Chapter I: Part 1

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Transcriber's notes:

(1) Numbers following letters (without space) like C2 were originally
printed in subscript. Letter subscripts are preceded by an
underscore, like C_n.

(2) Characters following a carat (^) were printed in superscript.

(3) Side-notes were relocated to function as titles of their respective
paragraphs.

(4) Macrons and breves above letters and dots below letters were not
inserted.

(5) [root] stands for the root symbol; [alpha], [beta], etc. for greek
letters.

(6) The following typographical errors have been corrected:

ARTICLE FLORENCE: "... while the new structures erected in their
place, especially those in the Piazza Vittorio Emanuele, are almost
uniformly ugly and quite out of keeping with Florentine
architecture." 'Piazza' amended from 'Piaza'.

ARTICLE FLORIDA: "Not until the last decade of the 17th century did
the Spanish authorities attempt to extend the settlements beyond
the east coast." 'Not' amended from 'no'.

ARTICLE FLOWER: "The exine is a firm membrane, which defines the
figure of the pollen-grain, and gives colour to it." 'exine'
amended from 'extine'.

ARTICLE FOG: "... the cooling of air by rarefaction due to the
reduction of pressure on ascent, cannot be invoked, except in the
case of the fogs forming the cloud-caps of hills, which are perhaps
not fairly included." 'rarefaction' amended from 'rarefraction'.

ARTICLE FOOTBALL: "Association football is indeed, from the
standpoint of the spectator, a much brighter game than it was in
its infancy, the result of the new methods bringing every one of
the eleven players into full relief throughout the game."
'throughout' amended from 'throughtout'.

ARTICLE FOOTBALL: "This means that one or more of his fellows must
accompany and shield him as he runs, blocking off any opponent who
tries to tackle him." 'tries' amended from 'trys'.

ENCYCLOPAEDIA BRITANNICA

A DICTIONARY OF ARTS, SCIENCES, LITERATURE
AND GENERAL INFORMATION

ELEVENTH EDITION

VOLUME X, SLICE V

Fleury, Claude to Foraker

ARTICLES IN THIS SLICE:

FLEURY, CLAUDE FLYGARE-CARLEN, EMILIE
FLIEDNER, THEODOR FLYING BUTTRESS
FLIGHT and FLYING FLYING COLUMN
FLINCK, GOVERT "FLYING DUTCHMAN,"
FLINDERS, MATTHEW FLYING-FISH
FLINSBERG FLYING-FOX
FLINT, AUSTIN FLYING-SQUIRREL
FLINT, ROBERT FLYSCH
FLINT, TIMOTHY FOCA
FLINT (Michigan, U.S.A.) FOCHABERS
FLINT (county of North Wales) FOCSHANI
FLINT (town of North Wales) FOCUS
FLINT (crystalline substance) FOG
FLINT IMPLEMENTS AND WEAPONS FOGAZZARO, ANTONIO
FLOAT FOGELBERG, BENEDICT ERLAND
FLOCK FOGGIA
FLODDEN FOHN
FLODOARD FOHR
FLOE FOIL
FLOOD, HENRY FOIL-FENCING
FLOOD FOIX, PAUL DE
FLOOD PLAIN FOIX
FLOOR FOLARD, JEAN CHARLES
FLOORCLOTH FOLD
FLOQUET, CHARLES THOMAS FOLENGO, TEOFILO
FLOR, ROGER DI FOLEY, JOHN HENRY
FLORA FOLEY, SIR THOMAS
FLORE AND BLANCHEFLEUR FOLI, ALLAN JAMES
FLORENCE, WILLIAM JERMYN FOLIGNO
FLORENCE OF WORCESTER FOLIO
FLORENCE (Alabama, U.S.A.) FOLIUM
FLORENCE (capital of Tuscany) FOLKES, MARTIN
FLORES (Atlantic Ocean island) FOLKESTONE
FLORES (East Indies island) FOLKLAND
FLOREZ, ENRIQUE FOLKLORE
FLORIAN, SAINT FOLLEN, AUGUST LUDWIG
FLORIAN, JEAN PIERRE CLARIS DE FOLLEN, KARL
FLORIANOPOLIS FOLLETT, SIR WILLIAM WEBB
FLORIDA FONBLANQUE, ALBANY WILLIAM
FLORIDABLANCA, DON JOSE FOND DU LAC
FLORIDOR FONDI
FLORIN FONNI
FLORIO, GIOVANNI FONSAGRADA
FLORIS, FRANS FONSECA, MANOEL DEODORO DA
FLORUS FONSECA, BAY OF
FLORUS, JULIUS FONT
FLORUS, PUBLIUS ANNIUS FONTAINE, PIERRE FRANCOIS LEONARD
FLOTOW, FRIEDRICH ADOLF VON FONTAINEBLEAU
FLOTSAM, JETSAM and LIGAN FONTAN, LOUIS MARIE
FLOUNDER FONTANA, DOMENICO
FLOUR and FLOUR MANUFACTURE FONTANA, LAVINIA
FLOURENS, GUSTAVE FONTANA, PROSPERO
FLOURENS, MARIE JEAN PIERRE FONTANE, THEODOR
FLOWER, SIR WILLIAM HENRY FONTANES, LOUIS
FLOWER FONTENAY-LE-COMTE
FLOWERS, ARTIFICIAL FONTENELLE, BERNARD LE BOVIER DE
FLOYD, JOHN FONTENOY
FLOYD, JOHN BUCHANAN FONTEVRAULT
FLOYER, SIR JOHN FOOD
FLUDD, ROBERT FOOD PRESERVATION
FLUGEL, GUSTAV LEBERECHT FOOL
FLUGEL, JOHANN GOTTFRIED FOOLS, FEAST OF
FLUKE FOOLSCAP
FLUME FOOL'S PARSLEY
FLUMINI MAGGIORE FOOT
FLUORANTHENE FOOT-AND-MOUTH DISEASE
FLUORENE FOOTBALL
FLUORESCEIN FOOTE, ANDREW HULL
FLUORESCENCE FOOTE, MARY HALLOCK
FLUORINE FOOTE, SAMUEL
FLUOR-SPAR FOOTMAN
FLUSHING (New York, U.S.A.) FOOTSCRAY
FLUSHING (Zeeland, Holland) FOOT-STALL
FLUTE FOPPA, VINCENZO
FLUX FORAGE
FLY FORAIN, J. L.
FLYCATCHER FORAKER, JOSEPH HENSON

