1885.] 



and on the Motion of Glaciers. 



95 



under the influence of moderate forces applied continuously for a con- 

 siderable time. In some of these, small bodies, mostly metallic, were 

 forced into or through masses of ice. These experiments may be §et 

 aside as irrelevant. They were, or may have been, simply instances 

 of the melting of ice through the lowering of the freezing point 

 by pressure, and of subsequent freezing where the pressure is less. 

 In fact some of the most striking results have been very properly 

 published as examples of this action (c/. "Nature," vol. v, p. 185; 

 vi, 396). The remaining experiments are for the most part experi- 

 ments on the bending or twisting of masses of ice either under the 

 influence of their own weight only or by means of superimposed 

 weights of moderate size. Bianconi seems to have made some experi- 

 ments of this kind as early as December, 1866, but he did not publish 

 his results until 1871, when his early experiments, as well as others 

 made in January and February of that year, were published in the 

 " Memorie della Accademia di Bologna," Serie 3a, vol. i, pp. 155 — 

 166. In the meantime Mr. W. Mathews had made and published 

 some interesting experiments in the winter of 1869-70 ("Alpine 

 Journal," vol. iv, p. 426 ; " Nature," vol. i, p. 534). In these the influ- 

 ence of temperature was very marked. The middle point of a plank 

 of ice 6 feet long and 2 J- inches thick, the ends of which were sup- 

 ported, sank 7 inches in about as many hours during a thaw. A some- 

 what thinner plank of the same length sank only about 3^- inches in 

 nearly three days of frosty weather. Results similar in kind were 

 obtained by Tyndall (with glacier ice) ("Nature," vol. iv, p. 447), 

 Pfaff (" Phil. Mag.," vol. 1, p. 335), and others. Pfaff quotes Kane 

 as having been the first to make such observations, but gives no 

 reference. 



These experiments show conclusively that the continuous action 

 for a considerable time of comparatively small forces will produce 

 effects upon ice which the same forces are quite incapable of pro- 

 ducing in a short time, but they do not necessarily throw much light 

 upon the actual processes which take place in a glacier. 



When a glacier is descending in the usual river-like manner in a 

 straight and uniform bed and down a uniform slope, the central part 

 moving most rapidly, and the parts nearest to the bottom and sides of 

 the channel being retarded by them, it is clear that the motion must 

 take place by the ice shearing along cylindrical surfaces whose gener- 

 ating lines are parallel to the direction of flow of the glacier. In 

 Canon Moseley's experiments, and in those of my own which are re- 

 corded below, the motion is essentially the same, the shearing taking 

 place, approximately at all events, uniformly in one plane. On the 

 other hand, when a beam of ice sags under the influence of its own 

 weight the motion is much more complicated. Assuming that there 

 is nowhere any change of density, but that the transformation takes 



