in Geometry, the arch of a circle containing 90°, or the fourth part of the entire periphery.

Sometimes also the space or area, included between this arch and two radii drawn from the centre to each extremity therefore, is called a quadrant, or, more properly, a quadrantial space, as being a quarter of an entire-circle.

Quadrant, also denotes a mathematical instrument, of great use in astronomy and navigation, for taking the altitudes of the sun and stars, as also for taking angles in surveying, &c.

This instrument is variously contrived, and furnished with different apparatus, according to the various uses it is intended for; but they all have this in common, that they consist of a quarter of a circle, whose limb is divided into 90°. Some have a plummet suspended from the centre, and are furnished with sights to look through.

The principal and most useful quadrants are the common surveying quadrant, astronomical quadrant, Adams's quadrant, Cole's quadrant, Gunter's quadrant, Hadley's quadrant, horodiatical quadrant, Sutton's or Collins's quadrant, and the nautical quadrant, &c. Of each of which in order.

1. The common surveying quadrant, is made of brass, wood, or any other solid substance; the limb of which is divided into 90°, and each of these farther divided into as many equal parts as the space will allow, either diagonally or otherwise. On one of the semidiameters is fitted two moveable sights; and to the centre is sometimes also fixed a label, or moveable index, bearing two other sights; but in lieu of these last sights there is sometimes fitted a telescope: also from the centre there is hung a thread with a plummet; and on the under side or face of the instrument is fitted a ball and socket, by means of which it may be put into any position. The general use of it is for taking angles in a vertical plane, comprehended under right lines going from... Quadrant. from the centre of the instrument, one of which is horizontal, and the other is directed to some visible point. But besides the parts already described, there is frequently added on the face, near the centre, a kind of compartment, called the quadrat, or geometrical square. See Quadrat.

This quadrant may be used in different situations: for observing heights or depths, its plane must be disposed perpendicularly to the horizon; but to take horizontal distances, its plane is disposed parallel thereto. Again, heights and distances may be taken two ways, viz. by means of the fixed sights and plummet, or by the label: As to which, and the manner of measuring angles, see Geometry and Mensuration.

2. The astronomical quadrant is a large one, usually made of brass, or wooden bars faced with iron plates; having its limb nicely divided, either diagonally or otherwise, into degrees, minutes, and seconds; and furnished with two telescopes, one fixed on the side of the quadrant, and the other moveable about the centre, by means of the screw. There are also dented wheels which serve to direct the instrument to any object or phenomenon.—The use of this curious instrument, in taking observations of the sun, planets, and fixed stars, is obvious; for being turned horizontally upon its axis, by means of the telescope, till the object is seen through the moveable telescope, then the degrees, &c. cut by the index give the altitude required. See Astronomy Index.

3. Cole's quadrant is a very useful instrument invented by Mr Benjamin Cole. It consists of six parts, viz. the staff AB (fig. 1); the quadrantal arch DE; three vanes A, B, C; and the vernier FG. The staff is a bar of wood about two feet long, an inch and a quarter broad, and of a sufficient thickness to prevent it from bending or warping. The quadrantal arch is also of wood; and is divided into degrees, and third-parts of a degree, to a radius of about nine inches; to its extremities are fitted two radii, which meet in the centre of the quadrant by a pin, round which it easily moves. The sight-vane A is a thin piece of brass, almost two inches in height and one broad, placed perpendicularly on the end of the staff A, by the help of two screws passing through its foot. Through the middle of this vane is drilled a small hole, through which the coincidence or meeting of the horizon and solar spot is to be viewed. The horizon vane B is about an inch broad, and two inches and a half high, having a slit cut through it of near an inch long and a quarter of an inch broad; this vane is fixed in the centre-pin of the instrument, in a perpendicular position, by the help of two screws passing through its foot, whereby its position with respect to the sight-vane is always the same, their angles of inclination being equal to 45 degrees. The shade-vane C is composed of two brass plates. The one, which serves as an arm, is about four inches and a half long, and three quarters of an inch broad, being pinned at one end to the upper limb of the quadrant by a screw, about which it has a small motion; the other end lies in the arch, and the lower edge of the arm is directed to the middle of the centre-pin; the other plate, which is properly the vane, is about two inches long, being fixed perpendicularly to the other plate, at about half an inch distance from that end next the arch; this vane may be used either by its shade or by the solar spot cast by a convex lens placed therein. And, because the wood-work is often apt to warp or twist, therefore this vane may be rectified by the help of a forew, so that the warping of the instrument may occasion no error in the observation, which is performed in the following manner: Set the line G on the vernier against a degree on the upper limb of the quadrant, and turn the screw on the backside of the limb forward or backward, till the hole in the sight-vane, the centre of the glass, and the spot in the horizon-vane, lie in a right line.

