Aërial navigation; a popular treatise on the growth of air craft and on aëronautical meteorology

Front matter

AEftlAL

NAVIGArriON :

ALB E R^ 1 . ::vi^ • ■ ^ An M

Preface

The purpose of thiw work is to portray in popular tonus the substantial progress of aeronautics from its carli(^st beginning- to the present time. Beyond the introductory account, little note is taken of experiments, however picturesque or clever, which constitute no advance in the art, or lead to no useful result. At times some minutiae are presented to complete the story of an important series of achievements ; but the unproductive efforts of impractical zealots, however prominent or widely known in their day, receive scant, if any, attention. Failures and tragedies where introduced, are described for the lessons involved rather than for any curious interest investing them. The griefs and grotesque follies of aeronautic imbeciles form a long story, but a futile and unprofitable one, of slight concern in the evohitionary history of a veritable science. A general history of aerial locomotion would naturally be divided into four parts, treating respectively of passive balloons, power balloons, passive Dyers, and power flyers ; but in this work a separate treatment has not been allotted to passive flyers because of their too backward state of development. Passive gliders which maneuver in the air merely by virtue of gravitational force, or acfpiired momentum, are familiar enough ; but the much more interesting passive flyers of human construction, adapted to rise without motive power considerably beyond their initial level, or to soar far aloft, and sail long distances by virtue of favorable winds, are still in their infancy. It may be hoped, however, that the vulture's art which now is

V

PEEFACE

well nigh ovorlooked, because of the triumphant advance of dynamic flight, will soon receive such attention that future treatises may relate human achievements in soaring that shall rival the dexterous and marvelous feats of the condor and albatross, even as the majestic sweep of the dynamic aeroplane now rivals the powerful rowing flight of the strongest birds of prey.

Following the story of the evolution of air ships, a brief account of the medium they navigate has been added. In particular, the circumstances which affect the density and motion of the air have been studied ; for the density of the air determines the static lift of air ships; the density and speed of impact of the air together determine the dynamic lift and the resistance to progression ; while the velocity of the air current conditions the possible speed of travel in any direction. It is important, therefore, that the aeronautical student should have some acquaintance with the general properties of the air which affect its density, and some knowledge of the generation and prevalence both of the great currents of the atmosphere, and of the local winds and invisible turmoils which so nearly concern the safety and eff'ective progress of the aerial navigator.

The French units of measurement have been freely used, as well as the English. This seems advisable because the official rules and records of international aeronautic events are partly expressed in the metric system. Moreover, the navigation of a universal mediiun seems to call for such iiniversal standards. Indeed a peculiar jnission of world travel is to eliminate provincialism, and to promote universalisiii of thought, of sentiment, and of custom.

In order to lighten the book for the popular reader, some interesting historical facts and much important quantitative data are placed in the Appendices, where they may be available to the technical or special student.

It is a pleasant duty to acknowledge here my obligations to the U. S. Signal Corps, the Smithsonian Institution, and the U. S. Weather Bureau, for much assistance in col-

vi

PREFACE

lecting- the materials for this work. Dr. W. J. Humphreys, of the U. S. Weather Bureau, has very kiudly read the manuscript for the chapters on the atmosphere.

My thanks are due also to the Scientific American and to Aeronautics for the use of photograplis for the illustrations, as also to the manufacturers of various aircraft, and to Mr. W. J. Hammer, Mr. Carl Dientsbach, and Mr. A. S. Levino.

A. F. Zahm.

Cosmos Club

Washington, D. C,

January, 1911.

