Ventilation. 47 



large cowl, which forms an effective inlet 

 when it is kept trimmed to the wind. If 

 the cowl is turned in a direction opposite to 

 that of the wind, it will generally act as an 

 outlet. We may often beneficially employ 

 one of two adjacent ventilators in the former 

 way, and the other in the latter manner. 

 Cowl ventilators are sometimes provided with 

 an arrangement which prevents water going 

 down them, but which offers no impediment 

 to the entrance of air. 



Exhaust fans are worked either by steam 

 or electricity ; the latter being the better 

 form of propelling force, because its conduct- 

 ing wires are free from the objection possessed 

 by the pipes which convey steam, of raising 

 the temperature of the stalls near which they 

 pass, and of thus endangering the health of 



