Page:Cyclopaedia, Chambers - Volume 1.djvu/813

 FLY

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FOC

again, with Steps every where of the fame Breadth and Length as before. See Stair-Case.

FLYING, the progreffive Motion of a Bird, or other winged Animal in the liquid Air. See Flight, and Bird.

Flying is either Natural, or Artificial.

Natural Flying is that perform *d by an Apparatus or Structure of Parts concerted for that end by Nature her felf. Such is that of mod Birds, and Infects 5 and fome Fifties.

In Virginia, and Neiv England, they have alfo flying Harts. <Philofoph. TranfaB. N g 127. And in LanguedoCi flying Grafhoppers, about an Inch long, wherewith the Ground, in fcveral Parts, in the Year 15S5 was cover'd one third of a Foot deep. — —Ibid. N p 182.

The Parts of Birds, f$c. chiefly concern'd in Flyings are the Wings, and Tail: By the firft, the Bird fuftains and wafts himfelf along 5 and by the fecond he is afiifted in af- cending, and defending ; to keep his Body pois'd and up- right, and to obviate the Vacillations thereof. See Wing and Tail.

s Tis by the Largenefs and Strength of the temporal Muf- cles, that Birds are {b well difpofed for quick, ftrong, and continued Flying.

Thefe Mufcles, which in Men are fcarce T \ Part of the Mufcles of the Body, in Birds, exceed and outweigh all the other Mufcles taken together : Upon which Mr. Wiliotighly makes this Reflexion, that if it be poffible for Man to fly, his Wings muft be fo contrived and adapted, that he may make ufe of his Legs, and not his Arms in managing them. See Pectoral Mufcle.

The Flying of Birds is thus effected :

The Bird, firft, bends his Legs, and fprings with a vio- lent Leap from the Ground : Then, opens or expands the Jointures of his Wings, fo as to make a Right-line, perpen- dicular to the Sides of his Body. Thus, as the Wings, with the Feathers therein, conftitute one continued Lami- na ; being now rais'd a little above the Horizon, and vibrat- ing the Wings with great Force and Velocity, perpendicu- larly, againfl: the fubject Air ; the Air, tho' a Fluid, refills thofe Succuffions both from its natural Inactivity, and from its Elafticity, which makes it reftore it felf, after it has been comprefs'd, and react afmuch as it is acted on: By fuch means is the whole Body of the Bird protruded.

The Sagacity of Nature is very remarkable in the open- ing and recovering of the Wing for frefti Strokes.

To do it directly, and perpendicularly, it would needs have a great Refiftance to overcome : To avoid which, the bony Part, or Bend of the Wing into which the Feathers are inferted, moves iidewife with its fharp End foremoft 3 the Feathers following it like a Flag.

The Refiftance the Air makes to the withdrawing of the Wings, and confequcntly the Progrefs of Bird, will be fo much the greater, as the Waft, or Stroke of the Fan of the Wing is the longer : But, as the Force of the Wing is continually ditninifh'd by this Refiftance ; when the two Forces come to be in Equilibrio, the Bird will remain fu Im- pended in the fame Place : For the Bird only afcends fo long, as the Arch of Air the Wing defcribes, makes a Re- fiftance equal to the Excefs of the fpecific Gravity of the Bird above the Air. If the Air therefore be fo rare as to «ive way with the fame Velocity as it is ftruck withal, there will be no Refiftance, and confequently the Bird can never mount on fuch unliable Steps. — ■ —

Mr. Ray, Willoughby, &C. have fuppos'd the Tail to do the Office of a Rudder, in fleering and turning the Body this way or that: But Borelli has Ihewn it unfit for any fuch Office.

The Flying of a Bird, in effect, is quite a different Mo- tion from the Sailing of a Ship: Birds don't vibrate their Wings towards the Tail, as Oars are ftruck towards the Stern : but waft them downward : Nor does the Tail of the Bird cut the Air at right Angles, as the Rudder does the Water $ but is difpofed horizontally, and preferves the fame Situation what way foever the Bird turns.

In effect, as a Veffel in the Water is turn'd about on its Centre of Gravity to the right, by a brilk Application of the Oars to the left; fo a Bird, in beating the Air with its right Wing alone, towards its Tail, its Fore -part will be turn'd to the left : As when in fwimming, by only flri- Icin" out with the right Arm, and Leg, we are driven to the left.

Thus, we fee Pidgeons, changing their Courfe to the left- ward, labour it with the right Wing 5 keeping the other al- moft at reft. ■

Add, that Birds with long Necks have another way of altering their Courfe : For by only inclining the Head and Neck towards this or that Side j the Centre of Gravity of the whole being Ihifted, the Bird will proceed according to his new Direction.

Birds never fly upwards in a perpendicular Line, but al- ways in a Parabola, the Line defcribed by Projectiles.

In a direct: Afcent, the Natural and Artificial Tendency would oppofc and deftroy each other ; fo that the Progrefs

would be very flow : In a direct Defcenr, they would aid one another ; fo that the Fall would be too precipitate.

