Page:Cyclopaedia, Chambers - Volume 2.djvu/548

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A C will reprefent a Parallel, or Line of EaU and Well '• and all the other Linos parallel to A B wi 1 atfo be Meri* dians ; and all thole parallel to A C, Eaft and Welt Paral- lels, or Ealt and Wett Lines. -^f Again, the eight Spaces into which the Arches are divided

QUA ( 02c. ) Q.UA

4. floe Surfs "Place being given, to find bis right Afcen- e. gr. A B, may reprefent the Meridian ; and the fion; or contrar i ly—— Lay the Thread on the Sun's "

Place in the Ecliptic, and the Degree it cuts on the Limb is

the right Afcenfion fought Contrarily, laying the Thread

on the right Afcenfion, it cuts the Sun's Place in the Ecliptic.

5. The Surfs Altitude being given, to find his Azimuth ; by the Radii, reprefent theeight Points" of theCompafsk

and contran-wife Reaify the Bead for the Time (usinthe aquarter of the Horizon j each containing n" i«'

fccond Article) and obferve rhe Sun's Altitude : bring the The Arch BC is likewife divided into 90° and each Thread to the Compliment of that Altitude j thus the Bead Degree fubdivided into 12' Diagonal-wife. '

will give the Azimuth fought, among the Azimuth Lines. To the Center is fixed a Thread, as A Li which beins

6. To find the Hour oj the Night from form of the five laid over any Degree of the Quadrant, ferves to divide the Stars laid down on the gnadrant—i. Tut the Bead to Horizon.

the Star you intend to oblerve, and rind how many Hours If the Sinecal Quadrant be taken for a fourth part of he is off the Meridian, (by Article 2.) then from the right the Meridian 5 one fide thereof, AB, maybe taken for the Afcenfion of the Star, fubftraft the Sun's right Afcenfion common Radius of the Meridian and the Equator; and converted into Hours ; and mark the difference : Which then the other fide AC, will be half the Axisofthe World— d.fterence added to the obferv'd Hour of the Star from the The Degrees of the Circumference B C will reprefent De- Meridjan, Jhews how many Hours the Sun is gone from the grees of Latitude, and the Parallels to the fide A P, alTu- Meridian, whkh is the Hour of the Night. med from every Point of Latitude to the Axis A C, will be

Suppofe, e. gr. on the 15th of May, the Sun being in Radii of the Parallels of Latitude, as likewife the Sine- the fourth Degree of Gemini, I fet the Bead to Arcturm ; Complements of thofe Latitudes.

Suppofe, then, it be requir'd to find the Degrees of Lon- gitude contain'd in 83 of the leiTer Leagues, in the Parallel of48° — Lay the Thread over 48 of Latitude on the Cir- cumference, and count thence the 83 Leagues, or A B, be- ginning at A : This will terminate in H, allowing every

1 obferving his Altitude, find him to be in the Wett about 51° high, and the Bead to fall on the Hour-Line of two after Noon : then will the Hour be 11 Hours 50 Minutes pait Noon, or 10 Minutes fiiort of Midnight.

For, 62^, the Sun's right Afcenfion converted into Time.

makes 4 Hours 8 Minutes, which fubftracted from 13 Hours imall Interval, four Leagues. Then tracing out the Pa- 5 3 Minutes, the right Afcenfion of 'At 'Bunts, the Remain- rallel H G, from the Point H to the Thread; the part der will be 9 Hours 50 Minutes ; which added to 2 Hours, A G of the Thread iliews that 125 greater, or Equinoctial tbeobferv'd diRzncc af Arfittrus from the Meridian, fhews Leagues, make 6 9 15' 5 and therefore that the 83 letter the Hour of the Night to be 11 Hours 50 Minutes. Leagues A H which make the difference of Longitude of

Sutton s Quadrant, fometimes, alfo, call'd CoUins's theCourfe, and are equal to the Radius of the Parallel G I

pocket Quadrant One of the beft of Mr. Sutton's make <J Q 15? of the fa id Parallel.

Quadrants, (reprefented Tab. Astronomy, Fig. ytfO is a If the Ship fail an oblique Courfe, fuch Courfe, befides Stenographic Projection of that Quarter of the Sphere be- the North and South greater Leagues, gives letter Leagues tween the Tropics, upon the Plane of the Equinoctial, the Eaflerly and Wefterly ; to be reduced to Degrees of Con- Eye being in the North Pole. gttude of the Equator—— 3ut thefe Leagues being made 5 Tis fitted to the Latitude of London— The Lines run- neither on the Parallel of Departure, nor on that of Arrival, ning from the right Hand to the left are Parallels of Alti- but in all the intermediate ones ; we mutt find a mean pro- tude, and thofe crofling them are Azimuths : The lefs of portional Parallel between 'em.

the two Circles bounding the Projection is I of the Tropic To find this, we have on the Inttrument a Scale of crofs of Capricorn, the greater* of that of Cancer— The two Latitudes. Suppofe, then, it were requir'd to find a mean Ecliptics are drawn from a Point on the left Edge of the Parallel between the Parallels of 40 and 6o Q, With your Quadrant, with the Characters of the Signs upon 'em ; and Compaffes take the middle between the 40th and tfoth the two Horizons are drawn from the fame Point- -The Degree on the Scale: This middle Point will t ■rminate Limb is divided both into Degrees, and Time $ and by againttthe 51ft Degree, which is the mean Parallel requir'd. having the Sun's Altitude, the Hour of the Day may be _

here found 10 a Minute. ■. u f e °f the Sinecal QjrApRANT.

