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The Canterbury Tales and Other Works of Chaucer (Middle English), by Geoffery Chaucer, [14th cent.], at

A Treatise on the Astrolabe

Part 1

 Lyte Lowys my sone, I aperceyve wel by certeyne
 evydences thyn abilite to lerne sciences
 touching nombres and proporciouns; and as wel
 considre I thy besy praier in special to lerne the
 tretys of the Astrelabie. Than for as moche as a
 philosofre saith, "he wrappith him in his frend,
 that condescendith to the rightfulle praiers of his
 frend," therfore have I yeven the a suffisant Astrolabie
 as for oure orizonte, compowned
10 after the latitude of Oxenforde; upon
 which, by mediacioun of this litel tretys, I
 purpose to teche the a certein nombre of conclusions
 aperteynyng to the same instrument. I
 seie a certein of conclusions, for thre causes. The
 first cause is this: truste wel that alle the conclusions
 that han be founde, or ellys possibly
 might be founde in so noble an instrument as is
 an Astrelabie ben unknowe parfitly to eny mortal
 man in this regioun, as I suppose. Another
20 cause is this, that sothly in any tretis of the
 Astrelabie that I have seyn, there be somme
 conclusions that wol not in alle thinges parformen
 her bihestes; and somme of hem ben to
 harde to thy tendir age of ten yeer to conceyve.
 This tretis, divided in 5 parties, wol I shewe
 the under full light reules and naked wordes in
 Englissh, for Latyn canst thou yit but small,
 my litel sone. But natheles suffise to the these
 trewe conclusions in Englissh as wel as sufficith
30 to these noble clerkes Grekes these
 same conclusions in Grek; and to Arabiens
 in Arabik, and to Jewes in Ebrew, and to
 Latyn folk in Latyn; whiche Latyn folk had
 hem first out of othere dyverse langages, and
 writen hem in her owne tunge, that is to seyn,
 in Latyn. And God woot that in alle these
 langages and in many moo han these conclusions
 ben suffisantly lerned and taught, and yit
 by diverse reules; right as diverse pathes
40 leden diverse folk the righte way to Rome.
 Now wol I preie mekely every discret persone
 that redith or herith this litel tretys to have
 my rude endityng for excusid, and my superfluite
 of wordes, for two causes. The firste cause
 is for that curious endityng and hard sentence
 is ful hevy at onys for such a child to lerne.
 And the secunde cause is this, that sothly me
 semith better to writen unto a child twyes a
 god sentence, than he forgete it onys.
50 And Lowys, yf so be that I shewe the in
 my lighte Englissh as trewe conclusions
 touching this mater, and not oonly as trewe
 but as many and as subtile conclusiouns, as
 ben shewid in Latyn in eny commune tretys
 of the Astrelabie, konne me the more thank.
 And preie God save the king, that is lord of
 this langage, and alle that him feith berith and
 obeieth, everich in his degre, the more and
 the lasse. But considre wel that I ne usurpe
60 not to have founden this werk of my labour
 or of myn engyn. I n' am but a lewd compilator
 of the labour of olde astrologiens, and have it
 translatid in myn Englissh oonly for thy doctrine.
 And with this swerd shal I sleen envie.
 Prima pars. -- The firste partie of this tretys
 shal reherse the figures and the membres of
 thyn Astrelabie by cause that thou shalt have
 the gretter knowing of thyn oune instrument.
 Secunda pars. -- The secunde partie
70 shal techen the worken the verrey practik
 of the forseide conclusiouns, as ferforth and
 as narwe as may be shewed in so small an
 instrument portatif aboute. For wel woot
 every astrologien that smallist fraccions ne
 wol not be shewid in so small an instrument as
 in subtile tables calculed for a cause.
 Tertia pars. -- The thirde partie shal contene
 diverse tables of longitudes and latitudes
 of sterres fixe for the Astrelabie, and tables
80 of the declinacions of the sonne, and tables
 of longitudes of citees and townes; and
 tables as well for the governaunce of a clokke, as
 for to fynde the altitude meridian; and many anothir
 notable conclusioun after the kalenders
 of the reverent clerkes, Frere J. Somer and
 Frere N. Lenne.
