Holmes Stereoscope, circa 1900

Stereoscopy is the process of creating the visual illusion of depth by the placement of two near identical images side by side. These images are slightly offset to represent the difference in perspective of the left and right eye. Known as stereograms and usually affixed to a card, they are viewed by using a device known as a stereoscope. The stereoscope contains lenses that slightly enlarge the images as well as make them appear more distant. The two separate images then fuse together and appear as a singular “stereo” image that is a virtual three dimensional recreation of the photographed image. This particular viewer, known as the Holmes Stereoscope, was developed by physician and poet Oliver Wendell Holmes, Sr. (1809-1894) as a portable and economical alternative to the more expensive and bulky earlier models. Perhaps partially because Holmes did not patent his invention, it soon became the most popular and common type of viewer.