

1891.] Problem of the Soaring Birds. 793 
plane and air meet. They do not all go about it in the same 
way, but in the end that is where they locate it. So far as I can 
determine, the error is on the increase, the later authorities being 
more emphatically astray than the earlier ones. The last utter- 
ance that I have seen is contained in a lecture delivered to the 
students of Sibly College, Cornell University, in May, 1890, by 
O. Chanute, C.E. On pages 28 and 29 of the published paper 
the error comes out glaringly. In speaking of M. Drzewieki’s 
work on Duchemin’s formula, he says: “ Next he calculates the 
horizontal components of the normal pressure, this being the 
resistance to the advancement of the plane.” His entire exposi- 
tion is saturated with the blunder, for no horizontal resistance 
exists. Mr. S. P. Langley, in his recent submission of experi- 
ments and suggestions in aérodynamics, entertains the same 
delusion in its full force, otherwise he seems notably free from a 
priori bias. ; 
But my thanks are due to some unknown friend who has just 
sent me a copy of Science, dated May ist, 1891, in which 
I find marked a letter to the editor on “Flying Machines,” 
by H. A. Hazen. The writer is wholly unknown to me; 
but I infer that he is neither a “crank” nor a dabbler in 
science, but a well-grounded expert of wholly intelligent attain- 
ments. Without presuming to defend Mr. Langley in the 
remotest manner, I am justified in holding that Hazen’s statements 
are accepted by the mechanical schools, and I herewith call 
attention to the utterly erroneous nature of such teaching by con- 
trast to the following facts. 
1. A bird does support itself in soaring flight by going fast, 
and in no other way. 
2. There is no evidence that a bird in the act of soaring ever 
remained stationary in still air for an instant; and whether air is 
hurled against bird or bird against air, the result is the same; 
meeting in opposition of bird and air is required by the very 
nature of soaring flight. 
3. “ Solution of the problem ” is unchanged by “ great velocity.” 
4. As parallel motion on the upward slant is what gives 
“velocity ” to the bird, and as atmospheric friction is the only 


