WARMING AND VENTILATION. 309 



102. Ohserrations at Chateau de Ferri'eres. — The most striking example 

 of these eftects which I have had occasion to observe is presented by 

 the great reception-hall of the Chateau de Ferrieres, and it has furnished 

 me with some facts which enable me to determine the amount of heat 

 which such glass roofs may transmit, and, consequently, to determine 

 approximately the methods of heating to be employed to prevent this 

 cooling. 



The main reception-room of the Chateau de Ferrieres, called the Hall, 

 is 75 feet long and 40 feet wide, or 3,000 square feet in area. 



It is completely surrounded by other reception-rooms, corridors, ves- 

 tibules, &c. By means of heaters, all these are comfortably warmed, as 

 well as the reception-room, which has no side-windows, but is lighted 

 by a glass ceiling with a surface of 1,035 square feet, covered by a glass 

 roof in seven sections, having together 2,459 squarefeet of cooling sur- 

 face. 



A large fire-place, in the form of a monument, placed on one of the 

 long sides of the room, completes its system of heating. 



When in winter the space between the glass roof and ceiling is not 

 warmed during the day, the effects previously mentioned become the 

 most unpleasant. The cousiderable draught of air produced by the fire- 

 place draws to it the air cooled by contact with the ceiling; and the 

 vicinity of thisfire-place, to which persons are naturally drawn byabright 

 fire, becomes unendurable. 



At night, the room is lighted up by 1,000 gas-burners above the ceil- 

 ing, which consume 3,500 cubic feet of gas an hour; there beiug then 

 about one burner to every three square feet of floor-surface in the room. 

 The heat given out by this abundant combustion more than suffices to 

 prevent the cooling of the air of the room and the unpleasant eftects 

 which would result from it. 



To obtain at least to a certain degree the same result during the day, 

 it has beeu found necessary to keep up coke-fires in four cast-iron stoves, 

 placed in the roof-space, in order to maintain there a temperature higher 

 than that of the room. 



Observations made on the consumption of coke during the day and 

 of gas at night, as well as upon the internal and external temperatures, 

 enable us to calculate at least approximately the amount of heat re- 

 quired in the space between the glass roof and ceiling in order to pre- 

 vent the unpleasant cooling ettect. 



For this purpose, calling — 



C the number of units of heat which can pass in an hour through 



a pane of glass having the surface S ; 

 T the temperature of the air on the warmer side ; 

 T' that of the air on the colder side ; 



K a constant co-efiBcieut, representing the number of units of heat 

 to a square foot of glass surface, and to a degree of difterence 

 of temperature between the two faces : 



