tag="{http://www.w3.org/1999/xhtml}a">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