Stereoscope

Having a look at a pile of stereoview photographs of the Boer War through this stereoscope is really impressive.
A Pre-runner of 3D glasses this simple optical device allows you to see in relief the special photographs.

The photographs themselves are two images mounted side by side. Each picture is taken from a slightly different viewpoint that corresponds closely to the spacing of the eyes. The left picture represents what the left eye would see, and likewise for the right picture. When observing the pictures through a special viewer, the pair of two-dimensional pictures merge together into a single three-dimensional photograph.

These were one of America's most popular forms of entertainment in the late 1800s and early 1900s. The first patented stereoscope was invented by Sir Charles Wheatstone in 1838. (this isn't him in the picture!)