&BAINIHI& $aOSANGF.lfj^ 2 1 1 30 3 c 1 2 X 2 s AttE-UNIVER - : OF-CAUFQ8to s^^- 2- Q\ B> O i Si ^UBAHCH^* W i? '/HBAINfl-3^ ftTOiflJVfc ^FCALIFO/?^ ^ f 1 1 s is> ^lIBRARYQr i i tyojmo-^ AjclOS ANGELA ^tLIBRARYl ^tfOJITVOJO^ %OJITV3-JO^ ^OFCAIIFO/?^ ^OF-CAIIFO^ IVP^I r ^OJITVJJO^ ^OJITV3-JO^ A TREATISE ON PLANE SURVEYING BY DANIEL CARHART, C.E. .PROFESSOR OP CIVIL ENGINEERING IN THE WESTERN UNIVERSITY OF PENNSYLVANIA 48504 GINN & COMPANY BOSTON* NEW YORK CHICAGO LONDON Entered, according to Act of Congress, in the year 1887, by DANIEL CARHART in the Office of the Librarian of Congress, at Washington 68.5 JCfje atfcenacutn PREFACE. rr^HIS work, as its name indicates, extends over the field of J- plane surveying. It illustrates and describes the instru- ments employed, their adjustments and uses ; it exemplifies the best methods of solving the common problems occurring in Y practice, and furnishes solutions for many special cases which ?^ not unfrequently present themselves. An experience of twenty - years in the field and in technical schools confirms the opinion that a work of this kind should be eminently practical ; that the student who desires to become a reliable surveyor needs frequently to manipulate the various surveying instruments in the field, to solve many examples in the class-room, and to exercise good judgment in all these operations. With this in ^ view, therefore, the different methods of surveying are treated, ^ directions for using the instruments are given, and these are ^ supplemented by numerous examples to be solved, by various field exercises to be performed, and by many queries to be answered. Chapter I. is devoted to Chain Surveying, in which direc- tions are given for measuring and ranging out lines, and methods of overcoming obstacles, recording field notes, obtain- ing areas, and plotting a chain survey. Chapter II. treats of Compass and Transit Surveying, or when, in addition to the chain, an instrument for measuring angles is employed. In this chapter the compass and transit, the solar attachment, the adjustments of these, and auxiliaries of the transit, such as the stadia wires, gradienter, etc., are fully illustrated and described, and their uses shown. Here the various methods of obtaining the data requisite to deter- IV PREFACE. mine the area, as well as the different methods employed in calculating the contents of laud, are exhibited. Tests of the accuracy of a survey are indicated, numerous methods of over- coming obstacles, supplying omissions, of ascertaining heights and distances, of keeping the field notes, and of plotting a sur- vey are given, while the uses of the solar attachment in deter- mining the latitude of a station and its geographic meridian are exemplified. The student now having been taught how to survey land, using a needle instrument, should become acquainted with the declination of the magnetic needle, or variation of the compass, as it is frequently called. This subject is accordingly dis- cussed in Chapter III. Some of the tables and much of the matter is taken from the Reports of the United States Coast and Geodetic Survey. The student will do well to give this chapter a careful inspection, examining the tables and formu- las and the directions for determining the true meridian, thus being prepared with facts, figures, and methods, which will en- able him intelligently to undertake the retracing of old lines, as well as to establish with considerable precision his geo- graphic meridian, and thereby obtain the declination of the needle. Chapter IV. is devoted to Laying Out and Dividing Up Land. This subject is of more importance than some suppose, especi- ally to practitioners in the older States of the Union, and is here treated very fully. The principal cases are exemplified, and general directions and suggestions given, so that, it is believed, with a thorough knowledge of this chapter, the student will be enabled, without embarrassment, to meet the requirements of an extensive practice. The description, adjustment, and use of the Plane Table form the subject of Chapter V. This instrument is being employed more frequently than formerly in park surveys, in determining positions in harbors, along the lines of proposed highways, in "filling in" large surveys, and 'generally in locating points where extreme accuracy is not required. PREFACE. V In Chapter VI. the system employed by the government in the Survey of the Public Lands is set forth. The description and adjustment of the Solar Compass, which is used quite ex- tensively in these surveys, precede au account of the origin of the system, and the leading points in the " Instructions to Sur- veyors-General " from the commissioner of the land office. A form of recording the notes extracted from the " Instructions" is also given, the chapter closing with formulas and a table for determining the inclination of meridians and deviation of par- allels. Chapter VII., on City Surveying, is from the pen of my friend and former colleague, Frederic H. Robinson, C.E., City Engineer of Wilmington, Del. This subject has received but little notice from writers on surveying, although the need of some systematic and practical treatment of it has long been recognized. It therefore affords me much pleasure to acknowl- edge my indebtedness to Professor Robinson for supplying this want, and so enhancing the value of this publication as a text- book. Experience in teaching, and ten years' practice in city- surveys and improvements, eminently qualify him to speak on this important subject with authority and in a manner readily understood by students. The special instruments needed in this branch of surveying are illustrated and described ; the adjustment of the Y-level and directions how to level and to record the notes are given ; more refined means of measuring lines are discussed ; tempera- ture, pull, sag, wind, etc., are considered, and corrections indi- cated ; best directions and width of streets, together with the subject of grades, sewers, the establishment of permanent reference points, and adjusting property lines, are fully set forth. To my college classmate and esteemed friend, F. Z. Schel- lenberg, C.E., Superintendent of Westmoreland Coal Co., Irwin, Pennsylvania, I am indebted for Chapter VIII., on Mine Surveying. This chapter, though in general explanatory of what is applicable and peculiar to this branch of surveying, vi PREFACE. includes directions for running contours and sketching topog- raphy. It is replete with suggestions that will be valued when, by the aid of the study of mine workings themselves and their ground, illustrations will be afforded which otherwise, as drawings alone, cannot readily be understood. The Judicial Functions of Surveyors, as given by Chief Jus- tice Cooley, are set forth in an Appendix. Those who are familiar with the elegant tables of logarithms of numbers and of trigonometrical functions prepared by Pro- fessor Wentworth, will likely recognize the use of his electro- plates, from which I have been permitted to print Tables I., III., IV., and VII. To him mv personal acknowledgments are due. The plates from which Tables II., V., VI., VIII., and IX. are printed were prepared expressly for this work. It is thought that the four-place tables of the natural trigonometri- cal functions will be found very useful in connection with sur- veying and engineering operations. They are believed to be correct, having been very carefully compared with others whose accuracy is unquestioned. In addition to acknowledgments made elsewhere, I take pleasure in expressing here my thanks to Messrs. W. and L. E. Gurley, of Troy, New York, for the use which I have been per- mitted to make of their valuable catalogue, in the description of certain instruments, and for the loan of several plates for the engraving of instruments ; also to Messrs. Fauth and Co., "Washington, D.C., and to Messrs. Heller and Brightly, and Messrs. Young and Sons, Philadelphia, Pa., for plates which they kindly furnished for the illustration of the subject. D. C. WESTERN UNIVERSITY OF PENNSYLVANIA, DECEMBER, 1887. CONTENTS. PAGE Definitions, and division of the subject 1 CHAPTER I. CHAIN SURVEYING. SECTION I. INSTRUMENTS. Gunter's chain . 8 Two-pole or half chain 8 The engineer's chain 4 The tape measure 4 Marking-pins 4 Straight poles 4 SECTION II. CHAINING. How to chain 4 Tallying : 5 Error in chaining 6 Chaining on sloping ground 8 Field exercises 10 Ranging out lines '. 10 Over a hill ; across a valley 11 Through a wood 12 Field exercises 13 To set off a perpendicular from a line 13, 14 To let drop a perpendicular from a point to a line 14, 15 Through a point to run a line parallel to a given line 16, 17 Obstacles to alignment 17, 18 Viil CONTENTS. PAGE Obstacles to measurement ... 18-20 Measurement of heights 20 Examples and field exercises 21 SECTION III. RECORDING THE FIELD NOTES. By sketch 22 In columns 23-25 SECTION IV. MAPPING AND PLOTTING. Instruments useful for plotting a chain survey 26 Drawing-board, T-square, triangles, etc 26, 27 Scales 28 Drawing to scale 29 To ascertain unknown scale 30 SECTION V. ON AREAS, AND ILLUSTRATIVE EXAMPLES. Areas : The area of a triangle 31 " " rectangle 31 " " parallelogram 31 " " trapezoid 31 " " regular hexagon 31 " " " octagon 31 " " " polygon 32 Table of areas of regular polygons 33 The area of a circle 33 " " quadrant 34 " " sextant 34 " " circular ring 34 " " segment 34 " ellipse 35 EXAMPLES INDICATING HOW TO SURVEY LAND, TO PLOT THE SURVEY, AND TO COMPUTE THE AREA. To survey a triangle 35, 36 " " rectangle . . 37 Examples 37 CONTENTS. ix PAGE To survey a parallelogram 38 " " trapezoid , 38 Examples 38, 39 To survey, plot, and compute the area of a trapezium 39 Examples 40 To survey, plot, and compute the area of a polygon, regular or irreg- ular 40, 41 Examples 41, 42 To survey, plot, and compute the area of a circle and a circular ring. 43 " " " sector and a segment 43 Examples 43 SECTION VI. OFFSETS AND TIE-LINES. Remarks and illustrations 44 Rectangular co-ordinates and their application to the computation of areas 45 Formula and rule 46 Examples 47 Additional formulas and rule 48 Examples 48-50 Tie-lines used to survey a lake or pond 51 Miscellaneous examples 51, 52 Field exercises 53 CHAPTER II. COMPASS AND TRANSIT SURVEYING. SECTION I. DEFINITIONS AND DESCRIPTION OF INSTRUMENTS. A meridian plane; meridian line; the magnetic needle; the magnetic meridian 54 The azimuth, bearing, and meridian distance of a line 56 Horizontal angle ; vertical angle ; angle of elevation ; angle of depres- sion 55 The surveyor's compass 55, 66 To adjust the compass 56 Engraving of compass 57 Caution when handling the compass 58 X CONTENTS. PAGE To re-magnetize the needle 60 Weight of compass . 60 The vernier 61 Formulas for determining the least count 61 How to space a vernier for a given least count 62 To read an instrument having a vernier 62 Exercises on designing verniers 62 Engraving of surveyor's transit 64 Description of transit, and section of telescope and cross-wires 65, 66 Sectional view through the spindle of transit . 67 The needle, tangent movements, levels, and verniers 68, 69 The sockets, levelling-plate, and tripod 70, 71 To adjust the transit ., 71-75 To use the transit - 76 Transit attachments and their adjustments 77, 78 The solar attachment 79, 80 Engraving of solar attachment (Gurley's) 81 The adjustment of the solar attachment 83-85 To find the latitude by means of the solar attachment 85 To run lines with the solar attachment 87 Saegmuller's solar attachment and its adjustments 88 Engraving of Saegmuller's attachment 89 Latitude by means of Saegmuller's attachment 91 Latitude by a circumpolar star 91 Table of refraction 92 To find the meridian and declination of the needle, using the attach- ment 93 Time and azimuth with the solar attachment 94 Error in declination or latitude causing an error in azimuth 94 Table of errors in azimuth for one-minute error in latitude or declina- tion 95 The stadia or micrometer 95, 96 Formula when stadia is perpendicular to level line of sight 97 Formula when line of sight is not level 99 Examples 100 Gradienter 100, 101 SECTION II. BEARINGS WITH COMPASS, AND ANGLES WITH TRANSIT. To obtain the bearing of a line 102 Reverse bearing ; local attraction 103 CONTENTS. Xi PAGE Proof -bearings and tests of accuracy 104 Suggestions and field exercises 105 To measure angles with the transit, by repetition 106 " " " " by series ; remark 107 Deflection angle ; traversing, or surveying by the back angle 108-110 To traverse a road or a small stream Ill Problems on bearings and angles 112-115 To change the bearings of the sides of a survey 116 Examples and field exercises 117-119 SECTION III. PROBLEMS ON PERPENDICULARS AND PARALLELS. To let fall a perpendicular from a given point to a line 120, 121 To prolong a line past an obstacle (various methods) 121-124 To measure a line past an obstacle (various methods) 124-127 Examples and field exercises 127, 128 SECTION IV. HEIGHTS AND DISTANCES. Measurement of accessible heights , 129 Examples 130 Measurement of inaccessible heights 130-132 Examples 132, 133 Inaccessible distances 135 The three-point problem 136-138 Miscellaneous problems and field exercises 140,141 SECTION V. RECORDING THE FIELD NOTES. Tabular form 142 By sketch 142-144 In columns 147-149 Large plot of a survey 153 SECTION VI. LATITUDES AND DEPARTURES. Definition of latitude and departure 154 Formulas and examples on latitudes and departures 155 The traverse table and explanation of the same 156, 157 Xii CONTENTS. PAGB The use of the traverse table exemplified 157, 158 Table of sines and cosines employed ; examples 159 Testing a survey 160 Correcting latitudes and departures 161 " " " " sides weighted 165 SECTION VII. SUPPLYING OMISSIONS. General observations on supplying omissions 166 Determination of one side 167 " " the length of two sides 169 " " bearing of two sides 172 " " bearing of one side and length of another 174 SECTION Vin. PLOTTING A COMPASS OR TRANSIT SURVEY. Using the protractor 178, 179 By latitudes and departures 180, 181 Using cross-section paper 182 SECTION IX. ON DETERMINING AREAS. Determining the area of triangles and parallelograms 183 " " trapezoids and trapeziums 184 Examples 185 Determining the area of polygons 186 General method for determining the area of any rectilinear figure. 187-190 Examples 191-193 Method by total latitudes and departures 193, 194 Examples 194-196 Determining areas when offsets are taken ... 196, 197 Field exercises 197, 198 CHAPTER III. DECLINATION OF THE NEEDLE, OR VARIATION OF THE COMPASS. Irregular changes 199 The diurnal variation . . 200 CONTENTS. Xiii PAGE Table for reducing observed declinations 201 The secular variation 201 Line of no declination, or agonic line .201, 202 Formulas expressing the magnetic declination 203 Tables exhibiting annual variation, etc 206 Effects of the secular change 208 Rule for obtaining bearings when variation is known 209 Change determined by old lines 210 Examples 211, 212 To obtain the true bearing of a line 212 To determine the declination, by Polaris 214 Tables of elongation and azimuth of Polaris 216, 217 To establish a true meridian with a transit 218 To obtain approximately the meridian , . . . . 219 CHAPTER IV. LAYING OUT AND DIVIDING LAND. SECTION I. LAYING OUT LAND. Triangles ; examples 221-223 Squares 223 Rectangles ; examples 224, 225 Parallelograms ; examples 225, 226 Polygons ; examples 227, 228 Circles and ellipses ; examples 228-231 Additional problems 232 SECTION II. DIVIDING LAND. Triangles, various cases ; numerous examples 232-240 Trapezoids, " " 241-246 Trapeziums, " " 246-252 Polygons, " " 253-258 Irregular boundary 258 Straightening boundary lines 258 Miscellaneous examples 259-261 xiv CONTENTS. CHAPTER V. PLASE TABLE SURVEYING. PAGE The plane table ................................................ 262 Engraving of plane table ........................................ 263 The alidade and declinator ...................................... 265 Adjustments ................................................... 266 Surveying by radiation, progression ... ....................... 267, 268 " " intersection, resection .............................. 269 The three-point problem ......................................... 270 Bessel's method by inscribed quadrilateral ---- . ................... 270 The two-point problem .............................. ............ 271 Practical suggestions ............................................ 273 Field exercises .... ................................ . ......... 274 CHAPTER VI. THE SURVEY OF THE PUBLIC LANDS. The solar compass .............................................. 275 The latitude and declination arcs ................................. 276 Engraving of solar compass ...................................... 277 The hour arc and polar axis ....................................... 279 Principles of the solar compass ........................ ' ........... 280 Allowance for declination ............................... ....... 281 To adjust the solar compass .................................. 283-285 To use the solar compass ....................................... 285 To set off the declination ..................................... 285, 286 Allowance for refraction ........... ............................ 287 Table of refractions in declination ............................. 288, 289 Explanation of the table of refractions ........................... 290 Problems in declination and refraction ........................ 290, 291 To set off the latitude ........................... ............... 291 To run lines with the solar compass .............................. 292 Allowance for the earth's curvature .................... ......... 293 Time of day by the sun ... ....................................... 294 Caution as to the false image ................................... 294 Approximate bearings, and time for using solar compass ............ 295 Origin of the system for the survey of the public lands ............. 295 Plan of a township, showing sections ........... , ................. 2% CONTENTS. XV PAGE System of rectangular surveying 297 Conformity to the meridian required 298 How to survey section lines ; plan of township 299 An instrument operating independently of needle required 300 The four-pole chain to be adjusted to 66.06 feet 301 Process of chaining 302 Marking lines- 303 Obstacles in line ; witness points 304 Establishing corners 304 Miscellaneous directions 305, 306 Quarter-section corners ; witness corner 307 Meandering ., 307 Base line 308 Principal meridian ; standard parallels 809 Auxiliary meridians ; township lines 310 Method of subdividing townships 311, 313 Subdivision of sections ." 314-316 Re-establishment of lost corners 316 Objects required to be noted 316, 317 Specimen field notes 318-321 Inclination of the meridian 322, 323 Convergency of meridians ; deflection of range-lines 324 Table of inclination and convergency of meridians 325 CHAPTER VII. CITY SURVEYING. Introduction 326, 327 SECTION I. FIELD INSTRUMENTS, THEIR ADJUSTMENTS AND GENERAL USE. Transit, engraving of, showing gradienter, etc .328, 329 Rods, steel tapes, etc. 331, 332 Locke's hand-level 333 Effects of temperature, sag, and wind considered 334 Corrections for these ; illustrations 335, 336 Suggestions on measurement 336 The Y-level 337 Engravings of Y-level 338,339 Adjustments of the level 340-343 XVi CONTENTS. PAGE To use the level 844 Engravings of New York and Philadelphia levelling-rods 345 Description of " " " " " 347,348 The rod-level ; engraving of same 349 Levelling defined 349, 350 Curvature and refraction considered 350, 351 Exercises ; levelling by fore and back sights 352, 353 Levelling, general method 354, 355 Form of record ; observations on bench marks 356 General method of running a grade line 357 Office instruments 358 SECTION II. A. FIELD WORK. Public work ; street lines ; direction and width of streets 358, 359 The alignment, how made 360 Preservation of points in line 361 Street grades ; the profile 362, 363 llecord of levels for profile 365 Marking of lines and grades 366 Private work 366 Diagram of lot and block 367 Locating lot corners from descriptions in deed 369 How to proceed when obstacles intervene 370 B. OFFICE WORK. Public work ; plans, profiles ; exercise 372, 373 Determination of grades , 374 Diagram 375 Drainage 377 Private work 378 Conclusion ; books 378, 379 CHAPTER VIII. MINE SURVEYING. Its purpose 380 Instruments employed in making the alignment 381, 382 Stations, where made, and how designated 382 Angles ; initial course ; reduced courses , . . . 382 CONTENTS. XVli PAGE Curves, how laid out 383, 384 The record 385 Mapping and plotting ; inside and outside work 385, 386 The use of the level and rod 387, 388 The use of the vertical circle 388, 389 Transference of points from surface to bottom of shaft 389 Special appliances for taking courses on pitches at high angles 390 The hanging compass and hanging clinometer 390, 391 Topography, its use, how taken 391, 393 Employment of the plane table 393 Contour lines 393 Angular cross-sectioning 394 Transit as first made' in 1831 .. , 396 APPENDIX. The judicial functions of surveyors 897-411 TABLES. Logarithms of numbers 1-19 Approximate equation of time 20 Logarithms of trigonometric functions 21-49 For determining with greater accuracy than by the preceding 50, 51 Lengths of degrees of latitude and longitude 52 Miscellaneous formulas, and equivalents of metres, chains, and feet, 53 Traverse 54-61 Natural sines and cosines 62-70 Natural tangents and cotangents 71-79 For tables in the body of the book, see " Tables " in Index. SURVEYING. DEFINITIONS, AND DIVISION OP THE SUBJECT. 1. Surveying is the art of determining and delineating the relative position of points upon the surface of the earth. It consists principally in measuring, laying out, and dividing land ; in establishing lost positions ; in the measurement of heights and distances ; and in the graphical representation of the pecu- liarities of any part of the earth's surface. 2. It mav be divided into two parts : PLANE SURVEYING and GEODETIC SURVEYING. In Plane Surveying the spherical form of the earth is neg- lected ; in other words, the portion of the earth included in the survey is regarded as a horizontal plane. This may be done without sensible error where, as in ordinary land surveying, the operations are limited to surfaces of small extent. In Geodetic Surveying the shape of the earth is regarded, since the surfaces under consideration are so extensive, as in the United States Coast and Geodetic Surveys, sensible errors would otherwise arise. RKMARK. The spherical excess of a spherical triangle, each of whose sides is one mile, is less than six-thousandths of a second. The excess amounts to only one second for an area of 75.5 square miles, each side of the equilateral triangle being then about 13 miles. 2 SURVEYING. 3. In the following pages Plane Surveying only will be con- sidered, and the subject treated under the following heads : CHAIN SURVEYING. COMPASS AND TRANSIT SURVEYING. PLANE TABLE SURVEYING. GOVERNMENT SURVEYING CITY SURVEYING. MINE SURVEYING. In Plane Surveying there are usually three operations : 1. The Field Work. 2. The Graphical Representation, or Plot 3. The Computation. CHAPTER I. CHAIN SUKVEYING, SECTION I. INSTRUMENTS. 4. Chain Surveying has chiefly for its object the determina- tion of areas from data obtained by direct measurement of distances between points. The instruments needed are there- fore simply those for measuring lines. 5. Gunter's Chain, so called from its inventor, is generally used for this purpose. It is made of iron or steel wire, is 66 feet in length, and divided into 100 links, so that each link, with half the rings connecting it with the adjoining links, is seven and ninety-two hundredths inches (7.92), or one-hundredth of a chain. Swivels are inserted to keep it from twisting, and every tenth link has a metallic mark attached, so that the number of tens from either end is readily ascertained. Its advantages in surveying farms or fields are apparent : there being 4840 square yards in an acre, and the chain 22 yards long, a square chain will contain one-tenth of an acre ; or, there being 10,000 square links in a square chain, which is one-tenth of an acre, 100,000 square links are equivalent to an acre. Hence, if the area of a field is calculated in links, the area is at once shown in acres, by cutting off the last five figures. If the area is found in chains, then since there are ten square chains in an acre, the area is given in acres by cutting off -the last figure. 6. A Two-Pole, or Half-Chain is sometimes used instead of Gunter's Chain. It is quite convenient for measuring lines where the ground is rough and hilly. 4 PLANE SURVEYING. 7. The Engineer's Chain is used in surveying railroads and canals, and generally where extensive line surveys are being conducted ; hence not unfrequently it is employed in connection with these surveys, as well as otherwise, in determining areas. It is 100 feet in length, and is divided into 100 links, every tenth link being marked by a piece of brass, as in the four-pole chain. 8. The Tape Measure is very convenient for taking offsets in a survey, for measuring the boundaries of city lots, cross- sectioning in railroad work, etc. Tapes are "metallic," or steel, and made of various lengths,* 50 feet or 100 feet are commonl}" used, and divided into feet and inches, or feet and tenths of a foot. The latter graduation is preferable for the railroad engineer, and the former for the city engineer. 9. Eleven Marking-Pins, 12 or 14 inches long, one of which is made of brass, the others of No. 4 iron wire or No. 6 steel, all pointed at one end and formed into a ring at the other, are used in chaining. 10. Straight Poles about 8 feet long, shod at the bottom with a conical shoe, point down, and painted alternately red and white in foot-width bands, are used to indicate the direction of the line which is being measured, or the position of points to be located.f SECTION II. A. CHAINING. 11. Two men are required, a " leader " and a " follower," or head and hind chainman. The chain is first thrown out in the general direction of the line which it is desired to measure, and * Steel tapes 1000 feet in length have been frequently used for special purposes. See Mine Surveying, p. 380. t See Article 383. CHAINING. 5 examined carefully to see if there are any kinks in it, or bends in the links ; the leader having the inarking-pins in one hand takes hold of the forward end of the chain with the other, and moves on as nearly as he may judge in the direction of the line ; the follower places the rear end of the chain at the station whence the line is to be measured, directs the leader by signals as he approaches the chain's length to get in line, and then calls, "halt"; then the chain must be drawn taut and straight, and the follower having his end of the chain precisely at the starting- point, calls out, "down"; the leader then thrusts one of the iron marking-pins into the ground exactly at the end of the chain and calls out, "down," which is the signal to the follower to advance : proceeding as before until the second length of chain is measured, which is indicated by the follower coming to the pin set in the ground b^y the leader, when the follower cries, "halt," and after placing his end of the chain at the pin, the chain having been drawn taut and straight as before, calls, "down" ; the leader, as before, leaving a pin to mark the end of the chain, repeats, "down" ; the follower then takes up the pin first placed by the leader, and moves on ; thus the party proceeds until the end of the line is reached, the leader placing the pins at his end of the chain, and the follower picking them up at his end. If the line ends with less than the length of the chain, the leader places his end at the point which marks the extremity of the line, calls out, "down"; the follower then reads off the number of links between the last pin and the end of the line. The number of whole chain's length of the line is shown by the pins in the hands of the follower, and the number of links counted off added thereto will give the total length in chains and links. 12. Tally. If the line exceeds eleven chains in length, a transfer of pins from the hind chainman to the head chain man is necessary ; this is called tallying, and is performed in the following manner: At the end of the eleventh chain, the brass 6 PLANE SURVEYING. pin the last pin left in the hands of the leader is placed, when he call out "tally"; at this signal the follower drops his end of the chain, advances to the leader, counts over with him the ten iron pins which he has gathered up, and transfers them to the leader, who then withdraws the brass pin, sets an iron one in its place, and the measuring is continued as before.* Each tally should be recorded, especially when chaining very long distances, to avoid error in the final count, t It is obvious that the total length of the line will be equal to the chains and links as indicated above, plus the number of tens shown by the tallies. 13. The surveyor should guard against error in chaining, by frequently testing his chain, to see that it is of the proper length, if it has been stretched, make a file mark showing its true length, and when in use, see that it is drawn straight, that the forward chainman sticks the pin in line exactly at the end of the chain, or at the mark indicating its true length, and as nearly vertical as possible ; \ and when obtaining the number of links at the end of the line, see that they are not counted * Some surveyors use only ten marking-pins, and tally by marking the end of the eleventh chain with a pencil, the finger, or a scratch on the ground, and when the ten pins are transferred to the leader, one of them is thrust in the place thus indicated, and the work is continued as before. t In chaining long distances where there are several tallies, the leader and follower may, at each tally, change places, and thereby lessen the liability to error in the final count. See Articles 352, 353. } " It has been found by many trials with as good men as can generally be obtained, that with two sets of chainmen instructed alike in the proper manner of keeping their chain level and straight on the line, and of setting the tally pins plumb, as well as holding the ends of the chain to them, a difference has sometimes been made of 36 links, and an average differ- ence of 15 or 16 links to a mile in common timbered land." Hurt, " Gov- ernment Surveying," p. 35. The surveyor should have laid down by means of a standard steel tape or otherwise, in a convenient place, and between permanent marks in the ground or on the floor of a large hall, the exact length of a standard chain by which he could test his chain from time to time. CHAINING. 7 from the wrong end of the chain, nor the wrong way from the brass mark. The pull on the chain, when in use, has a tendency to in- crease its length ; and moreover, since there are a great number of wearing surfaces, if each of these be worn by an extremely small amount, the chain will be considerably elongated. In either the surveyor's or engineer's chain there are two small links which connect with the two pieces of wire which form the principal part of what is called the 'link of the chain, thus giving six wearing surfaces to every link ; therefore, if each of these surfaces wears only .005 of an inch, the chain will be increased in length three inches, so that in measuring only a quarter of a mile with a four-pole chain, the error from this cause alone would be Jive feet,* making an error in area of about 4.9 acres in a tract one mile square. This stretching of the chain is partially compensated by the difficulty, and often impracticability, of drawing the chain precisely straight; and so long as the chain is not elongated beyond one-tenth or one-twelfth of one per cent of its length, it may be relied on for accurate work.f The true length of a line which has been measured by a chain stretched beyond the standard length may be found from the proportion : The length of standard chain : the length of chain used : : the distance measured : the true distance. * Tliis error, it is perceived, increases directly with the number of appli- cations of the chain : it is called cumulative. The error arising from erro- neous setting of the pin is termed compensative, that is, it is as likely to be additive as subtractive, and it is shown by the Method of Least Squares, that for this class of errors the square root of the number of errors are probably not compensated. If the error in setting is one inch, in chaining a mile with a Gunter's chain, the probable error would be VbO = about 9 inches. t To remove the difficulty of drawing the chain perfectly straight, the instructions issued from the United States Land Office, 1880, to Govern ment Surveyors-General, states that the 66 feet chain must be 66.06 feet. See p. 301. 8 PLANE SURVEYING. For example, if, with a chain stretched one link over the standard, a line be measured for 2000 feet, we should have 100 : 101 = 2000 : 2020, the true distance. In like manner, for the area of a tract measured with a stretched chain : The square of the length of the standard chain : the square of the length of the chain used : : the computed area : the true area. If the chain was stretched one link, as in the above example, and the area computed therefrom 20 acres, we should have 100 2 : 101 2 = 200 sq. chs. : 204.02 sq. chs. for the true area = |$f of the computed area, nearly. In general, if A = true area, A l = computed area, L length of chain, and d-L = error in its length (always small). Then A : A, = (L dL) 2 : L\ Reducing and rejecting d 2 as inconsiderable, there results A = (l2d)A 1 ; or, the correction to be applied to obtain the true area = 2 dA^. This correction is additive when the chain is too long, which is the usual case, and subtractive when the chain is too short. 14. The surfaces to be measured are in general uneven and broken, not plane ; but however great the inequalities, the area of a tract is considered to be that part of the horizontal plane which is intercepted by vertical planes through its boundaries.* The horizontal distance is therefore required ; hence, when the * A vertical line is a line directed to the centre of the earth, or it is a line having a plummet freely suspended to it, and at a state of rest ; a plumb line. A vertical plane is a plane embracing a vertical line. A horizontal line is a line perpendicular to a vertical line. A horizontal plane is a plane perpendicular to a vertical line. CHAINING. 9 ground slopes, it is necessary to raise the down-hill end of the chain. If the slope is considerable, only a part of the chain should be used. For example, to measure from L down to JV, the follower holds one end of the chain at L, while the leader, stretching the other towards N, takes as much of it as he can raise to a horizontal position &, and, holding a plummet there, fixes the point c ; the follower, who is now signalled to come for- ward, places at c that point in the chain whence the plummet was suspended to fix c, while the leader advances and, using as much of the chain as possible, locates e, and so on : when the end of the chain is reached, a pin should be transferred from the leader to the follower. Where great accuracy is not required, a marking-pin or pebble may be dropped to indicate the points c, e, etc.* To measure up hill from JVto L is less accurate, on account of the difficulty experienced by the fol- lower in holding his end of the chain at the points A,/, d, etc., over their counterparts, i, g, e, etc. When chaining steep hills, especially if through a wood or over rough, rocky ground, the work may be greatly facilitated by an extra chain man. He may assist in getting line, straighten- ing the chain, noting the points c, e, etc., marked by the plumb bob, and other duties. f * If in connection with the chain a survey is being made with an instrument for measuring angles, vertical and horizontal, the inclina- tion of a slope may be observed, and the length of it measured ; then the horizontal distance required will be equal to the measured distance multiplied by the natural cosine of the angle of inclination. t For extreme accuracy in measuring lines, see Chapter VII. Article 10 PLANE SURVEYING. EXERCISES. 1. Set two marks on gently undulating ground and about 1000 feet apart, and measure forward and back between these points several times ; the same party once at least each way. 2. The same between points on hilly and, if possible, bush land. 3. Chain down a steep hill, and chain up between the same points. B. RANGING OUT LINES. 15. If m chaining any line, as LN, from L toward N, a rod at N can be constantly seen by the rear chainman, he can keep the leader in line by ranging him with L N the flagstaff at N. If, however, a hill intervenes, a valley, or brush or woodland interferring with the alignment, then the line must be first ranged out or points determined in it before the chaining can be performed. 16. Ranging out a Line. To range out a line requires three persons, each having a rod eight or ten feet long, and a plum- met to indicate when his rod is vertical. Calling these men A, -B, and (7, and supposing A and B in the line, C goes for- ward, and sighting back to A and B, puts his rod in line ; A then advances beyond C and sets his rod in line with C and B ; next B advances and places his rod in line with C and A, and so on the line may be extended any desired length. If, as frequently is the case, one of the party has had more experi- ence or is naturally better qualified for sighting a line, the best results would be obtained by such an one setting all the rods ; for examp\e, C would place his rod in line, then call up A, to whom he would turn over the rod just set, and go forward to line the next ; after which call up B, exchange rods with him, and so on. RANGING OUT LINES. 11 17. Over a Hill. To fix points in a line over a hill, both ends of which are visible from points near the summit, proceed as follows : .17 Place a flagstaff at L, another at N. A man at E 1 signals one at Z>'.in line with L ; D' then directs E' to E" in line with jV; and so on alternately, until the men are at D and E in the line LN. 18. Across a Valley. To locate points in a line, the ends of which may be seen from each other, but which are separated by a wide, deep valley. Fix a point C in line with LN; then a man holding a plumb line at C, and sighting N can direct the setting of the stakes D, E, F, and others. 12 PLANE SURVEYING. 19. Through a Wood. In chaining through a wood or thick brush land, where the ends cannot be seen from each other, a line * is measured as nearly as may be in the direction of the desired line, and stakes driven every two or three chains, or oftener if necessary. When the end of the line is reached, the distance to the corner is measured, and, b}* proportion, the amount to move each stake to bring it into line is determined. For example, let LNbe the true line, and LN 1 the measured line ; c, d, e, etc., points three chains apart. Now, if the length LN' equals 17.40 chains, and NN 1 measured at right angles to LN* = 35 links, LN-\ will equal and . LN' (1740 links) :NN' (35 links) = Lg (1500 links) : gG (30 links) ; or 30 links from g at right angles to LN' will indicate the posi- tion of G, a point in the true line LN. 1740 : 35 = 1200 : 24, the distance fF, 1740 : 35 = 900 : 18, the distance eE ; and so on. Or, after finding the first distance to set off, either gG or c<7, the others are readily obtained by taking a proportional part of this distance, shown by the several divisions of the line thus : gG represents the fifth division, fF the fourth, eE the third, and so on ; hence, if gG is 30 links, fF will be \ of 30, or 24, * Called a random line or trial line. t If the distance NN' is a s nail per cent of the total length of the line, the shortest distance between the ends of the lines may be taken for NN', and the length of the measured line for that of the true line. See Article 177. SETTING OFF PERPENDICULARS. 13 links ; eE, f of 30, or 18 ; (W, f of 30, or 12 ; and c(7, | of 30, or 6 links. EXERCISES. 1. Let each student range out a line of several hundred feet, setting all the poles forward, and hack again to the starting- point, and on different kinds of ground, undulating, hilly, and bushy. 2. Measure a line through a wood or where the ends are not visible from each other. Set stakes, as indicated in Article 19, in the true line 200 feet apart. See how near these stakes are placed in line by ranging. C. SETTING OFF PERPENDICULARS. 20. To erect a perpendicular at a giiven point in a line. Let MN be the given line, and P the point at which it is desired to erect a perpen- dicular. Since a triangle formed of the sides 3,4, and 5, or any multiple of these, will contain a right angle, we may take parts of a chain representing these distances M- or multiples, having the an- gle made by the shorter sides at P, and set off a perpendicular to a given line, thus: Fasten one end of the chain at K, 30 links from P, the end of the ninetieth link at P; then when both parts of the chain are drawn straight by a pull at the fiftieth link, the end of that link will indicate the point which if connected with P will give the perpendicular required. 21. If the perpendicular is to be of considerable length, then a greater length than PO = 40 links should be used, and the following method would be better : Fasten one end of the chain at P, and with the eightieth link describe an arc be ; measure 14 PLANE SURVEYING. PK= 60 links, and with K as a centre, and with a radius = 100 links, the whole length of the chain, describe another arc de ; the intersection of these arcs will give the point required. 22. Another Method. With the whole length of the chain as a radius, and P as a centre, describe an arc ab ; locate K a chain from P, and with the same radius, and with a centre K^ O K describe an arc cd cutting ab in Q ; extend KQ to 0, so that OQ = QK, then will OP be the perpendicular to the line MN at the point P. Why? 23. To let drop a perpendicular on a line from a without the line. P' !;iven point First, When the point is accessible. Let MN represent the line, and P the point. With a length SETTING OFF PERPENDICULARS. 15 of chain somewhat greater than PO, describe an arc cutting MN in the points R and K. With centres R and K, and any radius greater than the half of RK, describe arcs intersecting in Q. A line drawn from P to in the direction of Q will be the perpendicular required. If the point is at P 1 at or nearly opposite one end of the line, extend the line if it be possible to N 1 until a sufficient distance is obtained to describe the arcs required. 24. Or if it is impracticable to prolong the line, as in the figure, where a pond of water prevents, proceed as follows : Extend the chain or any convenient portion of it from P to any point R in the line NO. Fix the middle point of RP, as M, and with this as a centre, and a radius 3fP, or its equal MR, describe an arc cutting the given line in 0. Join PO for the perpendicular required.* 25. Second, When the point is inaccessible. Let P be the given point, and LN the line. At any conven- ient point Q in the line LN erect the perpendiculars QO and QR of equal length. Locate Fin the line PO and T in the line RP ; then if a point S be found at the intersection of the * The angle ROP is measured by one-half a semi-circumference, and is therefore a right angle. 16 PLANE SURVEYING. prolongation VR and OT, and a point M be located in ZJVand SP, a line joining M and P will be the perpendicular sought. Why? 26. Optical Square. To set off perpendiculars from a line, an instrument called the optical square may be used. It is a small cylindrical box containing a mirror, from the upper half of which the silvering is removed. The glass is placed so as to make half a right angle with the line of sight, hence two objects seen in it, the one by direct vision, and the other by reflection, subtend at the point of observation a right angle. Or the surveyor's cross, which is simply two pairs of sights set at right angles to each other, and supported upon a staff.* D. RUNNING PARALLELS. 27. Through a given point to run a parallel to a given line, the point and line both being accessible. * While these instruments may be employed in chain surveying, neither of them is used in the ordinary practice of a surveyor, as perpen- diculars are expeditiously set off by means of the compass or transit. RUNNING PARALLELS. 17 Let LN represent the line, and P the point. Let drop a perpendicular PO, and at some other point K\ erect a perpen- L K N dicular KR = PO. A line drawn through P and R will be the parallel required. 28. Otherwise. From any point O in LN run an oblique line to the point P. Through any point R in PO measure a N Q line MQ, so that RQ = ~j~* - A line passing through PQ will be the parallel required. If R be taken at the middle point of OP, and QR be made equal to MR, the direction of the parallel PQ would be shown at once. B. OBSTACLES TO ALIGNMENT. 29. To prolong a line when an obstacle, as a tree or building, prevents direct sighting, we may proceed as follows : M PR S By Perpendiculars. Let LN be the line which it is desired to prolong past a building B. At two points and N in the 18 PLANE SURVEYING. line, set off equal perpendiculars NP and OJf, of such length that a line MP through these may be extended past the obstacle to some point S. At R and S set off perpendiculars to X and F, of the same length as before, at and N, and join XF; it will be the prolongation of LN. 30. Otherwise : by Equilateral Triangles. On LN, the line to be prolonged, take a distance ON as a base, and construct on it an equilateral triangle NOP; extend the side OP to some point Q. Describe an equilateral triangle QRS, and prolong the side QR to F, making QF= QO; finally the construction of the equilateral triangle VXY will give XT the direction sought. P. OBSTACLES TO MEASUREMENT. 31. a. When Both Ends of the Line are Accessible. By Perpendiculars. For example, if it is desired to measure one side of a field or farm where a fence, hedge, or bushes prevent chaining on the line, set off perpendiculars, and measure the parallel line. Let LN represent a line which, on account of fence and brush, it is impracticable to make the measurement exactly on the line OBSTACLES TO MEASUREMENT. 19 Erect at Z, and N perpendiculars LI and Jtfw, of equal and suffi- cient length so. that a line connecting I and n will clear the obstruction. Measure In ; it will be the length of the required line. 32. b. When One End is Inaccessible. By Symmetrical Triangles. Suppose LP the line, P the inaccessible end, visible, but on the opposite bank of a river. Measure from any point JVnear the river, in a direction diverg- ing from its bank to -r R, making NI=IR. Through any other point Jf, in the line LN, measure through / to K, so MI= IK. If now a point be found in the prolonga- tion of RK, and in line with / and P, RO may be measured and taken for their distance NP.* 33- Otherwise. Measure from the line the perpendicular LP; erect at P a perpendicular to PN, and extend it to a point M in the prolongation of LN. Measure then the proportion ML:LP=LP:LN PL" ML gives LN: " The student will show that ROI and NIP are symmetrical triangles, and NP and RO are homologous. 20 PLANE SURVEYING. 34. c. When Both Ends are Inaccessible. By Symmetrical Triangles. Let LN be the line, the length of which it is required to determine. Take any point P, measure PO and PM, and find by one of the preceding methods OL, MN, and hence, the total length of PL and PN. Now take points R and Q in the lines PL and PN respectively, so that PR : PQ = PL : PN, and measure RQ ; then the required line LN may be calculated by the proportion PQ : PN= RQ : LN. G. MEASUREMENT OF HEIGHTS. 35. To measure the height of a tree or a flag-staff. Let BC represent the height required. At a point D set up a staff of a known height so that, with the eye at -4, C and E will be in line of sight ; measure AD and DB; then the similar triangles ADE and ABC give the proportion AD : DE = AB : BC. nn _DExAB AD Whence EXERCISES. 21 EXAMPLES. 1. If the height of a staff is 4 feet, and the distance from it to a tree = 80 feet, AD being 4^ feet, what is the height of the tree? Ans. 77|| feet. QUERIES. If the height of the staff is equal to AD, the length of neither being known, simply the distance AB given, could the height of the tree be ascertained ? If the ratio of the height of the staff to AD is known, but not the absolute length, could the required height be found by simply measuring AB1 Is this method applicable on other than horizontal ground ? 2. A liberty pole, whose height was 90 feet, standing on a horizontal plane, was broken off, and the extremity of the top struck the ground 28 feet from the bottom of the pole. Re- quired the length of the broken part. EXERCISES. 1. Set a stake 40 feet perpendicularly distant from a given point in a given line. 2. Through a given point 50 feet from a given line run a parallel 120 feet in length. 3. Prolong a line beyond a house or other obstacle. 4. Measure the width of a stream or pond without crossing it. 5. Run a line to the bank of a stream or lake, and let fall a perpendicular on the line near its extremity from a given point without it. 6. Measure the height of a tree, flagstaff, or church spire. 22 PLANE SURVEYING. SECTION III. RECORDING THE FIELD NOTES. 36. The Field Notes should be kept in a neat, concise, and intelligible manner, exhibiting a complete record of the work done, and the method of doing it, so that a surveyor unac- quainted with the work, and having the record before him, could make a plot of the tract, or go on the field and readily ascertain the position of any point indicated in the notes. Either of two methods may be employed, or a combination of them. 37. Sketch. One is to make a sketch of the tract as the survey progresses, writing the length of each line and indicating the intersection of fences, roads, streams, etc., as shown below. For surveying a field or small tract of land, this is a good method, but if the tract is large, many sided, and numerous points to be noted in and 'near the side-lines and diagonals, it would be difficult if not impossible to decipher the sketch on a page of the ordinary field-book, and to make an intelligible record of the work would require a book or sheet inconveniently large to carry about the field. RECORDING THE FIELD NOTES. 23 38. Columns. A method which will answer as well for com- plex as for simple surveys consists in drawing two parallel lines, about an inch apart, extending from top to bottom of the note- book, and near the middle of the left-hand page. Between the lines the distances and stations are to be recorded, commencing at the bottom of the page and proceeding upwards. Roads, fences, streams, etc., should be represented on either or both skies of the column as they naturally appear. The record of the measurements on any line being referred to the beginning of the line. The right-hand page may be used for sketching any part of the survey to further elucidate, where necessary, the work done. A station is indicated by a triangle (A) or a circle (O) . If the station is at the end of a line it is usual to name it by the letter or number, designating that corner as station A or station 1, and the line extending from A to B is called the line AB^ from 4 to 5, the line 4, 5 ; or a line may be designated by its length ; a line that is 3 chains and 52 links long would be referred to as the line 352. F. S. 4.78 4.78 A false station is a point in a line whence other measurements are to be made either to the right or left, and are desig- nated bv enclosing in a curve its distance from the end of the measured line, or by writing F. S. opposite that distance, as per margin, which shows that there is a false station at a distance of 3.62 chains from A on the line AB. A fence, brook, road, etc., intersecting the measured line, should be drawn so as to indicate, as nearly as possible, its inclination thereto, but not as a continuous line ; the ends on each side being directly opposite, as at 4.58 and 5.26, so that if the vertical column 24 PLANE SURVEYING. O 4.58 5.36 6.18 were to vanish by the two lines MN and OP coinciding, the fence or creek would be shown as continuous. When the record of a line, as JOT, is complete, and the meas- urement is continued from N, a horizontal line is drawn across the column as shown in the figure. But if the survey closes at the end of a line, as at 0, or if for any reason the work is to proceed from some other point, two lines are drawn across the column. 3.40 2.30 M 6.80 Y A mark (K) or (l~) placed at the beginning of a line indicates by shape, as well as position, that the line along which it stands bears to the right of the pre- ceding ; the reverse position of the angle (N or ~l) indicates a turn to the left. In the figure, MN bears to the right of KM, and NO to the left QtMN. RECORDING THE FIELD NOTES. 26 The record of the survey sketched in Article 37 would be represented by the column method as follows : 8.35 9.50 D D 13.00 C c 11.25 5.75 B B 12.50 e.oo A D 13.50 IS A s A 15.00 i 26 PLANE SURVEYING. SECTION IV. MAPPING AND PLOTTING. 39. A Map of a survey is a correct representation or copy of the tract surveyed, exhibiting not only its boundaries, roads, streams, etc., in relative dimensions and positions, but also the irregularities and appearances of its surface. A Plot (or Pkc) is an outline map, in which, in general, only the boundaries, roads, streams, and important lines are delin- eated, but no attempt is made to indicate the topography of the tract. The surveyor usually makes a plot of a field or farm survey. The civil engineer makes a map of a proposed railroad. INSTRUMENTS USEFUL FOR MAKING A PLOT OF A CHAIN SURVEY. 40. Drawing-Board, T-Square, Triangles, Dividers, Scale, Drawing Pen and Pencil.* A Drawing-Board is a rectangular, smooth board to which the paper that is to contain the drawing is fastened. There are two patterns : one consists of a frame of walnut, or other hard wood, with a detachable centre of soft white pine. The paper, which should be somewhat larger than the detachable centre, being moistened and laid on it, becomes well stretched when the parts of the board are buttoned together and the paper dries. The other is simply a rectangular white pine board made of several pieces of wood laid in different direc- tions to prevent warping. Both patterns are made of various dimensions. 41. A T -Square, as its name indicates, is a square or ruler with a cross-piece or head at one end, giving it the appearance * Other instruments used in drawing are described in Chapter II. Section VIII. MAPPING AND PLOTTING. 27 of a letter T. There are two patterns of these, one with a head fixed at right angles to the ruler or blade; the other, in addition to the permanent head, has another head attached to it with a clamp screw, so that by properly setting the movable head, lines of any desired inclination may be drawn. The blade, being long and thin, should be tested occasionally by means of a metallic straight edge or another T-square to see whether or not it is perfectly straight. The correctness of the angles should also be tested ; this may be done as indicated in the next article. 42. Triangles are made of hard wood, rubber, or metal, and are either solid or have an open centre. The angles are usually 30, 60, and 90 degrees, or 45, 45, and 90 degrees, and the longest side rarely exceeds 12 inches. The T-square and triangles are frequently employed together to draw parallels, perpendiculars, and many of the oblique lines of a plot.* The sides of triangles should be tested occasionally, to see if they are straight, by placing them against the edge of a metallic straight edge. The right angle may be tested by placing one of its sides against a straight edge ; mark the direction of the other side, reverse the triangle, but bring the same side against the straight edge, and having the right angle at the same point as before, mark the side again. If the two marks coincide, the angle is right ; otherwise, it is not. When correct, the right angle of the triangle may be used to test the correctness of the right angle of the T-square. 43. Dividers (or Compasses) are made of different sizes and numerous appendages. The surveyor will need at least one with a detachable leg, so that another leg, carrying a pen or * The results are tolerably accurate within the limits usually required in a farm survey. It may be well, however, to caution the student not to rely too much upon the accuracy of a point located by means of and near the extremity of a thirty-inch T-square. 28 PLANE SURVEYING. pencil point, may be inserted when necessary. These, it need hardly be said, are used for laying off lines, describing arcs, circles, etc. 44. Lead-Pencil. Fine quality, hard, used in outlining the work ; and a Drawing-Pen, medium size, for inking in the drawing. 45. Scales are made of box-wood, metal, ivory, or paper, and are of various kinds. Triangular and diagonal are gener- ally used for plotting chain surveys. The triangular scale for engineers and surveyors is usually 12 inches long, and made of good box-wood, each of the six bevelled faces being graduated with a single scale, viz. : one face contains 10 divisions to the inch, one 20, another 30, another 40, one 50, and one 60 divis- ions ; and generally one inch on each face is subdivided so that an extremely small fraction of an inch may be set off or read. This is a very convenient scale ; not only can very small divisions be readily transferred from it to a drawing, but by simply placing the instrument properly on a line of a drawing, the scale of which is known, its length may be directly deter- mined. The Diagonal Scale is usually six inches long, thin and flat, divided transversely into 6 equal parts of one inch each, and longitudinally into ten equal parts. At one end, as AD, one inch is divided by 10 oblique lines, as 8 wi, 6 ?i, etc., into 10 equal parts and numbered as shown in the figure. P nmA Now Fs being .1, the next division between the perpendicular FE and the oblique line sE is .09, the next .08, and the last MAPPING AND PLOTTING. 29 division, or one nearest -F, is .01. Hence the scale may be used to measure .01 of an inch, or one hundredth of any divis- ion taken as the unit. For example, to lay off 3.4, place one foot of the dividers at 3 on the line EC and extend the other foot to 4 between DE. To lay off 3.42, place one foot at the intersection of 3, 3, and 2, 2, and the other on the same line 2, 2, at its intersection with 4 p. The diagonal scale usually found with a box of drawing in- struments contains various graduations. The simplest are divided to inches, and halves, quarters, tenths, and twelfths of an inch ; each quarter and half subdivided diagonally into tenths, so that a tenth of a quarter can be taken off at once ; and even tenths of these are indicated on the scale besides other divisions of more or less utility. Paper scales are frequently employed, and regarding hygro- metric changes are better than the others, for the scale and the paper containing the drawing expand and contract more nearly alike. Generally, however, they are not divided with the same degree of accuracy. 46. Drawing to a Scale consists in drawing lines whose length shall be some fraction of the length of the line measured. Suppose, for example, a line is 13 chains long, and it is desired to draw it to a scale of 5 chains to an inch ; then 2y 6 ^ inches will evidently be the distance to transfer from the scale to the paper to represent the length of the line. A line 10 chains and 50 links in length drawn to a scale of 3 chains to an inch will be represented by a line 3| inches long, and so on. The length of the line divided by the number of units chains, yards, feet, etc. to the inch, always giving the distance to be taken off the scale. Obviously the converse of this is true ; that is, the real length of a line may be ascer- tained when the scale is known, by multiplying the units in the length of the line in the drawing bv the number of chains or feet which each unit represents. In the last example the length of the line being found 3.jr inches, and the scale 3 chains to an 30 PLANE SURVEYING. inch, the true length = 3.5 x 3 = 10.50 chains. The scale should always be given on the drawing. It may be stated thus: Scale, 3 chains to an inch, 1000 feet to an inch, 2 miles to an inch, or fractionally, and thereby indicating the relative length of the lines in the drawing to those which they repre- sent ; as, 1 : 500, 1 : 2000, etc. 47. Size of Drawing or Scale to Adopt. In farm surveys of small extent, 1 or 2 chains to an inch may be used ; for medium tracts 3 chains to an inch (1 : 2376) is perhaps the best. The shape of the farm, the length of the shortest and longest sides, as well as the object of the drawing, will, how- ever, influence the surveyor in his decision of the scale. 48. Scale Unknown. If the area of a tract of land is known but the scale not given, it ma}' be found by measuring the lines of the drawing referred to any convenient scale and comput- ing the area from these determined lengths. Then, since the areas of similar figures are to each other as the squares of their homologous sides, the true scale may be obtained by the pro- portion, computed area _ square of assumed scale # known area square of true scale SECTION V. ON AREAS, AND ILLUSTRATIVE EXAMPLES. A. AREAS. 49. The following are geometrical truths with which the student is supposed to have an acquaintance, but are given here for convenience of reference. *The protractor and other drawing-instruments used in connection with compass and transit surveying are described in Chapter II. AREAS. 31 The Area of a Triangle is equal to one-half the product ot its base and altitude. In Terms of the Three Sides the area is equd to the square root of the continued product of one-half the sum of the sides, and the half-sum minus each side severally, or in symbols, where A. = area, a, 6, c, the three sides, and s their sum, If the triangle is equilateral and s = length of a side, 50. The Area of a Rectangle is equal to the product of ite length and breadth, or A = bl where b = breadth and I = length. 51. The Area of a Parallelogram is equal to the product of its base and altitude, or A='bh where &= breadth and h= height. 52. The Area of a Trapezoid is equal to the product of one- half the sum of its parallel sides and the perpendicular distance between them, or A=^(m+n) where m and n are the parallel sides, and p the perpendicular distance between them. 53. The Area of a Regular Hexagon, where s denotes the g length of one of its sides, is ^4 = - E c BE, to the opposite side DC, and the / i / distance CE. Then A = AB x BE. / / To Plot. La\- off the base AB, and -4 B at the extremity B erect a perpendicu- lar equal BE. Through E draw DC equal to and parallel to AB, making EC its proper length. Join DA and CB, and the parallelogram ABCD will be formed. EXAMPLES. 1. The base of a parallelogram measures 10.54 chains. A perpendicular from one extremity of the base to the opposite side 5.16 chains, and the distance corresponding to EC in the last figure is 1.82 chains. Required the area and plot. Ans. 5.439 acres. 2. A surveyor employed to determine the area of a rhombus, and knowing that the obtuse angles were xiouble the acute, measured the shorter diagonal only, and found it 100 feet. Was the measurement sufficient? If so, give the area. QUERIES. Can the area of a rhombus be ascertained if the lengths only of the two diagonals be given ? If either diagonal and a side be given ? TRAPEZOIDS. 67. Measure EC, the perpendicular CD, and BA ; note E C where the perpendicular CD meets the / ~A base AB. CD. A D B To Plot. Lay off the base AB to the desired scale, and at D erect a perpendicular thereto equal to DC. Through C draw CE of the required length and parallel to AB. Join EA and CB. The figure resulting will be the trapezoid required. ILLUSTRATIVE EXAMPLES. 39 EXAMPLES. 1. The base of a trapezoid measures 12.62 chains, the parallel side 8.14 chains, and the perpendicular 7.44 chains. The distance corresponding to DB in the last figure is 1.12 chains. Required the area and plot. Area= 7.723 acres. 2. A railroad embankment extends 3240 feet perpendicularly across a farm intersecting parallel sides. At one end its base is 96 feet wide, and at the other 60 feet. Supposing the property line is 10 feet from the embankment on each side, how much of the farm is taken for railroad purposes? TRAPEZIUMS. 68. First Method. Measure either diagonal, and the per- pendiculars thereto from the opposite angles, noting the distances AH and EC. To Plot. Draw the diagonal AC to AL ^ ^ the desired scale, and fix the points H and E. At these points erect perpendiculars corresponding to the scale and measurements. Joining DA and DC, and BA and BC, will complete the plot required. Second Method. Measure all the sides and a diagonal as shown in the figure, thereby dividing the trapezium into two triangles, all the sides of which are known ; whence the area may be com- puted by the formula for the area of a triungle in terms of the three sides. To Plot. Lay off the diagonal AC, and locate the points B and D by methods heretofore given. Connect the points ABC I) A for the plot required. 40 PLANE SURVEYING. EXAMPLES. 1. The diagonal of a trapezium measures 120 rods, and the two perpendiculars 30 and 40 rods ; what is the area ? Ans. 26^ acres. 2. The sides of a trapezium taken in regular order are AB = 5, BC=9, CD = 11, and DA=13 chains, and the diagonal AC 12 chains. Required the area and plot. 3. The sides of a trapezium are 18.10, 22.14, 28.16, and 34.62 chains, and the diagonal from the first to the third corner is 30.76 chains. Determine the area. POLYGONS. Regular or irregular, five or more sides. 69. First Method. Measure all the sides and the diagonals, thus dividing the tract into three or more triangles. The area will equal the sum of the areas of the triangles thus formed. To Plot. Draw a line repre- senting the diagonal BE, and construct the triangle ABE on it ; on the other side of BE con- struct BCE; if a pentagon, the plot will be completed by add- ing ODE. If a hexagon, there must be measured another diagonal giving four triangles, and generally, for any number of sides n, there will be n 3 diagonals and n 2 triangles, the area of the tract being equal to the sum of the areas of the n 2 triangles. If the tract be a regular polygon, the measurement of one side by the aid of the table in (57) will be sufficient to deter- mine the area. ILLUSTRATIVE EXAMPLES. 41 70. Second Method.* Measure one or more diagonals, and perpendiculars from these to the opposite angles, or corners, thereby dividing the tract into right triangles, or right triangles and trapezoids. The sum of the areas of these figures will equal the area of the polygon. EXAMPLES. 1. The sides of a pentagon taken in regular order are, 6.80, 4.20, 5.30, 8.90, and 9.62 chains. The diagonals from the fifth corner to the second and third are each 10 chains. Find the area,t and make a plot. 2. A side of a regular heptagon measures 4.25 chains. What is the area? Given the following field notes to calculate the areas and make the plots. The distances are in chains. D D 16.75 12.50 C4.50 13.50 7.80 4.60 E 12.90 4.50 E C 2.80 5.90 9.00 S' 80 F B 5.50 3.20 B 4.50 4.80 2.60 3.00 F 8.20 6.25 G A A * Other methods are given in Chapter II. t The work may be abridged by using logarithms. 42 PLANE SURVEYING. -Proof Lines 7 - - r - - -> 5 re 8 S s s ILLUSTRATIVE EXAMPLES. 43 CIRCLES AND CIRCULAR RINGS. 71. Measure the radius or diameter of a circle, and the radii or diameters of a circular ring. The area of the former = TT^ = . The area of the latter = *(!? r 2 ). EXAMPLES. 1. The diameter of a circle is 10.16 chains. What is the area? 2. What is the 'area of a circular ring, the outer and inner radii measuring respectively 20 and 12 rods? SECTORS AND SEGMENTS. 72. Measure the chord AB, and the perpendicular distance or height of arc DE, from the centre of AB to the arc AEB. From these data the radius and the angle at the centre may be found ; and hence the area ob- tained. See (59) and (61). Otherwise, measure the radius BC, and by short chords the arc AEB; whence the area may be computed. (The student will supply the details for both cases.) G EXAMPLES. 1. If the length of the arc of a sector is 500 feet and the radius 1000 feet, how many acres does it contain? Ans. 5.739. 2. If the chord AB (last figure) =40 feet, and the height of arc DE = 10 feet, what is the area of the segment? Ans. 279.558 square feet. 3. Given the radius, which is bisected by the chord, = 100 feet. Required the area of sector and segment. 44 PLANE SURVEYING. SECTION VI. OFFSETS AND TIB-LINES. 73. When any portion of the boundary of a tract of land is irregular, as, for example, when it is a stream or crooked road, the survey along such sides is best effected by measuring a straight line, as LN, and setting off short perpendiculars ra'ra, o'o, and p'p at points m', o', and p', and extending them to the boundary line. Such short perpendiculars are called offsets, and they should be so chosen , that the part of the curve Lm, mo, op, etc., / m intercepted between any two consecutive ones may be considered straight ; whence the area of the part lying between the straight and curved lines may be obtained by adding to- gether the area of the triangles and trapezoids into which it is thus divided. If the field notes corresponding to the above figure are as below : N 9.00 7.00 2.50 1.20 L 1.30 p 1.40 o 1.00 m The area between straight line and boundary f Area triangle Lmm', 6000 square links, I Area trapezoid mm'oo', 15600 " " "~ 1 Area trapezoid oo'pp', 60750 " " [Area triangle p'pN, 16900 " " Their sum = 99250 " " cr, .9925 of an acre. OFFSETS AND TIE-LINES. 45 x' 74. Rectangular Co-ordinates. Let XX' and YT' be two straight lines intersecting each other at right angles at 0, and P'P", points in their plane. Then if perpendiculars be drawn thi-ough these points to the lines XX' and YY', the distances cut off on the former are called abscissas, and those on the lat- ter ordinates. The abscissa and ^ ordinate referring to one point, as P, are termed the co-ordi- nates of that point. , The lines to which the meas- urements are referred are called the axes; XX' being called the axis of abscissas or axis of X, and YY' the axis of ordi- nates or axis of Y. The axes being at right angles, the system is called the rectangular system of co-ordinates. is the origin.* Desig- nating the ordinates measured from the axis of X upward, and the abscissas measured to the right of the axis of Y, as plus, and those downward from the X-axis and to the left of the F-axis, as minus, it is evident that a point can be located in either quadrant very readily by this method. If the co-ordinates of P 1 are x = 6 and y = 4, it means simply that Ox' = 6 and Oy' = 4, and the point may be located by drawing the lines as indicated. If x = 5 and y=3, the point is five units to the left of the F-axis, and three units above the X-axis, etc. 75. Application of Rectangular Co-ordinates to the Computa- tion of Areas. Suppose it is required to find the area of any number of trapezoids formed by a broken line, and perpendiculars from its angles upon a straight line as indicated in the figure. XX', the * Axes inclined to each other are called oblique. 