Wheatstone's pseudoscope, mid 19th century.
© Science Museum / Science & Society Picture Library
Sir Charles Wheatstone (1802-1875), the English physicist, invented the first stereoscope using mirrors to reproduce the illusion of depth in pictures. Likewise, he was also interested opposite of stereovision, namely when things appear to be inside out. Known as pseudoscopic vision, he discovered this could be produced if an image intended for the right eye was directed to the left and vice versa. Wheatstone studied this in 1850 using the apparatus shown, a device that produced the desired phenomena using a prism. Later, this was developed into the pseudoscope, an optical toy that complemented the stereoscope.