90 POPULAR SCIENCE MONTHLY. 



air takes place at tlie ceiling, and is assisted by the heat from the 

 gas flames. 



The French engineer Peclet, an authority on heating and ven- 

 tilation, suggested a similar system of upward ventilation, but 

 instead of allowing the foul air to pass out through the roof, he 

 conducted it downward into an underground channel which had ex- 

 haust draught. Trelat, another French engineer, followed practi- 

 cally the same method. 



A large number of theaters are ventilated on the upward sys- 

 tem. I will mention first the large Vienna Opera House, the 

 ventilation of which was planned by Dr. Boehm. The auditorium 

 holds about three thousand persons, and a fresh-air supply of about 

 fifteen cubic feet per minute, or from nine hundred to one thou- 

 sand cubic feet per hour, per person is provided. The fresh air is 

 taken in from the gardens surrounding the theater and is eon- 

 ducted into the cellar, where it passes through a water spray, which 

 removes the dust and cools the air in summer. A suction fan ten 

 feet in diameter is provided, which blows the air through a con- 

 duit forty-five square feet in area into a series of three chambers 

 located vertically over each other under the auditorium. The low- 

 est of these chambers is the cold-air chamber; the middle one is 

 the heating chamber and contains steam-heating stacks; the highest 

 chamber is the mixing chamber. The air goes partly to the heat- 

 ing and partly to the mixing chamber; from this it enters the 

 auditorium at the rate of one foot per second velocity through 

 openings in the risers of the seats in the parquet, and also through 

 vertical wall channels to the boxes and upper galleries. The total 

 area of the fresh-air openings is 750 square feet. The foul air 

 ascends, assisted by the heat of the central chandelier, and is col- 

 lected into a large exhaust tube. The foul air from the gallery 

 passes out through separate channels. In the roof over the audi- 

 torium there is a fan which expels the entire foul air. Tele- 

 graphic thermometers are placed in all parts of the house and 

 communicate with the inspection room, where the engineer in 

 charge of the ventilation controls and regulates the temperature. 



The Vienna Hofburg Theater was ventilated on the same 

 system. 



The new Frankfort Opera House has a ventilation system mod- 

 eled upon that of the Vienna Opera House, but with improve- 

 ments in some details. The house has a capacity of two thousand 

 people, and for each person fourteen hundred cubic feet of fresh 

 air per hour are supplied. A fan about ten feet in diameter and 

 making ninety to one hundred revolutions per minute brings in the 

 fresh air from outdoors and drives it into chambers under the 