FLEURY, CLAUDE (1640-1723), French ecclesiastical historian, was born at Paris on the 6th of December 1640. Destined for the bar, he was educated at the aristocratic college of Clermont (now that of Louis-le-Grand). In 1658 he was nominated an advocate to the parlement of Paris, and for nine years followed the legal profession. But he had long been of a religious disposition, and in 1667 turned from law to theology. He had been some time in orders when Louis XIV., in 1672, selected him as tutor of the princes of Conti, with such success that the king next entrusted to him the education of the count of Vermandois, one of his natural sons, on whose death in 1683 Fleury received for his services the Cistercian abbey of Loc-Dieu, in the diocese of Rhodez. In 1689 he was appointed sub-preceptor of the dukes of Burgundy, of Anjou, and of Berry, and thus became intimately associated with Fenelon, their chief tutor. In 1696 he was elected to fill the place of La Bruyere in the French Academy; and on the completion of the education of the young princes the king bestowed upon him the rich priory of Argenteuil, in the diocese of Paris (1706). On assuming this benefice he resigned, with rare disinterestedness, that of the abbey of Loc-Dieu. About this time he began his great work, the first of the kind in France, and one for which he had been collecting materials for thirty years--the _Histoire ecclesiastique_. Fleury's evident intention was to write a history of the church for all classes of society; but at the time in which his great work appeared it was less religion than theology that absorbed the attention of the clergy and the educated public; and his work accordingly appealed to the student rather than to the popular reader, dwelling as it does very particularly on questions of doctrine, of discipline, of supremacy, and of rivalry between the priesthood and the imperial power. Nevertheless it had a great success. The first edition, printed at Paris in 20 volumes 4to, 1691, was followed by many others, among which may be mentioned that of Brussels, in 32 vols. 8vo, 1692, and that of Nismes, in 25 vols. 8vo, 1778 to 1780. The work of Fleury only comes down to the year 1414. It was continued by J. Claude Fabre and Goujet down to 1595, in 16 vols. 4to. In consulting the work of Fleury and its supplement, the general table of contents, published by Rondel, Paris, 1758, 1 vol. 4to, will be found very useful. Translations have been made of the entire work into Latin, German and Italian. The Latin translation, published at Augsburg, 1758-1759, 85 vols. 8vo, carries the work down to 1684. Fleury, who had been appointed confessor to the young king Louis XV. in 1716, because, as the duke of Orleans said, he was neither Jansenist nor Molinist, nor Ultramontanist, but Catholic, died on the 14th of July 1723. His great learning was equalled by the modest simplicity of his life and the uprightness of his conduct.

Fleury left many works besides his _Histoire ecclesiastique_. The
following deserve special mention:--_Histoire du droit francois_
(1674, 12mo); _Moeurs des Israelites_ (1681, 12mo); _Moeurs des
Chretiens_ (1682, 12mo); _Traite du choix et de la methode des etudes_
(1686, 2 vols. 12mo); _Les Devoirs des maitres et des domestiques_
(1688, 12mo). A number of the smaller works were published in one
volume at Paris in 1807. The Roman Congregation of the Index condemned
his _Catechisme historique_ (1679) and the _Institution du droit
ecclesiastique_ (1687).

See C. Ernst Simonetti, _Der Character eines Geschichtsschreibers in
dem Leben und aus den Schriften des Abts C. Fleury_ (Gottingen, 1746,
4to); C.F.P. Jaeger, _Notice sur C. Fleury, considere comme historien
de l'eglise_ (Strassburg, 1847, 8vo); Reichlin-Meldegg, _Geschichte
des Christentums, i._

FLIEDNER, THEODOR (1800-1864), German Protestant divine, was born on the 21st of January 1800 at Epstein (near Wiesbaden), the small village in which his father was pastor. He studied theology at the universities of Giessen and Gottingen, and at the theological seminary of Herborn, and at the age of twenty he passed his final examination. After a year spent in teaching and preaching, in 1821 he accepted a call from the Protestant church at Kaiserswerth, a little town on the Rhine, a few miles below Dusseldorf. To help his people and to provide an endowment for his church, he undertook journeys in 1822 through part of Germany, and then in 1823 to Holland and England. He met with considerable success, and had opportunities of observing what was being done towards prison reform; in England he made the acquaintance of the philanthropist Elizabeth Fry. The German prisons were then in a very bad state. The prisoners were huddled together in dirty rooms, badly fed, and left in complete idleness. No one dreamed of instructing them, or of collecting statistics to form the basis of useful legislation on the subject. Fliedner, at first singly, undertook the work. He applied for permission to be imprisoned for some time, in order that he might look at prison life from the inside. This petition was refused, but he was allowed to hold fortnightly services in the Dusseldorf prison, and to visit the inmates individually. Those interested in the subject banded themselves together, and on the 18th of June 1826 the first Prison Society of Germany (_Rheinisch-Westfalischer Gefangnisverein_) was founded. In 1833 Fliedner opened in his own parsonage garden at Kaiserswerth a refuge for discharged female convicts. His circle of practical philanthropy rapidly increased. The state of the sick poor had for some time excited his interest, and it seemed to him that hospitals might be best served by an organized body of specially trained women. Accordingly in 1836 he began the first deaconess house, and the hospital at Kaiserswerth. By their ordination vows the deaconesses devoted themselves to the care of the poor, the sick and the young; but their engagements were not final--they might leave their work and return to ordinary life if they chose. In addition to these institutions Fliedner founded in 1835 an infant school, then a normal school for infant school mistresses (1836), an orphanage for orphan girls of the middle class (1842), and an asylum for female lunatics (1847). Moreover, he assisted at the foundation and in the management of similar institutions, not only in Germany, but in various parts of Europe.

