Stereographs were made by a photographic method popularized in the 1840s. The technique capitalizes on the way the brain processes images, placing two nearly identical images side by side which, viewed together, form one three-dimensional image.
Boston’s own Oliver Wendell Holmes invented the stereoscope, a goggles-like device used to view the images. He wrote about the stereographs in the Atlantic Monthly in 1859: “the first effect of looking at a good photograph through the stereoscope is a surprise such as no painting ever produced. The mind feels its way into the very depths of the picture. The scraggy branches of a tree in the foreground run out at us as if they would scratch our eyes out. The elbow of a figure stands forth as to make us almost uncomfortable.”