46 PLANE SURVEYING. straight line, may be taken as the axis of X, and TV the axis of T. Let # x m , x n , etc., y y m , y n , etc., denote respectively the abscissas and ordinates of the points L, M, N, etc. I'm Y n F, XI Xm The area required By expanding and simplifying there results (y m - y Whence for calculating the area of a tract of land included between a straight line and a broken line, whose angles are given by their co-ordinates upon the straight line as base, we have the following RULE. Multiply the difference between each ordinate and the second succeeding one by the abscissa of the intervening ordinate. Multiply also the sum of the last two ordinates by the last abscissa. The half of the algebraic sum of these several products will be the area. EXAMPLES. Calculate the areas, and make the plots from the following field notes ; the distances are in chains. * A similar expression could evidently be found for any number of trapezoids. OFFSETS AND TIE-LINES. 47 13.60 .90 12.40 1.50 9.80 2.10 5.80 1.60 2.80 1.00 1.00 .60 18.90 1.60 16.70 2.00 12.40 2.40 7.40 1.50 4.20 1.00 1.70 .20 76. A slight modification of the rule just given will make it applicable to the case where a broken line encloses a tract or forms the boundary of a polygon. Let the tract enclosed be represented by the figures, then the area 48 PLANE SURVEYING. By expanding, cancelling, and factoring, we may obtain either of the following expressions : (y - &,) (a;, - x.) ].- (2) Whence, for the area of a polygon whose corners are given by their co-ordinates, we have the following RULE. Take one-half the sum of the products of each { and the difference of its adjacent <{ ^^^^ < l the subtraction in the same direction round the plot.* EXAMPLES. 1. Given the abscissas of the several corners of a field, L, M, N, 0, P, respectively : 2.00, 5.50, 12.00, 15.00, and 8.60 chains. The corresponding ordinates : 10.20, 1.80, 4.00, 9.40, and 14.00 chains; to compute the area. * The work of computation may be abridged when the abscissas are greater than the ordinates, by making the differences of the a"bscissas the factors with the ordinates ; and when the ordinates are greater than the abscissas, taking the differences of the ordinates with the abscissas. If the axis of ordinates pass through L, the abscissa of that point would vanish. Regard must, in all cases, be had to the resulting signs. OFFSETS AND TIE-LINES. The form of reduction is as follows : 49 CORNERS. OBDINATES. ABSCISSAS. DIFFERENCE BETWEEN ALTERNATE ABSCISSAS. DOUBLE AREAS. L 10.20 2.00 3.10. 31.6200 M 1.80 5.50 - 10.00 - 18.0000 N 4.00 12.00 - 9.50 - 38.0000 9.40 15.00 3.40 31.9600 P 14.00 8.60 13.00 182.0000 245.5800 - 56. v 2)189.5800 10)94.79 sq. chs. 9.479 acres. 2. Given the abscissas of the several corners of a field, L t M, N, 0, P, Q, R, respectively : 0, 6.50, 14.60, 22.80, 20.00, 16.70, 9.90; and the corresponding ordinates : 13.20, 3.72, 4.40, 3.90, 17.24, 16.90, and 17.30, all in chains ; to determine the area and make a plot. 3. Given the abscissas of the several corners of a field, A, B, (7, D, E, F, G, H, respectively : 100, 300, 360, 290, 400, 250, 120, 0; and the corresponding ordinates : 0, 0, 160, 300, 380, 520, 520, and 330, all in feet ; to determine the area, and make a plot. 4. Verify Example 3 by a method independent of that given on the preceding page. 50 PLANE SURVEYING. 5. Required the area and plot from the following field notes : t A E A 23.50 41.10 y F Y Diag. DF 25.80 F 21.90 Diag. CF 17.65 E Y B V E F A 20.50 30.10 D Y D A D C *e 17.40 28.90 ID 1.00 15.50 N F ii I T3 1.60 13.00 F OQ fi 5 1.75 1.00 1.20 8.50 6.00 3.50 26.75 B i C K 1 C On river bank. SB 18.00 o 2.00 13.50 3.50 10.00 2.50 5.50 V B Y j B ! 18.50 * i A Other examples containing offsets are given in Chapter II, OFFSETS AND TIE-LINES. 77. To find the area of a tract of land when it is impossible to measure the diagonals or perpendiculars, as in the case of a lake or swamp. Measure MN and ON, and continue the measurements past their intersection at N, making NH some fractional part of MN, and NK the same part of ON.* Now because of the similarity of the triangles MNO and HKN, MO may be found by measuring a tie-line HK, and divid- ing it by the fraction used. Similarly, LM may be found^ Then OL being , measured, the area of the polygon MNOLR can be computed. In case of a pond or lake, if offsets be taken from the sides of the polygon to the edge of the water, and the sum of the areas thus found included between the sides and the lake be deducted from the area of the polygon, the area of the body of water will be shown. MISCELLANEOUS EXAMPLES. 1. One side of an equilateral triangle measures 18.24 chains. Required the area. 2. The perpendicular of an equilateral triangular piece of ground measures 160 feet. What is the area? Ans. 14780.16 square feet. What part of an acre? * Great care should be exercised in the measurements, since the erroi is magnified in the computed lines. If the lines are so taken that KH is one-fourth of MO, an error of one link in measuring KH will make a difference of four links in MO. For methods of performing such work more accurately, see Compass and Transit Surveying, Chapter II. Section IX. 62 PLANE SURVEYING. 3. It is known that the base of an isosceles triangle is f the length of one of its equal sides. The perpendicular measures 80 feet. The sides and area are required. Ans. Each side, 100 feet; base, 120 feet. Area, 4800 square feet. 4. Desiring to ascertain the radius of a railroad curve (it being the boundary of a field), a surveyor measured from centre to centre of tracks, a chord of 200 feet ; also the per- pendicular distance from the centre of chord to the middle of tracks, 4 feet. Show that these measurements indicate the radius = 1252 feet. QUERY. How should the data obtained in Example 4 be em- ployed to determine the area, assuming that the curve is con- cave to the field ? 5. The circumference of a circle is 100 rods. How many acres does it contain ? Ans. 4.974. QUERY. Can Problem 5 be solved without first finding the radius or diameter? 6. If the number expressing the 'area of an equilateral tri- angle in square feet is the same as that showing the length of one of its sides in lineal inches, what is its area? Ans. 332.55. 7. The chord of a circle measures 60 feet, and the height of arc, or versed sine, 10 feet. Find in the same circle the versed sine of a chord of 90 feet. Ans. 28.2 feet. 8. The lengths of two chords lying on the same side of the diameter of a circle are 96 and 60, and their distance apart 26. Required the area between them. SUGGESTION. Let x = perpendicular distance from centre of short chord to the nearest point of circumference, and y = per- pendicular distance from centre of long chord to the farthest point of circumference ; that is, measured in the opposite direc- tion from the first OFFSETS AND TIE-LINES. 58 Then * (y + 26) = 900. y (x + 26) = 2304. Whence the diameter is readily determined and thence the area required. 9. Show that the area of the circumscribed hexagon is to the area of the circumscribed equilateral triangle as 2 is to 3. 10. Show that the area of a regular inscribed polygon of n . , n , . 360 sides = - r 2 sin 2 n 11. Show that the area of a regular circumscribed polygon 1 &0 of n sides = w 2 tan n 12. The distance between the centres of two circles, whose diameters are each 50, is equal to 30. What is the area common to the two circles? Ans. 559.15. 13. Three equal circles being tangent to each other ex- ternally enclose 40 rods. What is the radius of each circle? Ans. 15.75 rods. EXERCISES. 1. Survey a polygon, measure all the sides and necessary diagonals, run test-lines, record the notes, make a plot, and compute the area. 2. Take the boundaries as found above, and complete the survey by measuring one diagonal and perpendicular offsets to the corners. Make record, plot, and computation. 3. Measure a field partly bounded by a creek or lake, ren- dering it necessary to take offsets thereto. Record the notes, plot, and calculate area. 4. Survey a pond or small lake by tie-lines and offsets. CHAPTER H. COMPASS AND TEANSIT SUEVEYING. SECTION I. DEFINITIONS AND DESCRIPTION OP INSTRUMENTS. 78. The Axis of the earth is the imaginary line about which it rotates. The Poles are the points where the axis pierces the earth : one the north pole, the other the south pole. 79. A Meridian Plane is a plane embracing the earth's axis. 80. A Meridian Line, or true meridian, is the intersection of a meridian plane with the surface of the earth. In plane surveying the meridians passing through the ex- tremities of lines surveyed are considered parallel. 81. The Magnetic Needle is a thin bar of strongly magnet- ized steel, balanced on a pivot, so that it may turn freely, and always come to rest in the direction of the magnetic meridian. 82. The Magnetic Meridian is indicated by the direction of a bar magnet, when horizontal, freely suspended and at rest. It does not in general coincide with the geographic meridian. The angle included between them is called the declination of the needle, or variation of the compass.* and the change in this angle is termed the variation of the declination. * See Chapter III., on Declination of the Needle. DESCRIPTION OF INSTRUMENTS. 55 83 The Azimuth of a Line is the angle which the vertical plaue containing it makes with the plane of the meridian. 84. The Bearing of a Line, called also the course, is the angle which it forms with the direction of the magnetic needle. 85. The Meridian Distance of a Point is its perpendicular distance from an assumed meridian. 86. The Meridian Distance of a Line is the meridian dis- tance of the middle point of that line. 87. A Horizontal Angle is an angle included between two lines in a horizontal plane. A Vertical Angle is an angle included between two lines in a vertical plane. 88. An Angle of Elevation is a vertical angle, one side of which is horizontal, and the other inclined upward from the angular point. 89. An Angle of Depression is a vertical angle, one side of which is horizontal, and the other inclined downward from the angular point. In Compass and Transit Surveying, in addition to the meas- urement of lines, angles are observed ; hence, besides the instruments previously described, we present the following : THE SURVEYOR'S COMPASS. 90. The Surveyor's * Compass consists essentially of a brass plate carrying a horizontal graduated circle, in the centre of which is suspended, so as to turn freely, a magnetic needle ; and nt the extremities of the plate are attached vertically two flattened pieces of brass, called sights, having fine slits and * The Solar Compass is described in Chapter VI. 56 PLANE SURVEYING. circular openings in them, by which the instrument is directed upon any object or station. In addition to the essentials named, this instrument usually has two small spirit levels set on the plate at right angles to each other, a vernier scale for setting off the declination of the needle, a tangent scale for reading vertical angles, and a brass head for mounting the instrument upon a tripod or a single staff called Jacob's Staff. 91 The graduated circle is divided into half-degrees, and is figured from to 90 on each side of the centre line of zeros. The magnetic needle is from 4 to 6 inches long in the different sizes of compasses, having set in its centre a piece of hardened steel highly polished, which, resting upon the hardened point of the, centre-pin, allows the needle to turn freely, horizontally, and to take its direction in the magnetic meridian. 92. The needle is lifted from its support by a concealed spring actuated by a screw. The test of the delicacy of a magnetic needle is the number of vibrations which it will make in a certain arc before coming to rest. When the compass is not in use, the needle should be screwed up against the glass, and the instrument set so that the north end of the needle points towards the north. To ADJUST THE COMPASS. 93. The Levels. First bring the bubbles into the centre, by the pressure of the hand on different parts of the plate, and then turn the compass half-way around ; should the bubbles run to the end of the tubes, it would indicate that those ends were the highest : lower them by tightening the screws immedi- ately under, and loosening those under the lowest ends until, by estimation, the error is half removed ; level the plate again, and repeat the first operation until the bubbles will remain in the centre during an entire revolution of the compass. SURVEYOR'S COMPASS. DESCRIPTION OF INSTRUMENTS. 59 94. The Sights may next be tested by observing through the slits a fine hair or thread, made exactly vertical by a plumb. Should the hair appear on one side of the slit, the sight must be adjusted by filing off its under surface on that side which seems the highest. 95. The Needle is adjusted in the following manner : Having ;he eye nearly in the same plane with the graduated rim of the compass-circle, with a small splinter of wood or a slender iron wire bring one end of the needle in line with any prominent division of the circle, as the zero or ninety-degree mark, and notice if the other, end corresponds with the degree on the opposite side: if it does, the needle is said to "cut" opposite degrees ; if not, bend the centre-pin by applying a small brass wrench, about one-eighth of an inch below the point of the pin, until the ends of the needle are brought into line with the oppo- site degrees. Then, holding the needle in the same position, turn the com- pass half-way around, and note whether it now cuts opposite degrees ; if not, correct half the error by bending the needle, and the remainder by bending the centre-pin. The operation should be repeated until perfect reversion is secured in the first position. This being obtained, it may be tried on another quarter of the circle ; if any error is there manifested, the correction must be made in the centre-pin only, the needle being already straightened by the previous operation. 96. Electricity. A little caution is necessary in handling the compass, that the glass covering be not excited by the friction of cloth, silk, or the hand, so as to attract the needle to its under surface. When, however, the glass becomes electrified, the charge may be removed by breathing upon it, or touching different parts of its surface with the moistened finger. 60 PLANE SURVEYING. 97. The Needle is remagnetized as follows : The operator, being provided with an ordinary permanent magnet, and holding it before him, should pass with a gentle pressure each end of the needle from centre to extremity over the magnetic pole, describing before each pass a circle of about six inches radius, to which the surface of the pole is tangent, drawing the needle towards him, and taking care that the north and the south ends are applied to the opposite poles of the magnet. Should the needle be returned in a path near the magnetic pole, the current induced by the contact of the needle and magnet, in the pass just described, would be reversed, and thus the magnetic virtue almost entirely neutralized at each operation. When the needle has been passed about twenty-five times in succession, in the manner just described, it may be consid- ered as fully charged. A fine brass wire is wound in two or three coils on the south end of the needle, and may be moved back or forth in order to counterpoise the varying weight of the north end. 98. The Centre-Pin. This should occasionally be examined, and if much dulled, taken out with a brass wrench or with a pair of pliers, and sharpened on a hard oil-stone the operator placing it in the end of a small stem of wood or a pin-vise, and delicately twirling it with the fingers as he moves it back and forth at an angle of about 30 degrees to the surface of the stone. When the point is thus made so fine and sharp as to be in- visible to the eye, it should be smoothed by rubbing it on the surface of a soft and clean piece of leather. 99. Weight. The average weights of the different sizes of compasses, including the brass head of the Jacob-staff, be- ginning wth the smallest, are respectively 5, 7, and 9^ pounds. DESCRIPTION OF INSTRUMENTS. 61 THE VERNIER. 100. A Vernier is an auxiliary scale for measuring smaller divisions than those into which a graduated scale or limb is divided.* The smallest reading of the vernier, or least count, is the difference in length between one division on the gradu- ated scale or limb, and one on the vernier. If the divisions on the vernier are smnller than those on the limb, the vernier is direct; if the reverse, retrograde. 6 7 8 9 10 11 12 13 14 15 16 17 Let LM represent any scale divided into tenths, and we wish to measure or read to tenths of these divisions, i.e. to y^ v . Using a direct vernier, we should have 10 spaces on it equal to 9 on the scale, and each one of them equal to T 9 of y 1 ^, or y^, of the scale graduation ; giving a least count of y 1 ^ T f 7 = y-^, as desired. To read to twentieths of the divisions on the scale, we should have 20 divisions on the vernier corresponding to 19 on the scale, or each space on the vernier equal to if ' iV = '3inr> and giving a least count of -ffo ^fa = -^fa. In general, if s = the smallest division of the scale or limb, v = the smallest division of the vernier, n = number of divisions on the vernier, we shall have least count = s v = - n Or, the least count of a vernier is equal to the smallest division of the scale or limb divided by the number of divisions on the vernier.f If s = % degree, and n = 30, as ordinarily found on transit * It derives its name from Peter Vernier, 1631. t It is evidently immaterial whether LM be straight or curved. 62 PLANE SURVEYING. plates, the least count will be -$-30 = ^ of a degree = one minute. If s = $ degree, and n = 40, oftentimes found on vertical arcs to solar attachments, the smallest reading = \ -H 40 = T | 7 of a degree = minute. To space a vernier for a given least count, say 10", on a limb graduated to 10', we must have n = - = = 60 spaces, s-v | covering 59 spaces on the limb. 101. To read an Instrument having a vernier consists in determining the number of units and fractional parts thereof, into which its scale or limb may be divided, from the zero point on the limb, where the graduation begins, to the zero point of the vernier. It is accomplished as follows : Take the reading of the scale, as shown by the last graduation preceding the zero of the ver- nier ; then find a line on the vernier which coincides with a line on the scale. The number of this line, as indicated by the graduation on the vernier, shows how many units of the least count are to be added to the first reading. EXERCISES. 1. A levelling-rod is graduated into feet, tenths, and hun- dredths. It is required to space a direct vernier so that the rod may be read to thousandths of a foot. 2. An arc is graduated into quarter-degrees, and a vernier of 30 parts covers 29 parts of the arcs ; find the least count. 3. A scale is divided into inches and tenths of an inch ; plan a direct vernier by means of which the scale may be read to j-l^ of an inch. Plan a retrograde vernier to accomplish the same object. 4. Design a vernier which when applied to a limb graduated into 20' will give a least count of 20". SURVEYOR'S TRANSIT. NOTE. The principal part of the description of the Compass and Tran- sit, and the plates for the engraving of these instruments, were kindly furnished by Messrs. W. & L. E. Gurley, Troy, X.Y. DESCRIPTION OF INSTRUMENTS. 65 SURVEYOR'S TRANSIT. 102. The essential parts of the Tran- sit, as shown in the cut, are the telescope with its axis and two supports, the cir- cular plates with their attachments, the sockets upon which the plates revolve, the levelling-head, and the tripod on which the whole instrument stands. The telescope is from 10 to 11 inches long, firmly secured to an axis having its bearings nicely fitted in the stand- ards, and thus enabling the telescope to be moved in either direction, or turned completely around if desired. The different parts of the telescope are shown in the marginal figure. The object-glass is composed of two lenses, so as to show objects without color or distortion, is placed at the end of a slide having two bearings, one at the end of the outer tube, the other in the ring (7(7, suspended within the tube by four screws, only two of which are shown in the cut. The object-glass is carried out or in by a pinion working in a rack attached to the slide, and thus adjusted to ob- jects either near or remote as desired. The eye-piece is made up of four plano-convex lenses, which, beginning at the eye-end, are called respectively the eye, the field, the amplifying, and the object-lenses, the whole forming a compound microscope having its focus in the plane of the cross-wire ring BB. 66 PLANE SURVEYING. The eye-piece is brought to its proper focus usually by twist- ing its milled end, the spiral movement within carrying the eye- tube out or in as desired ; sometimes a pinion, like that which focuses the object-glass, is employed for the same purpose. 103. The Cross-Wires are two fibres of spider-web or very fine platinum wire, cemented into the cuts on the surface of a metal ring, at right angles to each other, so as to divide the open space in the centre into quadrants. 104. Optical Axis. The intersection of the wires forms a very minute point, which, when the\ r are adjusted, determines the optical axis of the telescope, and enables the surveyor to fix it upon an object with the greatest precision. The imaginary line passing through the optical axis of the telescope is termed the "line of collimation," and the opera- tion of bringing the intersection of the wires into the optical axis, is called the "adjustment of the line of collimation." This will be hereafter described. 105. The Standards of the Transit are firmly attached by their expanded bases to the upper plate, one of them having near the top, as shown in the cut, a little movable box, actu- ated by a screw underneath, by which the telescope axis is made truly horizontal, as will be hereafter described. DESCRIPTION OF INSTRUMENTS. 67 The sectional view here given shows the interior construction of the sockets of the transit, the manner in which it is detached from the spindle, and the means by which it can be taken apart if desired. In the figure, the limb BB is attached to the main socket C, which is itself carefully fitted to the conical spindle //, and held in place by the spring catch S. The upper plate, AA, carrying the compass-circle, standards, etc., is fastened to the flanges of the socket 7f, which is fitted to the upper conical surface of the main socket (7; the weight of all the parts being supported on the small bearings of the end of the socket, as shown, so as to turn with the least possible friction. A small conical centre, in which from below is inserted a strong screw, is brought down firmly upon the upper end of the main socket (7, and thus holds the two plates of the instrument securely together, while at the same time allowing them to move freely around each other in use. 68 PLANE SURVEYING. A small disc above the conical centre contains the steel cen- tre-pin upon which rests the needle, as shown ; the disc is fas- tened to the upper plate by two small screws, as represented. The main socket with all its parts is of the best bell-metal and is most carefully and thoroughly made, the long bearing of the sockets insuring their firm and easy movement, while at the same time they are entirely out of the reach of dust, or other source -of wear. When desii'ed, the whole upper part of the instrument can be taken off from the spindle by pulling out the head of the spring catch at S, and when replaced will be secured by the self-acting spring of the catch. The figure also shows the covers of the levelling-screws, the shifting centre of the lower le veiling-plate, and the screw and loop for the attachment of the plummet. The compass-box, containing the needle, etc., is covered by a glass to exclude the moisture and air; the circle is silvered, and is divided on its upper surface or rim into degrees and half-degrees, the degree marks being also cut down on its inner edge, and figured from to 90 on each side of the centre or line of zero. 106. The Magnetic Needle is four to five inches long in the different sizes of transits, its brass cap having inserted in it a little socket or centre of hardened steel, perfectly polished, and this resting upon the hardened and polished point of the centre- pin, allows the needle to play freely in a horizontal direction, and thus take its direction in the magnetic meridian. The needle has its north end designated by a scallop or other mark, and on its south end 'a small coil of fine brass wire, easily moved, so as to bring both ends of the needle to the same level. The needle is lifted from the pin by a concealed spring underneath the upper plate, actuated by a screw shown above, thus raising the button so as to check the vibrations of the needle, or bring it up against the glass when not in use, to avoid the unnecessary wear of the pivot. DESCRIPTION OF INSTRUMENTS. 69 107. The Clamp and Tangent Movement, shown in the en- graving, page 64, attached to the plates, serves to fasten the two plates together, so that by the tangent screw they can be slowly moved around each other in either direction, or loosened at will and moved by the hand, thus enabling one to direct the tele- scope rapidly and accurately to the point of sight. The Two Levels are shown placed at right angles to each other so as to level the plate in all directions, and adjusted by turn- ing the capstan-head screws at their ends, by a small steel adjusting-pin. The glass vials used in the- levels are ground on their upper interior surface, so as to make the bubble move evenly and with great sensitiveness. 108. The Lower Plate, or Limb BB, is divided on its upper surface usually into degrees and half-degrees and generally figured in two rows ; viz., from to 360, and from to 90 each way. 109. The Verniers are double, having on each side of the zero mark thirty equal divisions corresponding precisely with twenty-nine half-degrees of the limb ; they thus read to single minutes, and the number passed over is counted in the same direction in which the vernier is moved. The use of two opposite verniers in this and other instru- ments gives the means of " cross-questioning" the graduations, the perfection with which they are centred, and the dependence which can be placed upon the accuracy of the angles indicated. Reflectors of silver or celluloid, as in the mountain transit, are often used to throw more light upon the divisions, and more rarely shades of ground glass are employed to give a clear but more subdued light. 110. The Graduations are made commonly on the brass sur- face of the limb, afterwards filled with black wax, and then finished and silvered. Many instruments, however, have a solid silver plate put over the brass, and the graduations made on the silver itself. 70 PLANE SURVEYING. The last is more costly, but insures a finer graduation, with less liability to tarnish or change color. 111. The Sockets of the transit are compound ; the interior spindle attached to the vernier plate, turning in the exterior socket C when an angle is taken on the limb ; but when the plates are clamped together, the exterior socket itself, and with it the whole instrument, revolves in the socket of the levelling- head. The sockets are made with the greatest care, the surfaces being truly concentric with each other, and the bell-metal or composition of which the}" are composed, of different degrees of hardness, so as to cause them to move upon each other easily and with the least possible wear. The levelling-head also consists of two plates connected to- gether by a socket, having at its end a hemispherical nut, fitting into a corresponding cavity in the lower plate. The plates are 'inclined to each other or made parallel at will by four levelling-screws, of which only two are shown in the section. The screws are of bronze or hard composition metal and fitted to long nuts of brass, screwed into the upper parallel plate ; and, as will be noticed, have threads only on the upper ends, the lower part of their steins turning closely in the lower un- threaded part of the nuts. By this arrangement dust is excluded from the lower end of the screws, while the brass cover above equally protects the other end. The screws rest in little cups or sockets, which are secured to their ends and in which they turn without marring the sur- face of the lower plate, the cups also permitting the screws to be shifted from side to side, or turned around in either direc- tion on the lower plate. The clamp and tangent movement of the levelling-head serves to turn the whole instrument upon its sockets, so as to fix the telescope witli precision upon any given point, and when un- DESCRIPTION OF INSTRUMENTS. 71 clamped allowing it to be directed approximately by hand. The tangent screws, as will be seen, press on opposite sides of the clamp-piece, and thus insure a very fine and solid movement of the instrument. 112. The Lower Levelling-Plate is made in two pieces the upper one, which is screwed fast to the top of the tripod, having a large opening in its centre, in which the smaller lower one is shifted from side to side, or turned completely around. By this simple arrangement, termed a shifting centre, the instrument is easily moved over the upper plate, and the plum- met which hangs from the centre P, set precisely over a point, without moving the tripod. 113. The Levelling-Head of the engineer's transit is attached to the sockets by a screw and washer below ; it can be removed for cleaning, oiling, etc., but should be in place when the in- strument is in use, or packed for transportation. 114. The Tripod has three mahogany legs, the upper ends of which are pressed firmly on each side of a strong tenon on the solid bronze head by a bolt and nut on opposite sides of the leg ; the nut can also be screwed up at will by a wrench fur- nished for the purpose, and thus kept firm. The lower end of the leg has a brass shoe with iron point, securely fastened and riveted to the wood. 115. To Adjust the Transit. Every instrument should leave the hands of the maker in complete adjustment ; but all are so liable to derangement by accident or careless use, that we deem it necessary to describe particularly those which are most likely to need attention. The principal adjustments of the transit are : 1 . The Levels. 2. The Line of Collimation. 3. The Standards. 72 PLANE SURVEYING. 116. To Adjust the Levels. Set up the instrument upon its tripod as nearly level as may be, and having undamped the plates, bring the two levels above and on a line with the two pairs of levelling-screws ; then, with the thumb and first finger of each hand clasp the heads of two, opposite ; and, turning both thumbs in or out, as may be needed, bring the bubble of the level directly over the screws, exactly to the centre of the opening. Without moving the instrument, proceed in the same manner to bring the other bubble to its centre ; after doing this, the level first corrected may be thrown a little out ; bring it in again ; and when both are in place, turn the instrument half-way around : if the bubbles both come to the centre, they would need no correction, but if not, with the adjusting-pin turn the small screws at the end of the levels until the bubbles are moved over half the error ; then bring the bubbles again into the centre by the levelling-screws, and repeat the operation until the bubbles will remain in the centre during a complete revolution of the instrument, and the adjustment will be complete. 117. To Adjust the Line of Collimation. To make this adjustment, which is, in other words, to bring the inter- section of the wires into the optical axis of the telescope, so that the instrument, when placed in the middle of a straight line, will, by the revolution of the telescope, cut its extremities, proceed as follows : Set the instrument firmly on the ground and level it care- fully ; and then, having brought the wires into the focus of the eye-piece, adjust the object-glass on some well-defined point, as the edge of a chimney or other object, at a distance of from 200 to 500 feet ; determine if the vertical wire is plumb, by clamping the instrument firmly and applying the wire to the vertical edge of a building, or observing if it will move parallel to a point taken a little to one side : should any deviation be manifested, loosen the cross-wire screws, and by the pressure of the hand on the head outside the tube, move the ring around until the error is corrected. DESCRIPTION OF INSTRUMENTS. 73 The wires being thus made respectively horizontal and vertical, fix their point of intersection on the object selected ; clamp the instrument to the spindle, and having revolved the telescope, find or place some good object in the opposite direc- tion, and at about the same distance from the instrument as the first object assumed. Great care should always be taken in turning the telescope, that the position of the instrument upon the spindle is not in the slightest degree disturbed. Now, having found or placed an object which the vertical wire bisects, unclamp the instrument, turn it half-way around, and direct the telescope to the first object selected ; having bisected this with the wires, again clamp the instrument, revolve the telescope, and note if the vertical wire bisects the second object observed. Should this happen, it will indicate that the wires are in adjustment, and the points bisected are with that of the centre of the instrument, in the same straight line. If not, however, the space which separates the wires from the second point observed, will be double the deviation of that point from a true straight line, which may be conceived as drawn through the first point and the centre of the instrument, since the error is the result of two observations, made with the wires when they are out of the optical axis of the telescope. For, as in the diagram, let A represent the centre of the instrument, and BC the imaginary straight line, upon the ex- tremities of which the line of collimation is to be adjusted. B represents the object first selected, and D the point which the wires bisected, when the telescope was made to revolve. When the instrument is turned half around, and the telescope again directed to .B, and once more revolved, the wires will 74 PLANE SURVEYING. bisect an object -E, situated as far to one side of the true line as the point D is on the other side. The space DE, is therefore the sum of two deviations of the wires from a true straight line, and the error is made very apparent. In order to correct it, use the two capstan-head screws on the sides of the telescope, these being the ones which affect the position of the vertical wire. Remember that the eye-piece inverts the position of the wires, and therefore, that in loosening one of the screws and tightening the other on the opposite side, the operator must proceed as if to increase the error observed. Having in this manner moved back the vertical wire until, by estimation, one- quarter of the space DE has been passed over, return the instrument to the point jB, revolve the telescope, and if the correction has been carefully made, the wires will now bisect a point C, situated midway between D and E, and in the pro- longation of the imaginary line, passing through the point B and the centre of the instrument. To ascertain if such is the case, turn the instrument half around, fix the telescope upon B, clamp to the spindle, and again revolve the telescope towards C. If the wires again bisect it, it will prove that they are in adjustment, and that the points B, A, C, all lie in the same straight line. Should the vertical wire strike to one side of (7, the error must be corrected precisely as above described, until it is entirely removed. 118. To Adjust the Standards. In order that the wires may trace a vertical line as the telescope is moved up or down, it is necessary that both the standards of the telescope should be of precisely the same height. To ascertain this and make the correction if needed, proceed as follows : Having the line of collimation previously adjusted, set up the instrument in a position where points of observation, such as DESCRIPTION OF INSTRUMENTS. 75 the point and base of a lofty spire, can be selected, giving a long range in a vertical direction. Level the instrument, fix the wires on the top of the object, and clamp to the spindle ; then bring the telescope down, until the wires bisect some good point, either found or marked at the base ; turn the instrument half around, fix the wires on the lower point, clamp to the spindle, and raise the telescope to the highest object. If the wires bisect it, the vertical adjustment is effected ; if they are thrown to either side, this would prove that the stand- ard opposite that side was the highest, the apparent error being double that actually due to this cause. To correct it, one of the bearings of the axis is made mov- able, so that by turning a screw underneath this sliding piece, as well as the screws which hold on the cap of the standard, the adjustment is made with the utmost precision. OTHER ADJUSTMENTS OF THE TRANSIT. Besides the three adjustments already described which are all that the surveyor will ordinarily have to make there are those of the needle and the object-glass slide which may some- times be required. The first is given with the description of the compass ; the last will now be described. 119. To Adjust the Object-Slide. Having set up and levelled the instrument, the line of collimation being also adjusted for objects from 300 to 500 feet distant, clamp the plates securely, and fix the vertical cross-wire upon an object as distant as may be distinctly seen ; then, without disturbing the instrument, throw out the object-glass, so as to bring the vertical wire upon an object as near as the range of the telescope will allow. Having this clearly in mind, unclamp the limb, turn the instru- ment half-way around, reverse the eye-end of the telescope, clamp the limb, and with the tangent-screw bring the vertical 76 PLANE SURVEYING. wire again upon the near object ; then draw in the object-glass slide until the distant object first sighted upon is brought into distinct vision. If the vertical wire strikes the same line as at first, the slide is correct for both near and remote objects ; and, being itself straight, for all distances. But if there be an error, proceed as follows : first, with the thumb and forefinger twist off the thin brass tube that covers the screws CC shown in the sectional view of the telescope, p. 65. Next, with the screw-driver, turn the two screws CO on the opposite ides of the telescope, loosening one and tight- ening the other, so as apparently to increase the error, making, by estimation, one-half the correction required. Then go over the usual adjustment of the line of collimation , and having it completed, repeat the operation above described ; first sighting upon the distant object, then finding a near one in line, and then reversing, making correction, etc., until the adjustment is complete. 120. To Use the Transit. The instrument should be set up firmly, the tripod legs being pressed into the ground, so as to bring the plates as nearly level as convenient ; the plates should then be carefully levelled and property clamped, the zeros of the verniers and limb brought into line by the upper tangent-screw, and the telescope directed to the object by the tangent-screws of levelling-head. The angles taken are then read off upon the limb, without subtracting from those given by the verniers, in any other position. Before an observation is made with the telescope, the eye- piece should be moved in or out, until the wires appear distinct to the eye of the operator ; the object-glass is then adjusted by turning the pinion-head until the object is seen clear and well- defined, and the wires appear as if fastened to its surface. The intersection of the wires, being the means by which the optical axis of the telescope is defined, should be brought pre- cisely upon the centre of the object to which the instrument is directed. DESCRIPTION OF INSTRUMENTS. 77 The needle is used, as in the compass, to give the bearing of lines, and as a rough check upon the angles obtained by the verniers and limb ; but its employment is only subsidiary to the general purposes of the transit. 121. Attachments of Transits. The engraving of the Sur- veyor's Transit represents the attachments often applied to the Engineer's Transit, viz. : vertical circle, level on telescope, and clamp and tangent to telescope axis. They are of use where approximate levelling and vertical angles are to be taken in connection with the ordinary use of the transit, and with their adjustments, etc., will now be described. 122. The Vertical Circle firmly secured to the axis of the telescope is 4^ inches in diameter, plated with silver, divided to hnlf-degrees, and with its vernier enables the surveyor to obtain vertical angles to single minutes. 123. The Level on Telescope consists of a brass tube about 6| inches long, each end of which is held between two capstan- nuts connected with a screw or stem attached to the under side of the telescope tube. 124. The Clamp and Tangent consists of an arm at one end encircling the telescope axis, and at the other connected with the tangent-screw ; the clamp is fastened at will to the axis by a clamp-screw, inserted at one side of the ring, and then by turning the taugent-screw the telescope is raised or lowered as desired. 125. To Adjust the Vertical Circle. Having the instrument firmly set up and carefully leveled, bring into line the zeros of the circle and vernier, and with the telescope find or place some well-defined point or line, from 200 to 300 feet distant, which is cut by the horizontal wire. Turn the instrument half-way around, revolve the telescope, and fixing the wire upon the same point as before, note if the zeros are again in line. 78 PLANE SURVEYING. If not, loosen the capstan-head screws, which fasten the vernier, and move the zero of the vernier over half the error ; * bring the zeros again into coincidence, and proceed precisely as at first, until the error is entirely corrected, when the adjust- ment will be complete. This method is not applicable when only an arc of a circle is attached. The adjustment may then be made as follows: Observe successively from each of the two points to the other, and as before use half the error in adjusting the vernier. Verifv b t y repetition. A slight error may be most readily removed by putting the zeros in line and then moving the wire itself over half the interval. 126. The Level is Adjusted by bringing the bubble carefully into the centre by the nuts at each end ; and when there is a vertical circle on the instrument, this should be done when the zeros of circle and vernier are in line and in adjustment ; when there is no vertical circle, proceed as follows : 127. To Adjust the Level on Telescope. Choose a piece of ground nearly level, and having set the instrument firmly, level the plates carefully, and bring the bubble of the telescope into the centre with the tangent-screw. Measure in any direction from the instrument, from 100 to 300 feet, and drive a stake, and on the stake set a staff, and note the height cut by the horizontal wire ; then take the same distance from the instru- ment in an opposite direction, and drive another slake. On that stake set the staff, and note the height cut by the wire when the telescope is turned in that direction. The difference of the two observations is evidently the dif- ference of level of the two stakes. Set the instrument over the lowest stake, or that upon which * Called Index Error. It may be rectified as here shown, or each obser- vation corrected by this amount. DESCRIPTION OF INSTRUMENTS. 79 the greatest height was indicated, and bring the levels on the plates and telescope into adjustment as at first. Then, with the staff, measure the perpendicular distance from the top of the stake to the centre of one of the horizontal cross- wire screw-heads ; from that distance subtract the difference of level between the two stakes and mark the point on the staff thus found ; place the staff on the other stake, and with the tangent-screw bring the horizontal wire to the mark just found, and the line will be level. The telescope now being level, bring the bubble of the level into the centre, by turning the little nuts at the end of the tube, and noting again if the wires cut the point on the staff ; screw up the nuts firmly and the adjustment will be completed. 128. To Take Apart the Surveyor's Transit. When it is necessary to separate the plates of the transit, proceed as follows : (1) Remove the clamp-screw and take off the head of the pinion, both on the north end and outside the compass circle. (2) Unscrew the bezel ring containing the glass cover of the compass, remove the needle and button beneath it, and take out the two small screws so as to remove the disc. (3) Take the instrument from its spindle, and with a large screw-driver take out the screw from the underside of the coni- cal centre (see figure, p. 67). (4) Drive out the centre from below by a round piece of wood, holding the instrument vertical so that the centre will not bruise the circle. (5) Set the instrument again upon its spindle, take out the clamp-screw to the tangent movement of the limb, and the work is complete. To put the transit together again, proceed exactly the reverse of the operation thus described. 129. The Solar Attachment is essentially the solar apparatus of Burt placed upon the cross-bar of the ordinary transit, the polar axis only being directed above instead of below, as in the solar compass. 80 PLANE SURVEYING. A little circular disc of an inch and a half diameter, and hav- ing a short, round pivot projecting above its upper surface, is first securely screwed to tho telescope axis. Upon this pivot rests the enlarged base of the polar axis, which is also firmly connected with the disc by four capstan-head screws passing from the under side of the disc into the base already named. These screws serve to adjust the polar axis, as will be ex- plained hereafter. 130. The Hour Circle surrounding the base of the polar axis is easily movable about it, and can be fastened at any point desired by two flat-head screws above. It is divided to five minutes of time ; is figured from I. to XII., and is read by a small index fixed to the declination circle, and moving with it. A hollow cone, or socket, fitting closely to the polar axis, and made to move snugly upon it, or clamped at any point desired by a milled-head screw on top, furnishes by its two expanded arms below a firm support for the declination arc, which is securely fastened to it by two large screws, as shown. 131. The Declination Arc is of about 5 inches radius, is divided to quarter degrees, and reads by its vernier to single minutes of arc, the divisions of both vernier and limb being in the same plane. The declination arm has the usual lenses and silver plates on the two opposite blocks, made precisely like those of the ordi- nary solar compass, but its vernier is outside the block, and more easily read. The declination arm has also a clamp and tangent movement, as shown in the cut. The arc of the declination limb is turned on its axis, and one of the other solar lens used, as the sun is north or south of the equator ; the cut shows its position when it is north. The Latitude is set off by means of a large vertical limb hav- ing a radius of 2| inches ; the arc is divided to twenty minutes, TRANSIT WITH SOLAR ATTACHMENT. DESCRIPTION OF INSTRUMENTS. 83 is figured from the centre, each way, up to 80, and is read by its vernier to single minutes. It has also a clamp-screw inserted near its centre, by which it can be set fast to the telescope axis in any desired position. The vernier of the vertical limb is made movable by the tangent-screw attached, so that its zero and that of the limb are readily made to coincide when, in adjusting the limb to the level of the telescope, the arc is clamped to the axis. The usual tangent movement to the telescope axis serves, of course, to bring the vertical limb to the proper elevation, as hereafter described. A level on the under side of the telescope, with ground vial and scale, is indispensable in the use of the solar attachment. The divided arcs, verniers, and hour circle, are all on silver plate, and are thus easily read and preserved from tarnishing. THE ADJUSTMENTS. 132. The Solar Lenses and Lines are adjusted precisely like those of the ordinary solar, the declination arm being first de- tached by removing the clamp and tangent screws, and the conical centre with its two small screws, by which the arm is attached to the arc. The adjuster, which is a short bar f urn, shed with every instrument, is then substituted for the declination arm, the conical centre screwed into its place at one end, and the clamp-screw into the other, being inserted through the hole left by the removal of the tangent-screw, thus securing the adjuster firmly to the arc. The arm is then turned to the sun, as described in the article on the Solar Compass, and reversed by the opposite faces of the blocks upon the adjuster, until the image will remain in the centre of the equatorial lines. This adjustment is very rarely needed, as the lenses are cemented in their cells, and the plates securely fastened. 84 PLANE SURVEYING. 133. The Vernier of the Declination Arc is adjusted by set- ting the vernier at zero, and then raising or lowering the tele- scope by the tangent-screw, until the sun's image appears exactly between the equatorial lines. Having the .telescope axis clamped firmly, carefully revolve the arm until the image appears on the other plate. If preciseh' between the lines, the adjustment is complete ; if not, move the declination arm by its tangent-screw, until the image will come precisely between the lines on the two opposite plates ; clamp the arm and remove the index error by loosening two flat-head screws on the back, which fasten the movable arc to the declination limb ; place the zero of the limb and vernier in exact coincidence and the adjustment is finished. 134. To Adjust the Polar Axis. First level the instrument carefully by the long level of the telescope, using in the opera- tion the tangent movement of the telescope axis in connection with the levelling screws of the parallel plates, until the bubble will remain in the centre during a complete revolution of the in- strument upon its axis. Place the equatorial sights on the top of the blocks as closely as is practicable with the distinct view of a distant object ; and having previously set the declination arm at zero, sight through the interval between the equatorial sights and the blocks at some definite point or object, the declination arm being placed over either pair of the capstan-head screws on the under side of the disc. Keeping the declination arm upon the object with one hand, with the other turn the instrument half around on its axis, and sight upon the same object as before. If the sight strikes either above or below, move the two capstan-head screws imme- diately under the arm, loosening one and tightening the other as may be needed, until half the error is removed. Sight again and repeat the operation, if needed, until the sight will strike the same object in both positions of the instru- ment, when the adjustment of the axis in one direction will be complete. DESCRIPTION OF INSTRUMENTS. 85 Now turn the instrument at right angles, keeping the sight still upon the same object as before ; if it strikes the same point when sighted through, the axis will be truly vertical in the sec- ond position of the instrument. If not, bring the sight upon the same point by the other pair of capstan-head screws now under the declination arc, reverse as before, and continue the operation until the same object will keep in the sight in all positions, when the polar axis will be made precisely at right angles to the level and to the line of collimation of the transit. It should here be noted that as this is by far the most delicate and important adjustment of the solar attachment, it should be made with the greatest care, the bubble kept perfectly in the centre and frequently inspected in the course of the operation. 135. To Adjust the Hour Arc. Whenever the instrument is set in the meridian, as will be hereafter described, the index of the hour arc should read apparent time. If not, loosen the two flat-head screws on the top of the hour circle, and with the hand turn the circle around until it does, fasten the screws again, and the adjustment will be complete. To obtain mean time, of course the correction of the equa- tion for the given day, as given in the Nautical Almanac, must always be applied. 136. To Find the Latitude. First level the instrument very carefully, using, as before, the level of the telescope until the bubble will remain in the centre during a complete revolution of the instrument, the tangent movement of the telescope being used in connection with the levelling screws of the parallel plates, and the axis of the telescope firmly clamped. Next clamp the vertical arc so that its zero and that of its vernier coincide as near as may be, and then bring them into exact line by the tangent-screw of the vernier. Then, having the declination of the sun for 12 o'clock of the given day as affected by the meridional refraction carefully set 86 PLANE SURVEYING. off upon the declination arc, note also the equation of time and fifteen or twenty minutes before noon, the telescope being directed to the north, and the object-end lowered until, by moving the instrument upon its spindle and the declination arc from side to side, the sun's image is brought nearly into posi- tion between the equatorial lines. Now bring the declination arc directly in line with the telescope, clamp the axis firmly, and with the tangent-screw bring the image precisely between the lines and keep it there with the tangent-screw, raising it as long as it runs below the lower equatorial line, or, in other words, as long as the sun continues to rise in the heavens. When the sun reaches the meridian the image will remain stationary for an instant, and then begin to rise on the plate. The moment the image ceases to run below is of course ap- parent noon, when the index of the hour arc should indicate XII, and the latitude be determined by the reading of the ver- tical arc. It must be remembered, however, that the angle through which the polar axis has moved in the operation just described is measured from the zenith instead of the horizon, as in the ordinary solar, so that the angle read on the vertical limb is the complement of the latitude. The latitude itself is readily found by subtracting this angle from 90 ; thus at Troy, the reading of the limb being found as above directed to be 47 16', the latitude will be 90 -47 16' = 42 44'. It will be noticed that with this apparatus the latitude of any place can be most easily ascertained without any index error, as in the usual solar compass. 137, To Use the Solar Attachment. From the foregoing de- scription it will be readily understood that good results cannot be obtained from the solar attachment unless the transit is of good construction, furnished with the appliances of a level on telescope, clamp and tangent movement to axis, and vertical DESCRIPTION OF INSTRUMENTS. 87 arc with adjustable vernier, and the sockets or centres in such condition that the level of the telescope will remain in the cen- tre when the instrument is revolved upon either socket. 138. To Bun Lines with the Solar Attachment. Having set off the complement of the latitude of the place on the vertical arc, and the declination for the given day and hour as in the solar, the instrument being also carefully levelled by the tele- scope bubble, set the horizontal limb at zero, and clamp the plates together, loosen the lower clamp so that the transit moves easily upon its lower socket, set the instrument approxi- mately north and south, the object-end of the telescope point- ing to the north, turn the proper solar lens to the sun, and, with one hand on the plates and the other on the revolving arm, move them from side to side, until the sun's image is brought between the equatorial lines on the silver plate. The lower clamp of the instrument should now be fastened, and any further lateral movement be made by the tangent- screw of the tripod. The necessary allowance being made for refraction, the telescope will be in the true meridian, and being undamped, may be used like the sights of the ordinary solar compass, but with far greater accuracy and satisfaction in establishing meridian lines. Of course when the upper or vernier plate is undamped from the limb, any angle read by the verniers is an angle from the meridian, and thus parallels of latitude or any other angles from the true meridian may be established as with the solar compass. The bearing of the needle, when the telescope is on the meri- dian, will also give the variation of the needle at the point of observation. The declination of the needle being set off, and the needle kept then at zero, or " with the sun," lines may be run by the needle alone when the sun is obscured. Though when not inconsistent with the remarks following the table on page 95, the sun should be observed for direction at every station. 88 PLANE SURVEYING. THE SAEGMULLER ATTACHMENT. 139. As seen in the engraving on the opposite page, it consists essentially of a small telescope and level, the telescope being mounted in standards, in which it can be elevated or depressed. The standards revolve around an axis, called the polar axis, which is fastened to the telescope axis of the transit instrument. The telescope, called the " Solar Telescope," can thus be moved in altitude and azimuth. Two pointers, attached to the solar telescope to approximately set the instrument, are so adjusted that when the shadow of the one is thrown upon the other the sun will appear in the field of view. 140. Adjustments. When the apparatus is attached to the transit, which instrument must be in good adjustment, its polar axis should be at right angles both to the horizontal axis of the main telescope and to the line of collimation. TEST. Level the transit, and bring the bubble of each tele- scope to the centre of its run. Revolve the solar telescope about its polar axis, and if its bubble remains central, this ad- justment is complete. If not, correct half the movement by the adjusting screws at the base of the polar axis, and the other by revolving the solar telescope on its horizontal axis. 141. Second. The line of collimation of the solar telescope and the axis of its attached level must be parallel. TEST. Bring the telescopes into the same vertical plane, and the large bubble to the middle of its run. Direct then the tran- sit telescope to a mark at a convenient distance away, say 100 feet; point also the " solar" to a mark above this equal to the distance between their axes. If now the bubble of the solar telescope is not in the middle of the tube, make it so by the adjusting screws, and the instrument will be in adjustment. When the combined instrument is in proper adjustment the bubbles of the telescopes and plates will be in the middle of their tubes, and the lines of collimation parallel. TRANSIT WITH SOLAR ATTACHMENT, AS MADE BY FAUTH & C'<)., \VASUINOTON, D.C. DESCRIPTION OF INSTRUMENTS. 91 All the adjustments, including those of the transit, should be frequently examined, and kept as nearly perfect as possible. 142. The advantages of solar attachments over the ordinar} 7 solar compass consist principally in the telescopic sight, and the use of a vertical limb to set off declination and co-latitude. LATITUDE. By the Sun. With Saegmuller's Attachment. 143. Level the transit carefully, point the telescope south, and elevate or depress the object-end, according as the decli- nation of the sun is south or north, an amount equal to the declination.* Bring the solar telescope into the vertical plane of the main telescope, level it carefully, and clamp it. With the solar telescope observe the sun a few minutes before his culmination, bring the horizontal middle wire tangent to the upper limb by moving the transit telescope in altitude and azimuth, and keep it so by the slow-motion screws until the sun ceases to rise. Then take the reading of the vertical arc, cor- rect for index error, if any, for refraction due to altitude,! as per table below ; diminish the result by the sun's semi-diameter, and subtract the result from 90 for the latitude. * For declination, consult a nautical almanac. t Corrected for index error, the arc reading would be the sum of the co-latitude and refraction. The refraction being due to the meridian alti- tude of the sun, which altitude in the United States is equal to the alge- braic sum of the declination and co-latitude. 92 PLANE SURVEYING. TABLE OF MEAN REFRACTIONS OF CELESTIAL OBJECTS FOR TEMPER- ATURE 50, AND BAROMETER 29.6 INCHES. ALTITUDE. REFRACTION. ALTITUDE. REFRACTION. 10 5' 15" 20 2' 35" 11 4 47 25 2 02 12 4 23 30 1 38 13 4 03 35 1 21 14 3 45 40 1 08 15 3 30 45 57 16 3 17 50 48 17 3 04 60 33 18 2 54 70 21 19 2 44 80 10 By interpolation, the refraction, due to any altitude within the limits of the table may be found. LATITUDE BY CIRCUMPOLAR STAR. 144. The arc measuring the angle of elevation of the pole at any station indicates the latitude of that station. If, then, the place of the pole were indicated by a heavenly body, its altitude measured and corrected for refraction would give at once the latitude. There being no such body, a circumpolar star may be used. Take its altitude at either culmination, subtract refraction due to altitude, and the remainder, increased or diminished by the polar distance according as the lower or upper culmination was observed, will give the latitude. Better, when practicable, to observe both culminations, correct for re- fraction, and take the arithmetical mean of the result. Still greater accu- racy would be obtained by taking the mean of observations at upper and lower transit of several eircumpolar stars. If A and A' respectively denote the angles measuring, from the north, the altitudes of a circumpolar star at its upper and lower culminations, and r and r' the corresponding refractions, then, latitude = (r + r')]. DESCRIPTION OF INSTRUMENTS. 93 To FIND THE MERIDIAN AND DECLINATION OF THE NEEDLE, USING THE ATTACHMENT.* 145. First. Take the declination of the sun as given in the Nautical Almanac for the given day, and correct it for retrac- tion and hourly change. Incline the transit telescope until this amount is indicated by its vertical arc. If the declination of the sun is north, depress the object-end ; if south, elevate it. Without disturbing the position of the transit telescope, bring the solar telescope into the same vertical plane, and make it horizontal by means of its level. The two telescopes will then form an angle which equals the amount of the declination, and the inclination of the solar telescope to its polar axis will be equal to the polar distance of the sun. Second. Without disturbing the relative positions of the two telescopes, incline them and set the vernier to the co-latitude of the place. By moving the transit and the solar attachment around their respective vertical axes, the image of the sun will be brought into the field of the solar telescope, and after accurately bisecting it the transit telescope must be in the meridian, and the compass- needle indicates its deviation at that place. The vertical axis of the solar attachment will then point to the pole, the apparatus being in fact a small equatorial. Re- volve the main telescope on its horizontal axis, and set a mark at a convenient distance, 1000 feet if practicable. Make a reverse observation as follows : Turn the transit 180* in azimuth, and set off the declination, elevating or depressing now the eye-end, according as the declination is south or north; bring the object-end of the solar telescope to point in the direc- tion of the eye-end of that of the main instrument, and level it. Set the vertical arc to the co-latitude of the place, and complete the observation as before. Reverse the large telescope on its * For other methods, see Chapter III., p. 218, and Chapter VI., Solar Compass. 94 PLANE SURVEYING. horizontal axis, and see if it points to the mark set by the direct observation ; if it do not, take the mean of the two pointings for the meridian. If greater accuracy is required, make other observations at different hours of the day, under different conditions of the atmosphere, and compare results with those given in Chapters III. and VI. 146. Time and azimuth are calculated from an observed altitude of the sun by solving the spherical triangle formed by the sun, the pole, and the zenith of the place. The three sides, SP, PZ, ZS. complements respectively of the declination, latitude, and altitude are given, and we hence deduce SPZ, the hour angle, from apparent noon, and PZS the azimuth of the sun.* The " Solar Attachment " solves the same spherical triangle by construction, for the second process brings the vertical axis of the solar telescope to the required distance ZP from the zenith, while the first brings it to the required distance SP from the sun. If the two telescopes, both being in position one in the meridian, and the other pointing to the sun are now turned on their horizontal axes, the vertical remaining undisturbed, until each is level, the angle between their directions found by sighting on a distant object is SPZ, the time from appar- ent noon. This gives an easy observation for correction of time-piece. 147. An error either in the declination or latitude will cause an. error in the azimuth. These errors in azimuth corresponding to one-minute error in declination or latitude, for various hours and half-hours of the * A Table of Equation of Time is given at the end of this book which will be useful in solving analytically the spherical triangle PZS for time. DESCRIPTION OF INSTRUMENTS. 95 day, and for different latitudes, have been computed and tabulated.* THE SAEGMULLEB ATTACHMENT. The table indicates the best time to observe the sun for merid- ian, or to determine the true bearing of a line, to be soon after sunrise or just before sunset. However, on account of refraction at these times being great and very uncertain, it is best in general not to make the obser- vation when the sun is nearer the horizon than about 15 degrees. Moreover, the solar apparatus should not be relied on for very accurate work between 10 A.M. and 2 P.M. An error in latitude does not cause an error in azimuth when the sun is in the pole of the meridian. 148. The Stadia, or Micrometer, is a compound cross-wire ring or diaphragm, shown below, having three horizontal wires, of which the middle one is cemented to the ring as usual, while the others, bb and cc, are fastened to small slides, held apart by * By Professor H. T. Stewart, C. E., of the Western University of Pennsylvania. 96 PLANE SURVEYING. a slender brass spring hoop, and actuated by independent screws del, by which the distance between the two movable wires can be adjusted to include a given space ; as, 1 foot on a rod 100 feet distant. These wires will in the same manner include 2 feet on a rod 200 feet distant, or half a foot at a distance of 50 feet, and so on in the same proportion ; thus furnishing a means of measuring distances especially over broken ground much more easily, and even more accurately, than with a tape or chain. 149. Its principles may be explained more fully as follows : Let the above figure represent a section of a common tele- scope with but two lenses, between which the diaphragm with the stadia wires is placed, and assume that / = the focal distance of the object-glass ; p = the distance of the stadia wires a and b from each other ; d = the horizontal distance of the object-glass to the stadia . DESCRIPTION OF INSTRUMENTS. 97 a = stadia reading (BA) ; D = horizontal distance from middle of instrument to stadia. The telescope is levelled and sighted to a levelling or stadia rod, which is held vertically, hence at right angles with the line of sight. According to a principle of optics, rays parallel to the axis of the lens meet, after being refracted, in the focus of the lens. Suppose the two stadia wires are the sources of those rays, we have, from the similarity of the two triangles a'b'F and FAB, the proportion d -f:a=f: p. The quotient f:p is, or at least can be made, constant, and may be designated by k ; hence we may write d-f=FC = ka. * To get the distance from the centre N of the instrument there must be added to FC the value c = OF+ON. ON is mostly equal to half the focal length of the object- glass ; hence, c=1.5/. Therefore the formula for the distance of the stadia from the centre of instrument, when that stadia is at right angles to the level line of sight, is D = ka + c. (1) 150. When the line of sight is not level, it is impracticable, especially in long distances, to hold the rod in a vertical plane, and at the same time perpendicular to the line of sight ; hence it is customary to hold the rod vertical, as in the preceding case, and obtain the true distance by applying a correction depending upon the angle of inclination of the sight. This correction is deduced as follows : Let A GB = 2 w ; n = the angle of inclination ; 98 PLANE SURVEYING. MF= c + GF = c + k x CD = D' ; CD must be expressed by AB ; MP= the horizontal distance = D' cos -p Now the angle or, Hence, 4? sin m AF = sin[90 + (n- GF sin m and Z* But and cos (w m) BF sin m sin [90 (w (rF sin m cos (n -f m) r I = GFs\nm\ |- [_cos (n m) _ CD _ CD cos m 2tanm~ 2sinm. DESCRIPTION OF INSTRUMENTS. 99 Substituting this value of GF in the equation above, we obtain ^_CD cos m [cos (n + m)+ cos (n m)] 2 cos (n + m) cos (n m) ^r, cos 2 n cos 2 w sin 2 ?* sin 2 m Ol , Ui/ = U - - 7 cos n cos" w and Z>' = c + &o c 088 M . cosw cos 2 m Whence, D c cos ?i -f- fra cos 2 w fca sin 2 w tan 2 ra. The third term of second member of this equation may be neglected, as it is very small, even for long distances and large angles of elevation (for 1500', n = 45 and k = 100, it is but 0.07') ; therefore the final formula for distances, with a stadia kept vertical, and with wires equidistant from the centre wire, is the following: D = c cos n + ok cos 2 w. (2) The value of ccosw is usually neglected, as it amounts to but 1 or 1.5 feet ; it is exact enough to add always 1.25' to the dis- tance as derived from the formula (2o)* 151. The focal length /of the object-glass may be found by focussing the instrument upon some distant object, say a heavenly body, and measuring then the distance between the plane of the cross-wires and that of the objective. ON, being equal to the distance between the objective and the intersection of a plumb-line with the horizontal axis of the telescope, may be obtained by direct measurement. The distance p, between the stadia wires, may be determined as follows : Set up the instrument on level ground, or nearly so, and measure forward from the plumb-line a distance equal to c, and * The above explanation of the stadia is substantially that given by Mr. G. J. Specht, published by Van Nostrand, 1884, though corrected and simplified. 100 / PLANE SURVEYING. mark the point ; measure onward from the mark any convenient distance d, 400 or 500 feet, as a base. The telescope being level, observe carefully the space a intercepted by the stadia wires on a levelling-rod held vertically at the farther extremity of the base. Then from the proportion d f: a =f : p the required dis- tance p may be obtained. EXAMPLES. 