James Clerk Maxwell (1831-1879)
The Scottish physicist James Clerk Maxwell, b. Nov. 13, 1831, d. Nov. 5, 1879, did revolutionary work in electromagnetism and the kinetic theory of gases.
Maxwell's most important achievement was his extension and mathematical formulation of Michael Faraday's theories of electricity and magnetic lines of force. In his research, conducted between 1864 and 1873, Maxwell showed that a few relatively simple mathematical equations could express the behavior of electric and magnetic fields and their interrelated nature; that is, an oscillating electric charge produces an electromagnetic field. 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.
Maxwell also calculated that the speed of propagation of an electromagnetic field is approximately that of the speed of light. He proposed that the phenomenon of light is therefore an electromagnetic phenomenon. Because charges can oscillate with any frequency, Maxwell concluded that visible light forms only a small part of the entire spectrum of possible electromagnetic radiation.
Maxwell used the later-abandoned concept of the ether to explain that electromagnetic radiation did not involve action at a distance. He proposed that electromagnetic-radiation waves were carried by the ether and that magnetic lines of force were disturbances of the ether. Heinrich Hertz discovered such waves in 1888.
James Clerk Maxwell was born in Edinburgh on June 13th 1831, into a modestly wealthy Scottish family. (Maxwell was the family name which his father was required to adopt, by the terms of a legal entailment, in order to inherit the estate). As a child, Maxwell was enrolled in the Edinburgh Academy. It was here that he met Peter Guthrie Tait (1831-1901), a contemporary who pursued a very similar career to Maxwell's own, and who became a life-long friend. Tait later recalled that as a schoolboy Maxwell spent his free time 'drawing curious diagrams and making rude mechanical models'. These pursuits contributed to Maxwell's rather uncomplimentary school nickname of 'Dafty', but bore signs of talent and originality - characteristics which his father sought to nourish by introducing James to the intellectual societies of Edinburgh. Thus encouraged by his father and the natural philosopher James Forbes (1809-1868), the fourteen year old Maxwell produced his first publication: a paper describing a simple mechanical means of drawing mathematical curves with a piece of string. This combination of algebraic mathematics with elements of geometry would remain a distinctive feature of Maxwell's work.
In 1847, Maxwell attended Edinburgh University studying natural philosophy, moral philosophy, and mental philosophy. At Edinburgh, he studied under Sir William Hamilton. In his eighteenth year, while still a student in Edinburgh, he contributed two papers to the Transactions of the Royal Society of Edinburgh — one of which, On the Equilibrium of Elastic Solids, laid the foundation of one of the most singular discoveries of his later life, the temporary double refraction produced in viscous liquids by shear stress. In 1850, Maxwell left for Cambridge and initially attended Peterhouse but eventually left for Trinity College, where he was elected to a secret society known as the Cambridge Apostles. In November 1851, Maxwell studied under the tutor William Hopkins (nicknamed the "wrangler maker"). A considerable part of the translation of his electromagnetism equations was accomplished during Maxwell's career as an undergraduate in Trinity.
In 1854, Maxwell graduated with a degree as second wrangler in mathematics from Trinity (scoring second-highest in the mathematics exam) and was declared equal with the senior wrangler of his year in the higher ordeal of the Smith's prize examination. For more than half of his brief life he held a prominent position in the very foremost rank of scientists, usually as a college professor. Immediately after taking his degree, he read to the Cambridge Philosophical Society a novel memoir, On the Transformation of Surfaces by Bending. This is one of the few purely mathematical papers he published, and it exhibited at once to experts the full genius of its author. About the same time appeared his elaborate memoir, On Faraday's Lines of Force, in which he gave the first indication of some of the electrical investigations which culminated in the greatest work of his life.
From 1855 to 1872, he published at intervals a series of valuable investigations connected with the Perception of Colour and Colour-Blindness, for the earlier of which he received the Rumford medal from the Royal Society in 1860. The instruments which he devised for these investigations were simple and convenient. In 1856, Maxwell was appointed to the chair of Natural Philosophy in Marischal College, Aberdeen, which he held until the fusion of the two colleges there in 1860.
He obtained in 1859 the Adams prize in Cambridge for an original essay, On the Stability of Saturn's Rings;, in which he concluded the rings could not be completely solid or fluid. Maxwell demonstrated stability could be reached only if the rings consisted of numerous small solid particles. He also mathematically disproved the nebular hypothesis (which stated that solar system formed through the progressive condensation of a purely gaseous nebula), forcing the theory to account for additional portions of small solid particles.
