333 



that if a piece of ice, a straight prism for example, were placed in 

 a bent mould and submitted to pressure, it would break, but the 

 continuance of the force would bring its severed surfaces to reunite, 

 and that thus the continuity of the mass might be re-established. 

 Experiment, as we have seen, completely confirmed this surmise ; the 

 ice passed from a continuous straight bar to a continuous bent one ; 

 the transition being effected, not by a viscous yielding of the particles, 

 but through fracture and rey elation. 



All the phenomena on which the idea of viscosity has been 

 founded, are brought by experiments similar to the above into har- 

 mony with the demonstrable properties of ice. In virtue of these 

 properties the glacier accommodates itself to its bed ; crevasses are 

 closed up, and the broken ice of a cascade, such as that of the 

 Talefre or the Rhone, is recompacted to a solid continuous mass. 

 But if the glacier effects its movement in virtue of the incessant 

 fracture and regelation of its parts, this process will in all probability 

 be accompanied by an audible cracking of the mass, and thus a 

 noise of decrepitation may be expected to be heard, which would be 

 absent if the motion were that of a viscous body. It is well known 

 that such noises are heard, and they thus receive a satisfactory 

 explanation*. 



* It is manifest that the continuity of the fractured ice cannot be completely 

 and immediately re-established after rupture ; it is not the same surfaces that are 

 regelated, and hence the new contact cannot be perfect throughout. After rup- 

 ture the surfaces of fracture will enclose for a time capillary fissures, and thus the 

 above theory is in harmony with the known structure of glacier ice. Since the 

 paper was presented to the Society, I (on January 30th) made the following experi- 

 ments bearing upon this point : A piece of ordinary ice was taken, and a cavity 

 hollowed in it was filled with an infusion of cochineal ; the ice was perfectly 

 impervious to the liquid, which remained in it for half an hour without pene- 

 trating it in the slightest degree. A piece of the same ice was subjected to a 

 gradually increasing pressure. Flashes of light were seen to issue from it at 

 intervals, which indicated the rupture of optical continuity, and a low, and in 

 some instances, almost musical crackling was heard at the same time. Relieved 

 from the pressure, the ice appeared continuous to the naked eye, but a cavity 

 being formed and the cochineal infusion placed within it, the coloured liquid 

 immediately diffused itself through the capillary fissures, producing an appear- 

 ance accurately resembling the drawings illustrative of the infiltration experi- 

 ments of M. Agassiz on the glacier of the Aar. 



To account for a " bruit de orientation " heard upon the Aar glacier, M. Agassiz 



