and the surface more quickly than the bottom;
+the point of swiftest motion follows the same law as that observed in
+the flow of rivers, shifting from one side of the centre to the other as
+the flexure of the valley changes.
+
+9. These various effects may be reproduced by experiments on small
+masses of ice. The substance may moreover be moulded into vases and
+statuettes. Straight bars of it may be bent into rings, or even coiled
+into knots.
+
+10. Ice, capable of being thus moulded, is practically incapable of
+being stretched. The condition essential to success is that the
+particles of the ice operated on shall be kept in close contact, so that
+when old attachments have been severed new ones may be established.
+
+11. The nearer the ice is to its melting point in temperature, the more
+easily are the above results obtained; when ice is many degrees below
+its freezing point it is crushed by pressure to a white powder, and is
+not capable of being moulded as above.
+
+12. Two pieces of ice at 32 deg. Fahr., with moist surfaces, when placed in
+contact freeze together to a rigid mass; this is called Regelation.
+
+13. When the attachments of pressed ice are broken, the continuity of
+the mass is restored by the regelation of the new contiguous surfaces.
+Regelation also enables two tributary glaciers to weld themselves to
+form a continuous trunk; thus also the crevasses are mended, and the
+dislocations of the glacier consequent on descending cascades are
+repaired. This healing of ruptures extends to the smallest particles of
+the mass, and it enables us to account for the continued compactness of
+the ice during the descent of the glacier.
+
+14. The quality of viscosity is practically absent in glacier-ice. Where
+pressure comes into play the phenomena are suggestive of viscosity, but
+where tension comes into play the analogy with a viscous body breaks
+down. When subjected to strain the glacier does not yield by stretching,
+but by breaking; this is the origin of the crevasses.
+
+15. The crevasses are produced by the mechanical strains to which the
+glacier is subjected. They are divided into marginal, transverse, and
+longitudinal crevasses; the first produced by the oblique strain
+consequent on the quicker motion of the centre; the second by the
+passage of the glacier over the summit of an incline; the third by
+pressure from behind and resistance in front, which causes the mass to
+split at right angles to the pressure [strain?].
+
+16. The moulins are formed by deep cracks intersecting glacier rivulets.
+The water in descending such cracks scoops out for itself a shaft,
+sometimes many feet wide, and some hundreds of feet deep, into which the
+cataract plunges with a sound like thunder. The supply of water is
+periodically cut off from the moulins by fresh cracks, in which new
+moulins are formed.
+
+17. The lateral moraines are formed from the debris which loads the
+glacier along its edges; the medial moraines are formed on a
+trunk-glacier by the union of the lateral moraines of its tributaries;
+the terminal moraines are formed from the debris carried by the glacier
+to its terminus, and there deposited. The number of medial moraines on a
+trunk glacier is always one less than the number of tributaries.
+
+18. When ordinary lake-ice is intersected by a strong sunbeam it
+liquefies so as to form flower-shaped figures within the mass; each
+flower consists of six petals with a vacuous space at the centre; the
+flowers are always formed parallel to the planes of freezing, and depend
+on the crystallization of the substance.
+
+19. Innumerable liquid disks, with vacuous spots, are also formed by the
+solar beams in glacier-ice. These empty spaces have been hitherto
+mistaken for air-bubbles, the flat form of the disks being erroneously
+regarded as the result of pressure.
+
+20. These disks are indicators of the intimate constitution of
+glacier-ice, and they teach us that it is composed of an aggregate of
+parts with surfaces of crystallization in all possible planes.
+
+21. There are also innumerable small cells in glacier-ice holding air
+and water; such cells also occur in lake-ice; and here they are due to
+the melting of the ice in contact with the bubble of air. Experiments
+are needed on glacier-ice in reference to this point.
+
+22. At a free surface within or without, ice melts with more ease than
+in the centre of a compact mass. The motion which we call heat is less
+controlled at a free surface, and it liberates the molecules from the
+solid condition sooner than when the atoms are surrounded on all sides
+by other atoms which impede the molecular motion. Regelation is the
+complementary effect to the above; for here the superficial portions of
+a mass of ice are made virtually central by the contact of a second
+mass.
+
+23. The dirt-bands have their origin in the ice-cascades. The glacier,
+in passing the brow, is transversely fractured; ridges are formed with
+hollows between them; these transverse hollows are the principal
+receptacles of the fine debris scattered over the glacier; and after the
+ridges have been melted away, the dirt remains in successive stripes
+upon the glacier.
+
+24. The ice of many glaciers is laminated, and when weathered may be
+cloven into thin plates. In the sound ice the lamination manifests
+itself in blue stripes drawn through the general whitish mass of the
+glacier; these blue veins representing portions of ice from which the
+air-bubbles have been more completely expelled. This is the veined
+structure of the ice. It is divided into marginal, transverse, and
+longitudinal structure; which may be regarded as complementary to
+marginal, longitudinal, and transverse crevasses. The latter are
+produced by tension, the former by pressure, which acts in two different
+ways: firstly, the pressure acts upon the ice as it has acted upon rocks
+which exhibit the lamination technically called cleavage; secondly, it
+produces partial liquefaction of the ice. The liquid spaces thus formed
+help the escape of the air from the glacier; and the water produced,
+being refrozen when the pressure is relieved, helps to form the blue
+veins.
+
+
+
+
+APPENDIX.
+
+COMPARATIVE VIEW OF THE CLEAVAGE OF CRYSTALS AND SLATE-ROCKS.
+
+A LECTURE DELIVERED AT THE ROYAL INSTITUTION, ON FRIDAY EVENING THE 6TH
+OF JUNE, 1856.[A]
+
+
+When the student of physical science has to investigate the character of
+any natural force, his first care must be to purify it from the mixture
+of other forces, and thus study its simple action. If, for example, he
+wishes to know how a mass of water would shape itself, supposing it to
+be at liberty to follow the bent of its own molecular forces, he must
+see that these forces have free and undisturbed exercise. We might
+perhaps refer him to the dew-drop for a solution of the question; but
+here we have to do, not only with the action of the molecules of the
+liquid upon each other, but also with the action of gravity upon the
+mass, which pulls the drop downwards and elongates it. If he would
+examine the problem in its purity, he must do as Plateau has done,
+withdraw the liquid mass from the action of gravity, and he would then
+find the shape of the mass to be perfectly spherical. Natural processes
+come to us in a mixed manner, and to the uninstructed mind are a mass of
+unintelligible confusion. Suppose half-a-dozen of the best musical
+performers to be placed in the same room, each playing his own
+instrument to perfection: though each individual instrument might be a
+well-spring of melody, still the mixture of all would produce mere
+noise. Thus it is with the processes of nature. In nature, mechanical
+and molecular laws mingle, and create apparent confusion. Their mixture
+constitutes what may be called the _noise_ of natural laws, and it is
+the vocation of the man of science to resolve this noise into its
+components, and thus to detect the "music" in which the foundations of
+nature are laid.
+
+The necessity of this detachment of one force from all other forces is
+nowhere more strikingly exhibited than in the phenomena of
+crystallization. I have here a solution of sulphate of soda. Prolonging
+the mental vision beyond the boundaries of sense, we see the atoms of
+that liquid, like squadrons under the eye of an experienced general,
+arranging themselves into battalions, gathering round a central
+standard, and forming themselves into solid masses, which after a time
+assume the visible shape of the crystal which I here hold in my hand. I
+may, like an ignorant meddler wishing to hasten matters, introduce
+confusion into this order. I do so by plunging this glass rod into the
+vessel. The consequent action is not the pure expression of the
+crystalline forces; the atoms rush together with the confusion of an
+unorganized mob, and not with the steady accuracy of a disciplined host.
