144 Canon Moseley on the Mechanical Impossibility 



ported. At the point of contact it appeared bent at a sharp 

 angle, and was perfectly rigid in its altered form. The total de- 

 flection was 7 inches, which had been effected in about as many 

 hours under the influence of a thaw under which the plank 

 diminished very slightly in thickness With this pro- 

 perty of ice, viz. its power of changing its form under strains 

 produced by its own gravitation, combined with the sliding move- 

 ment demonstrated by Hopkins, we have, as it seems to me, 

 adequate causes of glacier-motion"*. 



" If/' says M. Heim, after describing an experiment analo- 

 gous to those of Tyndall on the moulding of ice by pressure, " if 

 I rightly understand the experiments of Professor Tyndall and 

 my own on the moulding of plates of ice, the ice therein and in 

 the glacier is not compelled to shear." 



The idea present in common to the minds of these gentlemen 

 seems to be that in bending so as to take a set, ice does not 

 shear. In this I venture to think there is a misapprehension. 

 In the bending of a plate of ice every particle, except those at 

 the points of support, is made to move in the direction in which 

 the plate is bent — those particles which are at the point of 

 greatest inflection being made to move furthest, and those nearer 

 to it being always made to move further than those more re- 

 mote ; so that every particle moves over that which is alongside 

 towards the nearest point of support ; and being assumed to 

 have taken a set, it must have sheared over it. If the resistance 

 to this shearing had been the only one to be overcome, then the 

 aggregate work of the shearing of all the particles of the plate 

 in the act of bending would have been exactly equal to the work 

 of the pressure which bent it ; and in the case of a glacier, it 

 would have been necessary to make (on these gentlemen's theory, 

 that it descends by bending) the same calculation that I have 

 made by equating the work of the resistances of its particles to 

 shearing to that of the forces which cause it to shear; from 

 which there would have followed precisely the result at which 

 I have arrived. But the resistances to bending are resistances to 

 shearing plus other resistances at right angles to these. If, 

 therefore, the weight of a glacier is insufficient alone to over- 

 come the resistances to shearing, a fortiori " it is insufficient to 

 overcome the resistances to bending. 



The pressure theory supposes, however, not exactly that the 

 ice is bent as in Mr. Matthews' s experiment, but that it is first 

 crushed or granulated by an exceedingly slow and imperceptible 

 process of molecular crushing and granulation, and then that, 

 being compressed, it is regelated. In the act of being thus 

 moulded it shears, for the reasons above stated, and is dislocated 

 * Alpine Journal, No. 28, February 1870. 



