Intelligence and Miscellaneous Articles. 79 



That glacier-ice possesses no such properties of viscidity or com- 

 pressibility as would cause it to descend by its weight along such 

 slopes as those on which some glaciers descend may be shown thus. 

 Let the Mer de Glace be conceived to .be cut up by vertical sections 

 at right angles to one another, into blocks, whose bases are large 

 enough to prevent them toppling over ; and let these blocks be 

 imagined to be separated from one another. Then (supposing it not 

 to slip) each block would stand in its place without the support of 

 the neighbouring blocks ; for its vertical sides would be walls of ice 

 needing no external support, like the ice-wall of the Glacier du Geant, 

 141 feet high near the Tacul, described by Tyndall* ; or that of the 

 Mer de Glace near the Augle, pictured by Forbes f . Needing no 

 external support when thus placed asunder, they could need none when 

 brought again together ; nor could they, by the fact of their being 

 so brought together, be made to exert any mutual pressure, or have 

 any more or other tendency to move than each block had separately. 

 If this reasoning be true, there is no physical property of ice, whether 

 it be called viscosity or plasticity, which would cause it to descend by 

 its weight alone on any surface along which it would not slide. It is 

 plastic no doubt — Tyndall has proved that by the Hydraulic Press, — 

 but not as to any pressure created in a glacier by the weight of the 

 glacier. If it were, or if it were semifluid, then under those enor- 

 mous pressures which it is supposed to sustain, it would bulge out at 

 the ice-wall of the Tacul, and mould itself to the sides of its channel ; 

 for it is the character of a compressible substance, not less than of a 

 semifluid, to yield not only in the direction in which pressure is ap- 

 plied to it, but in every other. 



Nor if it were sufficiently a fluid to flow by its weight alone, how- 

 ever slowly, down slopes of 3° or 5°, could it descend otherwise than 

 as a torrent down slopes, such as that of the Silberberg Glacier, of 40°, 

 on which its descent is nevertheless several times slower. The phe- 

 nomena of these secondary glaciers offer themselves as a test of rival 

 theories of glacier-motion. They lie on slopes so steep that it is 

 scarcely possible to conceive the ice, if solid, to be loosened from the 

 face of the rock, and not to descend in fragments ; or if viscous, not 

 to become a torrent. 



XIT. Intelligence and Miscellaneous Articles. 



ON THE CONDUCTIBILTTY OF SALINE SOLUTIONS. 

 BY M. MARIE -DAVY. 



1 . T CALL the calculated density of a solution the number obtained 

 ■*■ by adding to unity the weight of salt dissolved in a gramme of 

 water. The relation of the calculated to the true density gives the 

 measure of the degree of expansion which water experiences in 

 consequence of salt held in solution. 



2. I call the corrected conduclibility of a solution the product ob- 

 tained by multiplying its true conductibility by the ratio of its cal- 



* Glaciers of the Alps, p. 289. t Travels in the Alps, p. 76. 



