40 PNEUMATICS. 



air-tight. The copper ball being charged with condensed 

 air, by means of a condensing syringe, and screwed on ; 

 by pulling the trigger, the valve in the ball is struck with 

 the pin, when a quantity of air rushes into the barrel of 

 the gun, and forcibly acts on the bullet, sending it to a 

 very considerable distance. As only a portion of the air es- 

 capes from the ball, the gun may be loaded and discharged 

 several times successively without recharging the ball. 

 It is said that air condensed but ten times will discharge 

 a ball with a velocity equal to gunpowder. The writer of 

 this article has propelled a ball through an inch deal for 

 several times successively with the original charge. Air- 

 canes are on the same principle as air-guns ; they are 

 made to resemble walking-sticks, and unscrew in the 

 middle, the upper part forming a chamber for the con- 

 densed air, which, when charged, is again screwed on to 

 the other part, when it may be loaded, cocked,and fired. 



The CONDENSING SYRINGE consists of a solid piston 

 moving in a tube which must, of course, be perfectly air- 

 tight : when the syringe is screwed on to the ball, and 

 the piston forced up, the air which was in the tube is 

 propelled into the ball, and retained there by a valve. 

 The piston is then drawn down, and creates a vacuum 

 in the tube, until it arrives at a certain part where there 

 is a hole, through which the air rushes and fills the tube, 

 which is again forced into the ball : this action is re- 

 peated until the ball is sufficiently charged. By the con- 

 densation of the air, a very considerable degree of heat is 

 generated. Tinder and fungus may be lighted in a proper 

 condenser, by the sudden stroke of the air. 



The BAROMETER, a well-known instrument for exhibit- 

 ing the approaching change of the weather, which has been 

 already referred to, requires a slight explanation. In its 

 most simple form, it is a tube of glass, of about 30 inches 

 long, hermetically sealed at one end, filled with quick- 

 silver, and inverted into a vessel of the same metal, when 

 the quicksilver in the tube will descend until it arrives 

 at from between 28 to 31 inches above that in the vessel, 

 according to the state of the atmosphere. If the quick- 

 silver in the tube falls or becomes low, it indicates rain ; 

 if it rises, it indicates fine weather. The principle, which 





