ScienceWeek

JAMES CLERK MAXWELL (1831-1879)

The theory that killed the static electron -- eventually known as quantum mechanics -- evolved because physicists thought they ought to know more about light. In fact they already knew a lot; for instance they understood that light behaves as a wave. Waves bend around obstacles in their path (a day on the beach observing wave behavior may be in order), and waves interfere with each other. If they are out of phase, they cancel one another to create a calm; if they are in phase they combine to form larger waves. Light also behaves this way. In-phase waves of light projected through parallel pinholes create a pattern of concentric rings of light and dark called an interference pattern. Waves of /what/ was not known until the work of James Clerk Maxwell (1831-1879).

Maxwell demonstrated that a moving electric charge generates a magnetic field, and the magnetic field generates an opposing electric field. The opposing electric field generates an opposing magnetic field, and so on, with each field pushing the other out of the way. When Maxwell calculated the speed at which this occurs, he found it to be the known speed of light. He must have said something like "Aha". Light, he had discovered, is an oscillating electromagnetic wave.

There is a story that Maxwell was courting his wife at the time, and on the evening of the day on which he came to this conclusion, they were walking in a garden, gazing at the stars. He supposedly asked her how it felt to be the only other person to know the true nature of starlight. This may be a romanticized version of a true event because we know Maxwell's wife later worked with him on his experiments, so no doubt she discussed this important conclusion with him. Later (after Maxwell's death at an early age) his conclusion was confirmed experimentally by Heinrich Hertz (1857-1894), who showed that a spark from two charged spheres sets up an electromagnetic wave that can trigger a spark in similar charged spheres a distance away (which eventually became the basis for radio technology).

C. Cobb and H. Goldwhite: Creations of Fire: Chemistry's Lively History from Alchemy to the Atomic Age. Perseus Publishing, Cambridge MA 1995, p.313. More information at: http://www.amazon.com/exec/obidos/ASIN/073820594X/scienceweek