Part I Growth Of Aerostation

I. — Early History of Passive Balloons ... 29 II. — Practical Development of Passive Balloons . 54 III. — Early History of Power Balloons ... 78 IV. — Introduction of Gasoline-Driven Dirigibles 101 V. — Practical Development of Non-Rigid Dirigibles 115

VI. — Development of Rigid Dirigibles . . . 145

Part II

growth of aviation

VII. — Model Flying Machines 173

VIII. — Nineteenth Century Man-Flyers . . . 202

IX. — Aeroplanes of Adequate Stability and Power . 235

X. — Advent of Public Flying 256

XL — Strenuous Competitive Flying .... 283

XII. — Forcing the Art 307

ix

CONTENTS

CHAPTER PAGE

PART in

AERONAUTIC METEOROLOGY

XIII. — General Properties of Free Air . . 347

XIV. — General Distribution of PIeat and Pressure . 303

XV. — Permanent and Periodic Winds .... 376

XVI. —Cyclones, Tornadoes, Waterspouts . . . 394

XVni. — Thunderstorms, Wind Gusts .... 422

APPENDICES

I. — Stress in a Vacuum Balloon .... 443

II. — ^Aeronautic Letters of Benjamin Franklin . 446

III. — Successful Milit.ary Dirigible Balloons . 456 IV. — The Rel.'Vtions of Weight, Speed, and Power

OF Flyers 478

V. — CuRTiss' Hydro-Aeroplane Experiments . . 4S1

INDEX 487

LIST OF PLATES

FACING PAGB

Plate I 66

Glaisher and Coxwell.

Parseval Kite Balloon.

Plate II 98

Haenlein's Gas-driven Dirigible.

Wolfert's Benzine-driven Dirigible. Santos-Dumont's Dirigible, No. 16.

Plate III . 116

The Lebaudy.

La Patrie.

Lebaudy'.s I\Iorning Post.

Plate IV 124

La Ville de Paris.

Colonel Rcnard.

Plate V 128

Zodiac III.

Zodiac IV.

Plate VI 130

La Bcigiqiie.

Italian Military Dirigible No. I bis.

PL.iTE VII 132

Clement-Bayard I.

Clement-Bayard II.

Plate VIII 138

U. S. Signal Corps Dirigible I.

Gross II.

xi

LIST OP^ PLATES

FACING PAGE

Plate IX 140

Parseval I.

Parseval II.

Plate X 146

Gross III.

Zeppelin Airship Structure.

Plate XI 160

Zeppelin Dirigible Resting on the Water. Zeppelin Dirigible over Zurich.

Plate XII 182

Henson's Aeroplane.

Ader's Aeroplane.

Plate XIII 186

StringfcUow'.? Aeroplane (Front). Stringfellow's Aeroplane (Side).

Plate XIV 192

Phillips's Tethered Aeroplane.

Phillips's Aeroplane.

Plate XV 194

Langley's Steam Model.

Langlejr's Gasoline Model.

Langley's Two Surface Gasoline Model.

Plate XVI 212

Lilienthal's Monoplane Glider.

Lilienthal's Biplane Glider.

Pilcher's Monoplane Glider.

Plate XVII 218

Chanute's Five-Deck CJlider.

Herring in Chanute Biplane.

Herring's Compressed-air Biplane.

Plate XVIII 226

Maxim's Aeroplane.

Langley's Large Aeroplane.

Plate XIX 246

First Wright Glider.

Second Wright Glider.

xii

LIST OF PLATES

PAGE

Plate XX 248

First Wright Aeroplane (Rear).

First Wright Aeroplane (Side).

Plate XXI 252

Montgomerjf's Aeroplane.

Plate XXII 258

Santos-Dumont's Biplane.

Santos-Dumont's Demoiselle.

Plate XXIII 260

Farman Biplane, 190S.

Farman Biplane, 1909.

Harmon in Farman Biplane.

Plate XXIV 264

The Red Wing.

Cm'tiss Biplane.

Curtiss Biplane with Pontoon.s.

Plate XXV 208

Bleriot Flying Over Toury-Artenay Circuit. Bleriot Monoplane No. VIII.

Bleriot Monoplane No. IX.

Plate XXVI 272

Wright Biplane of 1908.

Standard Wright Biplane of 1910.

Wright Racing Biplane of 1910.

Plate XXVII 286

Bleriot XI with Moisant A\iator on Me.xican Border. Bleriot XII.

Plate XXVIII 288

Antoinette Monoplane of 1909.

