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or q, the 16th letter and 12th consonant of to the sonth-east of the mountains of Bohemia, on the Q,

Quadi our alphabet; but is not to be found either in banks of the Danube, and extending as far as the river Quadi.

Quadrant. the Greek, old Latin, or Saxon alphabets ; and in- Marus, or March, running by Moravia, which country deed some would entirely exclude it, pretending that they occupied. k ought to be used wherever this occurs. However, as QUADRAGESIMA, a denomination given to lent, it is formed in the voice in a difli-rent manner, it is un- from its consisting of 40 days. See LENT. doubtedly a distinct letter : for, in expressing this QUADRANGLE, in Geometry, the same with a sound, the cheeks are contracted, and the lips, particu- quadrilateral figure, or one consisting of four sides and Jarly the under one, are put into a canular form, for

four angles.
the passage of the breath.

QUADRANS, the quarter or fourth part of any
The q is never sounded alone, but in conjunction thing, particularly the as, or pound.
with u, as in quility, question, quite, quote, &c. and QUADRANS, in English money, the fourth part of a
never ends any English word.

penny. Before the reign of Edward I. the smallest
As a numeral, Q stands for 500; and with a dash coin was a sterling, or penny, marked with a cross; by
over it, thus ā, for 500,000.

the guidance of which a penny might be cut into halves
Used as an abbreviatare q signifies quantity, or quan- for a hallpenny, or into quarters or four parts for far-
tum. Thus, among physicians, q. pl. is quantum plucet, things ; till, to avoid the fraud of unequal cuttings, that

as much as you please” of a thing ; and q. s. is king coined halfpence and far things in distinct round
quantum sufficit, i.e. “as much as is necessary.” Q.E.D. pieces.
among mathematicians, is quod erat demonstrandum, i. QUADRANT, in Geometry, the arch of a circle,
" which was to be demonstrated :” and Q. E. F. is

containing 90°, or the fourth part of the entire peri-
quod erat faciendum, i. t. ” which was to be done.” pbery.
Q. D. among grammarians is quasi dictum, i.

Sometimes also the space or area, included between
it were said;" or, as wlio should say." In the notes this arch and two radii drawn from the centre to eaclı
of the ancients, Q stands for Quintus, or Quintius; extremity thereof, is called a quadrant, or, more pro-

Q. B. V. for quod bene vertat; Q. S. S. S. for quæ su- perly, a quadrantal space, as being a quarter of an en-
pra scripta sunt ; Q. M. for Quintus Miutius, or quomo- tire circle.
do; Qilint. for Quintilius; and Quæs. for quæstor. QUADRANT, also denotes a mathematical instrument,

QUAB, in Ichthyology, the name of a Russian fish, of great use in astronomy and navigation, for taking the
which is said to be at first a tadpole, then a frog, and altitudes of the sun and stars, as also for taking angles
at last a fish. Dr Mounsey, who made many inquiries in surveying, &c.
concerning the e pretended changes, considers them all This instrument is variously contrived, and furnished
as fabulous. He had opportunity of seeing the fish it- with diferent apparatus, according to the various uses
self, and found that they spawned like other fishes, and it is intended for; but they all have this in common,
grew in size, without any appearances to justify the re- that they consist of a quarter of a circle, whose limb is
port. He adds, that they delight in very clear water, divided into 90°. Some have a plummet suspended
in rivers with sandy or stony bottoms, and are never from the centre, and are furnished with sights to look
found in standing lakes, or in rivers passing through through.

marshes or mossy grounds, where frogs choose most to be. The principal and most useful quadrants are the

QUABES, are a free people of Africa, inhabiting common surveying quadrant, astronomical quadrant,
the southern banks of the river Sestos, and between that Adams's quadrant, Cole's quadrant, Gunter's quadrant,
and Sierra Leona. They are under the protection of Hadley's quadrant, horodiciical quadrant, Sutton's or
the emperor of Manow.

Collins's quadrant, and the sinical quadrant, &c. Of
QUACHA, or QUAGGA. See Equus, MAMMALIA each of which in order.

