Renowned for his pioneering use of radiation therapy to treat cancer, this late 19th and early 20th-century physicist and geologist is also remembered for his groundbreaking radium dating method of investigating geological data.
After earning an engineering degree from Trinity College, Dublin, he began teaching in the college's Geology and Mineralogy department.
Apart from his geological work, he invented the Joly Colour process of color photography.
He was born and raised in Bracknagh, Ireland. His cousin, Charles Jasper Joly, was a notable nineteenth-century astronomer.
He collaborated with nuclear physicist Ernest Rutherford on a 1913 geologic investigation that proved the Devonian period to have been at least 400 million years in the past.