Antoinette Monoplane of 1910.

Plate XXIX 302

Esnault-Pelterie Monoplane, Early Pattern. Esnault-Pelterie Monoplane of 1910.

Plate XXX 304

Grade Monoplane.

Cody Biplane.

xiii

LIST OF PLATES

FACING PAGii

Plate XXXI 332

Fabre Hydro-aeroplane.

Paulhan Hydro-aeroplane.

Moisant Metal Monoplane.

Plate XXXII 482

Curtiss Starting from the Water.

Curtiss Biplane for Land and Water. Curtiss Triplane Risen from the Water.

LIST OF ILLUSTRATIONS IN TEXT

2. — A possible air-soout .... ~ 3. — Blanchard's flying-machino .

4. — Lana's proposed vacuum Ijalloon

5. — Montgolfier's experimental balloon

6. — Charles' first hydrogen balloon

7. — Montgolfier's passenger balloon

8. — Charles' passenger balloon .

9.— La Flesselle .... 10. — The Great Balloon of Nassau 11. — Car of Nadar's balloon 12. — Diagram of a modern spherical balloon with ripping

panel

13. — Blanchard's dirigible balloon, ITS!

14. — Robert Brothers' dirigible,. 17S4 .

15. — General Meusnier's proposed dii-igilsle, 17S4

16.— Rufus Porter's dirigible, 1820

17.— Jullien's model dirigible, 1850

18.— Giffard's steam dirigible, 1852 .

19. — Dupuy de Lome's dii'igible, 1872

20.— Renard's dirigible, La France, 1884 .

75 SO

LIST OF ILLUSTRATIONS IN TEXT

21.— La Ville de Paris 121

22. — Le Petit Journal, Zodiac type 128

23.~Clenw7it-Bayard II, 1910

24. — Morning Post dirigible, 1910

25. — Route of British military dirigibles from France to

England, 1900

26. — Da Vinci's helicopter ....

27. — Da Vinci's parachute ....

28. — Veranzio's parachute ....

29. — Lenomiand's parachute, 1784

30. — Paper traveling parachute .

31. — Wenham's aeroplane, 1866 .

32. — Penaud's aeroplane toy, 1871

33. — Tatin's aeroplane model, 1879

34. — Hargrave's model screw monoplane, 1891

35. — Hargrave's kite

36. — Launoy and Bienvenu's helicopter, 1784

37. — Forlanini's helicopter, 1878 .

38. — Le Bris' aeroplane, 1855

39. — Mouillard's aeroplane ....

40. — Bl^riot's Toury-Artenay aeroplane circuit, 1908

41.— Map of the "Circuit del'Est" ....

42. — Diagram of Curtiss hydro-aeroplane

43.— The Etrich monoplane of 1910 ....

44. — Summer and winter average vertical temperature gradients

45. — General circulation of the atmosphere

46. — Normal wind direction and velocity for January and February (Koppen)

133 135

XVI

LIST OF ILLUSTRATIONS IN TEXT

FIG. PAGE

47. — Normal wind direction and velocity for July and August

(Koppen) 383

48. — Trade and counter-trade winds 384

49. — Velocity diagram in horizontal section of a cyclone . 398

50. — Funnel-like cloud sometimes observed in a tornado . 409 51. — Vertical section of the St. Louis, Mo., tornado of May

52.— Horizontal section of St. Louis tornado of May 27, 1896 412

53. — Vertical section of short tornado 414

54. — Vertical section of a tall tornado 415

55. — \'ertical section of a hail tornado 417

50. — Universal anemograph 428

57. — Records of wind variation in horizontal and vertical

direction 429

58. — Records of wind speed obtained by Langley . . . 433

FANCY AND FOLK-LORE

Of silver wings he took a sliining pair,

Fringed with gold, unwearied, nimble, swift; With these he parts the winds, the clouds, the air,

And over seas and earth himself doth lift. Thus clad he cuts the spheres and circles fair,

And the pure skies with sacred feathers clift; On Lebanon at first his feet he set

And shook his wings with rosy may-dews wet.