1. Given /= 8 inches, base = 500 feet, and a = 5. 25 feet. Find p=. 084 inches. 2. At what fractional part of the focal length must the stadia wires be separated so that one foot on the rod will cor- respond to 100 feet base? State also the distance between the wires in terms of the focal length, when one foot on rod cor- responds to 66 feet base. 3. Measure with a stadia one or more sides of a field, also the distance across a valley, or from one ridge to another, and compare the results with chain measurement between the same points. 4. Measure with the stadia up or down a hillside, and chain between the same points. Compare results. GRADIENTER. 152. This attachment, as shown on next page, is often used with transits for fixing grades, determining distances, etc. It consists mainly of a screw attached to the semicircular expanded arm of the ordinary clamp of the telescope axis ; the screw is accurately cut to a given number of threads, and pass- ing through a nut in one side of the arm, presses against a little stud A fixed to the inside surface of the right-hand standard. In the other side of the semicircular arm is inserted a hollow cylinder containing a pin actuated by a strong spiral spring, the end of the pin pressing against the side of the stud opposite that in contact with the screw. DESCRIPTION OF INSTRUMENTS. 101 Near the other end of the screw, and turning with it, is a wheel, or micrometer, the rim of which is plated with silver, and divided into one hundred equal parts. A small silver scale, attached to the arm and just above the micrometer wheel, is divided into spaces, each of which is just equal to one revolution of the screw ; so that by comparing the edge of the wheel with the divisions of the scale, the number of complete revolutions of the screw can be easily counted. It will be seen that when the clamp is made fast to the axis by the clamp-screw, and the gradienter-screw turned, it will move the telescope vertically, precisely like the tangent-screw ordinarily used. And as the value of a thread is such that a complete revolu- tion of the screw will move the horizontal cross-wire of the telescope over a space of one foot on a rod at a distance of one hundred feet, it is clear that when the screw is turned through fifty spaces on the graduated head, the wire will pass over fifty one-hundredths, or one-half a foot on the rod, and so on in the same proportion. 102 PLANE SURVEYING. In this way the gradienter can be used in the measurement of distances, precisely like the stadia just described. Grades can also be established, with great facility, as fol- lows : First, level the instrument ; bring the telescope level to its centre by the clamp and gradienter screw ; move the gradu- ated head until its zero is brought to the edge of the scale ; and then turn off as many spaces on the head as there are hun- dredths of feet to the hundred in the grade to be established. SECTION II. A. BEARINGS WITH COMPASS. 153. To Obtain the Bearing of a Line. At one end of the line, or at any other point in it, set up and level the compass, loosen the needle, and direct the sights toward the other end. The degree on which the needle comes to rest will indicate the angle between the magnetic meridian and the direction of the line, or the bearing. For example, if the line lies between the north and east points, as OP, and the angle NOP being, say 42 degrees, the bearing of the line OP\s written, N. 42 E., and read, "north forty-two degrees east." If, as OP', it lies between south and east, and the angle SOP' is, say 74 degrees, it is written, S. 74 E., and read, "south sev- enty-four degrees east" ; in like manner for lines in other quadrants. It will be observed that the bear- ing of a line does not exceed 90. A line which might be read " N. 90 W." or " S. 90 W." is recorded as west. The bearing can be read most accurately by placing the eye over one end of the needle and taking the reading from the other end. BEARINGS WITH COMPASS. 103 Since the graduations are usually made to half -degrees, the bearing can be taken quite accurately to quarter-degrees, and by practice, even closer, without the use of the vernier. In fact, the principal use of the vernier on a compass is to facili- tate the running of lines from old deeds, where, when the declination is ascertained, it is turned off on the vernier, and the surveyor may use then the bearings as given in the deed by which he is surveying the tract, without making a calculation for the bearing of each line. The vernier cannot be relied on to read bearings to minutes, on account of the difficulty of accurately manipulating it. 154. Reverse Bearings. Since in plane surveying the meri- dians passing through the extremities of a line are considered parallel, the direct and reverse bearings should indicate the same angle. That is to say, a line, as LM, the bearing of which, taken ati, called also fore-sight, is N. 40 E., when taken at M, back-sight, should be S. 40 W. ; the degrees being the same, the letters indi- cating the opposite cardinal points. When surveying a tract of land with the compass, the instrument should be set up at every corner, and the bearing and reverse , bearing of every line taken, as a check on the observer's reading and the working of the needle, since a disagreement in the angle thus measured would be evidence sufficient to war- rant a review of the work. 155. Local Attraction. If the readings of the needle of the fore-sight and back-sight have been correctly made, and there is found a disagreement, local attraction exists. It is usually caused by the presence of ferruginous matter. It may exist at both stations or at only one of them. Assuming that the direct and reverse bearings of the preced- ing line agree, then the difference in the reading at the two ends 104 PLANE SURVEYING. of the line, when the attraction exists, will show the local vari- ation at the last station, and this correction must be applied to the reading of the needle for the bearing of the next line. If, however, the needle will not reverse on the first line of a survey, then it will be necessary to set up at some other point of the tract ; or, if this is impracticable, select one or more stations near the suspected points, and by taking the bearings of these from the stations, and also the reverse bearings, the intensity and position of the attraction may be determined. 156. Proof Bearings and Tests of Accuracy. In any important compass survey it is well to check the work by sighting to distant prominent objects, such as buildings, trees, etc., and noting the readings. Since two bearings are required to locate each object, and until it is located it cannot serve as a check, it will be necessary to take at least three bearings to each. If, then, when plotting, the three lines intersect in a point, a proof is given of the correctness of the measurements thus connected. The lengths and bearings of diagonals of the tract may likewise be taken as checks on the accuracy of the work ; also, when in plotting, if the last bearing and distance close the survey, it is considered a proof of the work. The best test, however, of the accuracy of the survey is by Latitudes and Departures, which is explained in Section VI. Articles 207 and 208. It may be well to caution the student against the fallacy of a test sometimes given, that if the sum of the interior angles, determined from the bearings, equals twice as many right angles, less four, as the figure has sides, it proves the work. This "test," while it furnishes proof for a transit survey in which the interior angles have been measured, will not show that the bearings of a tract have been correctly taken. The student will readily perceive the truth of this statement if he makes or imagines a plot of a field with a certain side the meridian, then conceives the whole plot turned around so that another side comes to the meridian, it will be evident that BEARINGS WITH COMPASS. 105 though the bearings are changed, the sum of the interior angles is unaffected. The so-called test would prove the work in either case. 157. Suggestions. Test frequently to see that the instru- ment is in proper adjustment. Keep the same end ahead. Read from the same end of needle. Sight as low on the flag- staff as possible. Make the line of sight as nearly horizontal as practicable. When reading near the cardinal points, be care- ful that the bearing is not read in the wrong quadrant, also that the common error of reading 56 for 44 is not committed. See that the instrument is set precisely over the station from which the measurements are to be made ; that the flagstaff is exactly on the proper point, and that it is held plumb. Level the instrument carefully ; especially see that it is level across the line of sight. Take the bearing and measure the distance on the true line when practicable ; when not, because of a high fence, bushes, etc., set off the least perpendicular distance therefrom at both ends which will afford a clear view, and take the bearing and dis- tance of the extremities of these perpendiculars. EXERCISES. 1. With a surveyor's compass, by a constant and direct bear- ing only, run a line, say 40 chains in length, over hilly ground, and part of it, if possible, through brush ; then return, using the reverse bearing only. 2. With the same instrument run another line equally diffi- cult, using both direct and reverse bearings forward and back. 3. Make a survey of a lot one side of which is near to a railroad track. If local attraction is found, determine its intensity. 4. Determine the magnetic bearing of eacli part of a broken line of several turns along a railroad track, or where local attraction is known to exist. 106 PLANE SURVEYING. B. ANGLES WITH TRANSIT. 158. With the Transit the survey of a line or the measure- ment of an angle can be made with greater accuracy than with the compass, since the reading of the plates to minutes sup- plants the reading of the needle to quarter or half-quarter degrees, and the pointing power of the transit greatly exceeds that of the compass. 159. To measure a horizontal angle, as MON. Set up the instrument precisely at ; level it and direct the intersec- tion of the wires to either point, say N. Clamp the instrument firmly to the spindle, note the reading of the vernier, then loosen the vernier plate and bring the telescope quite near the other line so that its ex- tremity M is in the field of view. Clamp the plate, and with its tangent or slow- motion screw bring the line of collimation precisely on M. Again take the reading. The difference of the two readings will be the angle required. It is more convenient to make the first sight, ON, with the zero of the limb and plate coincident, since then the reading of the plates after observing M gives at once the angle. If at each observation but one vernier is read, it is best to read every time from the same one ; it is better at each observation, though, to read both verniers and take the mean of these, thereby eliminating eccentricit}*. If, however, great accuracy is required, the measurement of the angles should be taken more than once, by the method of repetition or by series. 160. By Repetition. Make an observation upon any point, and read both verniers ; clamp the lower plate tc the spindle, direct the telescope to another point, and, as a check, again read the verniers. Now, keeping the index at the last reading, turn both plates ANGLES WITH TRANSIT. 107 back, and observe again on the first point ; clamp, as before, the lower plate, and turn the upper one so as to sight on the second point. It is perceived that by this operation the angle has been measured twice, but on different parts of the limb. An angle may obviously be repeated any number of times : the mean of the several readings gives more nearly than a single measurement the true angle. The reading at each observation serves as a check on the work. An angle may be repeated by simply noting the reading at the first and last observation, taking their difference, and dividing by the number of repeti- tions. It must be footed, however, how often, if at all, the 360 point is passed. Now, if the telescope is plunged, the plates turned 180 in azimuth, and repetitions of the angle again be made, beginning at the second point, the mean of the two sets of readings will give still more nearly the true angle, since the errors of adjustment and twist of station are thus lessened and those of observation reduced. 161. By Series. Observe as before upon any point, and read the verniers, clamp the lower plate, turn the vernier plate until the telescope may be fixed upon another point, and again read ; thus continue to make observations upon each point desired in their order, sweeping round the horizon, and make the last observation upon the first point. The last reading should be the same as the first. Plunge the telescope, move the plates in azimuth, and observe on the points again, pro- ceeding in the contrary direction. Several series of observa- tions may thus be made, as in the method by repetition. The magnitude of each angle is obtained from the mean of its reading. RKMAEiK. Care should be exercised to have the instrument properly centred, that is, set precisely over the centre of the station, especially if the object sighted is near the observer. The error arising from an eccentric setting is inversely as the distance of the object sighted ; an eccentric setting of one inch producing an error of nearly three (3') minutes of arc in sight- 108 PLANE SURVEYING. ing 100 feet, while the error arising from a sight of 900 feet is less than oue-tln'rd (') of a minute. Read both verniers to eliminate eccentricity. See that the reading is not made from the wrong end of the vernier, and that a half-degree is not omitted, calling the reading, say, 36 15', instead of 36 45'. If great accuracy is required when running a straight or broken line, lessen errors of adjustment by re- versing the instrument in altitude and azimuth, making two sets of observations at each station, and take the mean of their readings. See Article 157. If it is desired to locate the lines surveyed with reference to the meridian, the bearing of one of them should be taken b} T the needle of the instrument ; the bearings of the others may be deduced therefrom. See Article 167. 162. Angle of Deflection. The amount of divergence which a line makes with the preceding is called the deflection, and the angle which measures it is termed the deflection angle. L~ In the figure POM is the deflection angle : it is evidently the supplement of LOP. To measure it, set the transit at 0, sight to L, clamp the limb to the spindle and the plates together, then plunge the telescope : it will point to M. Take the reading, unclamp the vernier-plate and move it until the wires intersect P. The difference between the reading now and the first read- ing is the deflection angle. If, when making the first observa- tion, the vernier was at zero, the reading, after sighting P, would indicate at once the angle. 163. Traversing, or surveying by the back angle, is a method ANGLES WITH TRANSIT. 109 of surveying by which the direction of each line of a survey is compared with the first as a meridian or reference line. It is effected as follows : ^*" P Let it be required to traverse the broken line LMNOPQ. Setup the instrument at M, clamp the vernier at zero, for con- venience, and, with the lower motion, sight L, clamp below, transit the telescope, loosen above and observe N: the reading will show the angle M'MN which the line MN forms with LM. Clamp the plates, move to N, plunge the telescope, and, with the lower motion, sight Jf, the index remaining as at M ; then clamp below, loosen above, transit the telescope, and direct it to O : the index will show the angle which the line NO makes with LM. And so continue until the end of the line. To guard against mistakes in reading, and to avoid recording whether the deflection is right or left, it is well to assume all angles measured in the same direction.' In the figure the readings are all to the right, or clockwise, as indicated by the circular arcs, and the record is as follows : STATIONS. AZIMUTHS WITH LM. BEARINGS WITH LM. MAGNETIC BEARINGS ASSUMING BEARING OP LM N. 50 E. L North. N. 50 E. M 18 N. 18 E. N. 68 E. N 340 N. 20 W. N. 30 E. 360 or North. N. 60 E. P 90 East. S. 4.0 E. From the nature of the operation it may be perceived that, algebraically, the azimuth of any line is equal to its deflection HO PLANE SURVEYING. plus the azimuth of the preceding line. This method is partic- ularly adapted to surveying roads, streets, water courses, etc., and even in farm surveying it possesses an advantage over the survey by interior angles, on account of the readiness it affords in obtaining the bearings from the azimuths, and the greater rapidity with which the work may be plotted, since the angle which each line makes with the assumed meridian, or reference line, is taken at once from the field notes. Suppose LM in the figure to be the meridian of the survey, and the azimuths of the several lines as recorded in the table. Now, assuming the direction of LM to be north, it is evident that MN will be in the northeast quadrant 18 from the north point, or N. 18 E ; NO will be 20 to the wost of north, or N. 20 W. ; OP, making no angle with the meridian, will have a bearing north, and PQ east. So that, in general, When the azimuth is less than 90, it equals the bearing, and the line is in the northeast quadrant. When the azimuth is between 90 and 180, the bearing is southeast, and is the supplement of the azimuth. When the azimuth is between 180 and 270, the bearing is southwesterly, and may be found by subtracting 180 from the azimuth. When the azimuth is between 270 and 360, the bearing is northwesterly, and is the difference between 360 and the azimuth. When the azimuth is 90, the bearing is due east. When the azimuth is 180, the bearing is due south. ' When the azimuth is 270, the bearing is due west. When the azimuth is 360, the bearing is due north. If it is required to find the magnetic or true bearing of any or all the lines, take the magnetic or true bearing of the meridian of the survey and apply it, by addition or subtraction, according as the bearing of the assumed meridian, or standard line, is north- east or southwest. In the example given, suppose the bearing of the assumed meridian LM to be N. 50 E. : then the bearing ANGLES WITH TRANSIT. ill of the second line MN will be recorded 18 to the east of the reference line, or N. 68 E. ; the line NO, having a deflection of 20 to the left of the reference line will be recorded N. 30 E. ; and OP, N. 50 E. Thus the fourth column is added to the table. 164. To Traverse a Road, as LMNO. Proceed as indicated in the last article, and in addition measure the lines LM, NO, and perpendicular offsets thereto, at proper distances. N . If the road deviates much from a straight line, it will be necessary, in order to obtain more correctly the area, to take two offsets at M, one perpendicular to LM, the other to MN\ ' and also two at N, one perpendicular to MN, and the other perpendicular to NO.* Likewise to Survey a Small Stream. Traverse and measure the distances between assumed stations, as L, M, N, O, P, so chosen as to make no more of them than is consistent with few and short offsets to the various bends of the stream. If the stream is small, not exceeding 10 feet in width, or even wider if shallow, and it is desired to survey it between X and Y, a good plan is to run a straight line between these points and measure offsets therefrom to the stream ; or, if such a line will make the offsets rather long, run RQ, and measure offsets from it to X and Y"and intermediate points. If, however, the stream is wide * Article 234. 112 PLANE SURVEYING. and the crossing difficult, it will probably be better to use more stations, as shown in the figure. If a compass is used, the bearings may be taken instead of the angles. If a river of considerable width is to be surveyed, it will be necessary, in addition to the measurement of broken lines on each side from which offsets are taken, to make a series of an- gular measurements connecting the lines on one side with those on the other, and thence by trigonometrical calculations deter- mine their relative positions, and ultimately the surface of the river. C. PROBLEMS ON ANGLES AND BEARINGS. 165. Angles between Lines. To determine the angle be- tween two lines, meeting at a point, given by their bearings. E W- 1. If the lines run between the same cardinal points, that is, in the same quadrant, take the difference of their bearings. Suppose the bearing of OP is N. 32 W. and that of OQ N. 60 W. ; the angle between them is obviously NOQ - NOP-, or, 60 - 32 = 28. 2. When the lines run in different quadrants and both above or both below the horizontal or E. and W. line, take the sum of tlreir bearings. If OP bears N. 60 E. and OL N. 20 W., the angle POL = PON+ NOL = 60 + 20 = 80. PROBLEMS ON ANGLES AND BEARINGS. 113 3. If the lines run in diagonally opposite quadrants, subtract the difference of the bearings from 180. Assuming the bear- ing of OP N. 28 E. and of OL S. 58 W., the angle POL = 180 - LOM = 180 - (58 - 28) = 150. 4. When the lines are in different quadrants, and both to the right or both to the left of the vertical or N. and S. line, sub- tract the sum of the bearings from 180. If OP bears N. 65 E. and OL S. 42 E., the angle POL = 180 - (NOP + SOL) = 180 - (65 + 42) = 73. ADDITIONAL EXAMPLES. 1. A line OP bears N. 40 W. and OL N. 40 E.,; required the angle POL. 2. Find the angle POL, when OP bears S. 50 E. and OL N. 89 E. 3. Required the angle at 0, when OP bears N. 80 W. and OL S. 79 E. 4. What is the angle O, if OP runs S. 89| W. and OL N. 89 E. ? 5. A line OP runs S. 70 W. and OL S. 45 W. Find the angle 0. 114 PLANE SURVEYING. 166. There may be given the bearing of a line, as MO, and the deflection angle LOP, to the right or left of the direction of MO, to find the bearing of OP ; or, the bearings of MO and OP may be given to determine the magnitude of the deflection angle LOP. a. Given the bearing of a line and the deflection of the next, to find its bearing. Suppose MO bears N. 32 W., and the deflection of OP= 20 to the left ; the bearing of OP is evidently 20 farther towards the west than MO or its prolongation OL. It is therefore N. 52 W. Again, assuming RO bears N. 60 E. and the de- flection of OQ 40 to the right, it is evident that OQ is in the southeast quadrant, 10 from the east point ; or, its bearing is S. 80 E. 6. When the bearings of the lines are given, to determine the deflection. Suppose LO (p. 115) bears N. 20 E. and OM N. 70 E. ; the deflection of 03/from LO, or its prolongation OP, is evidently 70 _ 20 = 50 to the right. Again, the bearing of LO re- maining the same, .and that of OQ N. 30 W., then it is readily seen that the deflection angle is 20 + 30 = 50 to the left. PROBLEMS ON ANGLES AND BEARINGS. JT ,P 115 General rules' might be given for the cases under the above heads, corresponding to those in the preceding article, but they are deemed unnecessary, as a little reflection will enable the student to determine the required bearing, or angle, in any given case. 167. Given the angle between two lines, and the bearing of one line, to find the bearing of the other. The solution of this problem is ordinarily required in transit surveying, for, when surveying with that instrument, it is com- mon to take the bearing of only one line, and deduce the courses of the others from that bearing and the measured angles. Suppose LO bears N. 24 W. and the angle LOP= 82, to find the bearing of OP. It is evi- dent that the bearing of OP or the angle NOP, which gives the degrees in the bearing, = 180- (24 + 82) = 74. Hence the bearing of OP is N. 74 E. Assume the angle POM= 100, and the bearing of OP as found above; then, since there are 100 74, or 26, more in the angle than lies between OP and the 116 PLANE SURVEYING. north point, the position of OM is to the west of north 26, or its bearing is N. 26 W. Some simple combinations, as indicated in the illustrations given, will enable the student, unencumbered with rules, to readily solve any of the problems coming under this head. EXAMPLES. 1. A line bears S. 89 15' W. What is the bearing of a line perpendicular to it? Also, the bearing of a line making an angle of 135 with it? Is there more than one answer to the last? 2. If OP bears S. 36 W., and the angle 0^=68, what is the bearing of PL? Ans. N. 32 W. M SUGGESTION. Pass a meridian ? O through the angle, and consider the given bearing reversed. 3. The angles L, M, 0, P, of the trapezium are respectively 62, 130, 80, and 88, and the bearing of LM N. 70 E. ; find the other bearings.* 168. To Change the Bearings of the Sides of a Survey. It is sometimes desirable to change the bearings of a survey so that a particular side shall become a meridian. The whole plat is conceived to revolve through an angle sufficient to make the desired side the meridian ; the relative position of the sides remains unaltered. The following rule is substantially that given by Gummere, who states that the method was communi- cated to him by Prof. Robert Patterson, late of Philadelphia. RULE. Subtract the bearing of the side that is to be made a meridian from those bearings that are between the same points that it is, * The calculation may be tested, after having deduced the bearings of all the sides, by taking the last bearing found, as PL, applying the angle L, and observing if it gives the proper bearing of LM. PROBLEMS ON ANGLES AND BEARINGS. 117 and also from those that are between points directly opposite to them. If it is greater than any of those bearings, take the differ- ence, and change west to east or east to west. Add the bearing of the side tvhich is to be made a meridian to those bearings tvhich are neither between the same points that it is nor between the points directly opposite to them. If either of the sums exceed 90, take the supplement, and change south to north or north to south,. The accompanying diagram of full and dotted lines exhibits the positions of the sides of the following described farm, be- fore and after turning through 16^ to the right: (1) N. 16^ W., 24.63 chains ; (3) S. W., 34.28 chains ; (2) S. 79 W., 27.00 chains ; (4) .N. 65 E., 37.20 chains, to the place of beginning. The bearings are changed so as to make the first side a meridian. EXAMPLES. 1. Given the bearings of a tract of land : (1) S. 10 E. ; (2) S. 30 W. ; (3) N. 60 W. ; (4) N. 20 W. ; (5) N. 80 E., 118 PLANE SURVEYING. to the place of beginning. Required the changed bearings that the fourth side may be a meridian. (1) S. 10 E. (4) North. 20 Changed bearing, S. 10 W. (2) S. 30 W. (5) N. 80 E. 20 20 Changed bearing, S. 50 W. 100 (3) N. 60 W. 20 Changed bearing, S. 80 E. Changed bearing, N. 40 W. The student who avails himself of the hints and methods referring to the manipulation of angles and bearings as given in the preceding articles, will have no difficulty in determining the changed bearings direct from the data, without the use of rules. Thus in the example above it will be observed that each line is turned through 20 to the right; that is, the fourth course is made due north. The next side to it going round to the right, N. 80 E., will be turned the same number of de- grees (20), which places it 10 from the east point in the south- east quarter, or its bearing is S. 80 7 E. ; the first side turning through the same angle (20) will be thrown 10 west of the south point, or S. 10 W. ; the second course will be 20 farther to the southwest, or S. 50 W. ; and the third course turned toward the north point 20 will be N. 40 W. 2. Find the bearings of all the sides of the following de- scribed tract of land when the second side is made a meridian : (1) N. 681 E., 8.42 chains ; (3) S. 78f W., 4.90 chains; (2) N. 27 W., 10.25 chains ; (4) S. 1 E., 4.40 chains ; (5) S. 12 E., 7.04 chains, to the place of beginning. PROBLEMS ON ANGLES AND BEARINGS. 119 3. Given the bearings of a tract of land as follows : (1) S. 39i W. ; (3) N. 15 W. ; (5) N. 2 E. ; (2) East ; (4) N. 79 E. ; (6) S. 73f W., to find the bearings of all the sides when the first becomes a meridian. 4. Given the bearings of a tract of land as follows : (1) S. 79 W. ; (3) N. 89LE. ; (5) S. 80f E. ; (2) S. W. ; (4) N. IfE. ; (6) S. 581 E. ; (7) N. 39 E. ; (8) N. 16}- W., to find the bearings when the eighth side becomes a meridian. EXERCISES. 1. With a transit, using back and fore sights, run a tangent forward and back over hilly and brush land requiring six or eight settings of the instrument. The last two points set for- ward will give the direction back. Note the distance, if any, between the corresponding positions occupied by the instru- ment. 2. Traverse, or survey by the back angle, a broken line of six stations, using the first line as the meridian, or reference line, of the survey. Record the notes, indicating the azimuthal angles and bearings. 3. Measure the three angles of a triangular piece of land, the cornei-s being visible from each other ; see how much, if any, their sum differs from two right angles. 4. Traverse a pentagonal field, the index at the beginning being sot nt zero, and see if, when finally sighting on the station first occupied, the reading is zero. 120 PLANE SURVEYING. SECTION III. OBSTACLES. A. PROBLEMS ON PERPENDICULARS AND PARALLELS. 169. The Obstacles which occur in field work are more easily and expedittously overcome with the compass, or transit, and chain, than with the chain alone. Methods for the latter were given and illustrated in Chapter I. Section II., Chain Survey- ing. To erect a perpendicular to a line at any given point. Set up the instrument over the point ; if a compass is used, take the bearing of the line, and then move the instrument in azimuth until a bearing differing 90 from the first is observed. The line of sights will then indicate the direction of the required perpendicular. If a transit is employed, centre on the point, sight to a point in the line, clamp to spindle, and turn the ver- nier plate 90 either way ; then the line of collimation will show the direction of the perpendicular sought. Of course b}- the methods explained above, a line can be run with either instru- ment from any given point and making any given angle thereat with a line. 170. To let fall a perpendicular from a given point to a line. Let P be the point, and LN the line. If the compass is used, take the bearing of LN, remove the instrument to P, and with a bearing differing 90 from the first, run PO for the required perpendicular. With N a transit centre on L, measure the angle OLP, remove to P, and make the angle LPO equal to the complement of L ; the line of sight of the instrument will then be in the direction of the required perpendicular. PERPENDICULARS AND PARALLELS. 121 171. To let fall a perpendicular to a line from an inaccessible point. Measure the distance between any two points, as L and N, in the line ; also the angles PLN and LNP. Then in the triangle PLN we have given the side LN and the angles to find PL or PN. Computing PL, the distance LO=PLcosPLO. Or we may deduce an expression for LO in terms of the meas- ured line and the observed angles, thus : LO=POcotPLO. NO = POcotPNO. LO:NO = cot PLO : cot PNO, LO:LO + NO= cot PLO : cot PLO + cot PNO ; jy LN cot PLO Hence and but therefore cot PLO + cot PNO QUERY. Could a line be run not perpendicular as above through an inaccessible point, making any angle with the given line? 172. To run a line through a given point parallel to a given line. With the compass obtain the bearing of the line, and then from the given point run a line with the same bearing. With -=*0 fa in which 6 is known ; and Developing the left-hand member, dividing through by cos ^, and simplifying, there results tan * = _ ; I sin + n sin a cos 6 or, cot./r = . ^ + oot0. n sin a sin There are therefore but three steps in the solution : 1. Calculate the angle 0, and thence obtain 0. 2. Find tan fa or cot fa 3. By sine proportion, calculate PN, P0, and PL. In the example given, since the sides are in the proportion 5:6:8, the angle may be readily found from the well-known formula for the cosine of an angle, cos = 25+36-64 _ _ Q5 _ ^ ^ uU and 0=213 38'; whence *=10953', < = 103 45'. sin 23 40' Ar. co. = 0.396406 : sin 109 53' = 9.973307 : : 3000 = 3.477121 : PO = 7028 = 3.846834 * Regard must be given to the signs of the trigonometrical functions. INACCESSIBLE DISTANCES. 139 sin 23 40' sin 46 27' 3000 Ar. co. = 0.396406 = 9.860202 = 3.477121 sin 29 50' sin 46 25' 3600 PL = 5242 = 3.733729 Ar. co. = 0.303225 = 9.859962 = 3.556303 = 3.719490 If the supplement of the observed angles at P equals the angle at 0, the circle will pass through the three points L, N, and 0, and P may be anywhere on the circumference, and hence its distance is indeterminate by the first method given above ; and, substituting in the formula the proper values to find coti/r by the second method, the numerator of the fraction will become in- finite, as also the cot0 ; hence, such an observation will fail in both cases to locate the point P. EXAMPLE. Suppose ^=960 rods, NO 576 rods, LO 640 rods, the angle LPO=19, and NPO = 25. Find the distances PO, PN, and PL. Ans. PL = 758 rods ; PO = 1310 rods ; PN= 1350 rods. 197. From the top of a mountain m miles high the angle of depression of a line tangent to the earth's surface is a degrees ; it is required thence to find an expression for the radius of the earth, assuming it to be a sphere. Let O represent the centre of the earth ; N the mountain top ; P the point of tan gen cy ; OP and OK radii of the earth; /22V" the height of mountain and prolongation of OR. 140 PLANE SURVEYING. Draw NL perpendicular to ON, and denote the radius of the earth by r ; then, since NL and NP are respectively perpendic- ular to NO and OP, the angle NOP = the angle of depression LNP=a. Hence (r + m) cos a = r. m cos a 1 cos a Ans. MISCELLANEOUS PROBLEMS. 1. Determine the height of a hill, knowing that the angle of elevation of its top from a certain station = 50, and at a station 800 feet more remote the angle of elevation = 36 20'. 2. The angle of depression, taken from a balloon to a station whose horizontal distance is known = 18 40'. Find the height of the balloon. 3. Two war vessels, desiring to ascertain their distances from a fort, remove from each other 2000 feet, anil measure the angle between each other and the fort ; the angles being 79 40' and 82 20', what were their distances? 4. Two observers on the same horizontal plane, 1500 feet apart, and in a vertical plane with a balloon, observe its angles of elevation to be 62 40' and 71 10'. Required the height of the balloon. 5. The passage between two objects L and N being ob- structed by a swamp, the lines P=420 feet, and PN= 540 feet, were measured, and the angle LPN observed = 86 42'. Find the distance LN. 6. What distance can a person whose eye is 5| feet above the ocean see its surface? Assume radius = 3960 miles. 7. If the sun subtend an angle of 32' 2", and his distance from the earth is 93,000,000 miles, what is his diameter? 8. What is the altitude of the sun when the shadow of a staff cast on a horizontal plane is to the height of the staff as 7 to 5 ? MISCELLANEOUS PROBLEMS. 141 9. If the horizontal parallax * of the moon be 56' 50" and the diameter of the earth 7920 miles, what is the distance of the moon from the earth? 10. If the moon subtend an angle of 31' 14", when its dis- tance is 240,000 miles, what is its diameter? 11. When the meridian altitude of the sun is 50, the shadow cast by the peak of a mountain reaches a certain point on a horizontal plain ; but when his meridian altitude is 60, the shadow strikes a point 2000 feet nearer the base of the moun- tain. Determine the height of the mountain above the plain. QUERIES. If on the same day two observations were made on the sun for altitude, one or both when he was not on the meridian, and the length of the shadow measured as in Ex. 11, would sufficient data be thus obtained to determine the height of the mountain ? Would it be possible with data obtained, as in the first query, to ascertain the height of the mountain if the sun was vertical over the mountain at noon ? 12. If the height of a mountain is m miles and its top is visi- ble d miles, find an expression for the diameter of the earth, assuming it to be a sphere. 13. The angle of depression taken on the top of Peak of Teneriffe, which is two and a half miles high, to the farthest visible point was 2 2'. It is required to determine the observed distance and the diameter of the earth, assuming it to be n sphere. Dist., 140,876 miles; Diam., 7936 miles. Ans. EXERCISES. 1. Measure the height of a flagstaff or church spire above the street. * The angle at the moon, or other heavenly body, subtended by the semi-diameter of the earth. 142 PLANE SURVEYING. 2. Measure the height of a monument, tower, or some other prominent building upon a hill, without obtaining the distance to the foot of the object. Also, if practicable, measure the distance to the foot of the object and the proper angles. Com- pute and compare results with each other, and with the actual height, if it can be ascertained. SECTION V. RECORDING THE FIELD NOTES. 198. The Field Notes may be recorded in various ways, de- pending upon the instrument used, and the extent and intricacy of the survey. First Method. If the compass is employed, the bearings simply to be taken, distances measured, and the tract bounded by straight lines (no offsets) , the simplest, most compact, and also most convenient form for the subsequent calculation of the area is to write the stations, bearings, and distances in three columns, thus : STATIONS. BEARINGS. DISTANCES. REMARKS. 1 S. 20 53' E. 13.11 To a maple. 2 N. 48 10' E. 13.62 " birch. 3 N. 43 40' W. 4.73 " stake and stones. 4 N. 45 08' W. 4.75 " white oak. 5 S. 51J W. 2.53 " sandstone. 6 S. 72 J W. 6.56 " red oak, beginning. 199. Second Method. If the tract is not large, and there are offsets in addition to the bearings and distances, or if simply the angles and distances are measured, a very good method, especially for a beginner, is to make a rough plat of the survey, RECORDING THE FIELD NOTES. 143 and indicate in their corresponding places on the sketch the bearings, or angles, and the lengths of the lines and offsets, as shown below : 6.09, The above is a sketch of a small field, showing offsets to stream, etc. The following are hasty surveys of boundaries, etc., of land for proposed park in City of Wilmington, Del., July, August, and September, 1885 : Instruments : Transit. Chesterman's 100-foot steel tape. Work: Lines run with transit, and carefully measured with steel tape from station to station. Angles between these lines taken, always from left to right. Magnetic bearings of lines taken. Stations numbered or lettered in regular order. Offsets (sometimes angles and distances) taken to locate houses, cor- ners of fences, etc., offsets made at right angles with lines joining stations. Notes : Taken free-hand in small note-books (size 5;}" X 3J"). Sketches made to suit the page and to make the matter clear for plotting. The usual checks used on field and office work. Explanation of Sketches : No. 1. Single page of note-book. Location of fences on boundary of land proposed for park. No. 2. Two opposite pages of note-book. Location of road through land proposed for park, showing railroad crossing. No. 3. Two opposite pages of note-book. Location of run between two adjoining owners of land proposed for park. No. 4. Two opposite pages of note-book. Location of houses, etc., in land proposed for park. 144 PLANE SURVEYING. 42V ^x / \ -V*! ssyir* jt- - fvp i s \ 1 j: "a S Static iPost No. 1. RECORDING THE FIELD NOTES. 145 Sta. R 5 107V No. 2. 146 PLANE SURVEYING. KECOKDLN'G THE FIELD NOTES. 147 177 2i- 200. Third Method. The column method, an- alogous to that shown in Article 38, Chain Surveying, is, however, the most general. If the bearings are taken, they may be inserted in the column either verti- cally or diagonally ; if only the angles are ob- served, they should be placed at the stations which indicate where the measurements were made. The objects to which offsets are meas- ured may be designated or delineated on the marginal side of the line as they naturally ap- pear. Where streams, roads, fences, etc., cross the line, representations of them are made, in- dicating approximately their direction ; or, if desirable, their bear- ings, or angular devia- tions from the line, may be taken and recorded. The following notes will more fully explain the method under con- sideration : No. 148 PLANE SURVEYING. 24.28 21.08 20.68 13.50 6.00 (6) 11.38 CO (5) (4) 17.54 M a CO f3) 33.10 24.75 (2) 11.90 0) Chestnut stump, cor. to J.S.K. in W.D.C. line. West Stone, 7 links S.E. of a butternut tree Cor. to A.L. & W.D.C. Limestone, middle of public road. Stake & Stones, cor. taL.R. in A.L.'s line Middle of road. White oak stump 10' S.W. stone house, north side public road, cor. to J.V. & J.L. RECORDING THE FIELD NOTES. 149 (i) H3.3Q =%=S := SP=5= 14.52 g- 5-^=^=^ _ -_ 14.12 . . _, ^^l^^r-^J'ftSt. fc (12) Limestone, cor. to W.V. in C.C.'s line 10.47 , Oi 00 CO (11) Limestone. 8.00 W fc' ! (10) Limestone, cor. to J.S.K. in C.C.'s line 30.60 CO (9) Limestone. 8.31 CO (8) Limestone. 4.45 8 i (7) 150 PLANE SURVEYING. k (4) Limestone. Sta. (4) in foregoing 10.49 description. Stone house |p 9.00 100' from line. ri oo 02 m Limestone. N. 12 W. 10.41 Lane leading to dwelling, S. 11 E. Road 9.00 Hf Barn. | i 6.40 M j 3 House 60' from line. -1 W 8 . 20.38 8 Stone house Wft, (i) White oak stump. Sta. (1) :u f near corner. foregoing description. RECORDING THE FIELD NOTES. 151 The bearing and distance of proof-line from P to Station (11)= S.62 W. 19.10. N. 79 10' E. 6.00 Housi o Spring Run and 15.82toEastlineof Survey 9.20 5.75 OD (#) 8.80 W 02 (I/) 36.20 22.38 W 02 Limestone at end of lane on north bank of " Big Brook." Limestone on bank of Spring Run. Point in lane. Limestone in middle of public road at end of lane. 152 PLANE "SURVEYING. The notes show that the sides of the tract were first surveyed ; which, with their bearings and distances, include also the loca- tion and general direction of road-crossings, streams, etc., a description of the corners, and the names of owners of property adjoining the survey. Next to traversing the bounding lines, the survey of the public road, crossing the farm from east to west, was made. This road enters the tract at station (1) ; at 6.40 chains from (B) it passes a house which is 60 feet to the right; at 9.00 chains a road to the left, the bearing of which is given ; at 10.41 chains is a corner at end of lane lead- ing to dwelling ; near the east end of road a stone house is located, at 100 feet north of the line ; and at 10.49, station (4) of sides survey is reached, at which point the road leaves the farm. The survey of the lane to the dwelling, and thence to the creek, is next recorded. Here are noted the intersection of a line S. 79 10' W., and the distances on this, east and west, to spring runs, as well as the distances to the east and west sides of the tract;* the dwelling and barn are located, and the limestone on the north bank of Big Brook reached. A line was run from this last point to station (11), which, in connection with the survey of the lanes, the public road, and the cross-line from L to F, gave proof of the accuracy of the work. * This line was made a boundary in the subsequent division of the land. KECOKDING THE FIELD NOTES. 153 154 PLANE SURVEYING. SECTION VI. LATITUDES AND DEPARTURES. 201. The Difference of Latitude of the two ends of a line is the perpendicular distance between the parallels of latitude which pass through them, and is reckoned north or south, according as the bearing is northerly or southerly. The Difference of Longitude of the two ends of a line is the perpendicular distance between the meridians which pass through them, and is reckoned east or west, according as the bearing is easterly or westerly. The difference of latitude of a line is often called briefly the latitude, or northing or southing ; and the difference of longitude, its departure, or easting or westing. It will be perceived from the definitions just given that, when a line bears either due north or south, the distance equals the latitude, and the departure is nothing ; but if the bearing is east or west, the distance and departure are equal, and the lati- tude is zero. Furthermore, it will be seen that in all other cases except those just cited, the latitude, departure, and dis- tance form the three sides of a right triangle : the distance being the hypotenuse, and the latitude and departure the sides about the right angle. Let LP represent a line given by its bearing and distance ; it is required to determine its latitude and departure. Let OL and PM represent parallels of latitude, and LM and OP meridians. The lengths of LM = OP and LO=MP are required. The problem stated simply is : Given in a right triangle LMP the hypotenuse LP (distance), the angle L (bearing), to find the side LM (latitude) , and MP (departure). LATITUDES AND DEPARTURES. From Trigonometry, LM^ LPvosL, 155 So it is seen that the latitude of a line is obtained by taking the product of the distance and the cosine of the bearing, and the departure is equal to the product of the distance and sine of the bearing. 202. The case just treated is the principal one which the surveyor will use, since it is necessary as will subsequently be seen in computing areas, to determine the latitudes and de- partures ; and by Jthese formulas he will generally obtain them, having taken in the field the bearings, or angles, and distances. Other cases, however, will occur in practice referring to the triangle LMP, and for convenience they are here subjoined. Designating the length of the line, or distance, by s, the bear- ing by 6, the latitude and departure respectively by I and d, then we may write the following formulas : CASE. GIVEN. KEQUIKED. FORMULAS. 1 b, s. /, d. / = s cos b, d = s sin b. 2 b, I. s, d. s = = lsecb, d = l tan b. cos b 3 b, d. s, I. sin 6 tan 6 4 5 s, I. s, d. b, d. b, I. cos 6 = -, d = Vs' 2 I' 2 , s sin 6 =-, /= V* 3 rf. s 6 I, d. b, s. tan b = -, s= VP + rf*. EXAMPLES. 1. Given the bearing and distance of a line, N. 23 54' W. 18.25 chains ; required its latitude and departure. 156 PLANE SU It V EYING. 2. Given the bearing of a line Jf . 87 40' E., and the depart- ure 2640 feet ; find its distance and latitude. 3. Given the length of a line 24.60 chains, and the departure 17.40 ; find its bearing and latitude. 4. Given the latitude 23.76 chains south, and the departure 0.94 chains west; required the bearing and distance. 5. Given the distance 1886 feet, and the latitude 943 ; deter- mine its bearing and departure. 6. It is required to find the distance and departure of a line, given the bearing S. 30' W., and latitude 10.80 chains. 203. The Traverse Table. By the use of Formula 1, last article, latitudes and departures have been calculated for every quarter-degree of the quadrant, corresponding to distances from 1 to 10, and even from 1 to 100 ; these results tabulated con- stitute the traverse table. Such a table was considered quite indispensable when the compass was the principal surveying instrument, but since the more accurate transit has to a great extent superseded the compass, and surveyors are now reading to minutes instead of quarter-degrees, the common traverse table reading only to quarter-degrees is of little practical value. When, therefore, the bearings are read to minutes, the lati- tudes and departures are generally best obtained from a table of natural sines and cosines.* However, for the benefit of those engaged in compass survey- ing, and for those who, though reading to minutes, prefer to obtain by interpolation the latitudes and departures from the traverse table, one is given near the end of this volume. * A traverse table in which the calculations are made to every minute of bearing for distances from 1 to 10 and extending to five decimal places, would answer the purpose admirably. Such a table is in existence, but it is not common. The common tables of natural sines and cosines are sim- ply tables of latitudes" and departures corresponding to a unit's distance. With a distance 2, the latitude and departure are twice those in the table; when the distance is 3, three times ; when n, n times. LATITUDES AND DEPARTURES. 157 Explanation of the Traverse Table. The number of degrees in the bearing if it does not exceed 45 is found in the left-hand column of the page, and the latitudes and departures, as indi- cated at the top, may be taken under the proper distance ; if the number of degrees is greater than 45, it is found in the right- hand column of the page, and the columns of latitudes and departures are indicated at the bottom. For example : 1. Let it be required to find the latitude and departure cor- responding to a bearing N. 34 30' E. and distance 5 chains. We find in the table, opposite 34 30' and under "distance 5," in the column headed "Lat.," 4.121, and in the column headed "Dep.," 2.832. Hence the latitude and departure are respec- tively 4.12 N. and 2.83 E. 2. Required the latitude and departure of a line bearing N. 72i W. 9 chains. Looking in the column at the right of the page for 72 15', and under "distance 9," we find, reading at bottom, in the Lat. column, 2.744 ; in the Dep. column, 8.572. Hence the latitude is 2.74 chains N., and the departure 8.57 chains W. 204. The table may be used to find the latitude and depart- ure for any distance however great. If, in first example above, we suppose the bearing to remain the same, but the distance to be 50 chains ; then, since for the same bearing the latitudes and departures vary directly as the distances, the latitude, or depart- ure, for 50 chains is 10 times that for 5 ; and, as multiplying by 10 is in effect removing the decimal point one place to the right, we may take directly from the table opposite 5 the lati- tude and departure of 50, or 41.21 N. and 28.32 E. If the distance is not a multiple of 10, but made up of units and tens, we may take out of the table the latitude and depart- ure for the units, and for the tens as indicated above. The sum of these will evidently be the latitude and departure required. 158 PLANE SURVEYING. 3. Let it be required to find the latitude and departure of a line S. 40 E. 34 chains. Looking in the table opposite 40 and under " distance 3," take out at ouce, by conceiving the decimal point removed one place to the right. For 30 chains, Lat. 22.98 Dep. 19.28 Then " 4 " " 3.06 " 2.57 34 chains, Lat. 26.04 S. Dep. 21.85 E. By an extension of the above principle, the table may be used to obtain the latitude and departure when the distance is com- posed of chains and links. 4. Given the bearing of a line S. 28 45' W. 26.58 chains, to find its latitude and departure. For 20 chains, Lat. = 17.53 Dep. = 9.62 6 .5 " .08 44 = 5.26 " = .44 44 = .07 44 = 2.89 44 = .24 4 ' = .04 26.58 chains, Lat, = 23.308. Dep. = 12. 79 W. 5. Find by the traverse table the latitude and departure of a line bearing N. 41 45' E. 17.29 chains. 6. Given the bearing of a line S. W., distance 23.48 chains, to find its latitude and departure. 7. What are the latitude and departure of a line bearing S. 8530'E. 135.42 chains? 8. If the bearing and distance are N. 89f W. 20.09 chains, what are the latitude and departure ? 205. By means of interpolation the traverse table may be used to find the latitude and departure when the bearing is given to minutes. Thus, the bearing being N. 34 20' E. any given distance, take out the latitude and departure corre- LATITUDES AND DEPARTURES. 159 spending to 34 15' and the given distance, and add* to that departure T 5 ^, or , of the difference between it and that corre- sponding to 34 30' and the given distance, for the departure required. Likewise obtain T 5 7 of the difference between the latitudes corresponding to 34 15' and 34 30' and the distance, and subtract* from the latitude first found for the latitude required. For a bearing 34 23', the fractional part to be taken of the difference between 34 15' and 34 30' would be T % ; the numer- ator being the excess in minutes above the quarter, and the denominator 15. 206. In the absence of a traverse table calculated to minutes, the table of natural sines and cosines, as before stated, is the best to use when the bearings are given to minutes. It is shown in Article 201 that the cosine of the bearing mul- tiplied by the distance gives the latitude, and the product of the distance and sine of bearing gives the departure. EXAMPLES. 1. The bearing and distance of a line are N. 37 43' W. 24.29 chains ; required its latitude and departure. Four places of decimals from the table will usually be sufficient. The cosine of 37 43' true to four places = .7911. The sine of 37 43' true to four places = .6118. .7911X24.29 = 19.21 N. Lat. .6118 x 24.29 = 14.86 W. Dep. The following contracted form of multiplication, using five decimal places, gives practically the same result : Cosine of bearing = .79105 ; sine of bearing = .61176. * The departure increases with an increase of the bearing; the latitude diminishes. 160 PLANE SURVEYING. chains, Lat. = 15.8210 Dep. = 12.2352 " = 3.1642 " = 2.4470 Distances .0712 " = .0551 24.29 chains, Lat. = 19.21 N. Dep. = 14.86 W. 2. Find the latitude and departure of a line bearing S. 62 1 7' E. 37.18 chains. 3. Required the latitude and departure of a line N.8857'W. 28.97 chains. 4. Required the latitude and departure of a line bearing S. i E. 2640 feet. 5. Given the bearings and distances of two lines running from the same point P, as follows: PO, N. 38 37' E. 1760 feet, and PL, N. 71 54' E. 1320 feet ; to find by means of lat- itudes and departures the distance OL. 6. Assuming PO bears N. 48 17' W. 27.42 chains, and PL S. 36 28' W. 19.24 chains, find, as in the last example, the distance OL between the extremities of the lines. 207. Testing a Survey. It is evident that when a surveyor has passed completely round a tract of land and returned to the place of beginning, he has gone in a northerly direction just as far as he has gone in a southerly direction, and as far easterly as westerly. Hence the sum of the north latitudes should equal the sum of the south latitudes, and the sum of the east depart- ures equal the sum of the west departures.* In practice, this degree of accurac}- is seldom attained, for various causes incident to the manipulation of the instruments, their inherent defects, imperfect chaining, etc. * If the survey is effected by traversing (Article 163), the reading at the last station should be 360 or 0. If the interior angles are measured, their sum should equal twice as many right angles less four as the figure has sides. If a small error exists, it must be distributed evenly among the angles, unless on account of the difficulty of observing one or more of the. angles, these should have a larger share of the error. See, also, Article 156 LATITUDES AND DEPARTURES. 161 On account of the varying conditions in different surveys, it is impracticable to state precisely how great an error should be allowed without a re-survey of the tract. A rule usually fol- lowed by compass surveyors is to allow an error of 1 link for every 5 chains, 1 : 500. This is perhaps a fair average for ordinary farm surveying. If the ground is exceptionally clear, and quite level, an error of 1 : 1000 is not too great ; if, on the other hand, the ground is uneven, rocky, and brush} 7 , 1 : 300, or even 1 : 200, might be allowed. The error resulting from a transit survey of the same ground should be much less. For the average case given above, instead of 1 : 500 it should not be much less than 1 : 1200. The above rules are cited simply as guides to the young sur- veyor to aid him in forming a standard for himself, based on his own experience. 208. Correcting Latitudes and Departures, or Balancing the Survey. (1) A survey is balanced when the northings equal the southings, and the eastings equal the westings. When these equalities do not exist, the error is distributed among the lines, proportioned to their lengths. This operation is called correct- ing the latitudes and departures. It is best illustrated by an example : 7. BEARINGS. DISTS. LATITUDES. DEPART- URES. CORREC- TIONS. CORRECTED LATITUDES. CORRECTED DEPART'S. f. S. E. W. j * N. S. E. W. i 8. 20 53' E. 13.11 . . . 12.25 4.67 1 1 12.27 4.68 I 1 4 f N. 48 10' E. N. 43 40' W. N. 45 08' W. 8. 51 30' W. 13.62 4.73 4.75 2.53 9.08 3.42 3.35 ... 10.15 3.26 3.36 1.98 9 1 1 1 1 9.06 3.41 3.34 10.16 3.26 3.35 1.98 1.57 ... 1.57 I S. 72 30' W. 6.56 ... 1.96 ... 6.26 7 1 4 ... 1.97 ... 6.25 45.30 15.85 15.78 14.82 14.86 15.81 15.81 14.84 14.84 15.78 14.82 Error in latitude, 7 links. 4 linkfl. Error in departure. 162 PLANE SUliV EYING. In the table the latitudes and departures corresponding to the several bearings and distances are obtained by means of a table of sines and cosines, and placed in their proper columns. The first course being between the south and east, the lati- tude found is written in the column headed S., the departure in column E., and so on, the letters of the course indicating the columns in which to place the latitudes and departures. The difference of the sums in the latitude columns is then taken, and' found to be 7 links : this is the error in latitude. The error in departure, found in a corresponding manner, is 4 links. The total distance round the field is showYi by the footing of the distance column to be 45.30 chains. The distribution of the error is effected then by the proportions : For the Latitude. Sum of the sides : length of any side = error : correction for that side. 45.30 : 13.11 = 7 : 2 45.30 : 13.62 = 7 : 2 For the Departure. 45.30 : 13.11 = 4 : 1 It is unnecessary usually to make but one proportion each for the latitude and departure correction, since the error for any other side may be found mentally by comparing its length with that of the side used in the proportion. Whole links only are used. The latitude correction for the second side is a little greater than 2, but it is nearer 2 than 3, and is therefore called 2. The corrections thus found are written in their proper col- umns, headed "Correction, Lat. Dep.," opposite the sides to which they refer, and are so applied by addition or subtraction as may be required to reduce the errors to zero. The quanti- ties thus obtained are placed in the columns of corrected lati- tudes and departures to the right of the corrections. LATITUDES AND DEPARTURES. 163 Since the southings are too small, the correction 2 is added to 12.25, making 12.27, for the first entry in the column of cor- rected latitudes. The eastings being too small, the correction 1 is added to 4.67, making 4.68, to be written under E. in the corrected departures ; and so on for the rest. If the corrections have been properly applied, the northings will equal the southings, and the eastings the westings, and the survey is balanced. In the example just given, the difference of latitude is 7 and the departure 4 links ; hence, the length of a line to close the survey = A /7 2 + 4* = about 8 links ; and as the perimeter of the tract =45. 30 chains, the "error of the survey," or " error of closure, "= 1 link for 5.66 chains, or 1 : 566. Some surveyors prefer a more compact table than that given above, and instead of a double set of latitudes and departures, use but one, and write in ink of different colors the corrected latitudes and departures over the first. Others, again, prefer two columns instead of four for the latitudes and departures, using the plus (-f) sign to indicate north latitudes and east departures, and the minus ( ) sign to indicate south latitudes and west departures. The form given above is, however, preferable to either, since a mistake in the application of the corrections is in that more easily detected, the footings are more expeditiously and accu- rately obtained, and the subsequent part of the work referring to the area is thereby facilitated. If a side of the survey passes over very rough ground, or through a dense wood, or for any reason it is rendered more difficult to measure than any of the others, the surveyor should exercise his judgment in deciding how much more of the error than the rule would indicate should be applied to that side. Regard must also be had to the probability of error in the bearings ; hence, when a side of considerable length is aligned through a thicket, or over very uneven ground, and where often- times the observations are made to top of rod, if it is found that a slight change in the bearing will diminish materially the error, the change should be made. 164 PLANE SURVEYING. The diurnal variation of the needle is not unfrequently a source of error in compass surveys. A range of 10 minutes is quite common, and even 15 minutes is occasionally noted. This error may be avoided by measuring the angles of the tract, or testing the compass every two or three hours by setting up and sighting on some line as standard. Some authors and surveyors affirm that when the bearing of a line is due east or due west, the error in latitude is nothing, and therefore such a line needs no correction. Likewise a due north and south line has no error in departure. The writer does not concur in this view ; for the errors in compass work are not confined to the chaining, and in transit surveying there is fre- quently considerable error in the angles. In the application of the rule these facts are assumed ; indeed, as soon as a correc- tion, made in the usual manner, is applied to any side, a change of bearing results, for the corrected latitudes and departures no longer belong to the original bearing, but to some other. More- over, there is no more reason for supposing a line runs due north because it is so read than that a line runs N. ^ E. or N. 89| E. being so read ; yet no surveyor would hesitate to apply the rule to either of these, thus assuming that an error in bearing as well as in chaining was committed ; and this is the correct assumption on which, without excepting any side, the distribution of the error, except as follows, should be made. (2) If, however, a survey is made with a transit in good ad- justment, the angles, either interior or deflection, being carefully observed, and the test hereinbefore mentioned when applied giv- ing the inference that the angles were accurately measured, and the error of closure therefore due to erroneous chaining, then the correction which should be applied is obtained as follows : Add up the columns of latitudes, and also those of departures, and say, as the arithmetical sum of all the -{ * } * to correction to be applied to that i, LATITUDES AND DEPARTURES. 165 (3) If greater accuracy is required than can be attained by the preceding methods, each side should be weighted ; that is to say, the surveyor determines the relative difficulties in measure- ment and alignment of the boundaries, considering some one side the standard. Calling the error probably made in the side chosen as standard one (1), another side, which in the judg- ment of the surveyor was, per unit, twice as difficult to measure, would be multiplied by 2, or, as it is termed, have a weight of 2 ; another multiplied by 3, or 1, etc. Then, instead of tak- ing the perimeter for the divisor, as was done in the first case above, the sum of the sides thus multiplied or weighted is used, and the proportion is as follows : As the sum of the multiplied distances is to any particular multiplied distance, so is the error in { l ^ iltwd * j. to the correction . ' The following illustrates the method of balancing a survey when the sides are weighted : STATIONS. BEARINGS. DISTANCES. WEIGHTS. 1 MULTIPLIED DISTANCES. LATITUDES. DEPART- URES. STATIONS. cc 02 2! fe! tej cr> *J Qt .is. rf^ il^. K5 fc^ H-* ^ CO GO O I i | | s s ^ ^ ^ ^ w w td H 1 05 fcO * rf^ CO CO S OS Cn 05 P DISTANCES. Oi Oi ^-q bo oo en co co jo ! .' en fcS CO ! S . LATITUDES. nks. Error 4 links. 2)240.6401 10)120.32005 12.032 acres. Cn ~i CO ,_, l_l to O Cn ' ' t? &3 bo t* H^ _ as . . . Oi *^J bq DEPABTUBES. bo be t* 01 O5 H-i CO CO ^ s g : : S -a h- ] H-" h-> bS tsS H a. COBBEC- TIONS. i*> ,- ; - ; MM i in CC co co co : : ss fc : ^ COBBECTED LATITUDES. ei CO M HJ h- ' ' ' t ^s 25 : : : is ?> * % s *> '. '. '. '. 00 ! COBBECTED DEPABTUBES. is o H-> co co g s g s : : ^ 1^ S 05 S * .if, & 2 fe g o k - b ii li : : g | | : Hi f K p : ; ; 25 CO ^J _ _ *. ^ CO . . . CO Cn OS O5 Hi 192 PLANE SURVEYING. the trapezoids are north, and those of the triangles south. If we had assumed the meridian to pass through the most easterly corner, the areas of the trapezoids then formed would be south, and those of the triangles north. If the bearings of the lines were reversed, or the survey made with the field to the right, the reverse of the preceding state- ment would be true. In either case, however, one-half the difference of the sums of the double areas will give the contents. As an exercise the student may obtain an expression for the area of POLMP, last figure, assuming the meridian to pass through L, and passing i-ound by MP, etc., that is, keeping the field to the right. He may also, with the meridian through P, and keeping the field to the left, obtain an expression for the area. As a further exercise he may verify the result in the last example solved, taking the meridian through the most easterly station. Calculate the areas from the following notes ; also make a plot of each : 1. 9 W. 31 E. 69 E. 0^ E. Of W. 89 W. (1) N. (2) N. (3) S. (4) S. (5) S. (6) N. 15.50 chains ; 25.40 " 10.00 19.70 14.60 21.00 2. STA- TIONS. LINES. DlSTS. AZIMUTH WITH LM. L LM 22.45 M MN 1.30 22 N NO 66.30 90 OP 23.85 180 P PL 67.10 270 L LM 360 nr 0" DETERMINING AREAS. 193 3. (1) N. llfE. (2) S. 87 W. (3) S. 201 W. (4) S. 82 E. 13.19 chains; 8.50 " 11.75 " 10.03 " AHS. acres. If in Article 76 we substitute respectively tor abscissa and ordiiiate of a corner of a tract, departure and latitude of the side ending at said corner, the rule there given may be applied to surveys made with an angular instrument. To illustrate, take the example given on page 191: CORRECTED LATITUDES. CORRECTED DEPARTURES. TOTAL LATITUDES. TOTAL DEPART- URES. DIFFER. BETWEEN ALTERNATE DEPARTS. DOUBLE AREAS. jr. S. E. W. 1227 468 000 9.06 10.16 -12.27 4.68 -14.84 182.0868 3.41 . . 3.26 - 3.21 14.84 -6.90 22.1490 3.34 . . 3.35 .20 11.58 6.61 1.3220 1.57 . . 1.98 3.54 8.23 5.33 18.8682 1.97 6.25 1.97 6.25 8.23 16.2131 2)240.6391 10) 120 .32 sq. ch. 12.032 acres. In this case the axes were taken through the most westerly station, thereby making the total departures all plus, but giving both plus and minus total latitudes. On account of the signs the double areas are all plus. The axis of ordinates passing through the most westerly station makes the total latitude of that station zero, and consequently there is one less multiplica- tion to be performed. The same would be the case if the f axis passed through the most easterly corner. 194 PLANE SURVEYING. Since the difference of the alternate total departures is equal to the sum of the adjacent departures, the rule just given may be stated as follows : Multiply the total latitude of each station by the sum of the departures of the adjacent sides, and take half the sum of these products for the area. To illustrate, take the following example : S i J ii | BEARINGS. N. S. E. W. II I DOUBLF AREAS. 5 3 $ i N. 25 E. 433 3PR 183 000 2 N.76'55'E. 191 43 186 393 369 145017 3 S. 6 3 41' W. 539 535 . . 62 436 124 54064 4 S. 25 W. 40 . . 36 . . 17 - 99 - 79 7821 5 N. 65 W. 320 135 290 -135 -307 41445 2)248347 43560) 124173.5 sq.ft. 2.852 acres. The'studeut may verify the preceding example by this method. 2. Given the bearings and distances of the sides of a field, as follows, to find the area by each of the two preceding methods. Ascertain, also, the error of the survey. (1) N. 61 W. (2) N. 65. V E. (3) S. 39 E. (4) S. 2 W. (5) S. 46 W. (6) N. 88 W. 9.38 chains; 8.25 " 6.51 " 4.45 " 5.00 " 6.79 " 8. Given the boundaries of a tract of land with the corre- sponding weights, as follows, to determine the area by double DETERMINING AREAS. 195 meridian distances, using the weights in balancing the survey as indicated in 3, Article 208. Determine, also, the error of the survey. ;i) S. 79 10' W., dist. 27.00 chains, weight, 1; " 3; " H; 2; 2; " 2; " i; " i. 4. The distances and interior angles of a farm, together with the bearing of one line, are given below. The angles were measured very accurately. It is required to calculate the area, by either of the preceding methods, balancing the survey by (2) Second Case, Article 208. Also make a plot. Angle L, 90 ; side LM, 28.00 chains. " M, 148|; " MN,25.2Q " (1) S. 79 10' W., dist. 27.00 (2) S. i W., " 34.08 (3) N. 89| E., " 10.47 (4) N. 155' E., " 15.30 (5) S. 80| E., " 7.15 (6) S. 58 E., " 11.50 (7) N. 39 E., " 9.20 (8) N. 16| W., " 24.63 ii N, 81 1 ; " NO, 11 .70 ii 0, 220 a. OP, 12 .IS tt P, 90 a PQ, 27 .DO ii Q, 90 a > QR, 15 .i<; R, 270 ; " RS, 11 .!)() ii S, 90 > " SL, 21 .(50 Bearing of LM, N. 10 E. 5. The notes of a survey are given below ; it is required to determine the area by double meridian distances after correct- ing the latitudes and departures by a combination of 2 and 3, Article 208. See also note in same article. The interior angles were observed. Angle L, 91 44'; side LM, 17. 16 chains; weight, 2. " M, 168 20'; " MN, 9.48 " " 1. " N, 104 49'; " NO, 8.39 " If ' f 0, 179 30'; " OP, 15.28 " " 2. 196 PLANE SURVEYING. Angle P, 90 19'; side PQ, 16.05 chains; weight, 2. Q, 90 05'; " Q.R, 15.68 " " 3. " R, 283 49'; " RS, 11.40 " " 1. " S, 71 24'; " SL, 13.80 " 1. 6. Select a tract of land, some of the sides being much more difficult than the others to align and measure, survey it, weight the sides, balance the latitudes and departures according to the weights, and calculate the area. 7. Let one party of students survey a tract of uneven or hilly land of considerable magnitude, by means of transit and stadia and rectangular co-ordinates ; another party at the same time, or the same party subsequently, survey the same tract in the usual way. Compare results. C. WHEN OFFSETS ARE TAKEN. 235. Let the annexed figure represent the case. The prop- erty lines are NO, OP, PL, and the centre of the creek * RS. Obtain sufficient data to compute the area of the rectilinear .0' * When a non-navigable stream forms a boundary of a tract of land, the middle of it is considered the property line, unless otherwise specified. In navigable rivers and tidal waters, the boundary is low-water mark. DETERMINING AREAS. 197 figure LNOP, and take offsets from the line LN to the middle of the stream, as directed in Offsets and Tie-Lines, Article 73 ; and in Traversing, Article 164. Calculate the area of LNOP by one of the preceding methods ; to this add * the sum of the areas of the trapezoids, and triangles formed by the offsets from the line LN to the middle of the creek. If the width of the stream is considerable, and especially if great accuracy is required, the surveyor must not ignore the small triangles f formed at L and N. O 236. To Find the Area of a Pond or Small .Lake, traverse, or take the bearings of the sides LM, MN, NO, etc., and measure them ; also take offsets, at proper points, from these lines to the edge of the water. Calculate the area included be- tween the right lines, and sub- tract therefrom the area found by the offsets ; the remainder will be the area required. EXERCISES. 