Proceedings of the Polytechnic Association. 725 



quantity of fresh air required, whatever may be the height from which 

 it has to he drawn, and whatever the quantity, can be obtained by 

 suction alone, and without the aid of any blowing; apparatus, by 

 giving to the inlet openings for the fresh air sufficiently large 

 dimensions, and placing them in suitable positions. Suctions can be 

 easily obtained either by means of open fireplaces with chimneys, or 

 similar heating apparatus, or by means of special fireplaces placed at 

 the bottom of the exhausting flues, and acting as auxiliaries when 

 the rooms are large. The air to be removed ought to flow toward 

 the bottom of these firepLices, and, whenever possible, by means of 

 special air-flues leading from openings close to the sources of ventila- 

 tion. Ventilation by suction through fireplaces and chimneys can 

 be adapted to the proportions and arrangements of every kind of 

 room, as it resembles the ordinary and natural ventilation of rooms, 

 and the volume and temperature of the fresh air can be varied as 

 required. It is only necessary to construct at small expense fire- 

 places with thin chimneys and air-flues, which, when completed, cost 

 but little for repairs, and to supply the fireplaces with fuel, which 

 any common attendant is competent to do. On the contrary, 

 ventilation by means of blowing and other mechanical apparatus, 

 necessitates, beside the flues and chimneys common to both systems, 

 the addition of blowing machines and engines with special air- 

 passages, special artisans, engineers, and firemen, and involves an 

 extra cost for keeping up. Besides this system does not afibrd the 

 same guarantee as that of suction, against difi'erence of vitiated air, 

 especially in hospitals several stories in height, where it may pass 

 from one room into another thi'ough the openings of the discharging 

 flues, when it happens that the pressure and movement of the air oi 

 a room are disturbed by the openings of doors or windows. 

 There ma}^ be special cases where it would be advantageous to use 

 meclianical apparatus in connection with suction ; for instance, where 

 the quantities of air to be removed difier greatly from one day and 

 from one hour to another, as in the case of St, George's Hall, 

 Liverpool, in which mechanical ventilation exclusively is used, and 

 the quantity of air required varies in the extreme proportion of one 

 to fifty. The following proportions for the quantity of air required 

 to be supplied j96r hour for each person are based on the results of a 

 large number of experiments by difterent observers, and although 

 larger than the rates formerly adopted, are not, in Gen. Morin's 

 opinion, at all exaggerated : 



