The study of long-distance radio-wave propagation, 1900-1919

at the beginning of the 20th century, scientists and engineers were puzzled by the fact that the long wireless waves could propagate along the earth's curvature without being blocked by the earth. Two explanatory theories were suggested: that the waves are diffracted along the earth's surface and that the waves are reflected back and forth between the earth and a conducting atmosphere. the surface diffraction theory, first proposed by Hector Munro Macdonald in 1901, was continuously elaborated by the British and German mathematical physicists. But its predictions were not consistent with the empirical Austin-Cohen formula obtained from the U.S. Navy's long distance experiments. The atmospheric reflection theory, first proposed by Arthur Kennelly and Oliver Heaviside in 1901/2, was more commonly believed to be the correct physical model. Yet it had problems yielding quantitative prediction because of its lack of mathematical developement. In 1919, the English mathematician, George Neville Watson, developed a mathematical theory of atmospheric reflection that generated predictions consistent with the Austin-Cohen formula on the analytic techniques established by the surface diffraction theorists.