You and a partner sit on opposite sides of a “two-way” mirror. You vary the amount of light illuminating your face while your partner varies the amount of light illuminating his or her face. As you adjust the light, you will see yourself gradually assume aspects of your partner’s features, so that your image becomes a “composite” person.

(1 hour or less)

You can make a two-way mirror from inexpensive Mylar™ reflecting film and ordinary window glass. The variable illumination is accomplished with dimmers commonly available at hardware stores.

To make a two-way mirror, put the reflecting film on one side of the glass, following the instructions for the particular brand of film used. Cover the edges of the glass with cloth tape to prevent the film from peeling and to avoid cuts from any sharp edges on the glass.

Place the lamps as shown in the diagram. Connect each lamp to a dimmer switch and an extension cord.

Stand the mirror on a table. This may be done by standing the mirror between two heavy masses (such as 2 pound [1 kg] lab masses), or by making a wooden stand of some sort. A “sandwich” of two pieces of wood with the mirror in the middle, all rubber-banded together, will work. If you have a table saw, cut a slot for the mirror in a piece of wood. Anything that works will do.

(15 minutes or more)

Sit across the table from your partner with the two-way mirror in between. The room should be dimly lit or dark. Be sure that you and your partner are the same distance from the mirror. You should be able to see both your partner’s face through the mirror and your own face reflected in the mirror. Line up your reflected eyes and nose so that they coincide with your partner’s. You will have to adjust your distance from the mirror as you do this. Point one lamp directly at your face and have your partner point the other lamp directly at his or her face. Adjust both lamps so they are initially very dim. Now use the dimmer to vary the amount of light reaching your face. Have your partner adjust his or her dimmer. Watch your features blend with your partner’s features.

Some light sources flash on and off many times a second. When you give them the “Bronx cheer,” you can see the their hidden flickering.

(5 minutes or less)

No assembly is required for the digital radio, circuit tester, or neon glow lamp; just plug them in and observe them from a few feet away.

A simple source for a neon glow lamp is a button-type nightlight. These are small orange night-lights advertised as 1/4 watt bulbs. They do not have a regular replaceable small lighibulb. Plug the nightlight into the wall or into an extension cord that is plugged in.

(5 minutes or more)

Observe the light source from 3 to 10 feet (90 to 300 cm) away and give it the “Bronx cheer.” (A Bronx cheer, also known as a “raspberry,” is a rude noise made by blowing air through your lips in a way that makes them vibrate.) Notice that the light seems to wiggle back and forth and flicker. Try shaking your head rapidly and notice whether the light still flickers. See if you can find other body motions that make the light flicker. Try the Bronx cheer on other light sources, such as incandescent lightbulbs. Notice whether the light flickers.

No part of the LEDs or the neon glow tube move when you give the Bronx cheer. Instead, your whole body is vibrating, including your eyes. you can feel this vibration by putting your hand on your head as you blow. The LEDs flash on and off sixty times a second (a neon glow tube glows on and off 120 times a second). This flashing is so fast that your eyes normally can’t separate the “blinks.” But when your body is vibrating, your eyes are in a different position each time the bulb flashes. As the image of the bulb traces a path across your eyes, it looks like the bulb is moving and flickering. An incandescent bulb won’t flicker when you give the Bronx cheer, because the bulb doesn’t flash on and off. Incandescent bulbs give a steady glow.