M. PERSON'S AND MB. FARADAY'S OBSERVATIONS. xxiii 



writings reprinted in this volume. It will also, I think, be 

 admitted on examination, that the new doctrine preserved all 

 that was sound and important in the old one, and added a new 

 feature not only to the explanations given by myself, but to what 

 was true in the writings of De Saussure and other older 

 authors. 



In 1850 I noticed M. Person's interesting observation de- 

 duced from his own experiments and those of M. Regnault, that 

 the dissolution of ice is a gradual, not a sudden process, and so 

 far resembles the more tardy liquefaction of fatty bodies, or of the 

 metals which absorb their latent heat by degrees, and pass 

 through intermediate stages of softness or viscosity. I hastened 

 to avail myself of this new confirmation of views which my 

 observations on glaciers had suggested. In like manner, had 

 Mr. Faraday's fact of the congelation of water placed between 

 two plates of ice, even though that ice be exteriorly melting, 

 been noticed by me when it was first published, I would have 

 unquestionably quoted it as a valuable auxiliary in explaining 

 the possible congelation of water in the minuter fissures of the 

 glacier, although since the change of views respecting the 

 consolidation of the glacier mentioned above as adopted by 

 me in 1846, the congelation of water in the crevices of the 

 glacier ceased to be essential to the mechanical explanation of 

 the movement and structure of the ice. The function of the 

 infiltrated water seems to be that of preserving the whole ice in 

 that state of softness which immediately precedes its dissolution, 

 as well as of conveying hydrostatic pressure ; and the cohesion of 



(pp. 90, 162) pointed out a similar accident in lavas. The width of the longitudinal 

 fissures in question shows that no lateral pressure was exerted sufficient to bring 

 their bounding surfaces into contact, and that they could not have been filled with 

 pellucid ice by any process short of the prolonged action of external cold upon infil- 

 trated water. I believe, however, that these appearances are confined to the 

 neighbourhood of the surface and sides of glaciers. 



