A periscope is a laboratory instrument used to view objects or scenes that are not directly visible due to obstructions or distance. It consists of a long, narrow tube with two mirrors set at opposite angles to each other, which allows light to be reflected at a 90-degree angle. By positioning the periscope above or around an obstruction, an observer can view the reflected image of an object or scene that is out of sight.

Periscopes are commonly used in physics experiments to study the principles of reflection, and in engineering applications where it is necessary to observe or inspect objects in hard-to-reach locations, such as in pipelines or inside engines.

Additionally, periscopes have military applications, such as allowing soldiers to observe their surroundings while remaining in a protected position, and in submarines where they are used to observe objects or vessels on the surface while the submarine remains submerged.