160 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



L'Aeronaute. No copy of this journal is accessible to me, but the 

 details of Penaud's machine, with pictures, are given in the memoir 

 quoted below. Penaud stated that he had obtained a flight of 60 

 meters during 13 seconds. Langley was never able to obtain such 

 results, but states that twisted rubber has a very high potential, be- 

 ing much more efficient than any steel spring he tried. 



From the start Langley proceeded in a truly scientific manner, 

 studying the mathematics and physics of the problem preliminary 

 to construction of apparatus. His results are set forth in two pub- 

 lications, The Internal Work of the Wind and Experiments in Aero- 

 dynamics. He discovered that the law laid down by Newton, and 

 accepted by most mathematicians and physicists— namely, that at- 

 mospheric resistance to inclined surfaces is proportionate to the square 

 of the sine of the angle of inclination, is not. founded in fact, the 

 resistance being really proportionate to the angle directly. The in- 

 teresting story of the invention of the practical aeroplane is to be 

 found in the ponderous quarto of over 300 pages, entitled The Lang- 

 ley Memoir on Mechanical Flight, published by the Smithsonian 

 Institution, and consisting of two papers, one mostly by Langley him- 

 self, the other by his faithful and efficient assistant, Charles M. 

 Manly. It is from this publication that I have drawn most of the 

 material for this essay. 



Notwithstanding that the problem of flight had engaged human 

 attention for many centuries, and had attracted all classes of per- 

 sons, ranging from such a profound genius as Da Vinci to mere 

 cranks and dreamers, yet when Langley took up the matter there 

 were but few data available, and there was almost no one disposed 

 to give him encouragement, tangible or sentimental. Distinguished 

 scientists deprecated investigations into the subject. As late as 

 1900 a prominent astronomer and mathematician declared that it 

 would be impossible to construct a machine capable of sustaining 

 the weight of the largest known birds, not knowing that two of 

 Langley's machines had already accomplished more than this. " The 

 truly blind are those who will not see." 



After several years' assiduous labor he was able to announce that 

 it is possible to give such velocity to inclined surfaces that bodies 

 indefinitely heavier than air could be driven through it with great 

 velocity. As a concrete instance he states that a plane surface, 7G.2 

 centimeters by 12.2 centimeters (about 1 square foot) weighing 500 

 grams, could be driven through air in absolutely horizontal flight 

 at the rate of 20 meters per second with 0.01 horsepower. This is 

 equivalent to a weight of 200 pounds driven through air by 1 horse- 

 power at 40 miles per hour. 



Following up this conclusion, a number of machines were con- 

 structed and tried out, some of them, of course, quite small, others of 



