116 Mr. D. Gilbert 0// <//t^ 



— 1.0425. Then w'-r X m X >Jx—\, or 



48 iV /I m 



V = ^ — 1.0425. Then ^/-~ % m % •sJx—\, or — r-j- 



480 V h ^ ' AJh 



X V ^ X V^^ = the velocity. But — ^ zi 8.0223 (log 



0.9042992) V Z =: V 30 and ^ -^ - 1 = V 0.0425, therefore v ~ 

 9.058 feet in a second, and these multiplied by — or ■ will 



give the quantity of elastic fluid reduced to atmospheric den- 

 sity passing through an aperture of one square foot in a 

 second = 8.680 cubit feet, or = 31280 cubic feet in an hour: 

 but the content of the room is 30 X 30 X 60 = 54000, requiring 

 therefore an aperture of 1.726 square feet, being a square of 

 1.31, or a circle of 1.48 diameter. 



This communication should not lead by a straight perpen- 

 dicular ascent into the open air ; as in that case currents of 

 cold air will inevitably pass into the room, in consequence of 

 their superior gravity. It seems probable that the best expedient 

 is to conduct the tube, furnished with a moveable cover 

 capable of elevation and depression, into an upper room, from 

 whence external openings may be made on its diflferent sides, 

 to be used according to the direction of the wind. 



Now, it is quite obvious that while 54.000 cubic feet of air 

 have been flowing into the atmosphere, an equal quantity 

 must have been admitted to supply their place ; this supply 

 can very seldom be provided in any other way than from 

 without, which rushing into the apartment with a velocity 

 nearly equal to that already found, produces great incon- 

 venience in crowded rooms, and endangers the health of more 

 delicate persons. One obvious expedient is to subdivide the 

 current into numerous streams ; and if these were made to 

 enter the sides of the apartment at perhaps half its height, and 

 then directed upwards, they would descend from the top with 

 an increase of temperature, and with considerable uniformity. 

 The section of the aperture must however in that case be 

 enlarged by the square root of two above those in the ceiling, 

 which latter should themselves receive some increase of size, to 



