At the age of 22, Bragg discovered that the regular pattern of dots produced on a photographic plate by an X-ray beam passing through a crystal could be regarded as a reflection of electromagnetic radiation from planes in a crystal that were especially densely studded with atoms. From this work the younger Bragg derived the “Bragg relation” or Bragg's law (nλ = 2d sin O). This relates the wavelength of the X-ray to the angle at which such a reflection could occur. See also: W. H. Bragg, “X-rays and Crystals,” Nature 90 (23 Jan. 1913) 572.

Discovery of X-ray crystallography. The father and son team of physicists, William Henry Bragg and William Lawrence Bragg, constructed the first X-ray spectrometer using crystals as gratings, using a known wavelength to determine the distances between atomic planes—and thus the structure—of crystalline substances. By the end of 1913 the Braggs reduced the problem of crystal structure analysis to a standard procedure. For further information see the entry at HistoryofInformation.com at this link. The Braggs' paper is available from the Royal Society at this link.

In 1915 the Braggs shared the Nobel Prize in Physics "for their services in the analysis of crystal structure by means of X-rays."

Digital facsimile from the Internet Archive at this link.