 Quarta pars. -- The fourthe partie shal ben
 a theorike to declare the moevyng of the celestiall
 bodies with the causes. The whiche
90 fourthe partie in speciall shal shewen a
 table of the verrey moeving of the mone
 from houre to houre every day and in every
 signe after thyn almenak. Upon which table
 there folewith a canoun suffisant to teche as
 wel the manere of the worchynge of the same
 conclusioun as to knowe in oure orizonte with
 which degre of the zodiak that the mone arisith
 in any latitude, and the arisyng of any planete
 after his latitude fro the ecliptik lyne.
100 Quinta pars. -- The fifthe partie shal
 be an introductorie, after the statutes of
 oure doctours, in which thou maist lerne a gret
 part of the generall rewles of theorik in astrologie.
 In which fifthe partie shalt thou fynden
 tables of equaciouns of houses after the latitude of
 Oxenforde; and tables of dignitees of planetes,
 and othere notefull thinges, yf God wol vouche
 saaf and his Moder the Maide, moo then I behete.
 Thyn Astrolabie hath a ring to putten on
 the thombe of thi right hond in taking the
 height of thinges. And tak kep, for from henes
 forthward I wol clepen the heighte of any thing
 that is taken by the rewle "the altitude," withoute
 moo wordes.
 This ryng renneth in a maner toret fast
 to the moder of thyn Astrelabie in so rowme a
 space that it distourbith not the instrument to
 hangen after his right centre.
 The moder of thin Astrelabye is thikkest
 plate, perced with a large hool, that resceiveth
in hir wombe the thynne plates compowned
 for diverse clymates, and thy reet shapen in
 manere of a nett or of a web of a loppe.
 This moder is dividid on the bakhalf with
 a lyne that cometh descending fro the ring
 doun to the netherist bordure. The whiche
 lyne, fro the forseide ring unto the centre of
 the large hool amidde, is clepid the south lyne,
 or ellis the lyne meridional. And the remenaunt
 of this lyne doun to the bordure is
 clepid the north lyne, or ellis the lyne of midnyght.
 Overthwart this forseide longe lyne ther
 crossith him another lyne of the same lengthe
 from eest to west. Of the whiche lyne, from
 a litel cros (+) in the bordure unto the centre
 of the large hool, is clepid the est lyne, or
 ellis the lyne orientale. And the remenaunt of
 this lyne, fro the forseide centre unto the bordure,
 is clepid the west lyne, or ellis the lyne
 occidentale. Now hast thou here the foure
10 quarters of thin Astrolabie divided after the
 foure principales plages or quarters of the firmament.
 The est syde of thyn Astrolabie is clepid
 the right syde, and the west syde is clepid the
 left syde. Forget not thys, litel Lowys. Put
 the ryng of thyn Astrolabie upon the thombe
 of thi right hond, and than wol his right side
 be toward thi lift side, and his left side wol be
 toward thy right side. Tak this rewle generall,
 as wel on the bak as on the wombe syde. Upon
 the ende of this est lyne, as I first seide, is
10 marked a litel cros (+), where as evere
 moo generaly is considerid the entring of
 the first degre in which the sonne arisith.
 Fro this litel cros (+) up to the ende
 of the lyne meridionall, under the ryng, shalt
 thou fynden the bordure divided with 90 degrees;
 and by that same proporcioun is every
 quarter of thin Astrolabie divided. Over the
 whiche degrees there ben noumbres of augrym
 that dividen thilke same degres fro 5 to 5, as
 shewith by longe strikes bitwene. Of whiche
 longe strikes the space bitwene contenith
10 a myle wey, and every degre of the bordure
 conteneth 4 minutes; this is to seien,
 mynutes of an houre.
