He was a pioneer of spectroscopy, and the first person to establish a relationship between the wavelengths of spectral lines of the elements and their positions in the periodic table (published in 1883), and he studied also the relationship between the structure and spectra of a wide variety of organic compounds.
In 1881, he hypothesized the presence of ozone in the atmosphere. His work led to his election to Fellowship of the Royal Society in 1884, and he was awarded a doctorate (Doctor of Science) by the Royal University of Ireland in October 1901. He was knighted in 1911.
He was Chair of Chemistry and Dean of Faculty of the Royal College of Science in Ireland.
Hartley married novelist Mary Laffan (1849-1916) in 1882. He was survived by one son, Walter John Hartley, who died at Gallipoli in 1915.
Royal Society.