In 1849 he resigned his pastoral charge, and from 1849 to 1851 he travelled over a large part of Europe, America and the East--the object of his journeys being to found "mother houses," which were to be not merely training schools for deaconesses, but also centres whence other training establishments might arise. He established a deaconess house in Jerusalem, and after his return assisted by counsel and money in the erection of establishments at Constantinople, Smyrna, Alexandria and Bucharest. Among his later efforts may be mentioned the Christian house of refuge for female servants in Berlin (connected with which other institutions soon arose) and the "house of evening rest" for retired deaconesses at Kaiserswerth. In 1855 Fliedner received the degree of doctor in theology from the university of Bonn, in recognition rather of his practical activity than of his theological attainments. He died on the 4th of October 1864, leaving behind him over 100 stations attended by 430 deaconesses; and these by 1876 had increased to 150 with an attendance of 600.

Fliedner's son FRITZ FLIEDNER (1845-1901), after studying in Halle and Tubingen, became in 1870 chaplain to the embassy in Madrid. He followed in his father's footsteps by founding several philanthropic institutions in Spain. He was also the author of a number of books, amongst which was an autobiography, _Aus meinem Leben. Erinnerungen und Erfahrungen_ (1901).

Theodor Fliedner's writings are almost entirely of a practical
character. He edited a periodical, _Der Armen und Kranken Freund,_
which contained information regarding the various institutions, and
also the yearly almanac of the Kaiserswerth institution. Besides
purely educational and devotional works, he wrote _Buch der Martyrer_
(1852); _Kurze Geschichte der Entstehung der ersten evang.
Liebesanstalten zu Kaiserswerth_ (1856); _Nachricht uber das
Diakonissen-Werk in der Christ. Kirche_ (5th ed., 1867); _Die evangel.
Martyrer Ungarns und Siebenburgens; and Beschreibung der Reise nach
Jerusalem und Constantinopel_. All were published at Kaiserswerth.
There is a translation of the German life by C. Winkworth (London,
1867). See also G. Fliedner, _Theodor Fliedner, kurzer Abriss seines
Lebens und Wirkens_ (3rd ed., 1892). See also on Fliedner and his work
_Kaiserswerth Deaconesses_ (London, 1857); Dean John S. Howson's
_Deaconesses_ (London, 1862); _The Service of the Poor_, by E.C.
Stephen (London, 1871); W.F. Stevenson's _Praying and Working_
(London, 1865).

FLIGHT and FLYING. Of the many scientific problems of modern times, there are few possessing a wider or more enduring interest than that of aerial navigation (see also AERONAUTICS). To fly has always been an object of ambition with man; nor will this occasion surprise when we remember the marvellous freedom enjoyed by volant as compared with non-volant animals. The subject of aviation is admittedly one of extreme difficulty. To tread upon the air (and this is what is really meant) is, at first sight, in the highest degree utopian; and yet there are thousands of living creatures which actually accomplish this feat. These creatures, however varied in form and structure, all fly according to one and the same principle; and this is a significant fact, as it tends to show that the air must be attacked in a particular way to ensure flight. It behoves us then at the outset to scrutinize very carefully the general configuration of flying animals, and in particular the size, shape and movements of their flying organs.

Flying animals differ entirely from sailing ships and from balloons, with which they are not unfrequently though erroneously compared; and a flying machine constructed upon proper principles can have nothing in common with either of those creations. The ship floats upon water and the balloon upon air; but the ship differs from the balloon, and the ship and the balloon differ from the flying creature and flying machine. The water and air, moreover, have characteristics of their own. The analogies which connect the water with the air, the ship with the balloon, and the ship and the balloon with the flying creature and flying machine are false analogies. A sailing ship is supported by the water and requires merely to be propelled; a flying creature and a flying machine constructed on the living type require to be both supported and propelled. This arises from the fact that water is much denser than air, and because water supports on its surface substances which fall through air. While water and air are both fluid media, they are to be distinguished from each other in the following particulars. Water is comparatively very heavy, inelastic and incompressible; air, on the other hand, is comparatively very light, elastic and compressible. If water be struck with violence, the recoil obtained is great when compared with the recoil obtained from air similarly treated. In water we get a maximum recoil with a minimum of displacement; in air, on the contrary, we obtain a minimum recoil with a maximum of displacement. Water and air when unconfined yield readily to pressure. They thus form _movable fulcra_ to bodies acting upon them. In order to meet these peculiarities the travelling organs of aquatic and flying animals (whether they be feet, fins, flippers or wings) are made not of rigid but of elastic materials. The travelling organs, moreover, increase in size in proportion to the tenuity of the fluid to be acted upon. The difference in size of the travelling organs of animals becomes very marked when the land animals are contrasted with the aquatic, and the aquatic with the aerial, as in figs. 1, 2 and 3.

