How cool would it be to own your own submarine? Of course, submarines are very expensive. They're also very large. You'd need a lot of water to be able to have fun with it. The average bathtub just wouldn't do.
If you had a submarine, where would you go? Searching for sharks? Exploring the depths of the Mariana Trench or the mysterious Bermuda Triangle? The depths of the sea contain many unexplored frontiers, so your adventures could be never-ending!
Every once in a while, you'd probably want to come up to the surface to see what's going on above water. But how would you do that in a submarine? It's not like submarines have sunroofs you could open to see what's happening up above.
Submarines feature a special device called a periscope that allows people inside the submarine to see what's going on above water. The word “periscope" comes from the Greek words peri and scopus, which mean “around" and “look."
Periscopes can be used in many ways beyond seeing above water from a submarine. Periscopes were used in World War I to see beyond the tops of trenches. They're also used frequently in armored vehicles, such as tanks, to see outside when all the vehicle's openings are shut tight.
Periscopes are similar to telescopes in how they're built and how they work. The main part of a periscope is a long tube that has a mirror at each end. The mirrors are attached so that they are parallel to each other at a 45-degree angle.
Arranged in this way, the mirrors bounce reflections of light between them. For example, light bounces off the object you're looking at with the periscope. That light enters the periscope and bounces off the top mirror. The light then hits the bottom mirror and bounces into your eyes.
Isn't it cool how a periscope uses simple scientific principles to let you see around corners or even above water from a submarine? Since submarines often can't come all the way to the surface of the water, their periscopes have special magnifying lenses that make the reflected images bigger, so that you can see them easier.
Historians haven't been able to pinpoint exactly who invented the periscope and when. However, they do know that Johann Gutenberg created a periscope-like device in the 1430s that allowed spectators to see over other people in a crowd at religious festivals.
Today, submarine periscopes feature all sorts of new technology to replace simple mirrors. Some use complex prisms that are much sturdier than regular mirrors. Some newer submarines don't even have periscopes any more. They use special electronic sensors that can be raised above water. These sensors then send electronic signals back to special computers inside the submarine!