Water-pipes and Syphons from disengaged Jir, <J-c. 109 



the lower valve^ The upper valve is then opened, when the 

 water in the cylinder A will descend, and displace the air in the 

 cylinder C, which will rise through the upper valve, and pass off 

 into the atmosphere. It will novv be found that the obstruction 

 is removed, and that the water flows freely. Then both cylin- 

 ders are to be again filled with water ; after which the upper 

 valve is shut, and the lower one opened as before. By the con- 

 necting lever these movements are made simultaneously. 



In practice it may possibly be found necessary, at least when 

 the air has been allowed to accumulate in the pipe, while the 

 valveyis shut, to interrupt, for a moment, the entrance of the 

 water into the mouth of the pipe or syphon, in order to allow 

 the air to rise freely into the cylinder. The reason of this seems 

 to be, that as soon as the opening of the lower valve, and the 

 ascent of the first bubble of air partially relieves the water in the 

 pipe from the pressure of the confined air, — the renewed impe- 

 tus of the water, in attempting to resume its motion, forces the 

 air forward, and partially prevents its ascent through the valve 

 into the cylinder. It may be also observed, that, in the drain- 

 ing syphon, it will be advantageous to prevent the access of the 

 atmospherical air at both its extremities : for if the water in the 

 reservoir or quarryhole is allowed to drain off until its surface 

 descends to the extremity of the shorter or drawing limb, the 

 air will instantly rush up and empty the syphon. And, again, 

 if, while its action is suspended by the accumulation of disen- 

 gaged air within, the lower or discharging extremity of the 

 longer limb be exposed to the atmospherical air, it will ascend, 

 and dislodge the water from that limb, when it will immediate- 

 ly fall in the other also ; and the operation of exhausting the 

 air must be repeated before the syphon can be made to work. 

 To prevent the first of these inconveniences, it would be ad- 

 visable to furnish the drawing limb with a valve, having on the 

 end of its axis a lever and air ball (B, fig. 2). When the re- 

 servoir is full, the air-ball will remain in the vertical position 

 B e, retaining the valve fully open ; as soon, however, as the 

 surface of the water falls below the level eg^ the air-ball will 

 descend along with it, gradually closing the valve ; which, when 

 the surface of the water, and, along with it, the air-ball, has 

 reached the level y//, is entirely shut, preventing both air and 



