CHAPTER XIII. 



PHYSICAL CONDITIONS OF THE ANTARCTIC ICE-SHEET. 



Sir Wyville Thomson on the Antarctic ice. — Testimony of iceberg. — 

 Temperature of the Antarctic ice. — Heat derived from beneath. — 

 Heat derived from the upper surface. — Heat derived from work 

 by compression and friction. — Temperature of the ice determined 

 by the temperature of the surface. — Temperature of the ice in 

 some regions determined by pressure. 



There are few subjects on which a greater amount of 

 misconception as well as diversity of opinion, prevails, 

 than in regard to the physical conditions of continental 

 ice. This is more particularly true in reference to 

 those physical and mechanical principles which limit 

 the thickness of the ice-sheet and determine its form 

 and mode of motion. These misapprehensions arise, 

 in part at least, from an attempt to explain the con- 

 ditions of continental ice on the principles of ordinary 

 glaciers by geologists, who forget that between a 

 continental ice-sheet and an ordinary glacier there is 

 but little analogy. 



At the present day, the only continental ice on the 

 globe, with the exception of that of Greenland, is of 

 course in the Antarctic regions. Here we have an ice- 

 sheet rivalling in magnitude those on the northern 

 hemisphere, even during the height of the Glacial 

 Epoch. I know of nothing which will better illustrate 

 the physical principles of continental ice than an 

 attempt to answer the question, What is the probable 



