History of the principle of interference of light (Q1201992)

The author is giving a thorough historical investigation, he does not only present the historical facts but also asks questions beyond these. He does not intend to give a mere history of the wave theory of light. The controversy of wave theory and emission theory in optics began in the 17th century, at the end of the 18th century however the wave theory was almost universally ignored. Contrary to that, the wave nature of sound was undisputed in acoustics. Thomas Young began his studies on sound waves; he was successful because he was concentrating on the process of interaction while other physicists had observed sound waves only before and after the intersection. Passing to optics Young was the first to realize that also Newton as the most eminent supporter of emission theory needed waves, he used ether waves for his theory of light and colours. In 1799 Young was convinced of the arguments in favour of wave theory. In 1801 he presented several slightly different formulations of his so- called ``law of interference'' which corresponds with the modern principle of interference. Though Young was known as a careful experimenter, his new theory did not arouse the interest of his contemporaries, it appeared at the wrong time at the wrong place. Young only found supporters in Wollaston and Fraunhofer. Reasons for this lack of interest were that the wave theory was usually ignored and that Young's theory was understood as non-Newtonian. Fresnel, at first not being familiar with Young's theory, rediscovered the principal of interference in 1815. Fresnel's theory was partly superior to Young's, partly inferior: he used the better mathematical language and gave a clearer presentation, but he was only able to explain a smaller number of phenomena than Young. Fresnel was much more successful, though it took more than 50 years that the principle of interference was understood sufficiently. In the meantime the majority of physicists believed in it only as in a mathematical concept, disregarding the wave nature of light. However, the principle of interference was able to raise steadily the status of wave theory. Thus the wave nature entered optics quite late and only through the back door.