William Brouncker, 2nd Viscount Brouncker, FRS (1620 - 5 April 1684) was an English mathematician.
Brouncker obtained a PhD at the University of Oxford in 1647. He was one of the founders and the first President of the Royal Society. His mathematical work concerned in particular the calculations of the lengths of the parabola and cycloid, and the quadrature of the hyperbola, which requires approximation of the natural logarithm function by infinite series. He was the first in England to take interest in generalised continued fractions and, following the work of John Wallis, he provided development in the generalised continued fraction of pi.
During the question period after Pepys' presentation, a member challenged Pepys to demonstrate Biblical fallibility before he presumed to substitute his theory for God's word. Lord Brouncker spoke up, citing Second Chronicles, Chapter 4, Verse 2. The verse indicated that a vessel in Solomon'sTemple was 10 cubits across and 30 around. Lord Brouncker indicated the true circumference would be just over 31 cubits as the gentleman could confirm himself with a piece of cord and a rule. Looking troubled, the questioner accepted this answer.