Stereoscopes were initially used to provide 3D images of Civil War battle scenes, but became useful in classrooms for historical purposes. The technology uses right and left eye photos to create a three-dimensional image.
Image: National Museum of American History
Jonathan Greig has nothing to disclose. He doesn't hold investments in the technology companies he covers.
Jonathan Greig is a freelance journalist based in New York City. He recently returned to the United States after reporting from South Africa, Jordan, and Cambodia since 2013.