John Leslie (16.04.1766-3.02.1832) was a Scottish experimental physicist and mathematician and a Fellow of the Royal Society (1807). He was born in Largo. He studied at the University of St Andrews and at the University of Edinburgh. He then engaged in literary work and translation in London. From 1804 he was professor of mathematics, and from 1819 of physics, at the University of Edinburgh.
His work in physics concerned heat and molecular physics. He invented the differential thermometer and the so-called Leslie cube, which he used to study thermal radiation. He initiated the quantitative study of the emissive and absorptive powers of bodies. He obtained relative values of the emissive power of various bodies (relative to soot) and confirmed the theoretical proposition of P. Prévost that strongly emitting bodies have correspondingly a greater absorptive power, and conversely; he proved that emission depends on direction (1804). He studied the quantity of heat received by the Earth's surface from the Sun. He checked Laplace's formula for capillary pressure. He proposed a method of producing artificial ice (1817). He built a hygrometer and a photometer.