The peculiarities of water and air as supporting media are well illustrated by a reference to swimming, diving and flying birds. A bird when swimming extends its feet simultaneously or alternately in a backward direction, and so obtains a forward recoil. The water supports the bird, and the feet simply propel. In this case the bird is lighter than the water, and the long axis of the body is horizontal (a of fig. 4). When the bird dives, or flies under water, the long axis of the body is inclined obliquely downwards and forwards, and the bird forces itself into and beneath the water by the action of its feet, or wings, or both. In diving or sub-aquatic flight the feet strike upwards and backwards, the wings downwards and _backwards_ (b of fig. 4). In aerial flying everything is reversed. The long axis of the bird is inclined obliquely upwards and forwards, and the wings strike, not downwards and backwards, but downwards and _forwards_ (c of fig. 4). These changes in the direction of the long axis of the bird in swimming, diving and flying, and in the direction of the stroke of the wings in sub-aquatic and aerial flight, are due to the fact that the bird is heavier than the air and lighter than the water.

The physical properties of water and air explain in a great measure how the sailing ship differs from the balloon, and how the latter differs from the flying creature and flying machine constructed on the natural type. The sailing ship is, as it were, immersed in two oceans, viz. an ocean of water and an ocean of air--the former being greatly heavier and denser than the latter. The ocean of water buoys or floats the ship, and the ocean of air, or part of it in motion, swells the sails which propel the ship. The moving air, which strikes the sails directly, strikes the hull of the vessel indirectly and forces it through the water, which, as explained, is a comparatively dense fluid. When the ship is in motion it can be steered either by the sails alone, or by the rudder alone, or by both combined. A balloon differs from a sailing ship in being immersed in only one ocean, viz. the ocean of air. It resembles the ship in floating upon the air, as the ship floats upon the water; in other words, the balloon is lighter than the air, as the ship is lighter than the water. But here all analogy ceases. The ship, in virtue of its being immersed in two fluids having different densities, can be steered and made to tack about in a horizontal plane in any given direction. This in the case of the balloon, immersed in one fluid, is impossible. The balloon in a calm can only rise and fall in a vertical line. Its horizontal movements, which ought to be the more important, are accidental movements due to air currents, and cannot be controlled; the balloon, in short, cannot be guided. One might as well attempt to steer a boat carried along by currents of water in the absence of oars, sails and wind, as to steer a balloon carried along by currents of air. The balloon has no hold upon the air, and this consequently cannot be employed as a _fulcrum_ for regulating its course. The balloon, because of its vast size and from its being lighter than the air, is completely at the mercy of the wind. It forms an integral part, so to speak, of the wind for the time being, and the direction of the wind in every instance determines the horizontal motion of the balloon. The force required to propel a balloon against even a moderate breeze would result in its destruction. The balloon cannot be transferred with any degree of certainty from one point of the earth's surface to another, and hence the chief danger in its employment. It may, quite as likely as not, carry its occupants out to sea. The balloon is a mere lifting machine and is in no sense to be regarded as a flying machine. It resembles the flying creature only in this, that it is immersed in the ocean of air in which it sustains itself. The mode of suspension is wholly different. The balloon floats because it is lighter than the air; the flying creature floats because it extracts from the air, by the vigorous downward action of its wings, a certain amount of upward recoil. The balloon is passive; the flying creature is active. The balloon is controlled by the wind; the flying creature controls the wind. The balloon in the absence of wind can only rise and fall in a vertical line; the flying creature can fly in a horizontal plane in any given direction. The balloon is inefficient because of its levity; the flying creature is efficient because of its weight.

Weight, however paradoxical it may appear, is necessary to flight. Everything which flies is vastly heavier than the air. The inertia of the mass of the flying creature enables it to control and direct its movements in the air. Many are of opinion that flight is a mere matter of levity and power. This is quite a mistake. No machine, however light and powerful, will ever fly whose travelling surfaces are not properly fashioned and properly applied to the air.

It was supposed at one time that the air sacs of birds contributed in some mysterious way to flight, but this is now known to be erroneous. The bats and some of the best-flying birds have no air sacs. Similar remarks are to be made of the heated air imprisoned within the bones of certain birds.[1] Feathers even are not necessary to flight. Insects and bats have no feathers, and yet fly well. The only facts in natural history which appear even indirectly to countenance the flotation theory are the presence of a swimming bladder in some fishes, and the existence of membranous expansions or pseudo-wings in certain animals, such as the flying fish, flying dragon and flying squirrel. As, however, the animals referred to do not actually fly, but merely dart into the air and there sustain themselves for brief intervals, they afford no real support to the theory. The so-called floating animals are depicted at figs. 5, 6 and 7.

It has been asserted, and with some degree of plausibility, that a fish lighter than the water might swim, and that a bird lighter than the air might fly: it ought, however, to be borne in mind that, in point of fact, a fish lighter than the water could not hold its own if the water were in the least perturbed, and that a bird lighter than the air would be swept into space by even a moderate breeze without hope of return. Weight and power are always associated in living animals, and the fact that living animals are made heavier than the medium they are to navigate may be regarded as a conclusive argument in favour of weight being necessary alike to the swimming of the fish and the flying of the bird. It may be stated once for all that flying creatures are for the most part as heavy, bulk for bulk, as other animals, and that flight in every instance is the product, not of superior levity, but of _weight_ and _power_ directed upon properly constructed flying organs.

