Pneumatics. 77 



Air, it is said, may be thus compressed into fifty 

 thousand times less compass than its natural bulk, 

 provided the apparatus is strong enough. On 

 this principle of condensed air is constructed the 

 air-gun, a very dangerous and destructive in- 

 strument. It was formerly a very complex ma- 

 chine, from having the chamber for containing 

 the condensed air within the body or rather the 

 butt end of the gun. That which is how in use 

 was invented by the late ingenious Benj. Martin : 

 see fig. 33. It is in shape exactly like a common 

 gun. Just below the lock, a copper ball A, 

 fig. 34, screws on, which is charged or filled 

 with condensed air by a condensing syringe, ex- 

 actly as we charge the brass fountain, only that 

 the ball contains no water; the ball has a stop 

 cock a, which is turned or shut when it is not on 

 the gun : the bullet is rammed in a<= w ~i - -- 

 musket, V* ~"^ nt me barrel very exactly. By 

 drawing the trigger, a small valve is opened at the 

 bottom of the barrel, and it is so contrived as to 

 let out only one charge of condensed air at each 

 pull of the trigger ; the bullet is discharged with 

 a force sufficient to kill an animal at the distance 

 of sixty or seventy yards. The copper ball con- 

 tains about ten charges. There are generally 

 two of these to each gun, and that which is 

 not immediately in use may be carried in the 

 pocket. 



In the next lecture we shall treat of the atmo- 

 spherical phenomena. 



