1 8 Thickness of the Antarctic Ice , and its [January, 
31 0 ; but if Mousson’s experiment is to be depended upon, 
a pressure of 400 atmospheres would be necessary to lower the 
melting-point from i° to o°. That is to say, were sufficient 
pressure applied to lower the melting-point to i°, it would 
require an additional 400 atmospheres to lower it to 0°. 
The rate at which the melting-point is lowered by pressure 
is evidently not uniform, but decreases with the increase of 
pressure. Were the temperature of the ice at the South 
Pole as low as 32 0 below the freezing-point, which doubtless 
it is not, it would according to Mousson’s experiment sup- 
port a thickness of not less than go miles. But if the rate 
did not diminish with the pressure, but remained uniform, 
a pressure of 16 miles would be the limit. 
From what has already been proved I think we may 
safely assume that the ice at the South Pole may be at least 
ten or twelve degrees below the freezing-point. We are 
unable to say what thickness of ice this temperature could 
support, but we know that it must be not under 6 nor over 
30 miles. 
But whatever the actual temperature of the Antarctic 
ice may be, if the sheet be as thick as the temperature 
will admit, then underground heat can never raise the tem- 
perature of the surface under the sheet sensibly above 
that of the ice. This is evident, because it cannot 
raise the temperature of the ice above the melting-point 
corresponding to the pressure, and the ice will always 
keep the floor at sensibly the same temperature as itself. 
In short, in determining the thickness of the Antardfic ice, 
underground heat does not enter as an element into our cal- 
culations, and, so far as the melting of the ice produced by 
the lowering of the melting-point is concerned, the Antarctic 
ice at the Pole may be a dozen of miles in thickness as 
readily as 1400 feet. 
( b .) Melting produced hy Work of Compression and Friction . — 
“The pressure upon the deeper beds of ice,” says Sir Wyville 
Thomson, “ must be enormous ; at the bottom of an ice- 
sheet 1400 feet in thickness it cannot be much less than a 
quarter of a ton on the square inch. It seems therefore 
probable that, under the pressure to which the body of ice 
is subjected, a constant system of melting and regelation 
may be taking place, the water passing down by gravitation 
from layer to layer until it reaches the floor of the ice-sheet, 
and finally working out channels for itself between the ice 
and the land, whether the latter be subaerial or sub- 
merged.” 
