James Clerk Maxwell (1831-1879), the Scottish physicist, did revolutionary work in electromagnetism and the kinetic theory of gases. He formulated, independently of Ludwig Boltzmann, the Maxwell-Boltzmann kinetic theory of gases. Maxwell showed that a few relatively simple mathematical equations could express the behavior of electric and magnetic fields and their interrelated nature. These four partial differential equations first appeared in fully developed form in Electricity and Magnetism (1873). Since known as Maxwell's equations they are one of the great achievements of 19th-century physics.