[ 66 ] ' 



the centre arc not meant to be fo fully perforated 

 as thofe at and beyond it; and may all be ftill lefs 

 fo, if in praftice found neccflary. But as the quan- 

 tity of air delivered by the forcing-pump, within five 

 feconds of time, is equal to the contents of fixty* 

 feet of four-inch pipe ; within the firfl minute, the 

 air (notwithftanding the manifold perforations, ob- 

 ftrufted as it is in meandring through a mafs fo 



nearly 



• Thus calculated: 



Inches. 

 60 feet 4 



X II inches X 4 



Produces 720 inches 16 the fquare of the diameter of the pipe, 



as a multiplier. X >7^54 



~ 12,5664 or area of the circle. 

 X 7^0 length of the pipe in inche*. 



Which divided by aj 1)9047,80801; 39, 1679 gallons and decimal parts, the wliole 

 . [capacity of 6q feet of pipe. 



4117 



..388 



1570 



1848 



221, Sec. 



Then a fingle difcharge of the forcing pump being 8 gallons, five 

 fuch difcharges amount to 40 gallons, which is more than equal to the 

 contents of 60 feet of four-Inch pipe. 



And as on the larger fcale of ventilators the pipes need not exceed 

 the fame diameter, the power of aif inje(5\ed when its egrefs is flopt 

 will increafe fufficiently to force its way through webs, matts, and other 

 obftru(flions, though impervious to the atniofpherick fluid, unafliflcd 

 by fuch mechanick aid. 



