Project Gutenberg
#OTD in 1843.
William Rowan Hamilton invents quaternions, a 3D system of complex numbers.
Important precursors to this work included Euler's four-square identity (1748) & Olinde Rodrigues' parameterization of general rotations by 4 parameters (1840), but neither of these writers treated the four-parameter rotations as an algebra. Carl Friedrich Gauss had discovered quaternions in 1819, but this work was not published until 1900.
https://en.wikipedia.org/wiki/Quaternion
Project Gutenberg
Three letters, one number, a knife and a stone bridge: how a graffitied equation changed mathematical history.
On October 16 1843, the Irish mathematician William Rowan Hamilton had an epiphany during a walk alongside Dublin’s Royal Canal. He was so excited he took out his penknife and carved his discovery right then and there on Broome Bridge.
By Robyn Arianrhod via @ConversationEDU
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