A series of experiments by Clinton Davisson and Lester Germer in the 1920s gave a clear indication of the wave nature of matter. The investigators scattered a relatively low energy electron beam from a nickel crystal. They found very strong reflections at certain angles that varied with the energy of the electron beam. The strong reflections were analogous to those observed in x-ray diffraction. The angles at which the intensity of the reflected beam peaks agreed with the Bragg condition if the electrons were assumed to have a wavelength given by the de Broglie formula. This was conclusive