Description of an Air Pump. 87 
it is another aperture communicating with the tube G: and the 
part EC is constructed in such a manner, that when E is upward, 
a passage is opened between the aperture F and tube A, and also 
between the tubes Band G. If the pump he now worked, it is 
evident the air will pass in at F' and out at G, that is, it exhausts 
at F and condenses at G._ If, however, we give EC a quarter of 
a revolution, and bring C upward, the jassages from A to F, and 
from B to G, are closed, and others opened from B to F’, and from 
A to G; and by working the pump the air will now be made to 
pass in at G, and out at F’, or in the reverse direction from that 
just described. This pump, therefore, like the one described by 
Dr. Hare, when worked is constantly exhausting and condensing. 
The uses to which this air pump may be applied, obviously 
include all those of a common air pump and condenser ; and 
also enables the operator to transfer any gas that will not corrode 
the metals from one vessel to another, (as does that of Dr. Hare.) 
To do this, it is only necessary to attach tubes at F' and G lead- 
