This book is the result of studies of the meanings of nature and life, which the author has pursued since the publication in 1902 of his Lowell Lectures, Through Science to Faith. Since then the author has from time to time taken up anew the conclusions to which he had been led in that volume, and it has been his aim to re view the reasonings of that earlier book as though it were the work of another. From more recent scientific researches and working-theories he has sought to know better what is the real meaning of the final and supreme fact in nature of the personal life. This is no easy task; for all ways of investigation lead up toward this ulti mate problem, yet no science by itself alone can tell the answer to the old question, What is your life? The reasonable answer, which religious faith seeks, is ulti mately to be found at the point where all the ways of knowledge meet. Though such inquiries must traverse many fields of the specialists and among confusing side paths, nevertheless, the method of such pursuit of truth may be simple and straightforward.