To find the sun's altitude by this instrument: Turn your back to the sun, holding the instrument by the staff with your right hand, so that it be in a vertical plane passing through the sun; apply your eye to the sight-vane, looking through that and the horizon-vane till you see the horizon; with the left hand slide the quadrantal arch upwards, until the solar spot or shade, cast by the shade-vane, fall directly on the spot or slit in the horizon-vane; then will that part of the quadrantal arch, which is raised above G or S (according as the observation respected either the solar spot or shade) show the altitude of the sun at that time. But if the meridian altitude be required, the observation must be continued; and as the sun approaches the meridian, the sea will appear through the horizon-vane, and then is the observation finished; and the degrees and minutes, counted as before, will give the sun's meridian altitude: or the degrees counted from the lower limb upwards will give the zenith-distance.

4. Adams's quadrant differs only from Cole's quadrant in having an horizontal vane, with the upper part of the limb lengthened; so that the glass, which casts the solar spot on the horizon-vane, is at the same distance from the horizon-vane as the sight-vane at the end of the index.

5. Gunter's quadrant, so called from its inventor Edmund Gunter, besides the usual apparatus of other quadrants, has a stereographical projection of the sphere on the plane of the equinoctial. It has also a calendar of the months, next to the divisions of the limb.

Use of Gunter's quadrant. 1. To find the sun's meridian altitude for any given day, or the day of the month for any given meridian altitude. Lay the thread to the day of the month in the scale next the limb; and the degree it cuts in the limb is the sun's meridian altitude. Thus the thread, being laid on the 15th of May, cuts 59° 30', the altitude sought; and, contrariwise, the thread, being set to the meridian altitude, shows the day of the month. 2. To find the hour of the day. Having put the bead, which slides on the thread, to the sun's place in the ecliptic, observe the sun's altitude by the quadrant; then, if the thread be laid over the same in the limb, the bead will fall upon the hour required. Thus suppose on the 10th of April, the sun being then in the beginning of Taurus, I observe the sun's altitude by the quadrant to be 36°; I place the bead to the beginning of Taurus in the ecliptic, and lay the thread over 36° of the limb; and find the bead to fall on the hour-line marked three and nine; accordingly the hour is either nine in the morning or three in the afternoon. Again, laying the bead on the hour given, having first rectified or put it to the sun's place, the degree cut by the thread on the limb gives the altitude. Note, the bead may be rectified otherwise, by bringing Quadrant: bringing the thread to the day of the month, and the bead to the hour-line of 12. 3. To find the sun's declination from his place given, and contrariwise. Set the bead to the sun's place in the ecliptic, move the thread to the line of declination, and the bead will cut the degree of declination required. Contrarily, the bead being adjusted to a given declination, and the thread moved to the ecliptic, the bead will cut the sun's place.

4. The sun's place being given, to find his right ascension, or contrariwise. Lay the thread on the sun's place in the ecliptic, and the degree it cuts on the limb is the right ascension sought. Contrarily, laying the thread on the right ascension, it cuts the sun's place in the ecliptic. 5. The sun's altitude being given, to find his azimuth, and contrariwise. Rectify the bead for the time, as in the second article, and observe the sun's altitude; bring the thread to the complement of that altitude; thus the bead will give the azimuth sought, among the azimuth lines. 6. To find the hour of the night from some of the five stars laid down on the quadrant. (1.) Put the bead to the star you would observe, and find how many hours it is off the meridian, by article 2. (2.) Then, from the right ascension of the star, subtract the sun's right ascension converted into hours, and mark the difference; which difference, added to the observed hour of the star from the meridian, shows how many hours the sun is gone from the meridian, which is the hour of the night. Suppose on the 15th of May the sun is in the 4th degree of Gemini; I set the bead to Arcturus; and, observing his altitude, find him to be in the west about 52° high, and the bead to fall on the hour-line of two in the afternoon; then will the hour be 11 hours 50 minutes past noon, or 10 minutes short of midnight: for 62°, the sun's right ascension, converted into time, makes four hours eight minutes; which, subtracted from 13 hours 58 minutes, the right ascension of Arcturus, the remainder will be nine hours 50 minutes; which added to two hours, the observed distance of Arcturus from the meridian, shows the hour of the night to be 11 hours 50 minutes.

