CHAP, ii.] TUP: ART OF WARMING. 349 



CHAPTEI! II. 



THE ART OF WARMING HEATING APPARATUS. 



I. HEATING BY HOT AIR. 



THE name " Heating Apparatus " must be kept for such arrange- 

 ments as are designed to communicate to a distance the heat that 

 is generated by combustion in a grate, and to spread it through 

 a certain number of apartments, distinct from that in which the 

 apparatus is fixed. 



Some of them have more or less of a resemblance to ventilating 

 fireplaces or stoves provided with inner chambers and openings 

 for the hot air, since they too carry hot air to the various rooms 

 that have to be warmed. These are hot air heating apparatus. 



Others are constructed upon a different principle. The vehicle of 

 the heat generated in the grate is in this case water, which, warmed 

 by contact with it, circulates through conducting pipes in the thick- 

 ness of the walls to all the places where the temperature is to be 

 raised. These are the hot water heating apparatus. 



And lastly there is a third system, in which the heat from the fire 

 is made latent in the vapour of boiling water, which, by circulating 

 in the conducting pipes, is cooled, condenses, and yields up all the 

 heat given out by condensation to the surrounding objects and to the 

 air in contact \tfith them. These are steam heating apparatus. We 

 will pass successively in review the apparatus of these three systems, 

 and note their respective advantages and drawbacks. 



The grates of the hot air apparatus are generally fixed in the 

 cellars of .the buildings they are required to warm, and in the centre 

 of a chamber, the air of which is renewed by an opening from the 

 outside, which has no direct communication with the fire itself, so 

 that the smoke and other gaseous products of combustion have no 



