Stereographs were first made in the 1850s and are still made today. They were most popular between 1870 and 1920. In 1851 stereo daguerreotypes were exhibited for the first time to the general public at the London International Exhibition (Crystal Palace). In June 1838, the British scientist Charles Wheatstone published a paper describing a curious illusion he’d discovered. If you drew two pictures of something—say, a cube, or a tree—from two slightly different perspectives, and then viewed each one through a different eye, your brain would assemble them into a three-dimensional view. This was, he noted, precisely how our vision works; each eye sees a slightly different perspective. Wheatstone created a table-size device to demonstrate the effect, with a viewer that sent a unique image to each eye: the world’s first stereoscope.