THE INTERNAL WORK OF THE WIND/ 



PART I. 



INTRODUCTORY. 



It has long been observed that certain species of birds maintain themselves 

 indefinitely in the air by " soaring," without any flapping of the wiug, or any 

 motion other than a slight rocking of the body; and this, although the body in 

 question is many hundred times denser than the air in which it seems to float with 

 an undulating movement, as on the waves of an invisible stream. 



No satisfactory mechanical explanation of this anomaly has been given, and 

 none would be offered in this connection by the writer, were he not satisfied that 

 it involves much more than an ornithological problem, and that it points to novel 

 conclusions of mechanical and utilitarian importance. They are paradoxical at first 

 sight, since they imply that, under certain specified conditions, very heavy bodies 

 entirely detached from the earth, immersed in, and free to move in, the air, can be 

 sustained there indefinitely, without any expenditure of energy from within. 



These bodies may be entirely of mechanical construction, as will be seen later, 

 but for the present we will continue to consider the character of the invisible sup- 

 port of the soaring bird, and to study its motions, though only as a pregnant 

 instance offered by Nature to show that a rational solution of the mechanical 

 problem is possible. 



Recurring, then, to the illustration just referred to, we may observe that the 

 flow of an ordinary river would afford no explanation of the fact that nearly inert 

 creatures, while free to move, although greatly denser than the fluid, yet float upon 

 it ; which is what we actually behold in the aerial stream, since the writer, like 

 others, has satisfied himself, by repeated observation, that the soaring vultures and 

 other birds appear as if sustained by some invisible support, in the stream of air, 



* This paper was read by title to the National Academy of Sciences in April, 1893, and in full 

 before the International Conference on Aerial Navigation at Chicago in August, 1893. 



