ioo Applications oj the Formulas 



time, we may heat it by warm air alone or by warm air and radi- 

 ation ; in both cases the loss of heat is made up of that trans- 

 mitted by the windows and that absorbed by the walls. 



The heat received by the walls through radiation or through 

 the currents of air cooled by contact with their surfaces, is propa- 

 gated step by step throughout their thickness according to 

 extremely complicated laws. When the air of the room has been 

 brought to a certain temperature and the heating ceases, the cool- 

 ing of the air takes place with rapidity, because the heat is 

 absorbed by the walls and windows, not alone by the air contact 

 action but also by the diffusion of the heat through the mass of 

 air; thus, to maintain the air at a sensibly constant temperature, 

 the heating must be continuous. 



