320 WARMING AND VENTILATION. 



of which .75x900,000 = 720,000 cubic feet an hour, or 200 cubic feet 

 a secoud, will be carried ofi" at the ceiling, and .25x060,000 = 240,000 

 cubic feet an hour, or G7 cubic feet a second, by the openiugs near the 

 floor. As the velocity of discharge near the ceiling may be as high as 3 

 feet a second, the openings to be made there — as far as possible directly 

 above the main chandelier — should have — 



-^- = 67 square feet of clear passageway, 



deduction being made for solid parts ; and the velocity of draught near 

 the floor beiug also 3 feet a second, the corresponding openings should 

 have a clear area of — 



Y = 22 square feet. 



The grating in nse has an area of but 116 square feet of total sur- 

 face, including solid portions, and scarcely presents 43 square feet of 

 clear passage. 



Above theopenings in the ceiling should be placed external ventilators, 

 having together the same clear area, which will increase the velocity of 

 discharge. 



In regard to the ventilating openings at the floor-level, they may easily 

 be made around the contour of the rooms under the steps on which the 

 seats are placed ; and their pipes should be carried in the piers of the 

 vaults of the lower vestibule to the cellar, where they should join the col- 

 lectiug passages terminating in a general ventilating-chimnej', at the 

 bottom of which a coal fire or a number of gas-burners should be kept 

 burning. 



The dimensions of these pipes should be calculated by the general 

 rules previously given. If there are serious difficulties in the way of 

 producing this down-draught, an up-draught may be used, produced by the 

 aid of gas-burners placed in vertical flues made in the thickness of the 

 walls. 



119. Introduction of air. — But it is not sufficient merely to secure the 

 discharge of the foul air; it is necessary to provide for the admission of 

 an equal amount of fresh air at a proper temperature. 



This air, which in winter should be warmed to a temperature of about 

 68°, may be admitted through an interjoist in the balcony, which is 20 

 feet above the floor. It should flow horizontally below the chandeliers, 

 above and away from the occupants, and its horizontal velocity of ad- 

 mission may, without inconvenience, be 3 feet a second. Its volume 

 being 954,000 cubic feet an hour, or 265 cubic feet a second, the total 

 sectional area of the interjoist and of the conducting passages should 

 be 81 square feet. 



The length around the inner edge of the balcony being about 200 feet, 

 it will suffice to give the openings — 



81 



^Twj = .4 foot of clear height. 



