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Improvements in Demonstration Boards or Devices for Teaching purposes.
Improvements in Demonstration Boards or Devices for Teaching purposes.
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机译:用于教学目的的演示板或设备的改进。
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摘要
29,280. Platt, H. H. Dec. 22. Magic-lantern apparatus.-A tracing-blackboard A fitted with a ground-glass front B is converted into a magic-lantern screen by removing the hinged back C, for which purpose the hinge pins are detachable.
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