 Under the compas of thilke degrees ben
 writen the names of the 12 Signes: as
 Aries, Taurus, Gemini, Cancer, Leo, Virgo,
 Libra, Scorpio, Sagittarius, Capricornus, Aquarius,
 Piscis. And the nombres of the degrees of
 thoo signes be writen in augrym above, and
 with longe divisiouns fro 5 to 5, dyvidid fro
 the tyme that the signe entrith unto the last
 ende. But understond wel that these degres
10 of signes ben everich of hem considred
 of 60 mynutes, and every mynute of
 60 secundes, and so furth into smale fraccions
 infinite, as saith Alkabucius. And therfore
 knowe wel that a degre of the bordure contenith
 4 minutes, and a degre of a signe conteneth
 60 minutes, and have this in mynde.
 Next this folewith the cercle of the daies,
 that ben figured in manere of degres, that contenen
 in nombre 365, dividid also with longe
 strikes fro 5 to 5, and the nombre in augrym
 writen under that cercle.
 Next the cercle of the daies folewith the
 cercle of the names of the monthes, that is to
 say, Januarius, Februarius, Marcius, Aprilis,
 Maius, Junius, Julius, Augustus, September,
 October, November, December. The names
 of these monthes were clepid somme for
 her propirtees and somme by statutes of
 Arabiens, somme by othre lordes of Rome.
 Eke of these monthes, as liked to Julius
10 Cesar and to Cesar Augustus, somme were
 compouned of diverse nombres of daies, as
 Julie and August. Than hath Januarie 31 daies,
 Februarie 28, March 31, Aprill 30, May 31,
 Junius 30, Julius 31, Augustus 31, Septembre
 30, Octobre 31, Novembre 30, Decembre 31.
 Natheles, all though that Julius Cesar toke 2
 daies out of Feverer and putte hem in his
 month of Juyll, and Augustus Cesar clepid the
 month of August after his name and ordeined
20 it of 31 daies, yit truste wel that the
 sonne dwellith therfore nevere the more
 ne lasse in oon signe than in another.
 Than folewen the names of the holy
 daies in the Kalender, and next hem the lettres
 of the A B C on whiche thei fallen.
 Next the forseide cercle of the A B C,
 under the cross lyne, is marked the skale in
 manere of 2 squyres, or ellis in manere of laddres,
 that serveth by his 12 pointes and his
 dyvisiouns of ful many a subtil conclusioun.
 Of this forseide skale fro the cross lyne unto
 the verrey angle is clepid Umbra Versa, and
 the nethir partie is clepid Umbra Recta, or
 ellis Umbra Extensa.
 Than hast thou a brod reule, that hath
 on either ende a square plate perced with certein
 holes, somme more and somme lasse, to
 resceyve the stremes of the sonne by day, and
 eke by mediacioun of thin eye to knowe the
 altitude of sterres by night.
 Than is there a large pyn in manere of
 an extre, that goth thorugh the hole that halt
 the tables of the clymates and the riet in the
 wombe of the moder; thorugh which pyn ther
 goth a litel wegge, which that is clepid the
 hors, that streynith all these parties to-hepe.
 Thys forseide grete pyn in manere of an extre
 is ymagyned to be the Pool Artik in thyn
 The wombe syde of thyn Astrelabie is
 also divided with a longe cros in 4 quarters
 from est to west, fro southe to northe, fro
 right syde to left side, as is the bakside.
 The bordure of which wombe side is
 divided fro the point of the est lyne unto the
 point of the south lyne under the ring, in 90
 degrees; and by that same proporcioun is every
 quarter divided, as is the bakside. That
 amountith 360 degrees. And understond wel
 that degres of this bordure ben aunswering and
 consentrike to the degrees of the equinoxiall,
 that is dividid in the same nombre as every
10 othir cercle is in the highe hevene. This
 same bordure is divided also with 23
 lettres capitals and a small cross (+) above
 the south lyne, that shewith the 24 houres
 equals of the clokke. And, as I have seid, 5
 of these degres maken a myle wey, and 3 mile-wei
 maken an houre. And every degre of thys
 bordure contenith 4 minutes, and every minute
 60 secundes. Now have I told the twyes.
