334 VENTILATION OF Mlx\£S OH HOSPITALS. 



desired, where such a one is applied. This engine bears 

 considerable resemblance to Mr. Pepys's gazometer, though 

 this did not occur to me until after it was put to work It 

 will readily be understood by an inspection of the drawing, 

 Pi, X, fig. 3, where the shaft of the mine is represented at 

 A ; and it may here be observed, that the machine may be 

 as well placed at the bottom of the shaft as at tiie top, and 

 that in either case it i« proper to fix it upon a floor, which 

 may prevent the return of the foul air into the mine, after 

 being discharged from the exhauster ; this floor may be fur- 

 nished with a trap-door to be opened occasionally for the 

 passage of buckets through it. 



B the air pipe from the mine passing through the bottom 

 of the fixed vessel or cylinder C, which is formed of timber 

 ^nd bound with iron hoops; this is filled with water nearly 

 to the top of the pipe B, on which is fixed a valve opening 

 upwards at D. , 



E, the air, or exhausting-cylinder, fnade of cast-iron, 

 open at the bottom and suspended over the air-pipe, im- 

 mersed some way in the water. It is furnished with a 

 wooden top, in which is an opening fitted M'ith a valve 

 likewise opening upwards at F. 



The exhausting-cylinder has its motion up and down 

 given to it by the bob G, connected to any engine by the 

 horizontal rod II, and the weight of the cylinder is ba- 

 lanced, if ne<;essary, by the counterpoise I. 

 It's mode of '^^® action is obvious. — When the exhausting cylinder is 



actien. raised, a vacuum would be produced, or rather the water 



would likewise be raised in it, were it not for the stream of 

 air from the mine rushing through the pipe and v^lve D. 

 As soon as the cylinder begins to descend, this valve closes 

 and prevents the return of the air which is discharged 

 through the valve F. 



The quantity of air exhausted is calculated of course 

 from the area of the bore of the cylinder, and the length 

 of the stroke. 

 Dimensions of The dimensions \rhich I have found sufficient for large 

 one for large ^orks are as follow : 



The bore of the exhausting cylinder two feet. 



The length six feet, go as to afford a stroke of foar feet, 



Th9 



