On April 17, 1761, English mathematician and Presbyterian minister Thomas Bayes passed away. He is best known as name giver of the Bayes' theorem, of which he had developed a special case. It expresses (in the Bayesian interpretation) how a subjective degree of belief should rationally change to account for evidence, and finds application in in fields including science, engineering, economics (particularly microeconomics), game theory, medicine and law.
On April 6, 1829, Norwegian mathematician Niels Henrik Abel passed away. Abel is well known in mathematics for proving the impossibility of solving the quintic equation by radicals. In parallel to Évariste Galois - who also died very young - , he laid the foundations of group theory.
On April 4, 1617, Scottish mathematician, physicist, astronomer and astrologer John Napier of Merchiston, the 8th Laird of Merchistoun passed away. John Napier is best known as the discoverer of logarithms. He was also the inventor of the so-called "Napier's bones", a kind of abacus for calculation of products and quotients of numbers. Napier also made common the use of the decimal point in arithmetic and mathematics.
On March 31, 1596, French philosopher, mathematician, and writer René Descartes was born. The Cartesian coordinate system is named after him, allowing reference to a point in space as a set of numbers, and allowing algebraic equations to be expressed as geometric shapes in a two-dimensional coordinate system. He is credited as the father of analytical geometry, the bridge between algebra and geometry, crucial to the discovery of infinitesimal calculus and analysis. Descartes was also one of the key figures in the Scientific Revolution and has been described as an example of genius. He has been dubbed the 'Father of Modern Philosophy'. His Meditations on First Philosophy continues to be a standard text at most university philosophy departments.
On April 23, 1882, German mathematician and physicist Emmy Noether was born, who is best known for her groundbreaking contributions to abstract algebra and theoretical physics. Albert Einstein called her the most important woman in the history of mathematics, as she revolutionized the theories of rings, fields, and algebras.