 The plate under the riet is discrived
 with 3 cercles, of whiche the leest is
 clepid the cercle of Cancre by cause that the
 heved of Cancre turnith evermo consentrik
 upon the same cercle. In this heved
 of Cancer is the grettist declinacioun northward
 of the sonne, and therfore is he clepid
 solsticium of somer; which declinacioun, after
 Ptholome, is 23 degrees and 50 minutes as
10 wel in Cancer as in Capricorn. This signe
 of Cancer is clepid the tropik of somer, of
 tropos, that is to seien "ageynward." For than
 beginneth the sonne to passen from us-ward.
 The myddel cercle in wydnesse, of these 3,
 is clepid the cercle equinoxiall, upon which
 turnith evermo the hevedes of Aries and Libra.
 And understond wel that evermo thys cercle
 equinoxiall turnith justly from verrey est to verrey
 west as I have shewed the in the speer
20 solide. This same cercle is clepid also
 Equator, that is the weyer of the day; for
 whan the sonne is in the hevedes of Aries and
 Libra, than ben the dayes and the nightes ylike
 of lengthe in all the world. And therfore ben
 these 2 signes called the equinoxiis. And all
 that moeveth withinne the hevedes of these
 Aries and Libra, his moevyng is clepid northward;
 and all that moevith withoute these
 hevedes, his moevyng is clepid southward,
30 as fro the equinoxiall. Tak kep of these
 latitudes north and south, and forget it nat.
 By this cercle equinoxiall ben considred the
 24 houres of the clokke; for evermo the arisyng
 of 15 degrees of the equinoxiall makith an
 houre equal of the clokke. This equinoxiall is
 clepid the gurdel of the first moeving, or ellis
 of the firste moevable. And note that the firste
 moevyng is clepid moevyng of the firste moevable
 of the 8 speer, which moeving is from
40 est to west, and eft ageyn into est. Also
 it is clepid girdel of the firste moeving for it
 departith the firste moevable, that is to seyn
 the spere, in two like partyes evene distantz
 fro the poles of this world.
 The widest of these 3 principale cercles is
 clepid the cercle of Capricorne, by cause that
 the heved of Capricorne turneth evermo consentrik
 upon the same cercle. In the heved of
 this forseide Capricorne is the grettist declinacioun
50 southward of the sonne, and therfore
 it is clepid the solsticium of wynter.
 This signe of Capricorne is also clepid the
 tropic of wynter, for than begynneth the sonne
 to come ageyn to us-ward.
 Upon this forseide plate ben compassed
 certeyn cercles that highten almycanteras, of
 whiche somme of hem semen parfit cercles and
 somme semen inparfit. The centre that stondith
 amyddes the narwest cercle is clepid the
 cenyth. And the netherist cercle, or the firste
 cercle, is clepid the orizonte, that is to seyn,
 the cercle that divideth the two emysperies,
 that is, the partie of the hevene above the
10 erthe and the partie bynethe. These almykanteras
 ben compowned by 2 and 2, all
 be it so that on diverse Astrelabies somme
 almykanteras ben divided by oon, and somme
 by two, and somme by thre, after the quantite
 of the Astrelabie. This forseide cenyth is
 ymagined to ben the verrey point over the
 crowne of thin heved. And also this cenyth
 is the verray pool of the orizonte in every regioun.
 From this cenyth, as it semeth, there
 comen a maner croked strikes like to the clawes
 of a loppe, or elles like the werk of a wommans
 calle, in kervyng overthwart the almykanteras.
 And these same strikes or divisiouns
 ben clepid azimutz, and thei dividen the orisounte
 of thin Astrelabie in 24 divisiouns. And
 these azymutz serven to knowe the costes of
 the firmament, and to othre conclusions, as
10 for to knowe the cenyth of the sonne and
 of every sterre.
 Next these azymutz, under the cercle
 of Cancer, ben there 12 divisiouns embelif,
 muche like to the shap of the azemutz, that
 shewen the spaces of the houres of planetes.
