English experimental physicist who achieved the first experimental identification of the atomic number and nuclear charge of an element. Born in Weymouth, Dorset, Moseley came from a distinguished family of scientists. After studying physics at Oxford, he joined Ernest Rutherford at Manchester. His initial work was on beta emission from radium, but he soon moved on to the study of X-ray spectra, using the technique of X-ray diffraction developed by W. H. Bragg and his son, W. L. Bragg. Ever since Mendeleev's proposal of the periodic table in 1869, chemists had striven to explain the fact that the chemical properties of the elements are a periodic function of their atomic weights. By means of X-ray diffraction, Moseley established, in 1913, a relationship between the frequencies of X-ray emission lines and what he concluded must be the atom's nuclear charge, thereby confirming the suggestion of A. van der Broek that the nuclear charge indicated an element's position in the periodic table. Moseley thus provided an experimental basis for equating nuclear charge with what he called atomic number. From now on it became possible to predict, from gaps in the series of X-ray frequencies, the existence of missing elements in the periodic table. Moseley moved back to Oxford to continue his work there, but was killed two years later in the battle of Sari Bair during the Gallipoli campaign.
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