Making Periscopes
A periscope lets you see over the top of things, such as fences or walls that you aren't tall enough to look over. You can also use it to see around corners.
People first started using periscopes in submarines in about 1860, to allow the sailors to see above the water. Later, soldiers in the First World War used them to look out of the trenches without having to put their heads out of the trench. Periscopes are still used today in tanks and some submarines.
A simple periscope is just a long tube with a mirror at each end. The mirrors are fitted into each end of the tube at an angle of exactly 45 degrees (45°) so that they face each other.
In the periscope, light hits the top mirror at 45° and reflects away at the same angle. The light then bounces down to the bottom mirror. When that reflected light hits the second mirror it is reflected again at 45°, right into your eye. You can see this in the picture on the right.
Light is always reflected away from a mirror at the same angle that it hits the mirror.
(You can try this game from BBC Bitesize to see how you can use mirrors to reflect light in different directions.)
We made our own periscopes using sheets of cardboard and small mirrors.
How to make a Periscope
Find a piece of cardboard A4 size or larger. Really big cereal boxes are perfect. You need two mirrors for one periscope. We used 5cm x 5cm mirrors which you can buy quite cheaply from Hobbycraft (or you can get them online for a little more).
Click on the picture to enlarge
If you - or your Mum or Nan! - has any old makeup mirrors of a suitable size (the sort you get in powder or eye makeup compacts) they should work fine too.
Now you need to either:
carefully copy out the template on the right onto your cardboard with a ruler
or
print out this PDF and glue it carefully on to the cardboard with a glue stick. If you use the printout, make sure your printer is set to print on to A4 size pages (not letter size). The template only just fits on a sheet of A4, so you might lose the edges and have to draw them back on.
› Periscope Template 
If you are using 5cm square mirrors, the important thing is to check that all four sides of your periscope are 5cm across before you cut it out.
The length of the periscope does not matter, so you can make one as long as your cardboard - great if you have a really big piece of card.
Now follow the instructions under the photos:
Glue the template securely to the cardboard.
If you can print it straight onto the card, even better.
Cut template out carefully along the solid lines.
Don't cut the tabs off!
This is the shape you should be left with.
Get an adult to score along every dotted line.
Fold carefully (you can fold round the ruler)
along all the scored dotted lines.
Use tape or strong glue to stick the periscope
together using the tabs.
Stick one mirror into each end, facing each other.
Strong glue or double-sided tape work best.
That's it! If you're feeling artistic you can decorate your periscope with felt pens or stickers, or cover it with bright wrapping paper.
Now try to see over something taller than you, or hold the periscope sideways and look round a corner. If you put your finger under one end and look into the other end, your finger will look as long as the periscope!