THEODOLITE. 



'' Having faid fo much iclalivc to the means of applying 

 live theodolite moft beneficially, I fliall now explain an 

 example of each of the methods I have alluded to ; in doing 

 which, I beg it may be underllood, that although the 

 difficulties I have enumerated may in fome cafes exiit, 

 yet it is pofTible a furvcy of moderate extent may be carried 

 on by the needle with caution fufficient to obviate them ; 

 though I am fully fatisfied, from experience, that the latter 

 method is the moll to be relied upon ; I fhall, liowever, 

 proceed to exemplify both ni the order before-mentioned. 



" The Method of vjlng ih- Theodolite in afcertmiiing ihi! 

 Betiii/igs by the Needle It will be feen by the field- 

 book, tliat I commence at (llation) " i, at the back of 

 the manfion : here, having the theodolite firmly fixed in 

 th^ ground, by means of the four adjulling-fcrews, I fet 

 it perfeftly level, firft in the direftion or the magnetic 

 north, and afterwards at right angles : being tluis fatis- 

 fied, I fet the vernier on the upper limb correctly to 

 360° on the graduated circle, and loofen the fcrew that 

 fixes the inftrumcnt. I then move the graduated circle 

 round until I afcertain that the needle points to N. in 

 the compafs-box, and then tighten the fame fcrew, which 

 prevents it from moving. Being now ready to take the 

 bearing from © I to © 2, I direft the tclefcope to fome 

 objeft in that direction, keeping as near to the boundary -fence 

 as can well be admitted, in order to reduce the length of the 

 offsets ; ai.d having brought the crofs-wires in the tclefcope 

 to bear upon the objetl, I then look to fee what part of the 

 limb is cut by the vernier, which I find to be 330° 2', and 

 in a north-WLfl direftion. This I note down as in the 

 field-book, and afterwards examine whether it is correft. I 

 then dir^ft the chain-man to move forward towards that 

 objeft, leaving a mark behind, to return to, and proceed by 

 firil takirg the following offset at 00 ; that is, at the place 

 of commencement, I find an offset to the right of 86 

 links to lady Buckinghamfhire's fence, and 40 from thence 

 back to the building, which I note down. I then proceed, 

 and at 212, I meafure 5 links to the right, to a tree ; and 

 going forwards at 274, I meafure 2 links to the left, to 

 another tree, (wliich objefts I am always induced to mark 

 in the furvey, for the purpofe of embellifhing the fair map) : 

 proceeding onwards at 310, the offset to the corner of lady 

 Buckinghamfhire's fummer-houfe is 10 ; at 360, the chain 

 touches the fence, confequently I mark the offset o (no- 

 thing) ; at 738, there is an offset to the left of 23 links, to 

 a tree ; and at 917, one to the fence of 13 : continuing the 

 line, I fet up a mark at 950, and write the fame down in the 



?ield-book, thus " (950^ (y) mark left," meaning it for 



a ftation,no join to hereafter : I call it ftation ^3^, being 



the next number following the ftation I am meafuring to- 

 wards ; and I mclofe it in a circle, to make it more pro- 

 minent to refer to ; and mark the 950, the number of hiiks 

 on the chain-line, alfo in a circle, that I may not err in 

 plotting off the fituation of the fame. I then go on, and 

 at 960 come to the outer edge of a fmall clump of trees ; 

 at 975, an offset to the left afcertains the width of the 

 clump that way to be 50 links, and one to the right of 1 3 

 links to the fence ; 986 paffes the outer edge of the 

 clump; at 1031, an offset of 31 links on the left to the 

 canal; at lioo, pafling clofe to the edge of the canal, 

 there being no offset on the left, I mark it o (nothing); 

