Part 25

_The Artificial Wing propelled at various degrees of speed during the Down and Up Strokes._--The tendency which the artificial wave wing has to rise again when suddenly and vigorously depressed, explains why the _elevator_ muscles of the wing should be so small when compared with the _depressor_ muscles--the latter being something like seven times larger than the former. That the contraction of the elevator muscles is necessary to the elevation of the wing, is abundantly proved by their presence, and that there should be so great a difference between the volume of the elevator and depressor muscles is not to be wondered at, when we remember that the whole weight of the body is to be elevated by the rapid descent of the wings--the descent of the wing being entirely due to the vigorous contraction of the powerful pectoral muscles. If, however, the wing was elevated with as great a force as it was depressed, no advantage would be gained, as the wing, during its ascent (it acts against gravity) would experience a much greater resistance from the air than it did during its descent. The wing is consequently elevated more slowly than it is depressed; the elevator muscles exercising a controlling and restraining influence. By slowing the wing during the up stroke, the air has an opportunity of reacting on its under surface.

_The Artificial Wave Wing as a Propeller._--The wave wing makes an admirable propeller if its tip be directed _vertically downwards_, and the wing lashed from side to side with a sculling figure-of-8 motion, similar to that executed by the tail of the fish. Three wave wings may be made to act in concert, and with a very good result; two of them being made to vibrate figure-of-8 fashion in a more or less horizontal direction with a view to elevating; the third being turned in a downward direction, and made to act vertically for the purpose of propelling.

_A New Form of Aërial Screw._--If two of the wave wings represented at fig. 122, p. 239, be placed end to end, and united to a vertical portion of tube to form a two-bladed screw, similar to that employed in navigation, a most powerful elastic aërial screw is at once produced, as seen at fig. 130.

This screw, which for the sake of uniformity I denominate _the aërial wave screw_, possesses advantages for aërial purposes to which no form of _rigid_ screw yet devised can lay claim. The way in which it clings to the air during its revolution, and the degree of buoying power it possesses, are quite astonishing. It is a self-adjusting, self-regulating screw, and as its component parts are flexible and elastic, it accommodates itself to the speed at which it is driven, and gives a uniform buoyancy. The slip, I may add, is nominal in amount. This screw is exceedingly light, and owes its efficacy to its shape and the graduated nature of its blades; the anterior margin of each blade being comparatively rigid, the posterior margin being comparatively flexible and more or less elastic. The blades are kites in the same sense that natural wings are kites. They are flown as such when the screw revolves. I find that the aërial wave screw flies best and elevates most when its blades are inclined at a certain upward angle as indicated in the figure (130). The aërial wave screw may have the number of its blades increased by placing the one above the other; and two or more screws may be combined and made to revolve in opposite directions so as to make them reciprocate; the one screw producing the current on which the other rises, as happens in natural wings.

_The Aërial Wave Screw operates also upon Water._--The form of screw just described is adapted in a marked manner for water, if the blades be reduced in size and composed of some elastic substance, which will resist the action of fluids, as gutta-percha, carefully tempered finely graduated steel plates, etc. It bears the same relation to, and produces the same results upon, water, as the tail and fin of the fish. It throws its blades during its action into double figure-of-8 curves, similar in all respects to those produced on the anterior and posterior margins of the natural and artificial flying wing. As the speed attained by the several portions of each blade varies, so the angle at which each part of the blade strikes varies; the angles being always greatest towards the root of the blade and least towards the tip. The angles made by the different portions of the blades are diminished in proportion as the speed, with which the screw is driven, is increased. The screw in this manner is self-adjusting, and extracts a large percentage of propelling power, with very little force and surprisingly little slip.

A similar result is obtained if two finely graduated angular-shaped gutta-percha or steel plates be placed end to end and applied to the water (vertically or horizontally matters little), with a slight sculling figure-of-8 motion, analogous to that performed by the tail of the fish, porpoise, or whale. If the thick margin of the plates be directed forwards, and the thin ones backwards, an unusually effective propeller is produced. This form of propeller is likewise very effective in air.

CONCLUDING REMARKS.

