It E T 



It E T 



Aries to Taurus, from Taurus to Gemini, Sec. that is, from 

 weft to eaft, it is faid to be direct. 



When it appears for fome days in the fame point of the 

 heavens, it is laid to be ftationary. 



And when it goes in antecedentia, i. e. towards the ante- 

 cedent figns, or contrary to the order of the figns, via. from 

 eaft to weft ; it is faid to be retrograde. 



The fun and moon always appear direct. Herfehel, Sa- 

 turn, Jupiter, Mars, Venus, and Mercury, foinetimes 

 direct, fometimes ftationary, fometimes retrograde. 



The fuperior planets are retrograde about their oppofition 

 with the fun ; the inferior ones about their conjunction. 

 The intervals of time between two retrogradations of the 

 feveral planets are unequal. 



Thele changes of the courfes and motions of the planets 

 are not real, but only apparent : when viewed from the 

 centre of the fyftem, i. e. from the fun, they appear always 

 uniform and regular. The inequalities arile from the motion 

 and pofition of the earth from which they are viewed, and 

 are thus accounted for : 



Suppole PNO {Plate XIX. Aflronomy, fig. 12.) a por- 

 tion of the zodiac, ABCD the earth's orbit, and 

 E M G H Z the orbit of a fuperior planet, e.gr. Saturn ; 

 and fuppofe the earth in A, and Saturn in E, in which cafe 

 lie will appear in the zodiac at the point O. If now Saturn 

 remained without any motion, when the earth arrives at B, 

 he will be feen in the point of the zodiac L, and would ap- 

 pear to have defcribed the arc O L, and to have maved ac- 

 cording to the order of the figns from weft: to eaft. But 

 becaufe, while the earth is palling, from A to B, Saturn 

 likewise moves from E to M, where he is feen in conjunc- 

 tion with the fun, he will appear to have defcribed the arc 

 O Q greater than that O JL. In this ftate the planet is 

 direct, and its motion is from weft to eaft, or according to 

 the order of the figns. And its motion, now that it is in 

 conjunction with the fun, and molt remote from us, is 

 quicker than at any other time. 



The earth arriving in C, while Saturn defcribes the arc 

 M G, he will be obferved in the zodiac at R. But the 

 earth being advanced to K, and Saturn to H, fo that the 

 line K H, joining the earth and Saturn, be for fome time 

 parallel to itfelf, «r nearly fo, Saturn will be feen all that 

 time in the fame point of the zodiac at P, and with the fame 

 fixed ftars ; and is therefore at this time ftationary. 



But the earth being come to D, and Saturn arrived in 

 oppofition to the fun in Z, he will appear in the zodiac in 

 V, and will feem to have been retrograde, or to have gone 

 backwards through the arc P V. Thus the fuperior 

 planets, on optical confiderations, are always retrograde, 

 when in oppofition to the fun. 



The arc which the planet defcribes while thus retrograde, 

 is called the arc of retrogradalion. 



The arcs of retrogradatiou of the feveral planets are not 

 equal. That of Saturn is greater than that of Jupiter ; that 

 of Jupiter than that of Mars, &c. 



Retroghadation of the Nodes, is a motion of the line 

 of the nodes, by which it continually fliifts its fituation from 

 eaft to weft, contrary to the order of the figns ; completing 

 its retrograde circulation in the compafs of about nineteen 

 years : after which time, either of the nodes, having re- 

 ceded from any point of the ecliptic, returns to the fame 

 again. See Noiu 3. 



Retrogradation of the Sun. When the fun is in the 

 torrid zone, and has his declination AM {Plate XIX. 

 Ajlronomy, fig. 13.) greater than the latitude of the place 

 A Z, but either northern or fouthem as that is, the fun will 

 appear to go backwards, or to be retrograde both before 



and after noon. This can never happen, without the tro- 

 pics, in a natural way. 



For, draw the vertical circle Z G N to be a tangent to 

 the fun's diurnal circle in G, and another Z O N through 

 the fun's riling, in O, it is evident all the intermediate ver- 

 tical circles cut the fun's diurnal circle twice ; firft, in the 

 arc G O, and the fecond time in the arc G I. Wherefore, 

 as the lun afcends through the arc GO, it continually ar- 

 rives at farther and further verticals. But as it continues its 

 afcent through the arc G I, it returns to its former ver- 

 ticals ; and, therefore, is feen retrograde for fome time 

 before noon. The fame it may be flievvn, after the fame 

 manner, it does for fome time after noon. Hence, as the 

 lhadow always tends the oppofite way to that of the fun, 

 the fliadow will be retrograde twice every day in all places 

 of the torrid zone, where the fun's declination exceeds the 

 latitude. 



RetrOgr vpation, or RetrogreJJion, in the Higher Geo- 

 metry, is the fame with what we otherwife call contrary flexion. 

 See FLEXURE and INFLEXION. 



The general rule given by the marquis de l'Hopital, for 

 finding the point of reflection in curves whofe ordinates are 

 parallel, is the fame as that for finding the point of contrary 

 flexure, and confifts in taking the fecond fluxion of the or- 

 dinate of the curve, and fuppofing it nothing or infinite : 

 but this rule admits of many exceptions. See Maclaurin's 

 Flux. b. i. c. 9. and b. ii. c. 5. 



RETROGRADE, Retrogradus, formed from retro, 

 backwards, and gradior, I go, lomething that goes back- 

 wards, or in a direction contrary to the natural one. 



If the eye and the object both move the fame way, but 

 the eye much failer than the object, the object will appear 

 to be retrograde, i. e. to go back, or to advance the con- 

 trary way from what it really does. 



Hence it is that the planets, in fome parts of their orbits, 

 appear to be retrograde. 



Retrograde order, in matters of numeration, is when, 

 in lieu of accounting 1, z, 3, 4, we count 4, 3, 2, 1. 



Retrograde Verfes are fuch as give the fame words, 

 whether read backwards or forwards : called alfo reciprocal 

 •verfes, and recurrents. Such is 



" Signa te figna ; tcmere me tangis et angi6." 



RETROGRADO, Ital. in Muftc, a retrograde motio* 

 of a melody, or fubject of canon. This motion is fome- 

 times termed by the Italians, imitatione cancheriwtnte; imita- 

 tion of the movement of a crab-fifh. See Canon. 



RETROGRESSION, or Retrocession, the fame with 

 retrogradatiou. 



RETROMINGENTS,compoundedofrrrro,£jr/'7<W./, 

 and mingo, J male water, in Natural Hiflory, a clafs or di- 

 vifion of animals, whofe characterise is, that they ftale bark- 

 wards, both males and females. Such are lions, cats, &c« 



RETROPANNAGIUM, Retropannage, in our An- 

 cient 7. aw Boohs, after-pannage; or what is left when the 

 bealls have done, or eaten the belt. See Pannage. 



" Et debent habere rctropannagium a fefto Sancti Martini 

 ufque ad felt um Pur. Beats Marix." Petit, in Pari. temp. 

 Edw. III. 



RETROSPECT, a look or view backwards. See Rf- 

 1 no u 1 i\ r. 



RETROVERSIO UTERI, in Surgery. The womb is 

 fubjedt to two particular changes in the pofition of its fun- 

 dus, which may be difplaced either forwards or backward!. 

 The firft cafe, fometimes termed antcverfton, is the lead fre- 

 quent ; the fecond, or retroverfwn, is more often mat with. 

 In the initan.ee of anteverfion, when the furgcon makes aa 

 M 2 exaroina- 



