1846.] LIMITS OF DUCTILITY OF ICE. 161 



what we may one day learn if willing to be taught : " Quand 

 on agit sur un morceau de glace, qu'on le frappe, on lui trouve 

 une rigidite qui est en opposition directe avec les apparences 

 dont nous venons de parler. Peut-etre que les experiences faites 

 sur de plus qrandes masses donneraient d'autres resultats.* " 



JL *s 



The " ductility" is indeed not great; the compact ice even 

 of the slowest moving glaciers bears evidence, in the veined 

 structure, or " blue bands," to the bruise which it has received 

 from the all-powerful strain which has acted on it. When the 

 difference of motions is excessive, or the slope occasions the 

 speed to be greater than permits the gradual molecular adapta- 

 tion of the semi-rigid parts to one another, the masses are 

 broken up and fall more or less tumultuously ; the strain being 

 then removed by the dislocation, the veined or bruised structure is 

 invariably extinguished at last. I shall quote a series of ex- 

 amples of the gradation of phenomena, which I conceive to be 

 plainly connected by a common cause. 



1. In any torrential glacier, such as the Glacier des Bossons, 

 the upper part of the glaciers of La Brenva, Allalein, or the 

 Rhone, and many others, the fractures are so numerous that the 



* Theorie des Glaciers de la Savoie, p. 84. Quoted in my Travels, p. 367, 2d 

 edit. Since this paper was read, Mr. Christie, Secretary of the Royal Society, has 

 kindly communicated to me a very striking remark upon a well-known and easily- 

 repeated experiment. The experiment is this : If, in the course of a severe winter, 

 a hollow iron shell be filled with water and exposed to the frost with the fuze-hole 

 uppermost, a portion of the water expands in freezing, so as to protrude a cylin- 

 der of ice from the fuze hole ; but if the experiment be continued, the cylinder con- 

 tinues to grow, inch by inch, in proportion as the central nucleus of water freezes. 

 " In the first instance,'' says Mr. Christie, " a shell of ice containing water was 

 formed, no doubt, within the iron shell, and the fuze-hole might be filled by the ex- 

 pansion of the water in the act of freezing ; so that there may be no reason for 

 attributing plasticity to the ice as far as this goes ; but the shell of ice once formed, 

 and the fuze-hole filled with ice, the subsequent rise of the ice must have proceeded 

 from the ice of the interior shell being squeezed through the narrow orifice. No 

 thawing took place during the process. Does not this show plasticity even in very 

 small masses of ice ? " I have also been lately informed, on excellent authority, 

 that in a new work by a most eminent German mineralogist, the plastic character 

 of ice in masses is assumed as an admitted fact. In corroboration of what has been 

 said in the text, I may farther add, that whilst these sheets are passing through the 

 press, I observe in the Athenaeum (June 20, 1846), an account of a patent process 

 for moulding solid tin into tubes and other utensils, in the course of which it is stated 

 that " tin under a pressure of about twenty tons to a circular inch will run accord- 

 ing to the law of fluids." 



M 



