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 thereof, is called a quadrant, or, more properly, a quadrantal 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, horodiectical quadradrant, Sutton's or Collins's quadrant, and the clinical quadrant, &c. of each of which in order.

1. The common surveying quadrant, ABC, fig. 1., is made of brass, wood, or any other solid substance; the limb of which BC 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 semi-diameters AC, are fitted two moveable sights; and to the centre is sometimes also fixed a label, or moveable index AD, 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 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, EF, called the quadrant, or geometrical square. See Quadrat.

This quadrant may be used in different situations: Quadrant, 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, p. [12.] [13.]

2. The astronomical quadrant is a large one, usually made of brass, or wooden bars faced with iron plates; having its limb, FE, (fig. 2.) nicely divided, either diagonally or otherwise, into degrees, minutes, and seconds; and furnished with two telescopes, one fixed on the side of the quadrant, at AB; and the other, CD, moveable about the centre, by means of the screw G. The dented wheels I, H, 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 AB, till the object is seen thro' the moveable telescope, then the degrees, &c. cut by the index give the altitude required. See Astronomy, p. 177, 182, &c.

3. Cole's quadrant is a very useful instrument invented by Mr Benjamin Cole. It consists of six parts, viz. the staff AB, (fig. 3.) 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, thro' 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 thro' 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 thro' 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 screw, 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 Quadrant, 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 sunk 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 thro' 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, is represented by fig. 4.; and, besides the apparatus of other quadrants, has a stereographic 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 limbs, 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 3 and 9; accordingly the hour is either 9 in the morning, or 3 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 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. Quadrant thread to the line of declination ET; 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 compliment 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, shews 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 2 in the afternoon; then will the hour be 11 hours 50 min. past noon, or 10 min. short of midnight: for 62°, the sun's right ascension, converted into time, makes 4 hours 8 minutes; which, subtracted from 13 hours 58 minutes, the right ascension of Arcturus, the remainder will be 9 hours 50 minutes; which added to 2 hours, the observed distance of Arcturus from the meridian, shows the hour of the night to be 11 hours 50 minutes.

6. Hadley's quadrant, (fig. 5.) so called from its inventor J. Hadley, Esq., consists of the following particulars: 1. An octant, or \( \frac{1}{8} \) part of a circle, ABC. 2. An index D. 3. The speculum E. 4. Two horizontal glasses, FG. 5. Two screens, K, K. 6. Two sight-vanes, H, I.

The octant consists of two radii, AB, AC, which are strengthened by the braces L, M, and the arch BC; which, tho' containing only 45°, is nevertheless divided into 90 primary divisions, each of which stands for degrees, and are numbered 0, 10, 20, 30, &c. to 90; beginning at each end of the arch for the convenience of numbering both ways, either for altitudes or zenith-distances. Again, each degree is subdivided into minutes.

The index D, is a flat bar, moveable round the centre of the instrument; and that part of it which slides over the graduated arch, BC, is open in the middle, with Vernier's scale on the lower part of it; and underneath is a screw, serving to fasten the index against any division.

The speculum E, is a piece of flat glass, quicksilvered on one side, set in a brass box, and placed perpendicular to the plane of the instrument, the middle part of the former coinciding with the centre of the latter. And, because the speculum is fixed to the index, the position of it will be altered by the moving of the index along the arch. The rays of an observed object are received on the speculum, and from thence reflected on one of the horizon-glasses, r, c; which are two small pieces of looking-glass placed on one of the limbs, their faces being turned obliquely to the speculum, from whence they receive the reflected rays of observed objects. This glass, F, has only its lower part quicksilvered, and set in brass-work; the upper part being left transparent to view the horizon. The glass G has in its middle a transparent slit, thro' which the horizon is to be seen. And because the warping of the wood-work, and other accidents, may displace them from their true situation, there are three screws passing thro' their feet, whereby they may be easily replaced. The screens are two pieces of coloured glass, set in two square brass-frames K, K, which serve as screens to take off the glare of the sun's rays, which would be otherwise too strong for the eye; the one is tinged much deeper than the other, and, as both of them move on the same centre, they may be both or either of them used: in the situation they appear in the figure, they serve for the horizon-glass F; but, when they are wanted for the horizon-glass G, they must be taken from their present situation, and placed on the quadrant above G.

The sight-vanes are two pins, H and I, standing at right angles to the plane of the instrument; that at H has one hole in it, opposite to the transparent slit in the horizon-glass G; the other, at I, has two holes in it, the one opposite to the middle of the transparent part of the horizon-glass F, the other rather lower than the quicksilvered part: this vanes has a piece of brass on the back of it, which moves round a centre, and serves to cover either of the holes.

There are two sorts of observations to be made with this instrument: the one, when the back of the observer is turned towards the object, and therefore called the back observation; the other, when the face of the observer is turned towards the object, which is called the fore-observation.

To rectify the instrument for the fore-observation: Slacken the screw in the middle of the handle behind the glass F; bring the index close to the button b; hold the instrument in a vertical position, with the arch downwards; look thro' the right-hand hole in the vane I, and thro' the transparent part of the glass F, for the horizon; and if it lies in the same right line with the image of the horizon seen on the quicksilvered part, the glass F is rightly adjusted; but, if the two horizontal-lines disagree, turn the screw at the end of the handle backwards or forwards, until those lines coincide; then fasten the middle screw of the handle, and the glass is rightly adjusted.

