QUA                           ( A
tife of the Coiwmo, or &ureying QVADVtANT.
x. 71o take the ieight, or Depth of an Objefd, with the
fixed Sights and Plummet-Place the Puadrant vertical-
ly, and the Eye under the Sight next the Arch of the Qua-
drant: Thus dire& the Infirument to the Obje&, v. gr.
the Top of a Tower, till the vifual Rays thereof firike
thro' the Sights upon the Eye.
This done, the Portion of the Arch intercepted between
the Thread and the Semidiameter, whereon the Sights are
fiften'd, Thew the Complement of the Obje&E's Height a-
bove the Horizon, or its Diflance from the Zenith; and the
other Portion of the Arch intercepted between the Thread
and the other Semidiameter, lhews the Height itfelf of the
Objeeit above the Horizon.
The fame Arch likewife gives the Quantity of the Angle
made by the vifual Ray, and a horizontal Line parallel to
the; Bafe of the Tower.
Note, to obferve Depths, the Eye muft be placed over
that Sight next the Centre of the Qi:adrant.
From the Height, or Depth of the Object, in Degrees
thus found, which fuppofe 35f, 3S', and the Diflance of
the foot of the Objea from the place of Obfervation care-
fully meafur'd, which fiuppofe 47 Foot; its Height or Depth
in F eet,Yards,&c. is eafily determin'd by the moil common
Cafe in Trigonometry. See TRIANGLE.
For we have here, in a Triangle, one Side given, viz. the
Line meafured; and we have all the Angles: for that of
the Tower is always fuppofed a right Angle, the other two
therefore are equal to another right Angle ; but the Angle
obferved is 35Q, 35'; therefore the other is 540, 25'.  See
ANGLE.
The Cafe then will be reduced to this; as the Sine of
54, 2 5', is to 47 Feet; fo is the Sine of 35", 35', to a 4th
Term, viZ. 33 2 Feet: to which add the Height of the
Obferver's Eye, fuppofed 5 Foot, the Sum 33 T Feet, is
the Height of the Tower required.
2. 7ihe further Ufe of the Quadrant in taking of Atlti-
tudes of ObjeWs, both acceffible and inacceffible; fee under
the Article ALTITUDE.
3. Ufe of the Quadrant in taking Heights and Difjances
by the Index and Sights.-To take, e.gr. a Heighr, as
that of a Tower, whofe Bafe is accefi'ole-Place the
Plane of the Inflrument at right Angles to the Plane of the
Horizon, and one of its Edges parallel thereto, by means
of the Plummet, which in that cafe will hang down along
the other-In this Situation turn the Index, till thro' the
Sight you fee the top of the Tower; and the Arch of the
Limb of the Qijadrant between that fide thereof parallel
to the Horizon, and the Index, will be the Height of the
Tower in degrees: whence, and from the Diflance mea-
fured as before, its Height in Feet, Wc. may be found by
Calculation, as in the former Cafee; or without Calculation,
by drawing, from the Data, on Paper, a Triangle fimilar
to the great one, whofe Bafe is the Diflance, and its Per-
pendicular meafured on the Scale, the Height of the Tower.
See SCALE.
4. Ufe of the Quadrant in meafuring horizontal Dif-
tances-Tho the Puadrant be a lefs proper Infirument
for this purpofe than a Theodolite, Semicircle, or the like,
by reafou Angles greater than Qucadrants cannot be taken
hereby; yet Neceffity fomertimes obliges Perfons to have
recourfe to it.
The Manner of its Application herein is the fame with
that of the Semicircle; all the difference between the two
Infiruments confiffing in this, that the one is an Arch of
ISo0, and can therefore take an Angle of any Quantity;
and the other only an Arch of So", and therefore confined
to Angles of that Quantity. See, therefore, SEMI-cRi.
CLE.
afironomical QUADRAN T, is a large Quadrant, ufually
made of Brafs, fometimes of wooden Bars, only faced with
Plates of Iron, or the like; having its Limb curioufly di-
vided, diagonally or otherwife, into Degrees and Minutes,
and even Seconds, if poflible; with plain Sights fixed to
one fide of it, or inflead thereof, a Telefcope 3 and an In-
dex moving about the Centre, carrying either plain Sights,
dr a Telefcope.
