hrj extracting the foul Air from them. 1 23 



by the alteration of the machines commonly applied, and 

 by producing an ascending stream of air through pipes by 

 a furnace constructed for the purpose. The latter mode 

 would, however, have been here expensive in fuel as well as 

 in attendance; and the others required power to overcome 

 the friction of pistons, and so on, or considerable accuracy 

 in construction. 



I at last erected the machine, of which the annexed is a 

 drawing; which, while it is so simple in construction, and 

 requires so small an expense of power, is so complete in its 

 operation, and its parts are so little liable to be injured by 

 wear, that, as far as I can imagine, nothing more can be 

 desired where such an one is applied. This engine bears 

 considerable resemblance to Mr.Pepys's gazomeler, 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. iV. 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 the top, and that 

 in either case it is proper to fix it upon a floor, which n)av 

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

 discharged from the exhauster: this floor may be furnished 

 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 

 and 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 made of cast-iron, open 

 at the bottom and suspended over the air-pipe, immersed 

 some way in the water. It is furnished with a wooden top, 

 in which is an opening fitted with 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 H, and the weight of the cylinder is balanced, 

 if necessary, by the counterpoise I. 



The action is obvious, — When the exhausting-cylinder 

 is raised, a vacuum would be produced, or rather the water 

 would likecvise be raised in it, were it not h)r the stream of 

 air from the mine rushing through the pipe and valve D. 

 As soon as ihecvlintler begins lo descend, this valve clo*cs, 

 and prevents the return of tlieair which is discharged throuc-li 

 the vdlve T. 



The quantity of air exhausted is calculated of course from 



the 



