STABLES 81 



construction; for example, the roof tiles may not be laid in mortar or 

 " torched " with mortar underneath, and the ceiling may be neither 

 plastered nor boarded. The result is that the warmth given off by the 

 horses is rapidly dissipated, and in winter the stable is much too cold while 

 in summer it may be too hot. Tiles laid in the way described above do 

 indeed allow a constant passage of air, and are therefore useful for 

 ventilation, but the ventilation is not (as it ought to he) under control. 

 The windows which have been recommended can be opened and closed at 

 will, and the exhaust ventilators are fitted with valves, operated with 

 cords and pulleys, and by these means the inlet and outlet of air can be 

 controlled. 



According to the table, 15,000 cubic feet of air are required by each 

 horse per hour. If the velocity of the air entering the stable is 2 feet per 



second, the size of the inlet opening must be ^ — ^r, — ^ = 2-^ sq. feet. 



This area would be provided by a window 3 feet wide, opening to the 

 extent of about 8 inches. If the windows on the opposite sides of the 

 building — that is to say, two for each horse — are of this size, the required 

 amount of air will be admitted when only one is open. To prevent 

 excessive velocity in the inflowing air, the top of the opening of the hopper 

 is sometimes covered with finely-perforated zinc, but this necessitates a 

 larger opening, as the effective area is reduced about onedialf by the metal 

 gauze. 



A higher velocity may be allowed for the air escaping through the 

 exhaust ventilator, (say) 5 feet per second, and on this basis the area 

 required for each horse will be f sq. foot. A ventilator with the internal 

 circular shaft 20 inches in diameter would, therefore, serve for three horses. 



In practice the areas of inlets and outlets are often less than those 

 given above, as a certain amount of ventilation takes place through the 

 walls and roofs and through open doors, and somewhat higher velocities 

 are considered to be admissible. 



When all is done, however, there are many days in our variable climate 

 when it is impossible with safety to provide by the system of " natural " 

 ventilation the full amount of fresh air which is theoretically required. 

 The cold draughts which would follow the attempt would be dangerous to 

 many animals, and the choice must be made between the two evils of cold 

 draughts and insufficient ventilation. In nine cases out of ten the latter 

 will be considered to be the less of the two. 



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