You may have heard of a View-Master…If you were like me, you might have even had one as a child (I loved mine). Using lenses and standard two-dimensional photographic images, these devices provide glimpses into a three-dimensional (3D) world, all contained within a bright plastic box. Before the View-Master however, 3D images were already being enjoyed by earlier generations thanks to an invention known as the Stereoscope (seen in the image below). Using stereo cards placed at a fixed distance from the viewer’s eyes, those from the mid-19th century and onward could visit foreign countries, witness ghostly manifestations, or observe historical events in all three of life’s dimensions!
Holmes-style stereoscope, late 19th c., with a collection of dermatological stereo cards.
The first stereoscope was invented by Sir Charles Wheatstone in 1838. Relying on a pair of mirrors mounted at 45 degree angles, viewers could fix an eye upon the left and right images to experiences a fusing of the images into one solid three-dimensional (3D) image. In 1849, David Brewster of Britain refined Wheatstone’s creation with the development of a lens-based or lenticular stereoscope. Lenses enabled a reduction in the size of the stereoscope, allowing for the production of handheld devices. Known as Brewster Stereoscopes, these devices were a hit when demonstrated at the Great Exhibition of 1851, famously gaining the admiration of Queen Victoria.
Upon further refinement by the Frenchman Jules Duboscq, a creator of stereoscopes and stereoscopic daguerreotypes (stereo cards), the 3D industry developed rapidly within the Western world.  Our Collection’s particular stereoscope most resembles the “American Stereoscope”. First developed by Oliver Wendell Holmes Sr. (a prominent physician and father of the well-known Supreme Court Justice of the same name), during the 1850’s, these stereoscopes allowed more light for visualizing, weighed less, and could comfortably be held in one hand. 
The medical profession found usages for the stereoscope, particularly for educational purposes. Stereo cards, able to provide a sense of space and dimension, introduced viewers to medical diseases and conditions, human anatomy, as well as procedural and technological standards. Using this method of instruction, doctors published both boxes of instructional images (textual descriptions explaining the images of the stereo card were printed on each card’s verso) and printed volumes which attached stereo cards to the bottom of thick, traditional-sized descriptive pages (See image below).
A page within Dr. James Case’s Stereoroentgenography of the Alimentary Tract (1914), providing an example of the proper way to perform a vertical roentgenoscope; note on the cabinet (from which the man is reaching out for a cup containing, most likely, bismuth) is specialized attachment for making stereoroentgenograms.
With the invention of reontgenography, or X-Ray technology, the interior of the living body itself was able to be captured in 3D. This was the first time technology could provide a 3D view of the living body’s interior for medical appreciation and study. The following quote offers a glimpse into the process of creating stereo-roentgenograms (and stereo cards in general, if we swap mention of “X-ray tubes” for “camera”). It is provided by James T. Case, M.D. within the introduction to his 1914 publication, Stereoroentgenography of the Alimentary Tract:
“Stereoscopic roentgenography involves the making of two roentgenograms, the second plate having exactly the position of the first. Before exposing the second plate, the tube [X-ray tube] should be shifted laterally a distance of six centimeters, which is the average interpupillary distance. A roentgenogram is thus made for each eye. The two roentgenograms are then studied in some device [a stereoscope] which permits the fusion of the two images upon the retina.” 
Despite its initial popularity and utility, medical instruction moved away from the stereoscope sometime after the 1920’s. Perhaps this was due to the increasing availability of cadavers, or the availability of moving pictures for instruction, or maybe this change was due to the ready availability of plastic anatomical models. Perhaps the rise of the beloved View-Master, introduced in 1939, shifted the opinions of medical educational community away from this form of 3D education. After all, medicine at this time was experiencing a professional upswing. The utilization of an object like the View-Master, which provided the public with such amusement, might have no longer been welcomed in medical classrooms, looking as they were to instill a sense of professionalism among their students.
If you are interested in learning more about the stereoscope, stereo cards, or the story of their rise and fall in medical education, feel free to stop by the Collection. There is so much history here just waiting to be uncovered!
3. James T. Case (1914). Stereoroentgenography of the Alimentary Tract: Southworth Compnay, p.4 .