552 The Sniithsonimi Institution 



keeping with the present knowledge of physics and en- 

 gineering. Of these none has pursued the subject more 

 assiduously, or made more valuable contributions toward the 

 solution of the problem, than the distinguished Secretary of 

 the Institution, Doctor Langley. The work is still in active 

 progress, but it is proper to say here that the foundation for 

 it was laid, in a large measure, in a series of experiments 

 in aerodynamics, principally carried on in the grounds of 

 the Allegheny Observatory, Allegheny, Pennsylvania. They 

 are to a great extent a study of the aeroplane, and Doctor 

 Langley's report of the work was published among the " Con- 

 tributions" of 1 89 1. A portion of the work done in Alle- 

 gheny, supplemented by additional studies made later at the 

 Smithsonian Institution in Washington, gave rise to another 

 very important memoir by the same author, published in the 

 same series in 1893. Its title is "The Internal Work of the 

 Wind." The principal conclusions reached in the investigation 

 are as follows: "That the wind is not even an approximately 

 uniform moving mass of air, but consists of a succession of 

 very brief pulsations of varying amplitude, and that, relatively 

 to the mean movement of the wind, these are of varying 

 direction." From this fundamental proposition, established 

 by experiment, it is inferred that there is a potentiality of "in- 

 ternal work " in the wind which is probably large ; that it is 

 no contradiction to known principles of dynamics to declare 

 that an inclined plane or properly-curved surface, heavier 

 than the air and immersed in it, may be supported, or even 

 rise, indefinitely without expenditure of energy other than 

 that necessary to change the aspect of its inclination at each 

 pulsation ; also that the possibility of such a surface making 

 advance against the direction of the wind follows not only 

 relatively to the wind, but absolutely in reference to a fixed 

 point. It is hardly necessary to say that these conclusions 



