75 6 THE POPULAR SCIENCE MONTHLY. 



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 imprac- 

 ticable one. This, I think, will prove the greatest of all the diffi- 

 culties. 



2. STABILITY IN PROGRESS. Once fairly up, as already seen, 

 there is no reason why a moving aeroplane should not sustain a 

 heavy flying machine indefinitely if nothing disturbs its equilib- 

 rium. 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 independ- 

 ent propellers and adjustable aeroplanes. In the bird we have 

 the last perfection of skill acquired by constant practice and in- 

 herited 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. SAFETY IN ALIGHTING. If the last i. e., stability in prog- 

 ress 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 cir- 

 cumstances. 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 suc- 

 cess gradually, and thus practicing the difficult art of managing 

 with safety. 



CONCLUSION. 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 insurmount- 

 able. 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 direc- 



* The Chinese have most ingeniously utilized this principle in the construction of little 

 kites shaped like a bird, with wings and tail. These require no long, steadying tail, because 

 the wings are made tubular at the tips, and the outrush of the air keeps the kite steady. 



