QUA 



QUA 



medicine will remove all kinds of com- 

 plaints. 



F.very medicine possesses active pro- 

 perties, or it does not. It' it be active, it 

 must be dangerous to apply it, indiscri- 

 minately, to persons of every age, and 

 without regard to their habits of living. 

 An active medicine, which might be very 

 useful in strengthening a debilitated con- 

 stitution, would be highly injurious if ex- 

 hibited in an acute rheumatism, or other 

 inflammatory disorder, and vice versa,- 

 consequently, an application of the same 

 remedy in all cases can hardly fail of be- 

 ing fatal in some. Should the medicine 

 be inactive, which happily is often the 

 case, it can be of no other utility than to 

 \vork upon the patient's imagination, and 

 amuse him while his pocket is picked. See 

 MEDICA.L DICT. 



QUADRANGLE, in geometry, the 

 same wiih a quadrilateral figure, or one 

 consisting of four sides and four angles. 

 To the class of quadrangles belong the 

 square, parallelogram, trapesium, rhom- 

 bus, and rhomboides. A square is a re- 

 gular quadrangle ; a trapesium an irregu- 

 lar 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 tak- 

 ing 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, gene- 

 rally ebony, mounted with ivory; but 

 such are subject to warp, which occasions 

 those made of brass to be preferred, for 

 very hot or very cold climates ; though 

 their expansion and contraction, under 

 various temperaments, 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 gene- 

 rally 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 ac- 

 tually measures two, while taking the ob- 

 servation, they do not receive their desig- 

 nation improperly. We have another de- 

 scription of this instrument, called the 

 sextant, which has 60 marked on its arch, 



and includes 120 in real measurement. 

 This is peculiarly calculated for the obser- 

 vation of various celestial bodies, so as to 

 ascertain their distances at any particular 

 moment : this often could not be effect- 

 ed by an instrument which embraced 

 only 90 ; whereas, we rarely find any 

 two planets suitable to the purposes of 

 navigation, at so great a distance 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 in- 

 stance, some difficulty may occur in suit- 

 ing 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- 

 servatiun. It may be called the " por- 

 table observatory." The first idea of this 

 machine 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 con- 

 siderably 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 error of one degree in the in- 

 dex makes two in the observation. 



Description of Hartleys Quadrant. (Fig. 

 1. Plate X11I. 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 parallel with the leg, A C ; 

 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 diminish the 

 lustre of the reflected planet. H and I, 

 the vanes, or sights. The arc, B C, is call- 

 ed 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 

 index is open, so as to show the grada- 

 tions on the arc : the lower edge is chanv 



