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Measures for Progress: A History of the National Bureau of Standards

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t<br />

Henry D. Hubbard, secretary to Dr.<br />

a contribution to instruction in physics that is still in use today, his modernization<br />

<strong>of</strong> Mendeleev's periodic chart <strong>of</strong> <strong>the</strong> atoms. First constructed in <strong>the</strong> 1920's, it has been frequently revised and reprinted. It now includes<br />

<strong>the</strong> isotopes <strong>of</strong> <strong>the</strong> elements, unknown to <strong>the</strong> twenties.

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