m Eiochaustiiig Air from Tubes, ^c. 3 



what overweighted, by the lever, r, r, and the weight, s. 

 The lower valve, n, opens by its own gravity, when not 

 closed by the lower lever, p, or supported by the pressure 

 of the atmosphere against a partial vacuum in the lower 

 part of the cylinder, a, a. The levers, p, and p, are con- 

 nected with an eccentric by the rod w, part of which only 

 is shown. 



The better to describe the operation or mode of action 

 of the before- described air-pump, it must be supposed 

 that the pump has already exhausted the main, or vessel 

 connected therewith, to half vacuum, and is making the 

 down stroke ; the air from the main, therefore, enters at 

 the upper valve, which was opened by the lever, l, 

 immediately after the commencement of the down stroke, 

 and the lower valve, h, was closed at the same time. 

 The upper outlet valve, m, was closed simultaneously with 

 the conclusion of the ascending stroke, and remains closed 

 during the down stroke ; and, at the same time, the end, 

 P a, of the lower lever, P, released the stud, or tappet, q, 

 leaving the lower valve, n, at liberty to open by its 

 gravity ; but the air in the cylinder of the pump having 

 had, at the commencement of the stroke, only half the 

 density of the external air, the valve, N, will have been 

 supported until the piston descended to about the middle 

 of the stroke. The gravity of the valve, n, will then 

 overcome the cohesion of its surface, and of the valve- 

 seat, and open, leaving a free passage for the air to be 

 expelled from the bottom of the cylinder. When the 

 piston approaches the bottom of the cylinder, the valve, 

 N, will begin to be raised by the lower lever, p, the 

 motion of the piston, from its connexion with the crank 

 of the engine actuating or driving it, will have become 

 slower, so that the aperture will, nevertheless, be adequate 

 for the expulsion of the air; but, at the turn of the stroke, 

 the last-mentioned lever, p, will close the valve, n, quietly, 

 so as to avoid any detrimental concussion consequent on 

 the change of the stroke. The upper inlet valve, g, will 

 be closed, and the lower inlet valve, h, will be opened. 

 The upper outlet valve, m, will be left free, but, as before 

 explained, will remain closed, until the density of the air 

 above and below it are nearly equal, when it will be raised 

 by the counterpoise, or weight, s. 



I have, for the sake of greater perspicuity in drawing 

 and description, described the pump as only having one 



B 2 



