My guess is that this set of 15 old stereographic drawings were a class assignment: most of them are signed, all with different names, except for L.H Wagner, perhaps the class overachiever, whose signature appears on two! Executed in ink or a few in pencil on heavy cream board, I really love them just as drawings and would be inclined to mount and frame them in small groupings--but if viewed through an old stereograph one could experience the 3-dimensional effect of the merger of each pair of images. Or just cross your eyes!
Stereographs came into widespread use in the second half of the 19th century, most typically used for viewing photographs, of which a wide variety were produced. They were ultimately replaced by the (far less beautiful!) ViewMaster in the 1940s, which allowed for clicking through multiple images on rotating cardboard disks.
Each card measures 3 1/2" tall x 7" long. There is some darkening to the boards around the edges and smudge marks here and there, but they are in overall very good condition, with no tears, bends, or holes.