386 Mr. 0. Fisher on the Thermal Conditions and 



when the thickness exceeds sixteen miles none will escape. 

 But if none escaped, so that the whole of F was employed in 

 melting the ice, Sir William Thomson asserts that it could 

 only melt one fifth of an inch annually at the ordinary tem- 

 perature and pressure. If, therefore, the snow-fall considerably 

 exceeds this small amount, there seems to be no reason why 

 the ice might not accumulate to a much greater thickness than 

 the above, as far as melting at the bottom is concerned. 



Note. — Professor Everett says, p. 45, that Sir Wm. Thomson's 

 results are given in terms of the foot and second, and that 

 consequently they have been multiplied by 929 to reduce them 

 to the C.G.S. system. Hence to bring back K and k, as given 

 by Professor Everett, to the system of units used here, we 

 must put 



_ -00581 



K= ^29" 

 and 



-00218 

 929 ' 



The thermometric scale used does not affect the value of the 

 conductivity. 



The next question which we will attempt to answer regards 



(3) The mode of origin of the stratification of the great tabu- 

 lar icebergs of the south. 



Supposing that each separate stratum, distinguished by 

 alternations of more or less clear ice, is the product of the 

 snowfall of a single year, Sir Wyville Thomson suggests the 

 following as the mode by which the lower strata may have 

 lost some of their original thickness: — "It is 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 submerged." 



Is this process of melting and regelation possible ? If we 

 consider the ice-sheet uniform in structure and at rest, it is 

 obvious that the pressure upon any given area of section will 

 be greatest at the bottom, where also the temperature will be 

 highest. Consequently, under these circumstances, the bot- 

 tom is the only place where the pressure would induce melting. 

 But it may be replied that the ice is not at rest, but is moving 

 outwards towards its free edge. And pressures in the hori- 

 zontal direction may be connected with this movement greater 

 than the vertical pressures due to the mere depth. It must, 



