In 1863 Congress founded the National Academy of Sciences for the encouragement of research and the diffusion of scientific knowledge, and to advise the federal government on matters of science and technology. The Centennial of the National Academy of Sciences was celebrated in the autumn of 1963. Representatives of sister academies, learned societies, and universities throughout the world brought greetings that stressed the world-wide scope and unity of the scientific endeavor. President John F. Kennedy and twenty-three distinguished members of the Academy delivered memorable addresses in which the History of the Universe, the Nature of Matter, the Determinants and Evolution of Life, and the spirit of The Scientific Endeavor were described in a score of remarkably relevant and coherent accounts. Because the addresses contained so much wisdom, were presented with clarity, and revealed the unity of science, it was agreed that they should be made available to a larger audience than could assemble for the Centennial. That is the purpose of this book.