THE notes of birds are produced at intervals as follows.
Take an
air-tight vessel (fig. 43), through which a funnel is inserted,
the tube being far enough from the bottom of the vessel to allow of the
passage of water. Above the funnel is placed a hollow vessel, turning on
pivots, and having a weight below, into which water is continually
carried. So long as the vessel on the pivots is empty it will be found
to remain upright, for a weight is attached to its bottom; but, when the
vessel is filled the water is overturned into the air-tight vessel, and
the air contained in the vessel being driven out through a
small pipe will produce the sound. The vessel is emptied of water by
means of a bent siphon, and, while it is being emptied, the vessel on
pivots is again filled and overturned. It will be requisite that the
stream of water should not fall into the centre of the vessel on pivots,
that when filled it may be inverted speedily.