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Sci Tech
Born experimenter
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Henry Mosley was the first to establish a connection between nuclear charge and the atomic number.
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HENRY MOSLEY was born on November 23, 1887 at Weymouth, England. He came from a family distinguished for its contributions to science. His father, a protege of Charles Darwin, was the founder of a strong school of zoology at Oxford.
He died when the boy was not four years old: so the mother moved to Chilworth in Surrey to educate her son. At the age of nine, Mosley was sent to a school that prepared students for entering Eton with a scholarship.
Here the unconventional educational approach of his science master ``a minimum of books and a maximum of challenging experiments'' inculcated in him a love for science.
Before leaving Eton, he had started quantitative analysis measuring the freezing point of saline solutions of different concentration.
He experienced the thrill of discovery when he found that helium, despite its lower boiling point, was denser than hydrogen.
In 1908 Mosley entered Trinity College, Oxford with a science scholarship and read physics. He built a primitive Wilson cloud chamber in the laboratory.
The curriculum did not provide him opportunity for the kind of independent work to which his master Porter had prepared him, but it confined to the pattern of bookish honours schools. So he obtained only a second class degree at Oxford.
Apprenticeship under Rutherford
Nonetheless, by a personal visit he paid to Rutherford, he was appointed demonstrator in the physics department at Machester University. He found the students dense and provincial and so did not find any enthusiasm in his teaching job.
But he worked happily for long hours on the research problem Rutherford had given him, namely determining the number of beta particles expelled in the process of disintegration of one atom of radium B or radium C. Mosley also collaborated on small projects that trained him to master the techniques of high vacuum and radioactivity. These exercises, typical of Rutherford's laboratory, prepared him to enjoy a research fellowship from April 1912.
Now Mosley decided to turn his research work in an independent direction: investigate how the wave-like properties of X-rays, established by Max Von Lane (1879-1960) and reconcile with the phenomena from which W.H.Bragg (1862-1942) deduced their particle-like properties.
For this investigation, Mosley needed the help of a mathematical physicist and approached Rutherford. The great master, who generally offered his paternal nod, refused on the ground that he knew nothing on the subject.
So Mosley shifted to Leeds to continue his work under Bragg who agreed to guide him. His earlier experience at Eton of circumventing inconvenient masters stood him in good stead and made possible the original work that established his reputation.
Mosley adopted Bragg's method with the important modification of substituting a photographic plate by an ionisation chamber for measuring intensity of reflection as a function of the glancing angle; results so obtained quickly became standard (`The Reflexion of X Rays' in Philosophical Magazine, 1913).
Calling the role of elements
In December 1913 Mosley migrated to Oxford and continued his experimental work in the electrical laboratory of Townsend.
A further paper presented his investigations on the X-ray spectra of nearly over thirty elements (1914). Several of the missing members were brought to light.
Mosley was the first to establish a firm connection between nuclear charge and the atomic number. This was vindicated in 1920 by Chadwick's experiments on alpha- particle scattering.
At the outbreak of the World War I, he enlisted in the Royal Engineers.
A few weeks later, he met with a tragic death at the age of 28. He was killed in action in Gelibolu, Turkey. Rutherford paid tribute to him as "a born experimenter''. Biographical Dictionary of Scientists, Harper Collins Publishers, 1994).
R. Parthasarathy
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