HARDWICKE'S SCIENCE-GOSSIP. 



22' 



THE WINGS OF BIRDS. 

 By J. Lancaster. 



WHILE engaged in ascertaining the methods 

 employed by the soaring birds, on reaching 

 a point where light began to break upon the obscurity, 

 it became evident that the flight of all birds would be 

 made comprehensible ; that not only the day-long 

 translation of frigate-birds in circular paths high in 

 the air, but the homeward passage of pigeons and the 

 migratory flight of wild-fowl, would emerge from the 

 realm of fancy and range themselves with allied 

 phenomena on the platform of recognized mechanical 

 activities. 



Indeed, many specimens of active wing flight have 

 hitherto as completely baffled the best efforts of 

 mechanical science as has soaring flight. When the 

 weight of the bird is considered as resistance to be 

 overcome by muscular force, flapping is incompetent 

 to do the work required, and in spite of such efforts 

 gravity would compel motion in its own direction to 

 the surface of the earth. 



The area of the two wings of a duck of four pounds 

 weight, which is effective on the air in the down 

 stroke is not more than two square feet. Counting 

 one up and one down vibration as a single stroke, 

 not more than three of these would be made in one 

 second, and a liberal estimate would be an average 

 of one foot of space travelled at each stroke for the 

 entire surfaces. This ignores loss in the upward 

 vibration. The effective work done on 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 per second. Turning to Hutton's Tables, 

 we find that a wind of about thirty feet per second 

 is required to furnish a normal pressure 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 hundred miles an hour, measured by air 

 passing the bird, its muscular exertion becomes still 

 more incompetent to effect the result, for now a 

 portion of the energy which before was used to 

 antagonise gravity must antagonise air resistance. 



Further- load is thus added to the working force, 

 which before 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. No screw motion, or 



wave-motion or figure-eight-motion, which the wing 

 may imitate, can produce results as good as the 

 direct motion. 



But bird flight, thus conceived, d®es not exist in 

 nature. As a 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 air 

 disturbance which falls to an equilibrium with sur- 

 rounding atmosphere after the passage -of the moving 

 body through it. 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 

 component acting in the plane of the wings and the 

 additional surface 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 slant of the wings, 

 being always at right angles thereto in obedience U> 

 the law of fluid pressures. The fall is always awc.-y 

 from the plane of the wings, or the bird's horizon, -se 

 that no weight is lifted in the lateral motion, as the 

 body is continually descending on its own .vertical. 

 This view completely transforms the aspect of ctmo- 

 spheric navigation, and brings order out of chaos. 



I have hitherto spoken of the expansion of the 

 compressed air in the rear of the wings producing the 

 thrust needed for the lateral motion. This was done 

 to avoid complicating the case. The significant 

 thing is the resolution of gravity and consequent 

 shifting of the vertical, and if this feet is seen the 

 method of utilising the pressures presents no diffi- 

 culty. 



I now wish to direct attention to the structure of 

 a bird's wing. The wing of a pigeon or any of the 

 barnyard fowls may be examined, as the peculiarities 

 I desire to point out are found in all of the large birds. 

 First, let us examine a feather. If we place one on 

 the table with the lower'surface upwards, and pass the 

 hand from the quill to the tip, it will seem smooth to 

 the touch, while reverse motion meets with much 

 roughness, which increases as the pressure of fbe 

 finger becomes'greater. If a small tube be taken into 

 the mouth and the breath blown quite slanting 

 towards the tip, the feather will remain smooth, and 

 the air slip over it easily. In the reverse direction 

 the blast will tend to open the ribs and increase .the 

 roughness. The feather is a little like a cat's back.; 

 a rub toward the rear is pleasant to all parties, walk- 

 one the other way tends to cause motion of the 

 animal to the front. Notice also that the tip is very 

 thin and elastic, yielding in a graceful curve to slight 

 pressure. The surface of the wing is composed 

 mainly of these feathers, having their general direction 

 across, with the tips to the rear. They are held by 

 the integument covering the bones of the wing, which 

 are located on the front edge, and while on the upper 

 front side the curve is smooth and regularly rounded, 

 beneath there is a projection downwards of the skin 



