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E o M E T y.. 7-:> r
Wc h~\"c Ihus britfiy ~nd plainly lremd of furveyiog,
Qnd Ihown by whal inllrumeots il is pelformed; hav,on
l voldeJ Ihole melhods whieh dcpend on Ihe ma)!nelie
needle, nO! 0011' bce¿uCe ils direllioo 10. 1' vary indlÍferenl
plaees 01' a l;elJ (Ihe eonlrar)' of Ihis 01 Jc.1I dOlh nOI ap'
pm ,) bUI bee. ule Ihe quanl;'y of ao angle obCerved by II
c.onol be ' knuwo ; for ao error of ' wo or lhrce
degrtes can fearedy be avoided in lakiog angles by il.
As fur lhe remainiog paTl of furveying, wheleby lhe
area uf a ficld already laid down on paper is fonnd in
acres, roods, or . ny o,her fuperfieial mealures; Ihis lOe
leave lO lhe following fcaioo, whieh lrealS of Ihe men o
fural,on of furfaee!.
.. improvcd thradolite from M, G~r,lnrr's rrd~ie,' fllr.
" v"ying inrproved. See a figu le of il io Plalc XCV1.
" In ,his ioilrun¡eol. ,he lhree nalfs, by braf; fmils
" at top, rere\\' in,o bdl·me,.1 join". ,hat are mOI't.lrlc
" beln een b"Cs p.IIAIS, fiX,d in a n",n~ h,.ls ph,e; "'
" whieh, rouOlI theeenlre. iSI;xedaCockel wilh ab.11010".–
" al,l. in ji, aoJ upon " hieh lhe four Cere,"s prefs, thal fel
" ,he linlb ho,i zont. I: Nexl .bove is ano,her Cueh
" Ihrough \Vltieh ,he Caid (ere'vs p"fs, alld on whieh,
.. round ,he centre, i. fixed a frunnlll of a eone of btll.
"metal, \Vhole axis (belog connea ed wi,h Ihe een're ,,(
•• Ihe bell) is ahvays perpeod,cu lar 10 lhe limb, by mean~
" o( a r~rril litted 'o i" whereon I! r,.en
" Ihe eompafs box i ,nd on it ,he limb, \Vhich is a nrong
" bell-melal ring, u'hereon are moveable Ihrce braCs in•
" dcxes; in \VhuCe plate are fixed four brafs pillars•
" joining Jt top, hold the eeotre pio of the bell•
"melal double CeX'Jnl, wh,,(e double index is fi xed 00
.' the eenrre of Ihe Came pl.tle : Wi,hin ,he double (ex–
" laO! is fi xed the Cpiri, , and ol'e, it ,he tcleCcope.
.. I.lefidcs lhe innrumeots deferibed above, a f"r"YM
.. oughl tO be provided with an off fel lI ,ff equal in
.. leogth 'o len lioks of Ihe ehain . aod divided io,o len
.. e~u.1 pHlS. He oughl likewiCe 'o have leo arro,"s or
.. fmall I!raighl nieks oc", IWO fcel loog, Ihod wilh iron
.. fmils. Wheo Ihe is fir/I opeoed, il oaghl 10 be
.. examined nI' Ihe off·Cel naif. In mearuring .ny line,
•, Ihe leader of lhe ehain is 10 have Ihe len arrow! al firn
.. felliog OUI. When Ihe chain is nrelehed in Ihe line,
.. and Iheoear end lOuehes Ihe pldce fromwhieh you mea.
u Cure, Ihe ledder lIiek, one of Ihe leo arrows in Ihe
u ground, al Ihe far end of Ihe ehaio. Theo Ihe leader
u leaviog Ihe arrolV, procced! wilh Ihe another
u leoglh; and the ehain being nrelehed in Ihe line, Co
.. Ihal the near cnd lOuehes Ihe firn arrolV, Ihe leader
u nick. dowo anolher arrow al hi! cnd of Ihe ehain. The
.. line is preCerved nraighl, if Ihe arrows be always Cet
.. fo as to be iD a rigbl lioe wi,h Ihe place you meaCure
u from, and that 10 whieh you.are going. In tbis mano
.. ner they proeeed till Ihe leader have no more arrows.
.. At Ihe eleventh , Ihe arrows are 10 be earried 10
.. him again, and he is 10 lliek one of Ihem inlo lhe
.. ground, at IhM nd of Ihe ehain. And lhe Came is 10
.. be done al lhe 2l. 3l. 4l. oc. eh, ins, if Ihere are
.. Co many in a right line tO be meafu red. In this mano
.. oer you can hardly commil an error in numbering Ihe
.. ehains, unleCs of len ehaios at once.
