290 Mr Thorn's Description of a Nezo Double Valve Sluice. 



est height ; the sluice AD and valve N being shut, and the 

 valve O open. 



Suppose, now, that water is drawn from the aqueduct, the 

 float P will fall with the water, and leave the spindle NO, 

 which, then falling by its own weight, shuts the valve O, and 

 opens the valve N. The water then passing from the cistern 

 KL, into the cylinder EF, raises the cylinder GH ; and then 

 the pressure of the water in front of the sluice AD, throws 

 it open. Again, when the water issuing from the aqueduct 

 is stopped, its surface rises, and with it the float P, which, 

 pushing up the spindle ON, shuts the valve N, and opens the 

 valve O, when the water in the cylinder EF escapes ; and 

 then the cylinder GH falling, shuts the sluice AD as before. 

 In this way, the surface of the water in the aqueduct is al- 

 ways kept at the same level, whether the quantity drawn from 

 it be great or small. 



In order to make this sluice operate also as a waster, it is 

 only necessary to have a tube communicating between the re- 

 servoir and cylinder EF, the end of which that opens into 

 the reservoir being placed at the greatest height to which the 

 water therein is allowed to rise. 



Whenever the water in the reservoir rises so as to flow into 

 this tube, the cylinder EF will be filled with water, and the 

 sluice AD will open ; and whenever the water again falls, so 

 as not to flow into this tube, the sluice AD will shut, and act 

 again as before. This tube must, of course, be made to pass 

 more water than the valve O can pass. 



An apparatus of this construction was erected at Rothesay 

 in 1819, and has been in constant operation ever since. The 

 cylinder EF is four feet one inch diameter, and five feet deep 

 inside. 



The cylinder GH is four feet diameter, and four feet deep 

 over all. 



Float P, about two feet square, and six inches deep. 



Valves O and N, two inches diameter. 



Pulleys B and J, twenty inches diameter. 



Sluice AD, four feet long, and six inches deep ; but the 

 cylinders, &c. are powerful enough to work one of nearly 

 twice that area. 



Thus, the area of the sluice is two feet; depth of water 



