ICE. 353 



A. 1st Water is a very bad conduc- 

 tor, and is heated or chilled by CONVECTION 

 only : 



2ndly If the ice on the surface were 

 to communicate its coldness to the water 

 beneath, the water beneath must com- 

 municate its heat to the ice, and the ice 

 would instantly melt : and 



3rdly The ice on the surface acts as 

 a shield to prevent the cold air from 

 penetrating the river to freeze it below 

 the mere crust. 



Q. Why does WATER FREEZE at the SURFACE 

 first f 



A. Because the surface is in contact 

 with the air, and the air carries away its 

 heat. 



Q. Why does the coat of ice grow THICKER 

 and THICKER, if the frost CONTINUES? 



A. Because the heat of the water 

 (immediately below the frozen surface) 

 passes through the pores of the ice into 

 the cold air. 



Q. Why then are not WHOLE RIYERS FROZEN 

 (layer by layer) till they become solid ice ? 



A. Because water is so slow a con- 



Had 



