MIDDLETHIRD HATCHING-HOUSE. 



Ill 



Water must never be passed through any valve unless the 

 water has first been passed through some screen sufficiently fine to 

 ensure the valve remaining free. This is a first principle of fish- 

 culture, and applies equally to taps and sluices. There is however 

 one form of sluice which is safe with unscreened spring-water. 

 This consists of a set of sluices, all fitting the same groove, and 

 bored with round holes with a brace and cutter-bit, the holes 

 varying in diameter from one just large enough to pass the 

 smallest supply used, to one that will pass the maximum. These 

 holes must all be centred the same height above the lower edge 

 of the sluice, so that the head of water is equal over the centre of 

 the aperture ; no difficulty will then be found in regulating the 

 supply through them. This is made plain in the sketch below 

 (Fig. 53). 



FIG. 53 scale 



PLANK FILTER. 



The filter, slightly modified from the one described by Living- 

 ston Stone on page 51 of his Domesticated Trout, was built of 

 2-inch plank (Fig. 54), and the screens fitted in grooves cut slanting 

 in the sides; a 1^-inch hole was bored in front of the lowest 



4' 10" > 



FIG. 54 scale fc. 



