224 'The American Geologist. October, 1902. 
In reference to the Thomson * theory of liquefaction 
by pressure, it does not seem to the writer of this paper 
that such influence can enter into glacier movement in other 
than a very elementary way. It is proved in thermo- 
dynamics that where ice and water are together at the same 
temperature, if \\= the volume of unit mass of the mixture 
in the higher state, and\',j=: the volume of unit mass of the 
mixture in the lower state, then L=:t (\\ — ^o)~T^> where 
{t) is the absolute temperature, or 274+o°C., and L=latent 
heat of unit mass in foot pounds. If we take L as latent heat 
of one pound of the material, and V^ and V, as volumes in 
cubic feet of one pound or the material, then the formula 
holds for (p) reckoned in pounds per square foot. Now in 
ice water ^"o= -01747 
A'i=.oi6o2 w'hen (f)=274+o°C., and (p)=:i4.7 
pounds per square inch, or 21 16 pounds per square foot. 
r dp . . 
Hence — =— = — 278100, a constant; the quantitative 
meaning of the expression-—— is, obviously, that the melting 
point lowers at the rate of .001 of a degree for an increase 
pressure of 278 pounds per square foot. 
If we consider a given glacier to be 1000 feet thick then 
the pressure upon one square foot at the base would be 
1000 X 62.5 x .918=57000 pounds (Approx.). At the rate 
then of .001 of a degree for every 278 pounds we have for 
the total 57000 pounds a lowering of the mei'ting point by 
only a little over two-tenths of a degree. It is true, however, 
that this decrease w^ould aid slightly in producing liquefaction 
at the under surface of the glacier. 
It is generally conceded that glacier ice acts like a viscous 
substance, and that its motion is fundamentally due to the 
weight of the ice itself. It seems that there are no available 
experiments bearing upon the sliding of ice over its bed other 
than those of Hopkins, f He used a number of pieces of 
ice on a rough sandstone slab, and found that the movement 
down the slope was uniform and approximately proportional 
to the pressure, and to the angle of inclination, for angles 
*Proc. Rov. Soc. lS5t5-7. 
fPhll. Mag. 1845, Vol. XXVI. pp. 3-6. 
