FLOATING. 



367 



(h) Sluice-gates made of logs. The roughest method 

 adopted for closing sluices is to place a number of round logs, 

 split in half, vertically alongside one another, with their 

 ends resting against two strong beams above and below. The 

 crevices between them are then stopped with moss, and a pile 

 of earth is often made behind them. When it is desired to 

 release the water, a hook attached to a rope is passed through 

 an iron ring in the central log, which, on being lifted, is 



Ki-r. i'io. IMuj,'- valve. 



carried down by the water ; the other logs are similarly lifted 

 out of the way. 



Balks of wood one above the other also may be suspended 

 horizontally, as is usual in the Black Forest, by chains before 

 the opening, as shown in Fig. 233. They are raised one after 

 the other by hooked poles. Fig. 240 shows the so-called 

 plug-valve which is much used, especially in Austrian Silesia. 

 The valve fits vertically into a channel (a) excavated under 

 the dam and projecting 4 or 5 yards into the reservoir, where 

 it is strongly closed, the open end of the channel leading 

 down-stream. The end under the reservoir is open at m and 