Tasso, Canto I, XIV.

How beautiful! May we hope ever to journey thus, on wings actuated by human power? It is an old question, once dear to the philosopher and fool alike, but now important mainly to the fool. Or say more kindly it is the affair of untechnical inventors — the amateur, the rustic, the man of chimerical dreams. For the wise aeronaut now numliers that project among the roseate illusions of his youth.^

Ovid relates a story, doubtless credible in his day, of a clever craftsman who with his son flew bravely aloft, the very first time they put on wings. Daedalus, a Greek architect, having fled from Athens for murder, went with his son Icarus to the island of Crete, where he built the celebrated labyrinth for Minos, the king. He offended that monarch and was cast into prison. In order to escape he made wings for himself and his son, with which they flew far

' With apologies to the California professor who will ride on wings worked by muscular force alone.

over the sea. But Icarus, in Ms elation, soared too near the sun, ruined his wings, fell into the sea and was drowned. For proof of tliis we have the Icarian Sea, named after the unfortunate boy. Also we have Ovid's charming poem :

In tedious exile now too long detain'd Daedalus languish'd for his native land; The sea foreclosed his flight, yet thus he said; " Though earth and water in subjection laid, O cruel Minos, thy dominion be, We'll go through air; for sure the air is free." Then to new arts his cunning thought applies, And to improve the work of nature tries. A row of quills, in gradual order placed. Rise by degrees in length from first to last; As on a cliff the ascending thicket grows; Or different reeds the rural pipe compose: Along the middle runs a twine of flax. The bottom stems are join'd by plaint wax; Thus, well compact, a hollow bending brings The fine composure into real wings.

His boy, young Icarus, that near him stood, Unthinking of his fate, with smiles pursued The floating feathers, which the moving air Bore loosely from the ground, and wafted here and there: Or with the wax impertinently play'd, And with his childish tricks the great design delay'd.

The final masterstroke at last imposed. And now, the great machine completely closed; Fitting his pinions on, a flight he tries, And hung self-balanced in the beaten skies. Then thus instructs his child: "My boj', take care To wing your course along the middle air: If low, the surges wet your flagging plumes; If high, the sun the melting wax consumes. Steer between both: nor to the northern skies, Nor South Orion, turn your giddy eyes. But follow me; let me before you lay Rules for the flight, and mark the pathless way. "

Thus teaching, with a fond concern, his son,

He took the untried wings, and fix'd them on:

But fix'd with trembhng hands; and, as he spcalcs,

The tears roll gently down his aged cheeks;

Then kiss'd, and in his arms embraced him fast,

But knew not this embrace must be the last;

And mounting upward, as he wings his flight,

Back on his charge he turns his aching sight;

As parent birds, when first their callow care

Leave the high nest to tempt the liquid air;

Then cheers him on, and oft, with fatal art,

Reminds the stripling to perform his part.

These, as the angler at the silent brook,

Or mountain shepherd leaning on his crook,

They stare, and view them with religious eyes.

And straight conclude them gods; since none but they

Through their own azure skies could find a way.

Now Delos, Paros, on the left are seen.

Upon the right, the isle Lebynthos named.

And fair Calymne for its honey famed.

When now the boy, whose childish thoughts a.spire

To loftier aims, and make him ramble higher,

Grown wild and wanton, more embolden'd flies

Far from his guide, and soars among the skies:

The softening wax, that felt a nearer sun,

Dissolved apace, and soon began to run:

The youth in vain his melting pinion shakes,

His feathers gone, no longer air he takes:

" Oh! father, father! " as he strove to cry,

Down to the sea he tumbled from on high.

And found his fate; yet still subsists by Fame,

Among those waters that retain his name.

The Father, now no more a father, cries :

"Ho, Icarus! where are you?" as he flies;

"Where shall I seek my boy?" he cries again.

And saw his feathers scatter'd on the main;

Then cursed his art; and funeral rites conferr'd

Naming the country from the youth interr'd.

