WAEMING AND VENTILATION. 319 



wliich is very unpleasant, and the supposition that it will be 1)5° near 

 the ceiliug is probably below the truth. 



The three precediug examples present extreme difficulties ; and it is 

 besides evident that if the proportions referred to be adopted, it would 

 be necessary to reserve means of regulating and of moderating, accord- 

 ing to circumstances, the amounts of air to be admitted and carried off. 

 For the winter season, the latter should be taken from places near the 

 rooms where a suitable temperature can be maintained. 



KECEPTION-ROOMS. 



117. What has already been said in regard to dining-rooms applies 

 equally to large reception-rooms, where many lights serve to a great 

 extent to heat and vitiate the air. 



There, as in evening drawing-schools, it will not be sufficient merely 

 to produce a change of air proportioned to the number of persons pres- 

 ent; it is necessary at the same time to carry off the hot gases of com- 

 bustion through the ceiling under the influence of the draught which 

 they produce, and to establish at the same time if possible an outward 

 draught near the floor, which will draw to it a part of the fresh air. The 

 fresh air should be introduced at a considerable height, and as far as 

 possible from the people in the room. 



In such cases, it will be advisable to secure the complete renewal of 

 the air six or eight times an hour. 



Observations made at the school in the Rue des Petits-Hotels having 

 shown that, with an external temperature of 50° and an internal tem- 

 perature of 79^, there will be produced from free openings, disconnected 

 from any chimney, a velocity of about 3 feet a second, the surfaces of 

 the openings to be made above may be calculated by assuming that 

 75 per cent, of the amount of air to be removed escapes through these 

 openings; and that the balance, or 25 percent., will be drawn off at 

 the bottom, with a velocity also equal to at least 3 feet a second. 



118. Application to the Hall of MarshaU in the Tuileries. — This recep- 

 tion-room is 03 feet long, 53 feet wide, having therefore 3,340 square 

 feet of floor-surface, and 48 feet in mean height, the cubic content 

 being about 160,000 cubic feet. It accommodates at most six hundred 

 people at balls, or about one person to every 5 square feet. 



It is lit up on reception-days b y 548 candles and by 166 lamps, 

 (equivalent to 498 candles,) which would develop together about 500,000 

 units of heat an hour.* 



The illumination corresponds then to — 



-^jTTTT- =^ 1.74 candles to an individual. 



If it is desired that the air be renewed in this hall six tinies, it will be 

 necessary to admit and discharge — 



6 X 160,000 = 960,000 cubic feet an hour, 



* £tudes 8ur la ventilation, 2^ vol., pp. 301-302. 



