This book details the life and work of physicist H. G. J. Moseley. It examines Moseley's days at Eton, Oxford, and the University of Manchester, where he worked with atomic physicist Ernest Rutherford. It also explains his work in x-ray spectroscopy and atomic structure, and his refinement of the periodic table of the elements. The last half of the book consists of most of Moseley’s known correspondence. In those letters he often mentions prominent scientists of his era, and the letters as a whole help illuminate the development of physics in the early twentieth-century.