The Michelson-Morley Experiment

    Michael Fowler, UVa

The Nature of Light

As a result of Michelson’s efforts in 1879, the speed of light was known to be 186,350 miles per second with a likely error of around 30 miles per second.  This measurement, made by timing a flash of light travelling between mirrors in Annapolis, agreed well with less direct measurements based on astronomical observations.  Still, this did not really clarify the nature of light.  Two hundred years earlier, Newton had suggested that light consists of tiny particles generated in a hot object, which spray out at very high speed, bounce off other objects, and are detected by our eyes.  Newton’s arch-enemy Robert Hooke, on the other hand, thought that light must be a kind of wave motion, like sound.  To appreciate his point of view, let us briefly review the nature of sound.