416 



ICE PHENOMENA. 



visible stretching and expanding of the field-ice, generally towards 

 the shores of the lake and of islands. The movement of the ice is at 

 times very gradual, and is accompanied by a slight crackling noise. 

 Again the expansion is rapid and violent, the movement being by a 

 succession of vigorous jerks accompanied by a hollow rumbling sound, 

 seemingly from under the field-ice, while at intervals there occur sharp 

 loud reports like that of cannon. 



That ice does expand under such circumstances is very evident, as 

 it may be seen creeping many feet on to the shores, without the appear- 

 ance in the lake of any compensating fissures whatever. Ice may 

 therefore be said to expand by a high temperature, that is, by a tem- 

 perature higher than that which had just previously existed. The 

 phenomena of ice contracting and expanding at the same temperature 

 on different occasions is sometimes witnessed. For instance, should 

 the thermometer indicate a temperature of minus 30^ and then sud- 

 denly rise to" zero, expansion would immediately be the result ; again, 

 should the temperature indicate plus 30° and suddenly fall to zero, 

 contraction of the ice would speedily follow. The force and violence 

 with -which ice expands or shoves depends entirely on the extent of the 

 change of temperature. The most violent shoves of ice occur previous 

 to rain storms. A rise in temperature of 20° or upwards produces 

 violent expansion. Various instances may be cited of the effects pro- 

 duced by ice when expanding ; evidence of its power is very indelibly 

 written on parts of the Railway Bridge before mentioned. Portions 

 of this structure on piles have been, for long distances, bent and 

 inclined even to an angle of 45° in a most uniform and extraordinary 

 manner. Strong oak piles that would not bend have been cracked 



and splintered, hundreds of heavy cap timbers of sound pine have 

 been snapped across like reeds, and heavy iron rails have been curved 

 and doubled up, by the almost irresistible pressure of the ice. 



