“It was not until the early eighteen-thirties that the English scientist and inventor Charles Wheatstone began to suspect that the disparities between the two retinal images were . . . crucial to the brain’s mysterious ability to generate a sensation of depth—and that the brain somehow fused these images automatically and unconsciously.

Wheatstone confirmed the truth of his conjecture by an experimental method as simple as it was brilliant. He made pairs of drawings of a solid object as seen from the slightly different perspectives of the two eyes, and then designed an instrument that used mirrors to insure that each eye saw only its own drawing. He called it a stereoscope, from the Greek for ‘solid vision.’ If one looked into the stereoscope, the two flat drawings would fuse to produce a single three-dimensional drawing poised in space.”

—Oliver Sachs, Stereo Sue: Why Two Eyes are Better than One, The New Yorker, June 19, 2006.