+Here, also, in this mass of bismuth we have an example of this confused
+crystallization; but in the crucible behind me a slower process is going
+on: here there is an architect at work "who makes no chips, no din," and
+who is now building the particles into crystals, similar in shape and
+structure to those beautiful masses which we see upon the table. By
+permitting alum to crystallize in this slow way, we obtain these perfect
+octahedrons; by allowing carbonate of lime to crystallize, nature
+produces these beautiful rhomboids; when silica crystallizes, we have
+formed these hexagonal prisms capped at the ends by pyramids; by
+allowing saltpetre to crystallize, we have these prismatic masses; and
+when carbon crystallizes, we have the diamond. If we wish to obtain a
+perfect crystal, we must allow the molecular forces free play: if the
+crystallizing mass be permitted to rest upon a surface it will be
+flattened, and to prevent this a small crystal must be so suspended as
+to be surrounded on all sides by the liquid, or, if it rest upon the
+surface, it must be turned daily so as to present all its faces in
+succession to the working builder. In this way the scientific man nurses
+these children of his intellect, watches over them with a care worthy of
+imitation, keeps all influences away which might possibly invade the
+strict morality of crystalline laws, and finally sees them developed
+into forms of symmetry and beauty which richly reward the care bestowed
+upon them.
+
+In building up crystals, these little atomic bricks often arrange
+themselves into layers which are perfectly parallel to each other, and
+which can be separated by mechanical means; this is called the cleavage
+of the crystal. I have here a crystallized mass which has thus far
+escaped the abrading and disintegrating forces which, sooner or later,
+determine the fate of sugar-candy. If I am skilful enough, I shall
+discover that this crystal of sugar cleaves with peculiar facility in
+one direction. Here, again, I have a mass of rock-salt: I lay my knife
+upon it, and with a blow cleave it in this direction; but I find on
+further examining this substance that it cleaves in more directions than
+one. Laying my knife at right angles to its former position, the crystal
+cleaves again; and, finally placing the knife at right angles to the
+two former positions, the mass cleaves again. Thus rock-salt cleaves in
+three directions, and the resulting solid is this perfect cube, which
+may be broken up into any number of smaller cubes. Here is a mass of
+Iceland spar, which also cleaves in three directions, not at right
+angles, but obliquely to each other, the resulting solid being a
+rhomboid. In each of these cases the mass cleaves with equal facility in
+all three directions. For the sake of completeness, I may say that many
+substances cleave with unequal facility in different directions, and the
+heavy spar I hold in my hand presents an example of this kind of
+cleavage.
+
+Turn we now to the consideration of some other phenomena to which the
+term cleavage may be applied. This piece of beech-wood cleaves with
+facility parallel to the fibre, and if our experiments were fine enough
+we should discover that the cleavage is most perfect when the edge of
+the axe is laid across the rings which mark the growth of the tree. The
+fibres of the wood lie side by side, and a comparatively small force is
+sufficient to separate them. If you look at this mass of hay severed
+from a rick, you will see a sort of cleavage developed in it also; the
+stalks lie in parallel planes, and only a small force is required to
+separate them laterally. But we cannot regard the cleavage of the tree
+as the same in character as the cleavage of the hayrick. In the one case
+it is the atoms arranging themselves according to organic laws which
+produce a cleavable structure; in the other case the easy separation in
+a certain direction is due to the mechanical arrangement of the coarse
+sensible masses of stalks of hay.
+
+In like manner I find that this piece of sandstone cleaves parallel to
+the planes of bedding. This rock was once a powder, more or less coarse,
+held in mechanical suspension by water. The powder was composed of two
+distinct parts, fine grains of sand and small plates of mica. Imagine a
+wide strand covered by a tide which holds such powder in suspension:[B]
+how will it sink? The rounded grains of sand will reach the bottom
+first, the mica afterwards, and when the tide recedes we have the little
+plates shining like spangles upon the surface of the sand. Each
+successive tide brings its charge of mixed powder, deposits its duplex
+layer day after day, and finally masses of immense thickness are thus
+piled up, which, by preserving the alternations of sand and mica, tell
+the tale of their formation. I do not wish you to accept this without
+proof. Take the sand and mica, mix them together in water, and allow
+them to subside, they will arrange themselves in the manner I have
+indicated; and by repeating the process you can actually build up a
+sandstone mass which shall be the exact counterpart of that presented by
+nature, as I have done in this glass jar. Now this structure cleaves
+with readiness along the planes in which the particles of mica are
+strewn. Here is a mass of such a rock sent to me from Halifax: here are
+other masses from the quarries of Over Darwen in Lancashire. With a
+hammer and chisel you see I can cleave them into flags; indeed these
+flags are made use of for roofing purposes in the districts from which
+the specimens have come, and receive the name of "slate-stone." But you
+will discern, without a word from me, that this cleavage is not a
+crystalline cleavage any more than that of a hayrick is. It is not an
+arrangement produced by molecular forces; indeed it would be just as
+reasonable to suppose that in this jar of sand and mica the particles
+arranged themselves into layers by the forces of crystallization,
+instead of by the simple force of gravity, as to imagine that such a
+cleavage as this could be the product of crystallization.
+
+This, so far as I am aware of, has never been imagined, and it has been
+agreed among geologists not to call such splitting as this cleavage at
+all, but to restrict the term to a class of phenomena which I shall now
+proceed to consider.
+
+Those who have visited the slate quarries of Cumberland and North Wales
+will have witnessed the phenomena to which I refer. We have long drawn
+our supply of roofing-slates from such quarries; schoolboys ciphered on
+these slates, they were used for tombstones in churchyards, and for
+billiard-tables in the metropolis; but not until a comparatively late
+period did men begin to inquire how their wonderful structure was
+produced. What is the agency which enables us to split Honister Crag, or
+the cliffs of Snowdon, into laminae from crown to base? This question is
+at the present moment one of the greatest difficulties of geologists,
+and occupies their attention perhaps more than any other. You may wonder
+at this. Looking into the quarry of Penrhyn, you may be disposed to
+explain the question as I heard it explained two years ago. "These
+planes of cleavage," said a friend who stood beside me on the quarry's
+edge, "are the planes of stratification which have been lifted by some
+convulsion into an almost vertical position." But this was a great
+mistake, and indeed here lies the grand difficulty of the problem. These
+planes of cleavage stand in most cases at a high angle to the bedding.
+Thanks to Sir Roderick Murchison, who has kindly permitted me the use of
+specimens from the Museum of Practical Geology (and here I may be
+permitted to express my acknowledgments to the distinguished staff of
+that noble establishment, who, instead of considering me an intruder,
+have welcomed me as a brother), I am able to place the proof of this
+before you. Here is a mass of slate in which the planes of bedding are
+distinctly marked; here are the planes of cleavage, and you see that one
+of them makes a large angle with the other. The cleavage of slates is
+therefore not a question of stratification, and the problem which we
+have now to consider is, "By what cause has this cleavage been
+produced?"
+
+In an able and elaborate essay on this subject in 1835, Professor
+Sedgwick proposed the theory that cleavage is produced by the action of
+crystalline or polar forces after the mass has been consolidated. "We
+may affirm," he says, "that no retreat of the parts, no contraction of
+dimensions in passing to a solid state can explain such phenomena. They
+appear to me only resolvable on the supposition that crystalline or
+polar forces acted upon the whole mass simultaneously in one direction
+and with adequate force." And again, in another place: "Crystalline
+forces have rearranged whole mountain-masses, producing a beautiful
+crystalline cleavage, passing alike through all the strata."[C] The
+utterance of such a man struck deep, as was natural, into the minds of
+geologists, and at the present day there are few who do not entertain
+this view either in whole or in part.[D] The magnificence of the theory,
+indeed, has in some cases caused speculation to run riot, and we have
+books published, aye and largely sold, on the action of polar forces and
+geologic magnetism, which rather astonish those who know something about
+the subject. According to the theory referred to, miles and miles of the
+districts of North Wales and Cumberland, comprising huge
+mountain-masses, are neither more nor less than the parts of a gigantic
+crystal. These masses of slate were originally fine mud; this mud is
+composed of the broken and abraded particles of older rocks. It contains
+silica, alumina, iron, potash, soda, and mica, mixed in sensible masses
+mechanically together. In the course of ages the mass became
+consolidated, and the theory before us assumes that afterwards a process
+of crystallization rearranged the particles and developed in the mass a
+single plane of crystalline cleavage. With reference to this hypothesis,
+I will only say that it is a bold stretch of analogies; but still it has
+done good service: it has drawn attention to the question; right or
+wrong, a theory thus thoughtfully uttered has its value; it is a dynamic
+power which operates against intellectual stagnation; and, even by
+provoking opposition, is eventually of service to the cause of truth. It
+would, however, have been remarkable, if, among the ranks of geologists
+themselves, men were not found to seek an explanation of the phenomena
+in question, which involved a less hardy spring on the part of the
+speculative faculty than the view to which I have just referred.
