ICE. 355 



A. Because the frosty air is at least 

 10 or 12 degrees colder than the water. 



(The water below the surface is at least 42o ; but the 

 air 82o, or even less.j 



Q. Why is SHALLOW water FROZEN QUICKER 

 than DEEP water ? 



A. Because (as the whole volume of 

 water must he cooled to 42 degrees 

 before the surface can be frozen} it will 

 take a longer time to cool down a deep 

 bed of water than a shallow one. 



Q. Why is SEA-WATER RARELY FROZEN ? 



A. 1st Because the mass of water 

 is so great that it requires a very long 

 time to cool the whole volume down to 

 42 degrees: 



2ndly The ebb and flow of the sea 

 interfere with the cooling influence of the 

 air: and 



3rdly Salt never freezes till the sur- 

 face is cooled down at least 25 degrees 

 below the freezing point. 



Q. Wliy do some LAKES RARELY if ever 



FREEZE ? 



A. 1st Because they are very deep : 



2ndly Because their water is supplied 



by springs, which bubble from the bottom. 