How tender and apprehensive that gentleman's farewell, compared with the modern vogue in like circumstances ! Of the two Americans at Berlin who fell four thousand feet in a balloon, it is not recorded that they either kissed or wept.^ But some Teutonic Ovid may yet adorn the tale with quaint embellishments.

Taking more serious note of Daedalus, it will be observed that he has had few imitators. It is because he never really flew, and no one else can fly, in such manner. That is to say, no man can achieve practical flight on wings actuated by his own muscular power. It may be physically possible for an athlete putting forth herculean energy for a few seconds to sustain himself on wings of enormous spread ; but in every lightest zephyr he would be as helpless as a thistle seed.

The actual area of wing required for a man of given weight and power may be roughly estimated ; at least its lower limit of size can be determined. Lord Eayleigh,- on purely theoretical ground, has computed that a man operating a screw propeller 280 feet in diameter, moving without frictional loss, could sustain his weight for a period of eight hours a day at a comfortable rate of work. But that estimate does not include the weight of the propeller. By exerting ten times his normal power the man could support his weight with a 28-foot propeller.

The physical basis of the computation is the same for every type of flyer, whether bird, man, or ma-

' Mr. A. Holland Forbes and Mr. Augustus Post, in the international balloon race of 1908, used a balloon having too long a neck, thus causing such pressure at its top as to burst the bag. A dreadful plunge ensued, landing them on a house, but without injury, as the netting and collapsed bag dampened their speed of fall. It is reported that they crashed through the skylight, and that the lady of the house regretted not being there to receive them.

' Mechanical Principles of Flight.

chine. Its weight must he sustained by hurling the air downward. The humming bird in its aerial pause, the bee floating beside a blossom, rests on a downdriven column of air. The home-gliding eagle at dusk may encounter a medium in stillest repose, but he leaves behind him a down-flowing wake, viewless, maybe, but none the less real. In all cases the downward impulse per second given to the air must equal the weight supported by its reaction. If the wings be very extensive a proportionate mass of air may be struck down, and jaeld support with so much the less exertion.

Horizontal flight promises little more than direct screw lift, with the feeble energy of the human muscle. The best modern aeroplanes carry less than 100 pounds per horse power, while an average man must weigh, with a light machine, not less than 200 pounds, and must therefore exert upwards of two horse power during flight. Such an output of energy would exhaust a powerful athlete in a few seconds. Hence from every point of view it appears that Daedalean flight, which still has its devotees in some form, was and always will he utterly impracticable.

Euskin finds another ol)jectiou to the disciples of the winged arm. In his disquisition on the equilibrium of angels he complains that those of the traditional two-wing type are devoid of gravitational balance. Such creatures vex the imagination with apprehensions for their stability; hence they cannot be entirely beautiful. The centroid of an angel is in the small of its back, whereas the center of wing support is well forward; therefore the horizontal poise is absurd and unajsthetic. The scientific artist, consequently, views with pain the picture of a fair lady floating level through space supported only at her front end.

Milton adroitly forestalls this censure. In the conception of his glorious Raphael, he provides consummately for uniform and adequate support :

Six wings he wore, to shade His lineaments divine; the pair that clad Each shoulder broad, came mantling o'er his breast With regal ornament; the middle pair Girt like a starry zone his waist, and round Skirted his loins and thighs with downy gold, And colors dipped in Heaven; the third his feet Shadowed from either heel with feathered mail. Sky-tinctured grain. Like Maia's son he stood. And shook his plumes, that heavenly fragrance filled The circuit wide.

Leonardo da Vinci, who was a gifted engineer as well as an artist, devised a flying gear for man which shows some dynamic improvement over the mechanism of the old-time angels, flying gods, and hobgoblins. As shown in the accompanying sketch, it provided for gravitational balance by use of an expanding tail projecting well to the rear. Moreover, the propulsion was to employ both arms and legs. This design is considered very remarkable for the time in which it was produced, probably a few years before the discovery of America ; and yet it is but one of Da Vinci's quaint aeronautical inventions, as will appear later.

