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as matters that need no particular description. Jn the eye-tube ofthe telescope AD, there are certain slender wires, placed in thelocus of the eye-lens, and perpendicular to the axis of (he tele-scope, which enable the observer to distinguish more accuratelywhen an object, that is seen through the telescope, reaches the axisof the telescope, or, as it is more commonly called, the line ofcollimatiou, &c. Now when the stars or planets are observed atn ght, those wires in the eve-tube cannot be seen ; therefore, torender them visible, an arm or wire is lixed occasionally at the endof the telescope, which arm holds a small piece of ivory or card z,set aslant to the axis ot the telescope ; for when a lighted candle,or lantern is situated at a little distance, and is directed so as toshine upon the above-mentioned ivory or card, the reflection ofthe light from it into the tube of the telescope will enable the r h-sfcrver to distinguish the wives at the same time that he beholds thecelestial object.

Quadrant, Mural, (fig. is a larger instrument like theabove, excepting that it has no stand; and its index is preventedfrom bending on account of its great length, by means of metallicbars, d,f, h, c. This instrument is linnly lived upon a wall ex-actly in the plane of the meridian of the observatory, for whichpurpose it has clamps, screws, and other adjustments. It haslikewise a plummet. See Observatory .

Quadrant of Altitude, is an appendage of the artificialglobe, consisting of a lamina, or slip of brass, the length of a qua-drant of one of the great circles of the globe, and graduated.

Quadrant, Sinical, (lig. 5,) consists of several concentricquadrantal arch.es, divided into eight equal parts by radii, with pa-rallel right lines crossing each other at right angles. Now anyone of the arches, as BC, may represent a quadrant of any greatcircle of the sphere, but is chiefly used for the horizon or meridian.If then BC he taken for a quadrant of the horizon, either of thesides, as AB, may represent the meridian ; and the other side,AC , will represent a parallel, or line of east and west: and all theother lines parallel to AB, will be also meridians ; and all thoseparallel to AC , east and west lines, or parallels. Again, the eightspaces into which the arches are divided by the radii, represent theeight points of the compass in a quarter of the horizon ; each con-taining 11“ 15'. The arch BC is likewise divided into 90°, andeach degree subdivided into It!', diagonal-wise. To the centre isfixed a thread, which, being laid over any degree of the quadrant,serves to divide the horizon. If the sinical quadrant he taken afourth part of the meridian, one side thereof, AB, may be taken forthe common radius of the meridian and equator ; and then theother, AC , will be half the axis of the world. The degtees of thecircumference, BC, will represent degrees of latitude ; and theparallels to the side, AB, assumed from every point of latitude tothe axis AC , will be the radii of the. parallels of latitude, as like-wise the shie-complement of those.latitudes. Suppose then, it berequired to find the degrees of longitude contained in 83 of theless leagues in the parallel'of 48°; lay the thread over 48° of lati-tude on the circumference, and count thence 83 leagues on AB,beginning at A ; this will terminate in H, allowing every smallinterval four leagues. Then tracing out the parallel rIE, from thepoint II to the thread ; the part AE of the tliread shews that 125greater or equinoctial leagues make 6° 15'; and therefore that theS3 less leagues All, which make the difference of longitude of thecourse, and are equal to the radius of the parallel HE, make 6° 15'cl the said parallel. If the ship sails an oblique course, suchcourse, besides (lie north and south greater leagues, gives lessleagues easterly and westerly, to be reduced to degrees of longbfnde of the equator. But these leagues being made neither onI he parallel of departure, nor on that of arrival, but in all the inter-mediate ones, we must find a mean proportional parallel betweenthem. To find this, we have on the instrument a scale of crosslatitudes. Suppose then it were required to find a mean parallelbetween the parallels of 40° and 60°; with your compasses'takethe middle between the 40th and 60th degree on this scale: themiddle-point will terminate against 51°, which is the mean parallelrequired. The principal use of the sinical quadrant is to form tri-angles upon, similar to those made by a ship’s way with the meri-dians and parallels ; the sides of which triangles are measured bythe equal intervals between the concentric quadrants and the linesN and S, E and W : and every fifth line and arch is made deeperthan the rest. Now, suppose a ship to have sailed 150 leagues

