The sliilce may also be so arranged that the horizcxital ti.ibe caim be made of glazed 

 clay pipes (xmglazed clay pipes are less effective especially n.ith acidulous water) of 

 at least 20 cm. diameter. The vertical wooden portion is then set dov.-n about 50 cm. into 

 the ground. In a similar manner the vertical shank or even the entire sluice can be con- 

 structed of brick at the site. In every case it must be free of fissures which will 

 allow bursting in frosty v.'eather. 



The 7,ater conduction povrer Q represents the quantity of water flavri.ng per second 

 from a pipe of q square meters cross section, and may be approxitaately calculated accord- 

 ing to the formula. 



Q = q.v liter seconds, 



in which v is the v;ater velocity in meter/seconds. The water velocity is approximately 



V = ^ 2g.h 



in which g is the acceleration of gravity which amounts to 10 meters per second, and h is 

 the head (height of water pressure) in meters. On account of friction urtiich increases with 

 the length of pipe line and which is inversely proportional to the pipe diameter, the 

 water quantity calculated in this v/ay, has been found by experience to be about l/3 too 

 high (Schaeperclaus, 1927). The exact calculation is, however, so intricate that I shall 

 refrain from giving it. 



Fig. 13. Perforated zinc sheets in three standard round and slit 

 perforations. Standard 1 for trout alevins, standards 2 and 3 for 

 trout fingerlings. Natural sizej Thickness - 1.5 mn. 



The little sluice boards are made about 30 cm. high and not too wide on account of 

 later swelling. Up to the closing edge of the uppermost and nethermost boards the little 

 boards are closely fitted to each other by roof-shaped slopes and indentations in the top 

 and bottom edges. On the central surface of each sluice board a ridge or cleat is nailed, 

 which allows the board to be pulled out (Fig. 10). At the desired v.-ater level, an Eckstein 

 grid box had best be inserted in place of the sluice board, to provide a large filtering 

 surface and an automatic removal and dropping of foliage carried in the v;ater current when 

 the pond is fiU^d rdth vrater. In Hungary similar sieve boxes of a triangular plan are 

 used. For ponds v/ith larger fishes, coarse rakes made of strongband iron or round iron rods, 

 are to be recommended. Perforated zinc sheets (see Fig. 13) are to be recommended for 

 strainers, as they nay be obtained, vdth standardized perforations for every size of fish 

 (for example at Seidl and L^yer, in L-onich '.712). V.'ire netting and v.lre screen of every 

 kind have too sl.ort a time of durability. Perforated and slitted metal sheets are more 

 easily cleaned on account of their smooth surfaces. 



During the fishing-out procedure two frames the same size as the sluice boards, which 

 are covered vdth netal sieve sheets or provided with grid rods, are required for each sluice. 



6S 