A less futile scheme of aviation may be to saddle the birds. If one eagle can float a child, a few may possibly carry a man. They are physically able ; they are inexpensive; they are unweared, nimble, swift. Some harness, some tuition may be required; but these come to the industrious. Apparently, such locomotion is a sport worth developing ; a royal art, if you please ; for who would not course the sky in a purple palanquin borne by imperial eagles?

Kai Kaoos, the King of Persia, is credited with a voyage of this kind, as described in the Shah-Nemeh, or King-Book, written in the tenth century:

" To the king it became a matter of great concern how he might be enabled to ascend the heavens, with-

PiQ 1 — D,,\ ViNOi's Desicns for Human Flyinc-Gear.

out wings; and for that purpose he consulted the astrologers, who presently suggested a way in which his desires might be successfully accomplished.

" They contrived to rob an eagle's nest of its young, which they reared with great care, supplying them with invigorating food.

" A frame of aloes-wood was then prepared, and at each of the four corners was fixed perpendicularly a javelin surmounted on the point with the flesh of a goat. At each corner again one of the eagles was bound, and in the middle the king was seated with a goblet of wine before him. As soon as the eagles became hungry they endeavored to get at the goat's flesh upon the javelins, and by flapping their wings, and flying upwards they quickly raised the throne from the ground. Hunger still pressing on them, and still being distant from their prey, they ascended higher and higher in the clouds, conveying the astonished king far beyond his own country. But after a long and fruitless exertion, their strength failed them, and, unable to keep their way, the whole fabric came tumbling down from the sky, and fell upon a dreary solitude in the Kingdom of Chin, where Kai Kaoos was left a prey to hunger, alone, and in utter despair."

One might prefer a single bird, which could be ridden bareback by a man or woman of common equestrian skill. The early philosophers, therefore, sought with some care for such a creature. The following is related by Bishop Wilkins :

" Cardan and Scaliger doe unanimously affirm, that there is a bird amongst the Indians of so great a bignesse, that his beak is often used to make a sheath or scabbard for a sword. And Acosta tells us of a fowl in Peru called Condores, which will of themselves kill and eat up a whole calf at a time. Nor is there any reason why any other body may not be supported and carried in the air, tliough it should as much exceed the quantity of these fowls as they do the quantity of a flie. Marcus Polus mentions a fowl in Madagascar which he cals a Euck, the feathers of whose wings are 12 paces, or threescore foot long, which can with as much ease soop up an elephant as our kites do a mouse. If this relation was anything credible, it might serve as an abundant proof for the present quaere."

As the roc has proved a myth, one questions whether a saddle bird may not be evolved by judicious breeding. But opposed to this is the squarecube law of the Greek geometer, by which a learned geologist demonstrated that nature has reached the limit of her resources in the production of large flyers, the ostrich, for example, being too bulky to navigate at all. As a last resource, then, the human dwarf may breed his weight downward to accommodate the bird. Assuredly, the most powerful flyer can carry the lightest human dwarf without difficulty.

Such aerial cavalry has been projected occasionally, and if fairly developed might have interesting employment. Its military value, to say nothing of its civil uses, would be considerable. An aerial scout that could hide in a tree top, or small cloud, then flit home with full intelligence of the enemy, would be effective and unique. In aggressive warfare it would serve the plan of that ingenious Englishman who proposes to repel a German invasion by dispatching birds to peck holes in the enemy's war balloons. But here the dwarf might be omitted, if the birds were taught to have a definite interest in attacking aerial cruisers with their beaks, or with steel-armed spurs like those of the Spanish fighting cock, or with talons treated chemically to strike fire. Sparrows with sulphur-pointed toes could easily annihilate an aerial squadron at all combustible.

Recurring to the geologist, it may be added that, having discovered the major limit of feathered navigators, he concluded, as a corollary, that human flight is forever impossible. That was in the latter eighties. In 1901 a versatile astronomer adduced the same law to prove that an aeroplane could not be

;sently, learning that this nau ueeii auuievcu, iie piuved, iu a second mellifluous paper, that an aeroplane could not carry several men.i Having erred twice, he wrote a final article announcing that a flyer is fatuous, anyhow, because she cannot repair her engines in the sky !

