April 30

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  1777: Mathematician, astronomer, and physicist Carl Friedrich Gauss born. He will have an exceptional influence in many fields of mathematics and science and be ranked as one of history's most influential mathematicians.

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  1897: J. J. Thomson of the Cavendish Laboratory announces his discovery of the electron as a subatomic particle, over 1,800 times smaller than a proton (in the atomic nucleus), at a lecture at the Royal Institution in London.

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  1913: Mathematician and cryptanalyst Genevieve Grotjan Feinstein born. Feinstein will work for the Signals Intelligence Service throughout World War II, playing an important role in deciphering the Japanese cryptography machine Purple, and will later work on the Cold War-era Venona project.

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  1916: Mathematician, engineer, and information scientist Claude Shannon born. He will be known as "the father of information theory".

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  1973: Watergate: U.S. President Richard Nixon announces that White House Counsel John Dean has been fired and that other top aides, most notably H. R. Haldeman and John Ehrlichman, have resigned.