Henry Moseley, in full Henry Gwyn Jeffreys Moseley, (born November 23, 1887, Weymouth, Dorset, England—died August 10, 1915, Gallipoli, Turkey), English physicist who experimentally demonstrated that the major properties of an element are determined by the atomic number, not by the atomic weight, and firmly established the relationship between atomic number and the charge of the atomic nucleus.

Read More on This Topic atom: Moseley’s X-ray studies Henry Gwyn Jeffreys Moseley, a young English physicist killed in World War I, confirmed that the positive charge on the nucleus revealed...

Educated at Trinity College, Oxford, Moseley in 1910 was appointed lecturer in physics at Ernest (later Lord) Rutherford’s laboratory at the University of Manchester, where he worked until the outbreak of World War I, when he entered the army. His first researches were concerned with radioactivity and beta radiation in radium. He then turned to the study of the X-ray spectra of the elements. In a brilliant series of experiments he found a relationship between the frequencies of corresponding lines in the X-ray spectra. In a paper published in 1913, he reported that the frequencies are proportional to the squares of whole numbers that are equal to the atomic number plus a constant.

Known as Moseley’s law, this fundamental discovery concerning atomic numbers was a milestone in advancing the knowledge of the atom. In 1914 Moseley published a paper in which he concluded that there were three unknown elements between aluminum and gold (there are, in fact, four). He also concluded correctly that there were only 92 elements up to and including uranium and 14 rare-earth elements.

Moseley’s death at the Battle of Suvla Bay (in Turkey) at the age of 27 deprived the world of one of its most promising experimental physicists.