Stereoscope

A stereoscope is a simple optical device — two lenses and a sliding holder — that presents a slightly different photograph to each eye, which the brain fuses into a single three-dimensional image. The mirror stereoscope was invented by Charles Wheatstone in 1838, but it was Oliver Wendell Holmes's cheap handheld viewer of 1861 that turned it into a craze.

Victorian parlors filled with stereograph cards: tourist views of Niagara Falls and the Pyramids, comic scenes, famous artworks, even early virtual-travel series. For a generation that would never leave its county, the stereoscope was armchair tourism — cards were printed in huge numbers, traded, and collected in albums.

It fascinates because it was the first mass medium to hack human vision — Victorian virtual reality, decades before cinema. The cards' strange double images, useless without the viewer, are a perfect emblem of how Victorians embraced new technology with total delight.