1. Let one party survey a field with compass and chain, taking bearings and distances of all the sides ; another party survey the same field, using transit and chain, and observing * If the base line LN is without the tract, as in LNO'P 1 , the area included between the middle of the stream and LN must be subtracted from that of LNO'P'. t Other things being equal, the areas of these small triangles depend upon the obliquity of PL and ON. There will be none formed when PL and NO are perpendicular to the base LN. In the case presented, the area of the triangle at L is to be added, and that of Nn'v subtracted from the sum of the areas of the trapezoids, to obtain the correct content between LNund the middle of the creek. 198 PLANE SURVEYING. the interior or deflection angles ; a third part}', using the chain only. Each party should use proof lines, make record, plot, and calculate the area. Compare results. 2. With a transit, survey a field, a part of which is bounded by a creek, lake, or some crooked line requiring offsets to be taken ; make a plot, and compute the area. 3. Triangulate a portion of a river or small lake ; make a plot, and compute the area. 4. Make the necessary measurements to write a description, to make a plot, and to compute the area of a portion of a crooked road. 5. Observe all the bearings and measure all the sides of a polygonal field, except the bearing and distance of one side. Compute the area, and length and bearing of omitted side. Subsequently observe the bearing and distance, and note, if any disagreement, how much the area is affected thereby. CHAPTER III. DECLINATION OF THE MAGNETIC NEEDLE, OE VAKIATION OP THE COMPASS. 237. It has been already remarked (Article 82) that the magnetic and geographic meridian do not in general coincide. The angle included by the vertical planes containing these lines, or the angle which the direction of the needle makes with the geographic meridian, is the declination of the needle, sometimes called the variation of the compass. It is different at different places, and is a variable quantity at any place. The declination is termed east or west, according as the north end of the needle points to the east or west of the geographic, or true meridian. The magnetic declinations of a few places for the year 1885 are given below : Eastport, Me., 19 10' W. Sitka, Alaska, 2850'E. Albany, N.Y., 1011'W. Milledgeville, Ga., 2 32' E. Pittsburg, Pa.,* 2 52' W. New Orleans, La., 6 11' E. Omaha, Neb., 10 06' E. City of Mexico, Mex., 7 24' E. San Francisco, Cal., 16 34' E. 238. Irregular Changes. The magnetic needle is subject to disturbances during a thunder storm, or an exhibition of aurora, solar changes, and sometimes it is considerably agioated with- out any apparent cause, but probably on account of magnetic or electric disturbances more or less remote. The changes, however, which especially concern the surveyor, are the diurnal and secular. * At this place, September, 1887, the magnetic declination = 8 01' W. 200 PLANE SURVEYING. 239. The Diurnal Variation. It has been ascertained, by repeated observations at various places, that the magnetic needle is subject to daily changes ; that at a time varying from two to three hours after sunrise the north end of the needle attains its maximum deviation to the east, or, as it is called, its eastern elongation ; from this time it is deflected westward, attaining its western elongation between 1 and 2 o'clock P.M., whence it retrogrades towards the east. There is sometimes an interruption of the motion at night, but generally a small reversed movement is exhibited, the magnetic meridian being crossed a second time between 7 and 9 P.M. The times at which these limits are reached vary with the seasons : during the north declination of the sun the averages for eastern and western elongations, respectively, are about 7.30 A.M. and 1.15 P.M. ; for the remainder of the year, about 8.45 A.M. and 1.45 P.M. The average daily direction or mean magnetic meridian is reached in summer about 10.15 A.M., and in winter about 10.45 A.M., at Philadelphia, and generally within half an hour of these times at other places. The angular range between these limits is not constant, but, as may be seen by the table subjoined, it is considerably greater in summer than in winter, amounting at Philadelphia to 10' 30" in August, and only 6' in November, or a yearly average of 8'. while at Key West, Florida, the average for the year is about 5' 30" ; in higher magnetic latitudes the average being more than in the lower. It is least in years of minimum sun spots (as in 1878, for instance), and greatest in years of maximum sun spots (as in 1870), the ratio being about as 7 to 13 of the average amount of these years respectively. The daily vari- ation is at times interrupted, at others enfeebled, and frequently in the winter there are days on which it cannot be recognized. On account of the daily movement of the needle, its variable range during the year, and disturbances from atmospheric phe- nomena, it is well, when taking the bearing of any important line, to record the date, time of day, and condition of the atmosphere, using the subjoined table as far as practicable. VARIATION OF THE COMPASS. 201 240. For reducing the direction of the needle observed at other hours to the mean magnetic meridian, the following table (taken from instructions to United States Deputy Surveyors), is furnished. It gives to the nearest minute the variations of the needle from its average position during the day, for each hour in the day, for the four seasons of the year. TABLE FOR REDUCING THE OBSERVED DECLINATION TO THE MEAN DECLINATION OF THE DAY. Hour 6 7 8 9 10 11 12 1 2 3 4 5 6 Spring 3' 4' fj 3' 1' V 4' & 5' 4' 3' 2' 1' Summer 4' 5' 5' 4' 1' 2' 4' & 5' 4' y 2' V Autumn 2' 3' 3' 2' 0' 2' 3' 4' 3' 2' i' I' 0' \Vinter 1' If 2' 2' 1' 0' 2' 3' 3' 2' i' 1' 0' 241. The Secular Variation. Observations extending through many years, at various places, indicate a continual change taking place in the declination of the needle ; that these changes are not continuous in direction nor uniform in intensity ; that in this country the movement which, at the end of the last century, was eastward is now westward at all places east of the Rocky Moun- tains, and that a period of 250 or 300 years may elapse before the needle will again resume the position it now occupies.* 242. The Line of no Declination,t or Agonic Line, is the locus of all points on the earth where the direction of the needle is * The explanation of the secular change must ultimately be referred to forces of a periodic character, acting for centuries with great regularity. So far no approach has yet been made towards the discovery of the cause of the motion. . . . The study of the variation of the declination so. far would seem to indicate a secular change cycle for stations in the United States, extending over, or varying between, the limits of about 220 or 360 years. The data, however, are very uncertain. (U. S. C. & G. S., 1879.) t Sometimes called the Line of no Variation. 202 PLANE SURVEYING. coincident with the geographic meridian. At all places on the American continent situated to the east of this line the declina- tion is west, and at all places to the west of it, the declination is east. The line of no declination has been moving westward during the present century. From a chart published by Professor Loomis, in the American Journal of Science, 1840, it appears that the lines of equal declination, or isogonic lines, crossed the United States in a N.N.W. direction j the deflection towards the west being greatest in Maine. The line of no declination at that time entered North Carolina about midway between Newbern and Wilmington, passed through the middle of Vir- ginia, and into Lake Erie at a point nearly equidistant from Erie, Pa., and Cleveland, Ohio. In 1885 the Agonic Line entered the United States a little to the east of Beach Inlet, S.C., thence through Greensboro, N.C., Christiansburg, Va., Point Pleasant, W.Va., St. Clairsville, Ohio, a short distance west of Detroit, and a few miles east of Fort Mackinac, Mich. In the year 1700 the declination at Philadelphia, Pa., was 8| west. During the next century it diminished, reaching a mini- mum in 1800 of IV west, since which time it has been increas- ing, and is now, January, 1887, at the Philadelphia State House, lat. 39 56' 54", long. 75 09', 6 50', with an annual increase of 5'. 243. Mr. Charles A. Schott, chief of the computing division of the U. S. C. & G. S., tabulated the declinations observed at various stations, and deduced from them formulas by which the magnetic declination at various places may be com puted.* The places are arranged geographically as far as practicable, and are given by latitude and longitude (west of Greenwich). The epoch to which the formulas refer is 1850, or ra = t 1850. * U. S. C. & G. S., 1882. App. 12. VARIATION OF THE COMPASS. 203 FORMULAS EXPRESSING THE MAGNETIC DECLINATION AT VARIOUS PLACES IN THE UNITED STATES, AND FOR ANY TIME WITHIN THE LIMITS OF OBSERVATION. NAME OF STATION AND LOCATION. LATI- TUDK. LONGI- TUDE. EXPRESSION FOR MAGNETIC DECLINATION. Portland Me .... 43 38.8' 70 16.6' D +10?72 + 2?68 Bin(1.33m + 24.1) Burlington, Vt 44 28.2' 43 36.5' 73 12.3' 72 55.5' Z>= +10.81 + 3.65 sin (1.30 m- 20.5) + 0.18 sin (7.0m + 132) D +10 03 + 3 82 sin(l am 243) Portsmouth, N.H. . . . Newburyport, Mass. . . 43 04.8' 42 48.4' 42 31. 9' 70 43.0' 70 49.0' 70 52.5' D= +10.63 + 3.17 sin(1.44m-4.7) D= +10.07 + 3.10 sin(1.4m + 1.9) D-+ 9.80 + 3.61 sin (1.50m 1.0) Boston, Mass '. Cambridge, Mass. . . . Nantucket, Mass. . . . Providence, R.I Hartford, Conn New Haven, Conn. . . . \lbany N Y 42 21.5' 42 22.9' 41 17.0' 41 49.5' 41 45.9' 41 18.5' 42 39.2' 71 03.8' 71 07.7' 70 06.0' 71 24.1' 72 40.4' 72 55.7' 73 45 8' D= + 9.52 + 2.93 sin(1.30 m + 5.0) D=+ 9.58 + 2.69 sin (1.3m + 7.0) + 0.18 ein (3.2 m + 44) D=+ 9.29 + 2.78 sin(1.35m + 5.5) D=+ 9.10 + 2.99 sin (1.45m -3.4) + 0.19 sin (7.2m + 116) D=+ 8.06 + 2.90 sin(1.25m 26.4) Z>=+ 7.78 + 3.11 sin(1.40i 22.1) D-+ 8.17 + 3.02 sin (1. 44 m 8.3) Oxford, N.Y Buffalo, N.Y Toronto, Can Erie Pa 42 26.5* 42 52.8' 43 39.4' 42 07.8' 75 40.5' 78 53.5' 79 23.4' 80 05.4' D = + 6.19 + 3.24sin(1.35m-18.9) D=+ 3.66 + 3.47 sin(1.4m 27.8) J)=+ 3. 60 + 2.82 sin (1.4m -44.7) + 0.09 sin (9.3m + 136) + 0.08 sin(19m + 247) D-+ 2.26 + 2 71 sin (1.55m 297) Marietta, Ohio .... Cleveland, Ohio .... Detroit, Mich Sault de St. Marie, Mich. Cincinnati, Ohio .... St. Louis, Mo New York, N.Y. . . . Hatborough, Pa Philadelphia, Pa. . . . Harrisburg, Pa 39 25.0' 41 30.3 ' 4220.0' 46 29.9' 39 08.6' 38 38.0' 40 42.7' 40 12.0' 39 56.9' 40 15.9' 39 17.8' 81 28.0' 81 42.0' 83 03.0' 84 20.1' 84 25.3' 90 12.2* 74 00.4' 75 07.0' 75 09.0' 76 52.9' 76 37.0' D=+ 0.02 + 2.89 sin(1.4m 40.5) D=+ 0.10 + 2.07 sin (1.40m 6.2) Z> = 0.97 + 2.21 sin (1.50m 15.3) D=+ 1.54 + 2.70 sin (1.45m -58.5) D = - 2.40 + 2.62 sin (1.42 m - 39.8) D = - 7.15 + 2.33 sin (1.4m -20.1) D=+ 6.40 + 2.29 sin (1.6m -5.5) + 0.14 ain (6.3m +6.4) D=+ 5.23 + 3.28 sin(1.54m-13.2) + 0.22 sin (4.1m + 157) Z> = + 5.38+ 3.29 sin(1.55m-23.9) + 0.39 sin(4.0nt + 161) D = + 2.93 + 2.98 sin (1.50 m + 0.2) D-+ 3.20 + 2.57 sin(1.45m 21.2) Washington, D.C. . . . Cape Henry, Va. . . . Charleston, S.C Sa'-annah, Ga Key West, Fla + 38 53.3' + 36 55.5' 32 46.6' 32 04.9' 24 33 5' + 77 00.6' + 76 00.5' 79 55.8' 81 05.5' 81 48.5' D=+ 2.47 + 2.52 sin (1.40m -14.6) D=+ 2.54 + 2.41 sin (1.50m -35.4) D=- 2.14 + 2.74 sin (1.35m -1.3) 7> = 2.54 + 2.32 sin (1.5m 28.6) D 3.90 + 2.93 sin(1.4m 33.5) 23 09.3' 82 21 .5' D 4.52 + 2.00 sin(1.3m- 26.7) 204 PLANE SURVEYING. FORMULAS EXPRESSING THE MAGNETIC DECLINATION. Continued: NAME OF STATION AND LOCATION. LATI- TUDE. LONGI- TUDE. EXPRESSION FOB MAGNETIC DECLINATION. Kingston, Jamaica . . . 17 55.9' 76 50.6' D = 4?64 + 2?04sin(1.2m + 15.9) Panama, New Granada . 8 57.1' 79 32.2' D=- 6.80 + 1.82 sin(0.9 m + 10.4) Florence, Ala 34 47.2' 87 41.5' D = - 4.25 + 2.33 sin (1.3 m - 52.8) Mobile Ala 30 41.4' 88 02.5' D= 4.40 + 2.69 sin (1.45 T/i 76.4) New Orleans, La. . . . 29 57. 2' 90 03.9' D = 5.61 + 2.57 sin(1.4 61.9) Vera Cruz, Mexico . . . 19 11.9' 96 08.8' />=- 4.38 + 5.04 sin (1.10 TO -65.0) Mexico, Mexico .... 19 25.9' 99 06.0' D= 4.34 + 4.44 sin(1.0w 79.2) Acapulco, Mexico . . . 16 50.5' 99 52.3' D=- 4.13 + 4.82 sin(1.0j 81.1) San Bias, Mexico . . . 21 32.6' 105 15.7' D=- 6.51 + 2. 74 sin (0.9 - 106.3) Magdalena Bay, L. Cal. . 24 38.4' 112 08.9' /)= - 7.52 + 3.27 sin (1.25 m -140.6) San Diego Cal 32 42.1' 117 14.3' 2> = 12.52 + 1.60 ein(l 2wi 179.8) Monterey, Cal 36 36.1' 121 53.6' D = 12.90 + 3.28 sin(1.0 m 142.6) San Francisco, Cal. . . . 37 47. 5' 122 27.2' D= -13.34 + 3.23 sin(1.00 m 130.3) Cape Disappointm't, W.T. 46 16. 7' 124 02.0' D = 20.26 + 2.36 sin (1.25 m 180.0) Sitka, Alaska 57 02.9 ' 135 19.7' D = -26.77 + 2.33 sin (1.4 m - 111.6) Unalashka, Alaska . . . 53 52.6' 166 31. 5' D = -18.34 + 1.45 sin(1.4 m - 67.8) Tyrone Pa 40 40.0' 78 15.5' Z)=+ 3.46 + 0.0550( 1875.5) Pittsburg Pa 40 27.6' 80 00.8' 7) + 2.36 + 00566( 1878.7) Chicago, 111 41 50.0' 87 36.7' Z> = - 6.03 + 0.0281 (t 1850) + 0.00082(<-1850)* Grand Haven, Mich. . . 43 05.2' 86 12.6' D = - 4.95 + 0.0380(< 1850) + 0.00120(<- 1850)2 Madison, Wis 43 04.6' 89 24.2' Z>=- 6.43 + 0.0655(^-1880.3) Duluth, Minn.; and Supe- 46 45.5' 92 04.5' D = -10.17 + 0.0868(* - 1875.8) rior City, Wis. . . . Rio Janeiro, Brazil . -22 54.8' 43 09.5' Z>=+ 0.282 + 0.1395(< 1850) + 0.00545 (<- 1850) 2 San Antonio, Tex. . . . + 29 25.4' 98 29.3' D= 10.14 + 0.0204(< 1850) + .000024(<- 1850)2 Omaha, Neb. ; and Council 41 15.7' 95 56.5' D= -11.66 + 0.0439(*-1850) Bluffs, Iowa Denver Col 39 45.3' 104 59 5 ' 2) 14.79 4- 0.0258( 1872 9) Salt Lake City, Utah. . . 40 46.1' 111 53.8' D = -15.51 - 0.0930(* 1850) + 0.00180(<-1850) 2 To illustrate the use of the table : Suppose it is desired to ascertain the declination of the needle at Harrisburg for the last of September, 1877, or t= 1877.75. Take from the table the expression for the declination at Harrisburg ; that is : D= +2.93 + 2.98 sin (1.50m + 0.2). VARIATION OF THE COMPASS. 205 Find m= 1877.75 -1850 = 27. 75; 1.50ra + 0.2 = 41.625 + 0.2 = 41.825, and 2.98 x natural sin 41.825 = 2.98 x .66686 = 1.987. .-. D = 2.93 + 1.987 = 4.917 = 4 55' west (the result being plus). The observed declination for the same time was 4 53' 5". The difference between the computed and observed declination is seen to be very small. In running old lines it may be necessary to determine the declination at a time anterior to 1850 ; then m will be negative. Suppose the declination at Washington, B.C., for the year 1841 is desired. The tabular expression is : D = 2.47 + 2.52 sin (1.4m - 14.6), m 1841 -1850 = -9, (1. 4m -14. 6) = -27.2, 2.52 sin (-27.2) ==-1.15. .. D = 2.47 1.15 = 1.32 west (the resulting sign beingpfots), which agrees practically with the observed declination. 244. The following table is taken from U. S. C. & G. S. Re- port, 1882, App. 12, Mr. Schott's paper on Secular Variation. It exhibits the computed epoch of greatest easterly deflection reached in the secular motion ; i.e., the date when last reached, or the date (in parenthesis) when it is next expected to be in that position ; the amount in degrees and fractions, and direction (+ west, east) at this, the nearest stationary epoch ; and the computed annual changes in tlie declination of the magnetic needle for the years 1870, 1880, and 1885, a plus sign indicating north end of needle moving westward, a minus sign indicating north end of needle moving eastward. 206 PLANE SURVEYING. LOCATION. NEAREST STATIONARY EPOCH OF EASTERLY DIGRESSION. AMOUNT AT EASTERLY DIGRESSION. ANNUAL CHANGE. IN 1870. IN 1880. IN 1885. Paris France 1581 10.6 7.0' 6.1' 9.5' Halifax, Nova Scotia . 1728 + 12.4 + 1.8' + 1.0' + 0.5' Quebec, Canada .... 1809 + 12.1 + 4.2' + 1.6' + 0.5' Montreal, Canada . . . 1816 + 7.6 + 5.1' + 3.1' + 2.8' Eastport, Me. 1760 + 12.5 + 3.3' + 2.7' + 2.3' Portland, Me 1764 + 8.0 + 2.4' + 1.6' + 1.2' Burlington, Vt 1810 + 7.2 + 5.0' + 6.0' + 5.8' Rutland, Vt 1806 + 6.2 + 6.0' + 5.6' + 5.3' Portsmouth, N.H. . . . 1791 + 7.5 + 4.4' + 3.7' + 3.3' Newburyport, Mass. . . 1784 + 7.0 + 3.9' + 3.3' + 2.9' Salem Mass 1791 + 6.2 + 5.0' + 4.1' + 3.5' Boston, Mass 1777 + 6.6 + 3.4' + 2.9' + 2.5' Cambridge, Mass. . . . 1783 + 6.9 + 2.9' + 2.1' + 1.8' Nantucket, Mass. . . . 1779 + 6.5 + 3.3' + 2.7' + 2.4' Providence, R.I 1780 + 6.1 + 3.8' Hartford, Conn 1799 + 5.2 + 3.8' + 3.7' + 3.6' New Haven, Conn. . . . 1802 + 4.7 + 4.6' + 4.3' + 4.1' Albany, N.Y 1793 + 5.2 + 4.3' + 3.7' + 3.4' Oxford, N.Y 1797 + 3.0 + 4.5' + 4.3' + 4.0' Buffalo, N.Y 1806 + 0.2 + 5.1' + 5.0' + 4.8' Toronto, Canada .... + 4.8' + 4.5' + 2.3' Erie, Pa 1811 - 0.5 + 4.4' + 4.2' + 4.0' Marietta, O 1815 - 2.9 + 4.2' + 4.2' + 4.2' Cleveland, O . 1790 2.0 + 2.8' + 2.5' + 2.2' Detroit, Mich 1800 - 3.2 + 3.4' + 3.0' + 2.8> Sault de St. Marie, Mich. 1828 - 1.2 + 3.6' + 4.0' + 4.1' Cincinnati, . . 1815 5.0 + 3.8' + 3.9' + 3.8' St. Louis, Mo 1800 - 9.5 + 3.4' + 3.2' + 3.0' New York, N.Y 1797 + 4.0 + 2.4' + 2.5' + 2.6' Hatborough, Pa 1797 + 1.8 + 4.6' + 4.5' Philadelphia, Pa 1800 + 1.9 + 4.9' + 4.9' + 5.3' Baltimore, Md 1802 + 0.6 + 3.9' + 3.6' + 3.2' Harrisburg, Pa. .... 1700 0.0 + 4.1' + 3.3' + 2.8' Washington, DC. . . . 1796 0.0 + 3.5' + 3.2' + 3.0' VARIATION OF THE COMPASS. 207 LOCATION. NEAREST STATIONARY EPOCH OF EASTERLY DIGKESSION. AMOUNT AT EASTERLY DIGRESSION. ANNUAL CHANGE. IN 1870. IN 1880. IN 1885. Cape Henry, Va Charleston, S.C 1814 1784 1809 1810 1801 1762 1739 1821 1841 1830 1827 1839 1841 1868 (1890) (1925) (1903) (1890) (1922) 1865 1834 + 0.1 - 4.9 - 4.9 - 6.8 - 6.5 - 6.7 - 8.6 - 6.6 - 7.1 - 8.2 - 9.4 - 8.8 - 9.0 - 9.3 10.8 -14.1 -16.2 - 16.6 -22.6 -29.1 -19.8 + 3.8' + 3.5' + 3.6' + 4.3' + 2.7' + 2.0' + 1.5' + 2.8' + 2.8' + 3.1' + 4.2' + 2.4' + 2.4' + 0.1' -1.8' -1.8' -1.8' -1.0' -2.8' + 0.4' + 1.6' + 3.7' + 3.0' + 3.5' + 4.2' + 2.7' + 1.6' + 1.4' + 3.1' + 3.4' + 3.6' + 4.9' + 3.0' + 3.2' + 0.5' -1.0' -1.6' -1.3' -0.5' -2.5' + 1.2' + 1.9' + 3.3' + 3.4' + 4.6' + 6.6' + 3.9' + 5.2' +10.3' + 2.1' + 2.6' + 1.6' + 0.9' + 3.6' + 2.7' + 3.3' + 4.1' + 2.6' + 1.4' + 1.3' + 3.2' + 3.7' + 3.7' + 5.2' + 3.3' + 3.6' + 0.7' -0.5' -1.5' -1.0' -0.3' 2.2' + 1.6' + 2.0' + 5.1' + 7.3' ' +10.7 + 2.2' + 2.0' Key West, Fla Havana, Cuba Kingston, Jamaica . . . Panama, New Granada Mobile Ala . . . New Orleans, La Vera Cruz, Mexico . . Mexico, Mexico .... Acapulco, Mexico . . . San Bias, Mexico . . . Magdalena Bay, L.Cal. San Diego, Cal San Francisco, Cal. . . C. Disappointm't, W.T. Sitka Alaska Unalashka, Alaska . . . Chicago 111 1833 1834 - 6.3 - 5.3 .... Grand Haven, Mich. . . Madison Wis Duluth, Wis ) Superior City, Wis. . > Rio Janeiro, Brazil . . San Antonio, Tex. . . . Omaha, Neb ) Council Bluffs, la. . . ) Denver Col . . 1876 -16.7 .... Salt Lake City, Utah . 208 PLANE SURVEYING. The variability of the change will be noticed. For example, take New York, Philadelphia, and Harrisburg, places compara- tively near together. At New York the change in 1870 was only one-half that at Philadelphia ; but, both increasing, this ratio was maintained throughout the 15 years. At Harrisburg, on the contrary, the annual change in 1870 was nearly six-sevenths that at Phila- delphia, but the change constantly increasing at the latter place while diminishing rapidly at the former, the annual variation at Harrisburg in 1885 was only a little more than one-half that at Philadelphia.* 245. Effects of the Secular Change. It is evident that if a surveyor should ignore this change, in attempting to establish the corners and to trace the boundary lines of a farm from their description in an old deed, it would be possible for him to return to his place of beginning, but probably none of his other corners would coincide with the true corners. A line in the vicinity of Philadelphia, which 12 years ago had a bearing N. 19 E., would now bear N. 20 E., and in the same locality a bearing which at that time was recorded N. 19 W. would now be N. 18 W. A variation which, if not cor- rected, would indicate the end of a line 15 chains long over 26 links from its true position. Take, for example, the notes given in Article 208, page 161, and suppose an interval has elapsed sufficient to make the vari- ation two degrees. The accompanying figure shows the true lines and corners ; also those corresponding to a survey made without taking the variation into account. The bearings and distances are as follows : (1) S. 20 53' E. 13,11 chains; (2) N. 48 10' E. 13.62 " (3) N. 43 40' W. 4.73 " * For extended investigations on magnetic declination, see U. S. C. & G. S. Reports, 1879, 1881, and 1882. VARIATION OF THE COMPASS. (4) N. 45 08' W. 4.75 chains ; (5) S. 51 30' W. 2.53 " (6) S. 72 30' W. 6.56 " ss To allow for a variation of two degrees, we should have the following bearings : (1) S. 18 53' E. ; (2) N. 50 10' E. ; (3) N. 41 40' W. ; (4) N. 43 08' W. ; (5) S. 53 30' W. ; (6) S. 74 30' W. 246. To deduce a general rule for obtaining the magnetic bearings of old lines when the variation is known. 210 PLANE SURVEYING. Let JV$ represent the direction of the magnetic meridian in the vicinity of a survey made several years ago ; N'S', its direction several years later, at the time of re-survey, aud that the north end of the needle points 2 farther west. It is evident that at the time of the re-survey, the line NS will bear N. 2 E., and OP, which accord- ing to the old survey bears N. 48 E., will have its bearing in- creased 2 or N. 50 E. ; but the line OM, the bearing of which was N. 42 W., will now bear N. 40 W. A line recorded as east will be traced by a course S. 88 E., and soon. Hence the rule : Increase by the change the bearings which are northeasterly or southwesterly, aud diminish by the same amount the bearings which are northwesterly or southeasterly. The foregoing rule is directly applicable now in the United States, except on the Pacific coast, because the variation is west. That is, the north end of the needle is moving west, thereby increasing the readings of bearings in the N. E. and S. W. quar- ters, and diminishing the readings of those in the N. W. and S. E. quarters. When it becomes east, the words "increase" and "diminish" should be interchanged to make it correct. If a vernier compass is used, the variation may be set off and the lines traced by the old bearings. 247. Change Determined by Old Lines. If the bearing and date of survey of a line are known, and its extremities visible from each other, setting the instrument on one end and sighting the other will give, by comparison with the recorded bearing, the variation. NOTE. Care must be taken by the surveyor, when called upon to run out old lines, the corners not being definitely marked, that the time of the former survey be known ; the date of the deed docs not indicate that of the survey. The description of the lines may have been copied, as they frequently are, from an older deed. VARIATION OF THE COMPASS. 211 The variation to be applied to correct magnetic bearings is frequently determined in this way. If the boundaries of a tract of land are to be traced, whether the date of the previous survey be known or not, the surveyor seeks to find, if possible, two consecutive marked corners ; then, taking the bearing of these and comparing with the record, he obtains the change sought. This change, properly applied to each side, should indicate its direction. It frequently, and in large tracts generally, happens that though the corners at the end of a line may be established, they cannot be observed from each other. In such case run a line as nearly as possible from one corner towards the other by the bearing given in the deed, or make first an allowance which may seem proper from the data at hand ; measure from the end of the line thus run the distance to the true corner, and by the 57.3, rule, Article 177 ; or, by the tangent method, same article, find the angle to be added or subtracted, as the case may require, to correct the bearing with which to run the line. The difference between the bearing given in the deed and the corrected bearing will be the change in the declination since the survey recorded in the deed. EXAMPLES. 1. A line, said to have been surveyed in 1860, recorded N. 18 30' E., 24.40 chains, was run in 1885 with a bearing N. 19 45' E., the variation being about 3' to the west per year in its locality, and the corner was 7 links to the right (farther easterly) of the end of the line run. The corrected magnetic bearing and variation are required. 1 15' + 57 ;^ X 7 = 1 15' + 10' = 1 25' = variation. Adding the variation to the bearing of the line run, since the true corner was farther to the east, there results N. 19 55' E. as the corrected magnetic bearing of the line. 212 PLANE SURVEYING. 2. If in Example 1 the corner had been found 7 links to the left, what would be the correct bearing of the line? 3. A line which in 1862 ran S. 34 15' W. 18.56 chains, in 1886 bore S. 35 35' W. What was the average change in the declination per year? 4. Give the corrected magnetic bearing for 1886 of a line in the same locality as that in Example 3, which in 1868 ran due east. 5. In 1876 a line had a bearing S. 89 45' W. 16.80 chains ; in 1886, running by the same bearing, the true corner was 20 links to the north. Give the average annual change, and cor- rect the bearing. 6. If a line 60.00 chains in length were surveyed in the early part of the day, where the needle deviates 5 minutes east of the mean magnetic meridian, and the same line surveyed soon after mid-dav, the needle then pointing 5 minutes west of the mean magnetic meridian, how far apart would the lines be at their ends, and what the area included between them? 248. To Obtain the True Bearing of a Line, that is, the bearing with respect to the geographical meridian, when the W declination is west. Assume NS and N'S' (left-hand figure) to represent respectively the true and magnetic meridian. Then it is evident that the bearing of any line between the north and VARIATION OF THE COMPASS. 213 east, or south and west, as OP or OP', will be less referred to NS than when referred to X'S' by the amount of the angle NON' = SOS' = the declination. A line running between north and west, as OM, or south and east, as OM', will evidently have its bearing increased by the amount of the change. The reverse is true where the declination is east, as may be perceived by reference to the right-hand figure. Hence, to get the true bearing from the magnetic for all places east of the line of no declination, i.e. where the declina- tion is tcest, subtract the declination from a bearing which is northeasterly or southwesterly, and add the declination to a bearing which is northwesterly or southeasterly. Where the declination is east, as at all places west of the line of no declination, add the declination to a bearing which is north- easterly or southwesterly, and subtract the declination from a bearing which is northwesterly or southeasterly. Where the declination is west, a bearing that reads north, when reduced to the true bearing, will evidently be west of north the amount of the declination ; if the declination is 3, the bearing will be N. 3 W., and supposing the same declination, a line running due east magnetically will be truly N. 87 E. The reverse of the last paragraph is true where the declina- tion is east. KKMARK. If, when applying the rule, a negative result is obtained, oare must be exercised in the interpretation of it. For example, if the declina- tion is 3 West, and the needle indicates the bearing of a line N. 1 E., there results, by the rule, 2. This shows simply that the true bearing is to the west of north, or N. 2 W. If the bearing is S. 89 E., adding the declination, as the rule requires, gives evidently the reading N. 88 E. Reduce to their true bearings the following, the declination being 2 55' W. : N. 2 15' E., East, S. 45 E., South ; S. 87 30' W., N. 88 15' W., North. Also the following, the declination being 3 40' E. : N. 88 E., East, S. 2 E., South ; S. 88 30' W., N. 40 W., North. 214 PLANE SURVEYING. 249. To Ascertain the Declination.* If a geographical merid- ian were traced on the earth convenient to the operations of the surveyor, he would have the means always at hand by which to determine the declination. He could simply set up his in- strument at a point on the meridian, take the bearing of another point in it, and the reading would be the declination. So the problem resolves itself into the determination of a geographic or true meridian. 250. By Polaris. If there was a celestial object precisely at the point where the prolongation of the earth's axis pierces the celestial sphere, the direction of the meridian could be ob- tained by simply sighting to the object. This, however, is not the case, but Polaris, or Alpha Ursae Minoris, is a star whose polar distance is, January, 1887, 1 17' 38", f and which appar- ently revolves about the north pole in 23 hours 56 minutes. It therefore culminates twice daily, and twice it attains its greatest distance directly east and west of the pole, called respectively its eastern and western elongation. If, therefore, the Pole Star could be observed at the instant of its culmination, the line of sight would be in the meridian plane ; but since in general the local time of transit is not precisely known, and since the star is then moving at right angles to the plane of the meridian respecting which its motion is at that time a maximum, and consequently a small difference in time would introduce a con- siderable error in arc, this method is not as reliable as that by means of Polaris at its eastern or western elongation, as then the star for a few minutes appears to move in the direction of the vertical wire, or compass-slit, thus affording a favorable * For other methods, see Chapter II. Section I,, Solar Attachment; and Chapter VI., Art. Solar Compass. t Its polar distance is diminishing at the rate of 20" (19.06") per year. This diminution will continue until the star is within half a degree of the pole, when it will recede. In 1890 its polar distance will be 1 16' 42". In 1900 its polar distance will be 1 13' 33". In 1910 its polar distance will be 1 10' 26". VARIATION OF THE COMPASS. 215 opportunity for observing it, and the precise time of observation need not be known. Conceive a spherical triangle, the vertices of which are, Z, the zenith of the observer ; P, the north pole ; and S, Polaris. This triangle, when the star is at an elongation, will be right-angled at the star. In this right-angled spherical triangle are known the co-latitude of the observer's station, and the co- declination or polar distance of the star, to find the azimuth * and hour angle. | Using natural functions, the formula for the hour angle is cos P = tan PS cot PZ, and for the azimuth, 5inZ= s[nPS = &[nP and 273. Given the area and one of the diameters, to find the other diameter. Denote the given diameter by (Z, the unknown by x, and the area as before ; then, since we have An ellipse of small size may be laid out as follows : Measure AB equal to the greater diameter (transverse axis)_, and from the centre lay off OF= OF', each equal to the square root of the difference of the squares of the semi- diameters OA, OC. Fix the ends of a steel wire or ribbon of the length AB at F and F 1 ', and with a continuous motion of a marking-pin P, held perpendicularly, keeping the wire taut, the required curve will be traced. * See any work on General Geometry or Conic Sections for the area of an ellipse. LAYING OUT AND DIVIDING LAND. 231 Or, having found the axis as above, P being any point in the curve, and PR perpendicular to AE at R, by setting off any number of points on AB, we may find from the proportion TR 2 : RB x AU = OC* : Od 2 , the corresponding values of PR. EXAMPLES. 1. Find the radius of a circle containing 1 acre. 2. Find the radius of a sector containing 20 square rods, the angle at the centre being 72. 3. The area of an ellipse is 1 acre, its diameters in the ratio of 3 : 2 ; find their length. 4. An ellipse contains 80 square rods, its greater diam- eter 12 rods ; find the lesser diameter. 5. The greater diameter of an elliptical plot of ground en- closed by a wall 1 foot thick is 240 links, and the lesser 160 links, inside measurements. What is the area of the plot, and how much land is occupied by the wall ? 274. Let it be required to lay out a circle circumscribing a triangle, the sides of which are m, ?i, and p. Let be the centre of the circle, R the radius, OL a perpendicular to MN, p = MN, and the other sides as in- dicated in the figure. Now NL = |, and angle NOL = P. .-. = 12 sin P, P R = suTP = 2 sin P To find an expression for R in terms of the three sides, sub stitute for sin P its value 232 PLANE SURVEYING. 2 sin *P whence fl = s - m) (is - ) (|s -p) in which s represents the sum of the sides of the triangle. ADDITIONAL EXAMPLES. 1. Circumscribe a circle about a triangle the sides of which are 10, 15, and 20 chains. 2. Find an expression for the radius with which to inscribe a circle in a triangle the sides of which are m, w, and^>. Ans. Twice the area of the triangle, divided by the sum of the sides. 3. Describe a circle in a triangle the sides of which are 30, 40, and 50 rods. 5. A circular walk, 6 feet wide, is to be made inside of a square which contains \ an acre ; required the area of the walk. 5. The area of a square is 1 acre, and a circular walk is required to be made in it, touching each side at a point, of such a width that it will take up \ the area of the square. Find the width of the walk and the length of its centre line. 6. The area of a circular sector of d is m rods ; find an expression for the radius. If d = 60 and m = 300, find R. SECTION II. DIVIDING LAND. A. TRIANGLES. 275. To divide a given triangle into two parts in the ratio of m : n by a line parallel to one side. LAYING OUT AND DIVIDING LAND. 233 To solve the problem fully, and furnish a check on the work, requires the location of the point or 72, and the length of OR. Denote OR by x, OP by ?/, and by p and 7c the sides respec- tively opposite the angles P and K; then p 2 : x 2 = ra + n : ra, Again, ft 2 : y 2 = m + n : whence If the triangle is to be equally divided, then m = n, and there results x _p and _k r QUERIES. Is it necessary that LK be known to find either PO or PR? Must LKbe given to find OR? EXAMPLES. 1 . Find a general expression for the distance RK (last figure) . 2. Show how to divide the triangle LKP into four equiva- lent parts by lines parallel to the base. 276. To divide a given triangle into two parts in the ratio of m: n by a line from a vertex to the opposite side. Let PO be the line, x = LO, and p as above. Then, since tri- angles having the same altitude are to each P other as their bases, we have p : x = m + n : n ; whence x = pn m + n EXAMPLES. 1. Locate on the supposition that the triangle is to be divided into two equivalent parts. 234 PLANE SURVEYING. 2. Find where the lines from P will meet the base dividing the triangle into three equivalent parts. 3. The same for any number n parts. 277. To divide a given triangle into two parts in the ratio of m : n by a line through a given point in one of the sides. Denoting PL by x, and the other sides in the usual manner, we have m + n : m = Jco : px ; - , triko p- ----- _L whence x = - p(m + n) If the parts are to be equivalent, m = ?i, and there results EXAMPLE. Show how the given triangle LKO may be divided into three equivalent parts by lines radiating from a given point R. NOTE. The lines may or may not fall on the same side. Examine both cases. 278. The same conditions as in the last case, except the tri- angle is to be isosceles. Using the same notation and figure as in that case, we have the following equality of ratios : m + n : m = ko : x 2 ; whence x = J*) . 2 (m + n) The student will give the reason. EXAMPLES. 1. Divide a given trapezoid into three equivalent parts by lines intersecting the parallel sides. 2. Divide a given trapezoid into three parts in the ratio of m : n :p, by lines intersecting the parallel sides. LAYING OUT AND DIVIDING LAND. 245 3. The bases of a trapezoid are, OP =20 chains, and QR = 15 chains. It is required to divide it into two parts in the ratio of 2 : 3. OL' = 8.50 chains ; locate D'. 4. Show that /, being the centre of the line connecting the middle of the bases of a trapezoid, is the point through which, if any straight line be drawn meeting the parallel sides, it will divide the trapezoid into two equivalent parts. 285. Given one side and the adjacent angles of a tract of land, to cut off a trapezoid of a gicen area by a line parallel to the given side. Let PO be the given base, P and the known angles indi- cating the direction of the p sides PQ and OR. Denote the area OPLD, to be cut off by A ; the given side ..---" OP by s, PD by y, OL by F "" : ce, DL by z, and suppose (0-f-P)<180. Produce OR and PQ until they meet in F. Then area OPV - area LDV = A ; s 2 sin sin P z 2 sin sin P 2 whence z = \ ( 's 2 -- M sin sin P When (0 + P) > 180, the produced lines meet in a point on the other side of OP, the sin (0 + P) is also negative, and therefore the fraction under the radical becomes positive. Draw LT parallel to VP; then in the triangle LOT, by sine pro- portion, sin L (= sin F) : sin T ( = sin P) = s z : x ; whence X=S sinF c,. ., _, (s z) sin Similarly, y = i -- 246 PLANE SURVEYING. REMARK. When great accuracy is not required, and espe- cially if the tract is small and the sides nearly parallel, an approximate perpendicular distance between the bases OP and DL may be obtained by dividing the area to be cut off by the given side OP; then measure the perpendicular and a line through its extremity parallel to the base for an approximate division line. Calculate the area thus cut off, divide the differ- ence between it and the required area by the approximate divis- ion line for a new perpendicular, and thence obtain more nearly the division line sought. EXAMPLES. 1. Deduce an expression for DL by another method. 2. Show by other methods how OL or PD may be determined. 3. Given OP, N. 16 30' W., 8.40 chains ; PQ, S. 62 15' W ; and OR, S. 82 W., to cut off a trapezoid containing 4 acres, by a line DL parallel to OP. The position and length of the division line are required. 4. Given a side of a tract of land 20 chains, and the adja- cent angles 105 and 130, to cut off 36 acres by a line parallel to the given side. Required the position and length of the division line. TRAPEZIUMS. 286. Given the area of a trapezium, one of its sides and adja- cent angles, to divide it by a line parallel to the given side into two parts having the ratio m : n. Produce the sides PQ and OR to meet in V. Let OP= s, OL = x, PD = y, DL= z. LAYING OUT AND DIVIDING LAND. 247 Calculate the area of ' 2 siuF then A'-A" j ,, , 2 2 sin sin P , A , A u\ and the formula - - = 2( A 1 A) sinF gives )2sinF(.i'-^. \ sin sin P Having found 3, x and y ma^y be deduced as in the foregoing case. (s z) sin P sinF (s-z)sin sinF REMARK. This problem may be solved by Article 285, taking for the given area to be cut off ' EXAMPLE. The boundaries of a trapezium are as follows : (1) N. 2 E. 8.00 chains; (2) N. 58 E. 13.85 " (3) S. 3H E. 14.80 k ' (4) S. 82^ W. 20.00 " It is required to divide it into two equivalent parts by a line parallel to the third side. Locate it, and determine its length. 287. Given the bearings of three adjacent sides of a tract of land and the length of the middle one. to cut off trapezium having a given Jtrat, by a line running in a given direction. 248 PLANE SURVEYING. Produce the sides PQ and OR till they meet at F. As before, denote OP by s, OL by ar, PZ) by ?/, and .LZ> by z. Ob- tain the angles from the bearings, calculate the area of PQY = A' = ** sin sin f \ 2 sin F and find area DL F= ^' - A. R L Whence the division line DL = z may be found from the formula 2 2 sinZ>siu Al -ZL "~~ *}.) 2siuF z = sin D sin Zr By the sine proportion sin F and FL = whence VO-VL=LO = x = n-sn sin F and _ ssin zsin L sin F REMARK. If (0 + P) > 180, ^ f -^4 in the equation for z will become A 1 -f- .4, and in the formulas for x and y the signs in the numerators will be interchanged, or z s * a -^ ~ sin F and y = zsin ^~' ss sin F LAYING OUT AND DIVIDING LAND. 249 EXAMPLE. Given LO, S. 76 E. ; OP, N. 8 W. 12.40 chains ; PD, S. 72 W. ; it is required to cut off 7 acres bv aline hearing N. 23 W. The length of the division line and the distances OL and DP are to be computed. 288. Given a trapezium, to divide it into two parts having a given ratio, by a line extending from a given point in one of the sides. Let OPQR represent the trapezium the area of which is A, m and n the given ratio. Prolong the sides PQ and OR till they meet in F. Let OR = v, the division line DL = z, RL the given distance to the point L= d, and QD = y. Calculate the area of QRV=A', and add it to - A, thereby obtaining areaofZ)F. p Find by the sine proportion VR, and add it to RL, thus obtaining VL. Putting VD = x, and VL = i>, .- V='2( - A+A\ Whence x = VD may be found. Finally, with the two sides VD and VL and the included angle V, compute the angle L, and the direction and length of the division line DL ; y may be calculated by a preceding method to check the work. EXAMPLES. 1. Given in a trapezium MNOP (no figure) : MN, 13.00 chains ; NO, 7.30 " OP, 10.40 " PM, 11.10 " and diagonal PN, 13.70 " It is required to divide it into two equivalent parts by a line running from a point in the side MN, 6 chains from M. Find 250 PLANE SURVEYING. the length of the division line and locate the other extremity of it. 2. Divide the tract described in Example 1 into two parts, in the ratio of 3 : 4, by a line DL running from some point in MN. and falling perpendicularly upon PO. The part PMDL is to be the greater. Locate the line required, and determine its length. 289. Given a trapezium, to divide it into two parts having a given ratio, by a line passing through a given point within the tract. Let OPQR represent the given trapezium T, the point within it, given by its bearing and dis- tance from some angle, as R. Produce the sides OR and PQ to meet in V. Denote the ratio by ra and n, the area OPQR by A, QR by v, DL by z, VL by , and VI) by y. Find by the sine pro- portion y R _ vsinQ V Q _ v sin R sin V" sin F' and thence the area VQR = A'. Then in the triangle VRT, having two sides and the included angle, compute FT, which call b, and the angle TVR = a. Putting F a = ft, and - A + A' = A", the following equations may be written : xysinV=2A", (1) and bx sin a + by sin ft= 2 A". (2) Substituting in (2) the value of y from (1), and reducing, there results, x = A " I A " 2 2 A" sin ft ^ b sin a. \ b~ sin 2 a sin a sin F *rtEL=x-VR=-^- J A " 2 _*A'*infl_vunQ b sin a \ b 2 sin 2 a sin a sin F sin F LAYING OUT AND DIVIDING LAND. 251 EXAMPLE. Given the boundaries of a trapezium as follows : (1) N. 16J W. 24. 63 chains; (2) S. 79 W. 27.00 " (3) S. iW. 34.28 (4) N. 65 E. 37.20 " To divide it into two equivalent parts by a line extending from the first to the third side, and passing through a point 20 chains distant from the first and second corners. Locate the line and find its length. 290. Given a trapezium, to divide it into two parts having a given ratio, by a line passing through a given point without the tract. P Let OQRT represent the trapezium given by the bearings and distances of its sides, P the point without, located by its bearing and distance from T, the ratio m : n. Extend the sides RT and QO until they meet in V. Then the problem may be solved in a similar manner to that in Article 281. 291. Given a trapezium, to divide it into four equivalent parts, by two lines intersecting opposite sides, one of the division lines being parallel to one of the given sides of the tract. Let ABCD represent the given trapezium, FE the division line parallel to DC, and GH the other division line. It is re- 252 PLANE SURVEYING. quired to locate both division lines. Prolong the sides AD and BCto meet in P; also DC and AB to Q. Find AE and EF by methods already given. Now, any line cutting the parallel sides of a trapezoid and dividing it into two equivalent parts must pass through a point (the middle of the middle line between the bases). See Article 284. Hence MO becomes known = 1 (CD + EF), and P Br- aise MC=\FC. In the triangle OMC, compute the angle MCO and the line 0(7; add Z MCO to Z MCQ, and having previously calculated QC, find in the triangle QCO the angle CQO and the side QO. Subtract Z CQO from Z CQB and obtain Z OQ-B. Then putting the side QO = a, QH=x, and Q(? = y, we may write the following equations : ay sin HQG = 2 area HQG, ax sin CQO + ay sin OQG = 2 area #Q#. From these equations obtain iy. Subtract it from AQ, found by sine proportion, and the distance from the corner A to the extremity of the division line GH at G will be the result. Then in the triangle QGH find QH', whence the length and bearing of GH may be computed. LAYING OUT AND DIVIDING LAND. 253 EXAMPLE. It is required to divide the farm described in 288 (Example 1 ) into four equivalent parts by two lines intersecting opposite sides ; one of the division lines is to be parallel to the first side. Locate the division lines, and determine their lengths. C. POLYGONS. 292. Given a polygon, to divide it into two parts having a given ratio, or to cut off a given area, by a line through a given point. Let OPQRTV 'represent the polygon given by its bear- ings and distances, or angles and sides, v and suppose the line be required to run from P, either an angle or any given point in a side. Calculate the area of the polygon , and take the m + n part of it as the area to be cut off to the right of the line extending from P. Q -B Run a trial line* from P as PT, calculate the area of PQET, and determine whether the area thus cut off is too small or too large, and how much. Suppose it is too small ; then the extrem- ity T of the division line PT must be moved towards V to some point T 1 . To find this point, denote TT 1 by x, the angle TTP by T, the distance PTby b, and the area of the triangle PTT by a ; then bx sin T = a, from which we find x = b sin T * The bearing and distance of PT may be calculated from the data given without a trial line as in supplying omissions. If, however, this is done, the surveyor should not omit to measure the division line to verify his work. In fact, it is the best practice, no matter what method is adopted to obtain the division line, to always test the computation by measurement. 254 PLANE SURVEYING. This distance measured from T to T will locate T', a point which connected with P will give the division line sought. 293. Given a polygon, to divide it into two parts in a given ratio, or to cut off a given area, by a line through a given point within the tract. Let the marginal figure represent the tract, Pthe given point. If the area to be cut off is not di- rectly given, calculate the contents of the tract, and then by the ratio deter- mine the quantity to be cut off, and denote it by A. Run a trial line TT through P, dividing the polygon as nearly as may be judged in the re- quired manner. Measure TP= b, PT' = c, and the angles T and T'. Calcu- late the area of either part of the polygon, and thus ascertain whether T should approach or recede from 0. Suppose the area TNMVT' is calculated and found too small by a quan- tity a, and that DL represents the division line. Put DP= x, PL = y, the angle PTD = T, PT'L = T', and the angle at the point P = P, which is required, since that will indicate the di- rection of the division line. Then cy sin P % bx sin P = a (1) =-^^W (2) (3) sin (T' + P) Substituting the values of x and y from (2) and (3) in (1), there results c 2 sin T' sin P b 2 sin T sin P in(7" + /') sin(T+P) = 2 a. (4) LAYING OUT AND DIVIDING LAND. 256 Expanding the denominators, dividing each fraction, numer- ator and denominator, by its numerator, and writing for t the cot, there results sin fS 7,2 . (5) cot P + cot T' cot P + cot T Putting cotP = ^>, cot!T=, and cot7" = ', we may write more simply : / c*-l>*\ tc* W (t + f - -^-) = ^ ~ tf ; whence - 2a Restoring values, we have cotP= -f cot T+cot T' 2a ) _ cot T cot r+ \ 2 a 4\ 2a The problem may be simplified when it is practicable to run the trial line at right angles to one of the sides of the polygon. In the tract given, suppose TT' to be run perpendicularly to R F; then cot T' = 0, and Equation (5) may be written * v cot P cot P + cot T & 4V 2o 256 PLANE SURVEYING. 294. Given a polygon, to cut off a given area by a line passing through a given point without the tract. Let the marginal figure represent the case. P h y M As in the preceding article, run a trial line PT' from P, and sup- pose it is made perpendicular to v RV. Calculate, as before, the con- tent of TNMVT', and ascertain the amount to be added to make the required area. Denote, as before, this area by a, PT=b, the angles at P, T, etc., by P, T, R PT' = c, PD = x, PL = y etc., and DL the division line ; then ^ cy sin P | bx sin P = a, 6 sin T (1) (*) Substituting the values of x and y from (2) and (3) in (1), and reducing as in the preceding problem, there results cot,P=- The student may verify the value found. 295. Given a polygon, to divide it into three parts having a given ratio, by lines radiating from a given point. a. Let the figure represent the polygon, and suppose the point is in one side at P. Calculate the area of the whole tract and ascertain how much each division is to contain ; then, by Article 292, cut off the required areas PVTSL and POQD, and the problem, is solved. LAYING OUT AND DIVIDING LAND. 257 6. If the point is within the tract,* cut off, by Article 293, one required portion DVTSKD by a line DK through P, and by the preceding article divide the remainder by the line PL as required. If PL cuts off a quadrilateral on either side, Article 288 may be used. c. If the point is without,* proceed, as in Article 294, to cut off the required portion KVTSDK and HOQLH; the remain- der HLRDKHvt\\\ be the third portion. It is evident that this principle may be extended to any number of parts. 296. To cut off from a given polygon a given area by a line running in a given direction. Let the figure represent a tract which it is required to divide into two equivalent parts by a line DL parallel to RS. Join QT, calculate its length and bearing, and also the content of QRST. Subtract said content from one-half the area of the whole tract, thereby obtaining the area DLTQ. Then, by Article 287, the length and position of the division line may be determined. It is evident that this principle may be extended to any number of subdivisions. * Calculate the area, and ascertain, by the ratio, how much eacb division is to contain. 258 PLANE SURVEYING. EXAMPLES. 1. The student may indicate how he would divide DQRSTL into two equivalent parts by a line perpendicular to DL. 2. Show how to divide DPONMVL into two equivalent pails by a line extending from the middle of DL. 3. Divide the farm described in Article 234, Example 4, into two equivalent parts by a line running due east. 297. From a tract of land of which one or more of the boun- dary lines is irregular, to cut off a given area. L n Q Let OPQRT represent the tract which it is required to divide into two equal pails by a line DL parallel to PQ. Survey the land, taking offsets along RO, and calculate the area. Then the problem may be solved by Article 285. 298. To Straighten Boundary Lines. It is sometimes re- quired to substitute a straight line for an irregular or crooked one between farms, and to leave the same quantitv of land as before in each tract. Let ORQ be the line which it is required to straighten by a line extend- ing from 0, the bearings and distances OR, RQ, and the bear- ing of QT being known. Run a trial line OP, noting the dis- tances RK, OK, KP, and PQ, and calculate the areas of the V triangle ROK and PQK. If it happens that the triangle ROK is equivalent to PQK, then OP will represent the line sought. If, as is generally the case, their areas are not equal, take the difference, and suppose in this case PQK the less. The problem, then, is simply this : Given one side, OP, of a triangle, and the direction of another, LAYING OFT AND DIVIDING LAND. 259 PT, to cut off a given area by a line OP*, to find the distance PP. The solution is given in Article 257. Otherwise, with the given bearings and distances calculate the area of the triangle ORQ and the length and bearing of the closing line OQ. Then, as before, having one side of a triangle, the direction of another, and the area, find QP 1 and the bearing and distance of OP. The work should be verified by actual measurement of angle and distance. EXAMPLE. Given OR, N, 59 30' E. 10.60 chains; KQ, S. 70 15' E. 19.32 chains ; QT, N. 12 W., to find QP' and the bearing and distance of a line OP' which will straighten the boundary. MISCELLANEOUS EXAMPLES. 1. It is required to lay out a lot to contain one acre, and having an equal frontage on two streets which intersect at an angle of 84 40'. Locate the corners of the property. 2. From a square tract of land OPQR, which originally contained 160 acres, the southwest quarter was sold. It is required to find the uniform width of a strip MNL VTS which shall contain 40 acres. How many rods of fencing will the tract require? 3. A rectangular tract of land 16.20 chains long, and 8. 60 chains wide, valued at $200 per acre, is to be divided among three persons so that the first shall have $1,000 worth of it ; the second, $900 ; and the third, the remainder. Locate the points of division on the long side. 4. The bearings of two sides of a triangle are OM, N 60 E., and ON, S. 40 E. It is required to cut off from the corner an isosceles triangle containing 16 acres. Locate and find the length of the division line. 260 PLANE SURVEYING. 5. There is a farm in the form of a trapezium the area of which is given as 87.78 acres. The description of its boun- daries is very much effaced ; all that is legible is as follows : Beginning at the northwest corner, thence (1) S. 76 E. (distance effaced) ; (2) S. 10 E., distance 25 chains; (3) S. 62 W. (distance effaced) ; (4) N. 6 W. (distance effaced). It is required to perfect the description. SUGGESTION. Prolong the second and fourth sides until they meet, and calculate the area of the triangle exterior to the tract. Add it to the given area, whence the length of the first side may be readily computed ; the second and fourth sides may be found easily by either of two methods. 6. Required the length of a chord which will cut off one-third part of a circle whose radius is 100 feet. SUGGESTION. Let 20 denote the central angle, and r the radius, for convenience. Then ^-- sin 20 = Whence 180 2 3 may be obtained, and hence the chord. The angle will be the same, no matter what the radius may be. 7. A trapezoidal field, the two parallel sides of which are 16 and 10 chains, and the perpendicular distance between them, 12 chains, is to be divided into two equivalent parts b3* a line parallel to the given sides. It is required to determine the length of the division line and locate its extremities, the sides being equally inclined to the bases. 8. Given the sides of a triangle OR, 280 yards ; RQ, 200 yards ; OQ, 300 yards ; the distance from to a point P outside the tract, 220 yards ; and the angle POQ, 20. It is required to run the centre line of a straight road through P and across the field, so as to divide the tract into two equal parts. Locate the points where the road will cross the triangle. 9. Given the sides of an irregular pentagon, and the per- pendicular distance to each from a point within. Show how to divide the tracts into their equivalent parts. Also into three parts, having the ratio m : n :p. LAYING OUT AND DIVIDING LAND. 261 10. Given in a trapezoid MNOP (no figure), PM= 38.50 chains ; MN, one of the parallel sides, 64.80 chains ; NO, 41 chains ; the angle M, 85 30 f ; and N, 75 40'. It is required to divide the tract into two parts in the ratio of 2 : 3, by a line DL parallel to the parallel sides. The part MNDL is to be the greater. Find the length and location of the division line. 11. Given one side of a triangular field, 120 yards ; the angle opposite, 20; and the ratio of the other two sides, 7:10. Find the area. 12. Show that the area of a trapezium is equal to one-half the product of its" diagonals, by the sine of the angle of their intersection. 13. From a point within a triangular field, the sides of which were equal, I measured the distances to the three angles, and found them 12.5, 10, and 7.5 chains respectively; required the area. Ana. 12 A. 1 R. 23 P. The above problem is given in Guinmere's Surveying, and by some surveyors it is considered difficult. The following is an outline of a solution ; the student will supply what is wanting : With the given distances form the triangle ABC. On AB de- scribe an equilateral triangle ABD ; join CD by a right line, and on it describe an equilateral triangle CDE. CDE is the triangle in question, and B the point within. For BC and BD are evi- dently two of the measured distances, and BE, it will be perceived, is the D other, through the similarity and equality of the triangles ADC and BDE. To find the area of CDE, compute the angle BAG, whence the angle CAD becomes known ; now with the two sides AC, AD, and the included angle CAD, CD is easily determined, and hence the required area of the triangle CDE. CHAPTER V. PLANE-TABLE SUEVEYING. 299. The Plane-Table, as its name indicates, is a table or board which, being covered with paper, and having certain appliances for levelling and sighting, enables the surveyor to determine points and lines, and to delineate them on the paper in their relative position. It is used in "filling in" the details of topographical work, and generally for the location of points where great accuracy is not required, on account of the rapidity with which surveys by it may be effected. 300. The Board, which is rectangular in shape, usually 24 by 30 inches, is made of pieces of well-seasoned wood joined advantageously together to prevent warping, and is furnished with rollers or clamps, by means of which the paper is kept securely stretched upon it. 301. The Plumbing- Arm, which is pointed at one end, and from the other a plummet is suspended, is used to determine the point on the ground immediately under its representative on the board, or vice versa. The lower part of it moves upon an axis which has an index at its extremity, by means of which it may be ascertained when the bob and point upon the table are in the same vertical line. 302. The Tripod and its Head are similar to those of the ordinary transit, though heavier. A metallic plate, screwed fast to the table and having a solid conical spindle projecting from its centre, affords the means of attaching the head to the table. PLANE-TABLE, As MADE BY HELLER & BRIGHTLY, PHILADELPHIA, PA. CHAPTER V. PLANE-TABLE SURVEYING. 299. The Plane-Table, as its name indicates, is a table or board which, being covered with paper, and having certain appliances for levelling and sighting, enables the surveyor to determine points and lines, and to delineate them on the paper in their relative position. It is used in "filling in" the details of topographical work, and generally for the location of points where great accuracy is not required, on account of the rapidity with which surveys by it may be effected. 300. The Board, which is rectangular in shape, usually 24 by 30 inches, is made of pieces of well-seasoned wood joined advantageously together to prevent warping, and is furnished with rollers or clamps, by means of which the paper is kept securely stretched upon it. 301. The Plumbing- Arm, which is pointed at one end, and from the other a plummet is suspended, is used to determine the point on the ground immediately under its representative on the board, or vice versa. The lower part of it moves upon an axis which has an index at its extremity, by means of which it may be ascertained when the bob and point upon the table are in the same vertical line. 302. The Tripod and its Head are similar to those of the ordinary transit, though heavier. A metallic plate, screwed fast to the table and having a solid conical spindle projecting from its centre, affords the means of attaching the head to the table. PLANE-TABLE, As MADE BY HELLER & BRIGHTLY, PHILADELPHIA, PA, THE PLANE-TABLE. 265 The tripod-head admits of a slight lateral motion to the board, and is provided with levelling-clamp and tangent- screws similar to the common transit. 303. Of Alidades there are several kinds. One of the best, however, for ordinarv purposes is indicated in the figure. It consists of a brass ruler or straight edge about 22 inches long and two inches wide, from which rises a column surmounted by a telescope. The power of the telescope at least equals that of the common transit, and it is provided with stadia wires, has an attached level, vertical arc, with the necessary adjusting movements. It is set on the column so that the line of collimation is in or near the same vertical plane with the bevelled edge of the ruler. A parallel ruler allowing a very slight deviation from this plane is sometimes used, and the work is thereby facilitated. A small level is placed on the top of the column, which serves to indicate any unequal settling of the instrument. Two spirit levels at right angles to each other are placed upon the table to indicate when by the levelling-screws it is made horizontal ; or, the levels are attached to the ruler of the alidade, one in the longitudinal direction of the ruler, the other perpendicular to it. 304. The Declinator is simply a box containing a magnetic needle which has a range of 12 or 15 degrees on each side of the zero. It is used in orienting the table ; that is, to place a given point on the table over that on the ground which it represents, and to cause a line of the paper to lie in the same vertical plane, or parallel thereto, with its counterpart on the ground. Before the table is removed from its first position, or at the time of drawing the first line of the survey, the declinator may be placed upon it, and the needle allowed to rest at zero ; then a pencil drawn alongside the box will trace a north and south line, since the sides of the box are made parallel to the line of 2(36 PLANE SURVEYING. zeros.* When the table is oriented at any other station, the declinator will give the same reading if placed along the same line. ADJUSTMENTS. 305. From the nature of the service in some sections of the country, the plane-table is often necessarily subjected to rough usage, and there is a constant liability to a disturbance of the adjustments ; still, in careful hands, a well-made instrument may be used under very unfavorable conditions for a long time without being perceptibly affected. One should not fail, how- ever, to make occasional examinations, and while at work, if any difficulty be encountered which cannot otherwise be accounted for, it should lead directly to a scrutiny of the adjustments. 306. The Fiducial Edge of the Ruler. This should be a true, straight edge. Place the ruler upon a smooth surface, and draw a line along the edge, marking also the lines at the ends of the ruler. Reverse the ruler, and place the opposite ends upon the marked points, and again draw the line. If the two lines coincide, no adjustment is necessary ; if not, the edge must be made true. There is one deviation from a straight line which, by a very rare possibility, the edge of the ruler might assume, and yet not be shown by the above test ; it is when a part is convex and a part similarly situated at the other end concave in ex- actly the same degree and proportion. In this case, on reversal, a line drawn along the edge of the ruler would be coincident with the other, though not a true right line ; this can be tested by an exact straight edge. 307. The Level Attached to the Ruler. Place the instru- ment in the middle of the table, and bring the bubble to the centre by means of the levelling-screws of the table ; draw lines * Any other bearing which may be read will answer the purpose. THE PLANE-TABLE. 267 along the edge and ends of the ruler upon the board to show its exact position, then reverse 180. If the bubble remain cen- tral, it is in adjustment; if not, correct it one-half by means of the levelling-screws of the table, and the othei half by the adjusting-screws attached to the level. This should be re- peated until the bubble keeps its central position, whichever way the ruler may be placed upon the table. This presupposes the plane of the board to be true. If two levels are on the rulers, they are examined and adjusted in a like manner. Great care should be exercised in manipulation, lest the table be disturbed. 308. Cause the line of sight to revolve in a vertical plane, make the bubble of the level attached to the telescope read zero when the line of sight is horizontal, and test the vernier arc for index error, each as in the transit. METHODS EMPLOYED IN PLANE-TABLE SURVEYING. 309. Points may be located with respect to one another by either of four methods. In actual practice, however, a combi- nation of some of them is frequently employed. 310. By Radiation. Suppose it is required to make a plot of a field KLMNO, all the corners of which can be SCCMI from a point P within it. Place the instrument at P, level and clamp it. Find a point p on the paper, directly over P on the ground, and, keeping the bevelled edge of the ruler on p, point the telescope to any corner of the tract, as K. By means of the stadia wires, or chain, obtain the distance PK, and lay it off to any desired scale in the direction of the point sighted, 268 PLANE SUEVEYING. thus plotting pk. In a similar manner, locate the other corners. Join by straight lines the points thus determined ; and the resulting figure klmno will represent the tract surveyed. It is obvious that the position of objects such as buildings, trees, etc., if visible, may be determined by this method, and that it is immaterial whether the instrument be set up in the field or at one of the angles, providing all the stations can be seen from the point selected. 311. By Progression. This method requires the instrument to be set up at every station of the tract to be surveyed. Let KLMNO represent, as be- fore, the field, and suppose the instrument is first placed at 7T, and that k on the paper designates this point. With the alidade directed towards />, draw along it an indefinite line. Obtain by stadia or chain the distance KL, and lay it off to a desired scale, thus locating L Remove the instrument to L, orient it, and locate m. Continue in the same manner to locate n and o. When the table is oriented at any station, as M, the line ML should lie in the vertical plane, with its representative ml on the plot, and, having gone round the tract, the last line should close with the first station k. This method, in conjunction with the preceding, may be employed advantageously in the survey of a road, stream, etc. The centre line of the road or bank of the stream may be trav- ersed by the instrument, placing it at each angle or bend, as in the survey of a field by progression, and determine by the method of radiation the position of prominent objects, such as buildings, bridges, trees, -etc. If there be added to the above a sketch of the general features of the ground, a complete map will be had of the belt of country traversed. METHODS EMPLOYED. 269 312. By Intersections. Let it be required to plot the stations M, 0, P. Measure carefully the base line LN, and draw to a convenient scale In on the paper to represent it. At the extremities of this base line orient and point the instrument to the several stations. The intersections of the pairs of lines drawn from the base line to these stations will indicate their position on the plot. Their dis- tances from the base line, if desired, may be obtained by applying the scale used in the construction of In. If a field or closed tract of land is to be surveyed, a portion or all of one side may be used as a base line, or a base may be chosen outside the tract. This method is obviously well adapted to the mapping of harbors, shore lines, and generally to inaccessible points. Of course in this, as in all triangulations, well-conditioned triangles give more satisfactory results ; that is to say, avoid, if possible, angles less than 30 or greater than 150. 313. By Resection. This method requires the measurement of one line and the accessibility of all the stations. Let KLMNO represent the points to be plotted. Obtain the distance between two of them, as OK, lay it off on the table to a suitable scale, and let ok represent it. Orient the table at k, point the alidade to L, and draw along its fiducial edge an in- definite line. Remove the in- strument to L, and orient it. Then with the alidade centring on o, point it in the direction of 0, and draw a line along its 270 PLANE SURVEYING. edge : this line will intersect kL in some point Z, which will locate L on the plot. Through I draw a line towards J/, remove the instrument to Jf, and proceed as before. Objects on either side of the lines may be determined by radiation or by intersection, and further details, if desired, sketched in as the work proceeds. 314. Determination of Position by Resection on Three Known Points. In this problem three stations, L, N, 0, are plotted, as Z, ?i, o, on the table, and the instrument being set up over a fourth point P, it is required to find the position of this point on the map. This is the three-point problem of which geometrical constructions and analytical solutions are given in Chapter II. Section IV. It may be solved thus : Fasten a sheet of tracing-paper on the board, fix a point p to represent the station at which the instrument is set ; with the alidade centring on p, direct the telescope successively to Z>, 0, and jV, and draw lines of indefinite length along the ruler's edge towards these stations. Then if the tracing-paper be shifted until the three lines thus drawn coincide with the points Z, o, and , the point p will indicate the position of P. The position of this point may now be transferred, by pricking, to the map, the tracing-paper removed, and the table oriented. 315.* Bessel's Method by Inscribed Quadrilateral. A quadri- lateral is constructed with all the angles in the circumference of a circle, one diagonal of wlr.ch passes through the middle one of the three fixed points and the point sought. On this line the alidade is set, the telescope directed to the middle point, and the table is in position. Resection upon the extreme points intersects in this line and determines the position of the point sought. Let a, 6, c, be the points on the sheet representing the signals A, B, (7, in the ground. The table is set up at the point to be determined (cZ) and * Articles 315 and 316 are from the U. S. C. & G. S. Report for 1880. METHODS EMPLOYED. 271 levelled. The alidade is set upon the line ca, and a directed, by revolving the table, to its corresponding signal A, and the table clamped ; then, with the alidade centring on c, the mid- dle signal B is sighted with the telescope, and the line ce drawn along the edge of the ruler. The alidade is then set upon the line oc, and the telescope di- rected to the signal (7, by re- volving the table, and the table clamped. Then, with the alidade centring on a, the .telescope is directed to the middle signal B, and the line ae is drawn along the edge of the ruler. The point e (the intersection of these two lines) will be in the line passing through the middle point and the point sought. Set the alidade upon the line be, direct 6 to the signal B by revolv- ing the table, and the table will be in position. Clamp the table, centre the alidade upon a, direct the telescope to the signal A, and draw along the ruler the line ad. This will inter- sect the line be at the point sought. Resection upon (7, cen- tring the alidade on c in the same manner as upon A, will verify its position. The opposite angles of the quadrilateral adce being supple- mentary, angle ace and angle ade are subtended by the same chord ae and cae and cde are subtended by the same chord ce ; consequently, the intersection of ae and ce at e must fall on the line db ; or, the segments of two intersecting chords in a circle being reciprocally proportional, the triangles ad/ and cef are similar, and the triangles cdf and aef are similar, and d, /, and e must be in a right line passing through 6. 