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I spy

This week we're looking at spy themed activities. These are mostly for fun, but there are some science and maths links too.

Codes and Ciphers

Kicking off our spy theme today we have codes and ciphers.  The two terms are often used interchangeably but codes are broadly where you disguise a written message by substituting whole words for other words or symbols and ciphers where you substitute or jumble up individual letters.  That means that most of the things I thought were codes when I was growing up were really ciphers.  There's a nice run down of some different codes and ciphers for kids on this page.

For something altogether more challenging (although it starts out a bit easier) for older kids try the National Cipher Challenge from the University of Southampton.  This contains the whole of the 2004 competition including solutions. 

As an aside, lots of books have ciphers in them, but I particularly like the ones in the bottom margin of the Artemis Fowl books by Eoin Colfer (substitution cipher) and for older readers the last pages of Red Shift by Alan Garner which uses a cipher method from Lewis Carroll. Have His Carcase by Dorothy Sayers has a nice breakdown of decoding a message that uses the Playfair method.

Secret Writing

The classic way of creating secret writing is to use lemon juice and a heat source as shown on this page although I'd recommend an iron as a heat source rather than a light bulb.  A more modern way of writing secret messages is to use a pen that glows under UV light.  UV stands for ultraviolet and it is a form of light that we can't normally see (although other animals, like bees, can).  You'll need to buy a UV torch (be careful not to look directly at the light) but you can then use UV security marking pens to write messages that only show up under UV light.  If you do buy a UV torch do take a look at bank notes, passports and credit cards as there are often hidden pictures that can only be seen with a UV light.  Can you think why? 

Another way of hiding writing is just to make it very very small.  You might have heard of things called microdots these allowed whole pages of information to be photographed and shrunk down to the size of a full stop.  You can see a picture of the camera they used on the CIA flickr account.  Although it isn't as small as on a microdot, you can see an example of microwriting on the £5 note below the queen's portrait as described here (under 'print quality'). This is probably best seen under a microscope, but I could just about see it by taking a photo on my smartphone and zooming in on it.  Find the word FIVE in capitals under the E II R on the portrait of the queen. The decorative line pattern round the word FIVE is actually made up of tiny tiny writing.

Dead Drops

Another way of passing messages was just to put them in a secret hiding place called a dead drop.  The modern day hobby of geocaching uses a similar idea and is great fun.  Follow the coordinates to a hidden container and sign the log to say you found it.  You can buy special GPS devices for this but nowadays you can just download the geocaching app to a smartphone instead.  It's free to sign up for a basic account at and the hidden containers vary from something the size of an address holder for a cat collar to a large suitcase.  I've found a few over the years including one where you had to twist a signpost round to release a catch to get at the container which was great once I'd figured it out on my fourth visit!  Most hides are much more straightforward though. Another useful skill for spies is map reading, particularly if you are having to travel somewhere unfamiliar.  There are some nice map reading activities available here, including one finding your way round a treasure map. 

Observation and memory

Spies have to be very good at both observing and memorising things. A good way to practice this is to play a memory game, often known as Kim's game where you try to remember different objects on a tray.  One way to help you remember might be to try to make up a story linking all the objects (the sillier the better as it will help to stick in your memory).  So for instance if you had to remember: a torch, a paperclip, a packet of crisps, a balloon, a mug and a model London Bus then you could make up a story where you were travelling on a London Bus at night when all the lights went out so you got out your torch and shone it through the window when you saw a mouse in a mug suspended under a balloon fishing for crisps with a fishing rod made out of a paperclip on a piece of string.  Have a go, it really helps if you create a picture in your mind of something actually happening.  

Footprints and Fingerprints 

When spies are investigating, like detectives, it may be useful to look at the footprints or tyre tread marks that get left behind in mud etc.  Have a look at the soles of your shoes, would the footprints left by them look the same as shoes that belong to other members of your family?  You could carefully take some impressions of a bicycle tyre tread by cycling over a muddy area or perhaps a disk made of playdough.  This web page has some instructions for making a plaster cast of animal footprints, but you could use the same techniques to create casts for footprints  or tyre tread marks if a car or bicycle has travelled on muddy ground. 

Fingerprints are unique to individuals and not even identical twins have the same fingerprints.  This page has a nice set of activities on fingerprints including dusting for them.  This forensic detective resource from the BBC includes a section on fingerprint analysis (as well as fibre analysis and chromatography).

That's all for this week.  Next week is my last regular blog post on kids activities and it is likely to feature lots of my favourite activities that I couldn't fit anywhere else!  If you've read my blog or had a go at any of the activities so far, do let me know.

And finally ... 

Sid hanging out on one of my bookshelves.

Black kitten on bookshelf