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scientific inquiry。 In 1867 he was appointed director of the Allegheny Observatory at Pittsburgh。 Here he remained until 1887； when； having made for himself a world…wide reputation as an astronomer； he became Secretary of the Smithsonian Institution at Washington。
It was about this time that he began his experiments in 〃aerodynamics。〃 But the problem of flight had long been a subject of interested speculation with him。 Ten years later he wrote：
〃Nature has made her flying…machine in the bird； which is nearly a thousand times as heavy as the air its bulk displaces； and only those who have tried to rival it know how inimitable her work is； for the 〃way of a bird in the air〃 remains as wonderful to us as it was to Solomon； and the sight of the bird has constantly held this wonder before men's minds； and kept the flame of hope from utter extinction； in spite of long disappointment。 I well remember how； as a child； when lying in a New England pasture； h watched a hawk soaring far up in the blue； and sailing for a long time without any motion of its wings； as though it needed no work to sustain it； but was kept up there by some miracle。 But； however sustained； I saw it sweep in a few seconds of its leisurely flight； over a distance that to me was encumbered with every sort of obstacle； which did not exist for it 。 。 。 。 How wonderfully easy； too； was its flight！ There was not a flutter of its pinions as it swept over the field； in a motion which seemed as effortless as that of its shadow。 After many years and in mature life； I was brought to think of these things again； and to。 ask myself whether the problem of artificial flight was as hopeless and as absurd as it was then thought to be〃。。。 In three or four years Langley made nearly forty models。 〃The primary difficulty lay in making the model light enough and sufficiently strong to support its power；〃 he says。 〃This difficulty continued to be fundamental through every later form； but； beside this； the adjustment of the center of gravity to the center of pressure of the wings； the disposition of the wings themselves； the size of the propellers； the inclination and number of the blades； and a great number of other details； presented themselves for examination。〃
By 1891 Langley had a model light enough to fly； but proper balancing had not been attained。 He set himself anew to find the practical conditions of equilibrium and of horizontal flight。 His experiments convinced him that 〃mechanical sustenation of heavy bodies in the air； combined with very great speeds； is not only possible； but within the reach of mechanical means we actually possess。〃
After many experiments with new models Langley at length fashioned a steam…driven machine which would fly horizontally。 It weighed about thirty pounds； it was some sixteen feet in length； with two sets of wings； the pair in front measuring forty feet from tip to tip。 On May 6； 1896； this model was launched over the Potomac River。 It flew half a mile in a minute and a half。 When its fuel and water gave out； it descended gently to the river's surface。 In November Langley launched another model which flew for three…quarters of a mile at a speed of thirty miles an hour。 These tests demonstrated the practicability of artificial flight。
The Spanish…American War found the military observation balloon doing the limited work which it had done ever since the days of Franklin。 President McKinley was keenly interested in Langley's design to build a power…driven flying machine which would have innumerable advantages over the balloon。 The Government provided the funds and Langley took up the problem of a flying machine large enough to carry a man。 His initial difficulty was the engine。 It was plain at once that new principles of engine construction must be adopted before a motor could be designed of high power yet light enough to be borne in the slender body of an airplane。 The internal combustion engine had now come into use。 Langley went to Europe in 1900； seeking his motor； only to be told that what he sought was impossible。
His assistant； Charles M。 Manly； meanwhile found a builder of engines in America who was willing to make the attempt。 But； after two years of waiting for it； the engine proved a failure。 Manly then had the several parts of it； which he deemed hopeful； transported to Washington； and there at the Smithsonian Institution he labored and experimented until he evolved a light and powerful gasoline motor。 In October； 1903； the test was made； with Manly aboard of the machine。 The failure which resulted was due solely to the clumsy launching apparatus。 The airplane was damaged as it rushed forward before beginning to soar； and； as it rose； it turned over and plunged into the river。 The loyal and enthusiastic Manly； who was fortunately a good diver and swimmer； hastily dried himself and gave out a reassuring statement to the representatives of the press and to the officers of the Board of Ordnance gathered to witness the flight。
A second failure in December convinced spectators that man was never intended to fly。 The newspapers let loose such a storm of ridicule upon Langley and his machine； with charges as to the waste of public funds； that the Government refused to assist him further。 Langley； at that time sixty…nine years of age； took this defeat so keenly to heart that it hastened his death； which occurred three years later。 〃Failure in the aerodrome itself；〃 he wrote； 〃or its engines there has been none； and it is believed that it is at the moment of success； and when the engineering problems have been solved； that a lack of means has prevented a continuance of the work。〃
It was truly 〃at the moment of success〃 that Langley's work was stopped。 On December 17； 1903； the Wright brothers made the first successful experiment in which a machine carrying a man rose by its own power； flew naturally and at even speed； and descended without damage。 These brothers； Wilbur and Orville； who at last opened the long besieged lanes of the air； were born in Dayton； Ohio。 Their father； a clergyman and later a bishop； spent his leisure in scientific reading and in the invention of a typewriter which； however； he never perfected。 He inspired an interest in scientific principles in his boys' minds by giving them toys which would stimulate their curiosity。 One of these toys was a helicopter； or Cayley's Top； which would rise and flutter awhile in the air。
After several helicopters of their own； the brothers made original models of kites； and Orville； the younger； attained an exceptional skill in flying them。 Presently Orville and Wilbur were making their own bicycles and astonishing their neighbors by public appearances on a specially designed tandem。 The first accounts which they read of experiments with flying machines turned their inventive genius into the new field。 In particular the newspaper accounts at that time of Otto Lilienthal's exhibitions with his glider stirred their interest and set them on to search the libraries for literature on the subject of flying。 As they read of the work of Langley and others they concluded that the secret of flying could not be mastered theoretically in a laboratory； it must be learned in the