78 YETEEINAEY HYGIENE 



enough and close enough to prevent rain drifting through; 

 the angle these boards are placed at is of far less importance 

 than their -width. 



As a means of ventilation the ridge is excellent ; as it 

 is desirable extraction should always take place at the roof, 

 fixed cowls on the ridge would be better than louvre boards 

 for small but not for large stables, as with the latter a 

 sufficient number could not be employed. 



The strong argument in favour of the open ridge with 



M i L - aj \i _ 



J 



Fig. 20. — Ventilating stable pillar on the principle of a Tobin's tube. 



louvre boards is that it cannot be closed, and this in the 

 case of large stables may be a great advantage, for even 

 if all doors and windows are shut the ridge both admits 

 and discharges air (Fig. 10, p. 72), and this it could not 

 do if only fixed extraction cowls existed. 



The relative size of inlets and outlets has been much dis- 

 cussed. It has been said that the outgoing air being 

 lighter, and thus occupying more space, the outlets should 

 be larger than the inlets ; as a cubic foot of air only 

 expands tV of its bulk for 30° Fahr., it is obvious 



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