The table on the right is one of the exhibits I worked on as part of a team that created a new illusions wall at Glasgow Science Centre in 2006. The wall replaced an earlier illusions wall that had a rather flat and dull appearance. Graham Rose designed the new housings, and we populated them with some of the old exhibits, and some new ones too.
Other people on the team were Lindsay Hogg, Clara Lim, and Robin Pollok. The construction was mostly done by Eastern Exhibition and Display.
More about the table
The table is a time-honoured conjuring illusion, but it takes some care to get it right. Underneath the table is a vertical mirror, slotted into the outermost legs, which hides my body. The parts of the carpet and white wall that you see between the table legs are not part of the back wall at all. They are the reflection of a low wall that is underneath the camera position. You can see a dark line at the base of the mirror. To make this line less obvious, we put gaps (out of shot) between the carpet tiles on the plinth, so that the line at the base of the mirror looked like just another gap. Similarly, we put grooves down the table legs, so that the join between the mirror and the legs stood out less. The table is out of shot on the general view of the wall below.
Crazy nuts
Also out of shot on the picture below are these nuts. From a distance, they appear quite normal. However, when you get close to them, you find that they aren't solid nuts at all, but hollow. What appear to be outside (convex) corners are really inside (concave) corners. This is a well-known exhibit (invented by Jerry Andrus) but like the table, it needs some effort to get it right. This exhibit was affectionately known by all on the project as "Ben's nuts".
The rest of the wall
This section describes the remaining exhibits on the wall, from left to right.
Hollow face illusion
The face in question is actually mine. I had my face cast in plaster by Hüttinger Exhibition Engineering during the original build. In the new version, we arranged to light the hollow face from below, which makes the face appear much more convincingly convex.
Strobe disc
This consists of a disc with a series on concentric chequered rings on it. As you spin the disc, the different rings appear to rotate in different directions as they strobe under the exhibition lights. There is a story behind this exhibit. When first designed, it was intended to show how rapidly alternating dark and light areas can blur into grey. The idea is that the outermost ring blurs first, and the innermost one last. However, when we first installed it in the original illusions wall, we discovered that it strobed beautifully. One quick rewrite of the exhibit text later...
Stroop effect
In the Stroop effect, a list of colour names is printed in inks that don't match - for example the word "red" may be printed in green ink. People find it easy to read out the printed words, but extremely difficult to quickly call out the colours of the inks. On the other side of the board, we had a similar list of colour names, but in Finnish. When you can't recognise the colour words, calling out the ink colours is very easy.
We had some ergonomic problems to solve with this exhibit. The board swivelled about a vertical axis to allow users to see both sides. We needed to arrange that the board would automatically return to the side with the English colour names when the user let go, and we also needed to arrange that the board could not be set violently spinning. Read about how we did this.
Motion aftereffect
This consisted of a constantly-rotating disc with a spiral on it. As the disc turns, the spiral appears to contract. When you look at the disc for 30 seconds, and then look away, anything you look at seems to expand for a few seconds. I built the motor mount for this exhibit (picture on the right).
Hollywood mirrors (non-reversing mirror)
This exhibit is made of two flat mirrors arranged at an exact right-angle to each other. When you look into them, you see nothing odd at first. But this combination of mirrors doesn't "reverse" your reflection (I use the quotes advisedly): when you move your left hand, your reflection also moves its left hand. As well as that, you don't need to stand exactly opposite the mirror to see yourself - wherever you stand, you see yourself in the mirror.
Breathing square
This exhibit is the breathing square from the original illusions wall. For this effect to work, the square has to be turned very slowly. Most people spin it too quickly, and walk away from the exhibit feeling faintly bewildered. Ideally, one would have some sort of speed-dependent brake, allowing the square to rotate freely at low speeds but preventing it from turning quickly. We didn't have time to develop that, so instead Robin Pollok and I designed and made a magnetic clutch so that the knob that the user turns slips if they try to apply to high a torque to it. A magnetic clutch is better than a friction-based arrangement because its "grippiness" can be adjusted (by altering the separation of the magnets) and because there is nothing to wear out. Although we made the clutch itself, by that stage of the project there was no budget to modify the exhibit to fit the clutch.
...and one that got away: the impossible crate
One exhibit that never made it was the Impossible Crate. The picture on the right shows one of my development models. Look carefully, and you'll see that what appears to be the back face of the crate is actually nearer to the camera than what appears to be the front face of the crate. The planks cross in front and behind each other in paradoxical ways. I wrote a rather elaborate spreadsheet to do the 3D geometry and calculate the plank sizes for a crate of any size seen from a specified viewpoint. The spreadsheet also drew a plan of the crate, which saved us a lot of work by showing how the crate would appear from the chosen viewpoint. The idea was to make the crate appear to enclose one of the pillars of the building, but we also had to avoid it hitting some walls that were close by. Again, doing the geometry in advance saved some nasty surprises. We made the crate, but it has never been hung up.