The mural quadrant has been already described under the article Astronomy. It is a most important instrument, and has been much improved by Mr Ramsden, who has distinguished himself by the accuracy of his divisions, and by the manner in which he finishes the planes by working them in a vertical position. He places the plumb-line behind the instrument, that there may be no necessity for removing it when we take an observation near the zenith. His manner of suspending the glass, and that of throwing light on the object-glass and on the divisions at the same time, are new, and improvements that deserve to be noticed. Those of eight feet, which he has made for the observatories of Padua and Vilna, have been examined by Dr Maskelyne; and the greatest error does not exceed two seconds and a half. That of the same size for the observatory of Milan is in a very advanced state. The mural quadrant, of six feet at Blenheim, is a most admirable instrument. It is fixed to four pillars, which turn on two pivots, so that it may be put to the north and to the south in one minute. It was for this instrument Mr Ramsden invented a method of rectifying the arc of 90 degrees, on which an able astronomer had started some difficulties; but by means of an horizontal line and a plumb-line, forming a kind of cross, without touching the circle, he showed him that there was not an error of a single second in the 90 degrees; and that the difference was occasioned by a mural quadrant of Bird, in which the arc of 90 degrees was too great by several seconds, and which had never been rectified by so nice a method as that of Mr Ramsden.

But the quadrant is not the instrument which stands highest in Mr Ramsden's opinion; it is the complete circle: and he has demonstrated to M. de la Lande, that the former must be laid aside, if we would arrive at the utmost exactness of which an observation is capable. His principal reasons are: 1. The least variation in the centre is perceived by the two diametrically opposite points. 2. The circle being worked on the turn, the surface is always of the greatest accuracy, which it is impossible to obtain in the quadrant. 3. We may always have two measures of the same arc, which will serve for the verification of each other. 4. The first point of the division may be verified every day with the utmost facility. 5. The dilatation of the metal is uniform, and cannot produce any error. 6. This instrument is a meridian glass at the same time. 7. It also becomes a moveable azimuth circle by adding a horizontal circle beneath its axis, and then gives the refractions independent of the menuration of time.

6. Hadley's quadrant is an instrument of vast utility both in navigation and practical astronomy. It derives its name from Mr Hadley, who first published an account of it, though the first thought originated with the celebrated Dr Hooke, and was completed by Sir Isaac Newton (see Astronomy, No. 32, and also No. 17, and 22.). The utility of this quadrant arises from the accuracy and precision with which it enables us to determine the latitude and longitude; and to it is navigation much indebted for the very great and rapid advances it has made of late years. It is easy to manage, and of extensive use, requiring no peculiar steadiness of hand, nor any such fixed basis as is necessary to other astronomical instruments. It is used as an instrument for taking angles in maritime surveying, and with equal facility at the mast head as upon the deck, by which its sphere of observation is much extended; for supposing many islands to be visible from the mast head, and only one from deck, no useful observation can be made by any other instrument. But by this, angles may be taken at the mast head from the one visible object with great exactness; and further taking angles from heights, as hills, or a ship mast's head, is almost the only way of describing exactly the figure and extent of shoals.

It has been objected to the use of this instrument for surveying, that it does not measure the horizontal angles, by which alone a plan can be laid down. This objection, however true in theory, may be reduced in practice by a little caution; and Mr Adams has given very good directions for doing so.

Notwithstanding, however, the manifest superiority of this instrument over those that were in use at the time of its publication, it was many years before the sailors could be persuaded to adopt it, and lay aside their imperfect and inaccurate instruments, so great is the difficulty to remove prejudice, and emancipate the mind from the slavery of opinion. No instrument has undergone, since the original invention, more changes than Quadrant than the quadrant of Hadley; of the various alterations, many had no better foundation than the caprice of the makers, who by these attempts have often rendered the instrument more complicated in construction, and more difficult in use, than it was in its original state.

