430 Prof. S. P. Langley on the 



the resulting potentiality of this internal work, and of attempts 

 which the writer has made to determine quantitatively its 

 amount by the use of special apparatus, recording the changes 

 which go on (so to speak) within the wind in very brief 

 intervals. These results may, it is hoped, be of interest to 

 meteorologists, but they are given here with special reference 

 to their important bearing on the future of what the writer 

 has ventured to call the science of Aerodromics *. 



The observations which are first given were made in 1887 

 at Allegheny, and are supplemented by others made at 

 Washington in the present year f . 



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 oppo- 

 sition to what at first may seem the teachings of physical 

 science) it is not impossible that a heavy and nearly inert 

 body ivholly immersed in the air can be made to do this. 



The observations on which the writers belief in this 

 mechanical possibility are founded will now be given. 



* From depodpofxeco, to traverse the air ; depodpop,os, an air-runner. 



f 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 1883, still less of the move- 

 ment 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 ex- 

 amination, 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 (1) or (2) ; but the question I wish to raise is 

 whether the cause suggested by (3) may not sometimes come into 

 operation," 



