The Case of the Graveyard Ghost (8 page)

MATERIALS

• measuring spoon

• water

• clear drinking glass or jar

• red food coloring

• celery stalk with leaves

PROCEDURE

1. Measure 3–6 tablespoons of water into the jar.

2. Add enough red food coloring to turn the water blood red (about 30–40 drops).

3. Slice 1 inch off the bottom of the celery stalk, then place the stalk, cut side down, into the jar. Make sure the cut surface of the celery is completely under water.

4. Record your observations every 15 minutes for the first hour. After 3 hours, rinse off the celery and then slice it crosswise in a few different places. Where are the capillaries located? Did the dye reach the very top? Are there capillaries in the leaves?

How does this work?

Water molecules have adhesive properties—they like to stick together and to other things. (Think of a glass of ice water on a hot day. Water clings in droplets on the outside of the glass. Only when the droplets get too heavy do they fall.) In the same way, water molecules can “climb” a thin tube, such as a capillary, by clinging to the sides of the tube and to each other.

P
icture this. London. 1863. A crowded theater. The lights dim. Suddenly everybody gasps. There, on stage, is a
ghost
. It moves and talks while other actors just walk right through it! AAAAHHHH!!!!!!

It’s a hit! The audience and newspapers love it!

And so, the special effect called Pepper’s Ghost was born, named after its inventor, Professor John Henry Pepper. (Before 1863, a stage ghost would likely have been an actor wearing a sheet. And if another actor had tried to walk through him, the ghost would likely have said, “Ow! You’re stepping on my big toe!” or “You big clumsy knuckle-brain! Watch where you’re going!” or some such.)

Scare yourself silly by making your own Pepper’s Ghost.

MATERIALS

• rectangular cardboard box (at least 15 inches x 10 inches)

• ruler

• scissors

• tape

• plastic glass (Plexiglas or another brand—see step #4)

• miniature ghost model (or scary action figure)

• black cloth (such as a black T-shirt)

• small flashlight

PROCEDURE

1. Make sure that the sides of the cardboard box are taller than your ghost model or action figure.

2. Look at the
diagram
. Measure side B of your box with a ruler. Cut away this amount from side A. (For instance, if side B measures 12 inches, then cut away 12 inches from side A. You should have at least 3 inches remaining on side A. If you have less than 3 inches, find a different box.) Cardboard can be tough to cut. Ask an adult for help if you’re having trouble.

3. With leftover cardboard from step #2, make a half wall (half the length of side B). Using tape, secure directly across from the cut end of side A. This creates a “backstage.”

4. Starting from the back right corner of the half wall, measure diagonally across the stage, ending at the left front corner. This is how long your piece of plastic glass should be. It should be at least as high as the cardboard box. Secure the plastic glass with tape. (Plastic glass—sometimes called Plexiglas—is available from hardware stores and some craft supply stores. They will cut the plastic glass for you.
Do not
attempt to cut it yourself. Edges may be sharp, so be careful!)

5. Place the ghost in the backstage opening. (It works best if you place a black cloth under and around the ghost so that the sides of the cardboard box aren’t reflected.)

6. Prop up a flashlight “backstage” so that it will shine directly on the ghost model.

7. Turn on flashlight.

8. Flip off room lights.

9. Scream.

How does this work?

Light from the flashlight shines onto the ghost model, lighting it up. The light is then projected from the ghost and reflects off the plastic glass back to you, the viewer. But
reflection
really isn’t the right word, because reflection is what happens at the surface of the glass, while what is really happening with Pepper’s Ghost occurs
behind
the glass. While the light is reflected off the glass surface, it
behaves
as if it were at a point in space behind the glass, creating a
virtual image
of the lighted object.

Again, a mirror is a good example. You don’t view your reflection as being flat on the mirror’s surface, as in a poster. Instead, you see yourself in a room behind the mirror. Of course, all of this is an
illusion.
There is no one behind the mirror, any more than there is a ghost behind the glass. What would Sloane have seen as she walked bravely through the ghost image? Nothing.