This fact is important as bearing on the construction of flying machines. It shows that a flying machine need not necessarily be a light, airy structure exposing an immoderate amount of surface. On the contrary, it favours the belief that it should be a compact and moderately heavy and powerful structure, which trusts for elevation and propulsion entirely to its flying appliances--whether actively moving wings, or screws, or aeroplanes wedged forward by screws. It should attack and subdue the air, and never give the air an opportunity of attacking or subduing it. It should smite the air intelligently and as a master, and its vigorous well-directed thrusts should in every instance elicit an upward and forward recoil. The flying machine must be _multum in parvo_. It must launch itself in the ocean of air, and must extract from that air, by means of its travelling surfaces--however fashioned and however applied--the recoil or resistance necessary to elevate and carry it forward. Extensive inert surfaces indeed are contra-indicated in a flying machine, as they approximate it to the balloon, which, as has been shown, cannot maintain its position in the air if there are air currents. A flying machine which could not face air currents would necessarily be a failure. To obviate this difficulty we are forced to fall back upon _weight_, or rather the structures and appliances which weight represents. These appliances as indicated should not be unnecessarily expanded, but when expanded they should, wherever practicable, be converted into actively moving flying surfaces, in preference to fixed or inert dead surfaces.

The question of surface is a very important one in aviation: it naturally resolves itself into one of active and passive surface. As there are active and passive surfaces in the flying animal, so there are, or should be, active and passive surfaces in the flying machine. Art should follow nature in this matter. The active surfaces in flying creatures are always greatly in excess of the passive ones, from the fact that the former virtually increase in proportion to the spaces through which they are made to travel. Nature not only distinguishes between active and passive surfaces in flying animals, but she strikes a just balance between them, and utilizes both. She regulates the surfaces to the strength and weight of the flying creature and the air currents to which the surfaces are to be exposed and upon which they are to operate. In her calculations she never forgets that her flying subjects are to control and not to be controlled by the air. As a rule she reduces the passive surfaces of the body to a minimum; she likewise reduces as far as possible the actively moving or flying surfaces. While, however, diminishing the surfaces of the flying animal as a whole, she increases as occasion demands the active or wing surfaces by wing movements, and the passive or dead surfaces by the forward motion of the body in progressive flight. She knows that if the wings are driven with sufficient rapidity they practically convert the spaces through which they move into solid bases of support; she also knows that the body in rapid flight derives support from all the air over which it passes. The manner in which the wing surfaces are increased by the wing movements will be readily understood from the accompanying illustrations of the blow-fly with its wings at rest and in motion (figs. 8 and 9). In fig. 8 the surfaces exposed by the body of the insect and the wings are, as compared with those of fig. 9, trifling. The wing would have much less purchase on fig. 8 than on fig. 9, provided the surfaces exposed by the latter were passive or dead surfaces. But they are not dead surfaces: they represent the spaces occupied by the rapidly vibrating wings, which are actively moving flying organs. As, moreover, the wings travel at a much higher speed than any wind that blows, they are superior to and control the wind; they enable the insect to dart through the wind in whatever direction it pleases.

The reader has only to imagine figs. 8 and 9 cut out in paper to realize that extensive, inert, horizontal aeroplanes[2] in a flying machine would be a mistake. It is found to be so practically, as will be shown by and by. Fig. 9 so cut out would be heavier than fig. 8, and if both were exposed to a current of air, fig. 9 would be more blown about than fig. 8.

It is true that in beetles and certain other insects there are the elytra or wing cases--thin, light, horny structures inclined slightly upwards--which in the act of flight are spread out and act as sustainers or gliders. The elytra, however, are comparatively long narrow structures which occupy a position in front of the wings, of which they may be regarded as forming the anterior parts. The elytra are to the delicate wings of some insects what the thick anterior margins are to stronger wings. The elytra, moreover, are not wholly passive structures. They can be moved, and the angles made by their under surfaces with the horizon adjusted. Finally, they are not essential to flight, as flight in the great majority of instances is performed without them. The elytra serve as protectors to the wings when the wings are folded upon the back of the insect, and as they are extended on either side of the body more or less horizontally when the insect is flying they contribute to flight indirectly, in virtue of their being carried forward by the body in motion.

_Natural Flight_.--The manner in which the wings of the insect traverse the air, so as practically to increase the basis of support, raises the whole subject of natural flight. It is necessary, therefore, at this stage to direct the attention of the reader somewhat fully to the subject of flight, as witnessed in the insect, bird and bat, a knowledge of natural flight preceding, and being in some sense indispensable to, a knowledge of artificial flight. The bodies of flying creatures are, as a rule, very strong, comparatively light and of an elongated form,--the bodies of birds being specially adapted for cleaving the air. Flying creatures, however, are less remarkable for their strength, shape and comparative levity than for the size and extraordinarily rapid and complicated movements of their wings. Prof. J. Bell Pettigrew first satisfactorily analysed those movements, and reproduced them by the aid of artificial wings. This physiologist in 1867[3] showed that all natural wings, whether of the insect, bird or bat, are screws structurally, and that they act as screws when they are made to vibrate, from the fact that they twist in opposite directions during the down and up strokes. He also explained that all wings act upon a common principle, and that they present oblique, kite-like surfaces to the air, through which they pass much in the same way that an oar passes through water in sculling. He further pointed out that the wings of flying creatures (contrary to received opinions, and as has been already indicated) strike downwards and _forwards_ during the down strokes, and upwards and _forwards_ during the up strokes. Lastly he demonstrated that the wings of flying creatures, when the bodies of said creatures are fixed, describe _figure-of-8 tracks_ in space--the figure-of-8 tracks, when the bodies are released and advancing as in rapid flight, being opened out and converted into _waved tracks_.

