Persons who care only for the accomplished fact may be inclined to underrate the interest and value of this record. But even they may be reminded that but for such patient and unremitting devotion as is here enregistered, the now accomplished fact of mechanical flight would still remain the wild unrealized dream which it was for so many centuries. To such men as Mr. Langley an unsuccessful experiment is not a failure but a means of instruction, a necessary and often an invaluable stepping-stone to the desired end. The trials of the large aerodrome in the autumn of 1903, to which the curiosity of the public and the sensationalism of the newspapers gave a character of finality never desired by Mr. Langley, were to him merely members of a long series of experiments, as much so as any trial of one of the small aerodromes or even of one of the earliest rubber-driven models. Had his health and strength been spared, he would have gone on with his experiments undiscouraged by these accidents in launching and undeterred by criticism and misunderstanding. Moreover, it is to be borne in mind that Mr. Langley’s contribution to the solution of the problem is not to be measured solely by what he himself accomplished, important as that is. He began his investigations at a time when not only the general public but even the most progressive men of science thought of mechanical flight only as a subject for ridicule, and both by his epoch-making investigations in aerodynamics and by his own devotion to the subject of flight itself he helped to transform into a field of scientific inquiry what had before been almost entirely in the possession of visionaries. The original plans for this publication provided for a third part covering the experimental data obtained in tests of curved surfaces and propellers. Owing to the pressure of other matters on the writer, the preparation of this third part is not yet complete and is reserved for later publication. CHARLES M. MANLY. NEW YORK CITY. CONTENTS PART I I. Introductory … 1 II. Preliminary … 5 Experiments with small models … 6 Abbreviations and symbols employed … 14 Experiments with Aerodromes Nos. 30 and 31 … 16 III. Available motors … 21 India rubber … 21 Steam engine … 24 Gunpowder, hot-water, compressed air … 25 Gas, electricity … 26 Carbonic-acid gas … 28 IV. Early steam motors and other models … 30 V. On sustaining surfaces … 41 Experiments in the open wind … 42 Relation of air to weight and power … 43 VI. Balancing the aerodrome … 45 Lateral and longitudinal stability … 45 VII. History of construction of frame and engines of aerodromes … 53 1893 … 53 1894 … 64 1895 … 75 1896 … 79 VIII. History of construction of sustaining and guiding surfaces of aerodromes 4, 5, and 6 … 80 Introduction … 80 1893, 1894 … 81 1895 … 85 1896 … 89