496 Intelligence and Miscellaneous Articles. 



ON STREAMS FROM GLACIERS. 



To the Editors of the Philosophical Magazine and Journal, 

 Gentlemen, Wellington March 7, 1876. 



In reference to Dr. Pfaff's experiments on the plasticity of ice, 

 is the following extract from my Address to the Philosophical 

 Society of Wellington of sufficient interest to appear among the 

 Miscellaneous Articles of the Magazine ? 



11 1 see in Geikie's late work, ' The Great Ice Age/ that reference 

 is made to the fact that, from the foot of glaciers in Greenland, 

 streams of water issue and unite to form considerable rivers, one of 

 which, after a course of forty miles, enters the sea with a mouth 

 nearly three quarters of a mile in breadth. 



" This flow of water, Geikie thinks, probably circulates to some 

 extent below every glacier ; and he accounts for it by the liquefaction 

 of ice from the warmth of the underlying soil. A more complete 

 explanation of this flow of water from glaciers estimated not less 

 than 3000 feet thick will be found in the suggestion first made by 

 Professor James Thomson, and subsequently proved by his brother 

 Professor W. Thomson, that the freezing-point of water is lowered 

 0°*23 Fahr. for each additional atmosphere of pressure. Now a 

 sheet of ice 3000 feet thick is equal to the pressure of about 80 

 atmospheres, at which pressure its temperature at the base should 

 not exceed 13° Fahr. to retain the solid form. In the state of run- 

 ning water beneath the glacier, it might readily, as Geikie states, 

 absorb heat from the underlying soil. In this we have a safe as- 

 surance that glaciers of such enormous thickness can exist only 

 where there is scarcely any or no inclination of the land to the sea 

 board. And we may hesitate to adopt with Geikie the views of 

 the Swiss glacialists, who speak of sheets of ice having existed in 

 the great Ice Age not less than 3000 feet thick, overtopping the 

 Jura and stretching continuously from the Rhine valley. 



" Sheets of ice 3000 or 5000 feet thick may exist, but not at the 

 temperature of 32° Fahr. throughout the whole mass. The tempera- 

 ture at the surface may be 32° Fahr. ; at the base it must be below 

 13° Fahr. The specific heat of water is far greater than that of ice. 

 One pound weight of ice at 32° Fahr. mixed with one pound of boiling 

 water gives 2 lbs. of water at 51° Fahr. ; so that 71 degrees of heat 

 are lost in the mere conversion of ice into water. Thus every pound 

 of ice converted by pressure into water demands a large supply of 

 caloric as a necessity of its change of condition, and absorbs it 

 instantly from the ice above. The ice in immediate contact with 

 the layer of water, hardened by loss of caloric, now robs the ice 

 above of caloric, and again softened can no longer bear the pressure, 

 and in its turn flows away as water ; and so the process goes on, 

 until a regular gradation of temperature is established throughout 

 the mass, and an equilibrium formed between the forces by which 

 the sheet of ice maintains a fixed altitude. No column of ice 3000 

 feet in height can maintain that elevation for an indefinite time, 

 unless the temperature of the air is much lower than 32° Fahr., and 

 the loss from liquidation beneath constantly supplemented by re- 

 newed accumulations above." 



