QUANTITY AND TRANSMISSION OF HEAT 149 







different rooms. In large systems fans are used to 

 supplement the convection currents, thus insuring a more 

 even distribution of heat in the building. 



The Thermostat. The thermostat is an instrument 

 used to regulate the temperature of rooms arid buildings. 

 Figure 130 shows the working principle of a simple form of 

 thermostat. The vertical bar is a part of two electric 



FIG. 129. Hot-wat2r System for House Heating. 



circuits. The uneven expansion and contraction of the 

 two elements of the compound bar throws the vertical 

 rod against A when the room becomes too hot and against 

 B when it becomes too cold. Electromagnets in the two 

 circuits control the supply of steam, hot water, or hot air 

 to the different rooms and thus regulate the temperature. 

 Ventilation. Since the lungs are constantly exchang- 

 ing large quantities of air laden with carbon dioxide for 

 oxygen, it is necessary that the air in the rooms in which 



