^ Mr. H. H. Howorth on 



closely together as to exclude interstices. The crystalline 

 particles are however united together at special points 

 determined by their polarity, hence, as Professor Tyndall 

 remarks, the reason why volume for volume ice is less dense 

 than water . . . When a crystalline molecule melts, capillary 

 attraction will cause it to flow into the interstices between 

 the adjoining molecules. The moment it parts with the 

 heat received it will resolidify, but not so as to fill the cavity 

 it occupied in the fluid state. The liquid molecule in 

 solidifying assumes the crystalline form, and as the interstice 

 in which it solidifies will be too narrow to contain it, the 

 result will be that the fluid molecule, in passing into the 

 crystalline form, will press the two adjoining molecules aside 

 in order to make sufficient room for itself between them, 

 and this it will do, no matter what amount of space it may 

 possess in all other directions. The crystal will not form to 

 suit the cavity, the cavity must be made to contain the 

 crystal, and what holds good of one molecule holds true of 

 every molecule which melts and resolidifies. The process is 

 therefore going on incessantly in every part of the glacier, 

 and in proportion to the heat which the glacier is receiving. 

 This internal molecular pressure, resulting from the solidify- 

 ing of the fluid molecules in the interstices of the ice, acts 

 on the mass of the ice as an expansion force, tending to 

 cause the ice to widen out in all directions." 



This is the theory of the mechanism of ice motion as 

 finally developed by Dr. Croll. It has been sifted with 

 critical skill and acumen by the Reverend J. F. Blake, in 

 the 3rd volume of the Geological Magaziney p. 493, and so 

 far as we can see has been completely shattered by him. 

 At all events his analysis has never been met in any way. 

 As Mr. Blake so well shewed, in speaking of crystalline 

 molecules and liquid molecules of the same substance as if 

 they were different in size or shape. Dr. Croll used language 

 without meaning in physical science ; a molecule is the 