Indeed, the Hawk we frequently find take that Advantage in feizing of the Partridge : But ordinarily, Birds keep their Wings expanded, and at reft, to retard then; Defcent ■ and at the fame time ftretch out their Feet, and Legs. •

Artificial Flying, is that attempted by Men, by the Af- fiftance of Mechanicks.

The Art of Flying is one of the great Defiderata of Me- chanicks ; attempted in divers Ages : The Difcovery where- of might prove of great Service, and great Differ vice to Man- kind.

No body feeiris to have bid (b fair for that Invention, as our famous Fryar R. "Bacon, who liv'd upwards of 500 Years ago. He not only affirms the Art feafible; but af- fures us he himfelf knew how to make an Engine, in which a Man fitting might be able to carry himfelf through the Air, like a Bird: And affirms, that there was another Per- fon, who had actually tried it with Succefs.

The Secret confifted in a Couple of large thin hollow Cop- per Globes, cxhaufted of Air ; which being much lighter than Air, would fuftain a Chair, whereon a Perfbn might fit. See Air-Pumj?.

Fa. Francifco Lane, in his 'Prodrome, propofes the fame thing, as his own Thought. He computes* that a round Veffel of Plate Brafs, fourteen Foot in Diameter, weighing three Ounces the fquareFoot; will only weigh 1848 Ounces 5 whereas a Quantity of Air of the lame Bulk, will weigh 315 5~ Ounces : So that the Globe will not only be fuftain'cl in the Air 5 but will carry with it a Weight of 3 7 3} Ounces 5 and by increafing the Bulk of the Globe, without increafing the Thicknefs of the Metal, he adds, a Veffel might be made to carry a much greater Weight.

But the Fallacy is obvious : A Globe of the Dimenfion3 he defcribes, Dr. Hook fhews, would not fuftain the Preffure of the Air ; but be cruhYd inwards. Befide, that in what- ever Ratio the Bulk of the Globe were increas'd, in the fame muft the Thicknefs of the Metal, and confequcntly the Weight, be increafed : So that there would be no Ad- vantage in fuch Augmentation.

The fame Author defcribes an Engine for Flyings invented by the Sieur Sefnier, a Smith of Sable, in the County of Maine. Philofopb. ColleB. N° 1.

Flying Bridges, in Fortification, are thofe made of two fmall Bridges, laid one upon the other, fo that the upper- moft, by means of Ropes and Pullies, is fore'd forwards, till the End of it is joined to the Place defigned. See Br ins e-

Flying Camp, a fmall Body of an Army, confirming of 4, 5, or tfoooMen, and fbmetimes a greater Number, as well Foot as Horfe, which continually keep the Field, mak- ing divers Motions, to prevent the Incurfions of the Enemy, or to fruftrate their Enterprifesj to hinder Convoys, to har- rafs the adjacent Country, and to be thrown into a befieged Place, as Ocean" on mail ferve. — - —

Flying 'Pinion, is a Part of a Clock, having a Fly or Fan, whereby to gather Air, and fo to bridle the Rapidity of the Clock's Motion, when the Weight defcends in the linking Part. See Pinion, Clock, &c.

FOCAGE, or Fuage, Fire-money, Hearth-money, or Chimney-money. See Fuage.

FOCILE, Focil, in Anatomy, a Name the Arabs give to the two Bones of the Arm, reaching from the Elbow, to the Wrift. See Arm.

The biggeft, which is what we call the Cubitus, and Ulna, they call the greater Focil, Focile majus.

The lefs, which we call Radius, they call Focile minus. See Cubitus, and Radius.

The like is obferv'd with regard to the Bones of the Leg. The biggeft of which, by the Latins called 'Tibia, the A- rab Writers, &c. call the great Focil : And the lefs, or Fi- bula, the leffer Focil. See Tibia, and Fibula.

FOCUS, in Geometry, and the Conic Sections, is ap- plied to certain Points in the Parabola, Ellipfis, and Hyperbo- la 5 wherein the Rays reflected from all Parts of thefe Curves do concur, or meet. See Curve.

"The Focus of a 'Parabola is a Point in its Axis % as F, ( Tab. Conicks, Fig. 18.) wherein the femi-ordinate F N, is equal to the Semi-parameter 5 or a Point in the Axis di- ftant from the Vertex, by a fourth Part of the Parameter, or Latus rectum. See Parabola.

'Tis demonftrated in Conicks, i u That in a Parabola, the Diftance of the Focus, from the Vertex, A F, is to the Pa- rameter, in a fubquadruple Ratio.

2 That the Square of the femi-ordinate is quadruple of the Rectangle of the Diftance of the Focus from the Ver- tex, and the Abfcifle.

3 9 That the Right-line F M drawn from the Focus F to the Extremities of the Semi-ordinate of the Parabola is equal^ to the aggregate of the Abfcifle A P j and the Diftance of the Focus from the Vertex A F.

The Foci of an Ellipfis are two Points, as F f {Fig- ipO in the Axis A B, on which, as Centres, the Figure is de- fcribed :