No. 4.] STABLE VENTILATION. 113 



The first of these forces is the chief one of the artificial 

 system of ventihition, where heated air is used in flues to 

 remove the foul air, and to ])ring in pure air to take its 

 place. Its action is based upon the fact that heated air is 

 more rarefied and lighter than cold air, and therefore has a 

 tendency to rise above it. In artificial systems of ventila- 

 tion, heaters, radiators, steam coils, etc., are placed at the 

 bottom of flues, which have openings into the rooms which 

 are to be ventilated, to create an upward and outward cur- 

 rent of heated air, which draws the foul air out, while the 

 pure air is introduced into the room through some other 

 opening. 



In natural ventilation, as in the ventilation of stables 

 where artificial heat is not used, we get considerable benefit 

 from the action of this force, the heat being derived from 

 the bodies of the animals. It is the force that takes the ex- 

 pired air from the animal. It causes upward currents in the 

 centre of the building, and, if there are suitable openings 

 above and below, the vitiated air escapes. In case no 

 openings exist above, the air cools from contact with the 

 ceilings and walls and again settles to the floor. The 

 currents which arise from this cause also assist in keeping 

 the air in a tightly closed stable or occupied room thoroughly 

 mixed and of even quality. Without suitable inlets for the 

 admission of pure air, or outlets for the escape of the foul 

 air, this force can do but little more than keep the air in a 

 well-mixed condition. The beneficial effects of this force are 

 frequently lost on account of the outlets being so fiir above 

 the floor. When such is the case, the warm air leaving the 

 body of the animal becomes cooled to such an extent that it 

 becomes heavier than the air below, consequently tends to 

 fall, displacing that below. 



In high, old-style stables, used for both storage and sta- 

 bling purposes, with high beams above the main floor and a 

 single large cupola opening in the roof, it frequently happens, 

 in cold weather, that little or no foul air escapes through the 

 cupola opening, owing to the fact that the upper i)ortion of 

 the building is filled with air that has become so much cooled 

 from contact with the exposed roof and walls that the tem- 

 perature of the rising warm current is lowered to such an 