It may be well to explain here that a claim has been set up by his
admirers for the celebrated artist, architect and engineer, Leonardo
da Vinci, to be regarded as the discoverer of the principles and
practice of flight (see Theodore Andrea Cook, _Spirals in Nature and
Art_, 1903). The claim is, however, unwarranted; Leonardo's chief work
on flight, bearing the title _Codice sul Volo degli Uccelli e Varie
Altre Materie_, written in 1505, consists of a short manuscript of
twenty-seven small quarto pages, with simple sketch illustrations
interspersed in the text. In addition he makes occasional references
to flight in his other manuscripts, which are also illustrated. In
none of Leonardo's manuscripts, however, and in none of his figures,
is the slightest hint given of his having any knowledge of the spiral
movements made by the wing in flight or of the spiral structure of the
wing itself. It is claimed that Leonardo knew the direction of the
stroke of the wing, as revealed by recent researches and proved by
modern instantaneous photography. As a matter of fact, Leonardo gives
a wholly inaccurate account of the direction of the stroke of the
wing. He states that the wing during the down stroke strikes downwards
and _backwards_, whereas in reality it strikes downwards and
_forwards_. In speaking of artificial flight Leonardo says: "The wings
have to row downwards and _backwards_ to support the machine on high,
so that it moves forward." In speaking of natural flight he remarks:
"If in its descent the bird rows _backwards_ with its wings the bird
will move rapidly; this happens because the wings strike the air which
successively runs behind the bird to fill the void whence it comes."
There is nothing in Leonardo's writings to show that he knew either
the anatomy or physiology of the wing in the modern sense.

Pettigrew's discovery of the figure-of-8 and waved movements made by the wing in stationary and progressive flight was confirmed some two years after it was made by Prof. E.J. Marey of Paris[4] by the aid of the "sphygmograph."[5] The movements in question are now regarded as fundamental, from the fact that they are alike essential to natural and artificial flight.

The following is Pettigrew's description of wings and wing movements published in 1867:--

"The wings of insects and birds are, as a rule, more or less
triangular in shape, the base of the triangle being directed towards
the body, its sides anteriorly and posteriorly. They are also conical
on section from within outwards and from before backwards, this shape
converting the pinions into delicately graduated instruments balanced
with the utmost nicety to satisfy the requirements of the muscular
system on the one hand and the resistance and resiliency of the air on
the other. While all wings are graduated as explained, innumerable
varieties occur as to their general contour, some being falcated or
scythe-like, others oblong, others rounded or circular, some
lanceolate and some linear. The wings of insects may consist either of
one or two pairs--the anterior or upper pair, when two are present,
being in some instances greatly modified and presenting a corneous
condition. They are then known as elytra, from the Gr. [Greek:
elytron], a sheath. Both pairs are composed of a duplicature of the
integument, or investing membrane, and are strengthened in various
directions by a system of hollow, horny tubes, known to entomologists
as the neurae or nervures. These nervures taper towards the extremity
of the wing, and are strongest towards its root and anterior margin,
where they supply the place of the arm in birds and bats. The neurae
are arranged at the axis of the wing after the manner of a fan or
spiral stair--the anterior one occupying a higher position than that
farther back, and so of the others. As this arrangement extends also
to the margins, _the wings are more or less twisted upon themselves_
and present a certain degree of convexity on their superior or upper
surface, and a corresponding concavity on their inferior or under
surface,--their free edges supplying those fine curves which act with
such efficacy upon the air in obtaining the maximum of resistance and
the minimum of displacement. As illustrative examples of the form of
wings alluded to, those of the beetle, bee and fly may be cited--the
pinions in those insects acting as _helices_, or _twisted levers_,
and elevating weights much greater than the area of the wings would
seem to warrant" (figs. 10 and 11).... "To confer on the wings the
multiplicity of movements which they require, they are supplied with
double hinge or compound joints, which enable them to move not only in
an upward, downward, forward and backward direction, but also at
various intermediate degrees of obliquity. An insect with wings thus
hinged may, as far as steadiness of body is concerned, be not inaptly
compared to a compass set upon gimbals, where the universality of
motion in one direction ensures comparative fixedness in another."...
"All wings obtain their leverage by presenting oblique surfaces to the
air, the degree of obliquity gradually increasing in a direction from
behind, forwards and downwards, during extension when the sudden or
effective stroke is being given, and gradually decreasing in an
opposite direction during flexion, or when the wing is being more
slowly recovered preparatory to making a second stroke. The effective
stroke in insects, and this holds true also of birds, is therefore
delivered _downwards and forwards_, and not, as the majority of
writers believe, vertically, or even slightly backwards.... The wing
in the insect is more flattened than in the bird; and advantage is
taken on some occasions of this circumstance, particularly in
heavy-bodied, small-winged, quick-flying insects, _to reverse the
pinion more or less completely during the down and up strokes_."...
"This is effected in the following manner. The posterior margin of the
wing is made to rotate, during the down stroke, in a direction from
above downwards and from behind forwards--the anterior margin
travelling in an opposite direction and reciprocating. The wing may
thus be said to attack the air by a _screwing movement_ from above.
During the up or return stroke, on the other hand, the posterior
margin rotates in a direction from below upwards and from before
backwards, so that by a similar but _reverse screwing motion_ the
pinion attacks the air from beneath."... "_A figure-of-8_, compressed
laterally and placed obliquely with its long axis running from left to
right of the spectator, represents the movements in question. _The
down and up strokes_, as will be seen from this account, _cross each
other_, the wing smiting the air during its descent from above, as in
the bird and bat, and during its ascent from below as in the flying
fish and boy's kite" (fig. 12).

... "The figure-of-8 action of the wing explains how an insect or bird
may fix itself in the air, the backward and forward reciprocating
action of the pinion affording support, but no propulsion. In these
instances the backward and forward strokes are made to counterbalance
each other. Although the figure-of-8 represents with considerable
fidelity the twisting of the wing upon its axis during extension and
flexion, when the insect is playing its wings before an object, or
still better when it is artificially fixed, it is otherwise when the
down stroke is added and the insect is fairly on the wing and
progressing rapidly. In this case the wing, in virtue of its being
carried forward by the body in motion, describes an undulating or
spiral course, as shown in fig. 13."

