35 
position, but as it fills with water the centre of gravity 
gradually alters until the box turns over and discharges 
the contents, immediately returning to the horizontal 
position again. The weight of the box and its frame 
should just ‘be sufficient to raise the arm carrying the 
frame with the wires, but without the weighted rods. The 
quantity of water required to lift the rods and weights 
is found ‘by weighing one rod with its weight, and then 
multiplying that by the number of weighted rods 
employed. The box should be made to contain rather 
more than the exact quantity of water required. In the 
Piel Hatchery the waste water from the apparatus and 
other tanks is used for filling the box. When the box is 
empty the rods are down and all the hatching boxes are 
depressed. The box (4) gradually sinks to the floor as 
the water pours in, pulling up the weighted rods (5). By 
the time the rods are raised high enough (6 inches) the 
box has lost its stability, and it falls over, discharging its 
contents at once. ‘The rods at the same instant return 
rapidly to rest, depressing the hatching boxes. The rate 
of movement is easily controlled by regulating the flow 
of water, and also by retarding or hastening the period 
of instability of the tumbling box. ‘This latter can be 
done by adding weights to the side of the box at B, or by 
placing pieces of wood on the frame under the box at D. 
The apparatus when fitted up can be attached to a beam 
in the root of the room, and the whole should be so placed 
that the framework carrying the wires attached to the 
rods is vertically above the point of attachment. 
Explanation of Plate A. 
The drawing represents the front view of the apparatus, 
1. Longitudinal beam resting on the cross beams 
supporting the roof. 