316. Determination of Position by Resection on Two Known Points. This is called the two-point problem, there being given 272 PLANE SURVEYING. bv their projections a, b, two points A and B, to put the plane- table in position at a third point C. (The capital letters refer to points on the ground, and the small ones to their correspond ing projections.) Select a fourth point Z), such that the intersections from C and D upon A and B make sufficiently large angles for good determinations. Put the table approximately in position at D, by estimation or by compass, and draw the lines Aa, Bb, inter- secting in d ; through d draw a line to C. Then set up at C, and assuming the point c on the line dC at an estimated dis- tance from d, and putting the table in a position parallel to that which is occupied at D, by means of the line cd, draw the lines from c to A, and from c to B. These will intersect the lines cL4, dB, at points a' and b', which form with c and d a quadrilateral similar to the true one, but erroneous in size and position. The angles which the lines ab and a'b' make with each other is the error in position. By constructing now through c a line cd', making the same angle with cd as that which ab makes with a'b', and directing this line cd 1 to D, the table will be brought into position, and the true point c can be found by the inter- sections of aA and bB. Instead of transferring the angle of error by construction, we may conveniently proceed as follows, observing that the angle which the line a'b' makes with ab is the error in the position of the table. As the table now stands, a'b' is parallel with AB, but we want to turn it so that 06 shall be parallel to the same. If, therefore, we place the alidade on a'b', and set up a mark METHODS EMPLOYED. 273 in that direction, then place the alidade on ab, and turn the table until it again points to the mark, then ab will be parallel to AB, and the table is in position. 317. Practical Suggestions in using the Plane-Table.* The board should be placed so low as to be readily reached, even at the most remote corner, and yet high enough to enable the observer to take sight with com fort. This will bring it a little below the elbow. Care must be taken that no part of the body touch or rest against the edge of the board. In using the alidade, steady the standard with the left hand, while the right swings the rear end of the ruler in the proper direction. Thumb-tacks and rollers for holding down the sheet are both found objectionable, especially in high winds. The edges may be pasted underneath, or spring clamps may be used to advan- tage. A scale graduated upon the fiducial edge of the alidade is inconvenient, and in some positious impracticable and waste- ful of time. A detached triangular boxwood or metal scale is greatly to be preferred. Umbrellas or shades, whilst a great relief to the eyes, are cumbersome and troublesome, and by blowing over on the table may cause damage or derangement. Colored glasses screening the eyes will be better, and by using tinted paper, as manilla, instead of white, still more relief is given, and the sheet can be kept cleaner. Before leaving the station, and at any intervals not otherwise employed, the " check" shots should be tesieu to determine any displacement of the board. Use as hard a pencil, and make as few lines, as possible. In locating points of contours, plot the distance at once along the edge of ruler by detached scale, making only a dot at the point which should receive the number of the contour. Objects on a straight line may be quickly located by plotting the ends and determining the intermediate points by intersecting shots. * From The Topographer, by L. M. Haupt, C.E., Philadelphia. 274 PLANE SURVEYING. EXERCISES WITH THE PLANE-TABLE. 1. Make a plane-table survey of a field, using one side as a base line. 2. Make a survey embracing 200 or 300 rods of a road or stream, locating prominent objects on either side. 3. Locate several points on the table by intersections, and check the work by resection from these points. 4. Locate a non-plotted point by resection on three known points tirst method; check by Bessel's method. CHAPTER VI. THE SUBVEY OP THE PUBLIC LANDS OF THE UNITED STATES. THE SOLAR COMPASS. 318. A description of the Solar Compass, the instrument that is extensively used in the survey of the public lands, its adjustment and use, will be given before describing the method employed by the government in these surveys. This instrument, so ingeniously contrived for readily deter- mining a true meridian or north and south line, was invented by William A. Burt, of Michigan, and patented by him in 1836. It has since come into general use in the surveys of United States public lands, the principal lines of which are required to be run with reference to the true meridian. The arrangement of its sockets and plates is similar to that of the Surveyor's Transit, as shown in Chapter II. Section I., except that the sight-vanes are attached to the under plate or limb, and this revolves around the upper or vernier plate on which the solar apparatus is placed. The limb is divided to half-degrees, is figured in two rows, as usual, and reads by the two opposite verniers to single minutes. THE SOLAR APPARATUS. 319. The Solar Apparatus is seen in the place of the needle, and in fact operates as its substitute in the field. It consists mainly of three arcs of circles, by which can be set off the latitude of a place, the declination of the sun, and the hour of the day. 276 PLANE SURVEYING. These arcs, designated in the cut by the letters a, 6, and c, are therefore termed the latitude, the declination, and the hour arcs respectively. 320. The Latitude Arc a has its centre of motion in two pivots, one of which is seen at d ; the other is concealed in the cut. It is moved either up or down within a hollow arc, seen in the cut, by a tangent-screw at /, and is securely fastened in any position by a clamp-screw. The latitude arc is graduated to quarter-degrees, and reads by its vernier e to single minutes ; it has a range of about 35 degrees, so as to be adjustable to the latitude of any place in the United States. 321. The Declination Arc b is also graduated to quarter- degrees, and has a range of about 28 degrees. Its vernier w, reading to single minutes, is fixed to a movable arm ^, having its centre of motion at the end of the declination arc at g ; the arm is moved over the surface of the declination arc, and its vernier set to any reading by turning the head of the tangent-screw k. It is also securely clamped in any posi- tion by a screw, concealed in the engraving. 322. Solar Lenses and Lines. At each end of the arm h is a rectangular block of brass, in which is set a small convex lens, having its focus on the surface of a little silver plate A (marginal figure) , fastened by screws to the inside of the oppo- site block. On the surface of the plate are marked two sets of lines intersecting each other at right angles ; of these bb are termed the hour lines, and cc the ^ equatorial lines, as having reference respec- tively to the hour of the day and the position of the sun in relation to the equator. In the cut the equatorial lines are those on the lower block, parallel to the surface of the THE SOLAB COMPASS. 279 hour arc c ; the hour lines are of course those at right angles to the first. 323* Equatorial Sights. On the top of each of the rec- tangular blocks is seen a little sighting-piece, termed the equa- torial sight, fastened to the block by a small, milled head-screw, so as to be detached at pleasure. They are used, as will be explained hereafter, in adjusting the different parts of the solar apparatus. 324. The Hour Arc c is supported by the two pivots of the latitude arc already spoken of, and is also connected with that arc by a curved arm, as shown in the figure. The hour arc has a range of about 120, is divided to half- degrees, and figured in two series, designating both the hours and the degrees, the middle division being marked 12 and 90 on either side of the graduated lines. 325. The Polar Axis. Through the centre of the hour arc passes a hollow socket p containing the spindle of the declina- tion arc, by means of which this arc can be moved from side to side over the surface of the hour arc, or turned completely round, as may be required. The hour arc is read by the lower edge of the graduated side of the declination arc. The axis of the declination arc, or indeed the whole socket p, is appropriately termed the polar axis. 326. The Adjuster. Besides the parts shown in the cut, there is also an arm used in the adjustment of the instrument as described hereafter, but laid aside in the box when that is effected. The parts just described constitute properly the solar apparatus. Besides these, however, are seen the needle-box n with its arc and tangent screw , and the spirit levels, for bringing the whole instrument to a horizontal position. 280 PLANE SURVEYING. 327. The Needle-Box n has an arc of about 86 degrees in extent, divided to half-degrees, and figured from the centre or zero mark on either side. The needle, which is made as in other instruments, except that the arms are of unequal lengths, is raised or lowered by a lever shown in the cut. The needle-box is attached by a projecting arm to a tangent- screw t, by which it is moved about its centre, and its needle set to any variation. This variation is also read off by the vernier on the end of the projecting arm, reading to three minutes a graduated arc, attached to the plate of the compass. 328. The Levals seen with the solar apparatus have ground- glass vials, and are adjustable at their ends like those of other instruments. The edge of the circular plate on which the solar work is placed is divided and figured at intervals of 10 degrees, and numbered, as shown, from to 90 on each side of the line of sight. These graduations are used in connection with a little brass pin, seen in the centre of the plate, to obtain approximate bearings of lines, which are not important enough to require a close observation. 329. Lines of Refraction. The inside faces of the sights are also graduated and figured, to indicate the amount of refraction to be allowed when the sun is near the horizon. PRINCIPLES OF THE SOLAR COMPASS. 330. The interval between two equatorial lines cc, in figure on page 276, as well as between the hour lines 66, is just suffi- cient to include the circular image of the sun, as formed by the solar lens on the opposite end of the revolving arm ft, figure on page 277. THE SOLAR COMPASS. 281 When, therefore, the instrument is made perfectly horizontal, the equatorial lines and the opposite lenses being accurately adjusted to each other by a previous operation, and the sun's image brought within the equatorial lines, his position in the heavens, with reference to the horizon, will be defined with precision. Suppose the observation to be made at the time of one of the equinoxes ; the arm /t, set at zero on the declination arc b ; and the polar axis p, placed exactly parallel to the axis of the earth. Then the motion of the arm h, if revolved on the spindle of the declination arc around the hour circle c, will exactly corre- spond with the motion of the sun in the heavens, on the given day and at the place of observation ; so that if the sun's image was brought between the lines cc in the morning, it would continue in the same position, passing neither above nor below the lines, as the arm was made to revolve in imitation of the motion of the sun about the earth. In the morning, as the sun rises from the horizon, the arm h will be in a position nearly at right angles to that shown in the cut, the lens being turned towards the sun, and the silver plate on which his image is thrown directly opposite. As the sun ascends, the arm must be moved around, until when he has reached the meridian, the graduated side of the declination arc will indicate 12 on the hour circle, and the arm h, the declination arc b, and the latitude arc a will be in the same plane. As the sun declines from the meridian, the arm h must be moved in the same direction, until at sunset its position will be the exact reverse of that it occupied in the morning. 331. Allowance for Declination. Let us now suppose the observation made when the sun has passed the equinoctial point, and when his position is affected by declination. Bv referring to the almanac, and setting off on the arc his declination for the given day and hour, we are still able to 282 PLANE SURVEYING. determine his position with the same certainty as if he remained on the equator. When the sun's declination is south, that is, from the 22d of September to the 20th of March in each year, the arc b is turned towards the plates of the compass, as shown in the en- graving, and the solar lens o, with the silver plate opposite, are made use of in the surveys. The remainder of the year the arc is turned from the plates, and the other lens and plate employed. When the solar compass is accurately adjusted, and its plates made perfectly horizontal, the latitude of the place, and the declination of the sun for the given day and hour, being also set off on the respective arcs, the image of the sun cannot be brought between the equatorial lines until the polar axis is placed in the plane of the meridian of the place, or in a position parallel to the axis of the earth. The slightest deviation from this posi- tion will cause the image to pass above or below the lines, and thus discover the error. We thus, from the position of the sun in the solar system, obtain a certain direction absolutely unchangeable, from which to run our lines and measure the horizontal angles required. This simple principle is not only the basis of the construction of the solar compass, but the sole cause of its superiority to the ordinary or magnetic instrument. For in a needle instrument the accuracy of the horizontal angles indicated, and therefore of all the observations made, depends upon " the delicacy of the needle, and the constancy with which it assumes a certain direction, termed the magnetic meridian." The principal causes of error in the needle, briefly stated, are the dulling of the pivot, the loss of polarity in the needle, the influence of local attraction, and the effect of the sun's rays, producing the diurnal variation. From all these imperfections the solar instrument is free. The sights and the graduated limb being adjusted to the solar apparatus, and the latitude of the place and the declination of the sun also set off upon the respective arcs, we are able not only THE SOLAR COMPASS. 283 to run the true meridian, or a due east and west course, but also to set off the horizontal angles with minuteness and ac- curacy from a direction which never changes, and is unaffected by attraction of anv kind. To ADJUST THE SOLAR COMPASS. The adjustments of this instrument, with which the surveyor will have to do, are simple and few in number, and will now be given in order. 332. To Adjust the Levels. Proceed precisely as directed in the account of the other instruments we have described', by bringing the bubbles into the centre of the tubes by the level- ling-screws of the tripod, and then reversing the instrument upon its spindle, and raising or lowering the ends of the tubes, until the bubbles will remain in the centre during a complete revolution of the instrument. 333. To Adjust the Equatorial Lines and Solar Lenses. First detach the arm h from the declination arc by withdrawing the screws shown in the cut from the ends of the posts of the tangent-screw k, and also the clamp-screw, and the conical pivot with its small screws by which the arm and declination arc are connected. The arm h being thus removed, attach the adjuster in its place by replacing the conical pivot and screws, and insert the clamp-screw so as to clamp the adjuster at any point on the declination arc. Now level the instrument, place the arm h on the adjuster, with the same side resting against the surface of the declination arc as before it was detached. Turn the instrument on its spindle so as to bring the solar lens to be adjusted in the direc- tion of the sun, and raise or lower the adjuster on the declina- tion arc, until it can be clamped in such a position as to bring the sun's image as near as may be between the equatorial lines on the opposite silver plate, and bring the image precisely into 284 PLANE SURVEYING. position by the tangent of the latitude arc or the levelling- screws of the tripod. Then carefully turn the arm half-way over, until it rests upon the adjuster by the opposite faces of the rectangular blocks, and again observe the position of the sun's image. If it remains between the lines as before, the lens and plate are in adjustment ; if not, loosen the three screws which con- fine the plate to the block, and move the plate under their heads, until one-half the error in the position of the sun's image is removed. Again bring the image between the lines, and repeat the operation until it will remain in the same situation, in both positions of the arm, when the adjustment will be completed. To adjust the other lens and plate, reverse the arm eud for end on the adjuster, and proceed precisely as in the former case, until the same result is attained. In tightening the screws over the silver plate, care must be taken not to move the plate. This adjustment now being complete, the adjuster should be removed, and the arm h with its attachments replaced as before. 334. To Adjust the Vernier of the Declination Arc. Hav- ing levelled the instrument, and turned its lens in the direction of the sun, clamp to the spindle, and set the vernier v of the declination arc at zero, by means of the tangent-screw at &, and clamp to the arc. See that the spindle moves easily and yet truly in the socket, or polar axis, and raise or lower the latitude arc by turning the tangent-screw/, until the sun's image is brought between the equatorial lines on one of the plates. Clamp the latitude arc by the screw, and bring the image precisely into position by the levelling-screws of the tripod or socket, and without dis- turbing the instrument, carefully revolve the arm /, until the opposite lens and plate are brought in the direction of the sun, and note if the sun's image comes between the lines as before. THE SOLAR COMPASS. 285 If it does, there is no index error of the declination arc ; if not, with the tangent-screw &, move the arm until the sun's image passes over half the error ; again bring the image be- tween the lines, and repeat the operation as before, until the image will occupy the same position on both the plates. We shall now find, however, that the zero marks on the arc and the vernier do not correspond, and to remedy this error, the little flat-head screws above the vernier must be loosened until it can be moved so as to make the zeros coincide, when the operation will be completed. 335. To Adjust the Solar Apparatus to the Compass Sights. First level the instrument, and with the clamp and tangent screws set the main plate at 90 by the verniers and horizontal limb. Then remove the clamp-screw, and raise the latitude arc until the polar axis is by estimation very nearly horizontal, and if necessary, tighten the screws on the pivots of the arc, so as to retain it in this position. Fix the vernier of the declination arc at zero, and direct the equatorial sights to some distant and well-marked object, and observe the same through the compass sights. If the same object is seen through both, and the verniers read to 90 on the limb, the adjustment is complete ; if not, the correction must be made by moving the sights or changing the position of the verniers. To USE THE SOLAR COMPASS. 336. Before this instrument can be used at any given place, it is necessary to set off upon its arcs both the declination of the sun as affected by its refraction for the given day and hour, and the latitude of the place where the observation is made. 337. To Set off the Declination. The declination of the sun, given in the ephemeris of the Nautical Almanac from year to year, is calculated for apparent noon at Greenwich, England, or Washington, D.C. To determine it for any other hour at a place in the United 286 PLANE SUKVEYING. States, reference must be had, not only to the difference of time arising from the longitude, but also to the change of declination from day to day. By the use of standard time, which is now quite general throughout the United States, it is very easy to obtain the declination required at any place. For those using 75th meridian time, a difference of five hours must be allowed for the difference in declination between the place of observation and Greenwich. The time-piece referred to the 75th meridian as standard in- dicating 7 A.M. when it is noon at Greenwich. Where the 90th meridian is used as standard, six hours must be allowed, etc. To obtain the declination for the other hours of the day, take from the almanac the declination for apparent noon of the given clay, and, as the declination is increasing or decreasing, add to or subtract from the declination of the first hour the difference for one hour as given in the ephemeris, which will give, when affected by the refraction, the declination for the succeeding hour ; and proceed thus in making a table of the declination for every hour of -the day. 338. Refraction. By reason of the increasing density of the atmosphere from its upper regions to the earth's surface, the rays of light from the sun are bent out of their course, so as to make his altitude appear greater than is actually the case. The amount of refraction varies according to the altitude of the body observed ; being when it is in the zenith, about one minute when midway from the horizon to the zenith, and almost 34' when in the horizon. 339. Effect of Incidental Refraction. It will be seen by referring to the instrument, that the effect of the ordinary refraction upon the position of the sun's image with reference to the equatorial lines, which, in fact, are the only ones to be regarded in running lines with the solar compass, is continually THE SOLAR COMPASS. 287 changing, not only with the change of latitude, but also with that of the sun's declination from hour to hour, and the motion of the revolving arm as it follows the sun in its daily revolution. If the equatorial lines were always in the same vertical plane with the sun, as would be the case at the equator at the time of the equinoxes, it is evident that refraction would have no effect upon the position of the image between these lines, and there- fore would not be of any importance to the surveyor. But as we proceed further north, and as the sun's declination to the south increases, the refraction also increases, and must now be taken into account. Again, the angle which the equatorial lines make with the horizon is continually changing as the arm is made to follow the motion of the sun during the course of a day. Thus, in the morning and evening they are more or less inclined to the horizon, while at noon they are exactly parallel to it. And thus it follows that the excess of refraction at morning and evening is in some measure balanced by the fact that the position of the sun's image with reference to the equatorial lines is then less affected by it, on account of the greater inclination of the lines to the horizon. 340. Allowance for Refraction. The proper allowance to be made for refraction in setting off the declination of the sun upon the solar compass for any hour of any day of the year is given in the following table : 288 PLANE SURVEYING. A TABLE OF MEAN REFRACTIONS IN DECLINATION. To apply on the declination arc of Solar Attachment of either Compass or Transits.* 1 DECLINATIONS. i FOR LATITUDE 30. 1 + 20 + 15* + 10 D + 5 -5 -10^ -15 3 -20^ Oh. 10" 15" 21" 27" 33" 40" 48" 57" 1'08" 2 14 19 25 31 38 46 54 1'05 1 18 3 20 26 32 39 47 55 1'06 119 136 4 32 39 46 52 1'06 1'19 135 157 229 5 I'OO I'lO 1'24 1'52 207 244 346 543 1306 FOR LATITUDE S2 5 30'. Oh. 13" 18" 24" 30" 36" 44" 52" 1'02" 1'14" 2 17 22 28 35 42 50 I'OO 1 11 126 3 23 29 35 43 51 I'Ol 1 13 128 147 4 35 43 51 I'Ol 1'IS 127 146 2 13 254 5 roa 116 1'Sl 153 220 305 425 736 FOB LATITUDE 35. Oh. 15" 21" 27" 33" 40" 48" 57" 1'08" 1'21" 2 20 25 32 38 46 55 1'05 1 18 135 3 26 33 39 47 56 1'07 121 138 200 4 39 47 56 1'07 1'20 136 1 59 232 325 5 1'07 1*20 1'38 200 234 329 514. 1016 FOR LATITUDE 37 30'. Oh. 18" 24" 30" 36" 44" 52" 1'02" 1'14'' 1'29" 2 22 28 35 42 50 I'OO 112 126 145 3 29 36 43 52 1'02 1 14 129 149 216 4 43 51 I'Ol 1'13 127 149 2 14 254 405 5 I'll 1'26 145 2 10 249 355 615 1458 * Computed by Edward W. Arms, C.E., for W. and L. E. Gurley Troy, N.Y. THE SOLAR COMPASS. 289 HOUR ANGLE. DECLINATIONS. FOB LATITUDE 40. + 20 3 + 15 + 10 + 5 -5 -10 -15 -20' Oh. 21" 27" 33" 40" 48" 57" 1'08" 1'21" 1'39" 2 25 32 39 46 52 1'06 1 19 135 1 57 8 33 40 48 57 1'08 121 138 202 236 4 47 55 1'06 1'19 136 158 230 321 459 5 1'15 1'31 1 51 220 305 425 734 2518 FOR LATITUDE 42 30'. Oh. 24" 30" 36" 44" 52" 1'02" 1'14" 1'29" 1'49" 2 28 35 39 50 I'OO 1 12 126 145 2 11 3 36 43 52 1'02 1 13 129 149 2 17 2 59 4 50 I'OO I'll 1 26 1 44 2 10 249 355 6 16 5 1'16 136 158 230 322 500 924 FOB LATITUDE 45. Oh. 27" 33" 40" 48" 57" 1'08" 1'21" 1'39 2'02" 2 32 39 46 52 1'06 1 19 1 35 1 57 229 3 40 47 56 1'07 121 138 200 234 329 4 54 1'04 1'16 133 1 54 224 311 438 8 15 5 1'23 141 205 241 340 540 1202 FOR LATITUDE 4T 30'. Oh. 30" 36" 44" 52" 1'02" 1'14" 1'29" 1'49" 2'18" 2 35 42 50 I'OO 1 12 1 26 145 201 251 3 43 61 I'Ol I 13 1 28 147 2 16 2 56 408 4 56 1'09 123 140 205 240 339 637 1118 5 1'27 146 212 252 401 630 1619 FOR LATITUDE 50. Oh. 33" 40" 48" 57" 1'08" 1'21" 1'39" 2'02" 2'36" 2 38 46 55 1'06 1 18 135 157 228 319 3 47 56 i'oe 1 19 1 36 229 231 323 502 4 1'02 1'14 1 29 1 48 2 16 258 418 669 1947 5 1 30 1 51 2 19 304 422 728 2410 290 PLANE SURVEYING. EXPLANATION OF THE TABLE OF REFRACTIONS.* The table is calculated for latitudes between 30 and 50 at intervals of 2^, that being as near as is required. The declination ranges from to 20, both north and south, the + declinations being north, and south, and is given for every 5 degrees, that being sufficiently near for all practical pur- poses. The hour angle in the first column indicates the distance of the sun from the meridian in hours, the refraction given for hours being that which affects the observed declination of the sun when on the meridian, commonly known as meridional re- fraction ; the refraction for the hours just before and after noon is so nearly that of the meridian, that it may be called and allowed as the same. When the table is used, it must be borne in mind that when the declination is north or + in the table, the refraction is to be added ; when the declination is south or the refraction must be subtracted. It will be noticed that the refraction in south or declina- tion increases very rapidly as the sun nears the horizon, show- ing that observations should not be taken with the sun when south of the equator, less than one hour from the horizon. Thus, suppose it be required to obtain the declination for any hour in the day, April 16, 1887, at Pittsburg, Pa., where 75th meridian time is used. The difference in time is 5 hours, so that the declination given in the ephemeris for apparent noon of that day at Green- wich would be that of 7 A.M. at Pittsburg. Proceed as follows : Declination at Greenwich, mean noon, April 16, 1887, N. 10 6' 29" Add 1' 51"=refract'n for 5 hrs. [lat. Pittsburg 40 28']. Or, N. 10 8' 20" =dec. 7 A.M. at Pittsburg. * See also Refraction Table, page 92. THE SOLAR COMPASS. 291 To get the declination for 8 o'clock, same day and place, add 53", the difference for one hour because the declination is increasing to the declination taken from the almanac, and this increased by the refraction corresponding to 4 hours from noon will give 10 8' 28" for the required declination. Again, suppose it be desired to obtain the corrected dec- lination for 8 A.M. Oct. 15, 1887, same place. The declination being now south, the refraction is to be sub- tracted, but the hourly difference is to be added because the declination is increasing, as in the first example ; thus : Declination at Greenwich, mean noon, Oct. 15, 1887, S. 8 30' 20" Add 56"= dec. for 1 hr., and increasing. S. 8 31' 16" Subtract 2' 23"= refr. 4 hrs. from noon. Or, S. 8 28' 53"= dec. at 8 A.M. ; and so on for any hour in the day, obtaining from the declina- tion at Greenwich, by the proper application of the hourly motion, the declination corresponding to the hour required, and correcting this for refraction due to altitude. To facilitate operations, the calculation of the declination for the different hours of the day should be made and noted before the surveyor commences his work. 341. To Set off the Latitude. Find the declination of the sun for the given day at noon, at the place of observation as just described, and with the tangent-screw set it off upon the declination arc, and clamp the arm firmly to the arc. Observe in the almanac the equation of time for the given day, in order to know about the time the sun will reach the meridian. Then, about fifteen or twenty minutes before this time, set up the instrument, level it carefully, fix the divided surface of the declination arc at 12 on the hour circle, and turn the instru- 292 PLA^E SURVEYING. ment upon its spindle until the solar lens is brought into the direction of the sun. Loosen the clamp-screw of the latitude arc, and with the tangent-screw raise or lower this arc until the image of the sun is brought precisely between the equatorial lines, and turn the instrument from time to time so as to keep the image also between the hour lines on the plate. As the sun ascends, its image will move below the lines, and the arc must be moved to follow it. Continue thus, keeping it between the two sets of lines until its image begins to pass above the equatorial lines, which is also the moment of its pass- ing the meridian. Now read off the vernier of the arc, and we have the latitude of the place, which is always to be set off on the arc when the compass is used at the given place. It is the practice of surveyors using the solar compass to set off, in the manner just described, the latitude of the point where the survey begins, and to repeat the observation and correction of the latitude arc every day when the weather is favorable, there being also an hour at mid-day when the sun is so near the meridian as not to give the direction of lines with the certainty required. 342. To Run Lines with the Solar Compass. Having set off in the manner just given the latitude and declination upon their respective arcs, the instrument being also in adjustment, the surveyor is ready to run lines by the sun. To do this, the instrument is set over the station and care- fully levelled, the plates clamped at zero on the horizontal limb, and the sights directed north and south, the direction being given, when unknown, approximately by the needle. The solar lens is then turned to the sun, and with one hand on the instrument, and the other on the revolving arm, both are moved from side to side, until the sun's image is made to appear on the silver plate ; when, by carefully continuing the operation, it may be brought precisely between the equatorial lines. THE SOLAR COMPASS. 293 Allowance being now made for refraction, .the line of sights will indicate the true meridian ; the observation may now be made, and the flag-man put in position. When a due east and west line is to be run, the verniers of the horizontal limb are set at 90, and' the sun's image kept between the lines as before. The solar compass being so constructed that when the sun's image is in position the limb must be clamped at in order to run a true meridian line, it will be evident that the bearing of any line from the meridian may be read by the verniers of the limb precisely as in the ordinary magnetic compass : the bear- ings of lines are read from the ends of the needle. 343. Use of the Needle. In running lines, the magnetic needle is always kept with the sun ; that is, the point of the needle is made to indicate on the arc of the compass-box by turning the tangent-screw connected with its arm on the oppo- site side of the plate. By this means the lines can be run by the needle alone in case of the temporary disappearance of the sun ; but, of course, in such cases the surveyor must be sure that no local attraction is exerted. The variation of the needle, which is noted at every station, is read off in degrees and minutes on the arc, by the edge of which the vernier of the needle-box moves. 344. Allowance for the Earth's Curvature. When long lines are run by the solar compass, either by the true meridian, or due east and west, allowance must be made for the curvature of the earth. Thus, in running north or south, the latitude changes about one minute for every distance of 92 chains 30 links, and the side of a township requires a change on the latitude arc of 5' 12", the township, of course, being six miles square. This allowance is of constant use where the surveyor fails to get an observation on the sun at noon, and is a very close approximation to the truth. 294 PLANE SURVEYING. In running due east and west, as in tracing the standard parallels of latitude, the sights are set at 90 on the limb, and the line is run at right angles to the meridian. If no allowance were made for the earth's curvature, these lines would, if sufficiently produced, reach the equator, to which they are constantly tending. Of course, in running short lines either east or west, the variation from the parallel would be so small as to be of no practical importance ; but when long sights are taken, the correction should be made by taking fore and back sights at every station, noticing the error on the back-sight, and setting off one-half of it on the fore-sight on the side towards the pole. 345. Time of Day by the Sun. The time of day is best ascertained by the solar compass when the sun is on the meridian, as at the time of making the observation for lati- tude. The time thus given is that of apparent noon, and can be reduced to mean time, by merel}' applying the equation of time as directed in the almanac, and adding or subtracting as the sun is slow or fast. The time, of course, can also be taken before or after noon, by bringing the sun's image between the hour lines, and noticing the position of the divided edge of the revolving arm, with reference to the graduations of the hour circle, allowing four minutes of time for each degree of the arc, and thus -obtaining apparent time, which must be corrected by the equation of time as just described. 346. Caution as to the False Image. In using the compass upon the sun, if the revolving arm be turned a little one side of its proper position, a false or reflected image of the sun will appear on the silver plate in nearly the same place as that occu- pied by the true one. It is caused by the reflection of the true image from the surface of the arm, and is a fruitful source of error to the inexperienced surveyor. It can, however, be SURVEY OF THE PUBLIC LANDS. 295 readily distinguished from the real image by being much less bright, and not so clearly defined. 347. Approximate Bearings. When the bearings of lines, such as the course of a stream, or the boundaries of a forest, are not desired with the certainty given by the verniers and horizontal limb, a rough approximation of the angle they make with the true meridian is obtained by the divisions on the outside of the circular plate. In this operation, a pencil, or thin straight edge of any sort, is held perpendicularly against the circular edge of the plate, and moved around until it is in range with the eve, the brass centre-pin, and the object observed. The bearing of the line is then read off at the point where the pencil is placed. 348. Time for Using the Solar Compass. The solar com- pass, like the ordinary instrument, can be used at all seasons of the year, the most favorable time being, of course, in the summer, when the declination is north, and the days are long, and more generally fair.* ORIGIN OP THE SYSTEM FOR THE SURVEY OF THE PUBLIC LANDS.f 349. The present system of survey of the public lands was inaugurated by a committee appointed by the Continental Congress, of which Thomas Jefferson was chairman. This committee, on May 7, 1784, reported an ordinance requiring public lands to be divided into " hundreds" of ten geographical miles square, and these again subdivided into lots of one mile square, each to be numbered from 1 to 100, commencing in the northwestern corner and continuing from west to east and from * See Article 147. t The following pages regarding the government surveys are from " Instructions of the General Land Office to the Surveyors-General of the United States relative to the Survey of the Public Lands." 296 PLANE SUKVEYING. east to west consecutively. By subsequent amendment, April 26, 1785, the ordinance required the surveyors " to divide the said territory into townships of 7 miles square, by lines running due north and south, and others crossing these at right angles. The plots of the townships, respectively, shall be marked by subdivisions into sections of 1 mile square, or 640 acres in the same direction as the external lines, and numbered from 1 to 49, and these sections shall be subdivided into lots of 320 acres." This is the first record of the use of the terms " town- ship " and " section." This ordinance was subsequently still further amended, and as finally passed on the 20th of May, 1785, provided for town- ships 6 miles square, containing 36 sections of 1 mile square. The first public surveys were made under this ordinance by the direction of the Geographer of the United States. 6 5 4 5 2 1 7 8 9 10 11 12 18 17 16 15 14 13 19 20 21 22 23 24 30 29 28 27 26 25 31 82 33 34 35 36 The act of Congress, approved May 18, 1796, provided for the appointment of a surveyor-general, and directed the survey of lands northwest of the Ohio River, and above the mouth of the Kentucky River, " in which the titles of the Indian tribes have been extinguished," and among other pro- visions, that the " sections shall be numbered respectively, SURVEY OF THE PUBLIC LAMDS. 297 beginning with the number one in the northeast section and proceeding west and east, alternately, through the township, with progressive numbers till the thirty-sixth be completed." This method of numbering sections, as shown by the preceding diagram, is still in use. The act of Congress, approved Feb. 11, 1805, directs the subdivisions of the public lands into quarter-sections. The act of April 24, 1820, provides for the sale of the public lands in half-quarter-sections, and that in every case of the division of a quarter-section, the division line shall run north and south. April 5, 1832, Congress directed the subdivision of the public lands into quarter-quarters, and requiring the division line to run east and west. 350. A surveyor-general for each surveying district is appointed by the President, by and with the advice of the Senate. He is required, while in the discharge of the duties of his office, to reside in the district for which he is appointed. His term of office is four years, and he must give bonds, with sufficient security for the penal sum of $30,000, for the faithful disbursement of all public money placed in his hands, and for the faithful performance of the duties of his office. Among other duties prescribed by law and set forth in the manual, the surveyor-general is required to engage a sufficient number of skilful surveyors as his deputies, and shall cause to be sur- veyed, measured, and marked, without delay, all base and meridian lines through such points, and perpetuated by such monuments, and such other correction parallels and meridians, as may be prescribed by law, or by instructions from the General Land Office, in respect to the public lands within his surveying district to which the Indian title has been or may be extinguished. 351. System of Rectangular Surveying. The public lands of the United States are ordinarily surveyed into rectangular tracts, bounded by lines conforming to the cardinal points. 298 PLANE SURVEYING. The public lands shall be laid off, in the first place, into bodies of land 24 miles square, as near as may be. This shall be done by the extension of standard lines from the principal meridian every 24 miles, and by the extension from the base and standard lines, of auxiliary meridians every 24 miles. Thereafter they shall be laid off into bodies of land 6 miles square, as near as may be, called townships, containing, as near as may be, 23,040 acres. The townships shall be sub- divided into 36 tracts, called sections, each containing, as near as may be, 640 acres. Any number or series of contiguous townships, situate north or south of each other, constitute a range. (a) The law requires that the lines of the public surveys shall be governed by the true meridian, and that the township shall be six miles square, two things involving in connection a mathematical impossibility. For strictly to conform to the meridian necessarily throws the township out of square, by reason of the convergency of meridians, and hence by adhering to the true meridian results the necessity of departing from the strict requirements of law, as respects the precise area of town- ships and the subdivisions! parts thereof; the township assum- ing something of a trapezoidal form, which inequality develops itself more and more as such, the higher the latitude of the surveys. It is doubtless in view of these circumstances that the law provides (see Section 2 of the act of May 18, 1796) that the section of a mile square shall contain the quantity of 640 acres, as nearly as may be; and, morever, provides (see Section 3 of the act of May 10, 1800) in the following words : "And in all cases where the exterior lines of the townships thus to be subdivided into sections or half-sections shall exceed, or shall not extend, 6 miles, the excess or deficiency shall be specially noted, and added to or deducted from the western or northern ranges of sections or half-sections in such township, according as the error may be in running the lines from east to west or from south to north ; the sections and half-sections bounded on the northern and western lines of such townships SURVEY OF THE PUBLIC LANl)S. 299 shall be sold as containing only the quantity expressed in the returns and plats, respectively, and all others as containing the complete legal quantity." Sections 5 and 6 of Township No. 6, North, Range No. 34, east, of the principal meridian, Montana, are exhibited below : (5) The section lines are surveyed from south to north on true meridians, and from east to west, in order to throw the excesses or deficiencies in measurements on the north and west sides of the township, as required by law. In a case where a township has been partially surveyed, and it is necessary to complete the survey of the same, or where the character of the land is such that only the north or west portions of the town- ship can be surveyed, this rule cannot be strictly adhered to ; but in such cases must be departed from only so far as is absolutely necessary. It will also be necessary to depart from this rule where surveys close upon State or Territorial bound- aries, or upon survej's extending from different meridians. (c) The townships are to bear numbers in respect to the base line, either north or south of it ; and the tiers of townships called "ranges" will bear numbers in respect to the meridian line, according to their relative position to it, either on the east or west. 300 PLANE SURVEYING. (d) The 36 sections into which a township io subdivided are numbered, commencing with number one at the northeast angle of the township and proceeding west to number 6, and thence proceeding east to number 12, and so on, alternately until the number 36 is in the southeast angle. In all cases of surveys of fractional townships, the sections should bear the same numbers as they would if the township were full. (e) Standard parallels shall be established at intervals of every 24 miles, north and south of the base line, and auxiliary meridians at intervals of every 24 miles, east and west of the principal meridian ; the object being to confine the errors result- ing from convergence of meridians and inaccuracies in measure- ments, within the tracts of land bounded by the lines so estab- lished. (/) The survey of all principal base and meridian standard parallels, and auxiliary meridian and township lines must be made with an instrument operating independently of the mag- netic needle. Burt's improved solar compass, or other instru- ment of equal utility, must be used of necessity in such cases ; and it is deemed best that such instrument should be used under all circumstances. Where the needle can be relied on, however, the ordinary compass may be used in subdividing and meander- ing. Whenever deputies use instruments with magnetic appa- ratus only, they must test the accuracy of their work and the condition of their instruments by at least three observations upon a circumpolar star, upon different days, between the com- mencement and close of surveying operations in any given township. Deputies using instruments with solar apparatus are not required to make observations of the star Polaris, but they must test their instruments by taking the latitude daily, weather permitting, in running base, standard, meridian, and range lines, and upon three different days, during the execution of subdivisional surveys in each township. They must make com- plete records in their field notes, under proper dates, of the making of all observations in compliance with these instructions, showing the style and condition of the instrument in use, and SURVEY OF THE PUBLIC LANDS. 301 the angle formed by comparing the line run with the meridian as determined by observations. (g) The construction and adjustments of all surveying in- struments used in the surveying of the public lands of the United States must be tested at least once a year, and oftener if necessary, by comparison with the true meridian, established under the direction of the surveyor-general of the district ; and the instruments must be so modified in construction, or in such a way corrected, as may be necessary to produce the closest possible approximation to accuracy and uniformity in the operation of all such instruments. A record will be made of such examinations, showing the number and style of the instru- ment, name of the maker, the quantity of instrumental error discovered by comparison, in either solar or magnetic apparatus, or both, and means taken for correction. The surveyor-general will allow no surveys to be made until the instruments to be used therefor have been approved by him. (ft) The township lines and the subdivision lines will usually be measured by a two-pole chain of 33.03 feet in length, con- sisting of 50 links, and each link being 7.92 inches long. On uniform and level ground, however, the four-pole chain may be used. The measurements will, however, always be represented according to the four-pole chain of 100 links. The four-pole chains must be adjusted to lengths of 66.06 feet, The object in adding six-hundredtlis of a foot to the 66 feet of a four-pole chain is to assure thereby that 66 feet will be set off upon the earth's surface without the application of a greater strain than about 20 pounds by the chainmen, thus providing for loss by vertical curvature of 'the chain, and at the same time avoiding the uncertain results attending the application of strains taxing its elasticity. The deputy surveyor must provide himself with a measure of the standard chain kept at the office of the sur- veyor-general, to be used by him as a field standard. The chain in use must be compared and adjusted with this field standard each working day ; and such field standard must be returned to the surveyor-general's office for examination when his work is 'ompleted. 302 PLANE SURVEYING. 352. Of Tally-Pins. You will use 11 tally-pins made of steel, not exceeding 14 inches in length, weighty enough toward the point to make them drop perpendicularly, and having a ring at the top, in which is to be fixed a piece of red cloth, or some- thing else of conspicuous color, to make them readily seen when stuck in the ground. 353. Process of Chaining. In measuring lines with a two- pole chain, every five chains are called a tally ; and in measur- ing lines with a four-pole chain, every ten chains are called a tally, because at that distance the last of the 10 tally-pins with which the forward chainman set out will have been stuck. He then cries "tally"; which cry is repeated by the other chain- man, and each registers the distance by slipping a thimble, but- ton, or ring of leather, or something of the kind, on a belt worn for that purpose, or by some other convenient method. The hind chainman then comes up, and having counted in the pres- ence of his fellow the tally-pins which he has taken up, so that both may be assured that none of the pins have been lost, he then takes the forward end of the chain, and proceeds to set the pins. Thus the chainmeu alternately change places, each setting the pins that he has taken up, so that one is forward in all the odd, and the other in all the even, tallies. Such pro- cedure, it is believed, tends to insure accuracy in measurement, facilitates the recollection of the distances to objects on the line, and renders a mis-tally almost impossible. 354. Levelling the Chain and Plumbing the Pins. The length of every line you run is to be ascertained by precise horizontal measurement, as nearly appi'oximating to an air line as is possi- ble in practice on the earth's surface. This all-important object can only be attained by a rigid adherence to the three following observances : Ever keeping the chain stretched to its utmost degree of ten- sion on even ground. On uneven ground, keeping the chain not only stretched as SURVEY OF THE PUBLIC LANDS. 303 aforesaid, but horizontally levelled. And when ascending or descending steep ground, hills, or mountains, the chain will have to be shortened to one-half its length (and sometimes more), in order accurately to obtain the true horizontal measurement. The careful plumbing of the tally-pins, so as to attain pre- cisely the spot where they should be stuck. The more uneven the surface, the greater the caution needed to set the pins. 355. Marking Lines. All lines on which are to be estab- lished the legal corner boundaries are to be marked after this method, viz. : Those trees which may intercept the line must have two chops or notches on each side of them, without any other marks whatever. These are called sight trees or line trees. A sufficient number of other trees standing within 50 links of the line, on either side of it, are to be blazed on two sides diagonally, or quartering toward the line, in order to render the line conspicuous, and readily to be traced, the blazes to be opposite each other, coinciding in direction with the line where the trees stand very near it, and to approach nearer each other the farther the line passes from the blazed trees. Where trees two inches or more in diameter are found, the required blazes must not be omitted. Bushes on or near the line should be bent at right angles therewith, and receive a blow of the axe at about the usual height of blazes from the ground sufficient to leave them in a bent position, but not to prevent their growth. 356. On Trial or Random Lines the trees are not to be blazed, unless occasionally, from indispensable necessity, and then it must be done so guardedly as to prevent the possibility^ of confounding the marks of the trial line with the true. But bushes and limbs of trees may be lopped, and stakes set on the trial or random line, at every ten chains, to enable the surveyor on his return to follow and correct the trial line, and establish therefrom the true line. To prevent confusion, the temporary stakes set on the trial or random lines must be pulled up when the surveyor returns to establish the true line. 304 PLANE SURVEYING. 357. Insuperable Objects on Line ; Witness Points. Under circumstances where your course is obstructed by impassable obstacles, such as ponds, swamps, marshes, lakes, rivers, creeks, etc., you will prolong the line across such obstacles by means of right-angle offsets ; or, if such be inconvenient, by a traverse or trigonometrical operation, until you regain the line on the opposite side. And in case a north and south, or a true east and west, line is regained in advance of any such obstacle, you will prolong and mark the line back to the ob- stacle so passed, and state all the particulars in relation thereto in your field-book. And at the intersection of lines with both margins of impassable obstacles you will establish a witness point (for the purpose of perpetuating the intersections there- with) , by setting a post, and giving in your field-book the course and distance therefrom to two trees on opposite sides of the line, each of which trees you will mark with a blaze and notch facing the post ; but on the margins of navigable watercourses or navigable lakes you will mark the trees with the proper number of the fractional section, township, and range. 358. The Best Marking-Tools adapted to the purpose must be provided for marking neatly and distinctly all the letters and figures required to be made at corners, Arabic figures being used exclusively ; and the deputy is always to have at hand the necessary implements for keeping his marking-tools in order. 359. Establishing Corners. To procure the faithful execu- tion of this portion of a surveyor's dutv is a matter of the utmost importance. After a true coursing and most exact measurement, the establishment of corners is the consummation of the work. If, therefore, the corners be not perpetuated in a permanent and workmanlike manner, the great aim of the sur- veying service will not have been attained. The following are the different points for perpetuating cor- ners, viz. : (a) For township boundaries, at intervals of every 6 miles. SURVEY OF THE PUBLIC LANDS. 305 (6) For section boundaries, at intervals of every mile, or 80 chains. (c) For quarter-section boundaries, at intervals of every half- mile, or 40 chains. Exceptions, however, occur, as fully set forth hereafter in that portion of the manual showing the man- ner of running township lines and method of subdividing. (d) Meander corners are established at all those points where the lines of the public surveys intersect the banks of such rivers, bayous, lakes, or islands, as are by law directed to be meandered. 360. Miscellaneous. When a rock in place is established for a corner, its dimensions above ground must be given, and a cross ( X ) marked at exact corner point. Where mounds of earth are raised " alongside " of corners on N. and S. lines, they must be placed on the W., and on the E. and W. lines on the N. side of corner. In case the character of the land is such that this cannot be done, the deputy will state in his notes instead of " alongside" " S." (on E.). In case where pits are practicable, the deputy prefers raising a mound of stone, or stone covered with earth, as more likely to perpetuate the corner ; he will use the form given for mound of stone, omitting the words "pits impracticable," and adding " covered with earth," when so established. Where the requisite number of trees can be found within 300 links of the corner point, three (3) bearing trees should be established for every standard or closing corner, four (4) for every corner common to four townships or sections, and two (2) for every quarter-section corner or meander corner. In case the requisite number cannot be found within limits, the deputy must state in his field notes, after describing those established, " no other trees within limits," and "dug pits in sees. & ," or " raised a mound of stone alongside." Stones 18 inches and less long must be set two-thirds, and over 18 inches long, three-fourths, of their length in the ground. No stones containing less than 504 cubic inches must be used 306 PLANE SURVEYING. for corners. Particular attention is called to the " summary of objects and data required to be noted," on pages and of these instructions, and it is expected that the deputy will thor- oughly comply with the same in his work and field notes. No mountains, swamp lands, or lands not classed as survey- able, are to be meandered, and all lines approaching such lands must be discontinued at the section or quarter-section corner. Where, by reason of impassable objects, the south boundary of a township cannot be established, an east and west line should be run through the township, first random, and then corrected, from one range line to the other, and as far south as possible, and from such line the section lines will be extended in the usual manner, except over any fractions south of said line, which may be surveyed in the opposite direction from the section corners on the auxiliary base thus established. When no part of the east or west boundaries can be run, both north and south boundaries will be established as true lines. Allowance for the convergency of meridians must be made whenever necessary.* All letters and figures cut in posts or trees must be marked over with red chalk to make them still more plain and durable. Township corners common to four townships, and section cor- ners common to four sections, are to be set diagonally in the earth, with the angles in the direction of the lines. All other corners are to be set square, with the sides facing the direction of the lines. The sizes of wooden posts, mounds, and pits, noted in foregoing descriptions of corners, are to be regarded as minimum, and whenever practicable to increase their dimen- sions, it is desirable to do so. In establishing corners, stones should be used whenever practicable ; then posts ; and lastly, mounds, with stake in pit. It is expected that deputy surveyors will carefully read and familiarize themselves with these instructions, and all others * See Table of Convergency of Meridians at end of chapter, and explanation of same. SURVEY OF THE PUBLIC LANDS. 307 contained in this volume, and will instruct their assistants as to their duties before commencing work. Extra copies will be furnished the deputies for the use of their assistants. 361. Standard Quarter-Section Corners on standard lines must be established in all respects like other quarter-section corners, with the addition of the letters S.C. ; and if bearing trees are established for such corners, each tree must be marked S.C. \ S.B.T. When a pit is dug at a meander corner, it must be 8 links from the corner on the side opposite the river or lake meandered. The letters M.C., for " meander corner," must be marked on the side facing the river or lake meandered. 362. A Witness Corner, in addition to the marks that would be placed upon the corner for which it is a witness, must have the letters W.C., and be established in all respects like such corner. If bearing trees are established for a witness corner, each tree must be marked W.C., in addition to the usual marks. 363. Meandering. Both banks of navigable rivers are to be meandered by taking the general courses and distances of their sinuosities. At those points, when either the township or section lines intersect the banks of a navigable stream, corners are to be established at the time of running these lines. These are called meander corners; and in meandering, you are to commence at one of these corners, coursing the banks, and measuring the distance of each course from your commencing corner to the next meander corner. By the same method, you are to meander the opposite bank of the same river. The crossing distance between meander corners on same line is to be ascertained by triang illation, that the river may be accurately protracted. Rivers not classed under the statute as navigable, but which are well-defined natural arteries of internal communi- cation, will only be meandered on one bank. 308 PLANE SURVEYING. All lakes, bayous, and deep ponds which may serve as public highways of commerce must be meandered. 364. Surveying. Initial points, from which the lines of the public surveys are to be extended, must be established when- ever necessary under special instructions, as may be prescribed in each case by the Commissioner of the General Land Office. The locus of such initial points must be selected with great care and due consideration for their prominence and easy identification, and must be established astronomically. The initial point having been established, the lines of the public surveys are to be extended therefrom as follows : 365. Base Line. The base line shall be extended east and west from the initial point by the use of solar instruments or transits, as may be directed by the surveyor-general in his special written instructions. Where solar instruments are used, the deputy must test said instruments in every 12 miles of line run, by taking the latitude, or by observation on the polar star ; and in all cases where he has reason to suppose that said instru- ment is in error, he must take an observation on the polar star ; and if error be found, must make the necessary corrections before proceeding with his survey. The proper corners shall be established at each 40 and 80 chains, and at the intersection of the line with rivers, lakes, or bayous that should be mean- dered, in accordance with the instructions for the establishment of corners. In order to check errors in measurement, two sets of chainmen, operating independently of each other, must be employed. Where transits are used, the line will be run by setting off at the point of departure on the principal meridians a tangent to the parallel of latitude, which will be a line falling at right angles to the said meridian. The survey will be continued on this, line for twelve (12) miles, but the corners will be estab- lished at the proper points by offsets northerly from said line, at the end of each half-mile. In order to offset correctly from SURVEY OF THE PUBLIC LANDS. 309 the tangent to the parallel, the deputy will be guided by the table of offsets and azimuths contained in the Manual of Instructions. As the azimuth of the tangent is shown, the angle thence to the true meridian at each mile is readily found, thus indicating the direction of the offset line. The computations are made for a distance of 12 miles, at the end of which observations on the polar star must be taken for the projection of a new tangent. The computations are also upon even degrees of latitude ; off- sets for intervening parallels can be readily determined by interpolation. Where offset distances quarter-section corners exceed 50 links, their direction to the parallel can be deter- mined in like manner by interpolation for azimuth. When said distances are less than 50 links, interpolation for determining the distances will not be required. 366. Principal Meridian. The principal meridian shall be extended north and south from the initial point, by the use of solar instruments or transits, as may be directed by the sur- veyor-general in his special written instructions. Where solar instruments are used, the line will be run in the same manner as prescribed for running the base line by solar instruments. Where transits are used, observations upon the polar star must be taken within each 12 miles of line run. In addition to the above general instructions, it is required that in all cases where the establishment of a new principal meridian seems to be necessary to the surveyor-general, he shall submit the matter, together with his reasons therefor, to the Commis- sioner of the General Land Office, and the survey of such prin- cipal meridian shall not be commenced until written authority, together with such special instructions as he may deem neces- sary, shall have been received from the Commissioner. 367. Standard Parallels. Standard parallels, which are also called correction lines, shall be extended east and west from the principal meridian, at intervals of every 24 miles north and south of the base line, in the same manner as pre- scribed for running the base line. 310 PLANE SURVEYING. Auxiliary Meridians. Auxiliary meridians shall be extended north and south from the base line, at intervals of every 24 miles east and west from the principal meridian, in the same manner as prescribed for running the principal meridian. It is contemplated that these base, principal meridian, stand- ard, and auxiliary meridian lines shall first be extended over the territory to be surveyed, and that afterwards township and section lines shall be run, where needed, within these tracts of 24 miles square, formed by the extension of these principal lines ; and each surveyor-general will therefore cause said prin- cipal lines to be extended as rapidly as practicable. 368. Exteriors, or Township Lines. The east and west boundaries of townships are always to be run from south to north on a true meridian line ; and the north and south boun- daries are to be run from east to west, or from west to east (according to the relation of the township to be surveyed with reference to prior surveys) , on a random or trial line, and cor- rected back on a true line. The distance north or south of the township corner to be closed upon, from the point of intersec- tion of these random lines with the east or west boundary of the township, must be carefully measured and noted. Should it happen, however, that such random line should fall short, or overrun in length, or intersect the east or west boundary more than three chains' distance from the township corner thereon, as compared with the corresponding boundary on the south (due allowance being made for convergency) the line, and if neces- sary the entire exterior boundaries of the township, must be retraced, so as to discover and correct the error. In running random lines, temporary corners are to be set at each 40 and 80 chains, and permanent corners established upon the true line as corrected back, in accordance with instructions, throw- ing the excess or deficiency on the west half-mile, as prescribed by law. Permanent corners are to be established, in accord- ance with instructions, on the east and west township bound- aries at the time they are to be run. Whenever practicable, SURVEY OF THE PUBLIC LANDS. 311 the township lines within these tracts of 24 miles square, must be surveyed in regular order from south to north; i.e., the exterior boundaries of the township, in any one range lying immediately north of the south boundary of such tract of 24 miles square, must first be surveyed, and the exteriors of the other three townships in said range extended therefrom, in regular order, from south to north ; and it is preferable to sur- vey first the entire range of townships in such tract adjoining the east boundary, or adjoining the west boundary, and the other three ranges in regular sequence. In cases, however, where the character of the land is such that this rule cannot be complied with, the' following will be observed. In extending the south or north boundaries of a township to the west, where the southwest or northeast corners cannot be established in the regular way by running a north and south line, such boundaries will be run west on a true line, allowing for convergency on the west half-mile ; and from the township corner established at the end of such boundary, the west boundary will be ruu north or south, as the case may be. In extending south or north of a township to the east, where the southeast or northeast corner cannot be established in the regular way, the same rule will be observed, except that such boundaries will be run east on a true line, and the ea.si.boundary run north or south, as the case may be. One set of chainmen only is required in running township lines. 369. Method of Subdividing. The first mile, both on the south and east boundaries of each township you are required to subdivide, is to be carefully traced and measured before you enter upon the subdivision thereof. This will enable you to observe any change that may have taken place in the magnetic variation as it existed at the time of running the township lines, and will also enable you to compare your chaining with that upon the township lines. Any discrepancy arising either from a change in the magnetic variation or a difference in measure is to be carefully noted in the field notes. 312 PLANE SURVEYING. After adjusting your compass to a variation which you have just found will retrace the eastern boundary of the township, you will commence at the corner to Sections 35 and 36, on the south boundary, and run a line parallel to the range line, 40 chains, to the quarter-section corner, which you are to establish between Sections 35 and 36 ; continuing on said course 40 chains farther, you will establish the corner to Sections 25, 26, 35, and 36. From the section corner last named, run a random line, with- out blazing, due east, for the corner of sections 25 and 36, on east boundary, and at 40 chains from the starting-point set a post for temporary quarter-section corner. If you intersect exactly at the corner, you will blaze your random line back, and establish it as the true line ; but if your random line inter- sects the said east boundary either north or south of said corner, you will measure the distance of such intersection, from which you will calculate a course that will run a true line back to the corner from which your random started. You will establish the permanent quarter-section corner at a point equidistant from the two terminations of the true line. From the corner of Sections 25, 26, 35, and 36, run due north between Sections 25 and 26, setting the quarter-section post, as before, at 40 chains, and at 80 chains establishing the corner of Sections 23, 24, 25, and 26. Then run a random due east for the corner of Sections 24 and 25 on east boundary ; setting temporary quarter-section post at 40 chains ; correcting back, and establishing permanent quarter-section corner at the equi- distant point on the true line, in the manner directed on the line between Sections 25 and 36. In this manner you will proceed with the survey of each suc- cessive section in the first tier until you arrive at the north boundary of the township, which you will reach in running up a random line between Sections 1 and 2. If this random line should not intersect at the corner established for Sections 1 , 2, 35, and 36, upon the township line, you will note the distance that you fall east or west of the same, from which distance you SUKVEY OF THE PUBLIC LANDS. 