PHYSICS 



refrigeration. The lake-ice often showed a banded appear- 

 ance resembling this, and the greater or lesser abundance 

 of air-bubbles set free from the frozen water and included 

 in the ice is due to a similar cause. The banding in the 

 sea-ice is due to an alteration of more and less opaque 

 layers of ice, of half an inch to several inches in thickness. 

 The sea salt mechanically separates from the ice as the 

 latter forms and is partially forced out into the sea water 

 below, and partially included in white vertical tracts 

 between the ice prisms. When the unfrozen sea surface 

 is agitated by winds at very low temperatures, the spray 

 is apt to freeze as it scuds through the air and it falls back 

 as ice. In this way the whole surface of the sea may 

 assume a pea-soup-like consistency. Strong winds, pro- 

 ducing a swell, may break up the solid sea-ice and drive 

 it along as a field of separate floating masses. This is 

 termed pack ice, and may eventually become frozen 

 together as an irregular surface field of ice. In cases of 

 this kind huge ice-bergs are not infrequently found frozen 

 in amongst the smaller ice. Where the wind drives floe 

 ice before it, pressure ridges may be formed by the mount- 

 ing of some of the ice upon that in front; fragments may 

 be piled up to many feet in height, an operation usually 

 accompanied by a great crunching and grinding noise. 



During the autumn, sea spray, dashing on the coast, 

 remains behind as ice. Thus a huge ice-foot develops 

 along the coast. Grottoes are not uncommon in this ice- 

 foot, resembling limestone caves of remarkable beauty, 

 filled with stalactites (up to several feet in length), and 

 stalagmites of ice. These owe their origin largely to the 

 fact that the more saline residual water dripping from the 

 roof is further chilled by exposure, and thus continual 

 additions are made to the formations from which the drip 

 has taken place. The water is highly saline and stalag- 



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