It is an essential property of this instrument, derived from the laws of reflection, that half degrees on the arc answer to whole ones in the angles measured; hence an octant, or the eighth part of a circle, or 45 degrees on the arch, serves to measure 90 degrees; and sextants will measure an angular distance of 120 degrees, though the arch of the instrument is no more than 60 degrees. It is from this property that foreigners term that instrument an octant, which we usually call a quadrant, and which in effect it is. This property reduces indeed considerably the bulk of the instrument; but at the same time it calls for the utmost accuracy in the divisions, as every error on the arch is doubled in the observation.

Another essential, and indeed an invaluable, property of this instrument, whereby it is rendered peculiarly advantageous in marine observations, is, that it is not liable to be disturbed by the ship's motion; for provided the mariner can see distinctly the two objects in the field of his instrument, no motion nor vacillation of the ship will injure his observation.

Thirdly, the errors to which it is liable are readily discovered and easily rectified, while the application and use of it is facile and plain.

To find whether the two surfaces of any one of the reflecting glasses be parallel, apply your eye at one end of it, and observe the image of some object reflected very obliquely from it; if that image appear single, and well-defined about the edges, it is a proof that the surfaces are parallel; on the contrary, if the edge of the reflected images appear miffed, as if it threw a shadow from it, or separated like two edges, it is a proof that the two surfaces of the glass are inclined to each other: if the image in the speculum, particularly if that image be the sun, be viewed through a small telescope, the examination will be more perfect.

To find whether the surface of a reflecting glass be plane. Choose two distant objects, nearly on a level with each other: hold the instrument in an horizontal position, view the left-hand object directly through the transparent part of the horizon-glass, and move the index till the reflected image of the other is seen below it in the silvered part; make the two images unite just at the line of separation, then turn the instrument round slowly on its own plane, so as to make the united images move along the line of separation of the horizon-glass. If the images continue united without receding from each other, or varying their respective position, the reflecting surface is a good plane.

To find if the two surfaces of a red or darkening glass are parallel and perfectly plane. This must be done by means of the sun when it is near the meridian, in the following manner: hold the sextant vertically, and direct the sight to some object in the horizon, or between you and the sky, under the sun; turn down the red glass and move the index till the reflected image of the sun is in contact with the object seen directly; fix then the index, and turn the red glass round in its square frame; view the sun's image and object immediately, and if the sun's image is neither raised nor depressed, but continues in contact with the object below, as before, then the surfaces of the darkening glass are true.

For a more particular description of Hadley's quadrant, and the mode of using it, see Navigation, Book II. chap. i.

This instrument has undergone several improvements since its first invention, and among these improvers must be ranked Mr Ramsden. He found that the essential parts of the quadrant had not a sufficient degree of solidity; the friction at the centre was too great, and in general the alidade might be moved several minutes without any change in the position of the mirror; the divisions were commonly very inaccurate, and Mr Ramsden found that Abbé de la Caille did not exceed the truth in estimating at five minutes the error to which an observer was liable in taking the distance between the moon and a star; an error capable of producing a mistake of 50 leagues in the longitude. On this account Mr Ramsden changed the principle of construction of the centre, and made the instrument in such a manner as never to give an error of more than half a minute; and he has now brought them to such a degree of perfection as to warrant it not more than six seconds in a quadrant of fifteen inches. Since the time of having improved them, Mr Ramsden has constructed an immense number; and in several which have been carried to the East Indies and America, the deficiency has been found no greater at their return than it had been determined by examinations before their being taken out. Mr Ramsden has made them from 15 inches to an inch and a half, in the latter of which the minutes are easily distinguishable; but he prefers for general use those of 10 inches, as being more easily handled than the greater, and at the same time capable of equal accuracy. See Sextant.

