36 Ventilation and Heating 



charges freely the hot air into the building. The outlets for 

 the cold air are through the floor, numerous and moderate in 

 size, opening into a flue below the floor, and carried to an up- 

 right flue, ending at or above the top of the building like a 

 chimney. The expected result from this arrangement, tracing 

 the air from its inlet, is — the air being admitted below the level 

 of the heating apparatus — none of the heated air is likely to 

 escape from a blow-down ; — also, having a flue full of heated air 

 of considerable height, force is added to the current in pro- 

 portion to the height. When discharging into the church 

 according to the law of lighter fluids, it will float on the colder 

 air, forming a sheet of warm air close under the ceiling. This 

 will constantly be supplied and displaced downwards by the 

 continuous flow of hot air from the flue, until ultimately all the 

 original cold air is displaced by the warm air. While this is 

 going on above, the coldest air is continuously being driven 

 down through the openings in the floor, carried through the 

 horizontal flue to the upright one, where, still having some 

 ascending power from the remains of its heat derived from the 

 apparatus and that added to it by the assembly, it will assist in 

 keeping up the circulation. The draught towards an outlet for 

 air is of a very different nature to that from an inlet, being more 

 diffused and tending to flow in radii towards the centre, namely, 

 the outlet. Those from an inlet may pass for a considerable 

 distance in an unbroken stream, and, if passing in with much 

 velocity, may stir up a wide area of draught by its friction. 

 This may be observed on a stormy night by opening a window 

 half-an-inch wide when the wind is blowing against it : this 

 will stir the whole air of a moderate sized room so that a draught 

 may be felt in almost any part of it. The two flues, when no 

 heat is being used, would still act to some extent as ventilators. 

 In the case of a room full of people, if there were only a very 

 slight current at first, it would soon increase by the heated air 

 from the assembly passing up the outlet flue, the pure cool air 

 being, as it were, pulled in up the inlet flue. The air in the 

 building should be as much as possible under the same condi- 

 tions as in that a diving-bell, where the only escape is at the 



