[Illustration: Diagram of apparatus as described in text]
The construction of a transparent globe containing air and liquid, and
also of a smaller globe, in the centre, in imitation of the world. Two
hemispheres of glass are made (fig. 46): one of them is covered with a
plate of bronze, in the middle of which is a round hole, To fit this
hole a light ball, of small size, is constructed, and thrown into the
water contained in the other hemisphere: the covered hemisphere is
next applied to this, and, a certain quantity of liquid having been
removed from the water, the intermediate space will contain the ball;
thus by the application of the second hemisphere what was proposed is
accomplished.