Template:Selected anniversaries/April 19

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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. He 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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  1882: Large herd of Flying bison (Bison pterobonasus) migrates from Periphery to New Minneapolis, Canada.

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  1912: Chemist Glenn T. Seaborg born. He 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. He is remembered as "the father of pragmatism".

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  1932: Mathematician Giuseppe Peano publishes new class of Gnomon algorithm functions which use set theory to detect and prevent crimes against mathematical constants.

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  2016: Chromatographic analysis of Violet Spiral reveals "at least two, probably three" previously unknown shades of violet.

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

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  2019: The Great Nerd Giveaway begins. By the end of Minicon 54, hundreds of nerd items will have found new homes, with lots of fun generated in the process.