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the theory of glaciers when he announced the following fact, viz. : — 

 That ice does not pass abruptly from the solid to the fluid state. 

 That it begins to soften at a temperature of 2° centigrade below its 

 thawing point : that, consequently between 28-°4 and 32° of Fahren- 

 heit, ice is actually passing through various degrees of plasticity, 

 within narrower limits, but in the same manner that wax, for ex- 

 ample, softens before it melts. M. Person deduces this from the 

 examination of the heat requisite to liquify ice at different tempera- 

 tures. The following sentences contain his conclusions in his own 

 words : — " II parait d'apres mes experiences que le ramoUissement 

 qui precede la fusion, est cii-conscrit dans une intervalle d'environ 2 

 degres. La glace est done un des corps dont la fusion est la plus 

 nette ; mais cependant le passage de I'etat solide a I'etat liquide s'y 

 fait encore par degres, et non par un saut brusque."* 



" Now it appears very clearly from M. Agassiz' thermometrical 

 experiments, and from my own observations, that from 28° to 32° 

 Fahr. is the habitual temperature of the great mass of a glacier ; 

 that the most rigorous nights propagate an intense cold to but a very 

 small depth ; and I am perfectly convinced that in the middle and 

 lower regions of glaciers which are habitually saturated with water 

 in summer, the interior is little, if at all, reduced below the freezing 

 point, even by the prolonged cold of winter ; it would be contrary to 

 all just theories of the propagation of heat if it were otherwise, when 

 we recollect that the enormous mass of snow which such glaciers bear 

 (luring the coldest months of the year, is a covering sufficient to pre- 

 vent any profound congelation in common earth ; and admitting that 

 ice is probably a better conductor of heat than the ground, it is quite 

 incredible that a thickness of many hundred feet of ice, saturated with 

 fluid water, should be reduced much below the freezing point, or 

 should even be frozen throughout. 



" It thus appears quite certain that ice, under the circumstances 

 in which we find it in the great bulk of glaciers, is in a state more 

 or less softened even in winter ; and that, during nearly the whole 

 summer, whilst surrounded by air above 32°, and itself at that tem- 

 perature, it has acquired a still greater degree of plasticity, due to 

 the latent heat which it has then absorbed. 



" I have mentioned that the observations of this and some previous 



* Comptes Reiidus, 29th April 1850. 



