164 The Drainage of Fens and Low Lands. 



No. of Hours Sluice Multiplier. 

 Doors open each aide. *^ 



13 I 



II i'09 



10 1*20 



9 i'33 



8 I'So 



7 1-71 



6 .. ,. 2*oo 



5 ^40 



4 • 3*oo 



3 4*00 



2 .. 6*00 



I ,, I2*00 



TABLE VIII. 

 To ascertain the time the doors of a sluice are closed by the tide. 



Having ascertained the level of the sill of the sluice with reference 

 to low-water in the sea or estuary into which the water is usually dis- 

 charged, divide the height of the water in the drain by the range of 

 the tide ; the constant in the table nearest the result will give the time 

 the doors will close with the rising tide and open again on the falling 

 tide. 



Time after High Water. Time before High Water. 



Falling Tide. Constant. Rising Tide. 



H.M. H.M. 



0*0 I'oo 6*00 



0-30 .. -96 .. .. .. .. 5-30 



i-oo '92 5-00 



i'30 '84 4-30 



2'oo *75 .. .. .. . 4-00 



2*30 '63 .. .. .. .. 3-30 



3*00 'SO 3*00 



3*30 - '3^ • 2-30 



4'oo .« '26 2*00 



4*30 .. .. .. .. '16 1*30 



5*00 'oS i*oo 



5*30 -025 0-30 



Example. — Supposing a tide rising 22' o" above low-water spring 

 tides, and the water to run in flood at 10 feet above the sill at low-water, 

 accumulating during tide time to 14 feet — ^then 10 divided by 22, the 

 rise of the tide, gives 0*45, which, being nearly the mean between 

 2 hours 30 minutes and 3 hours, the time given in the table the 



