The Oracular Mirror
Provide a round mirror of about three inches in diameter and whose
frame is an inch wide. Line the under part of the frame, in which
holes are to be cut, with very thin glass; behind this glass let a
mirror of about two inches diameter be placed, which is to be
moveable, so that by inclining the frame to either side, part of the
mirror will be visible behind the glass on that side.
Then take Spanish chalk
or cypress vitriol, of which you make a
pencil, and with this you may write on a glass, and rub it off with a
cloth, and by breathing on the glass, the writing will appear and
disappear several times. With this pencil write on one side of the
mirror, before it is put in the frame, the word yes, and on the
other side, no; and wipe them off with a cloth.
You propose to a person to ask any question of this mirror that can be
answered by the words yes or no. Then turning the glass to one
side, and putting your mouth close to it, as if to repeat the question
softly, you breathe on it, and the word yes or no will immediately
appear. This mirror will serve for many other agreeable amusements.