EXPERIMENTAL WORK. 267 



end was next carefully levelled, and two turn-buttons screwed 

 on to the sides of the rearing-box, against which it floated. 

 When the water is turned on to the rearing-box it falls clear 

 of the end of the deep box, and rising through the false 

 bottom, it passes through the grille, and upwards through the eggs, 

 and, falling over the edge of the deep box, is collected in the trough, 

 and discharged by the lead pipe into the outlet end of the rearing- 

 box, from which it passes through the 

 conducting-spout into the drain. The 

 great length of the overflow of the deep 

 box, it being equal to the perimeter of 

 the sides, seemed to ensure an even 

 upward current through the eggs, while 

 the box itself being held in position by 

 its own buoyancy acting against fixed FIG. 190 scale 



supports, it appeared that any sediment could be removed by 

 simply depressing the box and allowing it to rise slowly to its 

 place. On page 266 is a sketch of the deep hatching-box (Fig. 189). 

 I also built a large hatching-box, on the same principle of an 

 upward current, but so arranged that it could be used with a 

 downward current at the same time, and the results compared. 

 This I named the 



QUADRUPLE HATCHING-BOX. 



It consists of a box 5 feet 4^ inches long, 3 feet 8f inches wide, 

 and 3 feet 2 inches deep over all. It was built of 2-inch plank, 

 as it was intended to use it out in the open ; the planks jointed 

 with a slip feather as in the 20-feet ponds, and held together 

 by iron bolts tightened by nuts against a runner laid on the 

 bottom. Five grooves were ploughed in each side, three being 

 stopped 6 inches from the bottom, and two 4 inches from 

 the top. In these, five divisions of flooring were fitted with 

 red lead, so that all the joints were water-tight, and a fillet was 

 nailed with its upper edge touching the bottom of the three 

 divisions (Fig. 191). A pipe was fitted into one end near 

 the top to carry off the water, and the supply was obtained by 



