.^o6 



NA TURE 



[March 9, 1922 



In 191 4, when I was beginning the preparation of 

 my paper on the " Life and Work of Wilbur Wright," 

 which was read in 1916 as the fourth Wilbur Wright 

 Memorial Lecture, I visited America to collect 

 material for this lecture. During my stay, which 

 extended over several months, I also studied the 

 practical side of aviation and, at the age of forty- 

 seven, made over a hundred flights on the " unstable " 

 Wright machine. While in Dayton I was allowed to 

 examine, with the privilege of copying, much of the 

 personal correspondence and diaries, as well as the 

 records of the early purely scientific work, of the 

 Wrigiit Brothers. I saw the original balances and 

 twenty or thirty (out of the great number) of the 

 original test surfaces with which the Wright Brothers 

 in 1 90 1 made thousands of measurements in a wind 

 tunnel of the lift and drift and the travel of the centre 

 of pressure on plane and curved surfaces. Copies of 

 the tables obtained from these tests were also given 

 to others who were interested in the problem of 

 flight. 



These laboratory measurements {Century Magazine, 

 September 1908, pp. 646-647) covered a field many 

 times greater than had been covered by the work of 

 all other experimenters together. But the importance 

 of the measurements lay in their accuracy. These 

 tables did not agree with the measurements made by 

 Langley or by any of the other experimenters. The 

 Wright Brothers, finding that all marine propellers 

 at that time were based upon empirical formulae, 

 made a study of propellers by analysing the various 

 dynamic reactions. From these studies they evolved 

 a theory. The propellers used on their first power 

 machine were probably the first ever designed from 

 theory and not from experiment. They made ex- 

 tended studies into the principles of equilibrium, and 

 in this field made important scientific discoveries. 

 Their mechanical means for carrying some of these 

 principles into effect were patented, and the resulting 

 litigation attracted so much attention as to cause the 

 scientific work upon which the patents were based to 

 go without notice. It was upon their own tables and 

 other scientific work that the Wright Brothers built 

 their first power machine. 



These scientific experiments were made entirely at 

 the expense of the Wright Brothers themselves, and 

 with no thought or expectation of any other reward 

 than the satisfaction of discovering things unknown 

 before and the honour that naturally comes as a 

 result. It was not until they attempted to build a 

 power machine to carry this scientific knowledge into 

 practical use, an expense too great for their small 

 means, that they took out patents. 



My address on the " Langley Machine and the 

 Hammondsport Trials " was not a criticism of Langley 

 nor of his scientific work. This was not a point at 

 issue in my paper. But since the writer of the 

 articles in Nature now brings this into the discussion, 

 I feel that some of his statements should not be 

 allowed to pass uncorrected. 



Nature is in error in attributing the discovery to 

 Langley of the inherent stability effect of the dihedral 

 angle of the wings adopted by Langley in his models. 

 This method of maintaining lateral stability in calm 

 air was published by Sir George Cayley a hundred 

 years ago, and was used by Penaud in his flying 

 models in 1870 and 18 71. It has never yet been 

 solely relied on for lateral balance in actual human 

 fl.ght, having been always supplemented by aileron 

 control. 



The writer in Nature says : " So far back as July 23, 

 1 891, a paper on his (Langley 's) experimental re- 

 searches is to be found in Nature, showing that the 

 flight of a man-carrying aeroplane was possible, and 

 enunciating the fundamental principles for obtaining 



NO. 2732, VOL. 109] 



a design." The demonstration referred to as " show- 

 ing that the flight of a man-carrying aeroplane was 

 possible," was stated on page 107, " Experiments in 

 Aerodynamics," where I)r. Langley says, " such 

 mechanical flight is possible with engines we now 

 possess, since . . . one horse-power rightly applied, 

 can sustain over 200 pounds in the air at a horizontal 

 velocity of over 20 meters per second (about 45 miles 

 an hour) and still more at still higher velocities." 

 This statement was based upon the mistaken prin- 

 ciple published by Sir George Cayley in Nicholson's 

 Philosophical J otirnal of November, 1809, and accepted 

 by most experimenters thereafter, that the pressures 

 on a plane were normal to the surface of the plane, 

 and that the drag was equal to the lift multiplied by 

 the tangent of the angle of incidence. Langley's 

 actual measurements did not confirm this theory, 

 but he assumed (page 65, " Experiments in Aero- 

 dynamics ") that if he had made certain modifications 

 in the planes he was measuring other results would 

 have been secured which would have confirmed it. 

 It was this assumption that formed the basis of his 

 demonstration that one horse-power would sustain 

 200 pounds at a speed of 45 miles an hour. As a 

 matter of fact his actual measurements (page 64) 

 showed that one horse-power could carry only 60 

 pounds at 45 miles an hour. 



The other fundamental principle enunciated by 

 Langlej^ in 1891 was that known as the " Langley 

 Law," which was that the faster an aeroplane be 

 flown the less will be the power required to sustain 

 it. The fallacy of this law is well known to all 

 aeronautical engineers to-day, but up to 1910 this 

 was generally considered as Langley's chief contribu- 

 tion to the science of aerodynamics. In that year 

 when the Regents of the Smithsonian Institution 

 decided upon the placing of a bronze tablet in the 

 Institution commemorating Langley's work in aero- 

 dynamics, they ordered the following legend to be 

 inscribed upon it : — 



SAMUEL PIERPONT LANGLEY 

 1834-1906 



secretary of the SMITHSONIAN INSTITUTION 

 1888-I906. 



AERONAUTICS : 



Langley Law : " These new experiments show 

 that if in such aerial motion there be given a 

 plane of fixed size and weight, incUned at such 

 an angle, and moved forward at such speed that 

 it shall be sustained in horizontal flight, then 

 the more rapid the motion is, the less will be the 

 power required to support and advance it."— 

 Langley, " Experiments in Aerodynamics," 1891, 

 .P- 3- 



" I have brought to a close the portion of the 

 work which seemed to be specially mine — the 

 demonstration of the practicability of mechanical 

 flight." — Langley Aerodrome, Smithsonian Re- 

 port, 1900, p. 216. 



FLIGHTS : 



Steam model, Ma}' 6, and November 28, 1896. 



Gasoline model, August 8, 1903. 



Before the tablet was cast, the Wright Brothers 

 were consulted as to the advisabiUty of using this 

 "inscription and they, not wishing that anything dis- 

 creditable to Langley should appear on the tablet, 

 Mr. Wilbur Wright wrote a letter to Secretary Walcott, 

 from which the following is quoted : — • 



" I have often remarked to my brother that Prof. 

 Langley was ill-fated in that he had been especially 



