Proceedings of the P olytechnic Association. 727 



the abstraction of air sliould, on tlie contrary, be placed generally in 

 the lower part of the room. 



The velocity of the vitiated air, in its passage outward, should 

 continually increase through the several passages of the building, 

 which is best effected by the use of a single shaft. On its entrance 

 the air should move about three feet per second, and at its exit about 

 six feet. An excess of seventy to eighty degrees Fahrenheit, in the 

 temperature of the dischargihg shaft over that of the external air, 

 will, in most cases, produce the required increase of speed; but in 

 theatres, where the passages for air must be .complicated, a difference 

 of temperature of ninety-five to one hundred and five degrees Fah- 

 renheit is required to effect the desired result. When the supply 

 openings are on the side of the room at a considerable height, the 

 velocity of the entering air may be as high as one metre (thirty-three 

 inches) per second, without causing inconvenience ; but when such 

 openings are in the ceiling so that the air descends vertically, its 

 velocity should not be more than half that just stated. 



Tlie suction system has been objected to for causing strong drafts 

 when an outside door is opened, but this may be obviated by adopt- 

 ing suitable proportions and by warming the ante rooms and passages 

 leading out of the building. The chimneys of dwellings will gene- 

 rally produce sufiicient ventilation, even when there are no fires, on 

 account of the ordinary difference in the temperature within and 

 without. However, this ventilating power may be easily increased 

 by introducing into the chimney a vertical pipe containing a few gas 

 burners. In answer to a query whether it had been found essential 

 to introduce moisture wdth the air supplied. Gen. Morin remarked 

 that in the plan of heating adopted by him, a small portion of heated 

 air was mixed witli the cold air, and it was found there was moisture 

 enough to prevent any sensation of dryness in the air when breathed. 

 In reply to an inquiry whether the system described would answer 

 for ventilating in hot countries where it would be required to cool the 

 supply of fresh air, or wliether the points of admitting or discharging 

 air would in that case liave to be reversed, Gen. Morin said the Lec- 

 ture Theatre of the Conservatoire, in which they were then assem- 

 bled, was ventilated upon the plan described in his paper, and it was 

 found in practice that the room could be cooled, in wtwm weather, 

 more readily b}^ drawing off tlie vitiated air near the fioor and admit- 

 ting fresh air brought from below near the ceiling. In very hot coun- 

 tries it might be found essential to have recourse to a fine spray of 



