CONDITIONS OF CONTINENTAL ICE. 227 



ing in cases where the temperature is but very little 

 below 32°, we are at present, in the absence of experi- 

 ments, unable to say what would be the amount of 

 pressure necessary to lower the melting-point to any 

 assigned temperature. The experiment of Mousson 

 shows that Professor Thomson's formula, ^ = 0"0137°?i, 

 does not hold true when the pressure is excessively 

 great. A pressure of 73 atmospheres will lower the 

 melting-point from 32° to 31°; but if Mousson's experi- 

 ment is to be depended upon, a pressure of 400 

 atmospheres would be necessary to lower the melting- 

 point from 1° to 0°. That is to say, were sufficient 

 pressure applied to lower the melting-point to 1°, 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° below the frezing-point, which doubtless it is not, 

 it would, according to Mousson's experiment, support 

 a thickness of not less than 90 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 over 6 but under 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 

 temperature 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 



