Page:Cyclopaedia, Chambers - Volume 2.djvu/569

 RAD

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RAD

for his pare, he mould chufe to put the Male Canary-Bird to the Female Goldfinch, Linnet, &c. becaufe the Male ufually Races more than the Female, i. e. the young ones take more after the Male than after the Female.

RACHITIS, or Rhachitis, in Medicine, a Difeafe affect- ing the Bones of Children, more ufually called the Rickets. See Rickets.

RACK, an Engine furnimed with Cords, &c. for extorting Confeffion from Delinquents. See Torture.

The Duke of Exeter, Conftable of the Tower under Henry VI. with the Duke of Suffolk, and others, having a defign to in- troduce the Civil Law into England $ for a Beginning, the Rack, or Brake allowed in many Cafes by the Civil Law, was firft brought to the Tower, where it is itill preferv'd.

In thofe Days the Rack was call'd the Duke of Exeter's Daugh- ter.

Rack, in the Manage, a Pace wherein a Horfe neither Trots nor Ambles, but muffles, as it were between both. See Pace.

The Racking face is much the fame as the Amble; only that it is a fwifter Time and a fhorter Tread. See Amble.

RACKET, a kind cf Bat, to ftrike the Ball withal at Tennis. See Tennis.

It coniifts of a kind of Lattice, or Net-work of Cat-gut, ftrain'd very tight over a Circle of Wood with a Handle or Shaft of a moderate length-

Vafquier obferves, that antiently they ufed no Rackets at Ten- nis, but play'd with the Palm of the Hand; and hence, he con- jectures it is, that the French call Tennis-Play, Jeu de Paume.

He adds, that Rackets were not introduced till a little before his Time. The Englijb Wotd Racket is formed from the French, Raquette, which Menage derives from the Latin, Ref^uetta, a di- minutive of Retis, Reticttt, and Reticulum.

Racket, is alio a Machine, which the Savages of CanadahvaA to their Feet, to walk more commodiouily over the Snow; made much in the manner of a Tennis-Racket.

Its Figure is a Lozange, whereof the two obtufe Angles' are rounded off It is bound about with very fine Thongs of Leather, the Mafhes whereof are much fmaller and clofer than thofe of our Rackets.

In rhe middle is fitted a kind of Shoe, lined with Wool, or Hair ; and tied on to prevent its finking in the Snow.

They oblige the Perfon to take very long Steps, and as we fay, to walk a great pace, to keep them from knocking againlt each other.

To Rack Wmes, dec. is to draw them from off their Lees, after having flood long enough to clear and fettle. See Wine.

Hence ViAcvi-Vintage is frequently ufed tor the fecond Voyage our Wine Merchants nied to make into Fra?uefor rack'd Wines; whence they ufed to return about the End of December.

RADIAL Curves, is a Term ufed by fome Authors for Curves of the Spiral Kind, whofe Ordinates, if they may be fo call'd, do all terminate in the Center of the including Circle, and appear like fo many Radii of that Circle ; whence the Name. See Curve. See alio Spirel.

RADIALIS, or Radi^eus Extenfor, in Anatomy. See Ex- tensor Carpi.

Radialis, or Radt/EUS flexor. See Flexor Carpi.

RADIATED, in Botany, an Epithet applied to round flat Flowers, coniiffing of a Disk, and a fmglerow of longifh point- ed Leaves, ranged all around it in manner of Rays, or Spokes. See Flower.

The Word is alfo ufed in fpeaking of Medals, and in Heral- dry; where the antient Crowns are called radiated Crowns, Coro- na Radiate. See Crown and Coronet.

RADIANT-Po;"m?, or Radiating-Po(»/, is any Point of a vifible Object, whence Rays proceed. See Ray.

Every Radiant-Point diffufes innumerable Rays all around: But only thofe Radiants are vifible from which right Lines may be drawn to the Pupil T - becaufe the Rays are all right Lines.

All the Rays proceeding from the Came Radiant continually di- verge ; the CryftalHn collects or reunites 'em again. See Diverg- ing. See alfo Crystallin.

Every Ray carries with it the Species, or Image of theRadi- ant. See Species.

RADIATION, in Phyfick, the Aftion of a Body diffufing Rays of Light. See Ray.

Every vifible Body is a radiating Body; it being purely by means of its Rays that it affe&s the Eye. See Vision.

Yet no Body can radiate, unlefs it be either luminous or illu- minated ; fince the Rays it diffufes muft either be its own, or it muft receive them from another Body. Therefore no Body is Vifible unlefs it be either luminous or illuminated. See Body, Light, Colour, &c.

The Surface of a radiating Body may be conceived as confift- ingof Radiant-Points. See Radiant-Pojb/.

Place of Radiation is that Space in a transparent Body, or Medium, through which a vifible Body Radiates. See Medium,

Radiation, or Irradiation, is alfo ufed by fome Authors to exprefs the manner of the Motion of the Animal Spirits ; on a Suppofition that they ace diffufed from the Brain toward's all

Parts of the Body, through the little Canals of the Nerves, as Light is from a lucid Body. See Spirit.

