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.]