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Alexander Beckers of New York City patented a stereo-viewer on April 7, 1857. It had a revolving mechanism which allowed multiple views of different types to be inspected sequentially by turning a knob.
National Gallery of Canada, The Origins of Photography: The Matthew R. Isenburg and Enhanced Isenburg Collections 1840-1880
This stereo-viewer held 25 images but there was another version that held 50.