438 



Action of Lake-glaciers . 



embankment on a morass, caused upward motion of the peat and bog often as 

 far as the marsh extends. 



3. The effect of the congelation of the water produced by the friction of ice 

 upon ice expanding the lower part of the glacier, and producing the forward 

 motion. This third cause was De Charpentier's principal source of motion. 



The two resisting forces are the friction against the bottom and the resistance 

 of the mass, and the having to lift the bottom of the glacier against gravity. 



The chemical explanation has yet to be given, I think that meets the case 

 entirely. 



(3) The effect of evaporating ice and water even at low temperature in produ- 

 cing increased cold has not been alluded to, nor the absorption of water by the 



FIG 



Z,cdce (jtieccier gajsposed to he exccciratntq- 

 cclafos afrikeTate of imeh, in cc ycai> . 



m 



Ike sent level ^ 

 of -L alee . 



A.TYLOR. DEL 



pores of ice. This is also an action, I believe, equivalent to evaporation, and 

 causes great abstraction of heat from the surrounding ice, and great cold at the 

 surfaces, where absorption occurs. And this cold converts a certain quantity of 

 water into ice, joining surfaces of ice together at 32 degrees. That the now 

 well-known theory of regelation is a correct one I do not doubt. That heat is 

 produced by the friction of ice upon ice was proved by Sir H. Davy. Thawing 

 has been said to proceed at lower temperatures under pressure by Professor J. 

 Thomson, but little observation was adduced in proof of this in the Papers 

 published in 1857 and 1858 in the Proc. Roy. Soc. Edin. It is quite possible 

 that ice may not freeze at a temperature below 32 degrees under pressure ; as 

 we know water can be cooled much below 32 degress, if perfectly still. When 

 motion ensued, the production of heat by the friction of the particles would 

 warm the water, and raise the temperature at the moment to 32 degrees. The 



