310 



THE POPULAR SCIENCE MONTHLY. 



open ; the other two are normally closed. The automatic escape of 

 the lever G, at the end of each minute, moves the slide-valve, opens 

 the second orifice, and sends an impulse into the pipes ; at the end of 

 a number of seconds, determined by experience and dependent on 

 the length of the pipes (a number Avhich varies from ten to fifteen sec- 



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onds), the slide-valve is brought back to its original position by the 

 clock-work, closes the two orifices, and allows the extra pressure which 

 has been introduced to escape into the air. This operation is repeated 

 every minute. The motive-power for the clock-work of both move- 



