History of the Glass Lantern Slide:
The introduction of lantern slides in 1849, ten years after the invention of photography, allowed photographs to be viewed in an entirely new format. As a transparent slide projected onto a surface, photographs could be seen by a substantial audience. This new larger scale expanded the utility of photography, changing it from an intimate medium to one that was appropriate for entertainment and educational purposes.
This practice of projecting images from glass plates began centuries before the invention of photography. As early as the seventeenth century, the Magic Lantern was used to project painted images on glass for children’s picture shows and for religious displays.
In the 1840s, Philadelphia daguerreotypists William and Frederick Langenheim began experimenting with The Magic Lantern as an apparatus for displaying their photographic images. Because the opaque nature of the daguerreotype prevented its projection, the brothers looked for a medium that would create a transparent image. They employed the discoveries of the French inventor Niepce, who had discovered a way to adhere a light sensitive solution onto glass for the creation of a negative. By using that negative to print onto another sheet of glass rather than onto paper, the Langenheims were able to create a transparent positive image suitable for projection. The brothers patented their invention in 1850 and called it a Hyalotype (hyalo being the Greek word for glass).
The Langenheims envisioned their slides as a form of entertainment, charging a fee to watch their picture shows. While entertainment remained an important function well into the twentieth century, lantern slides had the greatest impact on educational lectures, especially in visual disciplines. They played a vital role in the development of disciplines such as art and architectural history, making possible the detailed study of objects and sites from around the world.
Use of lantern slides lasted until the 1950s when their popularity began to decline with the introduction of smaller 2x2 transparencies. Finally, the discovery of the Kodachrome three-color process made 35mm slides less expensive to produce than lantern slides. Although their production ended over 40 years ago, many academic slide collections still house and use glass slides. In some cases, the views that they represent are either drastically changed or no longer exist and thus they are invaluable images of the world during the nineteenth and early twentieth centuries.
Further Information on Glass Lantern Slides (Library of Congress)