Page:Cyclopaedia, Chambers - Volume 1.djvu/223

 A X I

(■lis)

A z i

The Conjugate is the iKorter of the two Axes of an Ellipfis. See Conjugate.

Conjugate* or ficond Axis of an {Hyperbola, is the Right Line FF, Fig 32. drawn through the Centre parallel to the Ordinates, M N, M N, perpendicularly to the Axis AP. See Hyper- bola.

The Length of this Axis, t hough mor e than infinite, may be found by this Proportion, 4/AM % PM : AP : : 'MN : FF.

Axis of a Parabola. See Parabola.

The Axis of a Parabola is of an indeterminate Length, that is is infinite. — The Axis of the Ellipfis is determinate.— The Para- bola has only one Axis ; the Ellipfis and Hyperbola two. See Curve.

Axis in Opticks.— Optick Axis, or Vifual Axis, is a Ray palling through the Centre of the Eye ; or it is that Ray which proceed- ing out of the Middle of the luminous Cone, falls perpendicular- ly on the cryftalline Humour, and confequently pafles through the Centre of the Eye. See Optick., Ray, Cone,- Vision,

Common or mean Axis, is a Right Line drawn from the Point of Concourfe of the two optick Nerves, through the Middle of the right Line, which joins the Extremity of the fame optick Nerves. See Optick Nerve. .

Axis of a Lens, or Glafs* is a right Line pafiGng along the Axis of that Solid whereof the Lens is a Segment. See Lens and Glass.

Thus a fpherical convex Lens, being a Segment of feme Sphere ; the Axis of the Leas is the fame with the Axis of the- Sphere ; or it is a right Line palling through the Centre there- of. See Convex, &t.

Or the Axis of a Glafs isa right Line joining the Middle Points of the two oppoftte Surfaces of the Glais. See Optick Glafs.

Axis of Incidence, in Dioptricks, is a right Line drawn through the Point of Incidence, perpendicularly to the refracting Surface. See Incidence.

Such is the Line DB, Tab. Opticks, Fig. 56.

Axis of Refraction, is a right Line continued from the Point of Incidence or Refraction* perpendicularly to the refracting Sur- face, along the further Medium. — Such is the Line BE.

Or it is that made by the incident Ray, perpendicularly pro- longed on the Sid-.: of the fecofld Medium. See Refraction.

Axis of a Magnet, or Magneticai Axis, is a Line palling thro' the middle of a Magnet, length-wife; in fuch manner, as that however the Magnet be divided, provided the Divilion be ac- cording to a Plane wherein fuch Line is found, the Loadftone will be made into two Loadftones. See Magnet and Mag- netism.

The extreams of fuch Lines are called the Poles of the Stone. See Pole and Polarity.

Axis, in Anatomy, is the third Vertebra of the Neck; reck- oning from the Skull. See Vertebra.

'lis thus called by reafon the two firft Vertebrse, with the Head, move thereon, as on an Axis. See Head and Neck.

Spiral Axis, Jn Architecture, is the Axis of a twifted Co- lumn, drawn (pirally, in order to trace the Circumvolutions with- out. See TwiJIed Column.

Axis of the Icnkk Capital, is a Line palling perpendicularly through the middle of the Eye of the Volute. See Ionic and Volute.

The Axis is otherwife call'd Cathetus. See Cathetus.

Axis in Peritrochio, is one of the five mechanical Powers, or limple Machines; contrived chiefly for the railing of Weights to a considerable Height. Sec Mechanical Power, Sec.

It conlifts of a Circle, reprefented AB, (Tab. Mechanicks, Fig. 44.) concentric with the Bale of a Cylinder, and moveable to- gether with it, about its Axis EF. — This Cylinder is call'd the^ Axis; the Circle, the Peritrochiu?//; and the Radii* or Spokes," which are fometimes fitted immediately into the Cylinder, with- out any Circle, the ScytaU: See PeritrocHium.

Round the Axis winds a Rope, whereby the Weight, &c. is to be rais'd.

The Axis in Peritrochio takes place in the Motion of every Machine, where a Circle may be conceived defcribed about a 6x'd Axis, concentric to the Plane of a Cylinder about which it is placed ; as in Crane-Wheels, Mill- Wheels, Capftans, &c. See Wheel.

Doclrine of the Axis in Peritrochio.

1. If the Power, applied to an Axis in Peritrochio* in the Di- rection AL,F/g, 7. perpendicular to the Periphery of the Wheel, or to the Spoke, be to a Weight G, as the Radius of the Axis CE, is to the Radius of the Wheel CA, or the Length of the Spoke ; the Power will juft fuftain the Weight, i. e. the Weight and the Power will be in Equilibria.

1. If a Power be applied to the Wheel in F, according to the Line of Direction FD, which is oblique to the Radius of the Wheel, though parallel to the perpendicular Direction; it will have the fame Proportion to a Power which acts according to the perpendicular Direction AL, which the whole Sine has to the Sine of the Angle of the Direction DFC

Hence, fince the Diftance of the Power in A, is the Radius CA; the Angle of Direction DFC being given, the Diftance DC

is eafily found.

