The Magnetic Cards

Draw a pasteboard circle; you then provide yourself with two needles,
similar to those used in the foregoing experiment, (which you must
distinguish by some private mark,) with their opposite points touched
with the magnet. When you place that needle whose pointed end is
touched, on the pivot described in the centre of the circle, it will
stop on one of the four pips, against which you have placed the pin
in the frame; then take the needle off, and, placing the other, it
will stop on the opposite point.

Having matters thus arranged, desire a person to draw a card from a
piquet pack, offering that card against which you have placed the pin
of the dial, which you may easily do, by having a card a little longer
than the rest. If he should not draw it the first time, as he probably
may not, you must make some excuse for shuffling them again, such as
letting the cards fall, as if by accident, or some other manoeuvre,
until he fix on the card. You then tell him to keep it close, and not
let it be seen. Then give him one of the two needles, and desire him
to place it on the pivot, and turn it round, when it will stop at the
colour of the card he chose; then taking that needle off, and
exchanging it, unperceived, for the other, give it to a second person,
telling him to do the same, and it will stop at the name of the
identical card the first person chose.

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