Page:Cyclopaedia, Chambers - Volume 2.djvu/301

 OBL

(<*o)

OBO

A Line filling obliquely on another, makes the Angle on one fide obtufe, and that on the other, acute. . Oblique Flams, in Dialling, are fuch as decline from the Zenith, or incline toward the Horizon. See Dial- Flain.

The Obliquity, or Quantity, of this Inclination, or Recli- nation, is eafily found, by a Quadrant j it being an Arch of fome Azimuth, or vertical Circle, intercepted between the Vertex of the Place and of that Plane.

This Azimuth, or vertical Circle, is always perpendicular to the Plane. See Dialling.

Okliq_ue Fercujjim, is that wherein the Direction of the ftriking Body, is not perpendicular to the Body ftruck j ox is not in a Line with its Center of Gravity. See Per- cussion.

The Ratio an oblique Stroke bears to a perpendicular one, isdemonllrated to be as the Sine of the Angle of In- cidence to the Radius.

Obliq_ue Powers. See Powers.

Oblique Froje&ion, in Mechanicks, is that where a Body is impell'd in a Line of Direction, which makes an oblique Angle with the Horizontal Line. See Projec- tion.

Oblique Sphere, in Geometry, is that whofe Horizon cuts the Equator obliquely j and one of whofe Poles is rais'd above the Horizon, equal to the Latitude of the Place. See Sphere.

'Tis this Obliquity that occafions the Inequality of Days and Nights. See Night and Day.

Thofe who live under an oblique Sphere (as we, and all thole in the temperate Zone, doj never have their Days and Nights equal 3 except in the Equinoxes. See Equi- nox.

Oblique Afcenfan, in Aftronomy, an Arch of the E- quator intercepted between the firft Point of Aries, and that Point of the Equator which rifes together with a Star, &c. in an oblique Sphere. See Ascension.

The oblique Afcenfion is numbred from Weft to Eaft ; and is more or lefs according to the different Obliquity of the Sphere.

Oblique Dcfcevfion, an Arch of the Equator, intercep- ted between the firft Point of Aries, and that Point of the Equator, which fets with a Star, fyc. in an oblique Sphere j and reckon'u from Weft to Eaft. See Descension.

The Difference between the right and oblique Afcenfion, is call'd the Afcenfion a I Difference. See Ascensional.

.To find the Obliq,ue Afcenfion and Defcenfion by the Globe. See Globe.

Oblique Sailing, in Navigation, is when the Ship is in fomc intermediate Rhumb, between the four Cardinal Points j and thus makes an oblique Angle with the Meri- dian, and continually changes both its Latitude and Longi- tude. See Rhumb.

Oblique Sailing is of three Kinds ; viz-. Plain Sailing, Mercator's Settling, and Great Circle Sailing. See Sailing.

The Seamen alfo call the Application of the Method of calculating the Parts of oblique plane Triangles, in order to fihd the Diftance of a Ship from any Cape, Head-Land, g?e. Oblique Sailing.

Oblique, Obliquus, in Anatomy, is ufed, fubftantively, for feveral Mufclcs of the Head and Eye$ particularly, the

Obliquus Capitis Major, or Par Oeliquum Infer'ms, the fixth Mufcle of the Head 5 fo calFd, becaufe ferving to turn the Head afide : tho' it has neither its Origin nor .Infertion in the Head. See Head.

It rifes fiefliy from the external Parts of the Spine of the fecond Vertebra of the IMeck, and fwelling into a flefhy Eelly, runs obliquely to the tranfverfe Procels of the firft Vertebra.

This fome rank among the Mufcles of the Neck, See Keck.

Obliquus Capitis Superior, or Minor, the feventh Mufcle of the Head, which fprmgrag flefhy from the tranverfe Proceffes of the fecond Vertebra of the Neck, and amend- ing obliquely, is inferred laterally into the Occiput.

Others will have its Origin to be in the Occiput, where the common Opinion places its Infertion ; its Infertion they make in the tranfverfe Proceffes of the Srt\ Vertebra, near that of the fame Side.*

The two oblique Mufcles, by pulling the tranfverfe Pro- cefs, give the Head a femi-circular Motion. See Ver- tebra.

Obliquus Oculi Superior, or Major, the fifth Mufcle of the Eye. See Eye.

It has its Origin in the upper part of the Orbit 5 whence tending upwards towards the inward Cautbus of the Eye it paffes thro' a Cartilage on the Bone of the Forehead, calVd Trochlea; whence alfo the Mufcle itfelf is call'd Trochlea- rs ; thence it is reflected to its Termination in the Sclerotica en the back part of the Ball of the Eye.

