Fortunately, there are ways of hearing and seeing things without being heard or seen yourself. Listening In You can't always be in the room when important matters are being discussed but if you get close enough, like the room next door, you may still be able to pick up all the information you want. All you need is a glass, so if someone walks in you won't have any incriminating equipment. Just practice your innocent smile first! Place the glass, with the bottom pointing into the room, against the wall separating the two rooms. Press your ear against the bottom of the glass and sounds should come through loud and clear. Make sure you keep your other ear alert for anyone who might catch you in the act. make sure your glass is empty How does it work? When we speak or make any sound we produce a sound wave by forcing air molecules to vibrate. At the point closest to where the sound is made, the air molecules are squashed together. These molecules then hit the molecules next to them and this compression travels outwards away from the person who made the noise. When someone is speaking they make a series of these compressions which travel through the air all around them. We can hear sound because these compressions cause our eardrums to vibrate. The sound wave also causes all the other surfaces in the room to vibrate too - including the walls and windows. Sound travels through solids as well as liquids and gases so the compression continues through the wall where you can pick it up. Putting a glass against a wall means that the air molecules contained in the glass receive the vibrations from the wall. The glass is better than just putting your ear against the wall because the glass forms a better seal and all the vibrations from the air hit the glass no matter what direction they are travelling in. This produces an increased area to collect the vibrations that your ear turns into recognisable sounds. Try experimenting with different sizes of glasses to see which works best. Real spies use a very similar but more hi-tech version of this. Instead of a glass they bounce lasers off the windows of the room they are listening in on. The reflected light is measured and any vibrations or movements in the glass can be analysed to reproduce the conversation going on inside. Looking Around Corners As a spy you may need to watch secret meetings - but how do you get to see them without being seen? By making your own periscope! A periscope will allow you to remain hidden behind a bush or around a corner whilst still seeing clearly what is going on. To make a periscope you need a long thin box (or two orange juice cartons taped togetherand two mirrors which are small enough to fit inside your box. 1. Cut a hole in the side of the box, right at the very end. The hole should be a similar size to your mirrors. 2. Next cut a hole in the side of the box at the other end, on the opposite side of the box as your original hole. Again this should be about the size of your mirrors. 3. The tricky bit is to insert the mirrors. The mirrored surface needs to face outwards and it should sit at an angle of 45 degrees to the hole. Tape the first mirror into place. 4. The other mirror goes in the other hole, again facing outwards and at an angle of 45 degrees to the hole. You may need to adjust each mirror slightly to make sure you can see through the periscope properly. How does it work? You can hide behind a wall with only the top mirror of your periscope poking up. Light from the secret meeting hits the top mirror, and is reflected downwards towards the second mirror. The light is reflected again and you can see the meeting clearly in the bottom mirror. Instead of periscopes spies use optical fibres pushed through tiny holes in the wall. These are very long thin fibres of glass coated in a second material. A bundle of them is required to make a picture but since each is very small, only about 0.1 mm across, it isn't hard to get a whole bundle through even the smallest gap. When light enters the optical fibre it is reflected off the boundary between the glass and its coating by a process called total internal reflection. The light bounces along the inside of the fibre until it comes out at the other end. This light is then fed into a camera to produce an image on a screen. receiving your instructions • gathering information • reporting back • spy box menu