HOUSE HEATING 



403 



to any point desired, provided the heater is below the point 

 to be heated. Heat is transmitted by conduction, radiation, 

 and convection, but convection is the agent made use of in 

 carrying the air or water from the source of heat to the region 



After University of Minnesota 



Fig. 308. Circulation of air produced by a stove. The arrows indicate the 



direction of the air currents. 



to be warmed. The outside of a stove becomes hot from the 

 fire within, which heats the air in contact with it. This air 

 in turn becomes lighter, rises, and is replaced by cold air 

 from below and at the sides. This displacement of warm 

 air by cold air continues and produces currents as indicated 

 by the arrows in Figure 308. 



A clear idea of circulation or convection may be gathered 

 from a study of Figure 309, page 404. An open tube of water 

 is held so that the flame strikes it a short distance from the 

 bottom. At this point the water will begin to heat and 

 expand, will become lighter than the water above it, and so 

 will rise from M to N, and the cold water at N will flow down 



