Physical Explanation of the Illusion

The science behind this wizardry is simply the physical properties of reflected light. The explanation for this famous illusion is illustrated in Figure 1. If two mirrors are positioned at right angles with their apex directly behind the table leg, the mirrors will reflect the sides of the box and create a false back.

In reality the head belongs to a body extending downward from the table-top. This kneeling human being is concealed from the audience by two very clean plate-glass mirrors, shown as “M” in sketch at the righthand side of Figure 1. The walls, floor, and ceiling of the box-like recess in which the table is placed are covered with the same material. When properly arranged, the mirrors reflect light from side walls to form virtual images that the audience assumes to be portions of the rear wall. Thus the table appears to be open underneath.

The body associated with the talking head can be hidden in the V-shaped space behind the mirrors, visible in Figure 2. The front table leg itself masks where the mirrors are joined. The audience rarely notices the absence of a fourth leg, if it noticed this at all assumed the back leg was obscured by the front leg.

The Sphinx: An Illusion with MirrorsRichard Gelderman, Michael Carini, Keith Andrew & Alexander Barzilov

Western Kentucky University, Bowling Green, KY 42101-1077

Torso on a Pole: Our Version of the Illusion

For our team’s Dematerialization we modified the classic Sphinx Illusion. The person in the box is introduced to the audience, sitting cross legged in a box. After this person annoys the the wizard once too many times, the wizard dematerializes the man’s lower body.

Our illusion utilizes mirrors that can be swung into place while a swirl of the wizard’s cape has blocked the audience’s view. As with the Sphinx Illusion, the body is hidden in the V-shaped space behind the mirrors, making it appear that he is just a head and torso. The pole masks where the mirrors are joined. The basic explanation for our variation is illustrated below.

Initially, the entire person was going to dematerialize; but we could not get either a limber enough volunteer or a big enough set of box and mirrors. Our compromise was to only dematerialize the lower portion of the person, using mirrors and the small cylinder upon which the box is mounted. Having the box high allowed for less sensitivity with the sight lines and gave a place for his legs to go. We chose to use vertical stripes for the material on the sides of the box. Any mismatches in the pattern were less noticeable without complicated or hard to reproduce patterns.

Figure 3: Examples of the modern Head on a Platter Illusion, a variation of the Sphinx Illusion.

History of the Sphinx Illusion

The expression "it's all done with mirrors" is largely due to popularity in the mid-1800’s of the Sphinx Illusion. This illusion wasinvented in 1865 by Thomas Tobin, a science lecturer at the Royal Polytechnic Institution; and made famous by English magician Colonel Stodare.

In the Sphinx Illusion, the magician greet the audience with a tale about during her travels in the deserts of Egypt she came upon an ancient statue of the Sphinx and the miraculous coming to life of the Sphinx’s head. The magician continues to set the scene by relating the tale of how a curse placed upon an unfortunate priestess by the wrathful pharaoh Rameses, imprisoning the priestess in the stone statue of a Sphinx. The magician explains that this head is now in the box in her hand. Walking to the table she places the box on the table and after some impressive words, presto! the Sphinxian head appears. The bodiless head proceeds to converse with the magician.

The original trick awed audiences for many nights and defied explanation until one night a keen observer noted finger-prints on what proved to be a mirror.

Figure 1: Schematic explanation of how the optical illusion created by the double-mirror creates the classic Sphinx Illusion.

References: Hiding the Elephant: How Magicians Invented the Impossible and

Learned to Disappear, J. Steinmeyer, 2003, Carroll & Graf Publishers.

The Haunted Physics Lab, T.H.Zepf, in The Physics Teacher, October 2004, Volume 42, Issue 7, pp. 404-408.

Figure 2: Modern example of a table and double-mirror used with the Sphinx Illusion. In this image the bottom edges of the mirrors can be seen against the rug. However, when the shag carpet is fluffed up to hide the edges of the mirrors and the lights are dimmed, the illusion is stunning.