313 will calculate a course that will run a true line south to the corner from which your, random started. If the north boundary of a township is a base or standard line, the line between Sections 1 and 2 is to be run north as a true line, and the closing corner established at the point of intersection with such base or stand- ard line ; and in such case, the distance from said closing corner to the nearest section or quarter-section corner on such base or standard line must be carefully measured and noted as a " connection line." In like manner proceed with the survey of each successive tier of sections until you arrive at the fifth tier ; and from each section corner which you establish upon this tier you are to run random lines to the corresponding corners established upon the range line forming the western boundary of the township ; setting as you proceed each temporary quarter-section corner at 40 chains from the interior section corner, so as to throw the excess or deficiency of measurement on the extreme tier of quarter-sections contiguous to the township boundary ; and on returning establish the true line, and establish thereon the per- manent quarter-section corner. It is not required that the deputy shall complete the survey of the first tier of sections from north to south before commenc- ing the survey of the second or any subsequent tier, but the corner on which the random line closes must have been pre- viously established by running the line north on which it is established, except as follows : where it is impracticable to establish such section corner in the regular manner, it may be established by running the east and west line east or west, as the case may be, on a true line, setting the quarter-section corner at 40 chains and the section corner at 80 chains. Quarter-section corners, both upon north and south and upon east and west lines, are to be established at a point " equi- distant" from the corresponding section corners, except upon the lines crossing on the north and west boundaries of the town- ship, and in those situations the quarter-section corners will always be established at precisely 40 chains to the north or 314 PLANE SURVEYING. west, as the case may be, of the respective section corners from which those lines respectively start, by which procedure the excess or deficiency in the measurements will be thrown, according to law, on the extreme tier of quarter-sections. 370. Prescribed Limits for Closing, and Length of Lines in Certain Cases. Every north-and-south section line, except those terminating in the north boundary of the township, must be 80 chains in length. The east-and-west section lines, except those terminating in the west boundary of the township, are to be within 80 links of the actual distance established on the south boundary line of the township for the width of said tier of sections, and must close within 80 links north or south of the section corner. The north boundary and south boundary of any one section, except in the extreme western tier, are to be within 80 links of equal length. The meanders within each fractional section, or between two meander posts, or of an island in the interior of a section, must close within 1 chain and 50 links. In running random township exteriors, if such random lines fall short or overrun in length or intersect the eastern or west- ern boundary, as the case may be, of the township at more than 3 chains north or south of the true corner, the lines must be retraced, even if found necessary to measure the meridional boundaries of the township. One set of chain men only is required in subdividing. 371. Subdivision of Sections. Under the provisions of the act of Congress approved Feb. 11, 1805, the course to be pur- sued in the subdivision of sections is to run straight lines from the established quarter-section corners United States surveys to the opposite corresponding corners, and the point of inter- section of the lines so run will be the corner common to the several quarter-sections ; or, in other words, the legal centre of the section. SURVEY OF THE PUBLIC LANDS. 315 In the subdivision of fractional quarter-sections where no opposite corresponding sections have been or can be fixed, the subdivision lines should be ascertained by running from the established corners due north, south, east, or west lines, as the case may be, to the watercourse, Indian boundary line, or other external boundary of such fractional section. The law presupposes the section lines surveyed and marked in the field by the United States deputy surveyors to be due north and south or east and west lines, but in actual experience this is not always the case ; hence, in order to carry out the spirit of the law, it will be necessary in running the subdivisioual lines through fractional sections to adopt mean courses where the section lines are not due lines, or to run the subdivision line parallel to the section line where there is no opposite section line. Upon the lines closing on the north and west boundaries of a township the quarter-section corners are established by the United States deputy surveyors at precisely 40 chains to the north or west of the last interior section corners, and the excess or deficiency in the measurement is thrown on the outer tier of lots, as per act of Congress approved May 10, 1800. In the subdivision of quarter-sections, the quarter-quarter corners are to be placed at points equidistant between the section and quarter-section corners, and between the quarter corners and the common centre of the section, except on the last half-mile of the lines closing on the north or west boundaries of a township, where they should be placed at 20 chains, propor- tionate measurement, to the north or west of the quarter- section corner. The subdivisional lines of fractional quarter-sections should be run from points on the section lines intermediate between the section and quarter-section corners due north, south, east, or west, to the lake, watercourse, or reservation which renders such tracts fractional. When there are double sets of section corners on township and range lines, the quarter corners for the sections south of the 816 FLANE SURVEYING. township lines and east of the range lines are not established in the field by the United States surveyors, but in subdividing such sections said quarter corners should be so placed as to suit the calculations of the areas of the quarter-sections adjoining the township boundaries as expressed upon the official plot, adopt- ing proportionate measurements where the present measure- ments of the north or west boundaries of the sections differ from the original measurements. 372. Re-establishment of Lost Corners. The original cor- ners, when they can be found, must stand as the true corners they were intended to represent, even though not exactly where strict professional care might have placed them in the first instance. As has been observed, no existing original corner can be dis- turbed, and it will be plain that any excess or deficiency in measurements between existing corners cannot in any degree affect the distances beyond said existing corners, but must be added or subtracted proportionately to or from the intervals embraced between the corners which are still standing. 373. Summary of Objects and Data required to be Noted. The precise length of every line run, noting all necessary off- sets therefrom, with the reason and mode thereof. The kind and diameter of all bearing trees, with the course and distance of the same from their respective corners, and the precise relative position of ivitness corners to the true corners. The kind of materials of which corners are constructed. Trees on line. The name, diameter, and distance on line to all trees which it intersects. Intersections by line of land objects. The distance at which the line first intersects and then leaves every settler's claim and improvements; prairie, river, creek, or other " bottom "; or swamp, marsh, grove, and windfall, with the course of the same at both points of intersection ; also the distances at which you begin to ascend, arrive at the top, begin to descend, and SURVEY OF THE PUBLIC LANDS. 31? reach the foot of all remarkable hills and ridges, with their courses, and estimated height, in feet, above the level land of the surrounding country, or above the bottom lands, ravines, or waters near which they are situated. Intersection by line of water objects. All rivers, creeks, and smaller streams of water which the line crosses ; the distances on line at the points of intersection ; and their icidtlis on line. In cases of navigable streams, their width will be ascertained between the meander corners, as set forth under the proper head. The land's surface whether level, rolling, broken, or hilly. The soil whether first, second, third, or fourth rate. Timber the several kinds of timber and undergrowth, in the order in which they predominate. Bottom lands to be described as wet or dry ; and if sub- ject to inundation, state to what depth. Springs of water whether fresh, saline, or mineral, with the course of the stream flowing from them. Lakes and ponds describing their banks and -giving their height, and also depth of water, and whether it be pure or stagnant. Improvements towns and villages ; houses or cabins ; fields, or other improvements ; sugar-tree groves, sugar camps, mill seats, forges, and factories. Coal bank or beds ; peat or turf grounds ; minerals and ores, with particular description of the same as to quality and extent, and all diggings therefor ; also salt springs and licks. All reliable information you can obtain respecting these objects, whether they be on your immediate line or not, is to appear on the general description to be given at the end of the notes. Roads and trails, with their directions whence and whither. Rapids, cataracts, cascades, or falls of water, with the esti- mated height of their fall in feet. Precipices, caves, sink holes, ravines, stone quarries, ledges of rocks, with the kind of stone they afford. Natural curiosities, interesting fossils, petrifactions, organic 318 PLANE SURVEYING. remains, etc. ; also all ancient works of art, such as mounds, fortifications, embankments, ditches, or objects of like nature. The variation of the needle must be noted at all points or places on the lines where there is found any material change of variation ; and the positions of such points must be perfectly identified in the notes. Besides the ordinary notes taken on line (and which must always be written down on the spot, leaving nothing to be sup- plied by memory), the deputy will subjoin, at the conclusion of his book, such further description or information touching any matter or thing connected with the township (or other survey) which he may be able to afford, and may deem useful or neces- sary to be known, with a general description of the township in the aggregate, as respects the face of the country, its soil and geological features, timber, minerals, waters, etc. 374. Specimen Field Notes of the survey of the Third Standard Parallel North, through Range No. 21 east, of the principal base and meridian in the Territory of Montana, as surveyed by James Page, U. S. Deputy Surveyor. On the night of August 22, 1880, I took observation on the star Polaris, in accordance with instructions contained in the " Manual of Surveys," and drove pickets on the line thus estab- lished. Survey commenced August 23, 1880, with a Burt's Improved Solar Compass. Before commencing this survey, I test my compass on the line established last night, and find it correct. I begin at the standard corner to townships 13 north, ranges 20 and 21 east, which is a post, 4 inches square, marked : S.C., T. 13 N., on N. ; R. 21 E., S. 31, on E. ; and R. 20 E., S. 36, on W. faces, with 6 notches on N., E., and W. faces, and pits N., E., and W. of post, 6 ft. dist., and mound of earth around post. Thence I run SURVEY OF THE PUBLIC LANDS. 319 East, on S. boundary Sec. 31. Variation 20 E. Ascend. A point about 200 ft. above township cor. top of ridge. Set a sandstone 18 x 8 x 5 ins., 12 ins. in the ground, for standard ^ sec. cor. marked S.C. \ on N. face ; dug pits 18x18x12 ins. E. and W. of stone, 51- ft. dist., and raised a mound of earth 1^ ft. high. 31 ft. base alongside ; thence Enter pine timber. Set a sandstone 24 x 10 x 7 ins., 18 ins. in the ground for standard cor. to sees. 31 and 32, marked S.C. with 5 notches on E. and 1 notch on W. edges ; from which A pine, 12 ins. diam., bears N. 77 E., 41 Iks. dist., marked T. 13 N., R. 21 E., S. 32 B.T. ; A pine, 18 ins. diarn., bears N. 50 W., 20 Iks. dist., marked T. 13 N., R. 21 E., S. 31 B.T. ; A pine, 7 ins. diam., bears S. 30 W., 119 Iks. dist., marked T. 12 N., R. 21 E., S. 5 B.T. Land, high, mountainous, hilly, and rolling. Soil, sandy, gravel, and rocky ; 4th rate. Timber, pine, 23 chs. ; mostly dead and fallen. East on S. boundary Sec. 32. Through timber. Va. 20| E. Ravine, course S., about 30 ft. deep. Ravine, course S. 20 E., about 20 ft. deep. Set a sandstone, 18 x 14 X 5 ins., 12 ins. in the ground, for standard \ sec. cor. marked S.C., \ on N. face, and raised a mound of stone alongside. Pits, impracticable. Top of ridge, about 100 ft. high. Ravine, course S., about 40 feet deep. 320 PLANE SURVEYING. 80.00 Set a post, 4-- ft. long, 4 ins. square, with marked stone, 12 ins. in the ground, for standard cor. to sees. 32 and 33, marked : S.C., T. 13 N., R. 21 E., on N. ; S. 33, on E. ; and S. 32, on W. faces, with 4 notches on E. and 2 notches on W. faces, and raised a mound of stone 2 ft. high, 4^ ft. base, around post. Land, high and mountainous. Soil, sandy, gravelly, and rocky ; 4th rate. Timber, pine, and fir, 80 chs. ; mostly dead and fallen ; some thick undergrowth, same. 375. Specimen Field Notes of the survey of Township No. 6 north, Range No. 34 east, of the principal base and meridian of Montana Territory. chains. 16.40 40.00 79.96 39.98 79.96 East, on random line, bet. sees. 5 and 8. Va. 18 45' E. Over rolling ground. Road to Williamsburg, course S. Set temporary \ sec. cor. Intersected N. and S. line 6 Iks. N. of cor. to sees. 4, 5, 8, and 9. Thence I run N. 89 56' W. on true line, bet. sees. 5 and 8. with same Va. Set a post 3 ft. long, 3 ins. square, with marked stone, 12 ins. in the ground, for \ sec. cor. marked ^ S. on N. face ; dug pits, 18 x 18 x 12 ins. E. and W. of post 5 ft. dist., and raised a mound of earth. 1^ ft. high, 31 ft. base, around post. The cor. to sees. 5, 6, 7, and 8. Land, rolling. Soil, sandy ; 2d rate. No timber. SUUVKY OF THE PUBLIC LANDS. 321 West, on random line, between sees. 6 and 7. Over rolling ground. Road to Williamsburg, course S. Set temporary ^ sec. cor. Intersect west boundary of township 15 Iks. S. of cor. to sees. 1, 6, 7, and 12, which is a post, 4 ft. long, 4 ins. square, marked : T. 6 N.S. 6 on N.E. R. 34 E.S. 7 on S.E. R. 33 E.S. 12 on S.W., and S.- 1 on N.W. faces, with pits, 18 x 18 x 12 ins. in each sec., 5^ ft. dist., and mound of earth, 2 ft. high, 4 ft. base, around post. Thence I run S. 89 54' E. on a true line, bet. sees. 6 and 7, with same Va. Set a sandstone, 18 x 14 x 3 ins., 12 ins. in the ground, for |- sec. cor., marked \ on N. side; dug pits 18 x 18 x 12 ins. E. and W. of stone 5J ft. distant, and raised a mound of earth, 1 ft. high, 3 base, alongside. The cor. to sees. 5, 6, 7, and 8. Land, rolling. Soil, sandy ; 2d rate. No timber. North, on a random line, bet. sees. 5 and 6. Va. 18 45' E. Over rolling ground. Set temporary \ sec. cor. Intersect N. boundary of township 20 Iks. E. of cor. to sees. 5, 6, 31, and 32, which is a sandstone 30 x 12x6 ins., marked with 5 notches on E. and one notch on W. edges, and mound of stone, 2 ft. high, 4 ft. base, alongside. Thence I run PLANE SURVEYING. 40.05 80.05 S. 09' E. on a true line bet. sees. 5 and 6, with same Va. Set a sandstone, 16 X 12 x 3 ins. 11 ins. in the ground, for ^ sec. cor. marked \ on W. face ; dug pits, 18 x 18 x 12 ins., N. and S. of stone, 5 ft. dist., and raised a mound, of earth, 1^ ft. high, 3^ ft. base, alongside. The cor. to sees. 5, 6, 7, and 8. Land, rolling. Soil, sandy ; 2d rate. No timber. INCLINATION OF THE MERIDIAN.* 376. In projecting arcs of a great circle it is of the utmost importance that the surveyor be able to tell the inclination of the meridians for any latitude, and for II any distance of eastings or westings. In the following figure, let the two arcs AG and BG be two arcs of a quadrant of the meridian 1 of longi- tude apart. Let AB = the arc of 1 F of longitude on the equator = 69.16 miles. Let DE be an arc of longitude on any parallel of latitude. Also, let EH and DH be the tangents of those me- ridians meeting in the earth's axis produced, and corresponding to the parallel of latitude DE. Then the line EF=DF=cos 7, = cos AD or BE. Also, the angle DFE = 1, and the angle DHE = the inclination of * These articles on the inclination and convergency of meridians, and the table calculated in accordance therewith, are substantially those given in the 1886 catalogue of engineers' and surveyors' instruments, by Buff and Berger, Boston, Mass. SURVEY OF THE PUBLIC LANDS. 323 the meridians, which is the angle we wish to find, aud which we will represent by X. And because the two triangles FDE and DHE are on the same base ED, and isosceles, their vertical angles vary inversely as their sides ; and we have the equation, 1 x EF= X x EH. But EF = cos L, and EH = cot ; hence X cot L = 1 cos L, or X = cos L -T- cot L = sin L. (a) That is to say, The inclination of the meridians for any difference of longitude varies as the sine of the latitude. Since the sine of the latitude is the inclination in decimals of a degree, for one degree of longitude, if we multiply by 3600" we shall have the inclination in seconds of arc. Then, if we divide this by the number of miles in one degree of longitude on that latitude, we shall have the inclination due to one mile on that parallel. Thus, for Latitude 43 log. sin = 9.833783 Multiply by 3600" " = 3.556303 3.390086 Divide by 50.66m. = 1 long, on that L. log. = 1.704682 48.46" = inclination for one mile of long. 1.685404 The use of the inclination, as found by the preceding article, is to show the surveyor how much he must deflect a line of survey from the due east or west, to have it meet the parallel at a given distance from the initial point of the survey ; for it will be remembered that a parallel of latitude is a curve having the cosine of the latitude for its radius. And the line due east or west is the tangent of the curve. Thus, on latitude 43, it is desired to project a six-mile line west, for the southerly line of a township. Remembering that in an isosceles triangle the angle at the base is less than a right angle by half the angle at the vertex, deflect a line towards the pole by the inclination due to three H24 PLANE SURVEYING. miles, or in this case 48.46" x 3 = 2'.25" ; i.e., deflection = \ inclination. The table on next page, which was computed from the for- mula (a) above, gives the inclination for one mile, and for six miles on any parallel, from 10 to 60 of latitude; also the convergency for six miles, on any latitude. 377. The Convergency of the Meridian is readily found for any given distance from the corresponding inclination, by mul- tiplying the sine of the inclination by the given distance. Thus, for latitude 43, the inclination for one mile is 48.46"; the sine of which is 0.000235. This, multiplied by the number of links in a mile, which = 8,000, we have the convergency for one mile, = 1.88 links. Multiplying this by the number of miles in a township, = 36, and we have the convergenc}* for a township, = 67.68 links. In this manner were the convergeucies of the Table com- puted. 378. Deflection of Range-Lines from Meridian. The second column of the table shows the surveyor how much he must de- flect the range lines between the several sections of a township from the meridian, in order to make the consecutive ranges of sections in a township of uniform width, for the purpose of throwing the effects of convergency into the most westerly range of quarter-sections, agreeably to law. Thus, say between 45 and 55 of latitude, the inclination is practically 1' for every mile of easting or westing. Then, bear- ing in mind that in the United States the surveys are regarded as projected from the east and south to the west and north, the surveyor must project the first range-line between the sections of a township in those latitudes 1' to the left of the meridian. The second, 2' ; the third, 3' ; and so on to the fifth, which must be 5' to the left of the meridian on the east side of the township. By this means all the convergency of the township is thrown into the sixth, or westerly range of sections, as the law directs. SURVEY OF THE PUBLIC LANDS. 325 The fourth column of the table below shows the amount of this convergence- This column is also useful in subdividing a block of territory embraced by two standard parallels and two guide meridians into townships. Thus, starting a meridian from a standard parallel on latitude 43 N., for the western boundary of a range of township, say the first one west from the guide meridian, and running north, say four townships, the surveyor must make a point that is east of the six-mile point on the northern standard parallel, 4 x 67.7 links = 270. 8 links. The second meridian should fall 8 x 67.7 links to the right of the twelve-mile point. TABLE OF INCLINATION AND CONVERGENCY OF THE MERIDIANS. 13 2 Inclination for one mile. Inclination for six miles. Oonvergency for one township of 36 miles. Inclination for one mile. Inclination for six miles. Convergency for one township of 36 miles. Latitude. Inclination for one mile. 1 Inclination for six miles. Convergency for one township of 36 miles. o // / // LINKS. // / // LINKS. / // / // LINKS. 10 9.18 55 13.0 27 26.52 239 36.9 11 50.19 501 70.1 11 10.13 101 14.2 28 27.66 246 38.6 46 52.00 512 72.6 12 11.07 106 15.5 20 28.85 253 40.2 46 53.83 523 75.2 13 12.02 112 16.8 80 30.03 303 41.9 47 55.67 534 77.8 14 12.98 118 18.1 31 31.26 307 43.6 48 57.67 546 80.6 15 13.96 124 19.4 82 32.49 315 45.4 49 59.83 559 83.5 16 14.93 130 20.7 88 33.83 323 47.2 50 1 02.00 612 86.5 17 15.92 136 22.0 34 35.17 331 49.1 61 1 04.17 625 89.7 18 16.91 141 23.4 86 36.50 339 50.9 62 1 06.67 640 93.0 19 17.93 147 24.9 86 37.83 346 62.7 68 1 09.17 665 96.4 20 18.94 164 26.5 37 39.17 355 54.7 64 1 16.67 710 100.0 21 19.98 200 27.8 38 40.67 404 56.8 66 1 14.33 726 103.7 22 21.02 206 29.3 39 42.17 413 58.8 56 1 17.17 743 107.6 23 22.10 213 30.8 40 43.67 422 60.9 57 1 20.00 800 111.8 24 2.3.17 219 32.3 41 45.17 431 63.1 58 1 22.00 819 116.2 25 24.30 226 33.8 42 46.85 441 65.4 59 1 26.66 840 120.9 26 25.38 232 35.4 1:5 48.52 451 07.7 60 130.00 900 125.7 For details of instruction in United States Government Surveying, see Iliiwcs' System of "Rectangular Surveying," Kurt's "Key to Solar Com pass," and Clevenger's "Government Surveying." CHAPTER VII. CITY SUKVEYING. INTRODUCTION. 379. In the broadest sense, the duties of a city engineer in a large city are many and varied. His knowledge and judg- ment are required in the location of the city, the laying out of streets, and the fixing of suitable grades therefor, the establish- ment of a proper water supply, the designing of a suitable sys- tem of sewers, the improvement of the waterways, and the planning of necessary bridges and buildings. Following his judicial functions as a designer are his ministerial functions as a constructor. The field which is thus opened before him, in carrying into execution the plans for the various public works, is a very wide one. As the borough grows and expands into the metropolis, its needs in the directions mentioned increase until a division of labor and responsibility becomes expedient and necessary. In securing the best results in engineering practice, as in other work, the tendency is towards specialties ; so that in many cities, in order to secure the services of the best men, and also the best results, the numerous and important duties connected with city engineering have been separated. The province of this work, which is not a treatise on engineering, but on land sur- veying, makes it proper to treat in this chapter, as thoroughly as the intention and limits of the work allow, only what may be classed under the head of surveying, whether it be performed as the special work of the city or town surveyor, or as among the duties of the city engineer, the qualifications of the CITY SURVEYING. 327 former by no means fitting a man to perform the varied duties of the latter. Although this work is intended for the instruction of the student, not of the experienced surveyor, and hence in many things may go into details which to the latter may seem unim- portant, it is impossible in the limits of a chapter to impart a thorough knowledge of the duties of a citv or town surveyor, indeed, even to mention all his duties and the many operations and methods which only a long and varied practice can impart. General methods will be given and discussed, but any survevor of a practical turn of mind will have his own methods of per- forming much of the routine work pertaining to his situation. It is not in harmony with the plan of this work to go into the statement in this chapter of any elaborate theories regarding surveying and the instruments used therein, but to endeavor to give some methods which are found to be applicable in practice and to give good practical results. A thorough knowledge of any one good method of performing a certain work is of much more value to the student than a misty idea of numerous methods. Under the two leading heads of this chapter, field instruments and work and office instruments and work, theoretical discus- sions will not be entered into ; not because they do not possess much value, but because we conceive that they are not adapted to the student's present needs and most rapid advancement. Under the former head, in the light of the work which is likely to engage the greater part of the surveyor's time, field instru- ments and methods of using them will be described. Under the latter, the nature of office plans and records will be de- scribed, the instruments and methods used in the work of pro- ducing the plans having been described in other chapters. In dividing land and locating the boundaries between parties it is evident that the greater the value or the prospective value of said lands, the more delicate should be the instruments, and the more exact the methods used in the work. The methods and instruments which would for all practical purposes be suffi- ciently exact for the location of a line fence iu the country, 328 PLANE SURVEYING. where land might be purchased for Si 00 per acre, would not at all meet the requirements in locating in a city a line between two parties on land worth $100 per front foot. This fact becomes the more evident when we consider that the structures placed upon party lines in a city are so much more substantial and per- manent in their nature than those thus located in the country. To meet these considerations we shall find that while some of the methods of land surveying previously described in this work, and the instruments used therein, are applicable to the purposes of city surveying, many of the methods will be more exact, and the instruments more numerous and delicate. Following the plan heretofore pursued in this work, we will, before discussing the work of the city surveyor, describe the instruments (not described in previous chapters) of most gen- eral use in his work, and explain their adjustments and the general methods of using them. These instruments are the transit and rods, steel tapes, measuring-rods, pocket-thermome- ter, hand-level, spring-balance, plummet, Y-level, le veiling-rods, and rod-levels. SECTION I. INSTRUMENTS, THEIR ADJUSTMENTS AND GENERAL USES. A. FIELD INSTRUMENTS. 1 380. The Transit. Full description of the transit, its adjust- ment and uses, may be found in Chapter II. 381. As precision is the distinguishing feature of city and town surveying, the magnetic needle, which is usually found upon the transits, is in this work of but little use. Angles in carefully made surveys are now taken on the horizontal gradu- ated circle of the transit. The instructions already given in this work regarding the magnetic needle are sufficient reason for the TRANSIT, WITH GRADIENTER, LEVEL TO TELESCOPE, AND VERTICAL ARC, AS MADE BV YOUNG & SONS, PHILADELPHIA, PA. FIELD INSTRUMENTS. 331 above. It is, however, desirable that in each city and town the true meridian should be determined and permanently marked. Besides being useful in many other ways which will suggest themselves, it will be of great use as an aid in determining the situation of lines described by their bearings in old deeds, the date of the old survey being known. 382. The stadia-hairs * and vertical circle for stadia-measure- ments are useful attachments, and the telescope should by all means have a long level-tube attached, as this is of much use in city and town work in running grade lines and in levelling for short distances. . After the level and the manner of using it have been described, the operation of running a grade line will be explained. 383. Rods. Besides the usual iron-pointed wooden rods, very convenient rods, or pickets, for use with the transit, may be made of gas-pipe about three-quarters of an inch in diameter drawn out on one end to a point, and painted in alternate sections of red and white, red preferred to black because against red the cross-hairs can be seen. 384. It is b}- no means as easy a matter to run a straight line with a transit as at first thought it may seem to the student. After the selection of suitable weather, reversing at every ex- tension, care in handling the instrument, and with a correspond- ing degree of care on the part of assistants, the results are not always what the most careful would desire. 385. In marking a line with stakes, it is convenient to have stake-wood which, in cross-section, has one dimension greater than the other. If, in setting the stake, it always be placed with its broader side towards the instrument, its position will afterwards tell one at a glance in which direction the line was run. This is important when several stakes are set on different * See Articles 148 to 152, Stadia Measurements. 332 PLANE SURVEYING. lines near their intersection, as it will often be the means of avoiding confusion and the resulting errors. 386. Steel Tapes, etc. Before making an}- important meas- urements for a city or town, it is necessary, in order to avoid subsequent confusion, that a standard of measurement should be adopted. In many parts of an old city or town the intro- duction of a new standard would bring inextricable confusion. If there be a standard, even though it has not been carefully preserved, it should, if possible, be ascertained and regarded. When, however, it is at the option of the surveyor to select his standard, the United States standard should, as tending to uni- formity, be adopted in this country. Standard rods may be procured of the government. With these rods tape lines and other instruments used for a line purpose should be compared, and the variation noted. It is desirable, also, for purposes of comparison, that a standard, 50 feet or 100 feet, at a known temperature, should be carefully laid down with these rods in the corridor of some building, or in some other convenient place. Very accurate measuring may be done with graduated wooden rods properly shod with metal ends. These rods are necessarily of but moderate length ; hence, work with them is correspondingly slow. For city work, steel tapes are now in very general use ; and, when properly handled, give very satisfactory results. They are of different lengths and of different widths. For measur- ing full hundreds over tolerably level ground the narrow tape, -^ inch wide and 200 feet long, is very convenient. For general city use the 100-feet tape, f inch in width, is most convenient. 387. As a rule measurements will be made with the tape in a horizontal position. If not so held, the measurements will afterwai'ds be reduced to the horizontal. In order to determine the horizontal, a hand-level is used to ascertain the difference in elevation of the ground at the two ends of the tape. A cut and description of this convenient little instrument is given below. FIELD INSTRUMENTS. 333 Locke's Hand-Level consists of a brass tube about 6 inches long, having, as shown in the figure, a small level on top and near the object end, there being also an opening in the tube beneath, through which the bubble can be seen, as reflected by a glass prism, immediately under the level. Both ends of the tube are closed by plain glass settings to exclude the dust, and there is at the inner end of the sliding or eye tube a semicircu- lar convex lens, which serves to magnify the level bubble, and cross-wire underneath, while it allows the object to be clearly seen through the open half of the tube. The cross-wire is fastened to a little frame moving under the level-tube, and adjusted to its place by the small screw shown on the end of the level-case. The level of any object in line with the eye of the observer is determined by sighting upon it through the tube, and bringing the air-bubble of the level into a position where it is bisected by the cross-wire. A short telescope is sometimes applied in place of the plain glass ends, enabling levels to be taken at greater distances and with increased accuracy. If one or both ends of the tape be held up, the point on the ground vertically under the end of the tape will be determined by means of the plummet, which here needs no description further than to sav that its sides should make such an angle with each other as not to prevent the observer when using it from seeing its point ; neither should it be so long as to be unsteady. In all extended and important measurements regard must be had in using the steel tape to standard, temperature, sag, and wind . Before using a tape its relation to the standard should be 334 PLANE SURVEYING. determined by comparison with the standard, marked as pre- viously described, and the variation noted. 388. All important measurements, no matter at what tem- perature made, should be reduced to a standard temperature ; for if, at a certain temperature, we determined with a steel taue the distance apart of two points, at a higher temperature that distance on the same tape would be less because the tape is longer ; or, at a lower temperature, greater, because the tape is shorter. The temperature of the air at the time of measurement is ascertained by means of a small thermometer which can be exposed with the tape, and which is so protected that, when not in use, it can be safely carried in the pocket. The standard temperature to which all measurements should be reduced may be taken at pleasure. The correction for expansion and con- traction of the steel tape by heat and cold is 0.000006 per unit per degree F. 389. When the tape is held suspended, it will always sag in a vertical direction. Hence the horizontal distance between the extreme graduations will be less than if there were no sag. For this reason, when used to measure the distance between two points, it will, without correction, give a result too great; when used without correction to lay down a given distance, it will give it too small. While a formula may be derived by which to make a correction for sag, it will be found quite as satisfactory to determine it by actual trial. The amount of sag will of course depend upon the tension, or pull. This may be regulated by using at one end of the tape a small spring- balance. It is, however, very desirable that on important work the same men at the same ends of the tape should make all measurements. The experience gained in working together will be a most important factor in securing uniform results. The effect of wind is in the same direction as that of sag. While much of the work of the surveyor, particularly that in- volving short measurements, must be done regardless of wind, FIELD INSTRUMENTS. 335 no good results in long and important measurements can be secured in windy weather. The best correction for wind is to wait for a calm. In windy weather a narrow tape, as it ex- poses less surface to the wind, is useful. 390. To illustrate what has been said in regard to the correc- tions to be applied to measurements made with the steel tape, let us suppose two examples. First. With a steel tape 100 feet long (f inch wide) sus- pended each length at one or both ends, the temperature of the air being 79 F., the distance on the tape between two points is found to, be 550 feet 6| inches. If the tape is inch longer than the standard, and parts of its length propor- tionately longer, the standard temperature, 60 F., and the sag inch in 100 feet, what are the corrections, and what is the actual distance between the points ? On account of differing from the standard, as the tape is too long, the distance obtained is too short ; the correction for standard is therefore additive. On account of difference in temperature, the temperature being higher than the standard, as the tape is too long, the distance obtained is too short; the correction for temperature is therefore additive. On account of the sag, as the tape is thereby made too short, the distance obtained is too long ; the correction for sag is there- fore subtractive. Correction for standard : | in. x 5 = | in. additive. Correction for temperature (79 60 = 19) : 0.000006 ft. x 550 x 19 = 0.0627 ft. 0.0627 ft. x 12 = 0.7524 in. = |f in. additive. Correction for sag : in. x 5 = |f in. subtractive. Total correction : + M. in. _f_ i i n . _ II i n . = + T ^ in. additive. 336 PLANE SUE V EYING. Actual distance between points : 550 ft. 6J in. + fa in. = 550 ft. 6ff in. Second. Suppose it be required, other things being as before, to locate with the steel tape, when the temperature of the air is 52 F., two points which shall at the standard temperature be 225 feet 4 inches apart. What length on the tape must be taken ? Correction for standard : { in. x 2^ = -2 m - subtractive. Correction for temperature (60 52 = 8) : 0.000006 ft. x 225 x 8 = 0.0108 ft. 0.0108 ft, X 12 = 0.1296 in. = fa in. additive. Correction for sag : \ in. x 2 = ^| in. additive. Total correction : fa in. -f u 4 2 in - + it in - = +if in - additive. Length to be taken on tape : 225 ft. 4| in. + if in. = 225 ft. 4ff in. When the tape is not suspended, correction for sag will not be made. In short and less important measurements the same attention to corrections is not necessary. In practice, the above method has been found to give satis- factory results. 391. In placing stakes to hold measurements, it is best, and in harmony with the method suggested for placing them on instrument lines, to set them with the greater dimension of cross-section in the direction in which the measurement is being made. Measuring is a very important part of the work of the sur- veyor. Even when done with the greatest care, it is difficult to obtain results entirely satisfactory. FIELD INSTRUMENTS. 337 Measurements which are to be directly compared, or are to be used in connection, as in locating parallel lines, should be made under circumstances as nearly as possible identical. Experience and a correct idea of the importance of the work will enable the surveyor to determine the degree of accuracy therein necessary. LEV ELLING-lNSTRUMENTS . 392. The Y-LeveL Of the different varieties of the levelling- instrument, that termed the Y-level has been almost Universally preferred by American engineers, on account of the facility of its adjustment and superior accurac}*. The engraving represents a twenty-inch Y-level as made by W. and L. E. Gurley, Troy, N.Y. 393. The Telescope has at each end a ring of bell-metal, turned very truly, and both of exactly the same diameter ; by these it revolves in the wyes, or can be at pleasure clamped in any position when the clips of the wyes are brought down upon the rings, by pushing in the tapering-pins. 394. The Level or ground bubble tube is attached to the under side of the telescope, and furnished at the different ends with the usual movements, in both horizontal and vertical directions. The aperture of the tube, through which the glass vial appears, is about 5 inches long, being crossed at the centre by a small rib or bridge, which greatly strengthens the tube. The level-scale which extends over the whole length is graduated into tenths of an inch, and figured at every fifth division, counting from zero at the centre of the bridge ; the scale is set close to the glass. The bubble vial is made of thick glass tube, selected so as to have an even bore from end to end, and finely ground on its upper interior surface, that the run of the air-bubble may be uniform throughout its whole range. 340 PLANE SURVEYING. 395. The Wyes are made large and strong, of the best bell- metal, and each has two nuts, both being adjustable with the ordinary steel pin. The clips are brought down on the rings of the telescope- tube by the Y-pins, which are made tapering, so as to clamp the rings very firmly. The clip of one of the wyes has a little pin projecting from it, which, entering a recess filed in the edge of the ring, insures the vertical position of the level and cross-wire. 396. The Level-Bar is made round, of the best bell-metal, and shaped so as to possess the greatest strength in the parts most STibject to sudden strains. Connected with the level-bar is the head of the tripod- socket. 397. The Tripod-Socket is compound ; the interior spindle Z>, sectional view, upon which the whole instrument is sup- ported, is made of steel, and nicely ground, so as to turn evenlv and firmly in a hollow cylinder of bell-metal ; this, again, has its exterior surface fitted and ground to the main socket EE of the tripod-head. The bronze cylinder is held upon the spindle by a washer and screw, the head of the last having a hole in its centre, through which the string of the plumb-bob is passed. THE ADJUSTMENTS. 398. The three adjustments of the level which the surveyor usually has to attend to are the following ; 1. To adjust the line of collimation, or, in other words, to bring both wires into the optical axis, so that their point of intersection will remain on any given point during an entire revolution of the telescope. 2. To bring the level-bubble parallel with the bearings of the V-rings, and with the longitudinal axis of the telescope. FIELD INSTRUMENTS. 341 3. To adjust the wyes, or to bring the bubble into a position at right angles to the vertical axis of the instrument. 399. To Adjust the Line of Collimation, set the tripod firmly, remove the Y-pins from the clips, so as to allow the telescope to turn freely, clamp the instrument to the tripod-head, and, by the levelling and tangent screws, bring either of the wires upon a clearly marked edge of some object, distant from 100 to 500 feet. . Then, with the hand, carefully turn the telescope half-way around, so that the same wire is compared with the object assumed. Should it be found above or below, bring it half-way back by moving the capstan-head screws at right angles to it, remem- bering always the inverting property of the eye-piece ; now bring the wire again upon the object, and repeat the first operation, until it will reverse correctlv. Proceed in the same manner with the other wire until the adjustment is completed. Should both wires be much out, it will be well to bring them nearly correct before either is entirely adjusted. When this is effected, unscrew the covering of the eye-piece centring-screws, shown in the sectional view at AA, and move each pair in succession with a small screw-driver, until the wires are brought into the centre of the field of view. The inverting property of the eye-piece does not affect this operation, and the screws are moved direct. To test the correctness of the centring, revolve the telescope, and observe whether it appears to shift the position of an object. Should any movement be perceived, the centring is not perfectly effected. It may here be repeated, that in all telescopes the position and adjustment of the line of collimation depends upon that of the object-glass ; and, therefore, that the movement of the eye- piece does not affect the adjustment of the wires in any respect. 342 PLANE SURVEYING. When the centring has been once effected, it remains per- manent, the cover being screwed on again to conceal and protect it from derangement at the hands of the curious or inexperienced operator. 400. To Adjust the Level-Bubble. Clamp the instrument over either pair of le veiling-screws, and bring the bubble into the centre of the tube. Now turn the telescope in the wyes, so as to bring the level- tube on either side of the centre of the bar. Should the bubble run to the end, it would show that the vertical plane passing through the centre of the bubble was not parallel to that drawn through the axis of the telescope-rings. To correct the error, bring the bubble entirely back, with the capstan-head screws, which are set in either side of the level-holder, placed usually at the object end of the tube. Again bring the level-tube over the centre of the bar, and the bubble to the centre ; turn the level to either side, and, if necessary, repeat the correction until the bubble will keep its position, when the tube is turned half an inch or more to either side of the centre of the bar. The necessity for this operation arises from the fact that when the telescope is reversed end for end in the wyes in the other and principal adjustment of the bubble, we are not certain of placing the level-tube in the same vertical plane ; and there- fore it would be almost impossible to effect the adjustment without a lateral correction. Having now, in great measure, removed the preparatory difficulties, we proceed to make the level-tube parallel with the bearings of the Y-rings. To do this, bring the bubble into the centre with the levelling- screws, and then, without jarring the instrument, take the telescope out of the wyes and reverse it end for end. Should the bubble run to either end, lower that end, or, what is equiva- lent, raise the other by turning the small adjusting-nuts, on one end of the level, until by estimation half the correction is made ; FIELD INSTRUMENTS. 343 again bring the bubble into the centre, and repeat the whole operation, until the reversion can be made without causing any change in the bubble. It would be well to test the lateral adjustment, and make such correction as may be necessary in that, before the hori- zontal adjustment is entirely completed. 401. To Adjust the Wyes. Having effected the previous adjustments, it remains now to describe that of the wyes, or, more precisely, that which brings the level into position at right angles to the vertical axis, so that the bubble will remain in the centre during 1 an entire revolution of the instrument. To do this, bring the level-tube directly over the centre of the bar, and clamp the telescope firmly in the wyes, placing it, as before, over two of the levelling-screws, unclamp the socket, level the bubble, and turn the instrument half-way around, so that the level-bar may occupy the same position with respect to the levelling-screws beneath. Should the bubble run to either end, bring it half-way back by the Y-nuts on either end of the bar ; now move the telescope over the other set of levelling-screws, bring the bubble again into the centre, and proceed precisely as above described, changing to each pair of screws, successively, until the adjust- ment is very nearly perfected, when it may be completed over a single pair. The object of this approximate adjustment is to bring the upper parallel plate of the tripod-head into a position as nearly horizontal as possible, in order that no essential error may arise, in case the level, when reversed, is not brought precisely to its former situation. When the level has been thus com- pletely adjusted, if the instrument is properly made, and the sockets well fitted to each other and the tripod-head, the bubble will reverse over each pair of screws in any position. Should the surveyor be unable to make it perform correctly, he should examine the outside socket carefully to see that it sets securely in the main socket, and also notice that the clamp does not bear upon the ring which it encircles. 344 PLANE SURVEYING. When these are correct, and the error is still manifested, it will probably be in the imperfection of the interior spindle. After the adjustments of the level have been effected, and the bubble remains in the centre, in any position of the socket, the surveyor should turn the telescope in the wyes until the pin on the clip of the wve will enter the little recess in the ring to which it is fitted, and by which is insured the vertical position of the spirit-level and cross-wire. When the pin is in its place, the vertical wire may be applied to the edge of a building ; and in case it should not be parallel with it, two of the cross-wire screws that are at right angles to each other may be loosened, and by the screws outside, the cross-wire ring turned until the wire is vertical ; the line of col- limation must then be corrected again and the adjustments of the level will be complete. 402. To Use the Level Set the legs firmly into the ground. The bubble should then be brought over each pan- of levelling- screws successively and levelled in each position, any correction that may appear necessary being made in the adjustments. Bring the wires precisely in focus and the object distinctly in view, so that all errors of parallax may be avoided. This error is seen when the eye of an observer is moved to either side of the centre of the eye-piece of a telescope, in which the foci of the object and eye-glasses are not brought precisely upon the cross-wires and object ; in such a case the wires will appear to move over the surface, and the observation will be liable to inaccuracy. In all instances the wires and object should be brought into view so perfectly that the cross-wires will appear to be fastened to the surface, and will remain in that position however the e % ye is moved. Care should be exercised during an observation, last the hand touching the instrument inadvertently, or a foot placed near the leg of the tripod, impair the adjustment. The weight of a level having a 20-inch telescope, with level- NEW YORK. P LEVELLING-RODS. FIELD INSTRUMENTS. 347 ling-head, exclusive of the tripod, is between thirteen and four- teen pounds. IiEVELLING-RODS . 403. The various levelling-rods used by American engineers are made in two or more parts, which slide from each other as they are extended in use. 404. The New York Rod. This rod, which is shown in the engraving as cut in two, so that the ends may be exhibited, is made of maple, in two pieces, but sliding one from the other, the same end being always held on the ground, and the gradu- ations starting from that point. The graduations are made to tenths and hundredths of a foot, the tenth figures being black, and the feet marked with a large red figure. The front surface, on which the target moves, reads to 6 feet ; when a greater height is required, the horizontal line of the target is fixed at that point, and the upper half of the rod, carrying the target, is moved out of the lower, the reading being now obtained by a vernier on the graduated side, up to an elevation of 12 feet. The target is round, made of thick sheet brass, having, to strengthen it still more, a raised rim, which also protects the paint from being defaced. The target moves easily on the rod, being kept in any posi- tion by the friction of the two flat plates of brass which are pressed against two alternate sides, by small spiral springs, working in little thimbles attached to the baud which surrounds the rod. There is also a clamp-screw on the back, by which it may be securely fastened to any part of the rod. The face of the target is divided into quadrants by horizontal and vertical diameters, which are also the boundaries of the alternate colors with which it is painted. 348 PLANE SURVEYING. The colors usually preferred are white and red ; sometimes white and black. The opening in the face of the target is a little more than a tenth of a foot long, so that in any position a tenth or a foot figure can be seen on the surface of the rod. The right edge of the opening is chamfered, and divided into ten equal spaces, corresponding with nine-hundredths on the rod ; the divisions start from the horizontal line which separates the colors of the face. The vernier, like that on the side of the rod, reads to thou- sandths of a foot. The clamp, which is screwed fast to the lower end of the upper slid ing-piece, has a movable part which can be brought by the clamp-screw firmly against the front surface of the lower half of the rod, and thus the two parts immovably fastened to each other without marring the divided face of the rod. 405. The Philadelphia Rod. This rod is made of two strips of cherry, each about f inch thick by l inches wide and 7 feet long, connected by two metal sleeves, the lower one of which has a clamping-screw for fastening the two parts together when the rod is raised for a higher reading than 7 feet. Both sides of the back strip and one side of the front one are planed out -fa inch below the edges ; these depressed sur- faces are painted white, divided into feet, tenths and hundredths of a foot, and the feet and tenths figured. The front piece reads from the bottom upward to 7 feet, the foot figures being red and an inch long, the tenth figures black and eight-tenths of an inch long. When the rod is extended to full length, the front surface of the rear half reads from 7 to 13 feet, and the whole front of the rod is figured continuously and becomes a self-reading rod 13 feet long. The back surface of the rear half is figured from 7 to 13 feet, reading from the top down ; it has a vernier also by which the rod is read to two-hundredths of a foot as it is extended. The target is round and made of sheet-brass, raised FIELD INSTRUMENTS. 349 on the perimeter to increase its strength, and is painted in white and red quadrants ; it has also a scale on its chamfered edge, reading to tvvo-hundredths of a foot. When a level of less than 7 feet is desired, the target is moved np or down the front surface, the rod being closed together and clamped ; but when a greater height is required, the target is fixed at 7 feet and the rear half slid out, the scale on the back giving the readings like those of the target to two- hundredths of a foot. This rod is so graduated that the leveller is enabled to take the reading direct from it, the rodman's duties being simply to hold the rod vertical over the points. It is hence called a self- reading or speaking rod. 406. The Rod-Level. The figures below represent a level re- cently devised, for the more accurate plumbing of levelling-rods. ROD-LEVEL. ROD-LEVEL AS APPLIED TO A ROD. The left-hand figure shows it when folded for convenience in carrying. Its convenience and value commend it to general favor. 407. Levelling is measuring in a vertical direction. In his treatise on levelling, Frederick W. Simms says: "Levelling is the art of tracing a line at the surface of the earth which shall 350 PLANE SURVEYING. cut the directions of gravity everywhere at right angles. . . . The direction of gravity invariably tends towards the centre of the earth, and may be considered as represented by a plumb- line when hanging freely, and suspended beyond the sphere of attraction of the surrounding objects. . . . The operation of levelling may be defined as the art of finding how much higher or lower any one point is than another, or, more properly, the difference of their distances from the centre of the earth." A surface like that of still water may be called a level sur- face. The curve formed by the intersection with such a sur- face of a vertical plane is a line of true level; a line tangent to the latter is a line of apparent level. Levelling is the art of determining the differences of elevation of two or more points, or of determining how much one point is above or below a line of true level passing through the other point. 408. From the foregoing it is evident that, on account of the curvature of the earth, a horizontal line is not really through- out its length a level line ; that of two points in the same level line each will have its own horizon. Hence, in levelling, the effect of the curvature of the earth upon the comparative eleva- tions of different points must be taken into consideration. The effect of the curvature is to make objects appear lower than they really are. The air nearer the surface of the earth is denser than that farther removed from the surface. This difference in density, causing refraction of light, will affect the elevation of a point as observed through the telescope of a level, so that it also must be taken into consideration. Its effect is to make objects appear higher than they really are. The error caused by refrac- tion is one-seventh as great as that caused by curvature. Let us first find an expression for the correction due to the curvature of the earth. That is 409. To find the deviation from its tangent of a line of true level. LEVELLING. 351 Let represent the centre of the earth, PN a line of true level, and PN' its tangent, or a line of p , apparent level. The distance NN' cor- responding to the length of sight PN is required. From Geometry, PN 1 '^ NN'(2 ON+NN') ; PN~' 2 20N+NN' For ordinary distances, the length of the arc may be regarded as that of the tangent, and NN' as inconsiderable in comparison with 2 ON, the diameter of u the earth. Therefore, calling the length of sight d, the cor- rection c, and the radius of the earth r, we have d 2 and the correction for refraction ~7 C ~7 X 2r~14r' then the correction due to curvature and refraction, which we will call (7, is _!=_.*., 7 2r Ur or, This correction must be added to the height of the object as found by the level. In practice, the necessity for using the above formula is avoided whenever it is possible to set the level at equal dis- tances from the points whose difference of height is required. 352 PLANE SURVEYING. EXERCISES. 1. Assuming the diameter of the earth 7,926 miles, show that for a mile sight c = about 8 inches. Find the value of C for the same distance. 2. What is the correction due to curvature for half a mile? 3. What is the length of sight when C equals one-tenth of a foot? 4. Show that, practically, the correction for curvature in feet is equal to two-thirds the square of the distance in miles. 410. If two points Jf, JV, whose difference of elevation is required, can be observed upon from some point P about equi- distant * from them, not necessarily in their line, set up the level at P, and note the reading of a rod held vertically over each point. The difference of the two readings will indicate the difference of level required. 411. If the above method is impracticable, set up the instru- ment at some point P either in or out of the line, no matter which from which a rod may be observed on the first station M, and also on another point in the direction of N, about equi- distant with M from the instrument. Remove the level to a * Placing the instrument in this position lessens the effects of inaccurate adjustment and renders unnecessary the corrections indicated in Article 409. LEVELLING. 353 new position P', whence observe again the rod on 0, also the rod reading at N. The difference between the readings of the rod at M and shows how much higher the latter is than the former, and in like manner the difference of the readings at and JV gives the differ- ence in elevation of these points, and so on, no matter what the number of stations. The difference in height of M and N = Mm Go + Oo' Nn ; or, Mm + Oo' Oo - Nn = Mm + Oo' (Oo + Nn) . Calling Mm and* Go' back-sights, and the other two, fore- sights, we perceive that the difference of level of two points is shown by subtracting the sum of the fore-sights from the sum of the back-sights. 412. Again, in levelling, we measure, by means of the rod, how much lower than the line of sight (height of instrument) certain points are. Thus we may determine the relative eleva- tions of the points. Suppose, for example, it be required to determine the difference in elevation of any two points. For reasons already given, set the level equally distant from the points. If this cannot be done, and both observations have to be taken from one of the stations, especially if the distance between them is considerable, correction as previously described must be made. But in this case suppose it is possible ; and suppose that when held on one point, the rod reads 7.255 ; that is, this point may be considered 7.255 below the line of sight, and 4.755 when held on the other; then the first may be con- sidered 7.255 4.755, or 2.500 farther than the second below the line of sight, or lower than the second. 413. Suppose it be required to determine the difference in elevation between two points, of which one is so much higher than the other that the rod is too short to give a reading on both points for one position of the instrument. In such a case 354 PLANE SURVEYING. one or more auxiliary points, called turning-points (T.P.), must be used, and their relative elevations determined. Sup- pose the reading on the first point is 0.824, and on a turning- point is 10.432 ; the latter is then 9.608 below the former. Now the instrument must be moved and set up so as to obtain a reading on the turning-point ; and (we will suppose) on the other of the given points. Suppose that on the former it is 1.302, and on the latter 8.634 ; the latter is then 7.332 below the turning-point, or 9.608 + 7.332, or 16.940, below the first of the two given points. The first sight taken after setting up the level is called a back-sight, or plus sight ; those taken after this, and before the instrument is moved, are called fore-sights or minus sights. As the difference of the readings of the rod on two points gives their difference of elevation, the difference of the sum of the plus sights, and the sum of the minus sights on T.P.'s and the last point will give the difference in elevation of the extreme points. In the above example 0.824 10.432 1.302 8.634 2.126 19.066 19.066 - 2.126 = 16.940, as before. This is used as a check on level-notes. In extended levelling, permanent elevations fixed during the progress of the work for future reference are called bench marks or benches (B.M.). 414. In levelling, it is customary to refer all elevations to an assumed level plane, called the plane of reference, the datum plane, or simply the datum. Points are then said to be so much above or below the datum. As this plane may be assumed at pleasure, it is generally so taken as to be lower than any point whose elevation is to be determined. In city levelling this plane may be assumed at the height of mean low water. LEVELLING. 355 which elevation may be called zero. Then a point which has the elevation 125.37 will be 125.37 above low water. If two points have the elevations 125.375 and 105.213 respec- tively, the former is 125.375 105.213, or 20.162 higher than the latter. The datum having once been determined, its elevation, or that of a point a known distance above it, should be perma- nently fixed for future reference and comparison. 415. The levels for profile given under Street Grades, on page 365, show how the field notes in levelling ma}' be kept. The elevation of the bench-mark from which they start is 51.415 above the datum. The first plus sight is 7.030, which, added to 51.415, gives 58.445, the height of the instrument (H.I.) above the datum. The first minus sight, which is on a turning-point (T.P.), is 0.870, which, subtracted from 58.445, gives 57.575, the height of the T.P. above the datum. The instrument is then moved, set up again in a convenient place, and the work proceeds. At one setting of the instrument, the elevations of any points, besides the turning-point, which are not too high or too low to be reached, may be ascertained. It is evident that if any error be made at a T.P., all the following elevations will thereby be affected ; but if made at one of these other points, only the elevation of that point will be affected. Hence the importance of careful observations at T.P's. In the above-mentioned form for the keeping of the field notes, all the observations (Obs.) are set in one column. If desired, plus sights and minus sights may be set in different columns ; and of minus sights, those on turning-points may be set in a column by themselves. It will then be easy to apply the check before described. However, the form given is in practice very convenient. EXERCISE. Tabulate in both of the above forms, also in the form headed 356 PLANE SURVEYING. ELEVATION. REMARKS the following level notes : Height of B.M 100.000. Obs. on B.M 5.132. " " Sta. 6.28. " " * 1 7.12. " '" " 2 8.84. " " T.P. 3 9.780. From new position of inst. obs. on Sta. 3, 2.160. Obs. on Sta. 4 5.89. " " " 5 7.92. " " " 6 ......... 10.18. " T.P. 7 12.020. Again on " 7 1.260. Obs. on Sta. 8 4.23. " M .>*... 9 5.87. " " " 10 6.94. 416. Wind and sunshine affect the accuracy of levelling, as of work with the transit. For very good work it is desirable to have a calm day on which the sun is obscured by clouds. In addition to a proper manipulation of the instrument, the sights should not be longer than from 200 to 300 feet, the rod should be held vertical, and the rod man should select for turning-points good and firm points on stones, pegs, etc., on which the rod may be freely turned or spun around. 417. Numerous bench-marks should be located in convenient places. In -a city such places are at the intersections of streets, on door-sills of buildings which have become thoroughly settled, on roots of trees, etc. There are many other suitable places which will suggest themselves. LEVELLING. 357 418. In city work, in making a circuit of levels for the establishment of grade elevations and bench-marks, the work should check out with no greater error than 0.01 foot in three miles. In levelling, as in all other work, regard must be had to the difference between actual mistakes, the results of carelessness, and the degree of accuracy actually obtainable by the observer. We will now describe a general method of running a grade- line with the transit. In the figure the irregular line represents the profile of the ground, and the straight line the grade-line. Let it be required to run a grade-line from ^4, elevation 30.29, to B, elevation 28.79 ; elevation of ping or ground at A 33.49, at B 27.26 ; therefore cut at A 3.20 and fill at B 1 .53. Set the transit over A ; and, using the long level-tube, take the elevation from a convenient bench. Suppose the H.I. is found to be 38.21 ; then the length of the rod for marking the grade-line (called working height) is 38.2130.29 = 7.92. The rod will then be taken to B and held on the plug. But as the plug is 1.53 below the grade-line at B, the target, when the rod is held for grade on that plug, will be set at 7.92 -f 1.53 = 9.45. When thus held, the observer will set the horizontal cross-hair on the middle of the target and clamp the telescope. The line of sight will then be a line parallel with the grade-line and 7.92 above it. Care must be taken to use the rod 7.92, and 358 PLANE SURVEYING, not 9.45, as the working height. Measurements may now be made from the line of sight to determine the cut to the grade- line at any intermediate point. Suppose at C the rod read 5.97 ; then the cut at that point is 7.92-5.97 = 1.95. How would you proceed if the instrument were set at B1 The cuts or fills to grade at any points may be determined by taking the elevations of the ground at those points and calcu- lating the grade elevations at the same points. The difference of elevation will be the cut or fill required. B. OFFICE INSTRUMENTS. 419. In addition to the various drawing-instruments previ- ously described the student should understand the use of that elegant instrument the polar planimeter. In ascertaining the areas of figures having irregular boundaries it will be found extremely useful. He should also become acquainted with the different methods for the rapid reproduction of drawings. SECTION II. WORK. 420. The work of the city surveyor may be divided into two classes : first, public work, or that which he is called upon to perform for the city government ; second, private work, or that which he performs for private citizens. The former is generally connected with the streets ; the latter, with the prop- erty between them. Again, all of his work may be classed as field work or office worlr, the former of which we will now consider. A. FIELD WORK. 421. Public Work. There are many and varied natural features and artificial influences affecting the original location FIELD WORK. 359 of a town or city. To the thoughtful student many of these will readily suggest themselves. While in the choice of a site the surveyor may have a voice, it is more than probable that his work will commence upon a site already selected. We will now describe some of his more important duties as performed for the town or city government. 422. Street Lines. The city consists of streets for public use, and of the blocks bounded by them, the land in which is divided and sold to individuals for their private use. Hence we have first to consider the general plan or arrangement of the streets, their widths (the distances between house lines), and their distances apart. There are many general plans which may be adopted, or may be used as the foundation for new ones. When general convenience and the economical division of property are considered, I believe there is none which better meets the requirements than that which is characterized by two systems of parallel streets crossing at right angles. With this general arrangement, and some well-located diagonal avenues, we have the lay-out of a beautiful and convenient city. The general directions of the streets should be such that the greatest number may during the day be visited by the sunshine. This will be accomplished if one set of parallel streets runs in a northeasterly and southwesterly direction. Every important street should be at least 60 feet wide, while some of the main streets should be at least 100 feet wide, with avenues even wider. The streets will then admit freely air and sunshine, which latter is too often in narrow streets cut off by tall buildings ; while the avenues will be in harmony with their design as elegant thoroughfares. Another important consideration which affects the width of streets is the expense of paving and of keeping them in order. The distances of the streets from each other will vary very much) according to the purposes for which the included prop- erty is to be used, and how it is to be divided. Thejf may vary 360 PLANE SURVEYING. from 300 to 600 feet. The sidewalks will be from one-fifth to one-fourth of the width of the streets. In small towns an elaborate design will not be attempted ; but it is alwa3"s best to have in view the possibilities of future growth. 423. With the transit', the surveyor will run and extend street lines, and will turn off required horizontal angles on the horizontal graduated circle of that instrument. It is convenient to work upon the centre lines of the streets. Two base lines having been carefully located at right angles with each other, the centrelines of the two sets of streets will, with the most reliable measuring-instruments at the disposal of the surveyor, be carefully located parallel with them respectively. If the land is quite level, a 200-foot steel tape is useful. If it be inclined and irregular, a 100-foot tape is better suited to the purpose. In any case, the hand-level, plummet, ther- mometer, etc., should be used. The work, like all work of the surveyor, should be carefully checked by a test of the different angles and distances. All this work should be done with the greatest care. It is desirable, in order to guard against future difficulties in regard to measurements by other pai-ties, to make streets and block distances a little full; that is, greater than they are actually required to be say about one-fourth of an inch in 100 feet. As the work pro- gresses, it will be properly marked with stakes, as before described. After the satisfactory location of the centre lines of the street, the house lines may easily be located therefrom. 