Oeology and Natural History. 67 



tlie moving glacier is found to be by at least from thivty to forty 

 times too great to permit of the ice being sluared l)y tlie 'mere force 

 of gravitation; how, then, is it that gravitation, without the direct 

 assistance of any other force, can manage to shear tlie ice ? Or 

 to put the question under another form : lieat does not reduce the 

 shearing force of the ice of a glacier to something like 1-;U9;3 U). 

 per square inch of surface, the unit required l>y Mr. MoseUy to 

 enable a glacier to shear by its weight; the' sheaiiiig-f uce of 

 the ice, notwithstanding all the heat "received, still remains at 

 about 75 lbs. ; how, then, can the glacier shear without any other 

 force than its own weight pushing it forward ? This is the tunda- 



tery of glacier-motion. We are compelled in the present state' of 

 the problem to admit that glaciers do descend with a ditferential 

 motion without any other force than tbeir own weiglit pusliing 

 them forward ; and yet the shearing-force of the ice is actually 

 found to be thirty or forty times the maximum that wouhl i)e)init 

 of the glacier shearing by its weight only. The explanation of 

 this apparent paradox will remove all our difficulties in refiniire 

 to the cause of the descent of glaciers. 



There seems to be but one explanation (and it is a very ol.\ ious 

 one), viz., that the motion of the glacier is moleculn: The ice 

 descends molecule by molecule. The ice of a glacier is in the hard 

 crystalline state, but it does not descend in this state. Gravitation 

 is a constantly acting force ; if a particle of the ice lose its shear- 

 ing-force, though but for the moment, it will descend by its weight 

 alone. But a particle of the ice will lose its shearing-force for a 

 moment if the particle loses its crystalline state for the moment. 

 The passage of heat through ice, whether by conduction or by 

 radiation, in all probability is a molecular process ; that is, the 

 form of energy termed heat is transmitted from molecule to mole-' 



cule of the ice. A particle takes the energy 

 on the one side and hands it over to its neighl 



s neighbor B on the opposite 

 side.^ But the particle must be in a different state at the moment 

 It is in possession of the energy from what it was before it received 

 it from A, and from what it will be after it has handed it over to 

 B. Before it became possessed of the energy, it was in the crys- 

 talline state— it was ice ; and after it loses possession of the energy 

 it will be ice ; but at the moment that it is in possession of the 

 passing energy is it in the crystalline or icy state ? If we assume 

 that it is not, but that in becoming possessed of the energy, it loses 

 its crystalline form and for the moment becomes water, all our 

 difficulties regarding the cause of the motion of glaciers are re- 

 moved.* We know that the ice of a glacier in the mass cannot 

 become possessed of energy in the form of heat without becom- 

 ing fluid ; may not the same thing hold true of the ice particle ? 



The alleged limit to the thickness of a ff lacier. —In his memoir, 

 " On the Mechanical Properties of Ice," published in the Philo- 

 sophical Magazine for January, 1870, Canon Moseley arrives at a 

 conclusion in regard to the crushing of ice to which I am unable, 

 without some qualifications, to agree. In his experiments ice was 

 » See Phil. Mag. for March 1869, p. 201. 



