1863.] 677: 



as a viscous state as to permit (not indeed a sensible and finite change 

 of figure of a small portion of the mass without fracture, but) a cer- 

 tain freedom of movement in the individual molecules, to some sen- 

 sible depth within the surface, so as to allow of a gradually progressive 

 deviation of their axes from exact parallelism, and thus to effect a 

 transition from one crystalline arrangement to another not by 

 macling, but by curvilinear distortion, such as may be conceived to pre- 

 vail in pearl-spar and other similar disturbed forms of crystals. Nay, 

 I can conceive it possible that by very long continuance at this exact 

 temperature (especially if aided by tremors short of disruption pro- 

 pagated through the mass, which, as we see in the crystallization of 

 cold wrought iron in the axle-trees of railway carriages, powerfully 

 favour the crystalline rearrangement of molecules even in the most 

 rigid solids) the contiguous blocks may influence each other's cry- 

 stallization to a greater and greater depth through the medium of the 

 cementing film, thus tending continually to straiten the curve of the 

 connecting chain of axes, and after a very long time to bring the 

 two blocks into perfect conformity, so as to form an uninterrupted 

 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 be 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 finding 

 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 



VOL. XII. 3 B 



