FLOATING. 



367 



by means of hinges, but the gates are closed by various contriv- 

 ances. The usual method of closing them is shewn in fig. 207. 

 A is the gate revolving on hinges at (a). jB is a revolving 

 elliptical cylinder of wood, which is kept closed by means of a 

 peg (b), a lever placed between (b) and the wall of the dam 

 and the pressure of the water in the reservoir, until the lever (m) 

 is withdrawn ; the pressure on B then causes it to revolve on its 

 axis through an angle of 90'^ and present its smaller diameter to 



A, so that the latter can open, {b) entering a recess in the wall 

 made to receive it. 



Another mode of opening a sluice-gate is shown in fig. 208 : 

 as long as the end (m) of the lever (s d m) rests against the 

 peg (b), the cylinder is kept closed, but when (s) is pressed 

 down, (b) is released and the gate opens. This mode of opening 

 is chiefly used when the walls of the dam are high. 



Fig, 209, represents another mode of opening sluice-gates, 

 where the bar (m) is fastened back by an iron pin which fits 

 through a projecting stone at P, and can be easily withdrawn. 



[In the case of all the above sluice-gates, there is danger of the 

 giite swinging violently against the wall of the dam, and being 

 broken or injured. This is avoided by having the hinge at a short 

 distance from the wall, so that when the gate is opened, there may 

 be a passage for the water between the hinge and the wall of the 

 dam ; the intervening water then breaks the force with which the 

 sluice-gate swings, and prevents its striking the wall. — Tr.] 



