A stereoscope is an optical device that allows users to view two slightly different images of the same scene, creating a three-dimensional effect. This device works by presenting one image to each eye, mimicking the way human vision perceives depth. Stereoscopes were popular in the 19th and early 20th centuries for viewing photographs and illustrations. The invention of the stereoscope is often attributed to Sir Charles Wheatstone, who demonstrated the principle in 1838. Later, devices like the View-Master became popular for entertainment, allowing users to view 3D images on special cards. Today, stereoscopic technology is also used in virtual reality and 3D films.