Chemical and Physical Notes 49 



not hard and brittle but soft and yielding, and this is seen 

 when the sea freezes in polar regions. The difference between 

 land-ice and sea-ice is one of degree and not of kind. Sea-ice 

 is mixed with mucJi brine and flows easily : land-ice contains 

 little brine and flows with difficulty. 



A ship floats in the smallest basin as perfectly as in the 

 largest ocean. We can imagine a dock being built round 

 a ship, and so exactly moulded to its shape, that between the 

 inner surface of the dock and the outer surface of the ship, 

 the clearance shall be so small that a pitcher of water poured 

 into it will float the ship. The floating of a grain in the 

 inside of a glacier is of this kind, and as it is enclosed on all 

 sides, it will press against the ice above it in preference to 

 that beneath it. 



This feature of glacier-ice permits us to understand how 

 glaciers can move, and begin to move, even when their 

 temperature is very low. Before von Drygalski's work on 

 Greenland, we had no trustworthy information regarding the 

 temperature throughout the year of the inner mass of the ice 

 of any glacier. He carried out, at regular intervals of time, 

 a series of observations of the temperature at different depths 

 below the surface of one of the Greenland glaciers, and parallel 

 observations within the ice covering a neighbouring lake. 

 These observations showed that the temperature of the glacier 

 increases rapidly from the surface downward, and they render 

 it probable that the greater part of the thickness of a Green- 

 land glacier is, even at the coldest time of the year, at or near 

 the ordinary temperature of melting ice 1 . The heat required 

 to support this temperature can only be supplied by the 

 friction of the grains of the ice, called into being by the 

 motion of the glacier. The inland ice which forms the great 

 reservoir for the supply of the glacier was found to have little 

 or no appreciable motion. Series of temperatures were not 

 taken in its thickness, but, in the absence of motion, we may 

 believe that the very low temperature at its surface penetrates 

 far into its interior, if not to the very bottom. If the motion 



1 Compare Hugi, Ueber das Wesen der Gletscher und Winterreise in das 

 Eisnteer, p. 51. 



B. 4 