+
+The first step in an inquiry of this kind is to put oneself into contact
+with nature, to seek facts. This has been done, and the labours of
+Sharpe (the late President of the Geological Society, who, to the loss
+of science and the sorrow of all who knew him, has so suddenly been
+taken away from us), Sorby, and others, have furnished us with a body of
+evidence which reveals to us certain important physical phenomena,
+associated with the appearance of slaty cleavage, if they have not
+produced it. The nature of this evidence we will now proceed to
+consider.
+
+Fossil shells are found in these slate-rocks. I have here several
+specimens of such shells, occupying various positions with regard to the
+cleavage planes. They are squeezed, distorted, and crushed. In some
+cases a flattening of the convex shell occurs, in others the valves are
+pressed by a force which acted in the plane of their junction, but in
+all cases the distortion is such as leads to the inference that the rock
+which contains these shells has been subjected to enormous pressure in a
+direction at right angles to the planes of cleavage; the shells are all
+flattened and spread out upon these planes. I hold in my hand a fossil
+trilobite of normal proportions. Here is a series of fossils of the same
+creature which have suffered distortion. Some have lain across, some
+along, and some oblique to the cleavage of the slate in which they are
+found; in all cases the nature of the distortion is such as required for
+its production a compressing force acting at right angles to the planes
+of cleavage. As the creatures lay in the mud in the manner indicated,
+the jaws of a gigantic vice appear to have closed upon them and squeezed
+them into the shape you see. As further evidence of the exertion of
+pressure, let me introduce to your notice a case of contortion which
+has been adduced by Mr. Sorby. The bedding of the rock shown in this
+figure[E] was once horizontal; at A we have a deep layer of mud, and at
+_m n_ a layer of comparatively unyielding gritty material; below that
+again, at B, we have another layer of the fine mud of which slates are
+formed. This mass cleaves along the shading lines of the diagram; but
+look at the shape of the intermediate bed: it is contorted into a
+serpentine form, and leads irresistibly to the conclusion that the mass
+has been pressed together at right angles to the planes of cleavage.
+This action can be experimentally imitated, and I have here a piece of
+clay in which this is done and the same result produced on a small
+scale. The amount of compression, indeed, might be roughly estimated by
+supposing this contorted bed _m n_ to be stretched out, its length
+measured and compared with the distance _c d_; we find in this way that
+the yielding of the mass has been considerable.
+
+Let me now direct your attention to another proof of pressure. You see
+the varying colours which indicate the bedding on this mass of slate.
+The dark portion, as I have stated, is gritty, and composed of
+comparatively coarse particles, which, owing to their size, shape, and
+gravity, sink first and constitute the bottom of each layer. Gradually
+from bottom to top the coarseness diminishes, and near the upper surface
+of each layer we have a mass of comparatively fine clean mud. Sometimes
+this fine mud forms distinct layers in a mass of slate-rock, and it is
+the mud thus consolidated from which are derived the German
+razor-stones, so much prized for the sharpening of surgical instruments.
+I have here an example of such a stone. When a bed is thin, the clean
+white mud is permitted to rest, as in this case, upon a slab of the
+coarser slate in contact with it: when the bed is thick, it is cut into
+slices which are cemented to pieces of ordinary slate, and thus rendered
+stronger. The mud thus deposited sometimes in layers is, as might be
+expected, often rolled up into nodular masses, carried forward, and
+deposited by the rivers from which the slate-mud has subsided. Here,
+indeed, are such nodules enclosed in sandstone. Everybody who has
+ciphered upon a school-slate must remember the whitish-green spots which
+sometimes dotted the surface of the slate; he will remember how his
+slate-pencil usually slid over such spots as if they were greasy. Now
+these spots are composed of the finer mud, and they could not, on
+account of their fineness, _bite_ the pencil like the surrounding gritty
+portions of the slate. Here is a beautiful example of the spots: you
+observe them on the cleavage surface in broad patches; but if this mass
+has been compressed at right angles to the planes of cleavage, ought we
+to expect the same marks when we look at the edge of the slab? The
+nodules will be flattened by such pressure, and we ought to see evidence
+of this flattening when we turn the slate edgeways. Here it is. The
+section of a nodule is a sharp ellipse with its major axis parallel to
+the cleavage. There are other examples of the same nature on the table;
+I have made excursions to the quarries of Wales and Cumberland, and to
+many of the slate-yards of London, but the same fact invariably appears,
+and thus we elevate a common experience of our boyhood into evidence of
+the highest significance as regards one of the most important problems
+of geology. In examining the magnetism of these slates, I was led to
+infer that these spots would contain a less amount of iron than the
+surrounding dark slate. The analysis was made for me by Mr. Hambly in
+the laboratory of Dr. Percy at the School of Mines. The result which is
+stated in this Table justifies the conclusion to which I have referred.
+
+_Analysis of Slate._
+
+ Purple Slate. Two Analyses.
+ 1. Percentage of iron 5.85
+ 2. " " 6.13
+ Mean 5.99
+
+ Greenish Slate.
+ 1. Percentage of iron 3.24
+ 2. " " 3.12
+ Mean 3.18
+
+The quantity of iron in the dark slate immediately adjacent to the
+greenish spot is, according to these analyses, nearly double of the
+quantity contained in the spot itself. This is about the proportion
+which the magnetic experiments suggested.
+
+Let me now remind you that the facts which I have brought before you are
+typical facts--each is the representative of a class. We have seen
+shells crushed, the unhappy trilobites squeezed, beds contorted, nodules
+of greenish marl flattened; and all these sources of independent
+testimony point to one and the same conclusion, namely, that slate-rocks
+have been subjected to enormous pressure in a direction at right angles
+to the planes of cleavage.[F]
+
+In reference to Mr. Sorby's contorted bed, I have said that by
+supposing it to be stretched out and its length measured, it would give
+us an idea of the amount of yielding of the mass above and below the
+bed. Such a measurement, however, would not quite give the amount of
+yielding; and here I would beg your attention to a point, the
+significance of which has, so far as I am aware of, hitherto escaped
+attention. I hold in my hand a specimen of slate, with its bedding
+marked upon it; the lower portions of each bed are composed of a
+comparatively coarse gritty material, something like what you may
+suppose this contorted bed to be composed of. Well, I find that the
+cleavage takes a bend in crossing these gritty portions, and that the
+tendency of these portions is to cleave more at right angles to the
+bedding. Look to this diagram: when the forces commenced to act, this
+intermediate bed, which though comparatively unyielding is not entirely
+so, suffered longitudinal pressure; as it bent, the pressure became
+gradually more lateral, and the direction of its cleavage is exactly
+such as you would infer from a force of this kind--it is neither quite
+across the bed, nor yet in the same direction as the cleavage of the
+slate above and below it, but intermediate between the two. Supposing
+the cleavage to be at right angles to the pressure, this is the
+direction which it ought to take across these more unyielding strata.
