VENTILA TION. 67 



materially affecting the air in the roof. The iron gratings at 

 a, which extend for nearly the whole length of the stable, 

 allow the vitiated air to escape, whilst the fresh air enters at the 

 air bricks below the manger in every stall. 



The air is sometimes admitted at this place through a per- Perforated 

 forated iron pipe, with inlets in the external wall running the P^P^s. 

 whole length of the stable at a height of about i foot 9 inches 

 from the ground. 



At the Corporation stables of the police at Aberdeen, the Head-post 

 fresh air is admitted to the stables through the head-posts of ventilators, 

 the traverses, communicating with a longitudinal duct of this 

 description ; the foul air being carried off through openings in 

 the ceiling, connected with Buchanan's current ventilator on 

 the ridge of the roof. 



Inventors have departed so widely from the simple laws of Boyle's venti- 

 nature before referred to, and first applied successfully to build- ^^^ors. 

 ings by the Haydens, of Trowbridge, that the success achieved 

 by Messrs. Boyle in the appHcation of their air-pump exhaust 

 and down-cast ventilators is not surprising. By means of an 

 ingenious bell-mouthed arrangement, a large body of external 

 air is collected and forced into active operation. It exhausts a 

 central chamber which terminates the outlet pipe ; and to supply 

 the vacuum formed by this means, the foul air from 

 the stable rushes up the shaft, and passes from ^^' ^ ' 

 the building. Fig. 38 shows the form of this 

 ventilator, which can be attached to the end of 

 a pipe, or affixed to the ridge, as illustrated on 

 Plate 9. 



It will be seen that this system is especially 11 |||| Ventilation 



adapted for the ventilation of those buildings, vZT/ of upper 



, - , . . - YITt floors, 



already described as consistmg of more than one 



floor, as horizontal flues, having openings in the 



ceilings, can be carried between the floors, passed up the 



walls, and concentrated in these extraction ventilators on the 



ridge ; by means of a divisional plate, the currents from the 



branches are prevented from striking each other, and possibly 



F 2 