 at 1155, I crofs the gravel-walk, the width of which was 

 previoufly noted in the field-book to be 8 links ; and at 

 1 1 80, I halt, and mark the offset to the fence on the riglit 

 5 links. Here I again plant my tlieodolite, as before, 



9 



cxaftly over the (lation-hole ; and after fetting it pcrfcAly 

 level, and having brouglit the vernier 360'-' on the circle, and 

 afcertained that the needle was corrcdtly pointing to N. in 

 the compafs-box, I tighten the fixing fcrew, then jnove the 

 tclefcope round gently to the left, until the crofs-wires cut 

 a confpicuous objeft in the dircftion in which I mean to 

 proceed, and afcertain that the vernier cuts 235" 7' in a 

 fouth-weft direction in the box. This I note down imme- 

 diately in the field-book, as there rqirefented ; and after 

 examining that I had done fo corre<ftly, I proceeed on to 

 meafure the line from © 2 to '• 4, taking the oflsets right 

 and left, and making the neceffary remarks, to enable me to 

 give a correft map and defcription of the eflate, and fo on 

 throughout the furvey. I have been particular in the field- 

 book, which I trutt, by the above defcription, will be con- 

 fidered to be a plain and facile way. 



" The Method of ujiiig the Theodolite in afcertainwg the Anglts 

 upon the graduated Circle, "without Reference to the Needle. 

 — On commencing, I plant the theodohte firmly in the 

 ground, and after adjufting the level perfeftly, and fet- 

 ting the vernier to 360° on the hmb, I move the circle 

 round, imtil I afcertain that the needle in the compafs-box 

 points corredlly to N. ; then tightening tiie fcrew tliat fixes 

 the inflrumcnt, as before, I move the telefcope gently 

 round in the direftion of the Ime to © 2, in doing whicli, 

 I find that the vernier cuts upon 330° 2' N.W. This is noted 

 down, in order to fhew the bearing of the eflate upon the 

 map, and which, on being dedufted from 360'^, leaves an 

 angle to the left of the meridian of 29° 58', as lliewn in the 

 example : then leaving a mark at flation © I, and having 

 proceeded along the line to flation ' ■ 2, and taken the 

 offsets, and made the neceffary remarks in the field-book, 

 as in tlie former method, on arriving at (•) 2, I again 

 plant the theodolite firmly in the ground, and adjulling it 

 as before, move the telefcope round until the crofs-wires 

 cut the lower part of the mark left at . •, ' : then noting in 

 my field fl<etch the number of degrees . cut by the vernier 

 upon the limb, without regarding zero, I afterwards move 

 the telefcope carefully round to the right, and direft it to- 

 wards 4 ; and bringing the crofs-wires in the telefcope 

 to cut the objeft propofed to be meafured to, I look and fee 

 the number of degrees cut by the vernier on the limb, as 

 before : dedufting one from the other, I get the Z. at © 2, 

 •viz.. 85° 14'; and after having meafured the line,, on my 

 arriving at G 4, I proceed exaftly in a fimilar way, by 

 firil looking back to the laft flation, and then forward to 

 the next, dedufting the number of degrees and minutes 

 in one direftion from thofe read in the other, which gives 

 the angle 88*^ 18'. Following this courfe, I proceed on 

 the furvey until all the angles and fides are completed. 



" It is neceffary, however, before quitting each ftation, to 

 take particular care in reading off the angles by tiie vernier, 

 and alfo in writing them down correftly : and in this way 

 of proceeding, the trouble of adjufting for zero of the 

 vernier to 360"^ at every ftation is avoided. 



" By plotting, is un'derftood the making of a draught of 

 the eftate from the field-book ; and as the inftruments necef- 

 fary to be ufed by the furveyor, in taking the dimenfions 

 in the field, are fuch, that he may be enabled to afcertain 

 diftances and angles correftly ; it naturally occurs that 

 correfponding requifites are neceffary to make a ground- 

 plot, or draught thereof, for laying down the quantities of 

 the feveral angles, and of the diftances meafured by the 

 chain upon paper, wliich are ufually accomphfhed by means 

 of the protraftor for the former, and fcales of equal parts 

 for the latter. 



" With refpcft to the protraftor, I have hitherto ufed, 

 and recommended the young furveyor to ufe, one of eight 



inches 



