Maxwell, James Clerk (1831-1879)

Scottish physicist. His main achievement was in the understanding of electromagnetic waves: Maxwell's equations bring together electricity, magnetism, and light in one set of relations. He studied gases, optics, and the sensation of colour, and his theoretical work in magnetism prepared the way for wireless telegraphy and telephony.

In developing the kinetic theory of gases, Maxwell gave the final proof that heat resides in the motion of molecules.

Studying colour vision, Maxwell explained how all colours could be built up from mixtures of the primary colours red, green, and blue. Maxwell confirmed English physicist Thomas Young's theory that the eye has three kinds of receptors sensitive to the primary colours, and showed that colour blindness is due to defects in the receptors. In 1861 he produced the first colour photograph to use a three-colour process.

Maxwell was born in Edinburgh and educated there and at Cambridge. He was professor of natural philosophy at Aberdeen 1856-60, and of natural philosophy and astronomy at London 1860-65. From 1871 he was professor of experimental physics at Cambridge, where he set up the Cavendish Laboratory in 1874.

Maxwell studied Saturn's rings 1856-59 and established that they must be composed of many small bodies in orbit.

Having explained all known effects of electromagnetism, Maxwell went on to infer that light consists of electromagnetic waves. He also established that light has a radiation pressure, and suggested that a whole family of electromagnetic radiations must exist, of which light was only one. (This was confirmed in 1888 with the discovery of radio waves.)

Maxwell's mathematical basis for the kinetic theory of gases dates from 1860, when he used a statistical treatment to arrive at a formula to express the distribution of velocity in gas molecules, and related it to temperature. In 1865 Maxwell and his wife carried out experiments to measure the viscosity of gases over a wide range of pressures and temperatures, and their findings led to new equations. Maxwell's kinetic theory still did not fully explain heat conduction, and it was modified by Austrian physicist Ludwig Boltzmann in 1868, resulting in the Maxwell-Boltzmann distribution law. Both men thereafter contributed to successive refinements of the kinetic theory and it proved fully applicable to all properties of gases.

Maxwell's works include Perception of Colour 1860, Theory of Heat 1871, Treatise on Electricity and Magnetism 1873, and Matter and Motion 1876.