Page:Popular Science Monthly Volume 44.djvu/774

756 wrong and it is necessary to alight, how is the machine to rise again without the station device? A locomotive machine that can not stop anywhere and again resume its journey is an impracticable one. This, I think, will prove the greatest of all the difficulties.

2. .—Once fairly up, as already seen, there is no reason why a moving aëroplane should not sustain a heavy flying machine indefinitely if nothing disturbs its equilibrium. Therefore, once up, we might hope for success in still air, or even possibly in a perfectly uniform current. But air currents are extremely variable in time (puffs and gusts) and in space—i. e., air streams of varying velocities and varying directions. When we see the frantic evolutions of a badly made kite, or of any kite if the steadying string breaks, we are warned of the danger of our aeroplane at high speed and with variable wind, unless skillfully managed, perhaps by means of several independent propellers and adjustable aëroplanes. In the bird we have the last perfection of skill acquired by constant practice and inherited through successive generations. Even if the science of aviation were perfect, the exquisite art necessary to manage such a machine seems almost hopelessly unattainable.

3. .—If the last--i. e., stability in progress—be attained, I suppose this also may be. In still air, by checking the velocity by the use of the propellers, the aeroplane would let down the machine with all the gentleness desirable. With head wind, also, there is no reason why alighting should not be successful. With the wind aft, it would be necessary to turn about and face the wind, as a bird does under similar circumstances. A 'parachute, with tubular opening atop, descends with perfect steadiness.

4. To all these difficulties we must add the enormous hazard of a first attempt, the apparent impossibility of approaching success gradually, and thus practicing the difficult art of managing with safety.

. Under present lights, therefore, it is no longer justifiable to say, as I have previously done, that a flying machine is physically impossible. I therefore retract that expression. But the engineering difficulties are enormous and possibly insurmountable. At the present time the nearest approach to success in aerial locomotion is still to be found in the French dirigible balloon—i. e., a balloon propelled and steered by machinery—and for some time to come the best success may still be looked for in that