1. The common surveying quadrant, is made of brass, QUACHILTO, in Ornithology, is the name of a wood, or any other solid substance ; the limb of which ive's

very beautiful Brasilian bird, called also yacızintli and is divided into 90°, and each of these farther divided sf. Bra

porphyrio Americanus. It is of a fine blackish purple into as many equal parts as the space will allow, either
colour, variegated with white ; its beak is white while diagonally or otherwise. On one of the semidiameters
young, but becomes red as it grows older, and has a are fitted two moveable sights; and to the centre is
naked space at its basis, resembling in some sort the sometimes also fixed a label, or moveable index, bearing
coot ; its legs are of a yellowish green; it lives about two other sights; but in lieu of these last sights there
the waters, and feeds on fish, yet is a very well tasted is sometimes fitted a telescope : also from the centre
bird. It imitates the crowing of a common cock, and there is hung a thread with a plummet; and on the
makes its music early in the morning.

under side or face of the instrument is fitted a ball and
QUACK, among physicians, the same with empiric. socket, by means of which it may be put into any po-

sition. The general use of it is for taking angles in a QUADI, (Tacitus); a people of Germany, situated vertical plane, comprehended under right lines going ,


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Quadrant. from the centre of the instrument, one of which is ho- cast by a convex lens placed therein. And, because the quad.231

rizontal, and the other is directed to some visible point. wood-ivork is often apt to warp or twist, therefore this But besides the parts already described, there is fre- vane may be rectified by the help of a screw, so that the quently added to the face, near the centre, a kind of warping of the instrument may occasion no error in the compartment, called the quadrat, or geometrical square. observation, which is performed in the following manSee QUADRAT.

ner: Set the line G on a vernier against a degree on This quadrant may be used in different situations: the upper limb of the quadrant, and turn a screw on for observing heights or depths, its plane must be dispo- the backside of the limb forward or backward, till the sed perpendicularly to the liorizons but to take hori- bole in the sight-vane, the centre of the glass, and the zontal distances, its plane is disposed parallel thereto. sunk spot in the horizon-vane, lie in a right line. Again, heights and distances may be taken two ways, To find the sun's altitude by this instrument: Turn viz. by means of the fixed sights and plummet, or by your back to the sun, holding the instrument by the the label: As to which, and the manner of measuring staff with your right hand, so that it be in a vertical angles, see GEOMETRY and MENSURATION.

plane passing through the sun; apply your eye to the 2. The astronomical quadrant is a large one, usually sight-vane, looking through that and the horizon-vane

made of brass, or wooden bars faced with iron plates; till you see the horizon ; with the left hand slide the having its limb nicely divided, either diagonally or quadrantal arch upwards, until the solar spot or shade, otherwise, into degrees, minutes, and seconds; and fur. cast by the shade-vane, fall directly on the spot or slit nished with two telescopes, one fixed on the side of the in the horizon-vane; then will that part of the quadquadrant, and the other moveable about the centre, by rantal arch, which is raised above G or S (according means of the screw. There are also dented wheels as the observation respected either the solar spot or which serve to direct the instrument to any object or shade) show the altitude of the sun at that time. But if phenomenon.— The use of this curious instrument, in the meridian altitude be required, the observation must taking observations of the sun, planets, and fixed stars, be continued; and as the sun approaches the meridian, is obvious; for being turned horizontally upon its axis, the sea will appear through the horizon-vane, and then by means of the telescope, till the object is seen through is the observation finished; and the degrees and mithe moveable telescope, then the degrees, &c. cut by nutes, counted as before, will give the sun's meridian the index give the altitude required. See ASTRONOMY altitude : or the degrees counted from the lower limb Inder.

upwards will give the zenith distance. 3. Cole's quadrant is a very useful instrument invent- 4. Adams's quadrant differs only from Cole's qua

ed by Mr Benjamin Cole. It consists of six parts, viz. drant in having an horizontal vane, with the upper Plate

the staff AB (fig. 1.); the quadrantal arch DE; three part of the limb lengthened; so that the glass, which

vanes A, B, C; and the vernier FG. The staff is a casts the solar spot on the horizon-vane, is at the same fig. 1.

