Template:Selected anniversaries/April 9
1770: Physicist and academic Thomas Johann Seebeck born. Seebeck will discover the thermoelectric effect.
1805: Mathematician and crime-fighter Joseph-Louis Lagrange delivers lecture on applications of number theory to the detection and prevention of crimes against mathematical constants.
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.
1864: Engineer and physicist Wilhelm Röntgen uses X-rays generator to expose loaded dice, reveals organized math crime cartel in casinos around the world.
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.
1978: Musician and alleged math criminal Skip Digits performs at the Kennedy Center for the Arts.
2018: Green Tangle voted Picture of the Day by the citizens of New Minneapolis, Canada.