:J58 Rural Architecture. 



mit the warm air to rise so far above the animals as to leave 

 the stable cold at the floor. 



443. Forces Which Produce Ventilation. The movement 

 of air currents into and from a ventilated stable is caused 



1. By the wind pressure against the building tending to 

 force air into the stable. 



2. By wind suction on the leeward side of the stable 

 tending to draw air out. 



3. By aspiration across the top of the ventilator. 



4. By the difference in temperature between the air 

 in the stable and that outside. 



When the wind is blowing against a building there is an 

 increase of precsure above that inside which forces air into 

 the stable through any available opening and then out 

 again on the opposite side or up the ventilating flue. At 

 the same time there is a low pressure on the lee side which 

 tends to draw air through any openings on that side. 



Where the ventilator rises above the roof as a chimney 

 does the movement of air across its top produces a di- 

 minished pressure and the air is aspirated out on the prin- 

 ciple of the aspirator used on perfumery bottles. 



The difference of temperature causes a difference of 

 pressure because of the expansion making the air in the 

 stable relatively lighter than that outside ; and the longer 

 the chimney or ventilating flue the stronger will be the 

 draft, both from difference of temperature and the aspi- 

 ration across the top of the chimney. 



444. Essential Features of a Ventilating Flue. A good 

 ventilating flue must have all of the characteristics pos- 

 sessed by a good chimney. It should be constructed with 

 air-tight walls so that no air can enter except from the 

 stable. It should rise above the highest portion of the 

 roof so as to get the full force of the wind. It should be 

 as nearly straight as practicable and should have an ample 

 cross section. Stronger currents through the ventilators 



