Maxwell's Equations — Unification of Electricity, Magnetism, and Light
James Clerk Maxwell published a set of equations in 1865 showing that electricity, magnetism and light are the same thing. Electricity and magnetism had been known to be related since Ørsted found in 1820 that a current deflects a compass needle and Faraday showed that a moving magnet induces a current. Faraday had also proposed that the space around a magnet was filled with lines of force — a physical field rather than action at a distance — and had no mathematics to express it. Maxwell supplied the mathematics, and then found something in it that had not been put there. His equations required a term he called the displacement current, and with it they predicted waves of coupled electric and magnetic fields propagating through space at a speed calculable from two constants measured in a laboratory with no reference to light at all. The number came out at very nearly the measured speed of light, and Maxwell wrote that the conclusion could scarcely be avoided that light is an electromagnetic disturbance. That single inference united optics with electricity and predicted radio waves, which Hertz generated and detected in 1887, eight years after Maxwell died at forty-eight. It also implied a speed relative to nothing in particular, which is the problem that Einstein resolved in 1905. Maxwell also produced the kinetic theory of gases, the first colour photograph, and the analysis showing that Saturn's rings must be made of separate particles. Einstein kept his portrait on the study wall. His equations are also the first field theory, and the template every physicist since has worked from. Everything from radio to radar to the microwave to the mobile telephone is an application of a set of results a Scottish theorist derived from laboratory measurements of static charges and magnets.
- Year: 1865 CE
- Category: Scientific
