24 The American Naturalist. [J anuary, 
Ba 
But in no case of bird flight that I am acquainted with, can 
it be said that the normal factor is opposed by flapping. That 
is cancelled by its own work on air. Flapping goes on for the 
sole purpose of producing parallel motion by either increasing 
the energy of the condensations, or by a backward push 
against the air. 
It must be borne in mind that the nearer the bird’s wings 
approach horizontal, the less will be the obstructive gravity 
factor, but on the other hand, the more contracted will be the 
neutral zone. The moment this zone is encroached upon, 
more is lost in resistance of air, than is gained by lessening 
the small factor. > 
| 
Sie a 
In experimenting, I never pay the least attention to what I 
have called the “soaring force,” meaning thereby the force — 
required to push the plane to the resultant, after the small 
factor is neutralized. I have never used scales delicate 
enough to measure this force. The moment the small factor 
is out of the way, the plane runs to the front to the limit of , 
its freedom. : 
There is the narrowest possible margin between active and | 
fixed wing flight. The only group of white pelicans I ever — 
met with, eight in number, moved through the air in alternate 
flapping and gliding motion. Once only, I found them facing 
a southwester on fixed wings. They rested in the gale as 
firmly as if fastened to a rigid support. I had been observing 
them daily for five months and was rewarded by this very | 
unusual exhibition. I shot one of them and found its gullet mM | 
and intestines full of fish, and it could only spread one square — | 
foot of surface to each five pounds of weight, the greatest con- 
trast of surface to weight I ever found. : 
The entire subject of bird flight has been persistently mis- 
conceived. It must be recast in toto to rescue it from the 
mass of delusion that involves it. To speak of erroneous 
details is labor lost. It is all erroneous. There is no stress in 
the entire activity, either in direction or magnitude, where 
stresses are supposed to be. When it is seen that from eleven- 
twelfths to seventeen-eighteenths, approximately, of total 
weight is employed in overcoming total air resistance to the 