bar of wood about two feet long, an inch and a quarter distance from the horizon-vane as the sight-vane at the
broad, and of a sufficient thickness to prevent it from end of the index.
bending or warping. The quadrantal arch is also of 5. Gunter's quadrant, so called from its inventor Ed.
wood; and is divided into degrees, and third-parts of mund Ganter, besides the usual apparatus of other
a degree, to a radius of about nine inches; to its ex- quadrants, has a stereographical projection of the
tremities are fitted two radii, which meet in the centre sphere on the plane of the equinoctial. It has also
of the quadrant by a pin, round which it easily moves. a kalendar of the months, next to the divisions of the
The sight-vane A is a thin piece of brass, almost two Jimb.
inches in height and one broad, placed perpendicularly Use of Gunicr's quadrant. 1. To find the sun's me-
on the end of the staff A, by the help of two screws ridian altitude for any given day, or the day of the
passing through its foot. Through the middle of this month for any given meridian altitude. Lay the thread
vane is drilled a small bole, through which the coinci- to the day of the month in the scale next the limb; and
dence or meeting of the horizon and solar spot is to be the degree it cuts in the limb is the sun's meridian
viewed. The horizon vane B is about an inch broad, altitude. Thus the thread, being laid on the 15th of
and two inches and a half high, having a slit cut through May, cuts 59° 30', the altitude sought; and, contrari-
it of near an inch long and a quarter of an inch broad; ly, the thread, being set to the meridian altitude, shows
this vane is fixed in the centre-pin of the instrument, in the day of the month.. 2. To find the hour of the day.
a perpendicular position, by the help of two screws pas. Having put the bead, which slides on the thread, to
sing through its foot, whereby its position with respect the sun's place in the ecliptic, observe the sun's alti-
to the sight-vane is always the same, their angles of in- tude by the quadrant; then, if the thread be laid over
clination being equal to 45 degrees. The shade-vane the same in the limb, the bead will fall upon the hour
C is composed of two brass plates. The one, which required. Thus suppose on the roth of April, the
serves as an arm, is about four inches and a half long, sun being then in the beginning of Taurus, 1 observe
and three quarters of an inch broad, being pinned at the sun's altitude by the quadrant to be 36°; I place
one end to the upper limb of the quadrant by a screw, the bead to the beginning of Taurus in the ecliptic,
about which it has a small motion; the other end lies and lay the thread over 36° of the limb; and God the
in the arch, and the lower edge of the arm is directed bead to fall on the bour-line marked three and nine ; ac-
to the middle of the : the other plate, which cordingly the hour is either nine in the morning or three
is properly the vane, is about two inches long, being in the afternoon. Again, laying the bead on the hour
fixed perpendicularly to the other plate, at about half given, having first rectified or put it to the san's place,
an inch distance from that end next the arch; this vane the degree cut by the thread on the limb gives the alti-
may be used either by its shade or by the solar spot tude. Note, the bead may be rectified otherwise, by




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drarit bringing the thread to the day of the month, and the forming a kind of cross, without touching the circle, Quadrant.
bead to the hour-line of 12. 3.

