88 POPULAR SCIENCE MONTHLY. 



draught; in other words, its velocity at the inlets must be very 

 slight. The fresh air should enter the audience hall at numerous 

 points so well and evenly distributed that the air will be equally 

 diifused throughout the entire horizontal cross-section of the hall. 

 The air indoors should have as nearly as possible the composition 

 of air outdoors, an increase of the CO2 from 0.3 to 0.6 being the 

 permissible limit. The vitiated air should be continuously removed 

 by mechanical means, taking care, however, not to remove a larger 

 volume of air than is introduced from outdoors. 



Regarding the amount of fresh outdoor air to be supplied to 

 keep the inside atmosphere at anything like standard purity, au- 

 thorities differ somewhat. The theoretical amount, 3,000 cubic feet 

 per person per hour (50 cubic feet per minute), is made a require- 

 ment in the Boston theater law. In Austria, the law calls for 1,050 

 cubic feet. The regulations of the Prussian Minister of Public 

 Works call for 700 cubic feet, Professor von Pettenkofer suggests 

 an air supply per person of from 1,410 to 1,675 cubic feet per hour 

 (23 to 28 cubic feet per minute). General Morin calls for 1,200 

 to 1,500 cubic feet, and Dr. Billings, an American authority, re- 

 quires 30 cubic feet per minute, or 1,800 cubic feet per hour. 

 In the Vienna Opera House, which is described as one of the 

 best-ventilated theaters in the world, the air supply is 15 cubic 

 feet per person per minute. The Madison Square Theater, in 

 New York, is stated to have an air supply of 25 cubic feet jjer 

 person. 



In a moderately large theater, seating twelve hundred persons, 

 the total hourly quantity of air to be supplied would, accordingly, 

 amount to from 1,440,000 to 2,160,000 cubic feet. It is not an 

 easy matter to arrange the fresh-air conduits of a size sufficient to 

 furnish this volume of air; it is obviously costly to warm such a 

 large quantity of air, and it is a still more difficult problem to 

 introduce it without creating objectionable currents of air; and, 

 finally, inasmuch as this air can not enter the auditorium unless a 

 like amoaint of vitiated air is removed, the problem includes pro- 

 viding artificial means for the removal of large air volumes. 



Where gas illumination is used, each gas flame requires an ad- 

 ditional air supply — from 140 to 280 cubic feet, according to Gen- 

 eral Morin. 



A slight consideration of the volumes of air which must be 

 moved and removed in a theater to secure a complete change of 

 air three or four times an hour, demonstrates the impossibility of 

 securing satisfactory results by the so-called natural method of 

 ventilation — i. e., the removal of air by means of flues with currents 

 due either to the aspirating force of the wind or due to artificially 



