540 Royal Society : — 



crystal ; and this, or something like this, I take to be the process 

 by which the snow of a neve is converted into the imperfectly trans- 

 parent and sometimes fully transparent ice of a glacier. Tremors 

 of the kind here alluded to would not he wanting in a glacier in con- 

 tinued process of displacement, and in some part or other of which 

 disruptions consequent on violent strain are momentarily taking place. 



On the subject of the temperature of the interior of a glacier, I 

 would observe that there will be found in the archives of the Royal 

 Society, on the occasion of the Committee for recommending objects 

 of inquiry to Lieut. Foster during one of his Polar expeditions, a 

 recommendation of mine that the expedition should be furnished 

 with a set of boring-implements for the purpose of piercing some 

 very large and compact mass of ice, with the expectation of rinding 

 it much below the freezing-temperature. The heat of summer, it was 

 suggested, would all be carried off in the water resulting from surface- 

 melting ; while the intense cold of a polar winter would penetrate the 

 interior, and thus give rise to a mean temperature very far below that 

 of the external climate. The implements (if I remember rightly) 

 were furnished, but Lieut. Foster reported that no mass of ice suffi- 

 ciently large could be met with so free from fissures as not to be 

 permeated by infiltering water during the summer months ; and if 

 any results were obtained, they were not striking or definite enough 

 to be worth recording. That the lower surface of a glacier in contact 

 with the earth is in a constant state of fusion, even in those cold 

 regions, is proved by the phenomena recorded by Dr. Kane of the 

 Mary Minturn River in lat. 78° 54', and the feeder of the Kane 

 Lake, lat. 78° 18', which never ceases to flow, summer or winter. 

 Admitting this as a general fact, the sliding of a glacier on its bed is 

 an obvious necessity ; and that it should be unaccelerated is no more 

 a matter of wonder or difficulty of conception than the unaccelerated 

 descent of the weight of a clock which is never abandoned to its own 

 impetus, but brought to rest after every momentary descent by the 

 action of the scapement, — or the unaccelerated fall of a body in a 

 resisting medium when the resistance becomes equal to gravity, — 

 or of a weight gradually and uniformly lowered by the hand. Per- 

 haps the more general way of conceiving it would be to regard the 

 whole glacier as a mass propped up against a support anyhow inclined, 

 and prevented from tumbling over sideways by lateral stays. Such 

 a mass would rest in its position, if duly supported either by a base- 

 abutment, or by a heap of its own debris ; but if these were slowly 

 abraded, destroyed, or picked away, the whole mass would descend 

 bodily in the exact manner of the withdrawal of support. 



On the disruption of a nearly homogeneous elastic solid in a state 

 of strain, I would add a remark which seems to me of some moment, 

 as explanatory of the greater cohesive strength which is well known 

 to be imparted to cements, especially those of a resinous or gummy 

 nature, by the admixture of extraneous matter in fine powder. If 

 in such a solid there be one portion, however small, weaker than the 

 rest, the strainbeing uniform, a crack will originate in that place. Now 

 a crack, once produced, has a tendency to run — for this plain reason, 