+
+Thus we have established the concurrence of the phenomena of cleavage
+and pressure--that they accompany each other; but the question still
+remains, Is this pressure of itself sufficient to account for the
+cleavage? A single geologist, as far as I am aware, answers boldly in
+the affirmative. This geologist is Sorby, who has attacked the question
+in the true spirit of a physical investigator. You remember the cleavage
+of the flags of Halifax and Over Darwen, which is caused by the
+interposition of plates of mica between the layers. Mr. Sorby examines
+the structure of slate-rock, and finds plates of mica to be a
+constituent. He asks himself, what will be the effect of pressure upon a
+mass containing such plates confusedly mixed up in it? It will be, he
+argues--and he argues rightly--to place the plates with their flat
+surfaces more or less perpendicular to the direction in which the
+pressure is exerted. He takes scales of the oxide of iron, mixes them
+with a fine powder, and, on squeezing the mass, finds that the tendency
+of the scales is to set themselves at right angles to the line of
+pressure. Now the planes in which these plates arrange themselves will,
+he contends, be those along which the mass cleaves.
+
+I could show you, by tests of a totally different character from those
+applied by Mr. Sorby, how true his conclusion is, that the effect of
+pressure on elongated particles or plates will be such as he describes
+it. Nevertheless, while knowing this fact, and admiring the ability with
+which Mr. Sorby has treated this question, I cannot accept his
+explanation of slate-cleavage. I believe that even if these plates of
+mica were wholly absent, the cleavage of slate-rocks would be much the
+same as it is at present.
+
+I will not dwell here upon minor facts,--I will not urge that the
+perfection of the cleavage bears no relation to the quantity of mica
+present; but I will come at once to a case which to my mind completely
+upsets the notion that such plates are a necessary element in the
+production of cleavage.
+
+Here is a mass of pure white wax: there are no mica particles here;
+there are no scales of iron, or anything analogous mixed up with the
+mass. Here is the self-same substance submitted to pressure. I would
+invite the attention of the eminent geologists whom I see before me to
+the structure of this mass. No slate ever exhibited so clean a cleavage;
+it splits into laminae of surpassing tenuity, and proves at a single
+stroke that pressure is sufficient to produce cleavage, and that this
+cleavage is independent of the intermixed plates of mica assumed in Mr.
+Sorby's theory. I have purposely mixed this wax with elongated
+particles, and am unable to say at the present moment that the cleavage
+is sensibly affected by their presence,--if anything, I should say they
+rather impair its fineness and clearness than promote it.
+
+The finer the slate the more perfect will be the resemblance of its
+cleavage to that of the wax. Compare the surface of the wax with the
+surface of this slate from Borrodale in Cumberland. You have precisely
+the same features in both: you see flakes clinging to the surfaces of
+each, which have been partially torn away by the cleavage of the mass: I
+entertain the conviction that if any close observer compares these two
+effects, he will be led to the conclusion that they are the product of a
+common cause.[G]
+
+But you will ask, how, according to my view, does pressure produce this
+remarkable result? This may be stated in a very few words.
+
+Nature is everywhere imperfect! The eye is not perfectly achromatic, the
+colours of the rose and tulip are not pure colours, and the freshest air
+of our hills has a bit of poison in it. In like manner there is no such
+thing in nature as a body of perfectly homogeneous structure. I break
+this clay which seems so intimately mixed, and find that the fracture
+presents to my eyes innumerable surfaces along which it has given way,
+and it has yielded along these surfaces because in them the cohesion of
+the mass is less than elsewhere. I break this marble, and even this wax,
+and observe the same result: look at the mud at the bottom of a dried
+pond; look to some of the ungravelled walks in Kensington Gardens on
+drying after rain,--they are cracked and split, and other circumstances
+being equal, they crack and split where the cohesion of the mass is
+least. Take then a mass of partially consolidated mud. Assuredly such a
+mass is divided and subdivided by surfaces along which the cohesion is
+comparatively small. Penetrate the mass, and you will see it composed of
+numberless irregular nodules bounded by surfaces of weak cohesion.
+Figure to your mind's eye such a mass subjected to pressure,--the mass
+yields and spreads out in the direction of least resistance;[H] the
+little nodules become converted into laminae, separated from each other
+by surfaces of weak cohesion, and the infallible result will be that
+such a mass will cleave at right angles to the line in which the
+pressure is exerted.
+
+Further, a mass of dried mud is full of cavities and fissures. If you
+break dried pipe-clay you see them in great numbers, and there are
+multitudes of them so small that you cannot see them. I have here a
+piece of glass in which a bubble was enclosed; by the compression of the
+glass the bubble is flattened, and the sides of the bubble approach each
+other so closely as to exhibit the colours of thin plates. A similar
+flattening of the cavities must take place in squeezed mud, and this
+must materially facilitate the cleavage of the mass in the direction
+already indicated.
+
+Although the time at my disposal has not permitted me to develop this
+thought as far as I could wish, yet for the last twelve months the
+subject has presented itself to me almost daily under one aspect or
+another. I have never eaten a biscuit during this period in which an
+intellectual joy has not been superadded to the more sensual pleasure,
+for I have remarked in all such cases cleavage developed in the mass by
+the rolling-pin of the pastrycook or confectioner. I have only to break
+these cakes, and to look at the fracture, to see the laminated structure
+of the mass; nay, I have the means of pushing the analogy further: I
+have here some slate which was subjected to a high temperature during
+the conflagration of Mr. Scott Russell's premises. I invite you to
+compare this structure with that of a biscuit; air or vapour within the
+mass has caused it to swell, and the mechanical structure it reveals is
+precisely that of a biscuit. I have gone a little into the mysteries of
+baking while conducting my inquiries on this subject, and have received
+much instruction from a lady-friend in the manufacture of puff-paste.
+Here is some paste baked in this house under my own superintendence. The
+cleavage of our hills is accidental cleavage, but this is cleavage with
+intention. The volition of the pastrycook has entered into the formation
+of the mass, and it has been his aim to preserve a series of surfaces of
+structural weakness, along which the dough divides into layers.
+Puff-paste must not be handled too much, for then the continuity of the
+surfaces is broken; it ought to be rolled on a cold slab, to prevent the
+butter from melting and diffusing itself through the mass, thus
+rendering it more homogeneous and less liable to split. This is the
+whole philosophy of puff-paste; it is a grossly exaggerated case of
+slaty cleavage.
+
+As time passed on, cases multiplied, illustrating the influence of
+pressure in producing lamination. Mr. Warren De la Rue informs me that
+he once wished to obtain white-lead in a fine granular state, and to
+accomplish this he first compressed the mass: the mould was conical, and
+permitted the mass to spread a little laterally under the pressure. The
+lamination was as perfect as that of slate, and quite defeated him in
+his effort to obtain a granular powder. Mr. Brodie, as you are aware,
+has recently discovered a new kind of graphite: here is the substance in
+powder, of exquisite fineness. This powder has the peculiarity of
+clinging together in little confederacies; it cannot be shaken asunder
+like lycopodium; and when the mass is squeezed, these groups of
+particles flatten, and a perfect cleavage is produced. Mr. Brodie
+himself has been kind enough to furnish me with specimens for this
+evening's lecture. I will cleave them before you: you see they split up
+into plates which are perpendicular to the line in which the pressure
+was exerted. This testimony is all the more valuable, as the facts were
+obtained without any reference whatever to the question of cleavage.
+
+I have here a mass of that singular substance Boghead Cannel. This was
+once a mass of mud, more or less resembling this one, which I have
+obtained from a bog in Lancashire. I feel some hesitation in bringing
+this substance before you, for, as in other cases, so in regard to
+Boghead Cannel, science--not science, let me not libel it, but the
+quibbling, litigious, money-loving portion of human nature speaking
+through the mask of science--has so contrived to split hairs as to
+render the qualities of the substance somewhat mythical. I shall
+therefore content myself with showing you how it cleaves, and with
+expressing my conviction that pressure had a great share in the
+production of this cleavage.
