A small book that will arouse reader interest and focus attention on Oppenheimer in the role in which he is supreme -- the scientist, who lives in a world remote from common mortals. Six chapters of the book constitute the Reith Lectures, given over B.B.C. in November and December 1953. It is a text that almost demands excerpting, while at the same time giving as a whole a unity of poetic expression that carries even the scientific ignoramus along in its sweep and beauty. He aims to show ""with exaggerated simplicity and contrast, the state of knowledge and belief"" essential to understanding new developments. He sketches the physical world between Descartes' birth and Newton's death, and the methods, hopes, traits and program of that period, now deep in our tradition. He then goes on to those who contribute greatly to the cumulative sum of scientific knowledge, basic to atomic and nuclear physics. ""Our progress"" he says, ""is narrow: it takes a vast world unchallenged and for granted"". There are parts of these lectures where one senses the man's philosophy, his humility, his acceptance of a world bond of brotherhood. He rejoices in the privilege accorded the English-speaking world of open access to knowledge -- ""a freedom to resolve difference by converse...to let tolerance compose diversity...a freedom barely compatible with modern political tyranny"". And in closing he sums up what he feels the rewards of scientific research- ""in an earthy way, the power of betterment""...while ""we are anxiously aware that the power to change is not always necessarily good"". His personal creed is evident without being actually defined; he says that scientists ""like all men, bring a little light to the unending darkness of man's life and world"". Here is a man who should be his own best advocate.