85 



(c) Snow and ice. Compare snow, ice and water. Meaning of 

 frozen. Compare, snow, ice and hail. Uses of snow and 

 ice. Relations. 



Snow a warm covering for plant and animal life, poor 

 conductor of heat, prevents radiation of heat. Ice a protec- 

 tion to fish in rivers and lakes. 



ATMOSPHERIC PRESSURE. 



1. Air Presses Equally in all Directions. 



(a) Fill a glass with water. Press a blotter down on the top of it; 



invert the glass; turn in all directions. What causes the 

 blotter to remain? 



(b) Cut a circle from a soft piece of leather; draw a cord through 



a hole in tlie center, making it air tight; wet the leather; 

 press it on a slate or smooth stone, forcing all the air out. 

 Suspend slate by the string. What prevents it from fall- 

 ing? 



(c) Boil an egg hard. Remove the shell. Heat a bottle whose 



opening is almost the size of the egg. Put the egg in the 

 opening and put in a cool place. What forces the egg into 

 the bottle? 



(d) Weigh a corked test tube filled with air. Remove the cork 



and heat the test tube. Recork while hot and weigh. What 

 caused the difference in weight? 



(e) Fill a glass tube closed at one end with water and place open 



end under the surface of a vessel of water. What supports 

 the column of water? 



2. Variation of Pressure. 



(a) Altitude. 



(b) Latitude. 



(c) Amount of vapor contained. Consult barometer. 



3. Pumps. 



Relation of pressure of atmosphere to lifting pump. Construc- 

 tion, action and uses of lifting pump. Windmills. 



Relation of pressure, compressibility and elasticity of atmosphere 

 to force pump. Uses of force pump. 



4. Siphon. 



Formation of siphon, action, uses. Conducting water, emptying 

 casks, etc., flow of springs. 



HEAT. 



Expansion and Contraction, 

 (a) Gases air wind. 



