1862.] 117 



to be a solid body, believed as a matter of necessity that a glacier 

 must, on account of the external conditions to which it is subjected, 

 be excessively broken and dislocated in the course of its motion. The 

 author was himself one of those who fell into the error of attributing 

 too much influence to the larger and more visible disruptions of the 

 mass ; but the great difficulty was in the perfect subsequent reunion 

 of portions which had thus been separated, whether by larger or 

 smaller dislocations. And here it will necessarily be asked whether, 

 in the expressions above quoted, " re-attachment " and the " reunion 

 by time and cohesion " of separated portions when again brought 

 into contact, really mean the same thing as reg elation 1 This question 

 the author thinks can be answered only by saying that, whatever 

 might be the intended meaning of those expressions, they failed to 

 convey to the minds of others the most remote idea of regelation, as 

 a property of ice at a particular temperature. No better proof can 

 be given of this than the general conviction which appeared to flash 

 across the mind of every glacialist when he first heard of Professor 

 Tyndall's experiment, that the recognition of the property of instan- 

 taneous regelation was a well-marked and important discovery, which 

 had at once completely removed a great stumbling-block in glacial 

 theory. In fact, the viscous theory assigns no physical cause for 

 the reunion in question. All we could do, before the publication of 

 those experiments, was to infer from the observed facts that ice did 

 possess some property which facilitated the reunion of separate pieces 

 in contact ; but this was like the attempt to define viscosity by an 

 appeal to the phenomena which that property was intended to ex- 

 plain, Regelation has, in fact, no connexion with viscosity, but stands 

 in direct antagonism to it. 



An imperfect plasticity in ice has sometimes been spoken of. The 

 fact is, all solid bodies may be said to have an imperfect plasticity, if 

 we chose to admit this vagueness in scientific language, since all are 

 capable of greater or less extension or compression. As to the apparent 

 plasticity inferred from the motion of glacial masses, and arising from 

 the crevicing of the ice as already explained, it has no relation what- 

 ever to real plasticity. Such crevices are the necessary consequences 

 of the external forces acting on the glacier, and are as essential to the 

 theory of regelation as they are unconnected with any property of 

 plasticity. 



