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https://findingaids.library.iit.edu/repositories/2/resources/855
Collection: Lee de Forest correspondence, 1931 | University Archives and Special Collections...
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https://digital.sciencehistory.org/works/j9602142v
Letter from Lee de Forest to Arnold O. Beckman - Science History Institute Digital Collections
De Forest inquires about Beckman's progress toward a chemical coating that might change in opacity or color, and details the "very fine and uniform quality" of...
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