From the researches and experiments detailed in the present volume, it will be evident that a remarkable analogy exists between walking, swimming, and flying. It will further appear that the movements of the tail of the fish, and of the wing of the insect, bat, and bird can be readily imitated and reproduced. These facts ought to inspire the pioneer in aërial navigation with confidence. The land and water have already been successfully subjugated. The realms of the air alone are unvanquished. These, however, are so vast and so important as a highway for the nations, that science and civilisation equally demand their occupation. The history of artificial progression indorses the belief that the fields etherean will one day be traversed by a machine designed by human ingenuity, and constructed by human skill. In order to construct a successful flying machine, it is not necessary to reproduce the filmy wing of the insect, the silken pinion of the bat, or the complicated and highly differentiated wing of the bird, where every feather may be said to have a peculiar function assigned to it; neither is it necessary to reproduce the intricacy of that machinery by which the pinion in the bat, insect, and bird is moved: all that is required is to distinguish the properties, form, extent, and manner of application of the several flying surfaces, a task attempted, however imperfectly executed, in the foregoing pages. When Vivian and Trevithick devised the locomotive, and Symington and Bell the steamboat, they did not seek to reproduce a quadruped or a fish; they simply aimed at producing motion adapted to the land and water, in accordance with natural laws, and in the presence of living models. Their success is to be measured by an involved labyrinth of railway which extends to every part of the civilized world; and by navies whose vessels are despatched without trepidation to navigate the most boisterous seas at the most inclement seasons. The aëronaut has a similar but more difficult task to perform. In attempting to produce a flying-machine he is not necessarily attempting an impossible thing. The countless swarms of flying creatures testify as to the practicability of such an undertaking, and nature supplies him at once with models and materials. If artificial flight were not attainable, the insects, bats, and birds would furnish the only examples of animals whose movements could not be reproduced. History, analogy, observation, and experiment are all opposed to this view. The success of the locomotive and steamboat is an earnest of the success of the flying machine. If the difficulties to be surmounted in its construction are manifold, the triumph and the reward will be correspondingly great. It is impossible to over-estimate the boon which would accrue to mankind from such a creation. Of the many mechanical problems before the world at present, perhaps there is none greater than that of aërial navigation. Past failures are not to be regarded as the harbingers of future defeats, for it is only within the last few years that the subject of artificial flight has been taken up in a true scientific spirit. Within a comparatively brief period an enormous mass of valuable data has been collected. As societies for the advancement of aëronautics have been established in Britain, America, France, and other countries, there is reason to believe that our knowledge of this most difficult department of science will go on increasing until the knotty problem is finally solved. If this day should ever come, it will not be too much to affirm, that it will inaugurate a new era in the history of mankind; and that great as the destiny of our race has been hitherto, it will be quite out-lustred by the grandeur and magnitude of coming events.

INDEX.

PAGE

Aerial creatures not stronger than terrestrial ones, 13

Aërial flight as distinguished from sub-aquatic flight, 92

Aëronautics, 209

Air cells in insects and birds not necessary to flight, 115

Albatross, flight of, compared to compass set upon gimbals, 199

Amphibia have larger travelling surfaces than land animals, but less than aërial ones, 8

Artificial fins, flippers, and wings, how constructed, 14

Artificial wings, Borelli, 219

Do. Marey, 226

Do. Chabrier, 233

Do. Straus-Durckheim, 233

Do. how to apply to the air, 245

Do. nature of forces required to propel, 246

Artificial _wave_ wing of Pettigrew, 236

Do. how to construct on insect type, 240

Do. how to construct to evade the superimposed air during the up stroke, 241

Do. can create currents and rise upon them, 253

Do. can be driven at any speed; can make new currents and utilize old ones, 251, 255

Do. as a propeller and aërial screw, 256

Do. compound rotation of: the different parts of the wing travel at different speeds, 252

Do. necessity for supplying root of, with elastic structures, 247

Artificial _compound wave_ wing of Pettigrew, 242

Atmospheric pressure, effects of, on limbs, 24

Axioms, fundamental, 17

Balancing, how effected in flight, 118

Balloon, 210

Bats and birds, lax condition of shoulder-joint in, 190

Birds, lifting capacity of, 205

Body and wing reciprocate in flight, and each describes a waved track, 12

Bones, 21

Bones of the extremities twisted and spiral, 28, 29

Bones of wing of bat--spiral configuration of their articular surfaces, 176

Bones of wing of bird--their articular surfaces, movements, etc., 178

Borelli’s artificial bird, 220

Chabrier’s artificial wings, 233

Elytra or wing cases and membranous wings, 170

Feathers, primary, secondary, and tertiary, 180

Fins, flippers, and wings form mobile helices or screws, 14

Flight, weight necessary to, 3, 4, 110, 111, 112, 113

Flight the poetry of motion, 6

Flight the least fatiguing kind of motion, 13

Flight under water, 90

Flight of the flying-fish, 98

Flight, horizontal, in part due to weight of flying mass, 110

Flight--the regular and irregular, 201

Flight--how to ascend, descend, and turn, 201

Flight of birds referrible to muscular exertion and weight, 204

Fluids, mechanical effects of, on animals immersed in them, 18

Fluids, resistance of, 18

Flying machine, Henson, 212

Do. Stringfellow, 213

Do. Cayley, 215

Do. Phillips, 216

Do. M. de la Landelle, 217

Do. Borelli, 219

A flying machine possible, 2, 3

Forces which propel the wings of insects, bats, and birds, 186, 189

Fulcra, yielding, 8, 104, 165

Gravity, the legs move by the force of, 18

Gravity, centre of, 18

History of the figure-of-8 theory of walking, swimming, and flying, 15

Joints, 23

Kite-like action of the wings, 98

Kite--how kite formed by wing differs from boy’s kite, 166

Laws of natural and artificial progression the same, 4, 17

Legs, moved by the force of gravity, 18

Lever--the wing one of the third order, 103

Levers, the three orders of, 19

Life linked to motion, 3

Lifting capacity of birds, 205

Ligaments, 24

Ligaments, elastic, position and action of, in wing of pheasant, snipe, crested crane, swan, etc., 191

