This book makes no pretence of going minutely into the technical and scientific sides of human flight: rather does it deal mainly with the real achievements of pioneers who have helped to make aviation what it is to-day. My chief object has been to arouse among my readers an intelligent interest in the art of flight, and, profiting by friendly criticism of several of my former works, I imagine that this is best obtained by setting forth the romance of triumph in the realms of an element which has defied man for untold centuries, rather than to give a mass of scientific principles which appeal to no one but the expert.