Periscope

optics · submarines · spy gear · mirrors

Mirrors do the trick. A periscope uses two angled mirrors positioned inside a tube to bounce light from above down to your eyes below. When light bounces off the first mirror, it travels down the tube and bounces off the second mirror to reach your eye, letting you peek over walls or tall objects.

Submarines love them. Submarine crews use periscopes to look at the ocean surface and spot ships or land while staying safely underwater. This lets them navigate and see what is happening above without rising to the top where enemy ships might spot them.

See without being seen. A periscope lets you observe something or someone without them knowing you are looking, because the tube is thin and you can hide the bottom part. Soldiers, spies, and kids playing hide and seek have all used periscopes to gain a sneaky advantage.

Light travels straight. Periscopes work because light always travels in straight lines until it hits something like a mirror that bounces it in a new direction. By carefully angling the mirrors, you can control exactly where the light goes so it reaches your eye from a place you cannot see directly.