Chapter III: 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