98 Mr. H. H. Howorth on 



coming after the minute portion that had got entangled in 

 an interstice. Again, why should not in every case the 

 molecules whose attachment is loosened by melting go back 

 to their old place in solidifying?" " Unless some new force 

 is brought into play," says Mr. Blake, " on the instant, 

 whatever old forces they overcame originally in the act of 

 crystallising the first time, they can certainly overcome again 

 none that Mr. Croll mentions. Gravity always acted, and 

 the molecular forces of crystallization are just as competent 

 to push back the molecules against it as they were before 

 when first the ice was formed" {Geol. Mag.^ 1876,495 — 6). 



" There is nothing," he continues, " in Mr. Croll's theory, 

 to distinguish a glacier from an ordinary piece of ice, and if 

 one will flatten out as he supposes, the other ought to do 

 so too. But, whoever saw a block of ice bulge out under 

 the influence of heat ? Again, Mr. Croll, in arguing about a 

 small portion of ice melting and then resolidifying, and 

 passing its heat on to the next, and so on, seems to ignore 

 the elements of latent heat and of conductivity in ice. 

 Before a particle of ice can melt, it must first be brought to 

 the melting point, after which so many units of heat must 

 be added to it in order to melt it. Suppose a melted 

 particle in the midst of ice colder than at melting point, its 

 heat would be distributed in raising the temperature of the 

 surrounding ice, according to its conductivity, and what 

 was left would be insufficient to melt any other particle of 

 its own size. Hence, before the solidifying of one particle 

 could be sufficient for melting another, the whole surround- 

 ing mass must be at melting point, and there must further 

 be some cause for the devotion of the spare heat to one 

 particular particle, to say nothing of the cause which is to 

 bring about a perpetual doing and undoing of the same 

 operation. If there could be any such passing on of a 

 melted state through a body to the other end, we ought to 

 see a glass rod held in the fire melting at the end away 



