20 SMITHSONIAN MISCELLANEOUS COLLECTIONS. 



Among these may especially be noted his "Report on the New Spec- 

 trum," his study on "The Personal Equation," his discussion on 

 "Good Seeing," his paper on "The Observation of Sudden Phenom- 

 ena," and the intensely interesting article on "The Cheapest Form of 

 Light," this latter study being based upon the radiations from the 

 glow-worm and firefly, showing that these produce light virtually 

 without heat, and that this being actually effected by nature may 

 possibly yet be effected by science. 



I come finally to another field of Doctor Langley's work, one with 

 which his name was identified during the last fifteen years of his 

 life — the subject to which he applied the name aerodynamics. His 

 first communication to the scientific world and to the public generally 

 took the shape of a very brief letter to the Academy of Sciences of 

 the Institute of France, in July, 1890; also by a publication of an ex- 

 tended memoir in the Smithsonian Contributions ; and, thirdly, 

 through a brief popular article on the possibility of mechanical 

 flight, published in the Century Magazine. I have spoken regarding 

 the group of great leaders in industrial enterprise at Pittsburg, and 

 the name of one of them was now commemorated in the preface of 

 Langley's "Experiments in Aerodynamics," as follows : 



"If there prove to be anything of permanent value in these investi- 

 gations, I desire that they may be remembered in connection with the 

 name of the late William Thaw, whose generosity provided the 

 principal means for them." 



This memoir was at once published in French, and Doctor Lang- 

 ley followed it, in 1893, by a second study, "The Internal Work of 

 the Wind," which also appeared in English and French, and which 

 was designed to prove that aerial flight had an aid in the laws of 

 nature, hitherto little, if at all, known, which would be of great mo- 

 ment in the practical solution of the problem. 



But the painstaking experiments with the whirling-table and with 

 other forms of apparatus devised by Doctor Langley for the study of 

 this question did not content him, and he began the building of a 

 machine driven by a steam-engine which he hoped would practically 

 demonstrate the possibility of mechanical flight. There were in- 

 numerable mechanical difiiculties, both in its construction and its 

 launching, and after failures which would have disheartened most 

 men, a large measure of success came in the spring of 1896, when a 

 steam-driven aerodrome constructed under Doctor Langley's direc- 

 tion, in his own shops, engine and all, actually flew over the Potomac 

 River for three-quarters of a mile. 



This success had world-wide recognition. It was communicated 