424. The work of the surveyor may be not in laying out and regulating a new town, but in connection with one already laid out. The extensions of the old town may be carried on in harmony with the plan already existing, or they may be on a plan altogether different, and after the manner already described for a new town. He will find that the already built-up portions of the town have been previously regulated, or that they have FIELD WORK. 361 not been. If they have been, it is advisable in carrying on the work therein to adhere as closely as possible to established lines, elevations, standard of measurement, etc., lest any altera- tions should lead to expensive and unnecessary legal complica- tions. If the town has never been regulated, the first steps will be to regulate its streets. In doing this a complete survey will be required. Instrument lines will be carefully located with the transit on all streets, and the angles at their intersec- tions determined. These lines will be the basis for the location, by offsets, of all buildings, fences, etc. As the survey goes on, the results will be carefully plotted to a conveniently large scale ; and from the completed plot, an advantageous location of the streets may be determined upon. They will then be located upon the ground to correspond. All important measurements will be made, as before described, with the steel tape, with all the corrections carefully attended to. Offsets to fences, etc., need not be made with so much care, and the corrections will, as a rule, be superfluous. During the progress of the work in an old town, as in a new one, all important lines will be carefully marked with stakes, and upon permanent objects, as houses, etc. 425. The streets in any 'city or town having been satisfac- torily located according to the general plan, it is necessary, in order to preserve work already done, and to prevent conflict in future work, that the location of the street lines should be pre- served. On account of the perishable nature of wooden stakes, and the fact that they may soon be disturbed, it is necessary to use something more permanent. This is generally found in stones. Mere stones, or monuments used for permanently hold- ing the lines of streets, are differently located and are of differ- ent sizes, depending upon then- location. Sometimes they are placed in the sidewalks 5 feet from the house lines. Then they need not be more than 4 or 5 inches square and 2 feet in length. The line is determined by a small hole drilled in the top of the stone. Sometimes the top of the stone is placed below the surface of the pavement ; sometimes it is placed flush 362 PLANE SURVEYING. therewith. Larger stones set in the intersections of the streets, where their centre lines cross, are very conveniently situated for use, and afford a very satisfactory means of marking street lines. On account of their more exposed position, they must be larger than those previously described, and should be set with the greatest care, the materials around them being well packed and rammed. They should be paved about and well protected from danger from traffic. The stones should be square in cross-section about 3 feet long, about 8 inches square on the top, and about 1 foot square on the bottom, the top and bottom being at right angles with the axis of the stone. The line is determined as before by a hole drilled in the top of the stone. From their situation we call these stones centre stones. It is well also to mark substantial buildings standing at the corners of streets with their distances from the house lines of the streets, these distances having been carefully determined by measurements. In general, a line having once been deter- mined upon as satisfactory, every available means should be employed to preserve its location, as any change would ob- viously be attended with inconvenience and danger. 426. Street Grades. In the selection of a site for a town, and in the location of the streets of a town or city, a topo- graphical map will be of much service. This map will show at a glance the shape of the ground under consideration. If the surface of the earth were cut by horizontal planes 5, 10, 20, or more feet apart, and the curves in which these planes intersect the surface were projected upon a horizoual plane, the resulting lines would be called contour lines or contours. These curves would represent points of the same elevation. Their distances apart would represent relative inclination in the ground, the curves being nearer as the ground is steeper. The determina- tion of these contours is an important feature in topographical surveying. In addition to its other uses, such a map would be of service in locating sewers, also in fixing proper elevations and grades for streets. The field work necessary in the prep- FIELD WORK. 363 aratiou of topographical maps, which we will briefly notice, may bo done as follows : Two sets of parallel lines having been located at right angles with each other by means of the transit and tape, the level will be set up, and a number of points at any one elevation above the datum found with the level and the rod, and their locations with reference to the two sets of lines determined. Another set of points as far above or below the former as the planes are apart will in like manner be deter- mined and located, and so on until the entire ground has been gone over. The above method of topographical surveying in determining contours is not a very rapid one. The stadia method is more rapid, and is well adapted to large areas. In addition to the usual horizontal cross-hair in the transit, two others are introduced, one above and one below the former. The instrument has also a vertical circle. The stadia-hairs are so arranged that when the level rod is held at a certain distance from the transit, a certain number of feet on the rod is included between them. The distance of any point from the instrument can be determined, as it varies with the number of feet inter- cepted on the rod. The line of sight must be at right angles to the rod ; if it is not, a calculation must be made to deter- mine the distance. By this distance and a horizontal angle the point is located horizontally.* The elevation of the point above the station at which the instrument is placed is obtained by observing on the rod a point as much above the ground as the telescope is, and taking the vertical angle. The product of the horizontal distance and the tangent of the angle will give the required difference in elevation. The plane table also has been much used in making topographical surveys. Street grades themselves will be determined upon in the office, after the necessary data has been obtained in the field 427. A very convenient method of obtaining the data neces- sary for the determination of elevations and grades for the streets is to obtain a continuous profile of the ground on the * See Chapter II., Stadia Measurements, Articles 148-152. 304 PLANE SURVEYING. centre line of each street. The work is done in the following manner : The level having been set up, and the height of instrument determined from a convenient bench-mark, an elevation will be taken on a level plug set at the intersection of the centre lines of two streets. Elevations will then be taken at stations, say 50 feet apart, about on the centre line, ' measurements with the tape being commenced at the inter- section before mentioned, and made carefully enough to avoid any error that might affect the work. In addition to the eleva- tions at the stations, elevations should be taken at any interme- diate points where the shape of the ground abruptly changes ; and the points should be located by measurement. These intermediate points are called pluses. When the next inter- section is reached, measurements will be commenced anew, and the levelling continued in the same manner. Elevations on level plugs at intersections, on turning-points, and on benches, which, if not previously established should be established as the work progresses, should be carefully taken with the target. The elevations for the profile should be read without the target to the nearest hundredth. Such circuits should be made in levelling for profiles, and the levelling on the cross-streets should be so carried on as to check the work in every wa} 7 . The level notes, taken as described for the profile of the centre line of a street, are shown below. They are from actual prac- tice. The datum is mean low water in the River, the elevation of which is taken as zero. The manner of plotting these notes, and of determining grade lines is given under the head Office Work. 428. In order to avoid errors in giving grade lines, the grade elevations at the intersections of streets should be per- manently marked. This may be done by placing the centre stones before described so that their tops shall be at the grade elevation. In order to preserve these elevations in case of the removal or disturbance of the stones, bench-marks should be established on convenient door-sills, and in other safe and con- FIELD WOltK. 365 LEVELS ON FIFTH AVENUE, SOUTHERLY FROM MARY- LAND AVENUE. FOR PROFILE. Nov. 21, 1880, A.M. STA. OBS. H.I. EL. REMARKS. B.M. 51.415 On west end of door-sill, etc. + 7.030 ^58.445 s p - 0.870 57.575 1+ 10.005 67.580 ... B.M. &(P. 1.300 66.280 ( On highest point of red | rock, etc. i+ 0.900 67.180 Sta. 0. 0.000 67.180 ( Plug middle of 5th and \ Md. Aves. + 25. 1.55 65.63 + 35. 0.28 66.90 1. 1.50 65.68 ( 50-ft. Sta. meas. south | from mid. of Md. Ave. 2. 3.91 63.27 3. 0.20 60.98 4. 8.83 58.35 5. 11.80 55.38 6. 13.20 53.98 7. Plug & ( P. 11.352 55.828 .... ( Plug centre 5th Ave. and | Anchorage St. i + 4.365 60.193 B.M. 5.480 54.713 j Temporary on plug near I fence, etc. Sta. 1. 5.13 55.06 ( 50-ft. sta. meas. south from ( middle of Anchorage St. 2. 4.65 55.54 3. 4.93 55.26 4. 5.69 54.50 6. 7.26 52.93 6. Plug + 34. 11.00 12.224 .... 49.19 47.969 ( Plug centre 6th Ave. and I Brown St. 366 PLANE SURVEYING. venient places. Besides serving as benches for the stones, these bench-marks will be used in doing very close final level- ling, the tops of the stones being too uneven for that purpose. 429. Marking of Lines and Grades. The lines and grades of the streets having been finally determined, and the means of preserving them having been established, the marking of these lines and grades for any public work, as street extension and grading, curb setting, sewer and water-pipe laying, etc., can be readily done. Street lines will be run with the transit ; and, in the manner previously described, grade lines will be run with the same instrument. The marking of street lines and grades for the purposes mentioned, the giving of lines and ele- vations for other public work, and measurements of various kinds, as of earthwork, constitute the principal part of the field work to be done for the town or city government by the city or town surveyor ; or, as the officer who does this work may have more extended duties, the principal part of the surveying to be done by the city engineer. 430. Private Work. Continuing the description of the field work of the town or city surveyor, we will notice the second general class in which his work is comprised ; that is, work for individuals, or private work. In general, for other duties in this connection will fall to his lot, such as surveying large tracts according to methods already described, etc., this work will consist in marking property lines and in giving grades and elevations. As a rule, in a town or city more property lines are marked for buildings than for any other purpose. When the survevor is called upon to locate the lines of a lot, his first inquiry will be as to the data by which to locate them. It is of course understood that in this con- nection the only power of the surveyor is to locate lines accord- ing to given data, not, as man}' persons seem to think, to establish of his own volition new lines. So we will inquire what is proper data for locating such lines. In general, the J.I 24'6" r 24V v r FIKLD WORK. 369 party desiring to have the lines of a lot marked will produce his deed for the property. The young surveyor will be inclined to think that the distances given in deeds are, as to the loca- tion of lines, final. This is not always the case. When walls, alleys, stones, and other permanent landmarks are called for, and can be found, they will take precedence of distances in locating lines. When walls, fences, and other holdings prove undisputed possession for a period of years, though they may not be described in the deed, they govern. In such cases it would be superfluous to mark lines. In towns and cities lots are now as a rule located from the streets. Let us take, in marking the lines for a lot, an example from actual practice. The description taken from the deed is definite, and is as follows : Beginning at the easterly side of West Street, between Eighth and Ninth Streets, at the distance of 223 feet from the southerly side of Ninth Street; thence easterly, parallel with Ninth Street, 132 feet to a corner; thence southerly, parallel with West Street, 28 feet to a corner ; thence westerly, par- allel with the first-described line and Ninth Street, 132 feet to the aforesaid easterly side of West Street ; and thence thereby, northerly, 28 feet to the place of beginning. The lot is located as shown in the sketch. The owner desired to have marked upon the ground, for use in building, the two lines par- allel with Ninth Street and the line of the easterly side of West Street. In order that they may not be removed in making excavations for cellars, walls, etc., the nail plugs to mark the lines are set 3 or 4 feet outside of the lot. In the sketch, S, S, S, S represent the stone monuments set at the intersections of the centre lines of the streets to mark lines and grade elevations. Each street is 49 feet wide. In mark- ing the lot, points p, p, will be taken in the centre line of Ninth Street. From these points (if there are no obstructions that prevent) measurements will be made parallel with West Street. Twenty-four feet six inches, half the width of Ninth Street, and 223 feet, the distance from the southerly side of Ninth 370 PLANE SURVEYING. Street to the northerly side of the lot, will be laid down, and nails placed in nail plugs at a, a, to mark the northerly line of the lot. From these the southerly line will be located. In a similar manner the front and back lines will be located. Lines strained from a to a and from & to 6 will cross at c, giving a corner of the lot, the nail plugs being undisturbed as the work of building progresses. If, on account of impassable obstacles, as buildings, walls, etc., a measurement cannot be made from Ninth Street to the place for the nail plug a back o the lot, the marking O f the side lines will be done as follows : The southeast angle at the inter- section of Ninth and West Streets, 89 51', if not known, will be taken. In addition to the points taken in the centre line of West Street for use in locating the front and back lines of the lot, an additional point p' will be taken, and at this point the angle 89 51' will be thrown in, and the random line p'p 11 located parallel with Ninth Street. On this random line points for the location of the side lines will be taken. Now, suppose the point p' is found by measurement to be 257 feet and 6 inches from the centre of Ninth Street (all corrections having been made) , or 233 feet from the southerly side thereof. Then the northerly side line will be located by measuring northerly from the line p'p" 10 feet, and the southerly side line by measuring southerly from the line p'p" 18 feet. If the sur- veyor is in possession of an instrument thoroughly reliable for use in angular measurements, the latter method of marking side lines is to be preferred. When one measurement is made along a sidewalk where there are no obstructions, and the other through fences and over various obstructions, it is hardly possible to obtain the degree of accuracy that may be obtained by the angular method. Sometimes it may be necessary to turn off an angle from the random line in order to locate the back line of a lot. The location of lines is often marked by nails in fences, measurements to houses, walls, etc., instead of by nails in plugs. After the street lines have been located and marked, the OFFICE WORK. 371 work in each block should be done independently of the other blocks. In the intervals between routine work it is desirable, in connec- tion with gathering other data, to take and record in a suitable . book, for use as described above, the angles at the intersections of the streets, thus saving time in marking the lines of lots. The location from the deed of the lines of a lot is not always so easy as in the example given. It is frequently the case that the distances given are indefinite ; sometimes none are given. In such eases, in the absence of established holdings, or other means of determining the location of property lines, the matter must be settled by an arrangement between adjoin- ing owners. In some cases a lot is described in whole or part without distances, but as bounded by the property of other owners. In such a case the location of the lines may, if the descriptions in the deeds of these other proprietors are sufficiently definite, be determined by marking the lines of the other lots. 431. The city or town surveyor will frequently be called upon for surveys to locate new lines with reference to the street lines, or for surveys of tracts of land in or adjoining the city or town. In such cases his manner of working will be based upon the methods of land-surveying already described. Private parties will frequently require, for use in building operations, the marking of grade lines. This will be done in the manner previously described. In marking the grade and height of the building line in front of a lot, it will very often be found convenient to mark the tops of the front line plugs as so much above or below grade elevation. B. OFFICE WORK. 432. Like the field work, the office work of the surveyor may be classified as Public Work and Private Work. 433. Public Work. All field notes should be sufficiently elaborate to be understood by those who may have occasion to 372 PLANE SURVEYING. refer to them. They should be carefully arranged and indexed like all other office records for convenient reference. Plots of work should be made whenever they will aid in the preservation and proper understanding of work done in the field. When plans are sent from the office, copies should always be retained. 434. It is desirable that, besides the necessary general plans of the town or city, the surveyor should have in his office two sets of plans, of a size convenient for handling, representing the city in sections. For these plans a horizontal scale of 100 feet to the inch is suitable. The first set should represent street lines. On them should be placed all tha street lines, and, in figures, the widths of streets and block distances, also the location of street monu- ments, measurements made from time to time between centres, angles at the intersections of the centre lines of streets, and any other data of a like nature giving information in regard to horizontal measurements, whether of lines or angles. The second set should represent street grades. On them should be placed, as on those of the other set, the street lines and, in figures, the widths of streets, block distances, and location of street monuments. In addition, there should be placed upon them the profiles of the centre lines of the streets. These plans will be used in determining grade lines for the streets, which, after they have been determined, will be placed upon the plans, with the grade elevations (G.E.) and surface elevations at the intersections of the centre lines of streets, grade elevations at curb corners, and any other data giving information in regard to vertical measurements. The street lines having been laid down, we will explain, in connection with the accompanying sketch copied from a plan in actual use, how the data given on page 365 would be used in placing upon the plan the profile of the centre line of Fifth Avenue, and then how the plan would be used in determining suitable grades for the streets. OFFICE WORK. 373 435. If the points whose elevations have been determined by the level be connected by a line in a vertical plane, such a line is called a profile. The block distance from Maryland Avenue to Anchorage Street is 297 feet and 9 inches, from Anchorage Street to Brown Street is 294 feet, from Cedar Street to Fifth Avenue is 264 feet, and from Fifth Avenue to Sixth Avenue is 160 feet. Maryland Avenue is 64 feet and 6 inches wide, Anchorage and Brown Streets each 40 feet wide, and Cedar Street, Fifth Avenue, and Sixth Avenue each 50 feet wide. The sidewalks on 'Cedar Street and on Fifth, Sixth, and Mary- land Avenues are 12 feet and 9 inches wide, and on Anchorage and Brown Streets are 10 feet wide. By the use of the profile of Fifth Avenue we will illustrate how the profiles of the centre lines of the streets are placed upon the plan. The irregular lines represent profiles. The profile is commenced by consider- ing the centre line of Fifth Avenue, as drawn on the plan, to have the elevation 67.180, which is the elevation in the notes for the surface of the ground at the intersection of the centre lines of Fifth and Maryland Avenues. The stations and pluses as given in the notes are then laid down by scale on the centre line of Fifth Avenue, in the order in which they were taken in the field, beginning at the centre of Maryland Avenue. The elevation at each of the points thus located is then plotted, in a perpendicular to the centre line at that point, with reference to the centre line elevation 67.180. In this case the points ob- tained will all fall below the centre line. These points are points in the profile, and, being joined, will give the profile as shown. The profile of Fifth Avenue having been started at the elevation of the ground at the intersection of Fifth and Maryland Avenues, is said to be swung on Maryland Avenue. In the sketch, the profiles of Cedar Street and Sixth Avenue also are swung on Maryland Avenue. Those of Anchorage and Brown Streets are swung on Cedar Street. 436. A little thought will make it evident to the student that, as the differences of elevation are small as compared with the 374 PLANE SURVEYING. horizontal distances, if both were plotted to the same scale, or, as we say, if the vertical and horizontal scales were made equal, the differences in elevation will scarcely be apparent. This is remedied bv conveniently exaggerating the vertical scale. For example, if the horizontal scale be made 100 feet to the inch, the vertical scale might be made 10 feet to the inch. In the sketch the two scales have this ratio. EXERCISE. Let the student select scales, and, in the manner described above, prepare a profile from the field notes given on page 356. 437. Having thus plotted the streets and profiles in a large area, we may, by use of the plan thus made, determine suitable grades for the streets. This will involve careful study of the shape of the ground, location of watercourses, probable loca- tion of sewers, and effect upon property. The effect of a pro- posed grade for one street upon those which it crosses must be particularly noticed. To properly perform this work involves that knowledge and judgment which can only be acquired by long experience. The straight lines drawn in connection with the profiles represent the surface grades of the finished streets. In fixing the grade for Fifth Avenue, those of the other streets having been taken into consideration, it was found best to have a cut of 2 feet at Maryland Avenue, no cut or fill at Anchorage Street, and a cut of 2 feet at Brown Street. The elevations of the surface at the intersections of Fifth Avenue with Mary- land Avenue, Anchorage Street and Brown Street, are respec- tively 67.180 on the ground, 55.828 and 47.969 on plugs flush with the ground. The grade line having been fixed, the grade elevations (G.E.) at the centres are respectively 65.180, 55.828, and 45.969, and the descents 9.35 feet and 9.86 feet, as shown in the sketch. The nature of grades will depend much upon local considerations. Grades should always be steep enough to secure proper drainage. The inclination should not be less than 1 in 100. Considering the accumulations of dirt on many of our city streets, from 1 to 1.5 in 100 is to be preferred. OFFICE WORK. 377 438. In streets in which surface water is carried on the streets, some streets will carry the water in gutters across oth- ers. In the sketch such streets are indicated by having arrows drawn in their directions across intersections. In this manner Fifth Avenue carries the water across Brown Street, and An- chorage Street carries it across Fifth Avenue. The water flow- ing on Fifth Avenue, from Maryland Avenue towards Anchorage Street, will turn into Anchorage Street. The opposite side of Anchorage Street, at the house line, will be a knuckle as high as the centre of the street ; and the water will flow from that point i towards Brown Street. In fixing grades great care must be taken to so arrange them that one street shall not be overtaxed with water from the others. An outlet for the surface water is formed in the natural watercourses. If the grade of Anchorage Street were very heav}', so that if continued across it would make one side of Fifth Avenue much higher than the other, it would be desirable to break the grade of Anchorage Street at the curb lines of Fifth Avenue, giving only sufficient fall to carry the water across the Avenue. 439. If the section is sewered, and if the sewers are made "large enough to carry the surface water, the gutters across the streets will be dispensed with, and inlets to the sewers placed at the curb corners of the blocks. 440. It is often convenient and useful to have plotted on separate streets the profile and grades of each street. 441. Besides making street and grade plans, it will be a part of the office work of the surveyor to plot, in the usual manner of plotting such work, the surveys made in and about the city or town, for both the city and individuals. 442. In some cities a registry of property is kept. The plotting of lots in suitable record books, and the keeping up of the records, will be a part of the city surveyor's work. 378 PLANE SURVEYING. 443. Private Work. This includes the preparation of any plans ordered for their own use by parties other than those con- nected with the city government. CONCLUSION. 444. The student must bear in mind that he can never, from books, learn to be an accomplished surveyor. The practice is ever in advance of the books. Though he should store his mind with book knowledge upon the subject, he will yet be wanting in the knowledge and readiness regarding actual work which can only be acquired by a long experience. Many oper- ations which can with difficulty be understood from pages of explanation, will, when their actual performance is seen, be comprehended in a short time. Again, there is that which can never be learned from books ; that is, the judgment which must be constantly exercised in practising the delicate duties of a city surveyor. Among other things, this judgment will teach him to be very cautious about giving voluntary advice, and careful in giving even that which is requested ; to perform his duties con- scientiously, and to keep clear of all entangling alliances. Let him learn everything connected with a complete performance of his work, from the work of the axeman up ; that, when he directs, he may do it with the same grace with which he should ever follow the directions of his superiors. The practice of city surveying is a most excellent drill. If conscientiously performed, it will develop careful and thought- ful habits. However, in practice the student will also have to learn to avoid " fussing" over work, and to proportion to the importance of the work in hand the time and care spent upon a particular work. BOOKS. 445. Valuable information regarding the matters treated of in this chapter will be found in the following publications : The manuals and catalogues of instrument-makers. BOOKS. 379 "A Treatise on the Principles and Practice of Levelling," by Frederick W. Simms ; published by D. Van Nostraud, New York. "A Descriptive Treatise on Mathematical Drawing-Instru- ments," by William F. Stanley ; published by E. & F. N. Spon, New York and London. " A Manual of Drafting Instruments and Operations," by S. Edward Warren ; published by John Wiley & Son, New York. " The Draughtsman's Handbook of Plan and Map Drawing," by George S. Andre" ; published by E. & F. N. 'Spon, New York and London. The student of surveying who wishes to extend his studies into the field of city engineering will find information upon that subject in the numerous works upon its special branches, and in the current technical periodicals of that class. Much information regarding present American practice in city engi- neering will be found in the series of papers on " Municipal Engineering" now being published in '-Engineering News." When completed, these in book form will make a very useful v olume. CHAPTER VIII. MINE SUKVEYING. 446. The survey of underground excavations (mines) to determine their position and extent may be principally for the purpose of projecting the points upon a horizontal plane as in land surveying. But in strata of high inclination and in cavernous spaces various vertical projections will be needed to complete the graphical representation of the workings ; and in fissure veins the elevation may be more important than the plan. 447. Surveys to depict areas underground may be made with surveyors' compass and chain, but generally now the transit or theodolite is used to take the angles, and the steel tape to meas- ure the distances, and in some mines the tape may be with ad- vantage hundreds of feet in length ; but generally 50 feet for the chain or 100 feet for the tape are most convenient lengths. 448. The surveyor and each assistant, of course, requires a lamp, and "the sights" are ranged with lamp and plummet, the sight from the instrument being taken upon the flame of the miner's lamp (or candle, it may be) suitably held at the plummet line, which is held to depend from a point fixed or to be fixed in the " roof" or over a point in the " bottom." The plummet string itself may be seen within 300 feet. A chain- pin (arrow) can be used to plumb the light over or under a point. It is advised to display the light at a station for sight only, and therefore in moving it, for any reason, other than vertically, in giving the point, it should be hidden from the observer. MINE SURVEYING. 381 The point may be marked by a nail in the timber cap or sill, or be a nail in a peg ; the place of the point in smooth roof is to be made conspicuous by a ring of white paint around it, and also as it may be by reference marks at the sides (pillars) of the passage-way. It is a refinement to use a lamp which is also a plummet, and further to place an extra lamp on the bottom under it; two tights seen in the vertical line making its place more certain, and helping to decide that the sight is ready to be taken.* It may happen that the line of reflection from standing water can be taken for the line of incidence of a light held under a point, when the roof droops between, the passage being " in swamp" there. The surveyor's lamp is made entirely of brass or copper, so as not to affect the magnetic needle of the instrument. For use in low openings the tripod of the instrument must be one of short legs (an extra set of shifting legs will answer the purpose), or have extension legs. It has been suggested to use two extra tripods, one to set up in advance, for keeping the place of fore-sight and for receiv- ing the instrument, alone carried forward to be mounted there at the same exact spot with facility, while the tripod, left standing at the last place of the instrument, marks the point for back-sight with equal certainty : thus each of three tripods taking its turn in being at a place for fore-sight, remaining there for mounting the instrument upon it, and still remaining for back-sight after the instrument is taken for mounting at next station. There are obvious objections to this in the weight of the luggage, and that only some instruments are made for such ready separate handling. Some rays of light must be thrown into the telescope at its object end to make visible the cross-hairs therein. This is gen- erally done by the surveyor, while taking a sight, holding his * Eckley B. Coxe derised the plummet lamp, and also a form of it with wire-gauze covering, like the Davy Safety Lamp, for use where fire-damp may be expected. 382 PLANE SURVEYING. lamp in his left hand at the front, but a little to one side of the object-glass. A reflector mounted at the object end is a help. One is a silvered flat ring, standing bias, about "2 inches forward from a collar which is slipped over the object end of the tele- scope. It reflects light into the instrument as an annular beam. Another one is a diminutive hemisphere which scatters light caught from the lamp into the tube. The change to, and the equable temperature of, the mine require the trying and favor the making of the ordinary adjust- ments of the instrument there. 449. Stations are generally made only at the angle points of survey lines, and are therefore not regularly distanced. They may be numbered, lettered, or designated by the total distance from the zero of the measurements of their line. Intermediate points are made on the line where, opposite to lateral openings, other lines of survey or important short connections by measure- ment merely may start. The corners of chambers along the passage may be noted by distance without making points ; the size and position of parts of chambers being afterwards taken and noted by sketch with dimensions relatively marked thereon, there being mostly a parallelism in the rock measures which sim- plifies the position and shape that chambers take, so that no special survey of directions is regularly required for them. 450. Angles between vertical planes of sight (in azimuth) are noted for obtaining the courses as reduced courses from the initial course of survey, by the successive additions and sub- tractions to it and from it of the angles as taken, and modified according to the series of 90 in each quadrant of the circle. The initial course had better be referred to true meridian, and comparison with bearings made with allowance for the variation (declination) of the needle. But it has always been recognized that the course, in degrees and minutes, of a quadrant and therefore liable to mistakes as to the particular one of four quadrants would be absolute if the full circle be graduated MINE SURVEYING. 383 around to 90, 180, 270, and 360, in the successive quadrants. While it is not agreed whether north or south shall be the zero, the direction of graduation with the movement of the hands on the dial of a watch or clock is conventionally fixed. The bear- ings will be a key to which zero was used in the notes. 451. It is but seldom that in drifts of mines the alignment as well as the grade requires adjustment to the regularity of straight lines and curves similar to surface railroads ; for the tram-cars will run around very, sharp turns, and for them there is there- fore no necessity of expensive improvements in line. But when a locomotive is to be used, or wire-rope haulage is to be intro- duced, there is apt to be a call for regulation of the line, with regard, especially, to minimum radius of curvature. Unlike the longer, flat curves of a railroad, designated according to the American system by the even angular deflec- tions from each other of chords of 100 feet, these sharper curves will go by assumed even radii (in length not less than ten times the gauge of track), and the deflection angles for run- ning them in by the instrument upon short chords will have to be calculated. One-half the chord divided by the radius will equal the sine of the angle of deflection from tangent, which is half the angle that two such equal chords will make with each other, and also half the angle at the centre of the circle subtended by the chord. From any point on the circular curve as a position of the instru- ment, successive deflections of the angle will fix the ends of consecutive chords as measured in. Shorter chords (like those less than 100 feet in a railroad curve) have deflection angles approximately proportional to their lengths. For ranging the line of direction of a passage that is being opened into the solid, two points for placing lights are given at the start, necessarily near together, until the prolongation of open space allows testing the line by the instrument and giving new points of line. From the three points of a curve line that mark the chords of half the arc, obviously, by simple measure- 384 PLANE SURVEYING. ments, a like fourth point may be derived as the face (breast) of the working is advanced. In driving a passage-way describ- ing a semicircle to save weakening pillar at foot of shaft a long, curved gas-pipe was used in ranging around. A large- scale working plot showing offsets secures the proper location of curving and branching passages. Outside, besides the fixing of projected curves by deflection angles as above, the laying off of points of arc intermediate on the chord is by foot-rule measurement of ordinates at right angles. But without strict regard to data, an expedient way of uniting two intersecting straight lines of track 03* a circular curve (as an arc starting from the one straight line at any distance short of the apex of the lines and ending on the other line an equal distance from the apex) is to find points by linear measure- ment merely. Assuming any tangential distance back from apex to P.C. (point of curve), the beginning, and the same to P.T. (point of tangent), the end of curve, we find a third point of the arc, its middle, as a point midway between the middle of the chord of the whole arc and the apex. One-fourth of this versed sine will be the versed sine (middle ordinate) to be erected on each chord of half the arc for points of the arc. And any other middle ordinates will be as the squares of their arcs or chords. This principle applies in rounding off intersecting grades into vertical curves, either convex or concave ; by vertical allow- ances and according to horizontal distances, starting with that at the apex and proceeding similarly to the foregoing as to subdivisions. The laying off of curves by chords and versed sine so derived does not require knowledge of length of radius or of amplitude of angle. But when the extent of circular arc between two tangents is to be determined by the length of radius, the tan- gential distance from apex will equal radius multiplied by natural tangent of half the angle of intersection ; and between P.C. and P.T. there will be the same measures of chord as there are of chord singles in angle of intersection. MINE SURVEYING. 385 452. In the note-book the left-hand page is used for stations, distances, angles, courses (reduced), and bearings (magnetic), and the opposite right-hand page for offset distances marked relative to a perpendicular line dividing the page, together with sketches and remarks. The notes should begin at the bottom of the pages and proceed upwards, to appear as on the plan to which their results are to be transferred, in their proper relation of position and observation forward. The plan of underground work is begun with the plotted net- work of the lines of survey, then the outline of parts excavated is drawn in detail, and these are shaded, as the places become closed in and abandoned, to distinguish what is open work at any period. The scale of maps showing the workings, etc., of coal mines is now fixed by law in many of the States at 1 : 1200 as the least; that is, at not less than 1 inch for 100 feet; the purpose of the maps being to aid the official inspection and regulation of the mines for securing the health and safety of the miners. The plan will generally require to show the relation of the workings to surface openings, watercourses, and bounding lines, and to improvements, such as buildings, roads, and railroads. The line of outcrops (exposure at the surface of the ground of the mineral beds) within its range will appear on the map, but general topographical detail is reserved for the extended small- scale maps of the surface, which will represent what may be learned of mineral indications also ; from which data in advance of the workings may be derived and confirmed by special explorations, as of proof-holes and deep boring. But upon the mine plaii such elevations (heights of surface above datum) as seem most essential, such as principal ones along the outcrops, highest points of hills, and lowest of streams should be mapped. The use of the pantograph, for reducing the irregular figures of mine plans with all details from one scale to another, has found much approval ; and the plammeter is liked for labor- saving and accuracy in determining such areas. 886 PLANE SURVEYING. 453. In veins, the work being deep and narrow, and pursued from levels or galleries (horizons of working) generally about 60 feet apart in height, plans of these levels, drawn in different colors to distinguish them, are superimposed on the map of general plan. The}' show the openings, the gangways, the cross-cuts, etc., with the defining lines of the walls of the vein, and may embrace other separations of the mineral. Longi- tudinal elevation and vertical cross-sections will show the shafts and other connections between the levels, together with the chambers, whether open, filled in, or caved. Ore bodies occurring detached and of the most varying dimensions, though often resembling each other as lenticular in shape, make the workings appear in plan, elevation, and cross- section, as the results of exploration in patches. Shafts in the vein will be parallel to pitch of one wall, and therefore varying from the vertical. A stratified bed that is to be operated upon, opened, and won by mining, may be conceived as a seam of uniform small thickness extending within limits as a plane surface and in relative position defined by the " strike " (the course of all its level lines, which will all be parallel) and its "dip" (the greatest pitch at right angles to the course of the level-line). But upon the large scale the seam occurs of variable thickness, and with lines of level changing in direction and not parallel at different elevations, to the degree that instead of a plane it is a warped surface. The arrangement of permanent works upon the surface of the ground with reference to the lay of the bed as well as the topog- raphy and improvements existing or suited to it, the favorable connection of the lines of haulage and drainage inside, with all to govern outside, present to the mind of the mathematical surveyor applications of the theorems of Descriptive Geometry, as included in adaptation to the ends of practical economy. 454. Location upon the surface of the ground of the plan of inside work, is a repetition of courses and distances outside in the MINE SURVEYING. 387 same vertical planes. Any particular portion of the workings in progress can thus be compared in natural scale upon actual plan of surface of the ground over them. Overlaid plans with elevations and cross-sections of workings, such as were described for workings in veins, are required to show the development in high pitching beds. The " lifts " or levels in such of coal are 100 yards apart, measured on line of pitch. Overlaid plans of different parallel seams worked through same shaft are also made, but without systematic elevation and cross-section ; the connections (shafts, slopes, or tunnels) between the beds being through barren ground, and limited to the exigencies of hoisting, draining, and ventilating. 455. Following the determination in azimuth by courses and distances of the passages in the mine is the determination of their changes in level by the spirit levelling-instrument and the level-rod (as a separate operation, even if the transit be a com- bined instrument having a parallel spirit level attached to its telescope), the work being quite similar to such above ground. But the rod must be limited in height to the low spaces where it is to be used, and is preferably marked with red figures for the feet, and white figures for the tenths, upon a black ground. The top of a simple white target is safer to take, however, than the reading from the instrument of the figures themselves. For accuracy, sights, as above ground, should be limited to 300 feet in distance from the instrument. From the elevations of points taken by levelling, contour lines can be shown on plan as the mineral bed is exploited. Blue is the conventional color for these contour lines and the figures marking their elevation above the datum, on a mine plan, and brown suits for the contrasted surface elevations. 456. Levelling along passage-ways for the purpose of fixing better gradients of hauling-roads, or for fall of water by rectifi- cation of undulating bottom to improve drainage, requires sta- 388 PLANE SURVEYING. tions especially chained in at regular distances of 50 feet or less ; the marks being temporary ones on the sides to serve for taking the levels and to be referred to as to heights in grading, when the variation of level of bottom from the grade of a station governs the cutting or filling of bottom there, or change of the whole cross-section in height, as it may be. For the adoption of suitable gradients along an extended line, a longi- tudinal vertical section is drawn, called a profile, which exhibits the relation of ground-line levels, and allows the fixing of grade with assurance. The profile may include the line of top as well as of bottom, with section of rock measures to be affected by " ripping " of the roof and " cutting " of bottom. 457. A Drift or passage along with the measures of a bed will make undulating grade, if course be followed ; and if the drainage-rise be allowed to govern, the alignment will be sacri- ficed. Tunnelling, however, being arbitrary, across the measures, is mostly upon directed line and grade. Slopes are mostly upon directed course ; but if within the measures of an inclined bed will mostly be variable in grade. So with an adit, driven to give drainage outfall to the surface. For it, shortening of the distance will probably be the governing condition principally. 458. For the workings at high pitch, the determination of horizontal and vertical components of the distances on the sloph g lines of top and bottom in a bed, and " hanging wall " and "foot wall" in a vein, will bring the vertical arc of the instrument into requisition, for obtaining the vertical angle, which is always taken as the full angle above the horizontal. Vertical sections, besides such longitudinal ones following broken line of passage within a stratum and showing only adja- cent rock measures, may be made of particular places where there is folding, or fault, of the measures, and for geological or more general purposes they may exhibit the lay and thickness of the various rocks up to the surface, which will as a correct MINE SURVEYING. 389 margin show the outcroppings in profile. Vertical sections may be projections upon planes that traverse the measures according to various conditions, and may be constructed of related points from the map that were not determined for their relevancy to this purpose. It seems that vertical arcs have had versed sines correspond- ing to radius 1 marked around them for the purpose of telling the allowance upon slope measurement to obtain corresponding horizontal distances, the versed sine being the difference between the hypothenuse as the radius and the horizontal base as the cosine of the vertical right-angled triangle formed ; and the slope length for a given horizontal distance would be greater, according to the versed sine of the angle. Vertical arcs have had tangents as rises corresponding to the unit of horizontal distance for the different angles marked upon them. A method of dividing the arc according to the sines, without the intervention of the equal graduation into degrees neces- sarily, is the subject of a contribution to "Van Nostrand's Engineering Magazine" for July, 1876, and is appended at the end of this chapter. 459. The measurement down deep borings or shafts is best made by special flat steel wire, with suitable plummet heavy enough to insure its making the wire line taut. The transfer of points down a shaft, as of two to determine a base line for connecting surveys below with those on the surface of the ground, is made by very heavy plummets attached to ordinary wire run off of reels. A portable box to contain the reels, their cranks, and the plummets, is con- venient; the best arrangement being that of reels fixed in a frame that stays in the box. The suspended plummets are to be received below each in a bucket of water, or, if hanging from considerable height, in some thicker liquid to settle the wire lines to a steady position for ranged observation by the instru- ment below. And the observation will be easier upon wire that is whitened there by chalk or paint after being placed. 390 PLANE SURVEYING. The plummets in the shaft of the Washington Monument, for showing changes in the verticality of the structure, are steadied in vessels containing a mixture of glycerine and molasses. 460. For taking courses on pitches at high angles an extra telescope on the axis extended to the outside of one of the standards of transit has been used. Another mining transit has for the same purpose the sweep of the telescope to the ver- tical position, made possible by having its standards made inclined to overhang. But the object-prism placed before the object-glass, allowing sighting at true right angles in any plane, seems most simply to fulfil the requirements for sighting up or down, as well as side wise, and is a ready means applicable to the telescope of any ordinary instrument. A transit adapted in any of these ways for taking vertical sights enables the points of base line, as transferred by plummets to the bottom of the shaft, to be tested and compared with the extended line across the pit top, provided the atmosphere be clear in the shaft and obstructions do not intervene. The vertical adjustment of the instrument itself would be tested by this check, the usual test being on high objects, with reversal of standards to oppo- site sides by turning the horizontal plates. A heavy, substantial, simple transit, not weighted with "attachments," is the most reliable. 461. The use of the hanging compass and of the hanging clinometer of the olden time is retained in small and crooked passages of some metalliferous mines. And their subsidiary use in excavations inconvenient of access or footing of the ordinary (the standing instruments) has lately been recom- mended as of wider application, and they have been introduced into this country. Each of the instruments is to hang by its two hooks, turned opposite ways, to the cord that marks the line. The compass-box levels itself by its 'gimbals (double trunnions), like a ship's compass, in the frame of which the flat hooks with long bearings in line are a part. The clinometer MINE SURVEYING. 391 bangs as a vertical arc with plummet to give the inclination of the cord from the horizon, while the compass gives the needle course. The cord is stretched from one low stout tripod to another, or in a curving space may be fastened to a gimlet screwed into side timber beyond intersecting point or angle of two cords. The tripod serves as a stool also for the assistant holding cord to the point on it firmly. The distances are accu- rately measured along the cord by applying a graduated rod to it. The horizontal and vertical components of the measure- ments have to be calculated for plotting on plan and section. In the old mining regions of Europe the surface surveys were also carried on with the same appliances. With .care and patience surprisingly good results in locating connections were attained. The old instruments were graduated in hours and minutes, and the English designations of dial and dialling for the mine compass and operations with it seem to refer to the same original division of its circle. It seems strange to learn that the plotting was protracted by the same compass (swung there on horizontal plate used for straight edge), reference being had to a meridian line fixed in the office, and the drawing- table being a smooth and level stone slab resting on foundation independent of the office floor. 462. Formerly, when topography was used more for the pic- turing of the plan of landscape in mapping the features for the information of the tourist or the military commander, than for the projection of the contour accurately to fit the location of artificial ways of the different kinds to the ground, hachures were used to indicate character of sloping elevations, and they survive in use upon small-scale maps, to indicate moun- tain chains. They are intended to be lines of pitch, drawn close together so as to graduate changes naturally, and they should be broken at the intersection of the successive level planes with the surface to make terraces however narrow, and suggest level stages in measure of elevation. Now we have on topographical plans contour lines to represent the lines of sue- 392 PLANE SURVEYING. cessive levels, say 10 feet apart in rise. They are plotted by connecting all points of elevation that may be determined over the area with regard to the requirements of accuracy in noting the changes ; and they may be considered the margins made by a body of water that had successively risen or receded 10 feet in height at a time over the area. They are to be marked by their elevation above the lowest datum plane, preferably over that of mean tide of the ocean. They turn upon themselves where they enclose a peak or a basin according as the next ones indicate them as higher or lower in the series ; they are farther apart in horizontal distance as slopes are flatter, and where two or more coincide for any distance there is a precipice. These points of even elevations of the ground are determined from the levels run along the survey lines, and the cross-section profiles taken at the stations of the lines slopes being taken at right angles to the line with straight edge pole and clinometer or plummet slope level applied to it. Each of these angle instru- ments having a vertical graduated arc, the former with arm hinged at centre of arc and carrying a spirit-level to ascertain the vertical angle included between the levelled arm and the slope of the straight edge under it ; the latter, by the departure from the perpendicular of the plummet, showing the equal departure from the horizontal of the straight edge. From the profile of each slope sketched in the field-book and marked with distances and degrees of rise and fall across the survey line, the successive even 10-foot points can be laid off on plan, regard being had in starting with elevation of station to the partial changes required for the first even 10-foot point each way. A scale of horizontal distances for each degree of the arc, to gain 10 feet rise, is made by the topographer of Bristol- board to lay off the points derived by sloping at the stations, and saves the plotting of the profile of cross-section. The topographer prefers to draw the contours in the field as taken, using demi-sheets of paper that can be joined at their margins, and upon each of which a portion of the line corre- sponding to its number is plotted, the line having dots along it, spacing the successive stations intermediate of the angle points MINE SURVEYING. 393 of line, and having the elevations corresponding in pencil along- side. The sheets are held in a box that is carried by a shoulder- strap, and the side of which is used in the field as a drawing- board, the particular sheet in use at the time being tacked on it. 463. The topographer will sketch in the streams, buildings, etc., with reference to measurements however, and will have special lines with small compass, etc., run for him to make contour connections. The operations will rise to the scope of plane-table work, if the drawing-board have a socket with clamps, and be mounted and levelled (by applying a loose hand- level) upon a tripod ; the ruler used on it having small compass sights screwed to its ends for sighting to objects and fixing their position on plot by the graphic triangulation of intersected sight-lines from different stations on the survey -line ; the sta- tion on plot when over its place on ground having a needle stuck upright in it, that has a sealing-wax head for convenient handling, for the purpose of resting the ruler against when sight- ing. Interpolation, or resection, is the reverse sighting from without the line over the plot to two or three poles on stations of the line or other previously located objects, to attain posi- tion, it being understood that the plane table stands with plot in proper relative position always. Secondary triangulation will extend the area of topographic sketching, but this should be checked by connections beyond with surveyed lines and levels. The Locke level may be used for taking rises by finding all the points in sight that are at a level of the eye, and, in con- nection with the le veiling-rod, the fall of ground may also be determined by this instrument. For gently undulating ground the use of it is better than sloping. 464. Contour lines are drawn 10 feet apart in elevation on most plans of extended land and other surveys that are meas- ured in detail, but it is obvious that cases occur where for large- scale work they are taken closer in elevation or farther for small-scale mapping. In the fonm-r rase of large-scale work they may be required exactly as elevations directly located by 394 PLANE SURVEYING. spirit levelling-instrument, in the latter case as the approxima- tion from altitudes taken in a few places by the barometer. The scope of their usefulness on plans for projecting improve- ments it would be difficult to describe exhaustively. They may be for use in locating the drives and walks and terraces, etc., of a park; the shaping of grounds, under-draining, etc., about a residence ; the laying out of streets, etc., in a hilly town ; the leading of streams of water, large or small, for all purposes in partial or wholly artificial channels, for navigation, water power and supply, irrigation, etc. ; the location of roads and railroads with regard to ease of construction and of favorable gradients, as well as the uses in mining directly, and location of all surface erections collateral thereto or elsewhere, collec- tively known as " the Works." ANGULAR CROSS-SECTIONING. By F. Z. SCHELLENBERG, C.E. Written for "Van Nostrand's Engineering Magazine," July, 1876. A most direct and expeditious method to get differences in level between points in sight is by the use of a vertical arc grad- uated to the successive sines 1, 2, 3, ... 100, in quadrant, for the radius of arc 100. Multiplying the distance measured in hundreds on the slope by the rate per hundred indicated on the arc gives the difference in level in units. In the higher parts of the arc the correspond- ing cosines may be marked for deriving horizontal distances. The applicability of this graduation to such purposes, as described under this caption by R. Bell, C.E., in May number, is obvious, as may also be its use for more extended profiles, for geological cross-sections, for road-grading, or wherever between points obtained by the levelling-instrument its accuracy is not indispensable. A clinometer thus graduated enables contour lines for topo- graphical work to be most readily determined. The table following gives the 100 points in the quadrant in terms of the common graduation of 90 to the quadrant. MINE SURVEYING. 395 Vertical Horizontal Vertical Horizontal Distance for Distance for Angle Distance for Distance for Angle 100 measured 100 measured with Horizon. 100 measured 100 measured with Horizon. on Slope. on Slope. on Slope. on Slope. 000' 51 :;u 'in' 1 . ... 034' 52 ... 31 20' 2 109' 53 .. . . 32 00' 3 . .'.. 143' 54 32 41' 4 2 18' 55 88.6 33 22' 6 99.9 2 52' 56 34 03' 6 .... 3 26' 57 34 45' 7 4 01' 58 35 27' 8 4 35' 59 36 09' 9 5 10' 60 80.6 36 52' 10 99.6 5 44' 61 .... 37 35' 11 6 19' 62 38 19' 12 6 54' 63 .... 39 03' 13 7 28' 64 39 48' 14 8 03' 65 76.0 40 32' 15 98.9 8 38' 66 41 18' 16 9 12' 67 .... 42 04' 17 9 47' 68 42 51' 18 10 22' 69 43 38' 19 10 57' 70 71.4 44 26' 20 98.6 11 32' 71 45 14' 21 12 07' 72 46 03' 22 12 43' 73 46 53' 23 13 18' 74 47 44' 24 13 53' 75 66.2 48 35' 25 96.8 14 29' 76 49 28' 26 15 04' 77 50 21' 27 15 40' 78 .... 61 16' 28 16 16' 79 62 11' 29 16 51' 80 60.6 63 08' 30 95.4 17 27' 81 64 06' 31 18 04' 82 66 05' 32 18 40' 83 66 06' 33 19 16' 84 67 08' 34 19 53' 85 52.7 58 13' 35 93.7 20 29' 86 59 19 7 36 21 06' 87 .... 60 28' 37 21 43' 88 .... 61 39' 38 22 20 7 89 62 62' 39 22 57' 90 43.6 (il (I!)' 40 91J6 23 35' 91 66 30' 41 24 12' 92 6(5 66' 42 24 50' 93 .... 68 26' 43 25 28'' 94 70 03' 44 26 0(5' 95 31.2 71 is' 45 89.3 26 45' 9(5 73 44' 46 27 23' 97 .... 7:. :.(' 47 28 02' 98 78 81' 48 28 41' 99 81 64' 49 29 20' 100 00.6 90 00' 50 86.6 30 00' TRANSIT, A.S FIRST MADE IN 1831 BI THE INVENTOR, WILLIAM J. YOUNG, PHILADELPHIA, PA APPENDIX. THE JUDICIAL FUNCTIONS OF SUEVEYOES* A* WHEN a man has had a training in one of the exact sciences, where every problem within its purview is supposed to be sus- ceptible of accurate solution, he is likely to be not a little impa- tient when he is told that, under some circumstances, he must recognize inaccuracies, and govern his actions by facts which lead him away from the results which theoretically he ought to reach. Observation warrants us in saying that this remark may frequently be made of surveyors. In the State of Michigan, all our lands are supposed to have been surveyed once or more, and permanent monuments fixed to determine the boundaries of those who should become propri- etors. The United States, as original owner, caused them all to be surveyed once by sworn officers, and as the plan of sub- division was simple, and was uniform over a large extent of territory, there should have been, with due care, few or no mistakes : and long rows of monuments should have been perfect guides to the place of any one that chanced to be miss- ing. The truth unfortunately is, that the lines were very care- lessly run, the monuments inaccurately placed ; and, as the recorded witnesses to these were many times wanting in perma- nency, it is often the case that when the monument was not correctly placed, it is impossible to determine by the record, by the aid of anything on the ground, where it was located. The incorrect record of course becomes worse than useless when tin- witnesses it refers to have disappeared. It is, perhaps, generally supposed that our town plats were By Chief Justice Cooley of tlie Supreme Court of Michigan. 398 PLANE SURVEYING. more accurately surveyed, as indeed they should have been; for in general there can have been no difficulty in making them sufficiently perfect for all practical purposes. Many of them, however, were laid out in the woods ; some of them by proprie- tors themselves, without either chain or compass, and some by imperfectly trained surveyors, who, when land was cheap, did not appreciate the importance of having correct lines to deter- mine boundaries when land should become dear. The fact probably is, that town surveys are quite as inaccurate as those made under authority of the general government. It is now upwards of fifty years since a major part of the public survevs, in what is now the State of Michigan, were made under authority of the United States. Of the lands south of Lansing, it is now forty years since the major part were sold and the work of improvement began. A generation has passed away since they were converted into cultivated farms, and few, if any, of the original corner and quarter stakes now remain. The corner and quarter stakes were often nothing but green sticks driven into the ground. Stones might be put around or over these if they were handy, but often they were not, and the witness trees must have been relied upon after the stake was gone. Too often the first settlers were careless in fixing their lines with accuracy while monuments remained, and an irregular brush-fence, or something equally untrustworthy, may have been relied upon to keep in mind where the blazed line once was. A fire running through this might sweep it away, and if nothing was substituted in its place, the adjoining proprietors might in a few years be found disputing over their lines, and perhaps rushing into litigation, as soon as they had occasion to cultivate the land along the boundary. If now the disputing parties call in a surveyor, it is not likely that any one summoned would doubt or question that his duty was to find, if possible, the place of the original stakes which determine the boundary line between the proprietors. However erroneous may have been the original survey, the monuments that were set must nevertheless govern, even though APPENDIX. . 399 the effect be to make one half-quarter section 90 acres, and the one adjoining 70 ; for parties buy, or are supposed to buy, in reference to these monuments, and are entitled to what is within their lines, and no more, be it more or less. While the witness trees remain, there can generally be no difficulty in determining the locality of the stakes. When the witness trees are gone, so that there is no longer record evidence of the monuments, it is remarkable how many there are who mistake altogether the duty that now devolves upon the surveyor. It is by no means uncom- mon that we find men, whose theoretical education is thought to make them experts, who think that when the monuments are gone, the only thing to be done is to place new monuments where the old ones should have been, and would have been if placed correctly. This is a serious mistake. The problem is now the same that it was before : To ascertain by the best lights of which the case admits where the original lines were. The mistake above referred to is supposed to have found expres- sion in our legislation ; though it is possible that the real intent of the act to which we shall refer is not what is commonly sup- posed. An act passed in 1869 (Compiled Laws, 593), amend- ing the laws respecting the duties and powers of county survey- ors, after providing for the case of corners which can be identi- fied by the original field notes or other unquestionable testimony, directs as follows : "Second. Extinct interior section corners must be re-estab- lished at the intersection of two right lines joining the nearest known points on the original section lines east and west and north and south of it. " Third. Any extinct quarter-section corner, except on frac- tional lines, must be re-established equidistant and in a right line between the section corners ; in all other cases, at its pro- portionate distance between the nearest original corners on the same line." .The corners thus determined, the surveyors are required to perpetuate by noting bearing troes when timber is near. To 400 PLANE SURVEYING. estimate properly this legislation, we must start with the ad- mitted and unquestionable fact that each purchaser from gov- ernment bought such land as was within the original boundaries, and unquestionably owned it up to the time when the monuments became extinct. If the monument was set for an interior section corner, but did not happen to be "at the intersection of two right lines joining the nearest known points on the original section lines east and west and north and south of it," it nevertheless deter- mined the extent of his possessions, and he gained or lost according as the mistake did or did not favor him. It will probably be admitted that no man loses title to his land or any part thereof merely because the evidences become lost or uncertain. It may become more difficult for him to es- tablish it as against an adverse claimant, but theoretically the right remains ; and it remains as a potential fact so long as he can present better evidence than any other person. And it may often happen that notwithstanding the loss of all trace of a section corner or quarter stake, there will still be evidence from which anv surveyor will be able to determine with almost absolute certainty where the original boundary was between the government subdivisions. There are two senses in which the word "extinct" may be used in this connection : one, the sense of physical disappearance ; the other, the sense of loss of all reliable evidence. If the statute speaks of extinct corners in the former sense, it is plain that a serious mistake was made in supposing that surveyors could be clothed with authority to establish new corners by an arbitrary rule in such cases. As well might the statute declare that if a man loses his deed, he shall lose his land altogether. But if by extinct corner is meant one in respect to the actual location of which all reliable evidence is lost, then the following remarks are pertinent : 1. There would undoubtedly be a presumption in such a case that the corner was correctly fixed by the government surveyor where the field notes indicated it to be. APPENDIX. 401 2. But this is only a presumption, and may be overcome by any satisfactory evidence showing that in fact it was placed elsewhere. 3. No statute can confer upon a county surveyor the power to "establish" corners, and thereby bind the parties concerned. Nor is this a question merely of conflict between State and Federal law ; it is a question of property right. The original surveys must govern, and the laws under which they were made must govern, because the land was bought in reference to them ; and any legislation, whether State or Federal, that should have the effect to change these, would be inoperative, because dis- turbing vested rights. 