At the onset of the nineteenth century, the most widely accepted belief among physicists was that light was a particle that traveled through ether, an invisible substance that made up the heavens. Soon after the turn of the century, however, came the revival of an old belief; that light was actually a wave that needed no medium for travel. The debate that arose among scientists was furious, and there were few more successful spokesmen for the wave theory than Augustin Fresnel.

The son of an architect, Fresnel was born in Normandy in 1788. His future as a scientist was by no means obvious--in fact, Fresnel was eight before he learned to read. He entered the École Polytechique in Paris in 1804, with plans to pursue a career in engineering. After three more years, he became a civil engineer, working for the government for most of his adult life.

Fresnel's...