Science, Technology and Discoveries

Maxwell, James Clerk

Maxwell, James Clerk (1831-1879), British physicist, best known for his work on the connection between light and electromagnetic waves (traveling waves of energy). Maxwell discovered that light consists of electromagnetic waves (see Electromagnetic Radiation) and established the kinetic theory of gases. The kinetic theory of gases explains the relationship between the movement of molecules in a gas and the gas’s temperature and other properties. He also showed that the rings of the planet Saturn are made up of many small particles and demonstrated the principles governing color vision.

Maxwell was born in Edinburgh, Scotland. He was educated at Edinburgh Academy from 1841 to 1847, when he entered the University of Edinburgh. He then went on to study at the University of Cambridge in 1850, graduating with a bachelor’s degree in mathematics in 1854. He became a professor of natural philosophy at Marischal College in Aberdeen in 1856. Then in 1860 he moved to London to become a professor of natural philosophy and astronomy at King's College. On the death of his father in 1865, Maxwell returned to his family home in Scotland and devoted himself to research. In 1871 he moved to Cambridge, where he became the first professor of experimental physics and set up the Cavendish Laboratory, which opened in 1874. Maxwell continued in this position until 1879, when illness forced him to resign.


Maxwell’s first important contribution to science began in 1849, when he applied himself to examining how human eyes detect color. He built on the ideas of British physicist Thomas Young and German scientist Hermann Helmholtz on color vision. Maxwell spun disks painted with sectors of red, green, and blue to mix those primary colors into other colors. He confirmed Young's theory that the eye has three kinds of receptors sensitive to the primary colors and showed that color blindness is due to defects in the receptors. He also fully explained how the addition and subtraction of primary colors produces all other colors. He crowned this achievement in 1861 by producing the first color photograph. Maxwell took this picture, the ancestor of all color photography, printing, and television, of a tartan-patterned ribbon. He used red, green, and blue filters to expose three frames of film. He then projected the images through the appropriate filters to project a colored image.


Maxwell's development of the electromagnetic theory of light took many years. It began with the paper “On Faraday's Lines of Force” (1855–1856), in which Maxwell built on the ideas of British physicist Michael Faraday. Faraday explained that electric and magnetic effects result from lines of force that surround conductors and magnets. Maxwell drew an analogy between the behavior of the lines of force and the flow of a liquid, deriving equations that represented electric and magnetic effects. The next step toward Maxwell’s electromagnetic theory was the publication of the paper “On Physical Lines of Force” (1861–1862). Here Maxwell developed a model for the medium that could carry electric and magnetic effects. He devised a hypothetical medium that consisted of a fluid in which magnetic effects created whirlpool-like structures. These whirlpools were separated by cells created by electric effects, so the combination of magnetic and electric effects formed a honeycomb pattern.


Maxwell's other major contribution to physics was to provide a mathematical basis for the kinetic theory of gases, which explains that gases behave as they do because they are composed of particles in constant motion. Maxwell built on the achievements of German physicist Rudolf Clausius, who in 1857 and 1858 had shown that a gas must consist of molecules in constant motion colliding with each other and with the walls of their container. Clausius developed the idea of the mean free path, which is the average distance that a molecule travels between collisions.