Henry Gwyn Jeffreys Moseley | Biography

One of the truly great tragedies in the history of science was the death of Henry G. J. Moseley on August 10, 1915, in Gallipoli, Turkey. Moseley had enlisted in the Royal Engineers at the outbreak of World War I and had sailed for Turkey on June 15, 1915. During the Battle of Suvla Bay, a sniper's bullet ended his life. Thus, at the age of twenty-seven, one of England's most promising scientists met the end of his career.

Moseley was born in Weymouth, England, on November 23, 1887. He came from a family with a long scientific tradition. His father had been professor of anatomy at Oxford and his grandfather had been a well-known mathematician. Moseley studied natural science at Eton and Oxford and then, in 1910, joined Ernest Rutherford at Manchester. His first research involved the study of beta emission from radium. He then turned his attention to the research for which he is now famous, a study of the X-ray spectra of the elements.

William Henry Bragg (1862-1942) and his son, William Lawrence Bragg (1890-1971), had recently discovered that when elements are excited, they emit an X-ray pattern that consists not only of a continuous background spectrum, but also of a small number of bright lines that are characteristic for each element. Moseley compared the wavelengths of these lines with the atomic weights of the elements from which they were produced. He found that the wavelengths increased in a regular, orderly pattern going from one element to the next heavier element.

From these results, Moseley concluded that every element must have some characteristic that would account for this orderly progression. A clue to the puzzle had appeared in 1913 when A. van den Brock had suggested that nuclear charge might be associated with atomic weight in a linear way. That is, the position of an element in the periodic table might be indicated by its nuclear charge as well as by its atomic weight.

Moseley followed up on this idea by proposing that the factor accounting for the regular progression in spectral line patterns was nuclear charge. He gave the name atomic number to nuclear charge and showed that Dmitri Mendeleev's periodic law could be restated in terms of atomic number rather than atomic weight: The properties of the elements are periodic functions of their atomic numbers (rather than atomic weight). Moseley reported his initial findings in December 1913 and, a few months later, returned to continue his research at Oxford. His work was critical in establishing the probable maximum number of elements. Under Mendeleev's system, there was no theory that suggested how many additional elements might still be expected. It was even conceivable that whole new groups of elements (like the noble gases) might be found within the periodic table.

According to Moseley's scheme, elements can have only integral atomic numbers (nuclear charges). Thus, it would be impossible for there to be any more elements anywhere within Mendeleev's existing chart. This finding clearly showed experimentalists where to look for still undiscovered elements, a search that turned out to be very fruitful in a relatively brief time.