177 



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 { . 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. 



II. "Preliminary Note on the production of Vibrations and 

 Musical Sounds by Electrolysis/- By GEORGE GORE, Esq. 

 Communicated by Professor TYNDALL. Received April 4, 

 1861. 



If a large quantity of electricity is made to pass through a suitable 

 good conducting electrolyte into a small surface of pure mercury, 

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



