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  1. By: Heyl, Paul R
    Type: Article
    In: Proceedings of the American Philosophical Society held at Philadelphia for promoting useful knowledge
    Volume: 49
    Issue: 194
    Date: 1910
    Page Range: 49--51
    Publication Info: Philadelphia, American Philosophical Society,
  2. By: Heyl, Paul R - Briggs, Lyman J. (Lyman James),
    Type: Article
    In: Proceedings of the American Philosophical Society held at Philadelphia for promoting useful knowledge
    Volume: 61
    Issue: 220
    Date: 1922
    Page Range: 15--32
    Publication Info: Philadelphia, American Philosophical Society,
  3. By: Heyl, Paul R
    Type: Article
    In: Proceedings of the American Philosophical Society held at Philadelphia for promoting useful knowledge
    Volume: 52
    Issue: 208
    Date: 1913
    Page Range: 21--30
    Publication Info: Philadelphia, American Philosophical Society,