+
+The principle which I have enunciated is so simple as to be almost
+trivial; nevertheless, it embraces not only the cases I have mentioned,
+but, if time permitted, I think I could show you that it takes a much
+wider range. When iron is taken from the puddling furnace, it is a more
+or less spongy mass: it is at a welding heat, and at this temperature is
+submitted to the process of rolling: bright smooth bars such as this are
+the result of this rolling. But I have said that the mass is more or
+less spongy or nodular, and, notwithstanding the high heat, these
+nodules do not perfectly incorporate with their neighbours: what then?
+You would say that the process of rolling must draw the nodules into
+fibres--it does so; and here is a mass acted upon by dilute sulphuric
+acid, which exhibits in a striking manner this fibrous structure. The
+experiment was made by my friend Dr. Percy, without any reference to the
+question of cleavage.
+
+Here are other cases of fibrous iron. This fibrous structure is the
+result of mechanical treatment. Break a mass of ordinary iron and you
+have a granular fracture; beat the mass, you elongate these granules,
+and finally render the mass fibrous. Here are pieces of rails along
+which the wheels of locomotives have slidden; the granules have yielded
+and become plates; they exfoliate or come off in leaves. All these
+effects belong, I believe, to the great class of phenomena of which
+slaty cleavage forms the most prominent example.[I]
+
+Thus, ladies and gentlemen, we have reached the termination of our
+task. I commenced by exhibiting to you some of the phenomena of
+crystallization. I have placed before you the facts which are found to
+be associated with the cleavage of slate-rocks. These facts, as finely
+expressed by Helmholtz, are so many telescopes to our spiritual vision,
+by which we can see backward through the night of antiquity, and discern
+the forces which have been in operation upon the earth's surface
+
+ "Ere the lion roared,
+ Or the eagle soared."
+
+From evidence of the most independent and trustworthy character, we come
+to the conclusion that these slaty masses have been subjected to
+enormous pressure, and by the sure method of experiment we have
+shown--and this is the only really new point which has been brought
+before you--how the pressure is sufficient to produce the cleavage.
+Expanding our field of view, we find the self-same law, whose footsteps
+we trace amid the crags of Wales and Cumberland, stretching its
+ubiquitous fingers into the domain of the pastrycook and ironfounder;
+nay, a wheel cannot roll over the half-dried mud of our streets without
+revealing to us more or less of the features of this law. I would say,
+in conclusion, that the spirit in which this problem has been attacked
+by geologists indicates the dawning of a new day for their science. The
+great intellects who have laboured at geology, and who have raised it to
+its present pitch of grandeur, were compelled to deal with the subject
+in mass; they had no time to look after details. But the desire for more
+exact knowledge is increasing; facts are flowing in, which, while they
+leave untouched the intrinsic wonders of geology, are gradually
+supplanting by solid truths the uncertain speculations which beset the
+subject in its infancy. Geologists now aim to imitate, as far as
+possible, the conditions of nature, and to produce her results; they are
+approaching more and more to the domain of physics; and I trust the day
+will soon come when we shall interlace our friendly arms across the
+common boundary of our sciences, and pursue our respective tasks in a
+spirit of mutual helpfulness, encouragement, and good-will.
+
+
+FOOTNOTES:
+
+[A] Referred to in the Introduction.
+
+[B] I merely use this as an illustration; the deposition may have really
+been due to sediment carried down by rivers. But the action must have
+been periodic, and the powder duplex.
+
+[C] 'Transactions of the Geological Society,' Ser. ii. vol. iii. p. 477.
+
+[D] In a letter to Sir Charles Lyell, dated from the Cape of Good Hope,
+February 20, 1836, Sir John Herschel writes as follows:--"If rocks have
+been so heated as to allow of a commencement of crystallization, that is
+to say, if they have been heated to a point at which the particles can
+begin to move amongst themselves, or at least on their own axes, some
+general law must then determine the position in which these particles
+will rest on cooling. Probably that position will have some relation to
+the direction in which the heat escapes. Now when all or a majority of
+particles of the same nature have a general tendency to one position,
+that must of course determine a cleavage plane."
+
+[E] Omitted here.
+
+[F] While to my mind the evidence in proof of pressure seems perfectly
+irresistible, I by no means assert that the manner in which I stated it
+is incapable of modification. All that I deem important is the fact that
+pressure has been exerted; and provided this remain firm, the fate of
+any minor portion of the evidence by which it is here established is of
+comparatively little moment.
+
+[G] I have usually softened the wax by warming it, kneaded it with the
+fingers, and pressed it between thick plates of glass previously wetted.
+At the ordinary summer-temperature the wax is soft, and tears rather
+than cleaves; on this account I cool my compressed specimens in a
+mixture of pounded ice and salt, and when thus cooled they split
+beautifully.
+
+[H] It is scarcely necessary to say that if the mass were squeezed
+equally in _all_ directions no laminated structure could be produced; it
+must have room to yield in a lateral direction.
+
+[I] An eminent authority informs me that he believes these surfaces of
+weak cohesion to be due to the interposition of films of graphite, and
+not to any tendency of the iron itself to become fibrous: this of course
+does not in any way militate against the theory which I have ventured to
+propose. All that the theory requires is surfaces of weak cohesion,
+however produced, and a change of shape of such surfaces consequent on
+pressure or rolling.
+
+
+
+
+INDEX.
+
+
+ AEggischhorn, 100, 105.
+
+ Agassiz on glacier motion, 270, 310.
+
+ Air-bubbles, 359, 376.
+
+ Aletsch Glacier, 101.
+ -- --, bedding and structure observed on, 120, 391.
+
+ Aletschhorn, cloud iridescences on, 100, 238.
+
+ Allalein Glacier, 162.
+
+ Alpine climbers, suggestions to, 169.
+
+ Alps, winter temperature of, 168.
+
+ Altmann's theory of glacier motion, 296.
+
+ Ancient glaciers, action of, 99, 141.
+
+ Arveiron, arch of, 38, 217.
+
+ Atmosphere, permeability of, to radiant heat, 105, 243-247.
+
+ Atmospheric refraction, 35.
+
+ Avalanche at Saas, 164.
+ --, sound of, explained, 12, 14.
+
+
+ Bakewell, Mr., on motion of Glacier des Bossons, 337.
+
+ Balmat, Auguste, 169, 188.
+
+ Bedding, lines of, 391.
+
+ Bennen, Johann Joseph, 104, 118.
+
+ Bergschrund, 98, 325.
+
+ "Blower," glacier, 87.
+
+ Blue colour of ice, 256.
+ -- -- -- snow, 29, 83, 132, 203.
+ -- -- -- water, 33, 253, 259-262.
+
+ Blueness of sky, 22, 174, 257-261.
+
+ Blue veins, 376, 381.
+
+ Boiling-point, influence of pressure on, 408.
+ -- -- at different altitudes, 105, 106, 113, 120, 129, 175, 190.
+
+ Bois, Glacier des, 39, 275, 368.
+
+ Brevent, ascent of, 172.
+
+ Brocken, Spirit of the, 22, 238.
+
+ Bubbles, in ice, 44, 147, 359, 425.
+ -- in snow, 18, 251.
+
+
+ Capillaries of glacier, 335-339.
+
+ Cave of ice, 135.
+
+ Cavities in ice, 163, 356, 424.
+
+ Cells in ice, 147, see Bubbles.
+
+ Chamouni, 37.
+ --, difficulties at, 170, 192.
+ -- in winter, 198, 336.
+
+ Charmoz, view from, 45, 68, 368.
+
+ Charpentier's theory of glacier motion, 296.
+
+ Chemical action, rays producing, 240.
+
+ Chromatic effects, 235.
+
+ Cleavage, 406.
+ -- and stratification distinct, 2, 390, 431.
+ -- caused by pressure, 6, 436.
