Template:On This Day (nonfiction)/April 19

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  1567: Mathematician, monk, and academic Michael Stifel dies. Stifel was an Augustinian who became an early supporter of Martin Luther.

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  1860: On his phonautograph machine, Édouard-Léon Scott de Martinville makes the oldest known recording of an audible human voice.

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  1881: Mathematician Karl Mikhailovich Peterson dies. Peterson discovered equations which were subsequently named the Gauss–Codazzi equations, fundamental to the theory of embedded hypersurfaces in a Euclidean space.

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  1912: Chemist Glenn T. Seaborg born. Seaborg will share the 1951 Nobel Prize in Chemistry for the synthesis, discovery, and investigation of transuranium elements.

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  1914: Mathematician and philosopher Charles Sanders Peirce dies. Peirce is remembered as "the father of pragmatism".

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  2016: Theoretical physicist, theoretical chemist, and Nobel laureate Walter Kohn dies. Kohn developed density functional theory, which makes it possible to calculate quantum mechanical electronic structure by equations involving the electronic density.