SAMUEL PIERPONT LANGLEY. 3 1 



lation as to the rationale of flight, ^of the way of an eagle in the 

 air," but the question of power required was in hopeless confusion. 



Mr. Langley was then engaged in the study of astrophysics at the 

 observatory in Allegheny, Pennsylvania, and there, in the beginning 

 of 1887, through the liberality of the late WilHam Thaw, the work 

 was commenced by the construction of a turn-table of exceptional 

 size driven by a steam-engine. This served during three years to 

 impel against the air planes and appliances equipped with most in- 

 genious measuring and recording instruments designed by Langley 

 and attached to the arm of this rotating balanced beam. The whole 

 apparatus was very scientific and accurate. The results were pub- 

 lished in 1 89 1 by the Smithsonian Institution, under the title of 

 "Experiments in Aerodynamics," and at once attracted great atten- 

 tion and commendation. 



These epoch-making experiments probably constitute Mr. Lang- 

 ley's chief title to fame in aerodynamics. To avoid complexity, thev 

 were all made upon plane surfaces (which he stated might not be the 

 "best form of surfaces for support) ; but they gave to physicists and 

 to searchers, perhaps for the first time, firm ground on which to 

 stand, as to the long-disputed questions of air resistances and reac- 

 tions. They established (a) a more reliable coefficient for rectangu- 

 lar pressures than that of Smeaton. They proved (b) that upon 

 inclined planes the air pressures were really normal to the surface. 

 They disproved (c) the '"'Newtonian law," that the normal pressure 

 varied as the square of the angle of incidence on inclined planes. 

 They showed (d) that the empirical formula of Duchemin, proposed 

 in 1836 and ignored for fifty years, was approximately correct; that 

 (e) the position of the center of pressure varied with the angle of 

 inclination, and that on planes its movements approximately fol- 

 lowed the law formulated by Joessel; that (/) oblong planes, pre- 

 sented with their longest dimension to the line of motion, were more 

 efifective for support than when presented with their narrower side ; 

 that (g) planes might be superposed without loss of supporting 

 power if spaced apart certain distances which varied with the speed; 

 and (h) that thin planes consumed less power for support at high 

 speeds than at low speeds. This has been called "Langley's law." 

 It results from the fact that the higher the speed, the less need be 

 the angle of inclination to sustain a given weight and the less there- 

 fore the horizontal component of the air pressure. It is true only if 

 the plane alone be considered, without any adjuncts, but it leaves 

 out of the reckoning the head resistance due to the various parts of 

 a complete flying-machine, such as its framing, its hull, etc. 



