announcement of quaternions. A 10-euro commemorative silver proof coin was issued by the Central Bank of Ireland in 2005 to commemorate 200 years since his birth. Commemorations Hamilton's equations are a formulation of classical mechanics. Numerous other concepts and objects in mechanics, such as Hamilton's principle, Hamilton's principal function, the Hamilton–Jacobi equation, Cayley-Hamilton theorem are named after Hamilton. The Hamiltonian is the name of both a function (classical) and an operator (quantum) in physics, and, in a different sense, a term from graph theory. The algebra of quaternions is usually denoted by , or in blackboard bold by , in honour of Hamilton. The Hamilton Building at Trinity College Dublin is named after him. In literature It is believed by some modern mathematicians that Hamilton's work on quaternions was satirized by Charles Lutwidge Dodgson in Alice in Wonderland. In particular, the Mad Hatter's tea party was meant to represent the folly of quaternions and the need to revert to Euclidean geometry. In September 2022 evidence was presented to counter this suggestion, which appears to have been based on an incorrect understanding of both quaternions and their history. Family Hamilton married Helen Bayly, daughter of Rev Henry Bayly, Rector of Nenagh, County Tipperary, in 1833; she was a sister of neighbours to the observatory. They had three children: William Edwin Hamilton (born 1834), Archibald Henry (born 1835) and Helen Eliza Amelia (born 1840). Helen stayed with her widowed mother at Bayly Farm, Nenagh for extended periods, until her mother's death in 1837. She also was away from Dunsink, staying with sisters, for much of the time from 1840 to 1842. Hamilton's married life was reportedly difficult. In the troubled period of the early 1840s, his sister Sydney ran his household; when Helen returned, he was happier after some depression. See also List of astronomers List of things named after William Rowan Hamilton Theoretical physics References Sources Chow, Tai L. (2013). Classical Mechanics: Chaper 5: Hamilton Formulation of Mechanics: Description of Motion in Phase Spaces. CRC Press, External links Wilkins, David R., Sir William Rowan Hamilton. School of Mathematics, Trinity College, Dublin. Wolfram Research's William Rowan Hamilton Cheryl Haefner's Sir William Rowan Hamilton Hamilton Trust The Hamilton year 2005 web site The Hamilton Mathematics Institute, TCD Hamilton Institute Hamilton biography 1805 births 1865 deaths 19th-century Irish people 19th-century British mathematicians Linear algebraists Alumni of Trinity College Dublin Irish people of Scottish descent