north-east, one-fourth north, which is the third point, and makesan angle of 33° 44'with the north part of the meridian: here aregiven the course and distance sailed, by which a triangle may beformed on the instrument similar to that made by the ship’scourse; and hence the unknown parts of the triangle may befound. Thus, supposing the centre A to represent the place ofI departure ; count by means of the concentric circles along thepoint the ship sailed on, viz. AD, 150 leagues: then in the trian-gle AED, similar to that of the ship’s course, find AE = differ-ence of latitude, and DE= difference of longitude, which mustbe reduced according to the parallel of latitude come to.

Quadrant, Sutton’s or Collin’s, (fig. 6,) is a stereographicprojection of one-quarter of the sphere between the tropics, uponthe plane of the eehptic, the eye being in its north pole: it is fittedto the latitude of London . The lines running from the righthand to the left are parallels of altitude ; and those crossing themare azimuths. The less of the two circles, bounding the projec-tion, is one-fourth of the tropic of Capricorn ; the greater is one-fourth of that of Cancer. 1 he two ecliptics are drawn from apoint on the left edge of the quadrant, with the characters of thesigns upon them ; and the two horizons are drawn from the samejoint. The limb is divided both into degrees and time; and, bylaving the sun’s altitude, the hour of the day may be found hereto a minute. The quadrantal arches next the centre contain thecalendar of mouths; and under them, in another arch, is the sun’sdeclination. On the projection are placed several of the mostnoted fixed stars betwixt the tropics; and the next below the pro-jection is the quadrant and line of shadows. To find the time ofthe sun’s rising or setting, his amplitude, his azimuth, hour of theday, & c. by this quadrant: lay the thread over the clay and themonth, and bring the bead to the proper ecliptic, either of summeror winter, according to the season, which is called rectifying;,then, moving the thread, bring the bead to the horizon, in whichcase the thread will cut the limb in the time of the sun’s rising orsetting before or after six ; and at the same time the bead will cutthe horizon in the degrees of the sun’s amplitude. Again, observ-ing tiie sun’s altitude with the quadrant, and suppos.ng it found46“ on the fourth of May, lay the thread over the fifth of May,bring (he head to the summer-ecliptic, and carry it to the parallelof altitude 45° ; in which case the tliread will cut the" limb at 55°15', and the hour will be seen among the hour-lines to be either41'past nine in the morning, or 19'past two in the afternoon,.Lastly, the bead among the azimuths shews the sun’s distancefrom the south 50° 41'. But if the sun’s altitude be less than what,it is at six o’clock, the operation must lie performed among thoseparallels above the upper horizon ; the bead being rectified to thewinter-ecliptic.

QUADRANTAL, in antiquity, the name of a vessel in useamong the Romans for the measuring of liquids. It was at firstcalled amphora; and afterwards quadrantal, from its form, which,was square every- way like a die. Its capacity was eighty libra:, orpounds, of water, which made forty-eight sextaries, two urn®, oreight congii.

QUADRAS ISLES, islands on the N. \V. coast of NorthAmerica , between Rintard’s Sound and the Straits of Fuca.Nootka Sound lies among 'them.

QUADRAT, a mathematical instrument , called also a Geo-metrical Square, and Line of Shadows: it is frequently an.additional member on the face of the common quadrant, as also,on those of Gunter’s and Sutton’s quadrants. See Mensura-tion .

Quadrat, in printing, a piece ot metal used to fill up the voidspaces between words, &c. There are quadrats of different sizes;as m quadrats, n quadrats, &c. which are respectively of the di-mensions of these letters, only lower, that they may not receivethe ink.

QUADRATIC EQUATIONS. See Algebra .

QUADRATRIX. in geometry, a mechanical line, by meanswhereof we can find right lines equal to the circumference of cir-cles, or other curves, and their several parts.

QUADRATURE, in astronomy, that aspect of the moon whenshe is yt)° distant from the sun ; or when she is in a middle-pointof her orbit, between the points of conjunction and opposition,namely, in the first and third quarters, it is marked thus (o).See Astronomy.

Quadrature,