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POPULAR SCIENCE REVIEW. 
the attention of the French Academy to a method proposed many years ago 
by him for the separation of ores containing lead, copper, and silver. The 
general principle of the method consists in the employment of galvanic 
^‘couples ” composed of zinc, iron, and lead, associated with plates of copper 
or a piece of well-baked carbon. The plates of non-oxidable metal or the 
uon-metallic conductive substances are put in immediate contact with the 
argentiferous metallic solution, whilst the plates of oxidable metal are placed 
in a permeable diaphragm made with untanned hide. This is filled with 
salt and water, and the plates are then put in metallic commimication with 
each other. The mineral is placed in the vessel containing the saline solu- 
tion, and is rapidly stirred by machinery for the purpose. The mineral 
bemg deposited, the liquid is decanted into other basins, in which the galvanic 
couples are placed. Experience has shown, M. Becquerel says, that this 
process may be well employed for silver ores containing copper and lead, at 
least when sea-salt is cheap and when sufficient wood exists in the neigh- 
bourhood. — Vide ComiTitcs-Rendm^ March 1. 
The Electric Conductihility of Metals has had devoted to it a memoir 
which has been lately laid before the Berlin Academy of Sciences by Herr 
Paalzow. The paper is one of interest. The experiments recorded by the 
author are numerous, and the results obtained are of some importance. 
Many of them confirm the views formerly expressed by Beetz. Herr Paal- 
zow concludes from his researches that there is no relation between the con- 
ductibility for heat and that for electricity. He has experimented on the 
following substances, and found that they have the following order in point 
of conductihility of heat and electricity : — Heat : Mercury, water, sulphate 
of copper, sulphuric acid, sulphate of zinc, solution of sea-salt. Electricity : 
Mercury, sulphuric acid, solution of sea-salt, sulphate of zinc, sulphate of 
copper, water. — Vide E Institute Feb. 27. 
The Mechanical Descent of Glaciers. — The Bev. Canon Moseley, who has 
been studying the movement of glaciers, has inquired into the forces 
which impede the descent of these masses of ice, and thus summarises them : 
— 1st. The resistance to the sliding motion of one part of a piece of solid ice 
on the surface of another, wliich is taking place continually throughout the 
mass of the glacier, by reason of the difierent velocities with which its 
different parts move. This kind of resistance will be called in this paper (for 
shortness) shear, the unit of shear being the pressure in pounds necessary to 
overcome the resistance to shearing of one square inch, which may be pre- 
sumed to be constant throughout the mass of the glaciers. 2udly. The 
friction of the supenmposed laminae of the glacier (which move with dif- 
ferent velocities) on one another, which is gi-eater in the lower ones than 
the upper. Srdly. The resistance to abrasion, or shearing of the ice, at the 
bottom of the glacier, and on the sides of its channel, caused by the rough- 
ness of the rock, the projections of wliich insert themselves into its mass, 
and into the cavities of whicli it moulds itself. 4thly. The friction of the 
ice in contact with tlie bottom and aides so sheared over or abraded. He 
has gone into a mathematical calculation of the value of these forces, and 
he considers, ns the result of his inquiries, that the weight of a glacier is in- 
sulficicnt to account for its descent — that it is necessary to conceive, in addi- 
tion to its weight, the operation of some other and much greater force, which 
