This book presents the life and work of Professor Evan James Williams, described as one of Wales's most eminent scientists. Williams played a prominent part in the early twentieth-century revolution in physics with the emergence of quantum science, and was an able experimentalist and accomplished theoretician who made notable contributions in atomic physics and the discovery of a new elementary particle. From humble beginnings in rural Cardiganshire, his stellar career is charted in this book as he climbed the academic ladder at a number of universities, culminating in his appointment as Professor of Physics at Aberystwyth, and election to a Fellowship of the Royal Society. During the Second World War, Williams was instrumental in applying Operational Research to thwart the threat of German submarines in the Atlantic; his career was cut short, however, by his early death in 1945.