When this Mufcle acts, that part of the Ball of the Eye is drawn downwards towards the Trochlea, whereby the Pu- pil is directed downwards, towards the lefler Cantbus, and at the fame time the whole Ball of the Eye fomewhat out- wards.

Obliquus Oculi Inferior, ox Minor, rifes from the exter- nal Margin of the lower part of the Orbit, near the inner Canthus; whence rifing towards the outward Canthus, it terminates near the other.

It draws the Ball of the Eye outwards, and turns its Pu- pil upward, contrary to the former.

Obliquus Defcendens, or Dedi-vis, a very broad Fair of Mufcles of the Abdomen, each covering one half thereof, and part of the Thorax ; fo call'd from the oblique Courfe of its Fibres. It arifes from the two laft true Ribs and five fpurious ones 5 and is indented with the Serratus Major An- ticus by five or fix Digitations, each whereof receives a Nerve from the Interitices of the Rib : It fprings likewife from the Margin of the Ilium ; and ends in a broad Tendon in the Linca Alba.

Befides the ordinary Ufe afcribed to it by all Anatomifts which is to comprefs the Inteftines and Bladder; Cawper and Gl'Jon attribute to it another, which is to turn the Trunk of the Body without moving the Feet.

Obliquus Afctndew, or Acclivis, lies under the lower gart of the former 5 running with a Courfe juft contrary, from the lower part upwards. Its flemy Fibres have their Origin from the Edge of the Ilium, and end at the fpurious Ribs. It terminates with a large double Tendon in the Linca Alba ; the upper part whereof creeping over the Muf- culusRettus, and the other creeping under it, and joining together at the Lima Alba j do, as it were, iheath the ReBus.

Its Ufe is to /hut and comprefs the Belly, as alfo the Cavity of the Thorax in Refpiration i and itaflifts, with its Antagonists, the Dependents, in turning the Body without moving the Legs.

Obliquus Amis, lies in the external Part of the Canal of the Aqueduct j whence paffing upwards and back- wards, it enters the Tympanum, by a very oblique Sinuofity immediately above the Bony Circle, to which the Tym- P>am>.m is fix'dj and is inferted into the ilender Procefs of the Malleus.

Oblique Cafes, in Grammar, are all the Cafes of the Declenfions of Nouns, befides the Nominative- See Case.

OBLIQUITY, that which denominates a Thing ob- lique. See Oblique.

The Obliquity of the Sphere, is the Caufe of the Inequa- lity of Seafons, of Nights and Days. See Season, ££?c.

Obliquity of the Ecliptic, is the Angle which the E- cliptic makes with the Equator. See Ecliptic.

MeiT. Cajjtni and de la Hire, make the Obliquity of the Ecliptic, by their Obfervations, 23, 29'. M. le Chevalier de Lou-vtUe, from later Obfervations, makes it 23°, %V, 41".

The fame Author, giving the Hiftory of the feveral De- terminations of this Obliquity, by ail Aftronomers in all Ages, obferves, that it conilantly diminifhesj and thence takes occafion to fufpecr, that the real Obliquity of the E- cliptic itfelf may have been diminiih'd fince the time of the antient Aftronomers.

He goes fo far, as even to fix the Proportion of the Di- minution, which he makes to be at the rate of half a Mi- nute in fifty Years. According to an antient Tradition a- mong the Egyptians, mention'd by Herodotw, the Ecliptic was formerly perpendicular to the Equator.

The Libration of the Sphere makes fome Alterations in the Obliquity of the Ecliptic ; fo that Wolfxus reckons a great Obliquity of 23°, 53'; a mean Obliquity of 23°, 41' j and a fmall one of 23°, 30'.

OBLONG, in Geometry, a Figure longer than it is broad. See Figure.

Thus, a Rectangle, or Parallelogram, is an Oblong ; fee Parallelogram: and an Ellipfis an Oblong, fee El- lipsis.

OBOLATA Terra, in our antient Law-Books, is a cer- tain (Quantity of Land, which fome Authors fix at half an Acre; tho' others make it but half a Perch. Thomafiii: fays, that Oholum Terra contains ren Feet in length, and five in breadth. See Fardingdeal.

OBOLUS, an antient Silver Money, of Athens, the fixth part of a Drachma j worth fomewhat more than our Penny. See Drachma 5 fee alfo Coin.

The Word comes from theGree£ o^Aor, ofo^J?, Needle^ either becaufe it bore the Imprefiion of a Needle ; or be- caufe, according to Eufiachiits, it was in form thereof. But thofe now in the Cabinets of Antiquaries, are round.

Obolus was alfo ufed among our Anceftors for half a Noble, or Florin ; where the Noble was efteem'd as the Penny ; and its quarter part a Farthing.

In