232 



PNEUMATICS. 



VENTILATION. 



Impure air may be breathed for a short time with- 

 out any serious detriment, but to live in it and respire 

 it for years can not fail to produce permanent injury to 

 the health. During the heat of summer, open doors 

 and windows will usually furnish plenty of fresh air, 

 as long as this season lasts, which in the Northern 

 States is not one half of the year. During the rest of 

 the time rooms are heated with close stoves, and unless 

 special care is taken to secure fresh air, pale or sickly 

 inmates will be the most likely results. 



Even with a common open fire-place, which causes 

 more circulation of the air in a room than stoves, the 

 ventilation is very imperfect. The following figure 

 {Fig: 196) represents the fresh air as passing in from 



Fig. 196. 



A badly-ventUated Room. 



an open window opposite the fire, producing a direct 

 current from the window to the chimney, and leaving 

 all the upper portion of the room filled with bad air, 

 unaffected by the change. The cold air can not rise, 

 nor the hot air descend. This difficulty may be easily 