+ --, contortions of, 9, 59.
+ -- of crystals and slate rocks, lecture on, 427.
+ -- of glaciers, 26, 393, 425-426.
+ -- -- ice, 352, 407.
+ -- -- slate, &c., 1, 430.
+
+ "Cleft station," the, 47, 369.
+
+ Clouds, formation and dissipation of, 22, 97, 137, 146.
+ --, iridescent, 100, 105, 147, 154, 238.
+ -- on Mont Blanc, 82.
+ -- on Monte Rosa, 124.
+ --, winter, at Montanvert, 208.
+
+ Colour answers to pitch, 227.
+
+ Colours of sky, 257.
+ --, subjective, 37.
+
+ Comet, discovery of, 186.
+
+ Compass affected by rocks, 140.
+
+ Crepitation of glaciers, 44, 357.
+
+ Crevasses, 315
+ (_marginal_, 318;
+ _transverse_, 320;
+ _longitudinal_, 322), 424.
+ --, first opening of, 317, 327.
+
+ Crumples in ice, 174, 415, 419.
+
+ Crystallization of ice, 353.
+
+ Crystals, cleavage of, 3, 428.
+ -- of snow, 130, 205, 212.
+
+
+ Deafness, artificial, 167.
+
+ Differential motion, 395.
+ -- --, Dr. Whewell on, 396.
+
+ Diffraction, explanation of, 237.
+
+ Dirt-bands, 45, 46, 68, 95, 367, 373.
+ -- --, maps of, 367, 368, 369.
+ -- --, Forbes on, 371.
+ -- --, source of, 369, 425.
+
+ Disks in ice, planes of, 163, 358, 425.
+
+ Dollfuss, M., hut of, 18, 112.
+
+ Dome du Gouter, 68, 75.
+
+ Donny, M., on cohesion of liquids, 355.
+
+
+ Echoes, theory of, 15.
+
+ Eismeer, the, 13, 362.
+
+ Expedition of 1856, Oberland and Tyrol, 9-32.
+ -- -- 1857, Montanvert and Mer de Glace, 33-91.
+ -- -- 1858, Oberland, Valais, and Monte Rosa district, 92-192.
+ -- -- 1859, winter, Chamouni, and Mer de Glace, 195-219.
+
+
+ Faraday, Prof., on Regelation, 351.
+
+ Faulberg, cave of, 107.
+
+ Fee, glacier of, 165.
+
+ Fend, 32.
+
+ Finsteraarhorn, 104, 110.
+ --, summit of, 112.
+
+ Flowers, liquid, in ice, 147, 354-358, 424.
+
+ Forbes, Prof., comparison of glacier to river, 306, 308.
+ -- --, on glacier motion, 272, 304, 308.
+ -- --, on magnetism of rocks, 145.
+ -- --, on veined structure, 379.
+ -- --, viscous theory, 311, 327, 333, 335.
+
+ Freezing, planes of, 163, 358, 424.
+
+ Frost-bites, 191.
+
+ Frozen flowers, 130, 212.
+
+ Furgge glacier, structure crossing strata on, 160, 392-394.
+
+
+ Gases, passage of heat through, 243.
+
+ Geant, Col du, 50, 173.
+
+ Geant, glacier du, 53-57, 280, 369-373.
+ --, measurements on, 419-421.
+ --, motion of, 281, 286.
+ --, white ice seams of, 56, 413.
+
+ Gebatsch Alp, 23.
+ --, glacier of, 24, 26.
+
+ Geneva, Lake of, 33, 259-262.
+
+ Glaciers, ancient, action of, 99, 163.
+ -- "blower," 87.
+ --, capillaries of, 335-339.
+ --, crepitation of, 44, 357.
+ -- d'ecoulement, 301.
+ -- de Lechaud, see Lechaud.
+ -- des Bois, 39, 275, 368.
+ -- du Geant, see Geant.
+ -- du Talefre, see Talefre.
+ --, groovings on, 20, 56, 377.
+ --, measurement of, 276.
+ -- motion, 52, 269-295, 422.
+ -- --, earlier theories of, 296-314.
+ -- --, pressure theory of, 346.
+ --, origin of, 248-252.
+ -- reservoirs, 301.
+ --, ridges on, 42, 55.
+ --, structure of, 136, 148, see Veined structure.
+ -- tables, 44, 265.
+ --, veins of, 54, 376, 381.
+ --, wrinkles on, 370.
+
+ Goethe's theory of colours, 258.
+
+ Goerner glacier, 120, 138.
+
+ Goerner grat, 137, 145.
+
+ Goernerhorn glacier, 147, 149.
+
+ Grand Plateau, 187.
+
+ Grands Mulets, 73, 185.
+
+ Graun, 29.
+
+ Grimsel, the, 18, 99.
+
+ Grindelwald, lower glacier of, 13, 92, 321, 384.
+
+ Groovings on glaciers, 20, 56, 377.
+
+ Gruener's theory of glacier motion, 296.
+
+ Guides of Chamouni, rules of, 60, 170, 192.
+ -- lost in crevasse, 76.
+
+ Guyot, M., on veined structure, 378.
+
+
+ Hailstones, conical, 31.
+ --, spherical, 65.
+
+ Handeck, waterfall of, 17.
+
+ Hasli, valley of, 17, 99.
+
+ Heat and light, 223, 239, 241.
+ -- -- work, 328.
+ --, luminous, 241-247.
+ --, mechanical equivalent of, 329.
+ --, obscure, 240.
+ --, passage through gases, 243-245.
+ --, radiant, 239.
+ -- --, permeability of atmosphere to, 105, 243-247.
+ --, radiated, 242.
+ --, specific, 331.
+
+ Heisse Platte, the, 13.
+
+ Hirst, Mr., measurements on Mer de Glace, 38, 46, 275, 283, 289, 313,
+ 420.
+
+ Hochjoch, 32.
+
+ Hoechste Spitze of Monte Rosa, 128.
+
+ Hopkins, Mr., on crevasses, 318, 383.
+
+ Hotel des Neufchatelois, 19, 112, 270.
+
+ Hugi on glacier motion, 270.
+
+ Huxley, Mr., on glacier capillaries, 338.
+ -- --, on water-cells, 251, 359.
+
+ Hydrogen, effect on rays, 253.
+
+
+ Ice, blue colour of, 256.
+ -- cascades, 94, 384, 391.
+ -- cave, 135.
+ -- cells, 147, see Bubbles.
+ -- cones, 266.
+ --, cracking of, 317, 326.
+ --, crystallization of, 353.
+ --, effects of pressure on, 405, 409.
+ --, experiments on, 346.
+ --, friability of, 333.
+ --, liquefaction of, 353, 408.
+ --, liquid flowers in, 354-358, 424.
+ --, Thomson's theory of plasticity of, 340.
+ --, softening of, 333.
+ --, structure of, 136, 148.
+ --, temperature of, 241, 332.
+ --, white, seams of, 56, 413, 421.
+
+ Illumination of trees, &c., at sunrise and sunset, 178, 238.
+
+ Interference rings, 229.
+ -- spectra, 76, 178, 235, 238.
+
+ Iridescent clouds, 100, 105, 147, 154, 238.
+
+
+ Jardin, the, 61, 174.
+
+ Joch, the passage of a, 28.
+
+ Joule, M., on heat and work, 328.
+
+ Jungfrau, the, 11.
+ --, evening near, 106.
+
+
+ Laminated structure, 376, 378, 426.
+
+ Lechaud, glacier de, 53, 387.
+ -- -- --, motion of, 60, 286-288.
+
+ Lenticular structure, 381.
+
+ Light and heat, 223, 239, 241.
+ --, undulation theory of, 224.
+
+ Linth, M. Escher de la, 271.
+
+ Liquefaction of ice, 353, 408.
+
+ Liquid flowers, 147, 354-358, 424.
