STABLES 75 



which air can enter are plugged, the chimney itself becomes an inlet at 

 intervals, and consequently sudden rushes of downward currents occur, 

 bringing with them a quantity of smoke; but when the inlet of air is 

 properly regulated and provided for, the open fireplace with its chimney is 

 undoubtedly a very useful method of ventilation. It may be urged that 

 the method is not generally applied to a stable, but in the case of new 

 constructions there certainly is no reason why it should not be, provided 

 that a suitable wire screen is placed around the hearth to prevent any risk 

 of straw, &c, catching fire. 



Extraction of air by a steam jet requires apparatus not in common 

 use, and is not likely to be employed for the ventilation of stables. 



Extraction by means of fans is a method which has been employed 

 successfully in the ventilation of mines, and to a smaller degree in 

 buildings, but the plan involves cumbersome machinery, and can hardly 

 be called a practical method of ventilation for stable use. The place of 

 the fan may be, to some extent, supplied by means of different forms of 

 cowls, the chief objection to which is their uncertainty, owing to changes 

 in the direction of the wind, and in perfectly calm weather the absence 

 of any currents in the outside air. These appliances, however, form part 

 of the apparatus used in so-called " natural " ventilation. 



Ventilation by propulsion, although a powerful method of delivering 

 a quantity of air, is not one which is likely to be generally used in 

 stables. According to Dr. Parkes, the plan is an old one, invented 

 indeed by Desaguiliers in 1734. The machinery consisted of a fan or 

 wheel, enclosed in a box. The air passed in at the centre, and was driven 

 by the vanes of the fan into a conduit leading from the box to the 

 building to be ventilated. The principle of this system, which is now 

 generally known as the " Plenum" system, is that of pressure from behind, 

 the external air being forced in at a pressure proportionate to the speed 

 of the revolution of the fan, thus driving out the fouler air through the 

 openings provided for the purpose. Where expense is no object the plan 

 is no doubt an effective one, as air can be passed through water and 

 thus washed, or through heated tubes and thus raised to any temperature 

 which may be desired, but in practice its use has hitherto been confined to 

 very large establishments, towmhalls, hospitals, &c. AVhere electric current 

 is available, an electric fan, which can be installed at a trifling cost, is the 

 simplest method of applying the system. 



It must be admitted that all methods of ventilation which necessitate 

 the use of special apparatus are encumbered by the objections that they 

 are costly and in various ways inconvenient. Among others is the 

 very important one, that skilled attendance is necessary. 