To take the sun's altitude by the fore-observation. Having fixed the screws above the horizon-glass F, and suited them proportionally to the strength of the sun's rays, turn your face towards the sun, holding the instrument with your right hand, by the braces L, M, in a vertical position, with the arch downwards; put your eye close to the right-hand hole in the vane I, and view the horizon thro' the transparent part of the horizon-glass F, moving at the same time the index D with your left hand, till the reflex solar spot coincides with the line of the horizon; then the degrees counted from C, or that end next your body, will give the altitude of the sun at that time, observing to add Quadrant or subtractions, according as the upper or lower edge of the sun's reflex image is made use of. But to obtain the sun's meridian altitude, which is the thing wanted, in order to find the latitude; the observations must be continued, and, as the sun approaches the meridian, the index D must be continually moved towards B, in order to maintain the coincidence between the reflex solar spot and the horizon; and consequently, as long as this motion can maintain the same coincidence, the observation must be continued, and when the sun has attained the meridian, and begins to descend, the coincidence will require a retrograde motion of the index, or towards C; and then is the observation finished, and the degrees counted, as before, will give the sun's meridian altitude, or those from B the zenith-distance; observing to add 16° = semidiam. O; if the sun's lower edge is brought to the horizon; or to subtract 16°, when the horizon and upper edge coincide.

To take the altitude of a star by the fore-observation: Through the vane H, and the transparent slit in the glass G, look directly to the star; and at the same time move the index, till the image of the horizon behind you being reflected by the great speculum, is seen in the quicksilvered part of G, and meets the star; then will the index show the degrees of the star's altitude.

To rectify the instrument for the back-observation: Slacken the screw in the middle of the handle, behind the glass G; turn the button b on one side, and bring the index as many degrees before o, as is twice the dip of the horizon at your height above the water; hold the instrument vertical, with the arch downwards; look through the hole of the vane H; and if the horizon, seen through the transparent slit in the glass G, coincides with the image of the horizon seen in the quicksilvered part of the same glass, then the glass G is in its proper position; but, if not, set it by the handle, and fasten the screw as before.

To take the sun's altitude by the back observation: Put the stem of the screws K, K, into the hole r, and, in proportion to the strength or faintness of the sun's rays, let one, both, or neither of the frames of those glasses be turned close to the face of the limb; hold the instrument in a vertical position, with the arch downwards, by the braces L, M, with your left hand; turn your back towards the sun, and put your eye close to the hole in the vane H, observing the horizon thro' the transparent slit in the horizon-glass G; with your right-hand move the index D, till the reflected image of the sun be seen in the quicksilvered part of the glass G, and in a right line with the horizon; swing your body to and fro, and if the observation be well made, the sun's image will be observed to brush the horizon, and the degrees reckoned from C, or that part of the arch farthest from your body, will give the sun's altitude at the time of observation; observing to add 16° = the sun's semidiameter, if the sun's upper edge be used; and subtract 16° from the altitude, if the observation respected the lower edge.

The directions here given for taking of altitudes at sea, would be sufficient, were there not two corrections necessary to be made before the altitude can be accurately assigned, viz. one on account the observer's eye being raised above the level of the sea, and the other on account of the refraction occasioned in small altitudes by the haziness of the atmosphere.

We shall therefore give a table, shewing the corrections necessary to be made to altitudes on both these accounts.

| Height of the Eye in Feet | Corrections in Minutes | Corrections in Degrees | |--------------------------|-----------------------|-----------------------| | 5 | 2 | 1 | | 10 | 3 | 2 | | 15 | 4 | 3 | | 20 | 5 | 4 | | 25 | 6 | 5 | | 30 | 7 | 6 | | 35 | 8 | 7 | | 40 | 9 | 8 | | 45 | 10 | 9 | | 50 | 11 | 10 |

General rules for using this table of corrections: 1. In the fore-observations, add the sum of the corrections to the observed zenith-distance, for the true zenith-distance; or, take the sum of the corrections from the observed altitude, and the remainder will be the altitude. 2. In the back-observations, add the dips, or corrections for the height of the eye, and subtract the refractions for altitudes; and for zenith-distances, subtract the dips, and add the refractions.

Example: By a back-observation, the altitude of the sun's lower edge was found by Hadley's quadrant to be 25° 12′; the eye being 30 feet above the horizon. By the table, the dip on 30 feet is 6′, and the refraction on 25° is 2′; therefore 25° 12′ - 16′ (semidiam. O) = 24° 56′, and 24° 56′ + 6′ (by rule 2) = 25° 2′, and lastly 25° 2′ - 2′ (by rule 2) = 25° = the true or corrected altitude.

A considerable improvement has been 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 scarce 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... Quadrant. fun 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. 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 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 be thereby 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 screw, 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 Mr. Malkeleyne, 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. 6, 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 bead 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 then 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. 7.) 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 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 55° 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 bead being rectified to the winter ecliptic.

9. Sinical quadrant (fig. 8.) consists of several concentric quadrantal 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 sinical quadrant to 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 like- 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 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 6° 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 6° 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 crofs latitudes. Suppose then it were required to find a mean parallel between the parallels of 40° and 60°; with your compasses take the middle between the 40th and 60th degree on the scale; this middle point will terminate against the 51st degree, which is the mean parallel required.

The principal use of the sines 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° 42′ 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. 9.) 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 (fig. 10.) is an appendage of the artificial globe, consisting of a lamina, or slip 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, as represented in the figure referred to.—Its use is to serve as a scale in measuring of altitudes, amplitudes, azimuths, &c. See Astronomy, p. 370, &c.