Mathematics walks into history

摘要

Mathematician William Rowan Hamilton did indeed hit on the idea of quaternions - a complex-number system extending into four dimensions - while crossing a Dublin bridge in 1843 (Nature475,167; 2011). Yet it was what the Irishman was doing while absorbed in mathematics that gives him the last laugh, for quaternions are used in the clinical and laboratory analysis of bodily motion, notably of gait. So what was Hamilton doing? Walking into history.