A great improvement was also made in the construction of this quadrant by Mr Peter Dollond, famous for his invention of achromatic telescopes. The glasses of the quadrants should be perfect planes, and have their surfaces perfectly parallel to one another. By a practice of several years, Mr Dollond found out methods of grinding them of this form to great exactness; but the advantage which should have arisen from the goodness of the glasses was often defeated by the index-glass being bent by the frame which contains it. To prevent this, Mr Dollond contrived the frame so, that the glass lies on three points, and the part that presses on the front of the glass has also three points opposite to the former. These points are made to confine the glass by three screws at the back, acting directly opposite to the points between which the glass is placed. The principal improvements, however, are in the methods of adjusting the glasses, particularly for the back-observation. The method formerly practised for adjusting that part of the instrument by means of the opposite horizons at sea, was attended with so many difficulties that it was scarcely ever used: for so little dependence could be placed on the observations taken this way, that the best Hadley's sextants, made for the purpose of observing the distances of the moon from the sun or fixed stars, have been always made without the horizon-glass for the back-observation; for want of which, many valuable observations of the sun and moon have been lost, when their distance exceeded 120 degrees. Quadrant. To make the adjustment of the back-observation easy and exact, he applied an index to the back horizon-glass, by which it may be moved in a parallel position to the index-glass, in order to give it the two adjustments in the same manner as the fore horizon-glass is adjusted. Then, by moving the index to which the back horizon-glass is fixed exactly 90 degrees (which is known by the divisions made for that purpose), the glass will thereby be set at right angles to the index-glass, and will be properly adjusted for use; and the observations may be made with the same accuracy by this as by the fore-observation. To adjust the horizon-glasses in the perpendicular position to the plane of the instrument, he contrived to move each of them by a single foreword, which goes through the frame of the quadrant, and is turned by means of a milled head at the back; which may be done by the observer while he is looking at the object. To these improvements also he added a method invented by Dr Malkelyne, of placing darkening-glasses behind the horizon-glasses. These, which serve for darkening the object seen by direct vision, in adjusting the instrument by the sun or moon, he placed in such a manner as to be turned behind the fore horizon-glass, or behind the back horizon-glass; there are three of these glasses of different degrees of darkness.

We have been the more particular in our description and use of Hadley's quadrant, as it is undoubtedly the best hitherto invented.

7. Horological quadrant, a pretty commodious instrument, so called from its use in telling the hour of the day.—Its construction is this: From the centre of the quadrant, C, fig. 3, whose limb AB is divided into 90°, describe seven concentric circles at intervals at pleasure; and to these add the signs of the zodiac, in the order represented in the figure. Then applying a ruler to the centre C and the limb AB, mark upon the several parallels the degrees corresponding to the altitude of the sun when therein, for the given hours; connect the points belonging to the same hour with a curve line, to which add the number of the hour. To the radius CA fit a couple of sights, and to the centre of the quadrant C tie a thread with a plummet, and upon the thread a bead to slide. If now the thread be brought to the parallel wherein the sun is, and the quadrant directed to the sun, till a visual ray pass through the sights, the bead will show the hour; for the plummet, in this situation, cuts all the parallels in the degrees corresponding to the sun's altitude. Since the bead is in the parallel which the sun describes, and through the degrees of altitude to which the sun is elevated every hour there pass hour lines, the bead must show the present hour. Some represent the hour-lines by arches of circles, or even by straight lines, and that without any sensible error.

8. Sutton's or Collins's quadrant (fig. 4.) is a stereographic projection of one quarter of the sphere between the tropics, upon the plane of the ecliptic, the eye being in its north pole: it is fitted to the latitude of London. The lines running from the right hand to the left are parallels of altitude; and those crossing them are azimuths. The lesser of the two circles bounding the projection, is one-fourth of the tropic of Capricorn; the greater is one-fourth of that of Cancer. The two ecliptics are drawn from a point on the left edge of the quadrant, with the characters of the signs Quadrant, upon them; and the two horizons are drawn from the same point. The limb is divided both into degrees and time; and, by having the sun's altitude, the hour of the day may be found here to a minute. The quadrant arches next the centre contain the calendar of months; and under them, in another arch, is the sun's declination. On the projection are placed several of the most noted fixed stars between the tropics; and the next below the projection is the quadrant and line of shadows. To find the time of the sun's rising or setting, his amplitude, his azimuth, hour of the day, &c., by this quadrant: lay the thread over the day and the month, and bring the bead to the proper ecliptic, either of summer or winter, according to the season, which is called rectifying; then, moving the thread, bring the bead to the horizon, in which case the thread will cut the limb in the time of the sun's rising or setting before or after six; and at the same time the bead will cut the horizon in the degrees of the sun's amplitude.—Again, observing the sun's altitude with the quadrant, and supposing it found 45° on the fifth of May, lay the thread over the fifth of May, bring the bead to the summer ecliptic, and carry it to the parallel of altitude 45°; in which case the thread will cut the limb at 53° 15', and the hour will be seen among the hour-lines to be either 41' past nine in the morning, or 19' past two in the afternoon.—Lastly, the bead among the azimuths shows the sun's distance from the south 50° 41'. But note, that if the sun's altitude be less than what it is at six o'clock, the operation must be performed among those parallels above the upper horizon, the head being rectified to the winter ecliptic.

