METHODS OF HEATING BODIES 245 



Place your hand on the windowpane, then on the wood 

 of the window sash. Which conducts heat from your 

 hand more rapidly? Since these are side by side in the 

 room they are at the same temperature. The glass feels 

 colder because it takes the heat out of your hand so rapidly. 

 Which is the better conductor of heat, oilcloth or carpet? 

 Why are woolen clothes warmer than cotton? Have the 

 pupils make a list of good conductors of heat and of poor 

 conductors. 



While many solids are good conductors of heat, liquids 

 and gases are very poor conductors. Air is among the 

 poorest conductors known. Can you think of any prac- 

 tical application of this fact? Double windows make a 

 room warmer, not so much because of the extra panes of 

 glass but because of the layer of air between the two sashes. 



Since air is such a poor conductor, do you think it 

 would be possible ever to heat a room comfortably from a 

 stove standing in one corner or in the middle of the room 

 if there were no other method of heating ? How is a room 

 heated ? 



Light a piece of punk or a candle. A piece of punk is 

 better but a candle will do. When the punk is smoking 

 well, hold it a few inches from the stove, first on one side 

 and then on another. Does the smoke or candle flame in- 

 dicate any movement of air ? How is the air moving at the 

 sides of the stove ? Above the stove ? Halfway between 

 the stove and the wall of the room? In the corner of 

 the room ? Tie the punk on the end of a pointer or long 

 stick and note the movement of the air near the ceiling in 

 different parts of the room. Is the movement of the colder 

 air toward the stove or away from it ? What is the direc- 