+
+
+ Magnetic force, 144.
+
+ Magnetism of rocks, 140, 143, 145.
+
+ Maerjelen See, 101, 119.
+
+ Mastic, Bruecke's solution of, 259.
+
+ Mattmark See, 162.
+
+ Maximum motion, locus of point of, 285, 323.
+
+ Mayenwand, summit of, 20, 100, 323.
+
+ Mayer, on connexion of heat with work, 328.
+
+ Measurement of glaciers, 276.
+
+ Mer de Glace, 42-67, 86-90, 173.
+ -- -- --, dirt-bands of the, 367
+ (seen from Charmoz, 45, 368;
+ from Cleft station, 47, 369;
+ from the Flegere, 367).
+ -- -- --, map of, 53, 264.
+ -- -- --, motion of, 275-293.
+ -- -- --, winter motion of, 294, 343.
+ -- -- --, winter visit to, 195, 206-218.
+
+ Milk, cause of blueness of, 261.
+
+ Mirage, 36.
+
+ Montanvert, 40, 89, 173.
+ -- in winter, 204.
+
+ Mont Blanc, first ascent of, 68.
+ -- --, second ascent of, 177.
+ -- --, summit of, 81, 189.
+
+ Monte Rosa, first ascent of, 122.
+ -- --, second ascent of, 151.
+ -- --, summit of, 128, 156.
+ -- --, western glacier of, 138, 147.
+ -- --, zones of colour, 154, 238.
+
+ Moraines, 263.
+ -- of Talefre, 54, 63, 267, 387.
+
+ Motion of glaciers, 52, 269-295, 422.
+
+ Moulins, 362, 424.
+ --, depth of, 365.
+ --, motion of, 364.
+
+
+ Necker, letter from, 178.
+
+ Neufchatelois, Hotel des, 19, 112, 270.
+
+ Neve ice, 249, 251.
+
+
+ Oberland, the, visited, 9-22; 92-120; 390.
+
+ Oils, effect of films of, 236.
+
+
+ Person, M., on softening of ice, 333.
+
+ Pistol fired on summit of Mont Blanc, 82, 83, 224.
+
+ Pitch of musical sounds, 225.
+
+ Planes of freezing, 163, 358, 424.
+
+ Plasticity of ice, Thomson's theory of, 340.
+
+ Polar forces, 4.
+
+ Pressure and cleavage, see Cleavage.
+ -- and liquefaction of ice, 340, 408.
+ -- -- veined structure, 404; 147-149, 382-394, 412, 425-426.
+ --, effects of, on boiling point, 408.
+ -- -- -- -- ice, 405, 409.
+ -- theory of glacier motion, 346.
+
+
+ Radiant heat, 105, 239.
+
+ Rays, calorific, 240.
+ --, transmission of, 242.
+
+ Redness of sunset, 175.
+
+ Refraction on lake of Geneva, 35.
+
+ Regelation, 347, 351.
+
+ Reichenbach fall, 17.
+
+ Rendu, comparison of glacier to river, 306.
+ --, measurements of glaciers, 304.
+ --, notice of regelation, 301.
+ -- on conversion of snow into ice, 301.
+ -- on ductility, 298.
+ -- on law of circulation, 300.
+ -- on motion of glaciers, 305.
+ -- on veined structure, 301.
+ -- theory of glaciers, 299.
+
+ Rhone at lake of Geneva, 34, 261.
+ -- glacier, 20, 100, 323, 386.
+ -- --, chromatic effects, 21, 238.
+
+ Ridges on glaciers, 42, 55.
+
+ Riffelhorn, the, 133, 141-145.
+
+ Rings, interference, 229.
+ -- round sun, 21, 238.
+
+ Ripples deduced from rings, 400.
+
+ Ripple theory, Forbes on, 398.
+ -- -- of veined structure, 398.
+ -- waves, movement of, 232.
+
+ River and glacier, analogies between, 281-285, 423; 368.
+
+ Rocks, magnetism of, 140, 143, 145.
+
+
+ Saas, avalanche at, 164.
+
+ Sabine, Gen., on veined structure, 378.
+
+ Sand-cones, 266.
+
+ Saussure's theory of glacier motion, 52, 296.
+
+ Scheuchzer's theory of glacier motion, 296.
+
+ Seams, white, in ice, 56, 88, 413, 421.
+
+ Sedgwick, Prof., on cleavage, 2-5, 390, 431.
+
+ Seracs, 51, 75.
+
+ Serpentine, boulders of, 161.
+
+ Shadows, coloured, 38.
+
+ Sharpe, on slaty cleavage, 5, 432.
+
+ Silberhorn, the, 11.
+
+ Sky, blueness of, 22, 174, 175.
+ --, colours of, explained, 257.
+
+ Slate, cleavage of, 1, 430.
+
+ Snow, blue colour of, 29, 132, 203.
+ -- crystals, 130, 205, 212.
+ --, dry, 250.
+ -- line, 29, 248.
+ --, perpetual, 248.
+ --, sound of breaking, 202.
+ -- storm, sound through, 215.
+ --, whiteness of, explained, 250.
+
+ Sorby, Mr., on slaty cleavage, 5, 435.
+
+ Sound in a vacuum, 224.
+ --, intensity of, 83.
+ --, rate of motion of, 226.
+
+ Spectra, interference, 76, 178, 235, 238.
+
+ Spectrum, rays of, 240.
+
+ Stars, twinkling of, 72, 238.
+
+ Stelvio, pass of, 29.
+
+ Storm on Grands Mulets, 185.
+ -- -- Mer de Glace, 210.
+
+ Strahleck, glacier of, 94, 384.
+ --, passage of, 93, 97.
+
+ Strata of ice, 136.
+
+ Stratification of neve, 392.
+ -- -- slate, 1, 430.
+
+ Structure, doubts regarding, 44, 92, 389.
+ -- of ice, 136, 148, see Veined structure.
+
+ Subjective colours, 37.
+
+ Summary of glacier theory, 422.
+
+ Sun, rings round, 21, 238.
+
+ Sunrise at Chamouni, 39.
+ -- and sunset, illumination of trees, &c., at, 178, 238.
+
+ Sunset, gorgeous, 184.
+
+
+ Tables, glacier, 44, 265-266.
+
+ Tacul, motion of ice-wall at, 289.
+
+ Talefre, glacier of, 43, 61-62, 87.
+ --, moraines of, 54, 63, 267, 387.
+
+ Temperature, winter, of Alps, 168.
+
+ Theodolite, use of, 275.
+
+ Theory of cleavage, 5.
+
+ Thermometer at Jardin, 174.
+ -- buried on Mont Blanc, 190.
+ -- on Finsteraarhorn, 113.
+
+ Thomson, Prof., theory of plasticity, 340.
+ -- -- -- -- regelation, 352.
+
+ Twinkling of stars, 72, 238.
+
+ Tyrol, the, 23.
+
+
+ Undulation theory of light, 224.
+
+ Unteraar, glacier of, 18, 265, 388.
+
+
+ Vacuum in ice-cavities, 163, 356.
+
+ Veined structure, 376
+ (_marginal_, 383;
+ _transverse_, 384;
+ _longitudinal_, 387), 395, 404, 408.
+ -- --, experiments on, 382, 388.
+ -- -- caused by pressure, 147-149, 382-389, 412, 425-426.
+ -- -- crossing strata, 389-394.
+ -- --, Forbes on, 379.
+ -- --, Gen. Sabine on, 378.
+ -- --, M. Guyot on, 378.
+ -- --, ripple theory of, 398.
+
+ Viesch, glacier of, 109, 118.
+
+ Viscosity, 312, 325, 334, 350, 423.
+
+
+ Water absorbs red rays, 254.
+ --, blue colour of, 254; 33, 259, 261.
+ --, rippling waves of, 232.
+
+ Waves, frozen, 43, 55.
+ --, interference of, 231.
