23 November 1887 – 10 August 1915
Henry Gwyn Jeffreys Moseley was an English physicist, whose contribution to the science of physics was the justification from physical laws of the previous empirical and chemical concept of the atomic number. Henry Moseley was born in Weymouth in Dorset in 1887. Moseley had been a very promising schoolboy at Summer Fields School. In 1906 he won the chemistry and physics prizes at Eton. In 1906, Moseley entered Trinity College of the University of Oxford, where he earned his bachelor’s degree. While an undergraduate at Oxford, Moseley joined the Apollo University Lodge. After graduation from Oxford in 1910, Moseley became a demonstrator in physics at the University of Manchester under the supervision of Sir Ernest Rutherford. Moseley was shot and killed during the Battle of Gallipoli on 10 August 1915, at the age of 27.
Moseley discovered a systematic mathematical relationship between the wavelengths of the X-rays produced and the atomic numbers of the metals that were used as the targets in X-ray tubes. This has become known as Moseley’s law.
Moseley’s experiments in X-ray spectroscopy showed directly from their physics that cobalt and nickel have the different atomic numbers, 27 and 28, and that they are placed in the Periodic Table correctly by Moseley’s objective measurements of their atomic numbers. Hence, Moseley’s discovery demonstrated that the atomic numbers of elements are not just rather arbitrary numbers based on chemistry and the intuition of chemists, but rather, they have a firm experimental basis from the physics of their X-ray spectra.