70 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK i. 



of compressed air was the circular space comprised between the barrel 

 of the gun and a cylinder of much stronger make, which enveloped it. 

 The butt communicates with the stock or part of the gun where the 

 projectile rests, by an orifice furnished with a conical valve s, which 

 the compressed air constantly keeps shut, but which may be opened 

 by the working of the mechanism of the lock represented in detail in 

 the figure. 



By pressing the trigger d, the cock falls on the piece e, the lower 

 part o which pushes a rod, tt', communicating with the valve, which, 

 with this sudden impulsion, suddenly opens. A portion of the com- 

 pressed air escapes from the butt-end and projects the ball with a 



Fir,. 45. Air-gun : full view and section. 



force which depends upon the pressure of the air by which the air-gun 

 is charged. Generally this pressure amounts to 8 or 10 atmospheres. 

 As only a small quantity of air escapes at each discharge, several 

 successive shots can be discharged. In old air-guns the balls were 

 placed in a little reservoir furnished with a stop-cock, and, as one 

 shot was sent off, the stop- cock was opened and a fresh projectile 

 placed in the stock. It is easily understood that the force of pro- 

 jection diminishes as the reservoir of compressed air is emptied, so 

 that after a few discharges it is necessary to charge the gun afresh, 

 that is to say, to compress the air. 



