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Eureka! X-Ray Tube

Note:  This is the part of a series of posts about science activities to be done in the bathroom – the lav-oratory if you will.

Have you ever wished you could see through walls or inside your birthday gift before you were supposed to open it?

Well this magic tube won’t let you see into gifts or through walls but  you will be able to see right through your hand!

You would think such a tube must involve fancy nanotechnodoohicky engineering.


All you need is a toilet paper tube.

Here’s what you do.

Hold up your left hand so that your fingers are together and your thumb is pointing to the right. Your palm will face away from your face. Place the toilet paper tube between your fingers and thumb and hold it in place. Put the tube up to your right eye and slide your left hand back so that it touches your nose. Open both eyes. You will find that you are looking directly through your left hand! You can even tilt the tube slightly to the left to move the hole towards the center of your hand.

You may be wondering how such a powerful tool has been hiding in your bathroom for years but no one has shared its secret powers with you. That’s because it’s actually an illusion.

This illusion works because you have 2 eyes.

Having 2 eyes is very useful. It allows you to see in 3 dimensions and gives you a wider field of view.

Try this! Hold your hand out in front of your face. Close (or cover) one eye and then close the other eye, alternating back and forth. Did your hand move or everything behind it?   This motion illusion occurs because each eye has a different view of the world. Your brain combines these views together so that you see more with two eyes than you would with just one eye.

When you put the x-ray tube up to your eye you only see what is at the end of the tube. The sides of the tube block out everything else. When your hand is next to the tube your brain combines one eye’s view of your hand with the other eye’s view through the tube so that there appears to be a hole in the middle of your hand!

You can explore the X-ray tube or even use it in a science fair project. Investigate how the following affect the illusion.

  • What if you use a longer or shorter tube?
  • Or a tube that is smaller or bigger around?
  • What if you move your hand closer or further from your eyes?
  • What if you move the tube closer or further from your eyes?
  • How far can you move your hand or the tube before the illusion breaks?