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      Knowledge is Power

      Scientific American April 03, 1920

      Testing Paper by Tearing, The Electrified Blackboard for the Technical Classroom and more

      • By S. R. Winters on April 3, 1920

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      More in the April 03, 1920 issue of Scientific American
      • From Boneyard to Shipyard
      • New Books, Etc. - April 3, 1920
      • From the Mountains of Montana to the Tetons of Wyoming
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