NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT . 7 



the aerodrome to move upward or downward, and Urns deparl from horizontal 

 flight so widely as to bring prompt destruction. 



To secure tins balance, or equilibrium, we know in theory, that the center 

 of gravity must be brought nearly under the center of pressure, by which latter 

 expression we mean the resultant of all the forces which tend to sustain the 

 aerodrome; but this center of pressure, as may in fad he inferred from " Aero- 

 dynamics," 3 varies with the inclination of the surface. It varies also with the 

 nature of the surface itself, and for one and the same surface is constantly 

 shifted unless the whole be rigidly held, as it is on the whirling-table, and as it 

 cannot be in free flight. 



Here, then, are conditions of the utmost importance, our lcnowledge of which, 

 as derived from ordinary aerodynamic experiments, is almost nothing. A con- 

 sideration of this led me to remark in the conclusion of " Aerodynamics ": 



" I have not asserted, without qualification, that mechanical flight is prac- 

 tically possible, since this involves questions as to the method of constructing 

 the mechanism, of securing its safe ascent and descent, and also of securing the 

 indispensable condition for the economic use of the power I have shown to be 

 at our disposal — the condition, I mean, of our ability to guide it in the desired 

 horizontal direction during transport — questions which, in my opinion, are only 

 to be answered by further experiment and which belong to the inchoate art or 

 science of aerodromics on which I do not enter." 



It is this inchoate art of aerodromics which is begun in the following experiments 

 with actual flying machines. 



In all discussions of flight, especially of soaring flight, the first source to 

 which one naturally looks for information is birds. But here correct deductions 

 from even the most accurate of observations are very difficult, because the 

 observation cannot include all of the conditions under which the bird is doing 

 its work. If we could but see the wind the problem would be greatly simplified, 

 hut as the matter stands, it may be said that much less assistance has been de- 

 rived from studious observations on bird-flight than might have been anticipated, 

 perhaps because it has been found thus far impossible to reproduce in the fly- 

 ing machine or aerostatic model the shape and condition of wing with its flexible 

 and controllable connection with the body, and especially the instinctive control 

 of the wing to meet the requirements of flight that are varying from second to 

 second, and which no automatic adjustment can adequately meet. 



At the time I commenced these experiments, almost the only flying-machine 

 which had really flown was a toy-like model, suggested by A. Penaud, a young 

 Frenchman of singular mechanical genius, who contributed to the world many 

 most original and valuable papers on Aeronautics, which may be found in the 

 journal " L'Aeronaute." His aeroplane is a toy in size, with a small propeller 



'Chanter VIII. 



