The next illustration (Fig. 2) shows a more elaborate arrangement, in which there are four small birds being watched by an owl; the moment the owl’s back is turned the birds begin to sing, but cease as soon as he turns towards them. In this apparatus the birds are made to sing in precisely the same way as in the last illustration, namely, by the displacement by water of the air in the tank, but as soon as the level of the water in the tank reaches the top of a concentric siphon (F G) the water is discharged into a bucket, the birds cease to sing, and the bucket, owing to its increased weight, lifts the counterbalance weight (Z), and in doing so turns the spindle (P M) which supports the owl (R S). When the bucket is full its contents are discharged by a small siphon within it and it is drawn up by the weight (Z) the owl turns its back to the birds, and the cycle of operations is repeated. [Illustration: Fig. 2.] In the next figure a still more elaborate effect is produced. Here is a pedestal upon which are four little bushes each having a bird sitting in its branches; when water is allowed to flow into the funnel the first bird begins to whistle, and after a few minutes leaves off, when the next bird begins, and when he has finished the third bird sings, after a little time the fourth takes up the song, and when he has finished the first begins again, and so on as long as water is flowing into the funnel. These effects are produced in the simplest possible manner, by a combination of as many superposed tanks as there are birds to sing, the one emptying into the other by siphons. The illustration explains itself. [Illustration: Fig. 3.] In the next device (Fig. 4) we have a bird whose singing is _intermittent_. In this case the water flows into a little cup which topples over the moment it is full, emptying itself into the funnel and immediately righting itself (being loaded at its bottom), the sound is produced by the displaced air escaping through a whistle in the manner already described. [Illustration: Fig. 4.] [Illustration: Fig. 5.]