66 THE ATMOSPHERE. 



When sufficient air has been condensed, this chamber 

 is to be removed and attached to the gun, which is then 

 ready to receive the ball. This is placed in the mouth 

 of the barrel, and is made to fit closely by first laying it 

 on a small piece of linen, which, when forced down by 

 the rod, perfectly fills the bore. 



In discharging the gun, the force of the lock is di- 

 rected by a small steel piston, moving through a collar, 

 ngainst the valve of the chamber. The air instantly 

 escapes by its side, and rushing into the barrel, drives 

 out the ball. It is necessary to observe, that the action 

 of the lock being instantaneous, the power of the piston 

 is lost after its projection, and it immediately recedes, 

 while the elasticity of the air forces the valve to its 

 place, thereby preventing the escape of more than was 

 intended. The discharges may be continued until the 

 resistance of the condensed air is reduced to its ordinary 

 pressure. 



There were two other applications of this principle, 

 recently exhibited in this city, in the model of a cannon 

 and in a common walking-cane, the workmanship of Mr 

 Adam Stewart, an accomplished mechanician. The im- 

 provements in his use of the principle, evince great 

 skill and ingenuity in their projector. 



The estimates offeree possessed by the airgun, when 

 fully charged, have been very Various. Even in its 

 earliest days there existed wonderful stories of its power. 

 By many, the expansive force of the air in the cham- 

 ber, has been compared with that of gunpowder. But 

 the only opinions worthy of attention are those founded 

 on experiment. The smallest result of the force of gun- 

 powder that we have met with, is that given by Mr 

 Robins. His calculation was, that the elastic force of 

 the fluid produced by ignited gunpowder, is at least one 

 thousand times greater than the ordinary pressure of 

 the air. And if we consider that pressure to be fifteen 

 pounds to the square inch, we have a result of fifteen 

 thousand pounds to every square inch of the surface 

 which confines it. 



The ordinary charge of airguns, has been equal to 

 between forty and fifty atmospheres, or between six 



