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What is a Periscope?

Mary McMahon
Updated May 21, 2024
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A periscope is an optical device that allows an observer to see things beyond his or her line of sight. One of its classical uses is in submarines: instead of needing to surface to see what is going on at sea level, the submarine can instead stay safely submerged under the water and extend a periscope to look around. These devices are widely used in the military, but also in other fields, such as medicine and hunting.

Several crude versions of the periscope were used as far back as the 1400s, but the modern design was developed in the late 1800s, when the obvious military applications began to be realized. By World War I, they were standard issue to many troops in the trenches, and they were also used in submarine warfare.

Periscopes are made up of a long tube that contains either mirrors or prisms. The mirror or prism at one end captures the image and bends or reflects it so that it can travel down the tube to hit the mirror or prism at the other side, bending the image again so that it can meet the eye of the viewer. If the tube is extremely long, magnifying glasses may be used to enlarge it so that the viewer can see clearly. These devices can be portable, as in the case of ones used in the trenches during the First World War, or they can be fixed into a housing such as a tank or submarine.

People can use periscopes to see above their current location, allowing them to stay concealed and protected behind armor or a wall, and they can also be used to look underground and around corners. The device may be camouflaged so that it will not be readily visible to observers in the distance, ensuring that the position of the viewer will not be given away.

The science behind this tool is fairly simple, and children being introduced to basic optics are sometimes encouraged to construct one to experiment with the principles. They can also be immensely useful aids to some children's games, such as play in which children want to be able to observe a situation while remaining hidden.

Optics stores sometimes carry periscopes or kits that can be used to make them, and specialized versions are also available from medical suppliers and stores which cater to hunters. Although the device is famous for its use on submarines, most navies today actually prefer to use other imaging devices.

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Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a All The Science researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By anon924618 — On Jan 06, 2014

I used to make periscopes when I was a kid. It was pretty fun, sneaking, spying, and looking over the neighbours' walls. Aside from being a fun spy instrument, what are other functions of periscopes?

By jlmk — On Mar 26, 2011

My cousin and I used to play spy all the time when we were kids. It was one of our favorite games, and basically consisted of the two of us sneaking around the yard and the house to spy on his brother and sister.

I remember bending tubes trying to make our own periscopes that we could use to see around corners. Of course they never worked, but we pretended that they did!

I'll bet you can buy toy periscopes these days. I would have loved to have one of those!

By geronimo8 — On Mar 25, 2011

I would love to make periscopes with my children. It sounds like a great activity, and I know they would love to play with them afterward. They get excited by looking through an empty toilet paper tube. I can't even imagine how much fun they would have with a periscope!

Where would I look to find directions on how to make a periscope? I would need something very simple, because my kids are still pretty young.

By upnorth31 — On Mar 22, 2011

I can't believe that periscopes were being used in the 1400's! That's a long time ago! Were these periscopes made with mirrors too, or was a different kind of technology employed.

I would love to see one of these crude periscopes? Are there any still in existence, maybe in a museum somewhere?

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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