QUA 
surd ; much more ridiculous is it then to 
suppose, that any medicine will remove all 
kinds of complaints. 
Every medicine possesses active proper- 
ties, or it does not. If it be active, it must 
be dangerous to apply it, indiscriminately, 
to persons of every age, and without regard 
to their habits of living. An active medi- 
cine, which might be very useful in strength- 
ening a debilitated constitution, would be 
highly injurious if exhibited in an acute rheu- 
matism, or other inflammatory disorder, and 
vice versa ; consequently, an application of 
the same remedy in all cases can hardly fail 
of being fatal in some. Should the medi- 
cine be inactive, which happily is often the 
case, it can be of no other utility than to 
work upon the patient’s imagination, and 
amuse him while his pocket is picked. See 
Medical Dict. 
QUADRANGLE, in geometry, the same 
with a quadrilateral figure, or one consisting 
of four sides and four angles. To the class 
of quadrangles belong the square, parallelo- 
gram, trapesium, rhombus, and rhomboides. 
A square is a regular quadrangle ; a trape- 
sium an irregular one. 
QUADRANS, the quarter or fourth 
part of any thing, particularly the as, or 
pound. 
QUADRANT, denotes a mathematical 
instrument, of great service in astronomy, 
and, consequently, in navigation, for taking 
the altitudes of the sun and stars ; as also 
for taking angles in surveying. Those 
chiefly in use, are Adams’s, Cole’s, Gun- 
ter’s, Hadley’s, Sutton’s, or Collins’s, the 
horodictical, the sinical, the astronomical, 
and the common surveying quadrant. Many 
of these are made of wood, generally ebo- 
ny, mounted with ivory ; but such are sub- 
ject to warp, which occasions tliose made 
of brass to be preferred for very hot or 
very cold climates ; though their expansion 
and contraction, under various tempera- 
ments, is some drawback on their merits ; 
however, that being the lesser evil, and 
scarcely ever amounting to more than two 
or three seconds in the whole arch of the 
quadrant, cannot be considered as any great 
defect. 
Although these instruments are generally 
termed quadrants, they are, in truth, but 
octants, since they occupy but one-eighth of 
a circumference ; but as each of the 45", 
they contain on the arch, actually measures 
two, while taking the observation, they do 
not receive their designation improperly. 
We have another description of this instru- 
ment, called the sextant, which has 60° 
QUA 
marked on its arch, and includes 120" in 
real measurement. This is peculiarly cal- 
culated for the observation of various celes- 
tial bodies, so as to ascertain their distances 
at any particular moment : this often 
could not be effected by an instrument 
which embraced only 90° ; whereas we 
rarely find any two planets suitable to the 
purposes of navigation, at so great a dis- 
tance as 120°. 
The manner in which the quadrant is 
held, relieves it from the effect of the ves- 
sel’s motion ; although, in the first instance, 
some difficulty may occur in suiting the 
body to the rolling, or pitching, of a vessel ; 
yet, in a very short time the operator will 
become so habituated, as to overcome that 
trifling impediment. 
Hadley’s quadrant (or his sextant) is the 
only instrument, hitherto known, on which 
the mariner can depend for a correct ob- 
servation. It may be called the “ portable 
observatory.” The first idea of this ma- 
chine originated with the celebrated Dr. 
Hooke ; it was completed by Sir Isaac 
Newton, and first offered to the public by 
Mr. Hadley : however, it has undergone 
many changes since that time. The great 
perfection it exhibits, with respect to the 
accuracy of the angles it defines, is consi- 
derably enhanced by the facility with which 
it may be rectified ; so that errors may be 
avoided : a matter of supreme importance, 
when we consider the rough usage to which 
the instrument is subject ; and, that an er- 
ror of one degree in the index makes two 
in the observation. 
Description of Hadley’sQuadrant. (Fig. 1, 
Plate XIII. Miscel.) shows the quadrant, as 
usually constructed. The following parts 
compose the instrument. B C, the arc of 
45° : A D, the index, moving on a pivot, 
under the centre of the index-glass, E : 
which glass is in the exact direction of the 
index, and stands at right angles upon it. 
F, the fore-horizon-glass, which receives 
the reflection from the index-glass. G, the 
back-horizon-glass. The former stands pa- 
rallel with the leg, AC; the latter at right 
angles thereto. K is a pivot, on which 
three dark glasses, or screens, move, so that 
any one, or more, may be placed between 
the index-glass and the horizon-glass, to di- 
minish the lustre of the reflected planet. 
H and I, the vanes, or sights. The arc, 
B C, is called the limb, or quadrantal arc ; 
what is beyond 0, is the arc of excess : the 
residue of the arc usually is graduated up as 
far as 100°. 
A large portion of the lower part of the 