To find the sun's decli. he showed him that there was not an error of a single
nation from his place given, and contrariwise. Set the second in the go degrees; and that the difference was
bead to the sun's place in the ecliptic, move the thread occasioned by a mural quadrant of Bird, in which the
to the line of declination, and the bead will cut the arc of go degrees was too great by several seconds, and
degree of declination required. Contrarily, the bead which had never been rectified by so nice a method as
being adjusted to a given declination, and the thread that of Mr Ramsden.
moved to the ecliptic, the bead will cut the sun's place. But the quadrant is not the instrument which stands
4. The sun's place being given, to find his right ascen. highest in Mr Ramsden's opinion; it is the complete
sion, or contrarily. Lay the thread on the sun's place circle : and he has demonstrated to M. de la Lande,
in the ecliptic, and the degree it cuts on the limb is the that the former must be laid aside, if we would arrive at
right ascension sought. Contrarily, laying the thread the utmost exactness of which an observation is capable.
on the right ascension, it cuts the sun's place in the His principal reasons are: 1. The least variation in the
ecliptic. 5. The sun's altitude being given, to find his centre is perceived by the two diametrically opposite
azimuth, and contrariwise. Rectify the bead for the points. 2. The circle being worked on the turn, the
time, as in the second article, and observe the sun's al- surface is always of the greatest accuracy, which it is
titude : bring the thread to the complement of that al- impossible to obtain in the quadrant. 3. We may al-
titude ; thus the bead will give the azimuth sought, ways have two measures of the same arc, which will
among the azimuth lines. 6. To find the hour of the serve for the verification of each other. 4. The first
night fron some of the five stars laid down on the qua- point of the division may be verified every day with the
drant. (1.) Put the bead to the star you would ob- utmost facility. 5. The dilatation of the metal is uni-
serve, and find how many hours it is off the meridian, form, and cannot produce any error. 6. This instru-
by article 2. (2.) Then, from the right ascension of ment is a meridian glass at the same time. 7. It also
the star, subtract the sun's right ascension converted becomes a movcable azimuth circle by adding a bori-
into hours, and mark the difference; which difference, zontal circle beneath its axis, and then gives the refrac-
added to the observed hour of the star from thie meri. tions independent of the mensuration of time.
dian, shows how many hours the sun is gone from the 6. Hadley's quadrant is an instrument of vast otility
meridian, which is the hour of the night. Suppose on both in navigation and practical astronomy. It derives
the 15th of May the sun is in the 4th degree of Ge- its name from Mr Hadley, who first published an ac-
mini, I set the bead to Arcturus; and, observing his al- count of it, though the first thought originated with
titude, find him to be in the west about 52° high, and the celebrated Dr Hooke, and was completed by Sir
the bead to fall on the hour-line of two in the afternoon; Isaac Newton (see Astronomy, N° 32. and also N°
then will the hour be 11 hours 50 minutes past noon, and 22.). The utility of this quadrant arises from the
or 10 minutes short of midnight : for 62°, the sun's accuracy and precision with which it enable us to de-
right ascension, converted into time, makes four hours termine the latitude and longitude; and to it is naviga-
eight minutes ; which, subtracted from 13 bours 58 tion much indebted for the very great and rapid advances
minutes, the right ascension of Arcturus, the remainder it has made of late years. It it easy to manage, and of
will be nine hours 50 minutes; which added to two extensive use, requiring no peculiar steadiness of hand,
hours, the observed distance of Arcturus from the me- nor any such fixed basis as is necessary to other astro-
ridian, shows the hour of the night to be 11 hours 50 nomical instruments. It is used as an instrument for

taking angles in maritime surveying, and with equal fa-
Tlie mural quadrant has been already described under cility at the mast head as upon the deck, by which its
the article AstroNOMY. It is a niost important instru- sphere of observation is much extended; for supposing
ment, and has been much improved by Mr Ramsden, many islands to be visible from the mast head, and only
who has distinguished himself by the accuracy of his di- one from deck, no useful observation can be made by
visions, and by the manner in which he finishes the any other instrument. But by this, angles may be ta-
planes by working them in a vertical position. He ken at the mast head from the one visible object with
places the plumb-line behind the instrument, that there great exactness ; and further taking angles from
may be no necessity for removing it wben we take an heights, as bills, or ship mast's head, is almost the
observation near the zenith. His manner of suspending only way of describing exactly the figure and extent of
the glass, and that of throwing light on the object-glass shoals.
and on the divisions at the same time, are new, and im- It has been objected to the use of this instrument for
provements that deserve to be noticed. Those of eight surveying, that it does not measure the horizontal angles,
feet, which be has made for the observatories of Padua by wbich alone a plan can be laid down. This objection,
and Vilna, have been examined by Dr Maskelyne ; and however true in theory, may be reduced in practice by
the greatest error does not exceed two seconds and a half. a little caution ; and Mr Adams has given very good
That of the same size for the observatory of Milan is in directions for doing so.
a very advanced state. The mural quadrant, of six Notwithstanding, however, the manifest superiority
feet at Blenheiın, is a most admirable instrument. It of this instrument over those that were in use at the
is fixed to four pillars, which turn on two pivots, so time of its publication, it was many years before the
that it

