THE AIR AND VENTILATION 22Q 



lion toward the warmer air of the ceiling. There it will become warm, 

 and finally will spread through the room like a gentle shower, instead 

 of in a rushing stream. 



A modification of the same idea is to raise the lower sash a few inches 

 and insert a narrow board in the lower opening, so that a space is left 

 between the sashes for the entrance of fresh air. The opening for fresh 

 air may be through the floor under the stove, and thus the air will be 

 heated as it enters the room. An open fireplace produces an upward 

 current of air. An opening into the chimney flue near the ceiling will 

 :arry off much of the foul air. 



In many churches a small part of the window is hinged so that its 

 top can incline inward. If the window is placed about two thirds of 

 the way between the floor and ceiling, the warm air will pass out above 

 the window, while the cool, fresh air will enter below it. The inclina- 

 tion of the window will cause the air to flow toward the ceiling at first, 

 where it will be warmed and scattered so tnat it cannot produce drafts 

 upon the heads of the listeners. The addition of an opening in the 

 center of the ceiling for the escape of the warm air forms an efficient 

 mode of ventilation. 



Hot air registers both heat and ventilate a room, if care is taken to 

 admit fresh air to the pipes. The hot air passes up from the furnace 

 because it is lighter than cold air. An opening in the window or into 

 the chimney is needed to allow the air of the room to escape, so that 

 the warm fresh air can enter. 



Since on a cold day the air inside a room is much warmer than the 

 air outside, a current of air will rush through every crack, so that 

 good ventilation will be secured by a very small opening. Since on a 

 warm summer's day the air inside and outside is nearly of the same 

 temperature, large openings are necessary to effect the change of air. 



400. Forced ventilation. In large buildings, such as factories 

 and theaters, warm fresh air is forced into the rooms by rotary fans, and 

 the impure air escapes through openings in the ceiling. Thus the 

 amount of heat and air admitted can be exactly regulated. 



Another way of ventilating large houses is to suck out the impure 

 air by rotary fans, while fresh warm air is admitted through small open- 

 ings near the floor, thus preventing drafts. This method is being 

 adopted in large buildings to the exclusion of other methods. 



401. Filtration of air. In forced ventilation the air is con- 

 ducted through a large box, which has partitions arranged so as to 