 The riet of thin Astrelabie with thy zodiak,
 shapen in manere of a net or of a lopweb
 after the olde descripcioun, which thou maist
 turnen up and doun as thiself liketh, contenith
 certein nombre of sterres fixes, with her longitudes
 and latitudes determinat, yf so be that the
 maker have not errid. The names of the sterres
 ben writen in the margyn of the riet there as thei
 sitte, of whiche sterres the smale point is
10 clepid the centre. And understond also that
 alle the sterres sitting within the zodiak of
 thin Astrelabie ben clepid sterres of the north,
 for thei arise by northe the est lyne. And all the
 remenaunt fixed oute of the zodiak ben clepid
 sterres of the south. But I seie not that thei arisen
 alle by southe the est lyne; witnesse on Aldeberan
 and Algomeysa. Generaly understond this
 rewle, that thilke sterres that ben clepid sterres
 of the north arisen rather than the degre of
20 her longitude, and alle the sterres of the
 south arisen after the degre of her longitude --
 this is to seyn, sterres fixed in thyn
 Astrelabie. The mesure of this longitude of
 sterres is taken in the lyne ecliptik of hevene,
 under which lyne, whan that the sonne and the
 mone be lyne-right, or ellis in the superficie of
 this lyne, than is the eclipse of the sonne or of
 the mone, as I shal declare, and eke the cause
 why. But sothly the ecliptik lyne of thy
30 zodiak is the utterist bordure of thy zodiak
 there the degrees be marked.
 Thy zodiak of thin Astrelabie is shapen as
 a compas which that contenith a large brede
 as after the quantite of thyn Astrelabie, in ensample
 that the zodiak in hevene is ymagyned
 to ben a superfice contenyng a latitude of 12
 degrees, whereas alle the remenaunt of cercles
 in the hevene ben ymagyned verrey lynes withoute
 eny latitude. Amiddes this celestial
40 zodiak is ymagined a lyne which that is
 clepid the ecliptik lyne, under which lyne
 is evermo the wey of the sonne. Thus ben
 there 6 degres of the zodiak on that oo syde
 of the lyne and 6 degrees on that othir. This
 zodiak is dividid in 12 principale divisiouns that
 departen the 12 signes, and, for the streitnesse
 of thin Astrolabie, than is every smal divisioun
 in a signe departed by two degrees and two, I
 mene degrees contenyng 60 mynutes. And
50 this forseide hevenysshe zodiak is clepid
 the cercle of the signes, or the cercle of the
 bestes, for "zodia" in langage of Grek sowneth
 "bestes" in Latyn tunge. And in the zodiak
 ben the 12 signes that han names of bestes,
 or ellis for whan the sonne entrith in eny
 of tho signes he takith the propirte of suche
 bestes, or ellis for that the sterres that ben
 ther fixed ben disposid in signes of bestes or
 shape like bestes, or elles whan the planetes
60 ben under thilke signes thei causen us by
 her influence operaciouns and effectes like
 to the operaciouns of bestes.
 And understond also that whan an hot planete
 cometh into an hot signe, than encrescith
 his hete; and yf a planete be cold, than amenusith
 his coldnesse by cause of the hoote sygne.
 And by thys conclusioun maist thou take ensample
 in alle the signes, be thei moist or drie,
 or moeble or fixe, reknyng the qualite of the
70 planete as I first seide. And everich of
 these 12 signes hath respect to a certeyn
 parcel of the body of a man, and hath it in
 governaunce; as Aries hath thin heved, and
 Taurus thy nekke and thy throte, Gemini thin
 armholes and thin armes, and so furth, as shall
 be shewid more pleyn in the 5 partie of this
 This zodiak, which that is part of the 8 speer,
 over-kervith the equinoxial, and he over-kervith
80 him ageyn in evene parties; and
 that oo half declineth southward; and that
 othir northward, as pleinly declarith the Tretys
 of the Speer.
 Than hast thou a label that is shapen like
 a reule, save that it is streit and hath no plates
 on either ende with holes. But with the smale
 point of the forseide label shalt thou calcule
 thin equaciouns in the bordure of thin Astralabie,
 as by thin almury.
90 Thin almury is clepid the denticle of
 Capricorne, or ellis the calculer. This same
 almury sitt fix in the heved of Capricorne, and
 it serveth of many a necessarie conclusioun in
 equacions of thinges as shal be shewid.

Next: Part 2