may be put to the north and to the south in one sailors could be persuaded to adopt it, and lay aside
minute. It was for this instrument Mr Ramsden in their imperfect and inaccurate instruments, so great is
yented a method of rectifying the arc of 90 degrees, on the difficulty to remove prejudice, and emancipate the
which an able astronomer had started some difficulties; mind from the slavery of opinion. No instrument bas
but by means of an horizontal line and a plumb-line, undergone, since the original invention, more changes
Vol. XVII, Part II.





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Quadrant. than the quadrant of Hadley; of the various altera- image is neither raised nor depressed, but continues in Quadrast,

tions, many had no better foundation than the caprice contact with the object below, as before, then the sur.
of the makers, who by these attempts have often ren- faces of the darkening glass are true.
dered the instrument more complicated in construction, For a more particular description of Hadley's qua-
and more difficult in use, than it was in its original drant, and the mode of using it, see NAVIGATION,

Book II. chap. i.
It is an essential property of this instrument, derived This instrument has undergone several improvements
from the larvs of reflection, that half degrees on the arc since its first invention, and among these improvers must
answer to whole ones in the angles measured: hence an be ranked Mr Ramsden. He found that the essential
octant, or the eighth part of a circle, or 45 degrees on parts of the quadrant had not a sufficient degree of co-
the arch, serves to measure go degrees; and sextants lidity; the friction at the centre was too great, and
will measure an angular distance of 120 degrees, though in general the alidada might be moved several minutes
the arch of the instrument is no more than 60 degrees. without any change in the position of the mirror; the
It is from this property that foreigners terns that in. divisions were commonly very inaccurate, and Mr Rams-
strunient an octant, which we usually call a quadrant, den found that Abbé de la Caille did not exceed the
and which in effect it-is. This property reduces in- truth in estimating at five minutes the error to which
deed considerably the bulk of the instrument; but at an observer was liable in taking the distance between
the same time it calls for the utmost accuracy in the the moon and a star; an error capable of producing a
divisions, as every error on the arch is doubled in the mistake of 50 leagues in the longitude. On this ac-

count Mr Ramsden changed the principle of construc-
Another essential, and indeed an invaluable, proper- tion of the centre, and made the instrument in such a
ty of this instrument, whereby it is rendered peculiarly manner as never to give an error of more than half a
advantageous in marine observations, is, that it is not minute ; and he has now brought them to such a de-
liable to be disturbed by the ship's motion ; for provid- gree of perfection as to warrant it not more than six
ed the mariner can see distinctly the two objects in the seconds in a quadrant of fifteen inches. Since the time
field of bis instrument, no motion nor vacillation of the of having improved them, Mr Ramsden has constructed
ship will injure bis observation.

an immense number; and in several wbich have been
Thirdly, the errors to which it is liable are readily carried to the East Indies and America, the deficiency
discovered and easily rectified, while the application and has been found no greater at their return than it had
use of it is facile and plain.

been determined by examinations before their being ta-
To find whetlier the two surfaces of any one of the ken out. Mr Ramsden has made them from 15 inches
reflecting glasses be parallel, apply your eye at one end to an inch and a half, in the latter of which the minutes
of it, and observe the image of some object reflected are easily distinguishable; but he prefers for general use
very obliquely from it; if that image appear single, those of 10 inches, as being more easily handled than
and well-defined about the edges, it is a proof that the the greater, and at the same time capal.le of equal ae-
surfaces are parallel : on the contrary, if the edge of curacy. See SEXTANT.
the reflected images appear misted, as if it threw a A great improvement was also made in the con-
shadow from it, or separated like two edges, it is a struction of this quadrant by Mr Peter Dollond, fa-
proof tlint the two surfaces of the glass are inclined to mous for his invention of acliromatic telescopes. The
each other: if the images in the speculum, particularly glasses of the quadrants should be perfect planes, and
if that image be the sun, be viewed through a small te- have their surfaces perfectly parallel to one another. By
Jescope, the examination will be more persect.