+ -- motion, Weber on, 232, 399.
+ -- of sound, 225.
+
+ Wengern Alp, 9.
+
+ Wetterhorn, echoes of, 15.
+
+ White ice, seams of, 56, 57, 88, 413, 421.
+
+ Whiteness of ice, 250, 268, 376.
+
+ Winter motion of Mer de Glace, 294.
+
+ Wrinkles on glacier, 370.
+
+
+ Young, Thomas, theory of light, 224.
+
+
+_Spottiswoode & Co. Printers, New-street Square, London._
+
+
+
+
+WORKS by JOHN TYNDALL.
+
+
+FRAGMENTS of SCIENCE: a Series of Detached Essays, Addresses, and
+Reviews. 2 vols. crown 8vo. 16_s._
+
+ VOL. I.--The Constitution of Nature--Radiation--On Radiant Heat
+ in Relation to the Colour and Chemical Constitution of
+ Bodies--New Chemical Reactions produced by Light--On Dust and
+ Disease--Voyage to Algeria to observe the Eclipse--Niagara--The
+ Parallel Roads of Glen Roy--Alpine Sculpture--Recent
+ Experiments on Fog-Signals--On the Study of Physics--On
+ Crystalline and Slaty Cleavage--On Paramagnetic and Diamagnetic
+ Forces--Physical Basis of Solar Chemistry--Elementary
+ Magnetism--On Force--Contributions to Molecular Physics--Life
+ and Letters of FARADAY--The Copley Medalist of 1870--The Copley
+ Medalist of 1871--Death by Lightning--Science and the Spirits.
+
+ VOL. II.--Reflections on Prayer and Natural Law--Miracles and
+ Special Providences--On Prayer as a Form of Physical
+ Energy--Vitality--Matter and Force--Scientific Materialism--An
+ Address to Students--Scientific Use of the Imagination--The
+ Belfast Address--Apology for the Belfast Address--The Rev.
+ JAMES MARTINEAU and the Belfast Address--Fermentation, and its
+ Bearings on Surgery and Medicine--Spontaneous
+ Generation--Science and Man--Professor VIRCHOW and
+ Evolution--The Electric Light.
+
+NEW FRAGMENTS. Crown 8vo. 10_s._ 6_d._
+
+ CONTENTS: The Sabbath--Goethe's 'Farbenlehre'--Atoms, Molecules
+ and Ether Waves--Count Rumford--Louis Pasteur, his Life and
+ Labours--The Rainbow and its Congeners--Address delivered at
+ the Birkbeck Institution on October 22, 1884--Thomas
+ Young--Life in the Alps--About Common Water--Personal
+ Recollections of Thomas Carlyle--On Unveiling the Statue of
+ Thomas Carlyle--On the Origin, Propagation, and Prevention of
+ Phthisis--Old Alpine Jottings--A Morning on Alp Lusgen.
+
+LECTURES on SOUND. With Frontispiece of Fog-Syren, and 203 other
+Woodcuts and Diagrams in the Text. Crown 8vo. 10_s._ 6_d._
+
+HEAT, a MODE of MOTION. With 125 Woodcuts and Diagrams. Crown 8vo.
+12_s._
+
+LECTURES on LIGHT DELIVERED in the UNITED STATES in 1872 and 1873. With
+Portrait, Lithographic Plate, and 59 Diagrams. Crown 8vo. 5_s._
+
+ESSAYS on the FLOATING MATTER of the AIR in RELATION to PUTREFACTION and
+INFECTION. With 24 Woodcuts. Crown 8vo. 7_s._ 6_d._
+
+RESEARCHES on DIAMAGNETISM and MAGNE-CRYSTALLIC ACTION; including the
+Question of Diamagnetic Polarity. Crown 8vo. 12_s._
+
+NOTES of a COURSE of NINE LECTURES on LIGHT, delivered at the Royal
+Institution of Great Britain, 1869. Crown 8vo. 1_s._ 6_d._
+
+NOTES of a COURSE of SEVEN LECTURES on ELECTRICAL PHENOMENA and
+THEORIES, delivered at the Royal Institution of Great Britain, 1870.
+Crown 8vo. 1_s._ 6_d._
+
+LESSONS in ELECTRICITY at the ROYAL INSTITUTION, 1875-1876. With 58
+Woodcuts and Diagrams. Crown 8vo. 2_s._ 6_d._
+
+FARADAY as a DISCOVERER. Crown 8vo. 3_s._ 6_d._
+
+
+London: LONGMANS, GREEN, & CO.
+
+
+
+
+Transcriber's Notes.
+
+
+The titles from the List of Illustrations were copied to the captions of
+the figures that otherwise had no caption, for the convenience of the
+reader.
+
+The "sidenotes" in the main body of the text were originally page
+headers. They have been moved to a place more fitting for the flow,
+typically to the head of the appropriate paragraph.
+
+Spelling variants where there was no obviously preferred choice were
+retained. These include: "Cleft-Station" and "Cleft Station," plus
+variants; "Cima di Jazzi" and "Cima de Jazzi;" "fanlike" and "fan-like;"
+"firewood" and "fire-wood;" "Flegere" and "Flegere;" "foreshorten(ed)"
+and "fore-shorten(ing);" "generalisation" and "generalization;"
+"judgment" and "judgement;" "Kumm" and "Kumme," which may be the same as
+"Kamm;" "lime light" and "lime-light;" "realize" and "realise(d);"
+"recognise" and "recognize(d);" "rearranged" and "re-arranged;"
+"refrozen" and "re-frozen;" "self-same" and "selfsame;" "semifluid" and
+"semi-fluid;" "sundial" and "sun-dial;" "Trift" and "Trifti," probably
+the same glacier; "weatherworn" and "weather-worn."
+
+In the Latin-1 encoded text version, the oe-ligature was replaced by
+the two separate characters, "oe."
+
+Changed "Hockjoch" to "Hochjoch" on page xi: "passage of the Hochjoch."
+
+Changed "39" to "239" on page xvii, as the page number for chapter 2.
+
+Changed "icefall" to "ice-fall" on page xxvi: "part of ice-fall."
+
+Changed "havresack" to "haversack" on page 71: "my waterproof
+haversack."
+
+Changed "affluent" to "affluent" on page 98: "Finsteraar affluent."
+
+Changed "184 deg.92" to "184.92 deg." on page 129.
+
+Changed "gulleys" to "gullies" on page 143: "fissures and gullies."
+
+Changed "SNOWSTORM" to "SNOW-STORM" in the sidenote from page 215:
+"SOUND THROUGH THE SNOW-STORM."
+
+Changed "neutralise" to "neutralize" on page 231: "oppose and
+neutralize."
+
+Moved the semi-colon inside the double quotes on page 285, around:
+"corresponding points."
+
+Changed "THOMPSON'S" to "THOMSON'S" in the chapter heading on page 340:
+"THOMSON'S THEORY."
+
+Changed "last" to "least" in the footnote to page 292: "at least as
+anxious."
+
+Changed "I" to "It" on page 377: "It was also."
+
+"Die Gletscher der Jetzzeit" on page 393 should probably be "Die
+Gletscher der Jetztzeit," but was not changed.
+
+Inserted a comma in the index entry for "Aletsch Glacier:" "-- --,
+bedding."
+
+Inserted a comma in the index entry for "Dirt-bands:" "-- --, maps of."
+
+Changed "Gouter" to "Gouter" in the index entry for "Dome du Gouter."
+
+Changed "Hoch-joch" to "Hochjoch" in its index entry.
+
+Inserted second em-dash in the index entry for "Mont Blanc:" "-- --,
+second ascent of."
+
+Inserted a comma in the index entry for "Rays:" "--, transmission of."
+
+Inserted a comma in the index entry for "Strahleck:" "--, passage of."
+
+
+
+
+
+End of Project Gutenberg's The Glaciers of the Alps, by John Tyndall
+
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