Of the numerous daring and industrious inventors who, during remote generations, have launched

' The reader may like to know that the basis of so much confidence was that ancient Euchdean theorem connecting the surfaces and vohmies of similar figures with certain powers of their homologous hnear dimensions.

themselves in the air on some species of rigid or vibrant wings, a few were men of considerable equipment in philosophy, or mechanics, and enjoyed a sufficient measure of success to deserve passing notice ; though it seems that no man before the middle of the eighteenth century made a permanent contribution to the real art of mechanical flight, if we except the ingenious suggestive devices of Leonardo da Vinci. However skilfully their flying apparatus may have been planned, or operated, the results were lost to the world, due to inaccurate or inadequate description. Such inventors were J. B. Dante, in the fifteenth century, and the Marquis de Bacqueville, in the seventeenth. Each of these made one, or more, considerable flights, if we may credit the unwavering testimony of their contemporaries; but neither has left a sketch of his device, nor a school of followers to continue his spectacular practice.

Jean-Baptiste Dante, a shrewd observer and profound mathematician, who flourished toward the end of the fifteenth centur}-, a contem])orary of Da Vinci and Columbus, is reported by the historians of that day to have sailed successfully through the air on nonviljrant wings designed by himself after a careful study of the great soaring birds. Perching above a steej) crag on the shore of Lake Trasimene, he set his wings to the wind at a nice angle, as one sets the sails of a vessel ; then, lifted by the swelling breeze, he rose grandly aloft and floated far over the waters. Again and again he repeated the experiment, until the fame thereof secured for him a request to make the demonstration at the marriage fetes of the illustrious general, Barthelmi Alviano. He accepted the invitation, and, starting from the top of the highest tower in the city of Perugia, he sailed over the public square, and balanced himself for a long time in space, amid the shouts and acclamations of the multitude, attracted to Perugia by the novelty of his performance. But, sad to relate, the very first time he perfoiTTied these wonderful maneuvers above the solid ground instead of the lake, one of the levers used to alter the impact angle of his wings gave way, disti;rbing his aerial poise, and causing him to pitch down upon Notre Dame church, breaking one of his legs. After this he taught mathematics at Venice, where he died of fever at the age of forty years.

In 1742, the Marquis de Bacqueville, at the age of sixty-two years, announced that on a certain day he would fly from his house on the Seine, traverse the river, and laud in the Garden of the Tuileries. A great multitude assembled, crowding both shores and the two bridges. At the appointed moment the Marquis appeared with his pinions, and launched himself from the terrace. He sailed forth in majestic and serene poise, on graceful wings not unlike those of the traditional angels. He was gliding directly toward the Tuileries, and he enjoyed a happy cruise quite to the middle of the river. Then something happened ; his movements became fitful and uncertain ; he plunged downward and broke his leg on a laundiy boat. The reason for his stopping there can only be surmised, for he had nothing to report. He did not quite fulfil his program, but he flew nine hundred feet delightfully, and he lauded without getting wet.

Commentators have marveled as to the nature of the mechanism used by Dante and by De Bacqueville. Historians have strongly attested the fact of the flights, but have overlooked the means. The inventors must have employed aerial gliders of some kiud, for adequate motive power was not available before the end of the nineteenth century. Even as an experiment in gliding, or soaring, the achievement of Dante was most daring and wonderful, eclipsing the

^4

INTEOBUCTION

best performances up to the twentieth century. It is strange that in that period of science the survivor of such an experience, and a college professor, should not have left to the world a careful account of such an extraordinary performance. The alleged flights, however, were unquestionably feasible, even in that remote period, for the construction of an aerial glider is a simple task not beyond the capacity of craftsmen in the fifteenth century a.d., or even the fifteenth century b.c, directed by a skilful designer.