The author has taken as the title that of the poem by Lucretius written over 2,000 years ago in which the Roman poet and philosopher endeavored to set forth the ideas that prevailed in his day regarding matter, motion, space, light and time. Dr. Woods discusses such modern questions as heat, electricity, magnetism and chemical action. As he remarks in his preface, "Science has reared its structures, as builders erect towers, on foundations more or less solid, but without closely considering the exact nature of the foundations—how they were formed and from what." The rapid development of practically all branches of scientific knowledge has so enormously increased the amount that has to be learned in any one branch of science as to require a lifetime for the mastery even of a limited field, with the result that few men, however well advanced in the details of practical scientific work, have