... "The down and up strokes are compound movements--the termination
of the down stroke embracing the beginning of the up stroke, and the
termination of the up stroke including the beginning of the down
stroke. This is necessary in order that the down and up strokes may
glide into each other in such a manner as to prevent jerking and
unnecessary retardation."[6]...

Extension (elbow). Flexion (wrist).

Flexion (elbow). Extension (wrist).]

"The wing of the bird, like that of the insect, is concavo-convex, and
_more or less twisted upon itself_ when extended, so that the anterior
or thick margin of the pinion presents a different degree of curvature
to that of the posterior or thin margin. This twisting is in a great
measure owing to the manner in which the bones of the wing are twisted
upon themselves, and the spiral nature of their articular
surfaces--the long axes of the joints always intersecting each other
at right angles, and the bones of the elbow and wrist making a quarter
of a turn or so during extension and the same amount during flexion.
As a result of this disposition of the articular surfaces, the wing
may be shot out or extended, and retracted or flexed in nearly the
same plane, the bones composing the wing rotating on their axes during
either movement (fig. 14). The secondary action, or the revolving of
the component bones on their own axes, is of the greatest importance
in the movements of the wing, as it communicates to the hand and
forearm, and consequently to the primary and secondary feathers which
they bear, the precise angles necessary for flight. It in fact ensures
that the wing, and the curtain or fringe of the wing which the primary
and secondary feathers form, shall be screwed into and down upon the
wind in extension, and unscrewed or withdrawn from the wind during
flexion. The wing of the bird may therefore be compared to a huge
gimlet or auger, the axis of the gimlet representing the bones of the
wing, the flanges or spiral thread of the gimlet the primary and
secondary feathers" (figs. 15 and 16).... "From this description it
will be evident that by the mere rotation of the bones of the forearm
and hand the maximum and minimum of resistance is secured much in the
same way that this object is attained by the alternate dipping and
feathering of an oar."... "The wing, both when at rest and when in
motion, may not inaptly be compared to the blade of an ordinary screw
propeller as employed in navigation. Thus the general outline of the
wing corresponds closely with the outline of the propeller (figs. 11,
16 and 18), and the track described by the wing in space _is twisted
upon itself_ propeller fashion[7] (figs. 12, 20, 21, 22, 23). The
great velocity with which the wing is driven converts the impression
or blur made by it into what is equivalent to a solid for the time
being, in the same way that the spokes of a wheel in violent motion,
as is well understood, more or less completely occupy the space
contained within the rim or circumference of the wheel" (figs. 9, 20
and 21).

... "The wing of the bat bears a considerable resemblance to that of
the insect, inasmuch as it consists of a delicate, semi-transparent,
continuous membrane, supported in divers directions, particularly
towards its anterior margin, by a system of osseous stays or
stretchers which confer upon it the degree of rigidity requisite for
flight. It is, as a rule, deeply concave on its under or ventral
surface, and in this respect resembles the wing of the heavy-bodied
birds. The movement of the bat's wing in extension is a _spiral_ one,
the spiral running alternately from below upwards and forwards and
from above downwards and backwards. The action of the wing of the bat,
and the movements of its component bones, are essentially the same as
in the bird" (figs. 17 and 18).

... "The wing strikes the air precisely as a boy's kite would if it
were jerked by its string, the only difference being that the kite is
_pulled forwards_ upon the wind by the string and the hand, whereas in
the insect, bird and bat the wing is _pushed forwards_ on the wind by
the weight of the body and the power residing in the pinion itself"
(fig. 19).[8]

The figure-of-8 and kite-like action of the wing referred to lead us to explain how it happens that the wing, which in many instances is a comparatively small and delicate organ, can yet attack the air with such vigour as to extract from it the recoil necessary to elevate and propel the flying creature. The accompanying figures from one of Pettigrew's later memoirs[9] will serve to explain the _rationale_ (figs. 20, 21, 22 and 23).

As will be seen from these figures, the wing during its vibration sweeps through a comparatively very large space. This space, as already explained, is practically a solid basis of support for the wing and for the flying animal. The wing attacks the air in such a manner as virtually to have no slip--this for two reasons. The wing reverses instantly and acts as a kite during nearly the entire down and up strokes. The angles, moreover, made by the wing with the horizon during the down and up strokes are at no two intervals the same, but (and this is a remarkable circumstance) they are always adapted to the speed at which the wing is travelling for the time being. The increase and decrease in the angles made by the wing as it hastens to and fro are due partly to the resistance offered by the air, and partly to the mechanism and mode of application of the wing to the air. The wing, during its vibrations, rotates upon two separate centres, the tip rotating round the root of the wing as an axis (short axis of wing), the posterior margin rotating around the anterior margin (long axis of wing). The wing is really eccentric in its nature, a remark which applies also to the rowing feathers of the bird's wing. The compound rotation goes on throughout the entire down and up strokes, and is intimately associated with the power which the wing enjoys of alternately seizing and evading the air.

The compound rotation of the wing is greatly facilitated by the wing being elastic and flexible. It is this which causes the wing to twist and untwist diagonally on its long axis when it is made to vibrate. The twisting referred to is partly a vital and partly a mechanical act;--that is, it is occasioned in part by the action of the muscles and in part by the greater resistance experienced from the air by the tip and posterior margin of the wing as compared with the root and anterior margin,--the resistance experienced by the tip and posterior margin causing them to reverse always subsequently to the root and anterior margin, which has the effect of throwing the anterior and posterior margins of the wing into figure-of-8 curves, as shown at figs. 9, 11, 12, 16, 18, 20, 21, 22 and 23.

The compound rotation of the wing, as seen in the bird, is represented in fig. 24.

