of Glacier Motion. 161 



then restoring the continuity of the mass, and repeating the 

 operation, any amount of deformity could be produced. It 

 therefore follows that if it can be shown that constant lique- 

 faction and resolidification is going on within a glacier, we 

 have all the essential requisites for producing glacier-motion. 



It would be difficult to say which is the most interesting of 

 the numerous properties of water in its liquid and solid states. 

 We are in the habit of considering its freezing-point as being a 

 fixed temperature; but Professor W. Thomson proved experi- 

 mentally that the melting-point of ice is lowered by about the 

 seventy-fifth part of a degree Fahrenheit for every additional 

 atmosphere of pressure. That is, ice under a pressure of about 

 eleven hundred pounds per square inch melts at 31° instead 

 of 32° Fahr. Hold a slab of lake-ice in the sun's rays. The 

 heat attacks the ice in its interior and produces liquid flowers 

 of great beauty. Watch a flower as it develops ! Suddenly 

 a clink is heard, and a bright vacuous spot appears like a 

 silver bead in the centre of the flower. Before the spot 

 formed, the water in the cavity was in a state of tension, and 

 the clink heard was the vibration produced by the tension 

 overcoming the cohesion of the particles of water, and causing 

 rupture. A condition somewhat similar to that of tension, or 

 negative pressure, exists in water when freed from air and 

 heated in a bath of linseed-oil and oil of cloves. In this way 

 it has been raised, while under a pressure of one atmosphere 

 only, to a temperature of 356° F. Now 356° F. would indicate 

 a cohesive force equal to nearly ten atmospheres. The negative 

 pressure of the water formed by the internal melting of ice, 

 in the absence of air-bubbles, probably exceeds this amount. 

 If positive pressure lowers the freezing-point, negative pres- 

 sure should raise it. From this it follows that the water in a 

 liquid flower or glacier cavity is surrounded by and in con- 

 tact with ice sufficiently cold to freeze it directly the source 

 of heat which produced liquefaction is removed. Professor 

 Tyndall. placed some lake-ice containing cavities filled with 

 water and air in a warm-water bath. As soon as a cavity 

 was reached by the melting of its walls the inclosed air-bubble 

 at once shrank to a small proportion of its original volume, 

 showing that even in this case the freezing-point of the water 

 was above that of the surrounding ice. Other experiments 

 which it is needless to relate have been made confirming this 

 fact. 



During fine sunny weather, or even with warm rain, 

 glaciers have been shown to move more rapidly than when 

 the weather is cold and snowy; and if the glacier could be 

 cooled several degrees below the freezing-point, and shaded 



Phil. Mag. S. 5. Vol. 25. No. 153. Feb. 1888. M 



