264 WELLS'S NATURAL PHILOSOPHY. 



Fig. 222 represents the lines of the currents descend- FiG. 222 



ing the chimney and circulating round an apartment. 



Tj . A room Ls well ventilated by openinp: 



IIow IS a room j s. r> 



best ventUat- the upper sash of a window ; because 

 * tlie hot vitiated air (which always as- 



cends toward the ceiling) can thus escape more easily. 

 If the lower sash of the window be also partially opened, 

 a corresponding current of cold air, flowing into tho 

 room, is created, and ventilation ■will be so effected more 

 perfectly. 



,,^ Open fire-places are ill adapted for tho 



why are open i i . i 



fire-places ill economical heating of apartments, be- 



arlapted for cause the air which flows from the room 

 heating ? 



to the fire becomes heated, and passes 



off directly into the chimney, without having an oppor- 

 tunity of parting with its heat for any useful purpose. 

 lu addition to this, a quantity of the air of the room, j^w^w^'w^^r^ 

 ■which has been ■warmed by radiation, is uselessly carried | t 



away by the draft. j ' I 



The advantages of a stove over an [* ' 



■Wtat are the ^ i /• n i' i 



advantages and open fire-place are as follows: ^ f 



disadvantages 1. Being detached from the walls of 



of StOV6S ? 



the room, the greater part of the heat 



"»r-«ac ■>— gg f-T^st 



■^' 



produced by combustion is saved. The radiated heat 

 being thrown into the walls of the stove, they become hot, and in turn radi- 

 ate heat on all sides of the room. The conducted heat is also received by 

 successive portions of the air of the room, ■which pass in contact with the 

 Btove. 



2. The air being made to pass through the fuel, a small supply is suffi- 

 cient to keep up the combustion, so that little need be taken out of the 

 room; and 



3. The smoke, in passing off by a pipe, parts -with the greater part of its 

 heat before it leaves the room. 



Houses warmed by stoves, as a general rule, are ill-ventilated. The air 

 coming in contact with the hot metal surfaces is rendered impure, which in> 

 purity is increased by the burning of the dust and other substances which 

 settle upon the stove. The air is, in most cases also, kept so dry as to ren- 

 der it oppressive. 



591. The method of warming houses by the common hot- 

 What is the . . . . ,, a ^ i. • i i- ,- 



method of air furnace is as follows : — A stove, havmg large radiating sur- 



jranning by faces, is inclosed in a chamber (general) v of masonry). This 



hot-air fur- ' ^:^ . J / 



naees? chamber is frequently built with double walls, tliat it may be 



a better non-conductor of heat. A current of air from ■with- 

 out is brought by a pipe or box, and delivered under the stove. A part of 

 this air is admitted to supply the combustion ; the rest passes upward in the 

 cavity between the hot stove and the walls of the brick chamber, and, after 



