Provide an opera-glass about two inches and a half long, the tube of
which is to be of ivory, and so thin that the light may pass through it.
In this tube place a lens of two inches and a quarter focus, so that a
card of about three quarters of an inch long may appear of the size of a
common card. At the bottom of the tube there is to be a circle of black
pasteboard, to which must be fastened a small card with figures on both
sides, by two threads of silk, in such manner that by turning the tube
either side of the card may be visible.
You then offer two cards in a pack to two persons, which they are to
draw, and which are the same as those in the glass. After which you show
each of them the card he has drawn, in the glass, by turning it to the
proper position.
The better to induce the parties to draw the two cards, place them first
on the top of the pack, and then, by making the pass, bring them to the
middle. When you can make the pass in a dextrous manner, it is
preferable, on many occasions, to the long card, which obliges you to
change the pack frequently; for otherwise it would be observed that the
same card is always drawn, and doubtless suspicion arise.