Moseley, Henry

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.

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 the atomic number is the number of positive charges in the atomic nucleus. He also stated that there were three unknown elements, with atomic numbers 43, 61, and 75, between aluminum and gold. (There are, in fact, four. Moseley identified gaps in the periodic table for technetium [43], promethium [61], and rhenium [75], but he missed hafnium [atomic number 72] because its discovery had been erroneously claimed.)

Moseley enlisted in the army when World War I broke out in 1914. He was shot in the head by a Turkish sniper at the Battle of Suvla Bay (in Turkey). His death at the age of 27 deprived the world of one of its most promising experimental physicists.