In this book I have tried to give the reader a bird's-eye view of the territory covered by the theory called 'Serialism'. Some of the chapters, greatly condensed, have been delivered in lecture form to the Royal College of Science (Mathematical Society and Physical Society). But the main outline of the subject is, I believe, clear enough to be appreciated by those who have no special technical knowledge. Where all is fog, a blind man with a stick is not entirely at a disadvantage. In my case, Fortune presented me with a stick; and I have used this with considerable temerity. Certainly, it has led me somewhere possibly only into the roadway, where I shall be run over by a motor-bus full of scientific critics. But, if I have crossed safely to the other side, then I should like to express my gratitude to Mr J. A. Lauwerys of the University of London, whose continuous encouragement has been the chief factor which has kept me tapping along.