The construction is after this manner. Let A (fig. 15) be a stream
perpetually running. Underneath place an air-tight vessel, B C D E,
provided with an inclosed diabetes or bent siphon F G, and having
inserted in it a funnel, H K, between the extremity of the tube of
which and the bottom of the vessel a passage is left for the water. Let
the funnel be provided with several smaller pipes, as described before,
at L. It will be found that, while B C D E is being filled with water,
the air that is driven out will produce the notes of birds; and as the
water is being drawn off through the siphon F G after the vessel is
filled, the birds will be mute.
[Illustration: Diagram of apparatus as described in text]
We are now to describe the contrivance by which the owl is enabled to
turn herself towards, or away from, the birds, as we have said. Let a
rod N X turned in a lathe rest on any support M: round this rod let a
tube O P be fitted, so as to move freely about it, and having attached
to it the kettle-drum top R S, on which the owl is to be securely
fixed. Round the tube O P let a chain pass, the two extremities of
which, T U, Q W, wind off in opposite directions, and are attached, by
means of two pullies, the one, T U, to a weight suspended at Y, and
Q W to an empty vessel Z, which lies beneath the siphon or inclosed
diabetes F G. It will be found that while the vessel B C D E is being
emptied, the liquid being carried into the vessel Z causes the tube O
P to revolve, and the owl with it, so as to face the birds: but when
B C D E is exhausted, the vessel Z becomes empty likewise by means of
an inclosed or bent siphon contained within it; and then the weight Y,
again preponderating, causes the owl to turn away just at the time when
the vessel B C D E is being filled again and the notes once more issue
from the birds.