Review oftJte Controversy Regarding the Motion of Glaciers. 137 



dynamical form of heat ; in other words, the molecule gives out heat in 

 the act of freezing. The heat then given out may be employed to 

 melt tlie adjoining molecule. The ice molecule takes on energy from 

 a heated body by melting. That peculiar form of motion or energy, 

 called heat, disappears in f )rcing the particles of the crystalline mole- 

 cule separate, and for the time being subsists on the form of a tendency 

 in the separated particles to come together again into the crystalline 

 form. 



" But it must be observed that although the crystalline molecule 

 Avhen it is acting as a conductor takes in energy under this form from 

 the heated body, it only exists in the molecule under such a form 

 during the moment of its transmission, that is to say, the molecule is 

 melted, but only for a moment. AVhen B accepts the energy from A, 

 the molecule A instantly assumes the crystalline form. B is now 

 melted, and when C accepts of this energy from B, then also h in turn 

 assumes the solid state. This process goes on from molecule to mole- 

 cule, till the energy is transmitted through to the opposite side and the 

 ice is left in its original solid state. This is the rationale of Faraday's 

 proj)erty of re gelation. 



" This point being established, every difficulty regarding the descent 

 of a ghicier entirely disappears ; for a molecule, the moment it assumes 

 the fluid state, is completely freed from shearing force, and can de- 

 scend by virtue of its own weight, without any impediment. All 

 that the molecule requires is simply room or space to advance in. If 

 the molecule were in absolute contact with the adjoining molecule be- 

 low, it would not descend, unless it could push that molecule before it, 

 which it probably would not be able to do. But the molecule actually 

 has room to advance in, for, in passing from the solid to the liquid state, 

 its volume is diminished by about one tenth, and it consequently can 

 descend. True, when it again assumes the solid state, it will regain 

 its former volume ; but the question is, will it go back to its old posi- 

 tion? If we examine the matter thoroughly, we shall find that it can 

 not. If there were only this one molecule affected by the heat, this 

 molecule would certainly not descend, but all the molecules are simi- 

 larly affected, although not all at the same moment of time. 



"Let us observe what takes place, say, at the lower end of the gla- 

 cier. The molecule A, at the losver end, say, of the surface, receives 

 heat from the sun's rays ; it melts, and in melting not only loses its 

 shearing force and descends by its own weight, it contracts also. B, im- 

 mediately above, is now, so far as A is concerned, at liberty to descend, 

 and will do so the moment that it assumes the liquid state. A, by this 

 time, has become sobd, and again fixed by shearing force, but it is not 



