In 1925, shortly before the development of the full mathematical description of quantum mechanics, Born drew Einstein's attention to the then-new idea of " de Broglie 's waves ". He wrote "It seems to me that a connection of a completely formal kind exists between these and that other mystical explanation of reflection, diffraction and interference using 'spatial' quantisation which Compton and Duane proposed and which has been more closely studied by Epstein and Ehrenfest." Examining the hypothesis of Duane on quantized translational momentum transfer, as it accounted for X-ray diffraction by crystals, and its follow-up by Compton, Epstein and Ehrenfest had written "The phenomena of Fraunhofer diffraction can be treated as well on the basis of the wave theory of light as by a combination of concept of light quanta with Bohr's principle of correspondence." Later, Born and Biem wrote: "Every physicist must accept Duane's rule."