A former President of the Magic Circle, three times awarded
the International Award for Magic, commented when he saw this
trick: “Absolutely incredible!”
It might be of interest to conjurers that it was a vaguely
similar trick that gave rise to the idea. The trick, called the
“Domino Box”, was published in the Magic Circular in April 1991,
and revealed the contents of a box by giving a parallel LED
readout through smoky Perspex. However, it used more than
tw1ice as many components, and the smoky Perspex was open to some
The elements of any good conjuring trick are a combination of
simplicity on the one hand, and bafflement on the other – both of
which are present in this trick.
The design uses tactile sense (or rather, neural sense) to
reveal the contents of a box. The box contains 4 shapes, as in a
child`s shape sorter. The conjurer asks a person to secretly
remove from the box any shape or shapes of his or her choosing,
then to close the box, and to place a silk over it. The conjurer
then rests a hand on the silk, and through “extra-sensory
powers” reveals the contents of the box.
The trick works as follows: each of the 4 shapes hides within
it a magnet or magnets. The circuit sends a series of low-current
high-voltage pulses to the surface of the box (by way of metal
hinges, screws, or studs). When a shape is removed from its
receptacle in the box, a reed switch (one of S1 to S4) under the
receptacle opens, causing the pulse for that receptacle to drop
out, so that one may identify which shapes are missing from
inside the box. There is also a longer “marker” pulse (D1 and D2)
so that one may identify the first shape in the sequence (the
sequence repeats indefinitely). Figure 2 shows the pulses when
all 4 shapes are inside the box:
Figure 3 shows the pulses when only the rectangular shape and the square shape are inside the box.
The trickiest part of the trick is to learn whether the circle
shape is missing or not, since its corresponding pulse is tacked
on to the “marker” pulse.
Figure 4 shows how the magnet is positioned in the square
shape, and the reed switch beneath it. An additional magnet may
be positioned in the shape in case it is inserted into its
receptacle upside down.
The high-voltage pulses are imperceptible to a dry hand (eg.
others handling the box), yet if the conjurer moistens a finger
or fingers with the tongue, and touches the electrodes (hinges,
etc.) through the silk, these pulses will be easily felt.
The best result is obtained when separate fingers of the same
hand touch the electrodes.
Though a high voltage is present, the circuit is safe, since
the current flowing through the electrodes is very low.
Especially if separate fingers of the same hand are used to
detect the pulses, there should be no risk to life or health
whatsoever. Nevertheless, any persons using a pacemaker, or
having any history of epilepsy, would be advised to avoid this
Ideally, the shapes will follow the usual conjuring sequence
as follows: 1 side (circle) – 2 sides (rectangle) – 3 sides
(triangle) – 4 sides (square). Since no switch should be visible,
a mercury switch (S5) was used to switch off the circuit when
the box was laid on its side. The circuit ought to operate
for 4 hours off a small PP3 9V battery.
IC1 is a slow astable multi vibrator, which sequences IC2
through 6 pulses, the first 2 of which form the “marker” pulse.
VR1 controls the speed of the pulses. S1 to S4 determine whether
any of the pulses will drop out, by altering the potential at TR1
emitter. NAND Schmitt triggers IC3a and IC3b convert TR1`s
emitter potential to a logical high or low, which is used to
switch IC4. IC4 is an astable multi vibrator, wired to obtain a
duty ratio of 10%. IC3c inverts the logic of IC4, while TR2
amplifies the output current from IC3c. Note that VR2 should
initially be turned to 33K, then slowly turned back to obtain the
desirable pulse strength across electrodes E1 and E2 – otherwise
one may receive a small shock. A perceptible sensation is
all one needs!
T1 is a 230V to 3V step-down transformer with its secondary
(3V) coil in circuit. The primary coil serves as the electrodes.
Note that the 555 IC`s both have the CN suffix – they are a low
power version of the 555, with slightly different characteristics
One might wish to have a visual read-out of the pulses in
order to practice the trick more easily. For this, a LED may be
connected temporarily across the electrodes (observing the
correct polarity). In fact a high-brightness LED could be mounted
behind a pinhole in the box to offer alternative visual pulses
to the conjurer instead of the “neural” pulses.