Reviexo of Vie Controversy Regarding the Motion of Glaciers. 1 41 



Instead of " pulsing through the great piles of ice," as Mr. Geikie 

 says, the small amount of heat that may succeed in entering the mass 

 crawls along at a rate almost imperceptible. If we assume the velocity 

 of transmission shown in Tyndall's experiment — a quarter of an inch 

 in two hours, or three inches per day — a whole year must pass before 

 the first wave of summer heat can penetrate the glacier to a depth of 

 90 feet, or, in other words, if the Alpine summer continues for 160 

 days, its effects can not be felt at a greater depth than 40 feet before 

 the ensuing winter changes the direction of the current. 



But not only does the acceptance of Mr. Croll's theory require the 

 admission of these two physical impossibilities — the ready conduction 

 of heat from one body to another of the same temperature, and its 

 ready transmission through one of the worst conductors known — but it 

 also assumes, as one of its fundamental propositions, that ice can not 

 rise in temperature above 32°, even to the slightest extent, without 

 becoming liquid. This is, we think, not only unproved, but contrary 

 to proljability. In speaking of the experiment above mentioned. Prof. 

 Tyndall says : 



" Tlie heat of a body Ls referred at the present day to a motion of its 

 particles. When this motion reaches an intensity sufficient to liberate 

 the particles of a solid from their mutual attraction, the body passes 

 into the liquid condition. Now, as regards the amount of motion 

 necessary to produce this liberty of liquidity, the particles as the 

 surface of a mass of ice must be ver}' differently circumstanced from 

 those in the interior, which are influenced and controlled on every side 

 by other particles. But if a cavity exist within the mass, the particles 

 bounding that cavity will be in a state resembling that of the particles 

 at the surface, and by the removal of all opposing action on one side 

 the molecules may be liberated by a force which the surrounding mass 

 has transmitted without prejudice to its solidity, just as the last of a 

 series of elastic baUs is detached by a force which has been trans- 

 mitted by the other members of the series, without visible sepa- 

 ration." 



Prof. Tyndall here evidently suggests the possibility of the con- 

 duction of heat thi'ough a mass of ice without melting it, in consequence 

 of the restraint imposed upon the inner particles by the close presence 

 of neighboring ones. This, it can not be doubted, involves the possi- 

 bility of raising its temperature above 32°, if only by a minute fraction 

 of a degree. But even the fraction of a degree is sufficient, and more 

 than sufficient, to enable the ice to convey away, ''without prejudice to 



