THE ATMOSPHERE. 65 



the lower valve into any vessel connected with the end 

 of the cylinder. 



This instrument is called a condenser, and is used 

 in all cases where we wish to force more air into a vessel 

 than it naturally contains. An experiment fully exhib- 

 iting this effect, may be shown by connecting with 

 the end of the condenser, a vessel whose only opening 

 has been covered with gum elastic or India rubber. 

 The first depression of the piston will cause this cov- 

 ering to protrude, and a repetition will increase the 

 distention. 



AIRGUN. 



The most wonderful effect of condensed air is exhibited 

 by the airgun. This instrument differs from a common 

 gun, in having a receptacle for air, which may either be 

 a hollow ball screwed to the lower end of the barrel at 

 its under part, or a cavity in the breech. These cham- 

 bers, when opened, communicate with the barrel, and 

 when the condensed air is suffered to escape, it rushes 

 into the barrel and drives out the ball with surprising 

 velocity. 



It is a curious fact, that, although the airpump is com- 

 paratively a modern invention, the airgun, so nearly 

 allied to it in the construction of its valves, should have 

 existed long antecedent to it. For it is recorded that 

 an airgun was made for Henry IV. by Marin, of 

 Lisieux, in Normandy, in 1408 ; and another was pre- 

 served in the armory of Schmetau, bearing date 1474. 

 That in present use is, however, very different in effect 

 from those originally made, which discharged but one 

 bullet after a tedious process of condensation. While 

 the present one may be made to discharge thirty or 

 forty with effect, with the same charge of air. 



The airchamber is charged by screwing it to the end 

 of the condenser, and forcing it down suddenly upon 

 the piston, which is securely held by the feet resting on 

 its handle. The air resting on the piston, is thus forced 

 into the chamber through the opening, which is covered 

 by a valve opening inwards. At each depression of 

 the chamber upon the piston, the air is driven up- 

 wards, whence it cannot return on account of the valve. 



VOL. i. NO. in. 6* 



