In spring 1912, in Munich, Max von Laue has the idea of passing an X-ray beam through a crystal, reasoning that if X-rays are electromagnetic waves of very short wavelength and crystals are regular three-dimensional atomic lattices, the crystal should act as a natural diffraction grating. Walter Friedrich, assistant to Arnold Sommerfeld, and Paul Knipping, a doctoral student, carry out the experiment: on June 8, 1912 they report to the Bavarian Academy of Sciences that irradiating a copper sulfate crystal with X-rays produces a regular pattern of dark spots on a photographic plate. The result simultaneously demonstrates that X-rays are electromagnetic waves and that the atoms of a crystal are arranged in a regular spatial lattice, resolving two open questions of physics with a single experiment. The news reaches William Henry Bragg, professor of physics at Leeds, and his son William Lawrence Bragg, then a 22-year-old student at Cambridge, in July 1912. The son reinterprets Laue's phenomenon in a much simpler way: X-rays are not diffusely diffracted by the lattice, but are specularly reflected from successive planes of atoms within the crystal, just as light reflects off parallel mirrors. This idea, presented on November 11, 1912 before the Cambridge Philosophical Society, is formalized in what is today known as Bragg's law (nλ = 2d sin θ), published jointly by father and son in 1913. While the son takes Laue diffraction photographs of alkali halide crystals at Cambridge, the father designs at Leeds the first X-ray spectrometer — an ionization chamber replacing the photographic plate and allowing precise measurement of the intensity of each reflected beam — the prototype of all modern X-ray diffractometers. In April 1913 they jointly record the first X-ray spectra, and before the year ends they succeed in determining the atomic structure of sodium chloride, pyrite, and other simple crystals, reducing crystal-structure analysis to a standard technical procedure. None of the three pieces — Laue's theoretical idea, the experimental verification by Friedrich and Knipping, and the Braggs' reinterpretation plus instrument — alone constitutes the complete method of X-ray crystallography: Laue's theory without experimental confirmation would have remained unproven; the experiment without Bragg's law would have produced patterns with no possible interpretation; and Bragg's law without W. H. Bragg's spectrometer would have lacked a precise measuring instrument. Together, within little more than a year, the three pieces found X-ray crystallography, a technique that would later allow determination of the structure of DNA, proteins, and virtually all known condensed matter.