The quadrantal Arches next the Centre contain the Ca- The Ufe of this Inttrument is to form Triangles upon, kndar of Months ; and under" them, in another Arch, is fimilar to thofe made by a Ship's way, with the Meridians the Sun's Declination. and Parallels ; the fides of which Triangles are meafur'd

between the concentric Quadrants,

d S. E. and W.

The Lines and Arches are dittinguifri'd, every fifth, by a

broader Line; fo that if each Interval be taken for one

League, there will be five between one broad Line and

another.

Now, fuppofe, a Ship to have fail'd 150 Leagues North-Eaitj one fourth North; which is the third Point, and makes an Angle of 35 45', with the North part of the Meridian Here are given two things; vim. theCourfe

On the Projection are placed feveral of the mofl noted by the equal Interval fixed Stars between the Tropics, and next below the Pro- and the Lines N. and jection is the Quadrat, and Line of Shadows, See Quadrat.

Ufe of Sutton' s or CollinsV Quadrant.

To find the T'ime of Stm-rifingor fitting* his Amplitude,

Azimuth, Hour of the tDay, &c. Lay the Thread

over the Day and the Month, and bring the Bead to the proper Ecliptic, either that of Summer or Winter, accor-

ding to the Seafon ; (which is call'd rectifying) then, mo- and Dittance fail'd, by which a Triangle may be form'd on

ving the Thread, bring the Bead to the Horizon 5 in which the Inttrument, fimilar to that made by the Ship's Courfe,

Cafe the Thread will cut the Limb in the time of the Sun's and her Longitude and Latitude ; and hence may the un-

rifing or fetting, before, or after fix j and at the fame time known parts of the Triangle be found. See Triangle.

the Bead will cut the Horizon in the Degrees of the Sun's Amplitude.

Again, obferving the Sun's Altitude with the Quadrant, and fuppofing it found 45° on the 24th of April ; lay the Thread over the 24th of April 3 bring the Bead to the Summer Ecliptic, and carry it to the Parallel of Altitude 45°. In which Cafe the Thread will cut the Limb at 55

15', and the Hour will be feen among the Hour-lines rence of Longitude and Latitude ;

to be either 41' paft nine in the Morning, or 19' paft two in Leagues for the difference of Latitude Northwards, which the Afternoon. makes 6 9 15', and the fide D E gives 83 letter Leagues

LalUy, the Bead among the Azimuths Ihews the Sun's anfwering to the Parallels, which being reduced, as fhewn dittance from the South, viz, 50° 41'. above, gives the difference of Longitude— — And thus is

But note, that if the Sun's Altitude be lefs than what it the whole Triangle found. isat fix a-clock, the Operation muft be performed among Quadrant, in Gunnery, call'd alfo

Thus fuppofing the Centre A to reprefent the place of Departure ; count, by means of the concentric Arches, along the Point the Ship fail'd in, as AD, 1 50 Leagues from A to D : Then is the Point D the place the Ship is ar-

riv'd at ; which note. 'This done, let D E be parallel

to the fide ; and then there will be form'd a right-angled, Triangle A E D, fimilar to that of the Ship's Courfe, diffe> The fide A E gives izj

thofe Parallels above the Winter Horizon 5 the Bead being rectify'd to the Winter Ecliptic.

Sinecal Quadrant, is an Inttrument of Ufe in Navi- gation (It is reprefented Tab, Navigation, Fig. •)

and coniifts of feveral concentric quadrantal Arches j di-

the Gunner's Square, is an Inttrument ferving to elevate or lower Can- nons, Mortars, &c. according to the Places they are to be levell'd or directed to. See Mortar, Level, $$c.

It confitts of two Branches, made of Brafs ; one about a Foot long, 8 Lines broad, and one Line in thicknefs; the v "ded into eight equal parts by Radii with parallel right other four Inches lone, and the fame length and breadth Lines crofling each other at right Angles. as the former — 'Between thefe Branches is a Quadrant divi-

Now, any of the Arches, e. gr. B C may be accounted a ded into 90 Degrees, beginning from the mortett Branch, Quadrant of any of the great Circles of the Sphere, chiefly furni/h'd with Thread and Plummet. See its Figure re- of the Horizon, and Meridian : If, then, B C be taken freftnted Tab. Fortification, Fig.li- for a Quadrant, e.gr. of the Horizon; either of the Sides, The Ufe of this Inttrument is eafyj nothing more H^in^

it C requir'd