Stereoscope

Having struggled to see the world in Bishop Berkeley's way, as colors on an essentially "flat" background, Stephen allows his mind to snap back into its normal perception of depth: "Ah, see now! Falls back suddenly, frozen in stereoscope. Click does the trick." The stereoscope was a 19th century invention, precursor to the 3D movie glasses of today, that allowed people to resolve a pair of two-dimensional images as one more or less three-dimensional scene. First invented by Sir Charles Wheatstone in 1838, the device had gone through many iterations by 1904.

JH 2017

The Brewster stereoscope, a type demonstrated at the Great Exhibition of 1851, where it impressed Queen Victoria. Source: Wikimedia Commons.

Illustration of two kinds of binocular vision in mammals, showing the rabbit's small sliver of stereoscopic depth perception and the monkey's larger one. Source: www.open.edu.

A cheaper type invented, patent-free, in 1861 by the American Oliver Wendell Holmes, photographed by Davepape in 2006. Source: Wikimedia Commons.