PART II.

1.—Light and Heat. 223

What is Light?—notion of the ancients; requires Time to pass through Space; Römer, Bradley, Fizeau; Emission Theory supported by Newton, opposed by Huyghens; the Wave Theory established by Young and Fresnel; Theory explained; nature of Sound; of Music; of Pitch; nature of Light; of Colour; two sounds may produce silence; two rays of light may produce darkness; two rays of heat may produce cold; Length and Number of waves of light; Liquid Waves; Interference; Diffraction; Colours of Thin Plates; applications of the foregoing to cloud iridescences, luminous trees, twinkling of stars, the Spirit of the Brocken, &c.

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 Brücke; Suspended Particles; singular effect on a painting explained by Goethe; Light separated without Absorption; Reflected and Transmitted light; blueness of milk and juices; the Sun through London smoke; Experiments; Blue of the Eye; Colours of Steam; the Lake of Geneva

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

Névé and Glacier; First Measurements; Hugi and Agassiz; Escher's defeat on the Aletsch; Piles fixed across the Aar glacier by Agassiz in 1841; Professor Forbes invited by M. Agassiz; Forbes's first observations on the Mer de Glace in 1842; motion of Agassiz's piles measured by M. Wild; Centre of the glacier moves quickest; State of the Question

10.—Motion of the Mer de Glace.275

The Theodolite; mode of measurement; first line; Centre Point not the quickest; second line; former result confirmed; Law of Motion sought; the glacier moves through a Sinuous Valley; effect of Flexure; Western half of glacier moves quickest; Point of Maximum Motion crosses axis; Eastern half moves quickest; Locus of Point of Maximum Motion; New Law; Motion of the Géant; motion of the Léchaud; Squeezing of the Tributaries through the Neck of the valley at Trélaporte; the Léchaud a Driblet

11.—Ice Wall at the Tacul,—Velocities of Top and Bottom.289

First attempt by Mr. Hirst; second attempt, stakes fixed at Top, Bottom, and Centre; dense fog; the stakes lost; process repeated; Velocities determined

12.—Winter Motion of the Mer de Glace. 294

First line, Above the Montanvert; second line, Below the Montanvert; Ratio of winter to summer motion

13.—Cause of Glacier Motion,—De Saussure's Theory. 296

First attempt at a Theory by Scheuchzer in 1705; Charpentier's theory, or the Theory of Dilatation; Agassiz's theory; Altmann and Grüner; theory of De Saussure, or the Sliding Theory; in part true; strained interpretation of this theory

14.—Rendu's Theory.299

Character of Rendu; his Essay entitled 'Théorie des Glaciers de la Savoie;' extracts from the essay; he ascribes "circulation" to natural forces; classifies glaciers; assigns the cause of the conversion of snow into ice; notices Veined Structure; "time and affinity;" notices Regelation; diminution of glaciers réservoirs; Remarkable Passage; announces Swifter Motion of Centre; North British Review; Discrepancies explained by Rendu; Liquid Motion ascribed to glacier; all the phenomena of a River reproduced upon the Mer de Glace; Ratio of Side and Central velocities; Errors removed

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°; 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 Flégère; Bands as seen from Les Charmoz; Skew Surface of glacier; aspect of Bands from the Cleft Station; Origin of bands; tendency to become straight; differences between observers

27.—Veined Structure of Glaciers.376

General appearance; Grooves upon the glacier; first observations; description by M. Guyot; observations of Professor Forbes; Structure and Stratification; subject examined; Marginal Structure; Transverse Structure; Longitudinal Structure; experimental illustrations; the Structure Complementary to the Crevasses; glaciers of the Oberland, Valais, and Savoy examined with reference to this question

28.—The Veined Structure and Differential Motion.395

Marginal Structure Oblique to sides; Drag towards the centre; difficulties of theory which ascribes the structure to Differential Sliding; it persists across the lines of maximum sliding

29.—The Ripple Theory of the Veined Structure. 398

Ripples in Water supposed to correspond to Glacier Structure; analysis of theory; observation of the MM. Weber; water dropping from an oar; stream cleft by an obstacle; Two Divergent lines of Ripple; Single Line produced by Lateral Obstacle; Direction of ripples compounded of River's motion and Wave motion; Structure and Ripples due to different causes; their positions also different

30.—The Veined Structure and Pressure. 404

Supposed case of pressed prism of glass; Experiments of Nature; Quartz-pebbles flattened and indented; Pressure would produce Lamination; Tangential Action

31.—The Veined Structure and the Liquefaction of Ice by Pressure.408

Influence of pressure on Melting and Boiling points; some substances swell, others shrink in melting; effects of pressure different on the two classes of bodies; Theoretic Anticipation by Mr. James Thomson; Melting point of Ice lowered by pressure; Internal Liquefaction of a prism of solid ice by pressure; Liquefaction in Layers; application to the Veined Structure

32.—White Ice-Seams of the Glacier du Géant. 413

Aspect of Seams; they sweep across the glacier concentric with Structure; Structure at the base of the Talèfre cascade; Crumples; Scaling off by pressure; Origin of seams of White Ice

33. 419

Glacier du Géant in a state of Longitudinal Compression; Measurements which prove that its hinder parts are advancing upon those in front; Shortening of its Undulations; Squeezing of white Ice-seams; development of Veined Structure

Summary 422

Appendix427

Index 441