8 Mr. J. Ball on the Cause of the Descent of Glaciers, 



I desire,, however, to go a step further, and to offer a still more 

 fundamental objection to the method of investigation adopted by 

 Canon Moseley — and the more so as it is frequently employed 

 by eminent men of science, and, when not applied with great 

 caution, leads to results which I believe to be altogether fallacious. 



The device adopted in order to bring such problems within 

 the grasp of strict mathematical reasoning is to break up the 

 mass under consideration into imaginary elements, and to assume 

 that the forces acting on each of these may be expressed by cer- 

 tain constants determined experimentally, and by functions of 

 variables depending on their position with reference to fixed co- 

 ordinates. The fundamental assumption that underlies the 

 application of this method is that of the uniform structure of the 

 entire mass. Already open to question when used in regard to 

 imperfect fluids, this method is altogether fallacious when applied 

 to solid bodies, for the simple reason that no solid body is ho- 

 mogeneous, and that pressures and tensions acting within it are 

 modified by the varying constitution of the mass. But if this 

 be true generally, the objection falls with tenfold force when it 

 is proposed to treat a glacier as a body made up of uniform 

 strata, slices, or cubes, identical in structure, and acted on by 

 similar forces. Not to speak of wide openings and narrower 

 fissures, of inequalities of composition made manifest by the 

 veined structure, air-bubbles, &c, there is this special charac- 

 teristic of ice at or very near the freezing-point — that under pres- 

 sure it changes its form and is partly converted into water, of 

 which some portion is carried off by infiltration. Hence nothing 

 can be less like a natural glacier than the ideal object whose 

 existence is assumed by Canon Moseley in order that he may be 

 able to pass it through his mathematical mill. Instead of being 

 a mass of homogeneous ice, lying on an even slope in a uniform 

 rectangular channel, each portion or vertical slice of which ad- 

 vances with a uniform motion uninfluenced by lateral thrusts 

 or tensions, the real glacier slides slowly on its bed, which is of 

 broken and irregular form : the vast weight of the mass is thus 

 made to exert pressure in various directions, by no means uni- 

 formly parallel to the direction of motion : forces of unknown 

 but enormous amount act in succession on each portion of the 

 mass, causing fracture in one direction, liquefaction in another ; 

 and the occurrence of each of these changes transfers the maxi- 

 mum pressure to a new point where similar results are produced. 

 Like a huge snake whose movements are effected by the trans- 

 mission of muscular energy from one point to another, the mass 

 works its way downwards, straining and groaning audibly as, 

 now here, now there, the pressure seems to crush its own vitals. 

 It is scarcely worth while to make the obvious remark, that if 