" The olr·fet lldfl' Cerves for me.furing readily Ibe di.
.. llanees of any Ihin&, proper 10 be replefenled in you r
" plan, from Ihe nalion·line while you go along. The(e
"dillanees ought to be enlered inlo your field.book,
.. with Ihe correCpooding diaanees from Ihe lan nation,
" and proper rtmarks, thal ,you may be enabled 10 plol
.. Ihem junly, and be in 00 danger of millaki ng one for
u anolher when you eXlend your plan. The ficld·book
" mal' be conveniently divided inlo five eolumns. In
.. the middle eolumo Ihe aogles a' Ihe Ceveral nalions
" takeo by Ihe ,heodoli,e are tO be entered, wilh di·
.. l!once¡ from ,he lIaliona. 11,edilld nees taken by lhe
.. off· fe, on eilher fide oflile n,tion·line, are tObe
.. entered into eolumns on ei,hel fide o( Ihe middle eo·
.. lumo, aeeordiog tO Iheir pofition wi,h refpea 10 that
.. /tne. 1 he names and enaraélers of the objeél., wiln
" proper rcmark!, mal' be eOler<d io eolumns on either
.. lide o( Ihefe la(l.
u Bmufe. i~ ,he pl~ee of Ihe graphomeler defcribes
" by OUr author, furveyors nolV ufe of Ihe Iheodo·
u li'e. we n,.1I Cubjoin a de(eriptionof Mr Silfon's laten
VOL. II. No. 55. 2
" The eompa(s box is grave'! witll I\VO diamoncls for
" nonh and Cou,h, and 1V\l1r 20 dccrecs on bOlh fides
" of eaeh, lhal ,he needle may be (e' 10 lhe varialion,
" and i,s error , Ifo known.
" T he I,mb has ,woJI,ur/ d, luCt againn lhe diamonds
" in Ihe box, inllead of teO ead,; and is euriouny di.
" vided inlo whole degrees, and nu¡nbered 10 Ihe left
" hanu al every len 10 IlViee 180, having Ihree indexes
" dillanl t20, (with Nonius's dlvifions on eaeh for Ihe
" decimal. of' a degree), Ihal are moved by ~ pinion fix–
.. ed below one of Ihem, WilhoUl moving Ihe limb i and
" in an01her is a terew and fpring under, to fix ic to ~y
" par! of Ihe limb. It has alCo divifions numbcred, '(or
u taking lhe quaner gin in inehes of round timber al the
u middle heigh', when nanding ten fee! horizontally
u dinaO! from il! centre; whieh at 20 mun be doubled,
u and at 30 lripled ; to whieh a Ihor,er index is ufed,
u having Noniu,'s divifions for ,he decimal! of ao ineh ;
u but an abatement mun be made for Ihe bark, if nOI la•
.. ken off.
u T he double fextant is divided on one fi"e from un.
u der ils centre (when Ihe fporil lube and lele(eope are
u levd ) tOabove 60 degrees eaeh way, , nd numhered at
u lO, 20, be. and Ihe double index (Ih rough whieh it
" is move, hle) n.ews 00 Ihe Came fide ,he degree ~nd de•
"cimal of any allitude or depreflj, n to thJt exteot
.. by Nonius's divifions , On the o,her fide are divifions
u Dumbered, fo r t,king Ihe uprighl heighl of limber, 6(.
u iD feet, when dillant 10 fcel ; whieh at 20 mun be
u doubled, and at 30 tripled; aod ,1(0 the quan,ities for
.. rcdueing hypolhenufal "n~ 10 horizonl.r1 lt is
" moveable by a pinion fixcd in ,he double indexo
.. The teltfcope is a lude n,o"er Ih.n the diameter
u of th( lio,b, Ihdt a fdll mal' no' hun il i yel il wil!
u magnify as much,' ao¡llhcw a dilldnt obj:a as .perfea,
.. as mon erf triple i" length. In its f..rus are \'ery fine
u eroCs IVires, whofe inltrCeaion is in ,he plane of Ihe
u double Cex"nt; and ,hi, was a IVh"le árde, and turno
u ed in a I.,he 10a Irue plane, aod I! lixed al right angle.
.. 10 Ihe limb ; ro ,hat, whenevtr Ihe limb i, Cel honzon–
.. tal, (wh,eh is m Jily done by m.,kin~ the Cpiril'lube
t 7O ".1 vtl