[Illustration: Diagram of apparatus as described in text]
If a bowl stands upon a pedestal and has an open water-spout, the
discharge shall suddenly cease, though there be no slide or tap
attached to shut the spout. Let A B (fig. 51), be the bowl on the
pedestal C: through the bottom of the bowl and the pedestal insert a
tube, D E F, terminating in a spout; and at the handle of the vessel
fix a bar, G H, against which another bar, K L, may move about the pin
H: at the extremity K place a vertical bar, K M, moving about the pin
K: to this bar let a box, N X, be attached at M, having weight, and
large enough to inclose the tube D E F. When the bowl is full, if we
depress the extremity L of the bar, the box N X will ascend, and, when
this is raised, the water in the bowl will be carried out through the
tube D E F: but if the extremity L be set free, the box will descend
and encompass the tube D E F, and the air it contains, having no way of
escape, will disconnect the liquid round the tube D E F, and prevent
it from being further carried out through the mouth D. When we again
depress the extremity L the spout will run as before.