1850.] M. PERSON'S OBSERVATIONS ON THE FUSION OF ICE. 225 



the same kind established by a French experimenter, M. 

 Person, who appears not to have had even remotely in his 

 mind 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 Fahrenheit, ice is actually passing through 

 various degrees of plasticity, within narrower limits, but in the 

 same manner that wax, for example, softens before it melts. 

 M. Person deduces this from the examination of the heat 

 requisite to liquify ice at different temperatures. The following 

 sentences contain his conclusions in his own words : " II 

 parait d'apres mes experiences que le ramollissement qui 

 precede la fusion, est circonscrit dans line intervalle d'environ 

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

 la plus nette ; mais cependant le passage de 1'etat solide a 

 ,1'etat liquide s'y fait encore par degres, et non par un saut 

 brusque."* 



Now it appears very clearly from M. Agassiz' thermome- 

 trical experiments, and from my own observations, that from 

 28 to 32 Fahrenheit 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 during the coldest months of the year is a cover- 

 ing sufficient to prevent 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 



* Comptfs Sendus, 29th April 1850. 

 Q 



