In 1913, the Braggs (father and son) established a relationship ??? known as Bragg???s law (see Hughes, 2007, for a further explanation of Bragg???s law) ??? between the wavelength (??) of the X-rays, the distance (d) between two atomic planes in a crystal, and the angle of incidence (??) of the X-rays: 2 d sin ?? = n ??, where n is an integer.