154 Mr. J. Croll on the Cause of the Motion of Glaciers. 



Rev. Canon Moseley has lately investigated this point, and 

 has found that the amount of work performed on a glacier (assu- 

 ming, of course, that the ice shears in the solid state) during its 

 descent through a given space is enormously greater than the 

 work of the weight of the glacier descending through that space. 

 He has determined the amount of work performed by gravitation 

 in the descent of a glacier, and the amount of internal work 

 performed on the ice during the descent ; and has found that, 

 in respect to a glacier of the same uniform rectangular section 

 and slope as the Mer de Glace at Les Fonts, and moving with 

 the same uniform velocity, the aggregate work of the resistances 

 which oppose themselves to its descent in a given time is about 

 thirty-four times the work of the weight in the same time ; 

 consequently it is physically impossible that the mere weight 

 alone of the glacier can be the cause of its descent. 



The impression left on my mind after reading Canon Moseley's 

 memoir in the Proceedings of the Royal Society for January 

 1869 was that, unless some very serious error could be pointed 

 out in the mathematical part of his investigation, it would be 

 Hopeless to attempt to overturn his general conclusion as re- 

 gards the received theory of the cause of the descent of glaciers, 

 by searching for errors in the experimental data on which the 

 conclusion rests. Had the result been that the actual shearing- 

 force of ice is by twice, thrice, four times, or even five times too 

 great to allow of a glacier shearing by its own weight, one might 

 then hope that, by some more accurate method of determining 

 the unit of shear than that adopted by Canon Moseley, his ob- 

 jection to the received theory of glacier-motion might be met; 

 but when the unit of shear is found to be not simply by three times, 

 four times, or even five times, but actually by thirty, forty, or fifty 

 times too great, all our hopes of overturning his conclusion 

 by searching for errors in this direction vanish, even although 

 there are some points connected with his unit of shear that are 

 not very satisfactory. 



The ice of a glacier is in the hard, solid, and crystalline state. 

 This is now generally admitted. Then, if the particles of the ice 

 shear in this state, Canon Moseley' s calculations show that the 

 glacier cannot possibly descend by its weight only, as is generally 

 supposed; and the generally received theory of glacier-motion 

 must therefore be abandoned. 1 can perceive no way of escape 

 from this conclusion. 



I presume that few who have given much thought to the 

 subject of glacier-motion have not had some slight misgivings 

 in regard to the commonly received theory. There are some 

 facts which I never could harmonize with this theory. For 

 example, boulder-clay is a far looser substance than ice; its 



