THEORY TESTED.

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The question now before us is,—Does a glacier exhibitthat power of yielding to a force of tension which wouldentitle its ice to be regarded as a viscous substance ?

With a view to the solution of this question Mi’. Hirsttook for me the inclinations of the Mer de Glace andall its tributaries in 1857 ; the effect of a change of incli-nation being always noted. I will select from those mea-surements a few which bear more specially upon thesubject now under consideration, commencing with theGlacier des Bois, down which the ice moves in that stateof wild dislocation already described. The inclination ofthe glacier above this cascade is 5° 10', and that of thecascade itself is 22° 20', the change of inclination beingtherefore 17° 10'.

In Fig. 22 I have protracted the inclination of the cascadeand of the glacier above it; the line A B representing the

Fig. 22.

former and B C the latter. Now a stream of molten lava,of treacle, or tar, would, in virtue of its viscosity, be ableto flow over the brow at B without breaking across; butthis is not the case with the glacier; it is so smashed andriven in crossing this brow, that, to use the words of Pro-fessor Forbes himself, “ it pours into the valley beneath ina cascade of icy fragments.”

But this reasoning will appear much stronger when werevert to other slopes upon the Mer de Glace. For ex-ample, its inclination above 1’Angle is 4°, and it afterwardsdescends a slope of 9° 25', the change of inclination being5° 25'. If we protract these inclinations to scale, we have

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