On This Day – November 23 : English physicist Henry Moseley was born on this day in 1887

He developed a law concerning the characteristic X-rays that are emitted by atoms, and thus allowed atomic numbers to be defined. Until this point, these numbers in the periodic table were simply an element’s place, rather than being associated with a physical property.

Related resources:

• Trouble in the periodic table
• Tribute at Oxford RSC Landmark event for First World War’s Lost Scientist