122 VISCOUS THEORY OF GLACIER MOTION. [1846. 



same direction, a hole was made with a blasting iron into the 

 solid ice at B, where the inclination was 20. The precise 

 position of these marks being determined relatively to the visual 

 line, the observation was finished at 4 o'clock P.M. .- 



On the 23d of July we returned. The mark A in the snow 

 (which was so firmly driven in that it could not be withdrawn 

 without breaking the pole) had' advanced in the direction of the 

 slope exactly four inches at 1 P.M., or in sixty-nine hours ; 

 whilst the mark B in the ice had advanced 5J inches in the 

 same time ; whence we have 



Velocity of A in twenty-four hours . . 1*4 inch. 



Velocity of B in twenty-four hours . . 1*8 inch. 

 The result was what I had anticipated, although it must be con- 

 fessed it might be expected to be nearly the same upon any 

 theory of glacier motion yet proposed. The slope of a glacier, 

 per se, is not an index of what should be the velocity of motion 

 on the viscous theory. No doubt, other things being equal, the 

 velocity will be proportional to some function of the declivity, 

 and such we have seen to be fully borne out by experiments on 

 the Mer de Glace of Chamouni ; and in the present case, the 

 velocity under a slope of 20 was about one-third greater than 

 that under a slope of 10. But the analogy of a river, as well 

 as theoretical considerations, show that the slope is but one of 

 numerous considerations ; such as (1.) the mass of the viscous 

 body ; the smaller the mass the smaller the velocity on a given 

 slope ;* (2.) the state of infiltration or wetness of the glacier 

 altering its resistance to change of form.f Without mentioning 

 other causes, these are quite sufficient to account for the small 

 velocity observed, when we recollect the very insignificant mass 

 of this glacier, and its dry state arising from its great elevation, 

 its northern exposure, and even the very inclination of its bed, 

 which keeps it in a state of perfect drainage, and leaves it 

 always in a state tending to the snowy, rather than that of 

 imbibition. 



* Travels in the Alps of Savoy, 2d edit., p. 387. f Ibid, pp. 148, 371. 



