46 S. P. Langley — Internal Work of the Wind. 



The observations which are first given were made in 1887 

 at Allegheny and are supplemented by others made at Washing- 

 ton in the present year.* 



What has just been said about their possible importance will 

 perhaps seem justified, if it is remarked (in anticipation of 

 what follows later) that the result of the present discussion 

 implies not only the theoretical, but the mechanical possibility, 

 that a heavy body wholly immersed in the air and sustained 

 by it, may without the ordinary use of wind, or sail, or steam, 

 and without the expenditure of any power except such as may 

 be derived from the ordinary winds, make an aerial voyage in 

 any direction, whose length is only limited by the occurrence 

 of a calm. A ship is able to go against a head wind by the 

 force of that wind, owing to the fact that it is partly immersed 

 in the water which reacts on the keel, but it is here asserted, that 

 (contrary to usual opinion and in opposition to what at first 

 may seem the teachings of physical science) it is not impossible 

 that a heavy and nearly inert body, wholly immersed in the air 

 can be made to do this. 



The observations on which the writer's belief in this 

 mechanical possibility are founded, will now be given. 



Part II. — Experiments with the use of special apparatus. 



In the ordinary uses of the anemometer, — (let us suppose it 

 to be a Robinson's anemometer, for illustration, — the registry 

 is seldom taken as often as once a minute ; thus, in the ordi- 

 nary practice of the United States Weather Bureau, the 

 registration is made at the completion of the passage of each 

 mile of wind. If there be very rapid fluctuations of the wind, 

 it is obviously desirable in order to detect them, to observe the 

 instrument at very brief intervals, e. g. at least every second, 

 instead of every minute or every hour, and it is equallv obvious 

 that in order to take up and indicate the changes which occur 

 in these brief intervals, the instrument should have as little 

 inertia as possible, its momentum tending to falsify the facts, 

 by rendering the record more uniform than would otherwise 

 be the case. 



*It will be noticed that the fact of observation here is not so much the 

 movement of currents, such as the writer has since learned was suggested by 

 Lord Rayleigh so long ago as ] 883, still less of the movement of distinct currents 

 at a considerable distance above the earth's surface, but of what must be rather 

 called the effect of the irregularities and pulsations of any ordinary wind, within 

 the immediate field of examination, however narrow. 



See the instructive article by Lord Rayleigh in Nature. April 5, 1883. Lord 

 Rayleigh remarks that continued soaring implies "(1) that the course is not 

 horizontal, (2) that the wind is not horizontal, or (3) that the wind is not uniform." 

 "It is probable," he says, "that the truth is usually represented by(l) or (2); 

 but the question I wish to raise is whether the cause suggested by (3) may not 

 sometimes come into operation." 



