James Clerk Maxwell (1831–1879), a Scottish physicist renowned for his pathbreaking work in electricity and magnetism, summarized in his work A Treatise on Electricity and Magnetism (1873). Basing his own study and research on that of Faraday, Kelvin, and Ampère, he developed the theory of the electromagnetic field on a mathematical basis, and made possible a much greater understanding of the phenomena in this field. Maxwell discovered in 1865 that electric and magnetic energy travel in transverse waves that propagate at a speed equal to that of light; light is thus only one form of electromagnetic radiation. The validity of the self-propagating electromagnetic wave suggestion was later demonstrated in experiments by Hertz, and was fundamental to the invention of radio. With Clausius, Maxwell developed the kinetic theory of gases and his studies of kinetic theory led him to propose the Maxwell's demon paradox in 1867. Maxwell's demon is a tiny hypothetical creature that can see and sort individual hot and cold molecules. Maxwell used the demon to show that the Second Law of Thermodynamics is a statistical law describing the properties of a large number of particles. In 1931, on the centennial anniversary of Maxwell's birth, Einstein described Maxwell's work as the "most profound and the most fruitful that physics has experienced since the time of Newton."

James Clerk Maxwell (1831–1879), a Scottish physicist renowned for his pathbreaking work in electricity and magnetism, summarized in his work A Treatise on Electricity and Magnetism (1873). Basing his own study and research on that of Faraday, Kelvin, and Ampère, he developed the theory of the electromagnetic field on a mathematical basis, and made possible a much greater understanding of the phenomena in this field. Maxwell discovered in 1865 that electric and magnetic energy travel in transverse waves that propagate at a speed equal to that of light; light is thus only one form of electromagnetic radiation. The validity of the self-propagating electromagnetic wave suggestion was later demonstrated in experiments by Hertz, and was fundamental to the invention of radio. With Clausius, Maxwell developed the kinetic theory of gases and his studies of kinetic theory led him to propose the Maxwell's demon paradox in 1867. Maxwell's demon is a tiny hypothetical creature that can see and sort individual hot and cold molecules. Maxwell used the demon to show that the Second Law of Thermodynamics is a statistical law describing the properties of a large number of particles. In 1931, on the centennial anniversary of Maxwell's birth, Einstein described Maxwell's work as the "most profound and the most fruitful that physics has experienced since the time of Newton."