WARMING AND VENTILATION. 329 



lu spite of the influence which these changes, and others equally seri- 

 ous, in part of the apparatus have had on their operation, I will describe 

 the results which have been obtained by continuous service when the 

 ventilation has been regularly kept up. 



135. Ground floor. — Part of the air supplied by the air-trunks passes 

 into two heaters i^laced under the main hall ; the rest flows into two mix- 

 ing-chambers, having together a capacity of 6,500 cubic feet. The two 

 heaters have a sectional area of 97 square feet, and the amount of warm 

 air which they can supply to the mixing-chamber being at a maximum 

 883,000 cubic feet an hour, or 245 feet a second, this corresponds to a 

 velocity of 2^ feet a second. 



From the air-chamber, and from each of its compartments, branch off 

 six pipes, of which — 



Two are intended to supply fresh air to the difi'erent galleries. 



Two were to supply air entering the room by the floor of the stage, 

 concentric with the foot-lights. This method of introduction had to be 

 abandoned, as it was unpleasant to the musicians. 



Two were to carry air in vertical pipes placed by the stage-opening 

 against the wall which separates it from the auditorium. 



There are, in addition, four heaters lor warming the vestibules, the 

 staircases, waiting-rooms, dressing-rooms, &c. 



136. Removal of foul air. — In the orchestra and parquet, the air is 

 drawn off under the floor by 101 openings, having altogether a clear 

 area of about 65 square feet. The passage under the floor, which should 

 have had a clear area of 118 square feet, has been reduced to 40 square 

 feet. 



The air drawn off at this height, carried by two pipes to the right and 

 left, is drawn to two ventilating-chimneys, which contain the smoke- 

 pipes of the heaters of the hall, and may also, when necessary, be heated 

 by a small special fire. 



Direct experiments, made during five consecutive evenings in May, 

 1863, with external temperatures comprised between 56° and 73°, have 

 shown that a mean consumption of 441 pounds of coal, costing about 

 $2 for each performance, effects the removal of about 600,000 cubic feet 

 of air an hour, which corresponds to about 1,400 cubic feet to a seat. 

 By means of this abundant ventilation, the temperature of the orchestra, 

 and parquet may be maiutained within proper limits. 



But the managers of the theater do not use the two ventilating-chim- 

 neys ; and if they have not been closed, instead of promoting the removal 

 of foul air, they may cause the entrance of cold air, in consequence of a 

 reversal of the direction of the motion of the air caused by the greater 

 power of the upper draught. 



For the first, second, third, and fourth galleries, the foul air is carried 

 out at the floor of the galleries or through the steps of the amphitheater, 

 as was reuiarked in § 120 ; and the observations made in May, 1863, 

 have shown that the amount of foul air extracted at the base of the 



