ee i A E eRe Pe Ne ge) atk eee ee pe Cle na ey ey ah Mee eta a ke a eee 
ote etic Ser ea BG oe RRA Ce tey: a a Meek wets Gee er © p i% PR 
Sy os R, T A NETE T ‘ity 3 fe i ip eb j 
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res, The Wings of Birds. ‘TAugust, 
the air would therefore be equal to that of two square feet of 
surface moving at right angles to itself at the rate of three feet 
5 per second, Turning to Hutton’s tables we find that a wind of 
about thirty feet per second is required to furnish a normal press- 
ure of two pounds on a plane of one foot square, so that if the 
wings of the duck were supposed to be rigid, and the motion a 
continuous fall, uniformity would not be reached under a velocity 
of thirty feet per second. If this velocity be transferred to the 
wing vibration, stability of the body could only be secured by a 
rapidity of stroke ten times as great as what actually occurs, But 
when we add the air resistance to lateral motion of, say one hun- 
dred miles an hour, measured by air passing the bird, its muscu- 
lar exertion becomes still more incompetent to effect the result, 
for now a portion of the energy which before was used to antago- 
_ nize gravity must antagonize air resistance. 
Further load is thus added to the working force, which before 
ia was hopelessly incompetent to its task. No method which is 
; supposed to differ from the direct motion will assist in the least. 
It is velocity which is wanting, As there can be no shorter line 
= between two points than a straight line, so there can be no more 
: effective method than continuous motion, normal to the surface, 
with no change whatever in the ‘character of the activities. A 
_ continuance of the maximum is the height of effectiveness. No 
_ Screw motion, or wave motion, or figure-eight motion, which e 
wing may imitate, can produce results as good as the direct 
motion. 
But bird flight thus conceived does not exist in nature. Ast 
fact, gravity is not resistance but motive power. The bird is a 
_ machine doing work on air under the dominion of that force. 
The work done is not the sustained bird but the quantity of a ‘4 
disturbance which falls tó an equilibrium with the surrounding es 
atmosphere after the passage of the moving body through Eo 
Gravity is not resisted, it is resolved. The bird is constantly 
moving in the direction of the normal component with a uniform 
_ velocity which develops air pressure sufficient to neutralize the 
mponent acting in the plane of the wings and the additional 
face friction of the air. The direction of the fall is that of the 
gravity of the bird’s mass, and this direction changes with the 
ant of the wings, being always at right angles thereto in obe- 
: to the law of fluid pressures. The fall is always away from 
See Ci eee Ee S 
Spe es 
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