9. Sinical quadrant (fig. 5.) consists of several concentric quadrant arches, divided into eight equal parts by radii, with parallel right lines crossing each other at right angles. Now any one of the arches, as BC, may represent a quadrant of any great circle of the sphere, but is chiefly used for the horizon or meridian. If then BC be taken for a quadrant of the horizon, either of the sides, as AB, may represent the meridian; and the other side, AC, will represent a parallel, or line of east and west; and all the other lines, parallel to AB, will be also meridians; and all those parallel to AC, east and west lines, or parallels.—Again, the eight spaces into which the arches are divided by the radii, represent the eight points of the compass in a quarter of the horizon; each containing 11° 15'. The arch BC is likewise divided into 90°, and each degree subdivided into 12, diagonal-wise. To the centre is fixed a thread, which, being laid over any degree of the quadrant, serves to divide the horizon.

If the finical quadrant be taken for a fourth part of the meridian, one side thereof, AB, may be taken for the common radius of the meridian and equator; and then the other, AC, will be half the axis of the world. The degrees of the circumference, BC, will represent degrees of latitude; and the parallels to the side AB, assumed from every point of latitude to the axis AC, will be radii of the parallels of latitude, as likewise the fine complement of those latitudes.

Suppose, then, it be required to find the degrees of longitude contained in 83 of the lesser leagues in the parallel of 48°; lay the thread over 48° of latitude on the circumference, and count thence the 83 leagues on Quadrant AB, beginning at A; this will terminate in H, allowing every small interval four leagues. Then tracing out the parallel HE, from the point H to the thread; the part AE of the thread shows that 125 greater or equinoctial leagues make $60^\circ 15'$; and therefore that the 83 lesser leagues AH, which make the difference of longitude of the course, and are equal to the radius of the parallel HE, make $60^\circ 15'$ of the said parallel.

If the ship sails an oblique course, such course, besides the north and south greater leagues, gives lesser leagues easterly and westerly, to be reduced to degrees of longitude of the equator. But these leagues being made neither on the parallel of departure, nor on that of arrival, but in all the intermediate ones, we must find a mean proportional parallel between them. To find this, we have on the instrument a scale of cross latitudes. Suppose then it were required to find a mean parallel between the parallels of $40^\circ$ and $60^\circ$; with your compasses take the middle between the 40th and 60th degree on this scale: the middle point will terminate against the 51st degree, which is the mean parallel required.

The principal use of the nautical quadrant is to form triangles upon, similar to those made by a ship's way with the meridians and parallels; the sides of which triangles are measured by the equal intervals between the concentric quadrants and the lines N and S, E and W: and every fifth line and arch is made deeper than the rest. Now, suppose a ship to have sailed 150 leagues north-east, one-fourth north, which is the third point, and makes an angle of $33^\circ 44'$ with the north part of the meridian: here are given the course and distance sailed, by which a triangle may be formed on the instrument similar to that made by the ship's course; and hence the unknown parts of the triangle may be found. Thus, supposing the centre A to represent the place of departure, count, by means of the concentric circles along the point the ship sailed on, viz. AD, 150 leagues; then in the triangle AED, similar to that of the ship's course, find AE = difference of latitude, and DE = difference of longitude, which must be reduced according to the parallel of latitude come to.

10. Gunner's quadrant (fig. 6.), sometimes called gunner's square, is that used for elevating and pointing cannon, mortars, &c., and consists of two branches either of brass or wood, between which is a quadrant arch divided into 90 degrees, beginning from the shorter branch, and furnished with a thread and plummet, as represented in the figure.—The use of the gunner's quadrant is extremely easy; for if the longest branch be placed in the mouth of the piece, and it be elevated till the plummet cut the degree necessary to hit a proposed object, the thing is done. Sometimes on one of the surfaces of the long branch are noted the division of diameters and weights of iron bullets, as also the bores of pieces.

Quadrant of Altitude, is an appendage of the artificial globe, consisting of a lamina, or flip of brass, the length of a quadrant of one of the great circles of the globe, and graduated. At the end, where the division terminates, is a nut rivetted on, and furnished with a screw, by means whereof the instrument is fitted on the meridian, and moveable round upon the rivet to all points of the horizon.—Its use is to serve as a scale in measuring altitudes, amplitudes, azimuths, &c. See Quadrant Astronomy.