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In this issue:
While modern spies rely on the latest technological advances, many of the principles of espionage have remained unchanged for hundreds of years. For example, the East German secret police used invisible ink to pass hidden messages during the Cold War, and the decades-old formula was deciphered just a few years ago. Likewise, the CIA only recently released formerly classified documents outlining the various types of invisible ink used during World War I. Among them is an ink made from one of the same ingredients as our invisible ink project. So don't think you need a sophisticated GPS (global positioning system) surveillance transmitter to conduct your own spying; submarines still use periscopes today and so can you!
Milk Carton Periscope
The word periscope comes from the Greek roots peri, meaning "around," and skopos, meaning "to look." The instrument is comprised of a tube with two parallel mirrors or prisms positioned facing each other at a 45-degree angle. Although most often associated with submarines, during World War I, infantry troops used periscopes to see out from the trenches without exposing themselves to enemy fire.Materials:
What to do:
(Ask an adult to do the cutting!)
We're able to see objects because electromagnetic energy in the form of light waves bounces off the objects and travels into our eyes, forming an image on the retina that our brains can read. However, since light travels only in a straight line, if something is not in our direct line of sight, the refracted light bouncing off it cannot enter our eyes. But periscopes redirect light waves, allowing us to see objects around corners, over obstacles, or, as in a submarine, from underwater. Light bounces off an object and hits the first mirror, then it's reflected through the tube, off the other mirror and into the eye of the viewer.
Can you think of ways to modify the periscope? How would using a longer tube or a smaller mirror change what you see? Can you use your periscope to see underneath objects, too? Can you think of other reflective objects you could use in place of the mirrors? How about old CDs or DVDs? What about the tubing? Could you make a periscope out of something besides juice cartons?
Invisible inks, also called sympathetic inks, can be made with many different substances. Sometimes they appear when you heat them up; other times another chemical reveals them. Get creative and see how many kinds of invisible ink you can find.
What to do:
What other sympathetic inks can you find? Which kind shows up best? Which kind lasts longest?
More Spy Science Projects
Learn more about light and optics.
Discover more periscope history.
More Spy Fun
Measure your spy savvy with these interactive spy games.
Visit the CIA kids' page and try to crack the code.
See how spy tools have changed through the years.