Template:On This Day (nonfiction)/April 9
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1770: Physicist and academic Thomas Johann Seebeck born. Seebeck will discover the thermoelectric effect.
1860: On his phonautograph machine, Édouard-Léon Scott de Martinville makes the oldest known recording of an audible human voice. A visual recording of audio data, it will first be played back in 2008.
1865: Mathematician and electrical engineer Charles Proteus Steinmetz born. Steinmetz will foster the development of alternating current, formulating mathematical theories which will advance the expansion of the electric power industry in the United States.