GREENLAND OR POLAR ICE, 271 



nately, however, the sun became obscured before 

 it was completed, and never made its appearance 

 again for a fortnight, during which time, the air 

 being mildv the lens was spoiled. 



The most dense kind of ice, which is per- 

 fectly transparent, is about one-tenth specifically 

 lighter than sea-water at a freezing temperature. 

 Plunged into pure water, of temperature 32°, the 

 proportion floating above to that below the sur- 

 face, is as 1 to 15, and placed in boiling fresh 

 water, it barely floats. Its specific gravity is 

 about 0.937. 



Fields, bergs, and other large masses, chiefly 

 consist of this kind of ice. Brash-ice likewise 

 affords pieces of it, the surfaces of which are al- 

 ways found crowded with conchoidal excavations 

 when taken out of the sea. 



On the Formation of Ice on the Sea, 



Some naturalists have been at considerable pains 

 to endeavour to explain the phenomena of the 

 progressive formation of the ice in high latitudes, 

 and the derivation of the supply, which is annually 

 furnished, for replacing the great quantities that 

 are dissolved and dissipated by the power of the 

 v/aves, and the wartath of the climate into Vv^hich 

 it drifts. It has frequently been urged, that the 

 vicinity of land is indispensable for its formation. 



