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"  DEGREE OF DIFFICULTY: 1/10 AGES: 4+ BUILD TIME: 2 Hours PARTS COST: About $20 MATERIALS  \u00B7 Two pieces 3 x 15-inch foam board \u00B7 Two pieces 3.5 x 18-inch foam board \u00B7 Two pieces 3 x 3-inch foam board \u00B7 Two 3 x 3-inch mirrors \u00B7 Duct tape Assemble this eye-spy device with your kids, and in a short time, your little ones will be peeking over your neighbors&amp;#039; fences and around bedroom corners. Hey, no one said espionage was ethical. HOW IT WORKS To understand the optics of periscopes, think of the letter Z. The light reflected from an object hits a mirror tilted at45 degrees at the top of the device. The light then bounces to an identically angled mirror at the bottom, providing the image we see when we look into a periscope. If you follow the path of light, it&amp;#039;s approximately Z-shaped.  HOW TO MAKE IT 1. Cut foam board to size. 2. Assemble a four-sided chamber by alternating the placement of the 3 x 15-inch and 3.5 x 18-inch pieces and securing them with tape; there should be 3-inch-square openings at the top front and lower back of the chamber. 3. Cap both ends by taping 3 x 3-inch foam-board pieces into place. 4. Fold two 3-inch-long strips of tape at a right angle, and stick them to two opposite edges of each mirror. 5. Fasten the mirrors inside the chamber. To get the 45-degree angle, position the mirrors so that their front edges align with those of the top and bottom openings; when viewed head-on, the mirrors should fill the 3-inch openings. "^^<http://www.w3.org/2001/XMLSchema#string>
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