If one of the mechanical singing-bird toy-boxes is opened so that the
machinery is laid bare, the mystery will disappear.
[Illustration: Fig. 154.]
The little bird who pops up on his feet when the lid of the box is
opened, flutters his wings, and opens his mouth as the trill comes
forth, has nothing to do with the sound.
That comes from a short tube, which has a supply of air from a little
bellows, regulated by a piston. Its action is controlled by a lever,
acted on by the same clockwork which works the bellows, and turns a
barrel set with pins for the tune like any barrel-organ.
To make one, get a toy bird, and mount it on a box, concealed in which
is such an instrument as is found in musical albums and valentines; the
opening of its bill and wings needs a very simple connection with the
wheel of the barrel.