THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



I 



[FIFTH SERIES.] 



M A Y 1894. 



XLI. The Internal Work of the Wind* 

 By S. P. Langley*. 



[Plates V.-IX.] 



Pakt I. — Introductory. 



T has long been observed that certain species of birds 

 maintain themselves indefinitely in the air by " soaring," 

 without any flapping of the wing 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 connexion 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 cer- 

 tain 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, 



* A paper read (by title only) to the National Academy of Sciences, 

 in April 1893, and subsequently (in full) at the Aeronautical Congress, 

 at Chicago, in August, 1893. Communicated by the Author, to whom 

 we are likewise indebted for cliches of the plates. 



Phil. Mag. S. 5. Vol. 37. No. 228. May 1894. 2 G 