a practice of several years, Mr Dollond found out mé-
To find whether the surface of a reflecting glass be thods of griņding them of this form to great exact-
plane. Choose two distant objects, nearly on a level ness; but the advantage which sbould have arisen from
with each other: hold the instrument in an horizontal the goodness of tbe glasses was often defeated by the
position, view the left-hand object directly through the index-glass being bent by the frame which contains it.
transparent part of the horizon-glass, and move the in- To prevent this, Mr Dollond contrived the frame so,
dex till the reflected image of the other is seen below it that the glass lies on three points, and the part that
in the silvered part; make the two images unite just presses on the front of the glass has also three points op-
at the line of separation, then turn the instrument round posite to the former. These points are made to confine
slowly on its own plane, so as to make the united images the glass by three screws at the back, acting directly
move along the line of separation of the horizon-glass. opposite to the points between which the glass is pla-

If the images continue united without receding from ced. The principal improvements, however, are in the
each other, or varying their respective position, the re- methods of adjusting the glasses, particularly for the
flecting surface is a good plane.

back-observation. The method formerly practised for
To find if the two surfaces of a red or darkening glass adjusting that part of the instrument by means of the
are parallel and perfectly plane. This must be done by opposite horizons at sea, was attended with so many
means of the sun when it is near the meridian, in the fol- difficulties that it was scarcely ever used : for so little
lowing manner: hold the sextant vertically, and direct dependence could be placed on the observations taken
the sight to some object in the horizon, or between you this way, that the best Hadley's sextants, made for the
and the sky, under the sun; turn down the red glass and purpose

of observing the distances of the moon from the move the index till the reflected image of the sun is in sun or fixed stars, have been always made without the contact with the object seen directly: fix then the index, borizon-glass for the back-observation ; for want of and turn the red glass round in its square frame ; view which, many valuable observations of the sun and moon the sun's image and object immediately, and if the sun's bave been lost, when their distance exceede dai 20 de


1 The qua”.

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Fig. 3.

Quadrant. grees. To make the adjustment of the back-observa- edge of the quadrant, with the characters of the signs Quadianta

tion easy and exact, he applied an index to the back upon them; and the two horizons are drawn from the
horizon-glass, by which it may be moved in a parallel same point. The limb is divided both into degrees and
position to the index-glass, in order to give it the two ad- time; and, by having the sun's altitude, the hour of
justments in the same manner as the fore horizon-glasg the day may be found here to a minute.
is adjusted. Then, by moving the index to which the drantal arches next the centre contain the kalendar of
back horizon-glass is fixed exactly go degrees (which months; and under them, in another arch, is the sun's
is known by the divisions made for that purpose), the declination. On the projection are placed several of
glass will thereby be set at right angles to the index- the most noted fixed stars between the tropics ; and the
glass, and will be properly adjusted for use; and the next below the projection is the quadrant and line of
observations may be made with the same accuracy by shadows. To find the time of the sun's rising or set.
this as by the fore-observation. To adjust the horizon- ting, his amplitude, bis azimuth, hour of the day, &c.
glasses in the perpendicular position to the plane of the by this quadrant : lay the thread over the day and the
instrument, he contrived to move each of them by a month, and bring the bead to the proper ecliptic, either
single screw, which goes though the frame of the qua- of summer or winter, according to the season, which is
drant, and is turned by means of a milled head at the called rectifying ; then, moving the thread, bring the
back; which may be done by the observer while he is bead to the horizon, in which case the thread will cut
looking at the object. To these improvements also the limb in the time of the sun's rising or setting before
he added a method invented by Dr Maskelyne, of or after six; and at the same time the bead will cut the
placing darkening-glasses behind the horizon-glasses. horizon in the degrees of the sun's amplitude.- Again,
These, which serve for darkening the object seen by observing the sun's altitude with the quadrant, and sup.
direct vision, in adjusting the instrument by the sun or posing it found 45° on the fifth of May, lay the thread
moon, he placed in such a manner as to be turned be- over the fifth of May, bring the bead to the summer
biod the fore horizon-glass, or behind the back horizon- ecliptic, and carry it to the parallel of altitude 45°; in
glass : there are three of these glasses of different de- which case the thread will cut the limb at 55° 15', and
grees of darkness.

