"Light is a Messenger" is the first biography of William Lawrence Bragg, who was only 25 when he won the 1915 Nobel Prize in Physics - the youngest person ever to win a Nobel Prize. It describes how Bragg discovered the use of X-rays to determine the arrangement of atoms in crystals and his pivotal role in developing this technique to the point that structures of the most complex molecules known to Man - the proteins and nucleic acids - could be solved. Although Bragg's Nobel Prize was for physics, his research profoundly affected chemistry and the new field of molecular biology, of which he became a founding figure. This book explains how these revolutionary scientific events occurred while Bragg struggled to emerge from the shadow of his father, Sir William Bragg, and amidst a career-long rivalry with the brilliant American chemist, Linus Pauling.