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