Not the least curious feature of the wing movements is the remarkable power which the wing possesses of making and utilizing its own currents. Thus, when the wing descends it draws after it a strong current, which, being met by the wing during its ascent, greatly increases the efficacy of the up stroke. Similarly and conversely, when the wing ascends, it creates an upward current, which, being met by the wing when it descends, powerfully contributes to the efficiency of the down stroke. This statement can be readily verified by experiment both with natural and artificial wings. Neither the up nor the down strokes are complete in themselves.

The wing to act efficiently must be driven at a certain speed, and in such a manner that the down and up strokes shall glide into each other. It is only in this way that the air can be made to pulsate, and that the rhythm of the wing and the air waves can be made to correspond. The air must be seized and let go in a certain order and at a certain speed to extract a maximum recoil. The rapidity of the wing movements is regulated by the size of the wing, small wings being driven at a very much higher speed than larger ones. The different parts of the wing, moreover, travel at different degrees of velocity--the tip and posterior margin of the wing always rushing through a much greater space, in a given time, than the root and anterior margin.

a, b, Short axis of the wing (axis for tip of wing, h).

c, d, Long axis (axis for posterior margin of wing, h, i, j, k, l).

m, n, Short axis of rowing feathers of wing.

r, s, Long axis of rowing feathers of wing. The rotation of the rowing
feathers on their long axis (they are eccentrics) enables them to open
or separate during the up, and close or come together during the down
strokes.

e f, g p, concave shape presented by the under surface of the wing.]

The rapidity of travel of the insect wing is in some cases enormous. The wasp, for instance, is said to ply its wings at the rate of 110, and the common house-fly at the rate of 330 beats per second. Quick as are the vibrations of natural wings, the speed of certain parts of the wing is amazingly increased. Wings as a rule are long and narrow. As a consequence, a comparatively slow and very limited movement at the root confers great range and immense speed at the tip, the speed of each portion of the wing increasing as the root of the wing is receded from. This is explained on a principle well understood in mechanics, viz. that when a wing or rod hinged at one end is made to move in a circle, the tip or free end of the wing or rod describes a much wider circle in a given time than a portion of the wing or rod nearer the hinge (fig. 25).

One naturally inquires why the high speed of wings, and why the progressive increase of speed at their tips and posterior margins? The answer is not far to seek. If the wings were not driven at a high speed, and if they were not eccentrics made to revolve upon two separate axes, they would of necessity be large cumbrous structures; but large heavy wings would be difficult to work, and what is worse, they would (if too large), instead of controlling the air, be controlled by it, and so cease to be flying organs.

There is, however, another reason why wings should be made to vibrate at high speeds. The air, as explained, is a very light, thin, elastic medium, which yields on the slightest pressure, and unless the wings attacked it with great violence the necessary recoil or resistance could not be obtained. The atmosphere, because of its great tenuity, mobility and comparative imponderability, presents little resistance to bodies passing through it at low velocities. If, however, the speed be greatly accelerated, the action of even an ordinary cane is sufficient to elicit a recoil. This comes of the action and reaction of matter, the resistance experienced varying according to the density of the atmosphere and the shape, extent and velocity of the body acting upon it. While, therefore, scarcely any impediment is offered to the progress of an animal in motion in the air, it is often exceedingly difficult to compress the air with sufficient rapidity and energy to convert it into a suitable fulcrum for securing the necessary support and forward impetus. This arises from the fact that bodies moving in air experience a _minimum of resistance_ and occasion a _maximum of displacement_. Another and very obvious difficulty is traceable to the great disparity in the weight of air as compared with any known solid, and the consequent want of buoying or sustaining power which that disparity involves. If we compare air with water we find it is nearly 1000 times lighter. To meet these peculiarities the insect, bird and bat are furnished with extensive flying surfaces in the shape of wings, which they apply with singular velocity and power to the air, as levers of the third order. In this form of lever the power is applied between the fulcrum and the weight to be raised. The power is represented by the wing, the fulcrum by the air, and the weight by the body of the flying animal. Although the third order of lever is particularly inefficient when the fulcrum is rigid and immobile, it possesses singular advantages when these conditions are reversed, that is, when the fulcrum, as happens with the air, is _elastic_ and _yielding_. In this instance a very slight movement at the root of the pinion, or that end of the lever directed towards the body, is followed by an immense sweep of the extremity of the wing, where its elevating and propelling power is greatest--this arrangement ensuring that the large quantity of air necessary for support and propulsion shall be compressed under the most favourable conditions.

In this process the weight of the body performs an important part, by acting upon the inclined planes formed by the wings in the plane of progression. The power and the weight may thus be said to reciprocate, the two sitting as it were side by side and blending their peculiar influences to produce a common result, as indicated at fig. 26.

When the wings descend they elevate the body, the wings being active and the body passive; when the body descends it contributes to the elevation of the wings,[10] the body being active and the wings more or less passive. It is in this way that weight forms a factor in flight, the wings and the weight of the body reciprocating and mutually assisting and relieving each other. This is an argument for employing four wings in artificial flight,--the wings being so arranged that the two which are up shall always by their fall mechanically elevate the two which are down. Such an arrangement is calculated greatly to conserve the driving power, and as a consequence, to reduce the weight.

That the weight of the body plays an important part in the production of flight may be proved by a very simple experiment. If two quill feathers are fixed in an ordinary cork, and so arranged that they expand and arch above it (fig. 27), it is found that if the apparatus be dropped from a vertical height of 3 yds. it does not fall vertically downwards, but downwards and _forwards_ in a curve, the forward travel amounting in some instances to a yard and a half. Here the cork, in falling, acts upon the feathers (which are to all intents and purposes wings), and these in turn act upon the air, in such a manner as to produce a horizontal transference.