DOWNWARD SYSTEM OF VENTILATION. 767 



This, with more unfavourable conditions than can ever 

 obtain in domestic ventilation, and only rarely in the case of 

 public buildings ; for it is but seldom our halls are 80 feet in 

 height, and they are rarely in New South Wales surrounded 

 by an atmosphere at a temperature of 32° Fahr. : yet under 

 these circumstances fans working with the easily obtained 

 pressures of from two to three inches of watei' only have about 

 one-sixteenth to one-twentieth of their power employed in over- 

 coming that of the heated air. But in winter, when the room 

 has to be heated by artificial means, there is a decided 

 advantage in the downward system ; for the means of warming- 

 adopted universally in this country is the open fireplace, which 

 forms a most powerful exhaust at the floor level, just where 

 the system requires it, and we thus have in the open fireplace 

 a most valuable help towards efficient ventilation, both fire 

 and fan mutually assisting one another in accomplishing the 

 work that has to be done. 



Very different is it when a fire is burning in a room 

 ventilated by the upward system of ventilation ; we then 

 have the ludicrous spectacle of the ventilator pulling the air 

 at the ceiling, and the fire at tiie floor level — acting one 

 against the other to the detriment of both, and the great 

 inconvenience of the occupants. 



Another j)oint in favour of the downward system is that 

 in summer when the air in the room is naturally cooler (and 

 should for comfort be kept cooler), and therefi)re of greater 

 specific gravity than the external air, the natural movement 

 is downwards, and the niechanical ])0wer is then employed 

 only in assisting the natural laws. 



The downward system would also ])revent, to a considerable 

 extent, any inconvenience being felt from di'aughts through 

 crevices round doors and windows during strong winds : for 

 the pressure exerted by the fan would, under all ordinary 

 conditions, tend to force the air of the room outwards through 

 the crevices. The great discomfort experienced by all who 

 have had the misfortune to sit near a door in a crowded hall 

 on a cold night would also be avoided, for just as in the 

 upward system the air chooses the jiatli of least resistance 

 into the hall through the open door, so it would choose the 

 same ])ath in going out in pi-eference to passing through the 

 outlets provided at the floor level when the air is supplied at 

 the ceiling level ; and the air which would thus ])ass out 

 being of the same temperature as the air of the room, no 

 mconvenience would be created ; for the same reason no 



