FOE PLEASURE AND PROFIT. 55 



marked s, in all three drawings, in front of the sluice boards, 

 and so arranged that the top screen reaches at least a foot 

 above the top edge of the top sluice board. Of course, the 

 water now has to pass through the screen before escaping over 

 the sluice board, and down the surplus water drain. Put the 

 cap in position once more, and the controlling sluice is com- 

 plete. The real simplicity of it is best realised in Fig. 14. 

 When lowerir ~ the pond, release one sluice board at a time, 



INLET OF A HORIZONTAL BOX SCREEN. 



and always keep the screens well above the last board removed. 

 Each board may be fitted with a small screw-eye; they are 

 then quite easily removed by a hand hook. Char the wood 

 inside and out, and cover well with black varnish before plac- 

 ing the sluice in position. For ordinary ponds up to, say, 

 six or seven feet in det)th, these sluices need only be mads 

 of wood, but, in the case of very big lakes, and where they 

 have to control ai very large volume of water, they are prefer- 

 ably built up from brickwork, and strong iron graungs cake 

 the place of the p?rforated zinc screens. Otherwise the plan- 



