Sir John Leslie (April 16, 1766 – November 3, 1832) was a scientist and physicist during the Scottish Enlightenment. Born in Upper Largo, Fife to a family of modest means, but was recognized for his talents in science when he attended St. Andrews University at the age of thirteen. After having attended for six sessions, Leslie decided to study for the following three years at Edinburgh University. After graduating, he worked as a tutor in Virginia in 1788, and later was served as a teacher to the Wedgwood pottery family in Staffordshire, who later provided him with a laboratory. Leslie is famous for his experimental instruments, such as the hygrometer and differential thermometer, first produced in 1794. However, he is best known for his work Nature and Propagation of Heat (1804) that outlined basic laws of heat radiation. He became the Chair of Mathematics at the Edinburgh University in 1805 and later became the Chair of Natural Philosophy in 1819. On recommendation from Lord Brougham, the Lord Chancellor, he was created a Knight of the Guelphic Order, and was elected Corresponding Member of the Royal Institute of France in 1832. Leslie’s work in the sciences was viewed as controversial by the Church. However, his contributions to science and especially heat theory continue to be influential.