298 



WARMING AND VENTILATION, 



than with ascending draughts, the latter requiring the largest number 

 of flues to be made in the upper stories, where the walls are thinnest. 

 Figs. 27, 28, which represent onl^^ the general features, show the ad- 



FIQ.28 



vantages presented by down-cast draughts over up-cast draughts as re- 

 gards the weakening of the walls by the ventilating-flues. The down- 

 draught, besides, as we have said, renders it easy, in order to give due 

 force to the draught, to make use of the entire height of the main ventilat- 

 ing-chimney, to the bottom of which the flues are connected. It forms 

 a very economical means of utilizing the heat expended in producing it. 

 For a building of a construction similar to that of Lariboisiere Hospi- 

 tal, where the piers at the ground-floor have a mean width of 10 feet 

 and a thickness of 2 feet 7 inches, or 26 square feet of sectional area, if 

 the two flues are carried from the second and third stories to the base- 

 ment, they require, at most, in the walls — including the partition between 

 them and even the interior brick lining — a space 2xl'+l"=2' 1" broad, 

 and 9"+2"=:ll" deep, or a total sectional area of 1.9 square feet: that 

 is to say, one-fourteenth of the total sectional area of the pier, which could 



