How completely Langley's belief in flight by aeroplanes has been justified is known now to everyone, though his experiments are rarely mentioned. Faraday once said, referring to the electric dynamo, "I gave you this machine as an infant; you bring it back as a giant." Had Langley lived, the same remark could have been applied appropriately by him to the development of flying machines from his models. Purely scientific investigations gave the world the dynamo, and with the construction of this means of producing electricity there commenced a new era in engineering. In like manner, the work of a man of science opened a new epoch in the history of aerial navigation.

When, in May, 1896, Langley's power-driven model aeroplane flew over the Potomac River for a minute and a half (for which time only it was provided with fuel and water), and accomplished a flight of little over half a mile before it settled down upon the water with a gentle descent, the possibility of free dynamic flight was established. It was Langley, and no one else, who was the father of modern aeroplaning, both on account of his investigations of the scientific principles of air resistance and the work of the wind, and because he put the principles into practice by constructing a selfbalancing heavier-than-air machine which would sustain itself in the air so long as the power driving it lasted. No one before Langley had succeeded in building an aeroplane capable of sustained free flight with a man as pilot.

When Wilbur and Orville Wright commenced their experiments in artificial flight, the only exact experiments they could find as to the resistance of the air to machines driven at different velocities were those made by the man of science, S. P. Langley. They were the pioneers

of sustained flight with man-carrying aeroplanes, and they have acknowledged that their confidence in the practical solution of the problem was derived from Langley and his work.

The knowledge that the head of the most prominent scientific institution of America believed in the possibility of human flight was one of the influences that led us to undertake the preliminary investigations that preceded our active work. He recommended

to us the books which enabled us to form sane ideas at the outset. It was a helping hand at a critical time, and we shall always be grateful. Wilbur and Orville Wright.

In December, 1903, the Brothers Wright made the first actual flight with an aeroplane driven by a petrol motor. It is constantly stated that artificial flight would have been accomplished long before if engines light enough to drive them had been available, but that is not the case. Flights with two, three, or more passengers show that lightness of the motor is not the only consideration, and motors with equivalent weights were available ten years before the Wrights designed their man-carrying aeroplanes. It was by following the scientific guidance of Langley, and using mechanical ingenuity to extend it, that they were able to give practical effect to the desire of man to rise above the clouds.

Though the Wrights were the first aviators to make successful flights with a heavier-than-air machine driven by its own power, little was known of their work for about two years after 1903. During this period they were engaged in perfecting their aeroplane until, in 1905, they were able to remain in the air for half an hour and cover a distance of about twenty-four miles. They did not give a public demonstration of their achievements until 1908-two years after a young Brazilian, M. Santos Dumont, had made a short public flight in France, using

an aeroplane designed by him without any definite knowledge of what the Wrights had done. Since that period, the advance of dynamic flight has been rapid and marvellous; and aeroplanes of various types are now in everyday use, particularly for military purposes.

The performances of the earlier machines depended very largely upon the pilots, who had to give close attention to different controls in order to keep the planes in a condition of stability in the air. The problem of producing a machine which is automatically steady in free flight is largely mathematical; and it involves the theory of small oscillations about a state of steady motion developed by Lagrange, Kelvin, Routh and other men of science. Definite attention has been given to the mathematical conditions which have to be satisfied, in order to solve the problem of inherent stability, by G. H. Bryan and F. W. Lanchester; and their conclusions, with the results of experimental research on models at the National Physical Laboratory, largely by L. Bairstow, have led to the construction of the B.E. biplane, which is almost independent of the pilot except when near the ground, where personal control must be exercised.

The forms of early aeroplanes were determined chiefly by trial-and-error methods; and little inducement was given to scientific men to devote themselves to the experimental and theoretical studies by which the most efficient types of machine can be secured. Work in the laboratory and calculation in the study must, however, eventually determine the lines upon which a flying machine can be designed that may be launched into the air with as much confidence in its safety and inherent stability as a vessel can be trusted to leave the slips of the dockyard in which it has been built.

CHAPTER XI

ACROSS THE BORDER

Nature does not allow us to explore her sanctuaries all at once. We think we are initiated, but we are still only on the threshold. Seneca.

The seemingly useless or trivial observation made by one worker leads on to a useful observation by another : and so science advances, "creeping on from point to point." Prof. Silvanus P. Thompson.

One day telleth another and one night certifieth another. There is neither speech nor language but their voices are heard among them. Their sound is gone out into all lands: and their words into the ends of the world. Psalm XIX. 2, 3, 4.

We find ourselves, in consequence of the progress of physical science, at the pinnacle of one ascent of civilisation, taking the first step upwards out on to the lowest plane of the next. Above us still rises indefinitely the ascent of physical power-far beyond the dreams of mortals in any previous system of philosophy. Prof. Frederick Soddy.

SCIENCE advances by bringing into view facts and phenomena previously unknown. Galileo turns his simple telescope towards the heavens, and lo! thousands of stars beyond the grasp of unaided vision are revealed; the microscope is invented, and by its aid an unseen universe, the inhabitants of which are far more numerous than the stars in heaven, is made known. In neither

case were new worlds or organisms created, the extension of knowledge being but a consequence of the improved powers of seeing. The limits of visible light-waves have now been extended so that in wireless telegraphy we produce and detect electric waves which do not affect the organ of vision; and from darkness we derive by X-ray tubes and radium new radiations which light up a land of promise across the border.

Of all the achievements of science, that which creates the deepest impression upon the minds of most people is wireless telegraphy, the triumphs of which can be traced back to researches carried on in laboratory and study. Its development is due even more to theory than to practical work. When the effects of currents upon magnets, and upon one another, had been determined, science demanded an explanation of them. The effects can be produced in a vacuum, or through glass, wood, or similar substances; so evidently what seems to be empty space or material bodies must really be filled with something capable of transmitting the electric and magnetic forces. Ampère suggested that the observed facts could be explained by the presence of a universal medium which could convey these forces from one point to another. Henry and Faraday also held this view, and it was developed in detail by a mathematical physicist, James Clerk Maxwell, about the middle of the nineteenth century.

What Maxwell did was to extend by brilliant mathematical analysis the conception formed by Faraday as to the propagation of electro-magnetic action by an intervening medium. The theory of "action at a distance" assumed that no medium was actively concerned with the transmission of electric or magnetic forces, whereas Faraday, by experimental researches