But in lieu of a Radiation, many of the Moderns rather incline to the Opinion of the Circulation of the Spirits. See Cir- culation.

RADICAL, Radtcalis, in Phyficks, &c. fomething ferving as a Bafis or Foundation ; or which, like a Root, is the" Source, or Principle whence any thing aiifes. See Root.

The Schools talk much of a Radical Moifiure in all Animals, which nourifhes and preserves the vi:al Heat or Flame, as Oyl does a Lamp ; and which when exhaufted, Life is extin^uifhed.

Dr. gtuincj obferves that this radical Moifiure is a mere Chime- ra; unlets we thereby mean the Mafs of Blood which is the promptuary whence all the other Juices and Humours are deri- ved^ and which, while it circulates, fuftains Life, &c. See Calidum. See alfo Flamma, Blood, <&c.

In Grammar we ufe the Term Radical Words for Roots and Primitives; in oppohtion to Compounds or Derivatives. See Root and Primitive.

Radical %/;, in algebra, the Sign or Character of the Root of a Quantity. See Root.

y is the Character of Radicality, and expreffes the Square Root; 4/j the Cube Root, cS-c. See Character.

RADiCATION, in Phyfick, the Action whereby Plants take Root, or fhoot out Roots. See Root.

The French Royal Academy of Sciences have made a good number of curious Obfcrvations on the Germination and Radi- cation of Plants. See Vegetation, Seed, Planting, Perpendicularity, &c.

RADICLE, Radicula, little Root ; in Botany, is a a little Point discovered by the Microfcope in all Seeds, which in the growth of the Plant becomes the Root. See Root. See alfo Seed.

When, in fowing, the Radkh happens to light loweft; 'tis no wonder the Root ihould ipread it feif under Ground, and the Stem of the Plant rife up perpendicularly ; But when the Radi- cle falls uppermoft, by what means it is, that it changes its Po- rtion to favour the Afccnt of the Stem, is one of the Wonders of Vegetation. A more particular Account whereof tee under the Article Perpendicularity.

RADIOMETER, a Name fome Writers give to the Radius Aflronomicas, or "Jacob's Staff. See Jacob's Staff

RADIUS, Ray, in Geometry, the Semidiamerer of a Cir- cle; or a right Line drawn from the Centre to the Circumfe- rence. See Semi-Diameter, &c.

The Radius is alio called, efpecially in Trigonometry, pnus to- uts, whole fine. See Sine.

'Tis implied in the definition of a Circle, ■ and 'tis apparent from its Construction, that all the Radii of the tame Circle are equal. See Circle.

The Word is derived from the Greek p«'M«, rod. Fleta ufes the Word Radius for a Furrow.

Radius, in the higher Geometry. The Radius of the Evoluta. Radius Curvedinis, or Radius Ofculi, is the right Line CM, Tab. Analyfis Fig. 12. reprefenring a Thread, by whofe Evolution from off the Curve B C, whereon it was wound, the Curve A M7/;is fornfd, SeeEvoLUTA and Osculum.

Radius Aflronomhus, an Inftrument properly called Jacob's Staff, or Crop Staff. See Cross Staff.

Radius, in Opticks. See Ray.

Radius, in Mechanicks, is ufed for the Spokes, or Fellows of a Wheel ; becaufe iffuing like Rays, from the Centre thereof. See Wheel.

Radius, in Anatomy, is a long (lender Bone of the Arm, defcending along with the Ulna from the Elbow to the Wrift; called alfo, focile minus, the lejfer facile. See Focile.

The Radius only touches the Ulna at its Extremities; at the upper whereof it is both received by, and alfo receives it; [ma- king, by both Articulations, an imperfedt Kind of Ginglymus. See Ulna.

The upper End, rolling upon the Ulna, is covefd with a Car- tilage; and has a-top, a fmall round Sinus, which receives the outer Procels of the Humerus: The lower-end is thicker than the upper, and has befides the lateral Sinus, two other Sinus at its Extremity which receive the Bones of the Wrift.

The Radius and Ulna are both a little crooked ■ by which means they are kepta-part, excepting at their Extremities; and are tyed together by a itrong membranous Ligament. See Arm.

The Radius has tour proper Muicles, befides the Biceps com- mon to it and the Ulna: The proper are two Pronators, and two Supinators. See Pronator and Supinator. See alfo Biceps

RADIX. See Root.

Radix is ufed among fome Anatomifts, for the Sole of the Foot. See Foot.

Radix, among Grammarians. See Radical.

RAD-K?iights. See RoD-K?iigbts.

Rafters, in Building, are pieces of Timber, which ftand by Pairs upon the Reafon, meet in an Angle at the Top, and help to compofe the Roof of a Building. See Roof.

'Tis a Rule in Architecture, that no Rafters thou'd ftand far- ther than twelve Inches from one another.

For