In 1860, he was a professor at King's College in London. In 1861, Maxwell was elected to the Royal Society. Maxwell researched elastic solids and pure geometry during this time, also.
In 1865, Maxwell moved to the estate he inherited from his father in Glenlair, Kirkcudbrightshire, Scotland. In 1868 he resigned his Chair of Physics and Astronomy at King's College, London.
In 1866, he statistically formulated, independent of Ludwig Boltzmann, the Maxwell-Boltzmann kinetic theory of gases. His formula, called the Maxwell distribution, gives the fraction of gas molecules moving at a specified velocity at any given temperature. In the kinetic theory, temperatures and heat involve only molecular movement. This approach generalized the previous laws of thermodynamics, explaining the observations and experiments in a better way. Maxwell's work on thermodynamics led him to develop the thought experiment, Maxwell's demon.
The great work of Maxwell's life was devoted to electricity. Maxwell's most important contribution was the extension and mathematical formulation of earlier work on electricity and magnetism by Michael Faraday, Andre-Marie Ampere, and others into a linked set of differential equations (originally, 20 equations in 20 variables, later re-expressed in quaternion and vector-based notations). These equations, which are now collectively known as Maxwell's equations (or occasionally, "Maxwell's Wonderful Equations"), were first presented to the Royal Society in 1864, and together describe the behavior of both the electric and magnetic fields, as well as their interactions with matter.
Furthermore, Maxwell showed that the equations predict waves of oscillating electric and magnetic fields that travel through empty space at a speed that could be predicted from simple electrical experiments—using the data available at the time, Maxwell obtained a velocity of 310,740,000 m/s. Maxwell (1865) wrote: This velocity is so nearly that of light, that it seems we have strong reason to conclude that light itself (including radiant heat, and other radiations if any) is an electromagnetic disturbance in the form of waves propagated through the electromagnetic field according to electromagnetic laws.
Maxwell proved correct, and his quantitative connection between light and electromagnetism is considered one of the great triumphs of 19th century physics.
At that time, Maxwell believed that the propagation of light required a medium for the waves, dubbed the luminiferous aether. The existence of such a medium, permeating all space and yet apparently undetectable by mechanical means, proved more and more difficult to reconcile with experiments such as the Michelson-Morley experiment. Moreover, it seemed to require an absolute frame of reference in which the equations were valid, with the distasteful result that the equations changed form for a moving observer. These difficulties inspired Einstein to formulate the theory of special relativity, and in the process Einstein abandoned the requirement of a luminiferous aether.
Maxwell also made contributions to the area of optics and colour vision, being credited with the discovery that colour photographs could be formed using red, green, and blue filters. He had the photographer Thomas Sutton photograph a tartan ribbon three times, each time with a different colour filter over the lens. The three images were developed and then projected onto a screen with three different projectors, each equipped with the same colour filter used to take its image. When brought into register, the three images formed a full colour image. The resulting image's colours were somewhat unnatural, because the filters passed invisible wavelengths of light, but the principle was sound. The three photographic plates now reside in a small museum at 14 India Street, Edinburgh, the house where he was born.
Maxwell's work on colour blindness allowed him to win the Rumford Medal by the Royal Society of London. He wrote an admirable textbook of the Theory of Heat (1871), and an excellent elementary treatise on Matter and Motion (1876).
In 1871, he was the first Cavendish Professor of Physics at Cambridge. Maxwell supervised the development of the Cavendish laboratory. He superintended every step of the progress of the building and of the purchase of the very valuable collection of apparatus with which it was equipped at the expense of its generous founder, the seventh duke of Devonshire (chancellor of the university, and one of its most distinguished alumni). One of Maxwell's last great contributions to science was the editing (with copious original notes) of the Electrical Researches of Henry Cavendish, from which it appeared that Cavendish researched such questions as the mean density of the earth and the composition of water, among other things.
Maxwell married, but fathered no children. On November 5, 1879, he died in Cambridge of abdominal cancer. He was 48.
Maxwell had unified the work of previous electromagnetic and optical experiments at last, reducing their experimental results and observations into a series of mathematical equations. These equations (as well as the Maxwell distribution) have proven extremely useful in physics ever since. They hold true in all cases and therefore yielded several new laws of electromagnetism and optics, most importantly electromagnetic radiation. The equations are fundamental to radio and television, and can be used for studying X-rays, gamma rays, infrared rays, and other forms of radiation.