After making a few chalk marks on the board, you turn it and chalk the edges of the skeleton, the limbs, the ribs, &c., without moving it. Then take the pulling string in your left hand, held behind the board, whilst your right gesticulates and points out the osteological peculiarities, and set the figure dancing as you please.
If made of metal, strings can be adjusted to shake the head, unfold the fingers, &c.
Fig. 148.
Dolls with ball-and-socket joints to the limbs make excellent marionettes. Suspend them as in figure 148.
The rod A is held in the left hand, and the different threads are worked with the right fingers. If the figure has many articulations and threads to control their movements, hang the stick on a hook at its centre, and use both ends.
A proscenium is constructed, with “a scene flat” set far enough back to let your hands play freely in the intervening space.
THE GYROSCOPE.
This instrument illustrates the law, that the axis of rotation is preserved, in any fixed direction, immovable, while the particles surrounding it are in rapid rotary motion. Hence the humming and the peg-top stand erect, the axis of rotation—the spike or the peg—being kept in a vertical position while in motion; it falls as soon as this motion sinks below a certain rate. This power may be illustrated by placing a disc of wood, or of metal, upon one end of a weighing beam, from which one of the scales has been removed. The disc being equipoised by weights in the opposite scale, place the beam at an angle of 45—the disc being the lowest end—then, by striking the disc, get it into rapid rotation. It will be found that, while spinning, the beam is preserved rigidly in its position; but, as the disc comes to rest, the beam is restored to its horizontal position. Several small weights may be placed in the scale, while the disc is rotating, without disturbing the position of the beam.
