= 
"te 
J. LeConte on the Descent of CPRiers. 339 
ered in relation to the great mass of the glacier.* - Moreover, it 
is only during the cold season, that the superficial stratum of ice 
participates in the atmospheric oscillations of temperature ; and 
yet, this is the season in which the motion of the glacier is Jeast 
rapid! By some strange fatality, when the mechanical cause 
which the theory demands is least active, the effect, for which it 
is to afford an explanation, is at its maximum and vice versa. 
at an inconsiderable slope.” ‘“'This motion,” continues Mr. 
Moseley, “which Mr. Hopkins attributed to the dissolution of the 
ice in contact with the stone, would, I apprehend have taken place 
if the mass had been lead instead of ice; and it would have been 
but about half as fast, because the linear expansion of lead is only 
about half that of ice.” (p. 67 
ment, it is impossible to ascribe it to a similar cause ; for Mr. 
Hopkins expressly states, that the motion took place only during 
the melting of the ice,t and consequently, when its temperature, 
by virtue of the laws of change of state, must have been con- 
stantly at the freezing point of water. There can be no satis- 
actory solution of the mechanical problem of the motion of gla- 
ciers, which does not contemplate the peculiar laws of latent heat, 
as well as the structure and other mechanical conditions of the 
glacial masses. 
Athens, Georgia, Aug. 20th, 1855. 
* But even if—contrary to all observation and to all just theories of the propa- 
gation of heat,—we su »pose the cold of winter to penetrate to any sid i 
into the glaciers, the’ vast amount of latent heat which must be extricated by the 
solidification of the first portions of water which permeate the cold mass after the 
thawing season commences, would very soon eleyate its temperature to the 1 
point; after which, its temperature could undergo no variation from the percolation 
e 
of water. 
+ Vide Phil. Mag., 3d Series, vol. xxvi, p. 4, 1845 
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