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 physics, and was an able experimentalist and brilliant 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, he 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.