1887. | NEW YORK ACADEMY OF SCIENCES. 15 
THE MECHANISM OF FLIGHT IN SOARING BIRDS. 
(Abstract. ) 
Pror. TROWBRIDGE first read from Sir Samuel Baker to illus- 
trate the fact that birds, the condors and buzzards, for example, 
remain in the upper atmosphere for many hours at a time. 
This would indicate that, through some mechanism, such birds 
were largely relieved from muscular effort of the wings ; as it is 
impossible for any muscle to remain for a great length of time 
under continuous strain. (See Transactions, vol. VI., page 
118.) 
The discovery by Prof. Jeffries Wyman (Proc. Boston Soc. of 
Nat. Hist., vol. V., p. 169) of the locking and stiffening of the 
wrist and elbow joints in extended wings, added an important 
element to the mechanism for relief of the muscles. The lock- 
ing of the outer primary feathers, announced at the meeting, 
October 17th, was another element. A tendon or ‘‘ tie” to 
support the extended and stiffened wing, and supplement the 
weak point at the shoulder, would make a complete mechanism. 
From a partial examination, Prof. Trowbridge thought that 
such a tendon existed. 
He had found that many birds besides the soaring birds had 
the notched primaries. 
With regard to soaring ascent, Prof. Trowbridge remarked as 
follows: 
It has always excited wonder that a soaring bird can mount 
upwards in what appear to be circular evolutions without flap- 
ping its wings. Mechanically considered, such evolutions are 
possible only when there is a horizontal or upward vertical cur- 
rent of air. The ascent without flapping the wings, and a 
long-continued soaring flight, are impossible in stagnant air. 
Although almost self-evident, this proposition has not hereto- 
fore been clearly stated, as far as [am aware, in any discussion on 
the mechanics of flight, where birds mount upwards without 
flapping. 
But in a current of air, parallel to the earth’s surface, or 
obliquely or vertically upwards, such evolutions become possible. 
Suppose a bird with outstretched wings to be for a moment at 
rest with reference to the earth in a moving horizontal current; 
it is carried along by the wind, but not with the full rapidity of 
the air-current; its course, due to the action of gravity and 
the wind combined, being slightly downward. Jt soon acquires 
a momentum and kinetic energy due to these forces acting 
jointly, but mainly due to the velocity of the wind. 
A slight movement of the tail or of the wings without flap- 
