This is an episcope used in for the following.
projecting flat opaque images, like postcards, prints, photographs, pages of books, but also three-dimensional objects like coins, insects and leaves, on to a screen.
This is the literature from internet that explains it
In use, the episcope is simply placed upon the object to be shown on the screen; the externally mounted reversing mirror is tilted to bring the image to the required height; and the image is then brought into focus. Two 250-watt lamps are used for illuminating the field, which is 5 in.