3. Powers applied to the Wheel in feveral Points, F and E, according to the Directions, FD and KI, parallel to the perpen- dicular one AL, are to each other as the Diftances from the Centre of Motion CD and DI, reciprocally.

Hence, as the Diftance from the Centre of Motion increafesj the Power decreafes ; & vice verfa.H.znce alfo, fince the Ra- dius AC is the greateft: Diftance, and agrees to the Power act- ing according to the Line of Direction; the perpendicular Power will be the fmallefl: of all thofc able to fuftain the Weight G, according to the feveral Lines of Direction.

4. If a Power acting according to the Perpendicular AL, lift the Weight G - 3 the Space of the Power will be to the Space of the Weight, as the Weight to the Power.

For, in each revolution of the Wheel, the Power pafles thro' its whole Periphery ; and in the fame time the Weight is rais'd a Space equal to the Periphery of the Axis: The Space of the Power, therefore, is to the Space of the Weight, as the Peri- phery of the Wheel to that of the Axis: But the Power is to the Weights as the Radius of the Axis to that of the Wheel. There- fore, &c.

5 . A Power* and a Weight being give?>, to cmftruSl an Axis in Peritrochio, whereby itjhall be fuftai??d.

Let the Radius of the Axis be big enough to fupport the Weight without breaking. Then, as the Power is to the Weight; fo make the Radius of the Wheel, or the Length of the Spofee, to the Radius of the Axis.

He?ue* if the Power be but a fmall part of the Weight, the Radius of the Wheel muir, be vaftly great. — E. gr. S'uppofe the Weight 3000, and the Power 50, the Radius ot the YVheel will be to that of the Axis as do to 1.

This Inconvenience is provided againft by encreafing the num- ber of Wheels and A^es ; and making one turn round anorher, by means of Teeth or Pinions. See Wheel.

AXUNGIA, a kind of Fat, rhe fo:teit and moifteft. of any in the Bodies of Animals. See Fat.

It is different from Lard, which is a firm Fat ; and from Suet Leaf, or Adeps, which is a kind of dry Fat.

The Latins dill inguifh Fat into Pinguedo, call'd alfo Axungia; and Adept, or Sevxm; but many of our modern Writers confound them. SeePiNGUEDO.

The Phyficians make ufc of the Axungia of the Goofe, the Dog, the Viper, and fome others, efpecially that of Man, which is of extraordinary Service in the drawing and ripening of Tu^ mors, <£rc. See Attrahent. See alfo Viper, &c.

The Word is fuppofed to be form'd, ah Axe Rotarum ova wA- guntur.

Axungia of Glafs, call'd alfo the Gall, and Salt of Glafs, is a Scum taken from the Top of the Matter of Glafs before it be Vitrified. See Glass.

AYEL, in Law, a Writ which lies where the Grandfather be- ing feized in his Demefh. the Day he died, a Stranger enters the fame Day, and difpofleffes the Heir. See Writ.

AYRY, or Aery of Hawks, a Neft or Company of Hawks; fo call'd from the old French Word Aire* which iignihes rhe fame thing. See Hawk and Hawking

AYZAMENTA. See Easements.

AZIMUTH, in Aftronomy.— The Azimuth of the Sun* or a Star* is an Arch of the Horizon, compiehended between the Meridian of the Place, and any given Vertical. See Meridian and Vertical.

The Azimuth is the Complement of the Eaftern and Weftern Amplitude to a Quadrant. See Amplitude.

The Azimuth is found by this Proportion; as Radius is to the Tangent of the Latitude, fo is the Tangent of the Sun's Altitude to the Cofine of the Azimuth from the South, at the time of the Equinox.

To find the Azimuth by the Globe, fee Globe.

The Word is pure Arabick, where it fignifies the fame thing.

Magneticai 'Azimuth, is an Arch of the Horizon contained between the Sun's Azimuth-Circle, and the magneticai Meridian ; or it is the apparent Diftance of the Sun from the North or South Point of the Compafs. See Magnetical.

It is found, by obferving the Sun with an Azimuth Compafs, when he is about 10 or 15 Degrees high, either in the Forenoon Afternoon. See Azimuth Compass.

Azimuth Compafs is an Inftrument ufed at Sea for finding the Sun's magneticai Azimuth. See Magneticai Azimuth.

The Defcription and Ufe of the Azimuth Compafu fee under the Article Azimuth Compass.

Azimuth Dial* is a Dial whofe Style or Gnomon is at right , Angles to the Plane of the Horizon. See Dial.

Azimuths, call'd alfo vertical Circles, are great Circles mter- fedting each other in the Zenith and Nadir, and cutting the Ho- rizon at right Angles. See Vertical-

The Horizon being divided into 360 ; for this reafon they ufually conceive $60 Azimuths.— Thefe Azimuths are reprefent- ed by the Rhumbs on Sea Charts. See Horizon, Rhumb,

Chart, &c. _,

On