SCIENCE OF COMMON THINGS. 217 



Use of a blower upon a grate. Hottest arid coolest portions of a room. 



wind) would fall down the fiue, and drive the smoke 

 with it into the room. 



1444 Why do some chimneys smoJce ? 



Because fresh air is not admitted into a room as fast 

 as it is consigned by the fire ; in consequence of which 

 a current of air rushes down the chimney to supply the 

 deficiency, driving the smoke along with it. 



1445 Why do Mowers, when placed before a grate, tend to kindle the 

 fire? 



A blower is a sheet of iron that stops up the space 

 above the grate bars, and prevents any air from enter- 

 ing the chimney except that which passes through the 

 fuel and produces combustion. This soon causes the 

 column of air in the chimney to become heated, and a 

 draught of considerable force is speedily produced 

 through the fire. The increase of draught increases the 

 intensity of the lire. 



1446 Which is the hottest part of a room ? 



The upper part, near the ceiling. The warm air 

 being the lightest seeks the highest position. 



1447 Which is the coolest part of a room f 



The lowest part, near the floor. Cold air being dense 

 and heavy seeks the lowest position. 



144S By which means is a room better ventilated, by opening the uppef 

 or the lower sash ? 



A room is better ventilated by opening the upper 

 sash because the hot vitiated air (which always as- 

 cends towards the ceiling) can escape more easily. 



1449 What temperature is most proper for keeping an apartment in 

 a healthy and pleasant condition during the cold season f 



From 65 to 70 F., with a free ventilation. 



1450 How are houses and other buildings heated with hot air f 



The fire is kindled in a furnace which is erected in 

 the cellar. This fire heats the air in contact with it in 

 the air-chainber, as it is called, and as heated air 

 always ascends, it is forced up into the different apart- 

 ments of the building. 



