General Stoneman and General Naglee
Near Fair Oaks, Virginia, General George Stoneman (seated, right) and General Henry M. Naglee (seated, third from left), sit with members of their staffs in front of a tent during the Civil War. The photograph is a slide for a stereopticon, a projector with two lenses that projects two slides on top of each other. The two photographs are taken at the same time but at a slight distance apart to mimic the human eyes, so that when they are viewed together, the resulting image appears three-dimensional. (A View-Master works the same way.)
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