18 



ELEMENTS OF GENERAL SCIENCE 



in the cooler parts of the room, only to flow across the floor 

 toward the source of heat, where it will again be warmed 

 and be pushed up. Thus the circulation continues. Currents 

 of air that are caused by differences of temperature, such 

 as the currents of which we have been speaking, are called 



convection currents. 



16. Stoves, furnaces and 

 water heaters. The circula- 

 tion of air in hot-air heating 

 apparatus such as is com- 

 monly used in private houses 

 is maintained by convection 

 currents. The heater is located 

 in the lowest part of the 

 house, usually the basement, 

 and is surrounded by a jacket 

 which incloses a heating cham- 

 ber. Cold air is admitted to 

 this chamber from outdoors 

 through a large pipe, is ex- 

 panded by heating, is pushed 

 up through the pipes leading 

 from the top (Why?) of the 

 air chamber to the various 

 rooms of the house, and es- 

 capes out of doors through 

 available openings. In some 

 cases the apparatus is so 

 arranged as to take cold air from within the house, as from 

 the front hall, instead of from without, but this arrangement 

 is not desirable except as an emergency device in exception- 

 ally cold weather. In the latter case the same air is passed 

 through the rooms repeatedly, while fresh air from outdoors 

 esirable. The movements of hot and cold air and water 

 e well shown in cookstoves and water heaters (fig. 16). 



FIG. 17. Diagram showing end vie 

 of cookstove shown in figure 16 



