74 Ventilation with Heating. 



an enclosed space without an opening for its entrance, nor sent 

 into an enclosed space without an opening for its escape, we 

 need not give them any further consideration. The third plan 

 is wasteful and unscientific. It is wasteful of heat. The warm- 

 est being found at the ceiling will escape there, without benefit 

 to the audience below, no matter how that warm air is produced, 

 whether by hot water pipes, or heated air taken fresh from the 

 outside, or merely the foul air of the building passed over the 

 surface of a stove. The first act of such heated air is, to make 

 straight for the ceiling with a velocity in proportion to its height 

 of temperature. On its way upwards it mixes a little with the 

 cold air, warming it, and carrying it with it. The only part of 

 this warmed air which adds anything to the comfort of the 

 assembly, is the surplus which has not been hot enough and 

 active enough to escape by the openings in the ceiling. 



Suppose a building heated by a current of warm fresh air 

 introduced at the level of the floor, with openings in the ceiling 

 for the supposed exit of foul air. If these openings are capable 

 of discharging one half of the amount of hot air introduced, then 

 as the hot air rises immediately to the ceiling, and as the hottest 

 will rise fastest, and be the purest because it has lost the least 

 part of its heat by mixing with the contained air of the building, 

 the hottest and purest half of the hot fresh air introduced will 

 be immediately wasted. It can contribute nothing to the 

 ventilation, and very little to the heat of the room, though it 

 may heat the ceiling before it escapes. The other half of the 

 air will escape by seams in the windows, doors, and floor, and 

 that portion of it only which comes down to the level of the 

 assembly will be available [ for heating and respiration. It 

 seems doubtful if this plan of ventilation will give better results 

 than hot water pipes, or a source of heat that merely warms the 

 aerial contents of the building, mixing them all up into a homo- 

 geneous mass of foul air, and allowing a portion to escape at the 

 ceiling. By this method especially, if fresh warmed air is sent 

 in, very Httle of the respired and polluted air will get an oppor- 

 tunity of escaping by the outlets in the ceiling, the respired air 



