344 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK iv. 



In the other form of fireplace the grate is an apparatus of cast- 

 iron, and the flue is divided into several passages, along which the 

 warm gases pass. Thus the whole apparatus helps to warm the 

 chamber into which the outer air is received, and this, escaping into 

 the room by two lateral openings, after having its temperature raised 

 by contact with the sides of the apparatus, assists at the same time 



FIG. 237. Ventilating fireplace, on Joly's system. 



in warming and in ventilating the apartment. The heating effect 

 of ventilating fireplaces is considerably greater than that of ordinary 

 ones. It may reach as much as 30 per cent, of the heat developed 

 by the combustion. 



IV. STOVE?. 



Stoves only differ in reality from fireplaces in this one respect. 

 They are warming apparatus placed in the middle of the room that 

 has to be warmed, instead of being set back against, or even ensconced 

 in, the masonry of the walls. The consequence is that the warmth 

 of its sides is communicated in every direction to the air of the room 

 by radiation ; and in this way the heat of the grate is much more 

 completely utilised. The principle of the draught is the same, but 