the hour will be seen among the hour-lines to be either
We have been the more particular in our description 41' past nine in the morning, or 19' past two in the af-

and use of Hadley's quadrant, as it is undoubtedly the ternoon. Lastly, the bead among the azimuths shows
best hitherto invented.

the sun's distance from the couth 50° 41'. But note,
7. Horodictical quadrant, a pretty commodious in- that if the sun's aliitude be less than what it is at six
strument, so called from its use in telling the hour of o'clock, the operation must be performed among those
the day.--Its construction is this : From the centre of parallels above the upper horizon, the head being rec-
the quadrant, C, fig. 3. whose limb AB is divided into tified to the winter ecliptic.
90°, describe seven concentric circles at intervals at 9. Sinical quadrant (fig. 5.) consists of several conFig. 5.
pleasure ; and to these add the signs of the zodiac, in centric quadrantal arches, divided into eight equal parts
the order represented in the figure. Then applying a by radii, with parallel right lines crossing each other
ruler to the centre C and the limb AB, mark upon at right angles. Now any one of the arches, as BC,
the several parallels the degrees corresponding to the may represent a quadrant of any great circle of the
altitude of the sun when therein, for the given bours ; sphere, but is chiefly used for the horizon or meridian.
connect the points belonging to the same hour with a If then BC be taken for a quadrant of the horizon,
curve line, to which add the number of the hour. To either of the sides, as AB, may represent the meridian;
the radius CA fit a couple of sights, and to the centre and the other side, AC, will represent a parallel, or lino
of the quadrant C tie a thread with a plummet, and of east and west : and all the other lines, parallel to AB,
opon the thread a bead to slide. If now the thread be will be also meridians; and all those parallel to AC,
brought to the parallel wherein the sun is, and the qua- east and west lines, or parallels.- Again, the eight
drant directed to the sun, till a visual ray pass through spaces into which the arches are divided by the radii,
the sights, the bead will show the hour; for the plum- represent the eight poiuts of the compass in a quarter
met, in this situation, cuts all the parallels in the de- of the horizon ; each containing 11° 15. The arch BC
grees corresponding to the sun's altitude. Since the is likewise divided into 90°, and each degree subdivid-
bead is in the parallel which the sun describes, and ed into 12, diagonal-wise. To the centre is fixed a
through the degrees of altitude to which the sun is ele- tbread, which, being laid over any degree of the quad-
vated every hour there pass hour lines, the bead must rant, serves to divide the horizon.
show the present hour. Some represent the hour-lines If the sinical quadrant be taken for a fourth part of
by arches of circles, or even by straight lines, and that the meridian, one side thereof, AB, may be taken for
without any sensible error.

the common radius of the meridian and equator ; and
8. Sutton's or Collins's quadrant (fig. 4.) is a stereo- then the other, AC, will be half the axis of the world.
grapbic projection of one quarter of the sphere be- The degrees of the circumference, BC, will represent
tween the tropics, upon the plane of the ecliptic, the degrees of latitude ; and the parallels to the side AB,
eye being in its north pole : it is fitted to the latitude assumed from every point of latitude to tbe axis AC,
of London. The lines running from the right hand will be radii of the parallels of latitude, as likewise the
to the left are parallels of altitude ; and those crossing siue complement of those latitudes.
them are azimuths. The lesser of the two circles Suppose, then, it be required to find the degrees of
bounding the projection, is one-fourth of the tropic of longitude contained in 83 of the lesser leagues in the
Capricorn; the greater is one-fourth of that of Cancer. parallel of 48°; lay the thread over 48° of latitude on
The two ecliptics are drawn from a point on the left the circumference, and count thence the 83 leagues on

4 D 2


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Fig. 4.

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