Thefe QPadrants are of principal ufe in taking Obferva-
tions of the Sun, Planets, or fixed Stars. See OBSERVA-
TION.
The Antients ufed only plain Sights, but the Moderns
have found it of great benefit to ufe Telefcopes inflead of
them. See Stot and TELESCOPE.
Add, that the Contrivance of moving the Index, by the
help of a Screw on the Edge of the Limb, and of readily
and eafidy dire~ing it, and the PQUadrant upon its Pedeffal,
to ay defired Phlenomeron, by means of the Screws and
dented Wheels, is a fill greater Improvement of the In-
flrument.
The Particulars of the Mechanifm whereby this is effec-


4 )                  QUVA
ted, would Afford a very dry and intricate, as well as ure-
lefs Detail 3 which we flhall omit, as being fuifilcientd
known among the Infirument-Makers: And in lieu thereof,
content ourfelves with giving a Figure or Reprefentation,
(Tab. ASTRONOMY, fig. 53.)
The Ufe of this Infirurnent is obvious-Being adjufled
as above, and turned horizontally round on its Axis, till
thro' the moveable Telefcope the Obje&t be feen to' fall
in with the Point of Interfeffion of the crofs Bars, the De-
grees cut by the Index give the Altitude requir'd. See
TELESCOPE.
ThefIorodifical QUADRANTr, Is a pretty, commodious
Infirument, thus call'd from its Ufe in telling the Hour of
the -Day;5 whi ch is its only Ufe.
Its Confilruafion is fo fimple and eafy, and its Application
fo ready, that we Shall defcribe both, for the Ufe of fome
who may want other Conveniencies.
Conftru fion and Ufe of the lorodifical QUADR ANT.
From the Centre of the ,uadrant C, (Tab. ASTRONO-
MY, Fig. 54.) whofe Limb A B is divided into 900 3 de.
fcribe feven concentric Circles at Intervals at plealiure;
and to thefe add the Signs of the Zodiac in the Order they
ar=erefented in the Scheme. 2. Applying a'Ruler to the
Centre C, and the Limb A B, mark upon the feveral Pa-
rallels the Degrees corresponding to the Altitude of the Sun
when therein, for the given Hours;5 conne&l the Points be-
longing to the fame 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 Qujadran~t C, tic
a Thread with a Plummet, and upon the Thread a Bead to
flide.
If now the Bead be brought to the Parallel wherein the
Sun is, and the Quadrant direfled to the Sur7 till a vifual
Ray pafs thro' the Sights, the Bead will fhew the Hour.
For the Plummet in this fituation cuts all the Parallels in
the Degrees correfponding to the Sun's Altitude: Since,
then, the Bead is in the Paralle1l which the'Sun ther, de-
fcribes, and thro' the Degrees of Ab-itude to which the Sun
is elevated every Hour, there pafs hour-Lines i the Bead
muft lhew the prefent Hour-Some Pcrfons who are not
mighty nice, reprefent the Hour-Lines by Arches of Circles,
or even by ftraight Lines; and that without any fenfible
Error.
Gunter's QU ADR ANT, is a kind of Xuadrant (represented
Tab. ASTRONOMY, Fig. 55.) invented by our Countryman
Edm. Gunter.
This, befide the graduated Limb, fixed Sights, and a
Plummet, as the other Quadrants; has, likewife, a Ste-
reographical Projecfion of the Sphere on the Plane of the
Meridian, with the Eye placed in one of the Poles; by
which, befides the common Ufes of other ktaadrants, fe-
veral ufeful Queflions in Aftronomy, F!c. are eafily folved.
Ufe of Gunter's5UADRAINT.
I. 7 find the Sun's Meridian Altitude for any giveen
Day; or the D.ay of the Monthfor any given Meridian All-
titude-Lay the Thread to the Day of the Month in the
Scale next the Limb; the Degree it cuts in the Limb is
the Sun's Meridian Altitude.
Thus, the Thread being laid on the I 5th of A