160 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



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 roof 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, 



