Template:Selected anniversaries/September 21
1576: Gerolamo Cardano dies. He was one of the most influential mathematicians of the Renaissance.
1577: Mathematician, cosmographer, and crime-fighter Pedro Nunes publishes new class of Gnomon algorithm functions based on navigation and cartography to detect and prevent crimes against mathematical constants at sea.
1792: French Revolution: The National Convention declares France a republic and abolishes the absolute monarchy.
1853: Physicist and academic Heike Kamerlingh Onnes born. He will receive widespread recognition for his work, including the 1913 Nobel Prize in Physics for "his investigations on the properties of matter at low temperatures which led, inter alia, to the production of liquid helium".
1854: Signed first edition of Leonardo Draws Clock Head sells fifty thousand dollars.