First published in 1920. According to the Foreword: "Although successful heavier-than-air flight is less than two decades old, and successful dirigible propulsion antedates it by a very short period, the mass of experiment and accomplishment renders any one-volume history of the subject a matter of

selection. In addition to the restrictions imposed by space limits, the material for compilation is fragmentary, and, in many cases, scattered through periodical and other publications. Hitherto, there has been no attempt at furnishing a detailed account of how the aeroplane and the dirigible of to-day came to being, but each author who has treated the subject has devoted his attention to some special phase or section. The principal exception to this rule--Hildebrandt--wrote in 1906, and a good many of his statements are inaccurate, especially with regard to heavier-than-air experiment."