Try this: Pepper’s ghost

You will need

• 3 boxes (photocopy paper boxes are perfect)
• Small glass pane, about 20cm x 25cm (glass from a picture frame works well)
• Desk lamp
• Black felt (enough to cover the inside of one box)
• Coloured card (enough to cover the inside of one box)
• Window cleaner
• Glue
• Scissors
• Ruler
• Pencil
• Plasticine
• Doll’s furniture (optional)

What to do

Open one end of each of the two boxes. Place the open ends at right angles to form a single large ‘L-shaped’ box. Cut up the third box to complete the walls of the box, if you need to.

Choose one of the arms of the ‘L’ shape to be the dark room. Use your glue to stick the black felt onto the walls and the floor, covering them entirely.

The other arm of the ‘L’ is your viewing room. Use the coloured card to create walls and a floor. Be decorative.

Cut a square viewing hole out of one of the dark room’s walls close to the intersection. It must look down the arm into the viewing room. Look through it – you should see the decorated room without seeing much of the dark room.

Use window cleaner to clean the pane of glass as best as you can. It should be clear of smudges and dust.

At the intersection between the two rooms, sit the pane of glass so it runs between the two corners, separating the rooms at a 45 degree angle.

Use the plasticine to create a small figure (a ghost is a good idea, but you can use your imagination). Put the figure into the dark room.

Set up a scene in the viewing room.

Set up the lamp so it shines directly onto the dark room.

Look into the viewing hole at the scene. What do you see? What happens when you turn on the lamp? How can you make the ghostly image brighter?

What’s happening?

When light hits an object, several things can happen. Its energy can be absorbed, reflected, refracted or transmitted. It all depends on what the object is made of. Some particles will absorb some colours and reflect others, for example. If light doesn’t pass through it, it is described as ‘opaque’.

The particles that make up glass, however, usually transmit light, making it ‘transparent’. This means light energy enters the particles on one side and is emitted again on the other side with only a small amount being absorbed. This way we can see images through it rather clearly.

However if light hits the glass at an angle, some will reflect from its surface rather than pass through it completely. The partial reflection is why the reflection in the glass in Pepper’s Ghost is pale and ‘ghostly’. Each of your eyes sees a slightly different angle of the reflection (see this activity to understand how that works), which gives the ghostly image depth. Without any other clues, you perceive the ghost to be standing in the room, not reflecting from the sheet of glass.

To make the ghost appear stronger, the viewing room can be made darker while more light is shone on the model ghost, which creates more contrast between the ghost and the room you’re looking at.

Applications

Pepper’s Ghost has a rather interesting history. The Polytechnic in London was something like a science museum in the 19th century. John Henry Pepper worked there as its director from 1854, performing science demonstrations for the public. An inventor, Henry Dircks, brought Professor Pepper his idea for an illusion when it failed to sell elsewhere.

Professor Pepper built a stage showing this illusion, with the intention of revealing the science of it at the end of the performance. The crowd were so enthralled with the show that Professor Pepper kept its secret from them. Later, the illusion was picked up by a number of magicians for use in their shows.

Pepper’s Ghost can be seen all over the world today, including Disney’s Haunted Mansion attraction and the Cowra visitor centre in New South Wales.

• Try another Science by Email activity looking at the bending of light

More information

• Cowra visitor centre
• Pepper’s Ghost
• History of stage magic