How to make three little children dance in a glass upon a table.
Take little figures of glass that are made hollow, of an inch and a half high, representing little boys, which may be had at the glass-blowers; these little images have a small hole in one of their legs, and are lighter than water; immerge them into the water contained in the glass A. B. this glass is about a foot or 15 inches high, and covered with a bladder which is tied fast over the top; a small quantity of air is to be left between the bladder and surface of the water; so, when you command them to walk down, press your hand hard upon the top, and they will immediately come down, and so you may make them dance in the middle of the glass, at your pleasure; and when you would have them to go up to the top, take your hand away, and they will walk up.
I hope this is sufficient for your understanding; if not, you may have the glass and figures of me.