# Charles Glover Barkla

Charles Glover Barkla (7 June 1877 – 23 October 1944) was an English physicist who received the Nobel Prize in Physics in 1917 for his discovery of characteristic X-rays.

## Life

Barkla was born in Widnes, England, to John Martin Barkla, a secretary for the Atlas Chemical Company, and Sarah Glover, daughter of a watchmaker.
Barkla studied at the Liverpool Institute and proceeded to Liverpool University with a County Council Scholarship and a Bibby Scholarship. Barkla initially studied Mathematics but later specialised in Physics under Sir Oliver Lodge. During the absence of Oliver Lodge due to ill health, Barkla replaced him in lectures.
In 1899 Barkla was admitted to Trinity College, Cambridge, with an 1851 Research Fellowship from the Royal Commission for the Exhibition of 1851, to work in the Cavendish Laboratory under the physicist J. J. Thomson (discoverer of the electron). During his first two years at Cambridge, under the directions of Thomson, Barkla studied the velocity of electromagnetic waves along wires of different widths and materials.
After a year and a half at Trinity College, Cambridge, his love of music led him to transfer to King's College, Cambridge, in order to sing in their chapel choir. Barkla's voice was of remarkable beauty and his solo performances were always fully attended. He completed his Bachelor of Arts degree in 1903, and then his Master of Arts degree in 1907. He married Mary Esther Cowell in the same year, with whom he had two sons and one daughter.
In 1903 he studied secondary X-rays from gases radiated by other X-rays, developing a new experimental setup. This topic was relevant to the question of whether X-rays were indeed a type of electromagnetic radiation as many physicists suspected, because Lionel Wilberforce proposed to use these secondary rays to generate tertiary ones and prove the existence of polarization by rotating the detecting part of his experimental apparatus. Tertiary radiation was too feeble to measure, so Barkla assembled a slightly different setup. Using his new setup, he was able to prove that X-rays can indeed be polarized and are therefore electromagnetic. He published a brief summary of his findings in Nature in March 1904 and a more detailed account in the Philosophical Transactions of the Royal Society in 1905.
In 1913, after having worked at the Universities of Cambridge, Liverpool, and King's College London, Barkla was appointed as a Professor of Natural Philosophy at the University of Edinburgh in 1913, a position he held until his death.
Barkla made significant progress in developing and refining the laws of X-ray scattering, X-ray spectroscopy, the principles governing the transmission of X-rays through matter, and especially the principles of the excitation of secondary X-rays. For his discovery of the characteristic X-rays of elements, Barkla was awarded the Nobel Prize in Physics in 1917. He was also awarded the Hughes Medal of the British Royal Society that same year.
Barkla proposed the J-phenomenon as a hypothetical form of X-ray behaviour similar to X-ray fluorescence. However, other scientists were not persuaded that this was a different mechanism from other known effects such as Compton scattering, so the theory was not successful.
From 1922 to 1938 he lived at Hermitage of Braid in south-west Edinburgh.
He died at 12 noon on 23 October 1944 at his home "Braidwood" in Corrennie Gardens in Edinburgh.

## Personal life

A religious man, Barkla was a Methodist and considered his work to be "part of the quest for God, the Creator".

## Public recognition

The lunar crater Barkla was named in the honour of Charles Barkla.
A plaque exists on Barkla's house at Hermitage of Braid in Edinburgh. A commemorative plaque has been installed in the vicinity of the Canongate, near the Faculty of Education Buildings, at the University of Edinburgh. Additionally, a lecture theatre at the University of Liverpool's Physics department, as well as a Biophysics laboratory in the Biological science department, are named after him. In 2012 a gritter in Barkla's home town of Widnes was named in his honour, following a competition run by the local newspaper. In Widnes they have a Retirement housing Complex named Barkla Fields after Charles.