Ligaments, elastic, more highly differentiated in wings which vibrate quickly, 193

Locomotion, the active organs of, 24

Locomotion, the passive organs of, 21

Locomotion of the horse, 39

Locomotion of the ostrich, 45

Locomotion of man, 51

Marey’s artificial wings, 233

Membranous wings, 170

Motion associated with the life and well-being of animals, 1

Motion not confined to the animal kingdom, 2

Motion, natural and artificial, 4

Motion, of uniform, 17

Motion uniformly varied, 17

Muscles, their properties, mode of action, etc., 24

Muscles arranged in longitudinal, transverse, and oblique spiral lines, 28

Muscles, oblique spiral, necessary for spiral bones and joints, 31

Muscles take precedence of bones in animal movements, 29

Muscular cycles, 26

Muscular waves, 26

Pendulums, the extremities of animals act as, in walking, 9, 18, 56, 57

Plane, inclined, as applied to the air, 211

Pettigrew’s method of constructing and applying artificial wings as contradistinguished from that of Borelli, Chabrier, Durckheim, Marey, etc., 235

Pettigrew’s _wave_ wing, 236

Pettigrew’s _compound wave_ wing, 242

Progression on the land, 37

Do. on or in the water, 64

Do. in or through the air, 103

Quadrupeds walk, fishes swim, and insects, bats, and birds fly, by figure-of-8 movements, 15, 16

Screws--the wing of the bird and the extremity of the biped and quadruped screws, structurally and functionally, 12

Screws--difference between those formed by the wings and those employed in navigation, 151

Sculling action of the wing, 231

Speed attained by insects, 188

Speed of wing movements partly accounted for, 120

Spine, spiral movements of, transferred to the extremities, 33

Straus-Durckheim’s artificial wings, 233

Swimming of the fish, whale, porpoise, etc., 66

Swimming of the seal, sea-bear, and walrus, 74

Swimming of man, 78

Swimming of the turtle, triton, crocodile, etc., 89

Terrestrial animals have smaller travelling surfaces than amphibia, amphibia than fishes, and fishes than insects, bats, and birds, 8

The travelling surfaces of animals increase as the density of the media traversed decreases, 7, 8

The travelling surfaces of animals variously modified and adapted to the media on or in which they move, 34

Walking, swimming, and flying correlated, 5

Walking of the quadruped, biped, etc., 9, 10, 11

_Wave_ wing of Pettigrew, 236

Do. how to construct on insect type, 240

Do. how to construct to evade the superimposed air during the up stroke, 241

Do. can be driven at any speed, 251, 255

Do. can create currents and rise upon them, 253

Do. can make new currents and utilize existing ones, 251, 255

Do. as a propeller, 256

Do. as an aërial screw, 256

Do. forces required to apply to the air, 245, 246

Do. necessity for supplying root of, with elastic structures, 247

Wave wing, _compound_, 242

Weight necessary to flight, 110

Weight contributes to flight, 112

Weight, momentum, and power to a certain extent synonymous in flight, 114

Wing of the bird and the extremity of the biped and quadruped are screws, structurally and functionally, 12, 136

Wing in flight describes figure-of-8 curves, 12

Wing during its action reverses its planes and describes a figure-of-8 track in space, 140

Wing when advancing with the body describes looped and waved tracks, 143

Wing, margins of, thrown into opposite curves during extension and flexion, 146

Wing, tip of, describes an ellipse, 147

Wing and body reciprocate in flight, and each describes a wave track, 12

Wing moves in opposite curves to body, 168

Wing ascends when body descends, and _vice versâ_, 159

Wing during its vibrations produces a cross pulsation, 148

Wing vibrates unequally with reference to a given line, 150, 231

Wing, compound rotation of, 149

Wing a lever of the third order, 103

Wing acts on yielding fulcra, 8, 104, 165

Wings, their form, etc., all wings screws, structurally and functionally, 136

Wing capable of change of form in all its parts, 147

Wing-area variable and in excess, 124

Wing-area decreases as the size and weight of the volant animal increases, 132

Wing, natural, when elevated and depressed must move forwards, 156

Wing, angles formed by, when in action, 167

Wing acts as true kite both during down and up strokes, 165

Wing, traces of design in, 180

Wing of bird not always opened up to same extent in up stroke, 182

Wing, flexion of, necessary to flight of birds, 183

Wing flexed and partly elevated by action of elastic ligaments, 191

Wing, power of, to what owing, 194

Wing, effective stroke of, why delivered downwards and forwards, 195

Wing acts as an elevator, propeller, and sustainer both during extension and flexion, 197

Wings, points wherein the screws formed by, differ from those in ordinary use, 151

Wings at all times thoroughly under control, 154

Wings of insects, consideration of forces which propel, 186

Wings of bats and birds, consideration of forces which propel, 189

PRINTED BY T. AND A. CONSTABLE, PRINTERS TO HER MAJESTY, AT THE EDINBURGH UNIVERSITY PRESS.