4. In any case of disputed lines, unless the parties concerned settle the controversy by agreement, the determination of it is necessarily a judicial act, and it must proceed upon evidence, and give full opportunity for a hearing. No arbitrary rules of survey or of evidence can be laid down whereby it can be ad- judged. The general duty of a surveyor in such a case is plain enough. He is not to assume that a monument is lost, until after he has thoroughly sifted the evidence, and found himself unable to trace it. Even then he should hesitate long before doing anything to the disturbance of settled possessions. Occu- pation, especially if long continued, often affords very satis- factory evidence of the original boundary, when no other is attainable ; and the surveyor should inquire when it originated, how and why the lines were then located as they were, and whether a claim of title has always accompanied the possession, and give all the facts due force as evidence. Unfortunately, it is known that surveyors sometimes, in supposed obedience to the State statute, disregard all evidences of occupation and claim of title, and plunge whole neighborhoods into quarrels and liti- gation by assuming to "establish" corners at points with which the previous occupation cannot harmonize. It is often the case that where one or more corners are found to be extinct, all par- ties concerned have acquiesced in lines which were traced by the guidance of some other corner or landmark, which may or 402 PLANE SURVEYING. may not have been trustworthy ; but to bring these lines into discredit, when the people concerned do not question them, not only breeds trouble in the neighborhood, but it must often sub- ject the surveyor himself to annoyance, and perhaps discredit, since in a legal controversy the law, as well as common sense, must declare that a supposed boundary line long acquiesced in is better evidence of where the real line should be than any survey made after the original monuments have disappeared. Stewart v. Carleton, 31 Mich. Reports, 270; Diehl v. Zanger, 39 Mich. Reports, 601. And county surveyors, no more than any others, can conclude parties by their surveys. The mischiefs of overlooking the facts of possession must often appear in cities and villages. In towns the block and lot stakes soon disappear ; there are no witness trees and no monu- ments to govern, except such as have been put in their places, or where their places were supposed to be. The streets are likely to be soon marked off b}* fences, and the lots in a block will be measured off from these without looking farther. Now it may perhaps be known in a particular case that a certain monument still remaining was the starting-point in the original survey of the town plat ; or a surveyor settling in the town may take some central point as the point of departure in his surveys, and assuming the original plat to be accurate, he will then undertake to find all streets and all lots by course and dis- tance according to the plat, measuring and estimating from his point of departure. This procedure might unsettle every line and every monument existing by acquiescence in the town ; it would be very likely to change the lines of streets, and raise controversies everywhere. Yet this is what is sometimes done ; the surveyor himself being the first person to raise the disturbing questions. Suppose, for example, a particular village street has been located by acquiescence and used for many years, and the pro- prietors in a certain block have laid off their lots in reference to this practical location. Two lot-owners quarrel, and one of them calls in a surveyor that he may be sure that his neighbor APPENDIX. 403 shall not get an inch of land from him. This surveyor under- takes to make his survey accurate, whether the original was or not, and the first result is, he notifies the lot-owners that there is error in the street line, and that all fences should be moved, say, one foot to the east. Perhaps he goes on to drive stakes through the block according to this conclusion. Of course if he is right in doing this, all lines in the village will be unsettled ; but we will limit our attention to the single block. It is not likely that the lot-owners will generally allow the new survey to unsettle their possessions, but there is always a probability of finding some one disposed to do so. We shall then have a law- suit; and with what result? It is a common error that lines do not become fixed by acquiescence in a less time than twenty years. In fact, by statute road lines may become conclusively fixed in ten years ; and there is no particular time that shall be required to conclude private owners, where it appears that they have accepted a particular line as their boundary, and all con- cerned have cultivated and claimed up to it. McNamara v. Seaton, 82 111. Reports, 498 ; Bunce v. Bidwell, 43 Mich. Re- ports, 542. Public policy requires that such lines be not lightly disturbed or disturbed at all after the lapse of any considerable time. The litigant, therefore, who in such a case pins his faith on the surveyor, is likely to suffer for his reliance, and the surveyor himself to be mortified by a result that seems to impeach his judgment. Of course nothing in what has been said can require a sur- veyor to conceal his own judgment or to report the facts one way when he believes them to be another. He has no right to mislead, and he may rightfully express his opinion that an origi- nal monument was at one place, when at the same time he is satisfied that acquiescence has fixed the rights of parties as if it were at another. But he would do mischief if he were to attempt to " establish" monuments which he knew would tend to disturb settled rights ; the farthest he has a right to go as an officer of the law is to express his opinion where the monu- ment should be at the same time that he imparts the information 404 PLANE SURVEYING. to those who employ him, and who might otherwise be misled, that the same authority that makes him an officer, and entrusts him to make surveys, also allows parties to settle their own boundary lines, and considers acquiescence in a particular line or monument for any considerable period as strong, if not con- clusive, evidence of such settlement. The peace of the com- munity absolutely requires this rule. Foyce v. Williams, 26 Mich. Reports, 332. It is not long since that in one of the leading cities of the State an attempt was made to move houses two or three rods into a street, on the ground that a survej', under which the street had been located for many years, had been found on a more recent survey to be erroneous. From the foregoing it will appear that the duty of the sur- veyor, where boundaries are in dispute, must be varied by the circumstances. (1) He is to search for original monuments, or for the places where they were originally located, and allow these to control if he finds them, unless he has reason to believe that agreements of the parties express or implied have rendered thtm unimportant. By monuments in the case of government surveys we mean, of course, the corner and quarter stakes ; blazed lines or marked trees on the lines are not monuments ; they are merely guides or finger-posts, if we may use the ex- pression, to inform us with more or less accuracy where the monuments may be found. (2) If the original monuments are no longer discoverable, the question of location becomes one of evidence merely. It is merely idle for any State statute to direct a surveyor to locate or ' ' establish " a corner, as the place of the original monument, according to some inflexible rule. The surveyor, on the other hand, must inquire into all the facts, giving due prominence to the acts of parties con- cerned, and always keeping in mind, first, that neither his opin- ion nor his survey can be conclusive upon parties concerned ; and, second, that courts and juries may be required to follow after the surveyor over the same ground, and that it is exceed- ingly desirable that he govern his action by the same lights and same rules that will govern theirs. On town plats if a surplus or APPENDIX. 405 deficiency appears in a block when the actual boundaries are compared with the original figures, and there is no evidence to fix the exact location of the stakes which marked the division into lots, the rule of common sense and the law is that the sur- plus or deficiency is to be apportioned between the lots on an assumption that the error extended alike to all parts of the block. O'Brien v. McGrane, 29 Wis. Reports, 446 ; Quinnin v. Reixers, 46 Mich. Reports, 605. It is always possible when corners are extinct that the sur- veyor may usefully act as a mediator between parties, and assist in preventing legal controversies by settling doubtful Hues. Unless he is made for this purpose an arbitrator by legal sub- mission, the parties, of course, even if they consent to follow his judgment, cannot, on the basis of mere consent, be com- pelled to do so ; but if he brings about an agreement, and they carry it into effect by actually conforming their occupation to his lines, the action will conclude them. Of course it is desir- able that all such agreements be reduced to writing ; but this is not absolutely indispensable if they are carried into effect with- out. Meander Lines. The subject to which allusion will now be made is taken up with some reluctance, because it is believed the general rules are familiar. Nevertheless, it is often found that surveyors misapprehend them, or err in their application ; and as other interesting topics are somewhat connected with this, a little time devoted to it will probably not be altogether lost. The subject is that of meander lines. These are lines traced along the shores of lakes, ponds, and considerable rivers as the measures of quantity when sections are made fractional by such waters. These have determined the price to be paid when government lands were bought, and perhaps the impres- sion still lingers in some minds that meander lines are boundary lines, and all in front of them remains unsold. Of course this is erroneous. There was never any doubt that, except on the large navigable rivers, the boundary of the owners of the banks is the middle line of the river ; and while some courts have held 406 PLANK SURVEYING. that this was the rule on all fresh-water streams, large and small, others have held to the doctrine that the title to the bed of the stream below low-water mark is in the State while conceding to the owners of the bank all riparian rights. The practical differ- ence is not very important. In this State the rule that the centre line is the boundary line is applied to all our great rivers, includ- ing the Detroit, varied somewhat by the circumstance of there being a distinct channel for navigation in some cases with the stream in the main shallow, and also sometimes by the existence of islands. The troublesome questions for surveyors present themselves when the boundary line between two contiguous estates is to be continued from the meander line to the centre line of the river. Of course the original survey supposes that each purchaser of land on the stream has a water-front of the length shown by the field notes ; and it is presumable that he bought this particular land because of that fact. In many cases it now happens that the meander line is left some distance from the shore by the gradual change of course of the stream or diminution of the flow of water. Now the dividing line between two government sub- divisions might strike the meander line at right angles, or ob- liquely ; and in some cases, if it were continued in the same direction to the centre line of the river, might cut off from tbe water one of the subdivisions entirely, or at least cut it off from any privilege of navigation or other valuable use of the water, while the other might have a water-front much greater than the length of a line crossing it at right angles to its side lines. The effect might be that, of two government subdivisions of equal size and cost, one would be of very great value as water-front property, and the other comparatively valueless. A rule which would produce this result would not be just, and it has not been recognized in the law. Nevertheless, it is not easy to determine what ought to be the correct rule for every case. If the river has a straight course, or one nearly so, every man's equities will be preserved by this rule. Extend the line of division between the two parcels from APPENDIX. 407 the meander line to the centre line of the river, as nearly as pos- sible at right angles to the general course of the river at that point. This will preserve to each man the water-front which the field notes indicated, except as changes in the water may have affected it, and the only inconvenience will be that the division line between different subdivisions is likely to be more or less deflected where it strikes the meander line. This is the legal rule, and it is not limited to government sur- veys, but applies as well to water-lots which appear as such on town plats. Bay City Gas Light Co. v. The Industrial Works, 28 Mich. Reports, 182. It often happens, therefore, that the lines of city lots bounded on navigable streams are deflected as they strike the bank, or the line where the bank was when the town was first laid out. When the stream is very crooked, and especially if there are short bends, so that the foregoing rule is incapable of strict application, it is sometimes very difficult to determine what shall be done ; and in many cases the surveyor may be under the necessity of working out a rule for himself. Of course his action cannot be conclusive ; but if he adopts one that follows, as nearly as the circumstances will admit, the gen- eral rule above indicated, so as to divide as near as may be the bed of the stream among the adjoining owners in proportion to their lines upon the shore, his division, being that of an expert, made upon the ground and with all available lights, is likely to be adopted as law for the case. Judicial decisions, into which the surveyor would find it prudent to look under such circum- stances, will throw light upon his duties, and may constitute a sufficient guide when peculiar cases arise. Each riparian lot- owner ought to have a line on the legal boundary, namely, the centre line of the stream, proportioned to the length of his line on the shore ; and the problem in each case is, how this is to be given him. Alluvion, when a river imperceptibly changes its course, will be apportioned by the same rules. The existence of islands in a stream, when the middle line constitutes a boundary, will not affect the apportionment unless the islands were surveyed out as government subdivisions iu the 408 PLANE SURVEYING. original admeasurement. Wherever that was the case the pur- chaser of the island divides the bed of the stream on each side with the owner of the bank, and his rights also extend above and below the solid ground, and are limited by the peculiarities of the bed and the channel. If an island was not surveyed as a government subdivision previous to the sale of the bank, it is of course impossible to do this for the purposes of government sale afterwards, for the reason that the rights of the bank owners are fixed by their purchase : when making that they have a right to understand that all land between the meander lines, not sepa- rately surveyed and sold, will pass with the shore in the govern- ment sale ; and having this right, anything which their purchase would include under it cannot afterwards be taken from them. It is believed, however, that the Federal courts would not recog- nize the applicability of this rule to large navigable rivers, such as those uniting the Great Lakes. On all the little lakes of the State, which are mere expansions near their mouths of the rivers passing through them, such as the Muskegon, Pere Marquette, and Manistee, 7 the same rule of bed ownership has been judicially applied that is applied to the rivers themselves ; and the division lines are extended under the water in the same way. Rice v. Ruddiman, 10 Mich. 125. If such a lake were circular, the lines would converge to the centre ; if oblong or irregular, there might be a line in the middle on which they would terminate, whose course would bear some relation to that of the shore. But it can seldom be important to follow the division line very far under the water, since all private rights are subject to the public rights of navigation and other use, and any private use of the lands inconsistent with these would be a nuisance, and punishable as such. It is some- times important, however, to run the lines out for some consid- erable distance, in order to determine where one may lawfully moor vessels or rafts for the winter, or cut ice. The ice crop that forms over a man's land of course belongs to him. Lormau v. Benson, 8 Mich. 18 ; People's Ice Co. v. Steamer Excelsior, recently decided. APPENDIX. 409 What is said above will show how unfounded is the notion, which is sometimes advanced, that a ripai-ian proprietor on a meandered river may lawfully raise the water in the stream without liability to the proprietors above, provided he does not raise it so that it overflows the meander line. The real fact is, that the meander line has nothing to do with such a case, and an action will lie whenever he sets back the water upon the proprietor above, whether the overflow be below the meander lines or above them. As regards the lakes and ponds of the State, one may easily raise questions that it would be impossible for him to settle. Let us suggest a few questions, some of which are easily answered, and some not : (1) To whom belongs the land under these bodies of water, where they are not mere expansions of a stream flowing through them? (2) What public rights exist in them? (3) If there are islands in them which were not surveyed out and sold by the United States, can this be done now? Others will be suggested by the answers given to these. It seems obvious that the rules of private ownership which are applied to rivers cannot be applied to the Great Lakes. Perhaps it should be held that the boundary is at low-water mark, but improvements beyond this would only become unlaw- ful when they became nuisances. Islands in the Great Lakes would belong to the United States until sold, and might be surveyed and measured at any time. The right to take fish in the lakes or to- cut ice is public, like the right of navigation, but is to be exercised in such manner as not to interfere with the rights of shore-owners ; but, so far as these public rights can be the subject of ownership, they belong to the State, not the United States ; and so, it is believed, does the bed of a lake also. Pollard v. Hagan, 3 Howard's U. S. Reports. But such rights are not generally considered proper subjects of sale, but, like the right to make use of the public highways, they are held by the State in trust for all the people. What is said of the large lakes may, perhaps, be said also of many of the interior lakes of the State ; such, for example, as Houghton, 410 PLANE SURVEYING. Higgins, Cheboygan, Burt's, Mullet, Whitmore, and many others. But there are many little lakes or ponds which are gradually disappearing, and the shore proprietorship advances pari passu as the waters recede. If these are of any consider- able size, say, even a mile across, there may be questions of conflicting rights which no adjudication hitherto made could settle. Let an}' surveyor, for example, take the case of a pond of irregular form, occupying a mile square or more of territory, and undertake to determine the rights of the shore proprietors to its bed when it shall totally disappear, and he will find lie is in the midst of problems such as probably he has never grappled with, or reflected upon, before. But the general rules for the extension of shore lines which have already been laid down should govern such cases, or at least should serve as guides in their settlement. Where a pond is so small as to be included within the lines of a private purchase from the government, it is not believed the public have any rights in it whatever. Where it is not so included, it is believed they have rights of fishery, rights to take ice and water, and rights of navigation for business or pleasure. This is the common belief, and probably the just one. Shore rights must not be so exercised as to disturb these, and the States may pass all proper laws for their protection. It would be easy with suitable legislation to preserve these little bodies of water as permanent places of resort for the pleasure and recreation of the people, and there ought to be such legisla- tion. If the State should be recognized as owner of the beds of these small lakes and ponds, it would not be owner for the purpose of selling. It would be owner only as a trustee for the public use; and a sale would be inconsistent with the right of the bank owners to make use of the water in its natural condi- tion in connection with their estates. Some of them might be made salable lands by draining ; but the State could not drain, even for this purpose, against the will of the shore-owners, un- less their rights were appropriated and paid for. Upon many questions that might arise between the State as owner of the APPENDIX. 4H bed of a little lake and the shore-owners, it would be presump- tuous to express an opinion now, and fortunately the occasion does not require it. I have thus indicated a few of the questions with which sur- veyors may now and then have occasion to deal, and to which they should bring good sense and ssund judgment. Surveyors are not, and cannot be, judicial officers, but in a great many cases they act in a quasi judicial capacity, with the acquies- cence of parties concerned; and it is important for them to know by what rules they are to be guided in the discharge of their judicial functions. What I have said cannot contribute much to their enlightenment, but I trust will not be wholly without value. TABLES. TABLE I. THE COMMON OR BRIGGS LOGARITHMS OF THE NATURAL NUMBERS From 1 to 10000. 1-100 N log I log K log N log * log 1 0.00000 21 1. 32 222 41 1.61278 61 1.78533 81 1.90849 2 0. 30 103 22 1. 34 242 42 1. 62 325 62 1. 79 239 82 1.91381 3 0.47712 23 1. 36 173 43 1. 63 347 63 1.79934 83 1.91908 4 0.60206 24 1.38021 44 1. 64 345 64 1.80618 84 1.92428 5 0. 69 897 25 1. 39 794 45 1. 65 321 65 1. 81 291 85 1.92942 6 0. 77 815 26 1.41497 46 1. 66 276 66 1. 81 954 86 1.93450 7 0. 84 510 27 1.43136 47 1. 67 210 67 1.82607 87 1.93952 8 0.90309 28 1.44716 48 1. 68 124 68 1. 83 251 88 1.94448 9 0. 95 424 29 1.46240 49 1.69020 69 1.83885 89 1.94939 10 1.00000 30 1. 47 712 50 1.69897 70 1.84510 90 1.95424 11 1. 04 139 31 1.49136 51 1. 70 757 71 1. 85 126 91 1.95904 12 1.07918 32 1.50515 52 1.71600 72 1. 85 733 92 1.96379 13 1. 11 394 33 1.51851 63 1. 72 428 73 1.86332 93 1.96848 14 1.14613 34 1. 53 148 54 1. 73 239 74 1.86923 94 1.97313 15 1.17609 35 1.54407 55 1.74036 75 1. 87 506 95 1. 97 772 16 1.20412 36 1. 55 630 56 1.74819 76 1.88081 96 1.98227 17 1. 23 045 37 1.56820 67 1. 75 587 77 1.88649 97 1.98677 18 1. 25 527 38 1.57978 58 1.76343 78 1.89209 98 1.99123 19 1. 27 875 39 1.59106 59 1. 77 085 79 1.89763 99 1.99564 20 1. 30 103 40 1.60206 60 1.77815 80 1.90309 100 2.00000 I log log I log V log N N 1-100 100-150 If 01234 56789 100 101 102 103 104 00000 00043 00087 00130 00173 00432 00475 00518 00561 00604 00860 00903 00945 00988 01030 01284 01326 01368 01410 01452 01703 01745 01787 01828 01870 00217 00260 00303 00346 00389 00647 00689 00732 00775 00817 01 072 01 115 01 157 01 199 01 242 01494 01536 01578 01620 01662 01912 01953 01995 02036 02078 106 106 107 108 109 02119 02160 02202 02243 02284 02531 02572 02612 02653 02694 02938 02979 03019 03060 03100 03342 03383 03423 03463 03503 03743 03782 03822 03862 03902 02325 02366 02407 02449 02490 02735 02776 02816 02857 02898 03141 03181 03222 03262 03302 03543 03583 03623 03663 03703 03941 03981 04021 04060 04100 110 111 112 113 114 04139 04179 04218 04258 04297 04532 04571 04610 04650 04689 04922 04961 04999 05038 05077 05 308 05 346 05 385 05 423 05 461 05690 05729 05767 05805 05843 04336 04376 04415 04454 04493 04727 04766 04805 04844 04883 05115 05154 05192 05231 05269 05500 05538 05576 05614 05652 05881 05918 05956 05994 06032 115 116 117 118 119 06070 06108 06145 06183 06221 06446 06483 06521 06558 06595 06819 06856 06893 06930 06967 07188 07225 07262 07298 07335 07555 07591 07628 07664 07700 06258 06296 06333 06371 06408 06633 06670 06707 06744 06781 07004 07041 07078 07115 07151 07372 07408 07445 07482 07518 07737 07773 07809 07846 07882 120 121 122 123 124 07918 07954 07990 08027 08063 08279 08314 08350 08386 08422 08636 08672 08707 08743 08778 08991 09026 09061 09096 09132 09342 09377 09412 09447 09482 08099 08135 08171 08207 08243 08458 08493 08529 08565 08600 08814 08849 08884 08920 08955 09167 09202 09237 09272 09307 09517 09552 09587 09621 09656 125 126 127 128 129 09691 09726 09760 09795 09830 10037 10072 10106 10140 10175 10380 10415 10449 10483 10517 10721 10755 10789 10823 10857 11059 11093 11126 11160 11193 09864 09899 09934 09968 10003 10209 10243 10278 10312 10346 10551 10585 10619 10653 10687 10890 10924 10958 10992 11025 11227 11261 11294 11327 11361 ISO 131 132 133 134 11394 11428 11461 11494 11528 11727 11760 11793 11826 11860 12057 12090 12123 12156 12189 12385 12418 12450 12483 12516 12710 12743 12775 12808 12840 11561 11594 11628 11661 11694 11893 11926 11959 11992 12024 12222 12254 12287 12320 12352 12548 12581 12613 12646 12678 12872 12905 12937 12969 13001 135 136 137 138 139 13033 13066 13098 13130 13162 13354 13386 13418 13450 13 481 13672 13704 13735 13767 13799 13988 14019 14051 14082 14114 14301 14333 14364 14395 14426 13194 13226 13258 13290 13322 13513 13545 13577 13609 13640 13830 13862 13893 13925 13956 14145 14176 14208 14239 14270 14457 14489 14520 14551 14582 14O 141 142 143 144 14613 14644 14675 14706 14737 14922 14953 14983 15014 15045 15229 15259 15290 15320 15351 15534 15564 15594 15625 15655 15836 15866 15897 15927 15957 14768 14799 14829 14860 14891 15076 15106 15137 15168 15198 15381 15412 15442 15473 15503 15685 15715 15746 15776 15806 ' 15 987 16017 16047 16077 16107 145 146 147 148 149 16137 16167 16197 16227 16256 16435 16465 16495 16524 16554 16732 16761 16791 16820 16850 17026 17056 17085 17114 17143 17319 17348 17377 17406 17435 16286 16316 16346 16376 16406 16584 16613 16643 16673 16702 16879 16909 16938 16967 16997 17173 17202 17231 17260 17289 17464 17493 17522 17551 17580 ISO 17609 17638 17667 17696 17725 17754 17782 17811 17840 17S69 N 01234 36789 100-150 150-200 N O 1 2 3 4 56789 ISO 17609 17638 17667 17696 17725 17754 17782 17811 17840 17869 151 17898 17926 17955 17984 18013 18041 18070 18099 18127 18156 152 18 184 18213 18241 18270 18298 18327 18355 18384 18412 18441 153 18469 18498 18526 18554 18583 18611 18639 18667 186% 18724 154 18752 18780 18808 18837 18 865. 18893 18921 18949 18977 19005 155 19033 19061 19089 19117 19145 19173 19201 19229 19257 19285 156 19312 19340 19368 19396 19424 19451 19479 19507 19535 19562 157 19590 19618 19645 19673 19700 19728 19756 19783 19811 19838 158 19866 19893 19921 19948 19976 20003 20030 20058 20085 20112 159 20140 20167 20194 20222 20249 20276 20303 20330 20358 20385 160 20412 20439 20466 20493 20520 20548 20575 20602 20629 20656 161 20683 20710 20737 20763 20790 20817 20844 20871 20898 20925 162 20952 20978 21005 21032 21059 21085 21112 21139 21165 21192 163 21219 21245 21272 21299 21325 21352 21378 21405 21431 21458 164 21484 21511 21537 21564 21590 21617 21643 21669 216% 21722 165 21748 21775 21801 21827 21854 21880 21906 21932 21958 21985 166 22011 22037 22063 22089 22115 22141 22167 22194 22220 22246 167 22272 22298 22324 22350 22376 22401 22427 22453 22479 22505 168 22531 22557 22583 22608 22634 22660 22686 22712 22737 22763 169 22789 22814 22840 22866 22891 22917 22943 22968 22994 23019 17O 23045 23070 23096 23121 23147 23172 23198 23223 23249 23274 171 23300 23325 23350 23376 23401 23426 23452 23477 23502 23528 172 23553 23578 23603 23629 23654 23679 23704 23729 23754 23779 173 23805 23830 23855 23880 23905 23930 23955 23980 24005 24030 174 24055 24080 24105 24130 24155 24180 24204 24229 24254 24279 175 24304 24329 24353 24378 24403 24428 24452 24477 24502 24527 176 24551 24576 24601 24625 24650 24674 24699 24724 24748 24773 177 24797 24822 24846 24871 24895 24920 24944 24969 24993 25018 178 25042 25066 25091 25115 25139 25164 25188 25212 25237 25261 179 25285 25310 25334 25358 25382 25406 25431 25455 25479 25503 180 25527 25551 25575 25600 25624 25648 25672 25696 25720 25744 181 25768 25792 25816 25840 25864 25888 25912 25935 25959 25983 182 26007 26031 26055 26079 26102 26126 2615TT26174 26198 26221 183 26245 26269 26293 26316 26340 26364 26387 26411 26435 26458 184 26482 26505 26529 26553 26576 26600 26623 26647 26670 26694 185 26717 26741 26764 26788 26811 26834 26858 26881 26905 26928 186 26951 26975 26998 27021 27045 27068 27091 27114 27138 27161 187 27184 27207 27231 27254 27277 27300 27323 27346 27370 27393 188 27416 27439 27462 27485 27508 27531 27554 27577 27600 27623 189 27646 27669 27692 27715 27738 27761 27784 27807 27830 27852 190 27875 27898 27921 27944 27 967 27989 28012 28035 28058 28081 191 28103 28126 28149 28171 28194 28217 28240 28262 28285 28307 192 28330 28353 28375 28398 28421 28443 28466 28488 28511 28533 193 28556 28578 28601 28623 28646 28668 28691 28713 28735 28758 194 28780 28803 28825 28847 28870 28892 28914 28937 28959 28 981 195 29003 29026 29048 29070 29092 29115 29137 29159 29181 29203 196 29226 29248 29270 29292 29314 29336 29358 29380 29403 29425 197 29447 29469 29491 29513 29535 29557 29579 29601 29623 29645 198 29667 29 688 29710 29732 29754 29776 29798 29820 29842 29863 199 29885 29907 29929 29951 29973 29994 30016 30038 30060 300S1 200 30103 30125 30146.30168 30190 30211 30233 30255 30276 30298 N O 1 2 3 4 5 6 7 8 i> 150-200 200-250 N 01234 5 6 78 9 200 201 202 203 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45 117 45 133 45 148 45 163 45255 45271 45 2S6 45301 45317 45408 45423 45439 45454 45469 45 561 45 576 45 591 45 606 45 621 45712 45728 45743 45758 45773 45864 45879 45894 45909 45924 46015 46030 46045 46060 46075 46165 46180 46195 46210 46225 46315 46330 46345 46359 46374 46464 46479 46494 46509 46523 46613 46627 46642 46657 46672 46761 46776 46790 46805 46820 46909 46923 46938 46953 46%7 47056 47070 47085 47100 47114 47202 47217 47232 47246 47261 47349 47363 47378 47392 47407 47494 47509 47524 47538 47553 47640 47654 47669 47683 47698 47784 47799 47813 47828 47842 250-300 300-350 N 01234 56789 300 301 302 303 304 47712 47727 47741 47756 47770 47857 47871 47885 47900 47914 48001 48015 48029 48044 48058 48144 48159 48173 48187 48202 48287 48302 48316 48330 48344 47784 47799 47813 47828 47842 47929 47943 47958 47972 47986 48073 48087 48101 48116 48130 48216 48230 48244 48259 48273 48359 48373 48387 48401 48416 305 306 307 308 309 48430 48444 48458 48473 48487 48572 48586 48601 48615 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53020 53033 53046 53058 53071 52569 52582 52595 52608 52621 52699 52711 52724 52737 52750 52827 52840 52853 52866 52879 52956 52969 52982 52994 53007 53084 53097 53110 53122 53135 340 341 342 343 344 53148 53161 53173 53186 53199 53275 53288 53301 53314 53326 53403 53415 53428 53441 53453 53529 53542 53555 53567 53580 53656 53668 53681 53694 53706 53212 53224 53237 53250 53263 53339 53352 53364 53377 53390 53466 53479 53491 53504 53517 53593 53605 53618 53631 53643 53719 53732 53744 53757 53769 345 346 347 348 349 53782 53794 53807 53820 53832 53908 53920 53933 53945 53958 54033 54045 54058 54070 54083 54158 54170 54183 54195 54208 54283 54295 54307 54320 54332 53845 53857 53870 53882 53895 53970 53983 53995 54008 54020 54095 54108 54120 54133 54145 54220 54233 54245 54258 54270 54345 54357 54370 54382 54394 350 54407 54419 54432 54444 54456 54469 54481 54494 54506 54518 N O 1 2 3 4 56789 300-350 350-400 3 54407 54419 54432 54444 54456 54531 54543 54555 54568 54580 54654 54667 54679 54691 54704 54777 54790 54802 54814 54827 54900 54913 54925 54937 54949 55023 55035 55047 55060 55072 55145 55157 55169 55182 55194 55267 55279 55291 55303 55315 55388 55400 55413 55 425. 55437 55509 55522 55534 55546 55558 55630 55642 55654 55666 55678 55751 55763 55775 55787 55799 55871 55883 55 895 55907 55919 55991 56003 56015. 56027 56038 56110 56122 56134 56146 56158 56229 56241 56253 56265 56277 56348 56360 56372 56384 563% 56467 56478 56490 56502 56514 56585 56597 56608 56620 56632 56703 56744 56726 56738 56750 56820 56832 56844 56937 56949 56961 57054 57066 57078 57171 57 183 57194 57287 57299 57310 57403 57415 57426 57519 57530 57542 57634 57646 57657 57749 57761 57772 57864 57875 57887 56855 56867 56972 56984 57 089 57101 57206 57217 57322 57334 57438 57449 57553 57565 57669 57680 57784 57795 57898 57910 57978 57990 58001 58013 58024 58092 58104 58115 58127 58138 58206 58218 58229 58240 58252 58320 58331 58343 58354 58365 58433 58444 58456 58467 58478 58546 58557 58569 58580 58591 58659 58670 58681 58692 58704 58771 58782 58794 58805 58816 58883 58894 58906 58917 58928 58995 59006 59017 59028 59040 59106 59118 59129 59140 59151 59218 59229 59240 59251 59262 59329 59340 59351 59362 59373 59439 59450 59461 59472 59483 59550 59561 59572 59583 59594 59660 59671 59 682 59693 59704 59770 59780 59791 59802 59813 59879 59890 59901 59912 59923 59988 59999 60010 60021 60032 60097 60108 60119 60130 60141 60206 60217 60228 60239 60249 r, 54481 54494 54506 54518 54605 54617 54630 54642 54728 54741 54753 54765 54851 54864 54876 54888 54974 54986.54998 55011 55 0% 55 108 55 121 55 133 55218 55230 55242 55255 55340 55352 55364 55376 55461 55473 55485 55497 55582 55594 55606 55618 54469 54593 54716 54839 54962 55084 55206 55328 55449 55570 55691 55703 55715 55727 55739 55811 55823 55835 55847 55859 55931 55943 55955 55967 55979 56050 56062 56074 56086 56098 56170 56182 56194 56205 56217 56289 56301 56312 56324 56336 56407 56419 56431 56443 56455 56526 56538 56549 56561 56573 56644 56656 56667 56679 56691 56761 56773 56785 56797 56808 56879 56891 56902 56914 56926 56996 57008 57019 57031 57043 57113 57124 57136 57148 57159 57229 57241 57252 57264 57276 57345 57357 57368 57380 57392 57461 57473 57484 574% 57507 57576 57588 57600 57611 57623 57692 57703 57715 57726 57738 57807 57818 57830 57841 57852 57921 57933 57944 57955 57 %7 58035 58047 58058 58070 58081 58149 58161 58172 58184 58195 58263 58274 58286 58297 58309 58377 58388 58399 58410 58422 58490 58501 58512 58524 58535 58602 58614 58625 58636 58647 58715 58726 58737 58749 58760 58827 58838 58850 58861 58872 58939 58950 58961 58973 58984 59051 59062 59073 59084 59095 59162 59173 59184 59195 59207 59273 59284 59295 59306 59 318 59384 59395 59406 59417 59428 59494 59506 59517 59528 59539 59605 59616 59627 59638 59649 59715 59726 59737 59748 59759 59824 59835 59846 59857 59S6S 59934 59945 59956 59966 59977 60043 60054 60065 60076 600S6 60152 60163 60173 60184 60195 60260 60271 602S2 60293 60304 350-400 400-450 H 01234 56789 400 401 402 403 404 60206 60217 60228 60239 60249 60314 60325 60336 60347 60358 60423 60433 60444 60455 60466 60531 60541 60552 60563 60574 60638 60649 60660 60670 60681 60260 60271 60282 60293 60304 60369 60379 60390 60401 60412 60477 60487 60498 60509 60520 60584 60595 60606 60617 60627 60692 60703 60713 60724 60735 405 406 407 408 409 60746 60756 60767 60778 60788 60853 60863 60874 60 885 60895 60959 60970 60981 60991 61002 61066 61077 61087 61098 61109 61172 61183 61194 61204 61215 60799 60810 60821 60831 60842 60906 60917 60927 60938 60949 61013 61023 61034 61045 61055 61 119 61 130 61 140 61 151 61 162 61225 61236 61247 61257 61268 410 411 412 413 414 61278 61289 61300 61310 61321 61384 61395 61405 61416 61426 61490 61500 61511 61521 61532 61595 61606 61616 61627 61637 61700 61711 61721 61731 61742 61331 61342 61352 61363 61374 61437 61448 61458 61469 61479 61542 61553 61563 61574 61584 61648 61658 61669 61679 61690 61752 61763 61773 61784 61794 415 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64972 65031 65040 65050 65060 65070 65128 65137 65147 65157 65167 65225 65234 65244 65254 65263 64885 64895 64904 64914 64924 64 982 64992 65002 65011 65021 65079 65089 65099 65108 65118 65 176 65 186 65 196 65 205 65 215 65273 65283 65292 65302 65312 45O 65321 65331 65341 65350 65360 65369 65379 65389 65398 65408 N O 1 2 3 4 56789 400-450 450-500 O 3 o 8 497 498 65321 65331 65341 65350 65360 65418 65427 65437 65447 65456 65514 65523 65533 65543 65552 65610 65619 65629 65639 65648 65 706 65 715 65 725 65 734 65 744 65801 65811 65820 65830 65839 65896 65906 65916 65925 65935 65992 66001 66011 66020 66030 66087 66096 66106 66115 66124 66181 66191 66200 66210 66219 66276 66285 66295 66304 66314 66370 66380 66 389 66398 66408 66464 66474 664S3 66492 66502 66558 66567 66577 66586 665% 66652 66661 66671 66680 66689 66745 66755 66764 66773 66783 66839 66848 66857 66867 66876 66932 66941 66950 66960 66969 67025 67034 67043 67052 67062 67117 67127 67136 67145 67154 67210 67219 67228 67237 67247 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89713 89719 89724 89730 89763 89768 89774 89779 89785 89818 89823 89829 89834 89840 89873 89878 89883 89889 89894 89927 89933 89938 89944 89949 89982 89988 89993 89998 90004 90037 90042 90048 90053 90059 90091 90097 90102 90108 90113 90146 90151 90157 90162 90168 90200 90206 90211 90217 90222 90255 90260 90266 90271 90276 90309 90314 90320 90325 90331 87535 87541 87547 87552 87558 87593 87599 87604 87610 87616 87651 87656 87662 87668 87674 87708 87714 87720 87726 87731 87766 87772 87777 87783 87789 87823 87829 87835 87841 87846 87881 87887 87892 87898 87904 87938 87944 87950 87955 87 961 879% 88001 88007 88013 88018 88053 88058 88064 88070 88076 88110 88116 88121 88127 88133 88167 88173 88178 88184 88190 88224 88230 88235 88241 88247 88281 88287 88292 88298 88304 88338 88343 88349 88355 88360 88395 88400 88406 88412 88417 88451 88457 88463 88468 88474 88508 88513 88519 88525 88530 88564 88570 88576 88581 88587 88621 88627 88632 88638 88643 88677 88683 88689 88694 88700 88734 88739 88745 88750 88756 88790 88795 88801 88807 88812 88846 88852 88857 88863 88868 88902 88908 88913 88919 88925 88958 88964 88 969 88975 88981 89014 89020 89025 89031 89037 89070 89076 89081 89087 89092 89126 89131 89137 89143 89148 89182 89187 89193 89198 89204 89237 89243 89248 89254 89260 89293 89298 89304 89310 89315 89348 89354 89360 89365 89371 89404 89409 89415 89421 89426 89459 89465 89470 89476 89481 89515 89520 89526 89531 89537 89570 89575 89581 89586 89592 89625 89631 89636 89642 89647 89680 89686 89691 89697 89702 89735 89741 89746 89752 89757 89790 897% 89801 89807 89812 89845 89851 89856 89862 89867 89900 89905 89911 89916 89922 89955 89960 89966 89971 89977 90009 90015 90020 90026 90031 90064 90069 90075 90080 90086 90119 90124 90129 90135 90140 90173 90179 90184 90189 90195 90227 90233 90238 90244 90249 90282 90287 90293 90298 90304 90336 90342 90347 90352 90358 8 750-800 16 800-850 N 01234 56789 8OO 801 802 803 804 90309 90314 90320 90325 90331 90363 90369 90374 90380 90385 90417 90423 90428 90434 90439 90472 90477 90482 90488 90493 90526 90531 90536 80542 90547 90336 90342 90347 90352 90358 90390 90396 90401 90407 90412 90445 90450 90455 90461 90466 90499 90504 90509 90515 90520 90553 90558 90563 90569 90574 805 806 807 808 809 90580 90585 90590 90596 90601 90634 90639 90644 90650 90655 90687 90693 90698 90703 90709 90741 90747 90752 90757 90763 90795 90800 90806 90811 90816 90607 90612 90617 90623 90628 90660 90666 90671 90677 90682 90714 90720 90725 90730 90736 90768 90773 90779 90784 90789 90822 90827 90832 90838 90843 81O 811 812 813 814 90849 90854 90859 90865 90870 90902 90907 90913 90918 90924 90956 90961 90966 90972 90977 91009 91014 91020 91025 91030 91062 91068 91073 91078 91084 90875 90881 90886 90891 90897 90929 90934 90940 90945 90950 90982 90988 90993 90998 91004 91036 91041 91046 91052 91057 91089 91094 91100 91105 91110 815 816 817 818 819 91116 91121 91126 91132 91137 91169 91174 91180 91185 91190 91222 91228 91233 91238 91243 91275 91281 91286 91291 91297 91328 91334 91339 91344 91350 91142 91148 91153 91158 91164 91196 91201 91206 91212 91217 91249 91254 91259 91265 91270 91302 91307 91312 91318 91323 91355 91360 91365 91371 91376 820 821 822 823 824 91381 91387 91392 91397 91403 91434 91440 91445 91450 91455 91487 91492 91498 91503 91508 91540 91545 91551 91556 91561 91593 91598 91603 91609 91614 91408 91413 91418 91424 91429 91461 91466 91471 91477 91482 91514 91519 91524 91529 91535 91566 91572 91577 91582 91587 91619 91624 91630 91635 91640 825 826 827 828 829 91645 91651 91656 91661 91666 91698 91703 91709 91714 91719 91751 91756 91761 91766 91772 91803 91808 91814 91819 91824 91855 91861 91866 91871 91876 91672 91677 91682 91687 91693 91724 91730 91735 91740 91745 91777 91782 91787 91793 91798 91829 91834 91840 91845 91850 91882 91887 91892 91897 91903 830 831 832 833 834 91908 91913 91918 91924 91929 91960 91965 91971 91976 91981 92012 92018 92023 92028 92033 92065 92070 92075 92080 92085 92117 92122 92127 92132 92137 91934 91939 91944 91950 91955 91986 91991 91997 92002 92007 92038 92044 92049 92054 92059 92091 92096 92101 92106 92111 92143 92148 92153 92158 92163 835 836 837 838 839 92169 92174 92179 92184 92189 92221 92226 92231 92236 92241 92273 92278 92283 92288 92293 92324 92330 92335 92340 92345 92376 92381 92387 92392 92397 92195 92200 92205 92210 92215 92247 92252 92257 92262 92267 92298 92304 92309 92314 92319 92350 92355 92361 92366 92371 92402 92407 92412 92418 92423 840 841 842 843 844 92428 92433 92438 92443 92449 92480 92485 92490 92495 92500 92531 92536 92542 92547 92552 92583 92588 92593 92598 92603 92634 92639 92645 92650 92655 92454 92459 92464 92469 92474 92505 92511 92516 92521 92526 92557 92562 92567 92572 92578 92609 92614 92619 92624 92629 92660 92665 92670 92675 92681 845 846 847 848 849 92686 92691 92696 92701 92706 92737 92742 92747 92752 92758 92788 92793 92799 92804 92809 92840 92845 92850 92855 92860 92891 92896 92901 92906 92911 92711 92716 92722 92727 92732. 92763 92768 92773 92778 92 783 92814 92819 92824 92829 92834 92865 92870 92875 92881 92886 92916 92921 92927 92932 92937 850 92942 92947 92952 92957 92 962 92 967 92973 92978 92983 92 988 N 01234 56789 800-850 850-900 17 3 92942 92947 92952 92957 92962 92993 92998 93003 93 008 93013 93044 93049 93054 93059 93064 93095 93100 93105 93110 93115 93 146 93 151 93 156 93 16! 03 166 93197 93202 93207 93212 93217 93247 93252 93258 93263 93268 93298 93303 93308 93313 93318 93349 93354 93359 93364 93369 93399 93404 93409 93414 93420 934^0 93455 93460 93465 93470 93500 93505 93510 93515 93520 93551 93556 93561 93566 93571 93601 93606 93611 93616 93621 93651 93656 93661 93666 93671 93702 93707 93712 93717 93722 93752 93757 93762 93767 93772 93802 93807 93 812 93 81 7 93822 93852 93857 93862 93867 93 872 93902 93907 93912 93917 93922 93952 93957 93962 93967 93972 94002 94007 94012 94017 94022 94052 94057 94062 94067 94072 94101 94106 94111 94116 94121 94151 94156 94161 94166 94171 94201 94206 94211 94216 94221 94250 94255 94260 94265 94270 94300 94305 94310 94315 94320 94349 94354 94359 94364 94369 94399 94404 94409 94414 94419 94448 94453 94458 94463 94468 94498 94503 94507 94512 94517 94547 94552 94557 94562 94567 945% 94601 94606 94611 94616 94645 94650 94655 94660 94665 94694 94699 94704 94709 94714 94743 94748 94753 94758 94763 94792 94797 94802 94807 94812 94841 94846 94 851 94856 94861 94890 94895 94900 94905 94910 94939 94944 94949 94954 94959 94 988 949V3 94998 95002 95007 95036 95041 v5 046 95051 95056 95085 95090 95 005 95100 95105 95134 95139 95 1*3 95148 95153 95182 95231 95279 95328 95376 95187 95236 95 284 95332 95381 95192 95197 95202 95240 95245 95250 95289 95294 95299 95337 95342 95347 95386 95390 95395 92967 92973 92978 929S3 92988 93018 93024 93029 93034 93039 93069 93075 93080 93085 93090 93120 93125 93131 93136 93141 93171 93176 93181 93186 93192 93222 93273 93323 93374 93425 93475 93526 93576 93626 93676 93227 93278 93328 93379 93430 93480 93531 93581 93631 93682 93232 93237 93242 93283 93288 93293 93334 93339 93344 93384 93389 93394 93435 93440 93445 93485 93490 93495 93536 93541 93546 93586 93591 93596 93636 93641 93646 93687 93692 93697 95424 95429 95434 95439 95444 93727 93732 93737 93742 93747 93777 93782 93787 93792 93797 93827 93832 93837 93842 93847 93877 93882 93887 93892 93897 93927 93932 93937 93942 93947 93977 93982 93987 93992 93997 94027 94032 94037 94042 94047 94077 94082 94086 94091 94096 94126 94131 94136 94141 94146 94176 94181 94186 94191 941% 94226 94231 94236 94240 94245 94275 94280 94285 94290 94295 94325 94330 94335 94340 94345 94374 94379 94384 94389 94394 94424 94429 94433 94438 94443 94473 94478 94483 94488 94493 94522 94527 94532 94537 94542 94571 94576 94581 94586 94591 94621 94626 94630 94635 94640 94670 94675 94680 94685 94689 94719 94724 94729 94734 94738 94768 94773 94778 94783 94787 94817 94822 94827 94832 94836 94 866 94 871- 94 876 94 880 94 885 94915 94919 94924 94929 94934 94963 94968 94973 94978 94983 95012 95017 95022 95027 95032 95061 95066 95071 95075 95 080 95109 95114 95119 95124 95129 95 158 95 163 95 168. 95 173 95 177 95207 95211 95216 95221 95226 95255 95260 95265 95270 95274 95303 95308 95313 95318 95323 95352 95357 95361 95366 95371 95400 95405 95410 95415 95419 95448 95453 95458 95463 95 468 8 859-900 18 900-950 N O 1 2 3 4 56789 900 901 902 903 904 95424 95429 95434 95439 95444 95472 95477 95482 95487 95492 95521 95525 95530 95535 95540 95569 95574 95578 95583 95588 95617 95622 95626 95631 95636 95448 95453 95458 95463 95468 95497 95501 95506 95511 95516 95545 95550 95554 95559 95564 95593 95598 95602 95607 95612 95641 95646 95650 95655 95660 905 906 907 908 909 95665 95670 95674 95679 95684 95713 95718 95722 95727 95732 95761 95766 95770 95775 95780 95809 95813 95818 95823 95828 95856 95861 95866 95871 95875 95689 95694 95698 95703 95708 95 737 95 742 95 746 95 751 95 756 95 785 95 789 95 794 95 799 95 804 95832 95837 95842 95847 95852 95880 95885 95890 95895 95899 910 911 912 913 914 95904 95909 95914 95918 95923 95952 95957 95961 95966 95971 95999 96004 96009 96014 96019 96047 96052 96057 96061 96066 96095 96099 96104 96109 96114 95928 95933 95938 95942 95947 95976 95980 95985 95990 95995 96023 96028 96033 96038 96042 96071 96076 96080 96085 96090 96118 96123 96128 96133 96137 915 916 917 918 919 96142 96147 96152 96156 96161 96190 96194 96199 96204 96209 96237 96242 96246 96251 96256 96284 96289 96294 96298 96303 96332 96336 96341 96346 96350 96166 96171 96175 96180 96185 96213 96218 96223 96227 96232 96261 96265 96270 96275 96280 96308 96313 96317 96322 96327 96355 96360 96365 96369 96374 920 921 922 923 924 96379 96384 96388 96393 96398 96426 96431 96435 96440 96445 96473 96478 96483 96487 96492 96520 96525 96530 96534 96539 96567 96572 96577 96581 96586 96402 96407 96412 96417 96421 96450 96454 96459 96464 96468 96497 96501 96506 96511 96515 96544 96548 96553 96558 96562 96591 96595 96600 96605 96609 925 926 927 928 929 96614 96619 96624 96628 96633 96661 96666 96670 96675 96680 96708 96713 96717 96722 96727 96755 96759 96764 % 769 96774 96802 96806 96811 96816 96820 96638 96642 96647 96652 96656 96685 96689 96694 96699 96703 96731 96736 96741 96745 96750 96778 96783 96788 96792 96797 96825 96830 96834 96839 96844 930 931 932 933 934 96848 96853 96858 96862 96867 96895 96900 96904 96909 96914 96942 96946 96951 96956 96960 96988 96993 96997 97002 97007 97035 97039 97044 97049 97053 96872 96876 96881 96886 96890 96918 96923 96928 96932 9w937 96965 96970 96974 96979 96984 97011 97016 97021 97025 97030 97058 97063 97067 97072 97077 935 936 937 938 939 97081 97086 97090 97095 97100 97128 97132 97137 97142 97146 97174 97179 97183 97188 97192 97 220 97 225 .97 230 97 234 97 239 97267 97,271 97276 97280 97285 97104 97109 97114 97118 97123 97151 97155 97160 97165 97169 97197 97202 97206 97211 97216 97243 97248 97253 97257 97262 97290 97294 97299 97304 97308 940 941 942 943 944 97313 97317 97322 97327 97331 97359 97364 97368 97373 97377 97405 97410 97414 97419 97424 97451 97456 97460 97465 97470 97497 97502 97506 97511 97516 97336 97340 97345 97350 97354 97382 97387 97391 97396 97400 97428 97433 97437 97442 97 M7 97474 97479 97483 97488 97493 97520 97525 97529 97534 97539 945 946 947 948 949 97543 97548 97552 97557 97562 97589 97594 97598 97603 97607 97635 97640 97644 97649 97653 97681 97685 97690 97695 97699 97727 97731 97736 97740 97745 97566 97571 97575 97580 97585 97612 97617 97621 97626 97630 97658 97663 97667 97672 97676 , 97704 97708 97713 97717 97722 ; 97 749 97 754 97 759 97 763 97 768 , 950 97772 97777 97782 97786 97791 97795 97800 97804 97809 97813 N 01234 56789 900-950 950-1000 19 N 950 951 952 953 954 955 956 957 O 97772 97777 97782 97786 97791 97818 97823 97827 97832 97836 97864 97868 97873 97877 97882 97909 97914 97918 97923 97928 97955 97959 97964 97968 97973 98000 98005 98009 98014 98019 98046 98050 98055 98059 98064 98091 98096 98100 98105 98109 98137 98141 98146 98150 98155 98182 98186 98191 98195 98200 98227 98232 98236 98241 98245 98272 98277 98 281 98286 98290 98318 98322 98327 98331 98336 98363 98367 98372 98376 98381 98408 98412 98417 98421 98426 98453 98457 98462 98466 98471 98498 98502 98507 98511 98516 98543 98547 98552 98556 98561 98588 98592 98597 98601 98605 98632 98637 98641 98646 98650 98677 98682 98686 98691 98695 98722 98726 98731 98735 98740 98767 98771 98776 98780 98784 98811 98816 98820 98825 98829 98856 98860 98865 98869 98874 98900 98905. 98909 98914 98918 98 945. 98949 98954 98958 98 963 98989 98994 98998 99003 99007 99034 99038 99043 99047 99052 99078 99083 99087 99092 99096 99123 99127 99131 99136 99140 99167 99171 99176 99180 99185 99211 99216 99220 99224 99229 99255 99260 99264 99269 99273 99300 99304 99308 99313 99317 99344 99348 99352 99357 99361 99388 99392 99396 99401 99405 99432 99436 99441 99445 99449 99476 99480 99484 99489 99493 99520 99524 99528 99533 99537 99564 99568 99572 99577 99581 99607 99612 99616 99621 99625 99651 99656 99660 99664 99669 99695 99699 99704 99708 99712 99739 99743 99747 99752 99756 99782 99787 99791 99826 99830 99835 99870 99874 99878 99913 99917 99922 99957 99961 99 965 00000 00004 00009 99795 99839 99883 99926 99970 00013 00017 99800 99843 99887 99930 99974 8 9 97795 97800 97804 97809 97813 97841 97845 97850 97855 97859 97886 97891 97896 97900 97905 97932 97937 97941 97946 97950 97978 97982 97987 97991 979% 98023 98028 98032 98037 98041 98068 98073 98078 98082 98087 98114 98118 98123 98127 98132 98159 98164 98168 98173 98177 98204 98209 98214 98218 98223 98250 98254 98259 98263 98268 98295 98299 98304 98308 98 3 13 98340 98345 98349 98354 98358 98385 98390 98394 98399 98403 98430 98435 98439 98444 98 448 98475 98480 98484 98489 98493 98520 98525 98529 98534 98538 98565 98570 98574 98579 98583 98610 98614 98619 98623 98628 98655 98659 98664 98668 98673 98700 98704 98709 98713 98717 98744 98749 98753 98758 98762 98789 98793 98798 98802 98807 98834 98838 98843 98847 98851 98878 98883 98887 98892 988% 98923 98927 98932 98936 98941 98967 98972 98976 98981 98985 99012 99016 99021 99025 99029 99056 99061 99065 99069 99074 99100 99105 99109 99114 99118 99145 99149 99154 99158 99162 99189 99193 99198 99202 99207 99233 99238 99242 99247 99251 99277 99282 99 286 99291 99295 99322 99326 99330 99335 99339 99366 99370 99374 99379 99383 99410 99414 99419 99423 99427 99454 99458 99463 99467 99471 99498 99502 99506 99511 99515 99542 99546 99550 99555 99559 99585 99590 99594 99599 99603 99629 99634 99638 99642 99647 99673 99677 99682 99686 99691 99717 99721 99726 99730 99734 99760 99765 99769 99774 99778 99813 99 856 99900 99944 99987 00022 00026 00030 99804 99848 99891 99935 99978 99808 99852 998% 99939 99983 99817 99861 99904 99948 99991 00035 99822 99865 99909 99952 999% 00039 950-1000 TABLE II, APPROXIMATE EQUATION OF TIME. DATE. MINUTES. DATE. MINUTES. DATE. MINUTES. DATE. MINUTES. Jan. 1 4 Apr. 1 4 jj Aug. 9 5 : Oct. 27 16 ; " 3 5 4 3 1 " 15 4 ^ Nov. 15 15 " 5 6 " 7 2 ^ " 20 3 | " 20 14 I " 7 7 " 11 1 J " 24 2 | " 24 13 ! 9 8 " 15 o 3 " 28 i ; " 27 12 g " 12 9 . " 31 " 30 11 M " 15 10 " 19 i ; Dec. 2 10 | " 18 11 " 24 2 g Sept. 3 i ! 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9 log tan 9 log cot 10 log cos 9 t > log sin Q log tan log cot log cos t 79887 90 837 09 163 89 050 60 o SO 807 92381 10 07 619 9 88425 6O 1 79903 90863 09137 89040 59 1 80822 92407 07 593 88415 59 2 79 918 90889 09111 89030 58 2 80837 92433 07 567 88404 58 3 79934 90914 09086 89020 57 3 80 852 92 4SS 07 542 88 394 57 4 79950 90940 09060 89009 56 4 80 867 92484 07516 88383 56 5 79965 90966 09034 88999 55 5 80 882 92510 07 490 88372 55 6 79981 90992 09008 SS9S9 54 6 80897 92535 07 465 88362 54 7 79996 91018 08982 8S978 53 7 SO 912 92561 07439 88 351 53 8 80012 91043 OS 957 88968 52 8 80927 92587 07413 S8340 52 9 80027 91069 08931 SS958 51 9 80942 92612 07388 88330 51 10 80043 91095 08905 88 948 50 1O 80957 92 638 07362 88 319 5O 11 80 058 91 121 OS S79 88937 49 11 80972 92663 07 337 88308 49 12 80074 91 147 08853 S8927 48 12 80987 92689 07311 88298 48 13 80089 91 172 OSS2S 88917 47 13 81002 92 715 07 285 SS 287 47 14 80105 91 198 OS 802 88 906 46 14 81017 92 740 07260 88 276 46 15 80120 91224 08776 88896 45 15 81032 92 766 07234 SS 266 45 16 SO 136 91 250 08750 88886 44 16 81047 92792 07208 88255 44 17 80151 91276 08724 SS875 43 17 SI 061 92817 07 183 88244 43 18 80166 91301 08699 88 865 42 18 81076 92843 07 157 88 234 42 19 80182 91327 08673 SSS55 41 19 81091 92868 07 132 88223 41 20 80197 91353 08647 SS844 4O 20 81 106 92894 07 106 88 212 4O 21 80213 91379 08621 SS834 39 21 81 121 92920 07080 88 201 39 22 80228 91404 08596 88 824 38 22 SI 136 92945 07055 88 191 38 23 SO 244 91430 08570 88813 37 23 81 151 92971 07029 88 ISO 37 24 SO 259 91456 08544 88803 36 24 81 166 929% 07004 88169 36 25 80274 91 482 08518 88793 35 25 81 180 93022 06978 88 158 35 26 SO 290 91 507 08493 88782 34 26 81 195 93048 06952 SS148 34 27 SO 305 91 533 08467 88772 33 27 81210 93073 06927 88137 33 28 80320 91 559 08441 SS 761 32 28 SI 225 93099 06901 88126 32 29 80336 91 585 08415 88751 31 29 81240 93124 06876 88115 31 30 80351 91610 08390 88741 30 30 81254 93 150 06850 88105 30 31 SO 366 91636 08364 SS730 29 31 SI 269 93 175 06 825 88 094 29 32 80382 91662 0833S 88720 28 32 81284 93201 06799 88 083 28 33 80397 91688 08312 88709 27 33 SI 299 93227 06773 88072 27 34 80412 91713 08287 SS699 26 34 81314 93252 06748 88061 26 35 80428 91739 08261 88 688 25 35 81328 93278 06722 S8051 25 36 80443 91 765 08235 8S678 24 36 81343 93303 06697 88040 24 37 SO 458 91791 08209 88668 23 37 81358 93329 06671 88029 23 38 80473 91816 OS 184 88657 22 38 81372 93354 06646 88018 22 39 80 489 91 842 08158 88647 21 39 81387 93380 06620 88007 21 40 80504 91 868 OS 132 8S636 2O 4O 81402 93406 06594 87996 2O 41 SO 519 91893 OS 107 SS626 19 41 81417 93431 06569 87985 19 42 80534 91919 08081 88615 18 42 81431 93457 06543 87975 18 43 80550 91945 08055 88605 17 43 81446 93482 06518 87964 17 44 SO 565 91971 08029 88 594 16 44 81461 93 508 06492 87953 16 45 80 580 91996 08004 88584 15 45 81475 93533 06467 87 942 15 46 SO 595 92022 07978 SS573 14 46 81490 93559 06441 87931 14 47 80610 92048 07952 SS563 13 47 81505 93584 06416 87920 13 48 SO 625 92073 07927 88552 12 48 81519 93610 06390 87909 12 49 80641 92099 07901 88 542 11 49 81534 93636 06364 87898 11 50 80656 92 125 07875 88 531 1O 5O SI 549 93661 06339 87887 1O 51 80671 92150 07850 88521 9 51 81563 93687 06313 87877 9 52 80 686 92 176 07824 SS510 8 52 81578 93 712 062SS 87 866 8 53 80701 92202 07798 88 499 7 53 81 592 93738 06262 87855 7 64 80716 92227 07773 8S4S9 6 54 SI 607 93763 06237 87844 6 55 80731 92253 07747 SS47S 5 55 81622 93 789 06211 87833 5 56 80746 92279 07 721 8S468 4 56 81636 93814 X, 1S(, 87822 4 57 80762 92304 07696 88457 3 57 81 651 93 840 06160 87811 3 58 SO 777 92330 07670 88447 2 58 SI 665 93865 06135 87800 2 59 80792 92356 07644 SS436 1 59 81 680 93891 06109 87 789 1 60 80807 92381 07619 8S425 O 60 81694 93916 a 06084 10 87778 Q O t log cos log cot 10 ogtan log sin t t log 008 a log cot log tan log sin r 49 48 41 42 C f log sin log tan log cot log cos f > log sin log tan log cot 1 f\ log cos r 81694 93916 06084 87778 60 O 82551 95444 1U 04556 87 107 60 1 81 709 93942 06058 87 767 59 I 82565 95469 04531 87096 59 2 81 723 93967 06033 87 756 58 2 82579 95495 04505 87 085 58 3 81738 93993 06007 87745 57 3 82593 95 520 04480 87073 57 4 81752 94018 05982 87734 56 4 82607 95 545 04455 87 062 56 5 81 767 94044 05956 87723 55 5 82621 95 571 04429 87050 55 6 81 781 94069 05931 87712 54 6 82635 95 596 04404 87039 54 7 81 796 94095 05905 87701 53 7 82649 95622 04378 87028 53 8 81810 94120 05880 87690 52 8 82663 95647 04353 87016 52 9 81825 94146 05854 87679 51 9 82677 95672 04328 87 005 51 10 81 839 94171 05829 87668 50 1O 82691 95698 04302 86 993 50 11 81854 94197 05803 87657 49 11 82 705 95 723 04277 86982 49 12 81868 94222 05778 87646 48 12 82719 95 748 04252 86 970 48 13 81882 94248 05 752 87635 47 13 82733 95 774 04226 86959 47 14 81897 94273 05 727 87624 46 14 82747 95799 04201 86 947 46 15 81911 94299 05 701 87613 45 15 82761 95825 04175 86 936 45 16 81926 94324 05676 87601 44 16 82 775 95 850 04 150 86924 44 17 81940 94350 05650 87590 43 17 82788 95875 04125 86913 43 18 81955 94375 05625 87579 42 18 82802 95901 04099 86902 42 19 81969 94401 05599 87568 41 19 82816 95926 04074 86890 41 20 81983 94426 05 574 87557 40 20 82830 95 952 04048 86 879 40 21 81998 94452 05 548 87546 39 21 82844 95977 04023 86867 39 22 82012 94477 05523 87535 38 22 82S5S 96002 03 998 86 855 38 23 82026 94503 05 497 87524 37 23 82872 96028 03972 86 844 37 24 82041 94528 05472 87513 36 24 82SS5 96053 03947 86832 36 25 82055 94554 05446 87501 35 25 82899 96078 03922 86821 35 26 82069 94579 05421 87490 34 26 82913 96104 03896 86809 34 27 82084 94604 05396 87479 33 27 82927 96129 03871 86798 33 28 82098 94630 05370 87468 32 28 82941 96155 03 845 86786 32 29 82112 94655 05345 87457 31 29 82955 96 ISO 03820 86775 31 30 82126 94681 05319 87446 30 30 82968 96205 03 795 86 763 3O 31 82141 94706 05 294 87434 29 31 82 982 96231 03 769 86752 29 32 82155 94732 05 268 87423 28 32 82996 96256 03 744 86740 28 33 82169 94757 05243 87412 27 33 83010 96281 03 719 86728 27 34 82184 94783 05217 87401 26 34 83023 96307 03693 86717 26 35 82198 94808 05 192 87 390 25 35 83037 96332 03668 86 705 25 36 82212 94834 05 166 87378 24 36 83051 96357 03643 86694 24 37 82226 94859 05 141 87367 23 37 83065 96383 03617 86682 23 38 82240 94884 05 116 87356 22 38 8307S 96408 03 592 86 670 22 39 82255 94910 05090 87345 21 39 83092 96433 03567 86 659 21 40 82269 94935 05065 87334 20 40 83106 96459 03541 86647 20 41 82283 94961 05039 87322 19 41 83 120 96484 03516 86635 19 42 82297 94986 05014 87311 18 42 S3 133 96510 03490 86624 18 43 82311 95012 049SS 87300 17 43 83 147 96535 03 465 86612 17 44 82326 95037 04963 87 288 16 44 83161 96560 03440 86600 16 45 82340 95062 04938 87277 15 45 83 174 965S6 03414 86589 15 46 82354 95088 04912 87266 14 46 S3 188 96611 03389 86577 14 47 82368 95 113 04 887 87 255 13 47 83202 96636 03364 86565 13 48 82382 95 139 04861 87243 12 48 83215 96662 03338 86 554 12 49 82396 95 164 04836 87232 11 49 83229 96 687 03313 86 542 11 50 82410 95 190 04810 87221 1O 50 83242 96712 032SS 86530 10 51 82424 95215 04 785 87209 9 51 83256 96738 03262 86518 9 52 82439 95 240 04760 87198 8 52 83270 96763 03237 86507 8 53 82453 95266 04734 87187 7 53 83283 96788 03212 86495 7 54 82467 95291 04709 87175 6 54 S3 297 96814 03186 86 483 6 55 82 481 95317 04683 87 164 5 55 83310 96 839 03 161 86472 5 56 82495 95342 04658 87153 4 56 83324 96864 03136 86460 4 57 82509 95368 04632 87141 3 57 83338 96890 03110 S644S 3 58 82523 95393 04607 87130 2 58 S3 351 96915 03085 86436 2 59 82537 95418 04582 87 119 1 59 S3 365 96940 03060 86425 1 60 82 551 95444 04556 87107 O 60 83378 96966 03034 86413 9 Q 10 Q Q Q 1 fi ft ' log cos log cot log tan y log sin t f y log cos log cot u log tan log sin f 48 C 47' 43 44' 49 f log sin log tan log cot log cos t 9 9 10 rt . o 83378 96966 03034 86413 6O 1 83392 96991 03009 86401 59 2 S3 405 97016 02984 86389 58 3 83419 97042 02958 86377 57 4 83 432 97067 02933 86366 56 5 83 446 97092 02908 86354 55 6 83459 97118 02SS2 86342 54 7 83473 97143 02857 86330 53 8 83486 97168 02 832 86 318 52 9 83500 97193 02807 86306 51 10 83 513 97219 02 781 86295 5O 11 83 527 97244 02 756 86283 49 12 83540 97269 02 731 86 271 48 13 83 554 97295 02 705 86 259 47 14 83567 97320 02680 86247 46 15 83 581 97345 02655 86235 45 16 S3 594 97371 02629 86 223 44 17 83608 97396 02604 86211 43 18 S3 621 97421 02579 86200 42 19 83634 97447 02553 86188 41 20 S3 648 97472 0252S 86176 4O 21 83661 97 497 02503 86164 39 22 83674 97523 02477 86152 38 23 83688 97548 02 452 86 140 37 24 83 701 97573 02427 86 128 36 25 83 715 97598 02402 86116 35 26 83728 97624 02376 86104 34 27 S3 741 97649 02351 86092 33 28 83755 97674 02326 86080 32 29 83768 97 700 02300 86068 31 30 83 781 97 725 02275 86056 3O 31 83 795 97 750 02250 86044 29 32 83 SOS 97776 02224 86032 28 33 S3 821 97 SOI 02 199 86020 27 34 83834 97 826 02174 86008 26 35 83S4S 97851 02 149 85 996 25 36 83861 97877 02 123 85 984 24 37 83874 97902 02098 85 972 23 38 83887 97927 02073 85960 22 39 83901 97953 02047 85 948 21 40 83914 97978 02022 85936 2O 41 83927 98003 01997 85924 19 42 83940 98029 01971 85912 18 43 S3 954 98054 01946 85900 17 44 83967 98 079 01921 85 888 16 45 83980 98 104 01896 85876 15 46 S3 993 98130 01 870 85864 14 47 84 006 98155 01 845 85851 13 48 84020 98180 01820 85 839 12 49 84033 98206 01 794 85 827 11 50 84046 98231 01 769 85815 1O '61 84059 98256 01 744 85 803 9 62 84072 98 281 01 719 85 791 8 53 84 085 98 307 01693 85 779 7 54 84098 98332 01668 85 766 6 165 84112 98357 01643 85 754 5 1 66 84 125 98 383 01 617 85 742 4 57 84 138 98408 01 592 85 730 3 68 84151 98 433 01 567 85 718 2- 59 84164 98 458 01 542 85 706 1 60 84 177 98 484 01 516 85693 9 10 9 t log COB log cot log tan log sin f f log sin log tan log cot log cos f 9 Q 10 o 84 177 98 484 01516 85693 6O 1 84190 98509 01491 85681 59 2 84203 98534 01466 85669 58 3 84216 98560 01440 85657 57 4 84229 98585 01415 85645 56 5 84242 98610 01390 85632 55 6 84255 98635 01365 85620 54 7 84269 98661 01339 85608 53 8 84282 98686 01314 855% 52 9 84295 98711 01289 85 583 51 10 84308 98737 01 263 85571 5O 11 84321 98762 01 238 85559 49 12 84334 98787 01213 85 547 48 13 84347 98812 01 188 85 534 47 14 84360 98838 01 162 85 522 46 15 84373 98863 01 137 85 510 45 16 84385 98888 01 112 85497 44 17 84398 98913 01 087 85485 43 18 84411 98939 01061 85473 42 19 84424 98964 01036 85460 41 20 84437 98989 01011 85448 40 21 84450 99015 00985 85436 39 22 84463 99040 00960 85423 38 23 84476 99065 00935 85 411 37 24 84489 99090 00910 85399 36 25 84502 99116 00884 85386 35 26 84515 99141 00859 85374 34 27 84528 99166 00834 85361 33 28 84540 99191 00809 85349 32 29 84553 99217 00783 85337 31 30 84566 99242 00758 85324 30 31 84579 99267 00733 85312 29 32 84592 99293 00707 85299 28 33 84605 99318 00682 85287 27 34 84618 99343 00657 85274 26 35 84630 99368 00632 85262 25 36 84643 99394 00606 85250 24 37 84656 99419 00581 85237 23 38 84 669 99444 00556 85225 22 39 84682 99469 00531 85 212 21 4O 84694 99495 00505 85200 20 41 84707 99520 00480 85 187 19 42 84720 99545 00455 85 175 18 43 84733 99570 00430 85 162 17 44 84745 99596 00404 85 150 16 45 84758 99621 00379 85 137 15 46 84771 99646 00354 85125 14 47 84 784 99672 00328 85 112 13 48 84796 99697 00303 85 100 12 49 84 809 99722 00278 85087 11 5O 84822 99747 00253 85074 10 51 84835 99773 00227 85062 9 52 84847 99798 00202 85049 8 63 84860 99823 00177 85037 7 54 84873 99848 00152 85024 6 55 84 885 99874 00 126 85 012 5 56 84898 99899 00101 84999 4 57 84911 99924 00076 84986 3 58 84923 99949 00051 84974 2 59 84936 W 975 00025 84961 1 60 84949 00 OCX) 00000 84949 10 10 g t log cos log cot log tan log sin 46 45 50 TABLE IV. FOB DETERMINING WITH GREATER ACCURACY THAN CAN BE DONE BY MEANS OF TABLE III. : 1. log sin, log tan, and log cot, when the angle is between and 2 ; 2. log cos, log tan, and log cot, when the angle is between 88 and 90 ; 3. The value of the angle when the logarithm of the function does not lie between the limits 8. 54 684 and 11. 45 316. FORMULAS FOR THE USE OF THE NUMBERS S AND T. I. When the angle a is between and 2 : log sin a = log a" + S. log tan a = log a" + T. log cot a = colog tan a. log a" = log sin a S, = log tana T, = colog cot a T. II. When the angle a is between 88 and 90 : log COS a = log (90" -a)" + S. log COt a = log (90-a)"+ r. log tan a = colog cot a. log (90 a)" = log cos a S, = log COt a T, - colog tana-r, and a = 90 -(90 -a). TALIIES OF S AIS T D T, a" 3 log sin a a" T log tan a a T log tan a _ _ 5146 8. 39 713 4.68557 4.68557 4. 68 567 2409 8.06740 200 6,98660 5424 8.41999 4.68556 4. 68 558 4. 68 568 3417 8. 21 920 1726 7. 92 263 5689 8. 44 072 4. 68 555 4. 68 559 4. 68 569 3823 8. 26 795 2432 8. 07 156 5941 S. 45 955 4.68555 4.68560 4. 68 570 4190 8.30776 2976 8. 15 924 6184 8. 47 697 4. 68 554 4. 68 561 4. 68 571 4840 8. 37 038 3434 8. 22 142 6417 8. 49 305 4. 68 553 4. 68 562 4. 68 572 5414 8.41904 3838 S. 26 973 6642 8.50802 4. 68 552 4. 68 563 4. 68 573 5932 8. 45 872 4204 8. 30 930 6859 8. 52 200 4. 68 551 4.68564 4. 68 574 6408 8. 49 223 4540 8. 34 270 7070 S. 53516 4. 68 550 4. 68 565 4.68575 6633 8. 50 721 4699 8. 35 766 ! 7173 8. 54 145 4. 68 550 4. 68 565 4. 68 575 6851 8. 52 125 4853 8. 37 167 7274 8. 54 753 4. 68 549 4.68566 7267 8.54684 5146 8. 39 713 a." S log sin a a" T log tan a a T log tan a 51 TABLE IV. This table (page 50) must be used when great accuracy is desired in working with angles between and 2, or between 88 and 90. The values of S and T are such that when the angle a is expressed in seconds, 8 = log sin a log a", T = log tan a log a". Hence, follow the formulas given on the page containing the table. The values of S and T are printed with the characteristic 10 too large, and in using them 10 must always be annexed. Find log sin 58' 17". 58' 17" = 3497." log 3497 = 3.54370 8 = 4.68555-10 log sin 58' 17" = 8.22925 - 10 Find log tan 52' 47.5". 52' 47.5" = 3167.5." log 3167.5 = 3.50072 T = 4.68561 -10 log tan 52' 47.5" = 8.18633-10 Find log cos 88 26' 41.2". 90 - 88 26' 41.2" = 1 33' 18.8* log 5598.8 = 3.74809 8 = 4.68552-10 log cos 88 26' 41.2" = 8.43361-10 Find log tan 89 54' 37.362". 90 - 89 54' 37.362" = 322.638*. log 322.638 = 2.60871 T= 5.68558 -10 log cot 89' 54' 37 .362"= 7.19429-10 log tan 89 54 37.362 '' = 2.80671. Find the angle, if log sin = 6.72306 - 10. 6.72306 - 10 8 = 4.68557-10 Subtract, 2.03749 = log 10^.015. 109.015" = 0> 1 49.016''. Find the angle for which log cot = 1 .67604. colog cot = 8.32396 - 10 T = 4.68564 - 10 Subtract, 3.63832 = log 4348.3. 4348.3" = 1 12' 28.3". Find the angle for which log tan = 1.55407. colog tan = 8.44593 10 T = 4.68569 - 10 Subtract, 3.76024 = log 6757.6. 5757.6" = 1 35' 57.6", and 90 - 1 35' 67.6" = 88 24' 2.4" = angle required 52 TABLE V, SHOWING LENGTHS IN NAUTICAL MILES AND STATUTE MILES OF DEGREES OF LATITUDE AND LONGITUDE IN DIFFERENT LATITUDES. DEGREE OF THE PARALLEL. DEGREE OF THE MERIDIAN. Latitude of Parallel. Nautical Miles. Statute Miles. Latitude of Middle Point. Nautical Miles. Statute Miles. 20 56.404 65.018 20 59.664 68.777 21 56.039 64.598 22 55.657 64.158 23 55.258 63.698 24 54.843 63.219 25 54.411 62.721 25 59.706 68.825 26 53.962 62.204 27 53.497 61.668 28 53.016 61.113 29 52.518 60.540 30 52.005 59.948 30 59.749 68.875 31 51.476 59.338 32 50.931 58.709 33 50.370 58.063 34 49.794 57.399 35 49.203 56.718 35 59.7% 68.929 36 48.597 56.019 37 47.976 55.304 38 47.341 54.571 39 46.960 53.822 40 46.026 53.056 40 59.847 68.987 41 45.348 52.274 42 44.654 51.476 43 43.949 50.662 44 43.230 49.833 45 42.497 48.988 45 59.899 69.048 46 41.752 48.128 47 40.993 47.254 48 40.222 46.365 490 39.439 45.462 50 38.643 44.545 50 59.951 69.108 53 TABLE VI, MISCELLANEOUS FORMULAE, AND EQUIVALENTS OF METRES, CHAINS, AND FEET. : 3.14159265 : 0.31830989 : 9.86960440 : 0.10132118 Logarithm. 0.4971499 9.5028501 10 0.9942997 9.0057006-10 : 1.77245385 0.56418958 1.46459189 Logarithm. 0.2485749 9.7514251 - 10 0.1657166 Circumference of circle, diameter being unity, Area of circle, radius being unity Surface of sphere, diameter being unity . . . . Area of a circle, diameter being unity Volume of sphere, diameter being unity Volume of sphere, radius being unity . . Arc whose length is equal to the radius : Expressed in degrees Expressed in minutes . Expressed in seconds . . . . , If radius is unity : Length of arc for one degree Length of arc for one minute Length of arc for one second , Sine of one second 180 10800 648000 IT 180 10800 648000 Base of Hyperbolic or Napier's System of Logarithms . : Modulus of Common or Briggs' System of Logarithms . : Equatorial radius of the earth in feet Polar radius of the earth in feet ; Length of degree of latitude at the equator, in feet . . : Length of degree of latitude at 46, in feet : : 3.14159265 : 0.7853982 : 0.52359878 : 4.1887902 = 57.2957795 = 3437.74677' : 206264.806 = 0.0174533 = 0.0002909 = 0.00000485 = 0.00000485 ; 2.7182818 0.4342945 : 20923600 20853657 362748.33 364571.77 0.4971499 9.8950899 - 10 9.7189986-10 0.6220886 1.7581226 3.5362739 5.3144251 8.2418774 - 10 6.4637261 - 10 4.68557487 - 10 4.68557487 - 10 0.4342945 9.6377843-10 FEET. METRES. CHAINS. METRES 0.3048 0.6096 0.9144 1.2192 1.52-10 1.8288 2.1336 2.4384 2.7432 3.0480 0.0151 0.0303 0.0455 0.0606 0.0758 0.0909 0.1061 0.1212 0.1364 0.1515 FEET. 3.2809 6.5617 9.8426 13.1235 16.4044 19.6852 22.9661 26.2470 29.5278 32.8087 54 TABLE VII. TRAVERSE TABLE. . This table gives the latitude and departure to three places of deci- mals for distances from 1 to 10, corresponding to bearings from to 90, at intervals of 15'. If the bearing does not exceed 45, it is found in the left-hand column, and the designations of the columns under "Distance" are taken from the top of the page ; but if the bearing exceeds 45, it is found in the right-hand column, and the designations of the columns under "Distance" are taken from the bottom of the page. The method of using the table will be made plain by the following examples : 1. Let it be required to find the latitude and departure of a line running N. 35 15' E. 6 chains. On page 60, left-hand column, look for 35 15' ; opposite this bearing, in the vertical column headed "Distance 6," are found 4.900 and 3.463, under the head- ings "Latitude" and "Departure" respectively. Hence latitude, or northing, = 4.900 chains, and departure, or easting, = 3.463 chains. 2. Let it be required to find the latitude and departure of a Hue running S. 87 W. 2 chains. As the bearing exceeds 45, we look in the right-hand column on page 55, and opposite 87, in the column marked " Distance 2," we find (taking the designa- tions of the columns from the bottom of the page) latitude = 0.105 chains, and departure = 1.997 chains. Hence latitude, or southing, = 0.105 chains, and depart- ure, or westing, = 1.997 chains. 3. Let it be required to find the latitude and departure of a line running N. 15 45' W. 27.36 chains. In this case, we find the required number for each figure of the distance sepa- rately, arranging the work as in the following table. In practice, only the last columns under " Latitude " and " Departure " are written. Distance. Latitude. Departure. 20 = 2 X 10 7 0.3 =3-- 10 0.06 = 6 -5- 100 1.925x10 =19.25 6.737 2.887 + 10 =0.289 5.775 -T- 100 = 0.058 0.543 X 10 = 5.43 1.90 0.814+ 10 = 0.081 1.628 -T- 100 = 0.016 27.36 26.334 7.427 Hence latitude = 26.334 chains, and departure = 7.427 chains. 55 A TABLE OF THE ANGLES Which every Point and Quarter Point of the Compass makes with the Meridian. North. Points. 1 o 1 II 2 48 45 5 37 30 8 26 15 11 15 Points. V 1 South. N. by E. N. by W. S. by E. S. by W. N.N.E. N.N.W. 2 14 3 45 16 52 30 19 41 15 22 30 2 S.S.E. S.S.W. N.E. by N. N.W. by N. 2- ! /4 P 25 18 45 28 7 30 30 56 15 33 45 2 ~$ 3 S.E. by S. S.W. by S. N.E. N.W. 4 * 36 33 45 39 22 30 42 11 15 45 3_i 4 S.E. S.W. N.E.byE. N.W. by W. l:fc J : < 47 48 45 50 37 80 53 26 15 56 15 4 8 i 5 S.E. by E. S.W. by W. E.N.E. W.N.W. 5-^ 6 If 59 3 45 61 62 30 64 41 15 C7 30 70 IS 45 73 7 30 75 56 15 78 45 !:& ! : < E.S.E. W.S.W. E. by N. W. by N. 6-V* 7 "* E. by S. W. by S. East. West. 1:8 T-% g 81 33 46 84 22 30 87 11 15 90 J3 East. West. 56 TABLE VII. - TRAVERSE TABLE. Bearing. Distance 1. Distance 2. Distance 3. Distance 4. Distance 5. Bearing. o r Lat. Dep. Lat. Dep. Lat. Dep. Lat. Dep. Lat. Dep. / 015 1.000 0.004 2.000 0.009 3.000 0.013 4.000 0.017 5.000 0.022 8945 30 1.000 0.009 2.000 0.017 3.000 0.026 4.000 0.035 5.000 0.044 30 45 1.000 0.013 2.000 0.026 3.000 0.039 4.0CO 0.052 5.000 0.065 15 1 1.000 0.017 2.000 0.035 3.000 0.052 3.999 0.070 4.999 0.087 89 15 1.000 0.022 2.000 0.044 2.999 0.065 3.999 O.OS7 4.999 0.109 45 30 1.000 0.026 1.999 0.052 2.999 0.079 3.999 0.105 4.998 0.131 30 45 1.000 0.031 1.999 0.061 2.999 0.092 3.998 0.122 4.998 0.153 15 2 0.999 0.035 1.999 0.070 2.998 0.105 3.998 0.140 4.997 0.174 88 15 0.999 0.039 1.998 0.079 2.998 0.118 3.997 0.157 4.996 0.196 45 30 0.999 0.044 1.998 0.087 2.997 0.131 3.996 0.174 4.995 0.218 30 45 0.999 0.048 1.998 0.096 2.997 0.144 3.995 0.192 4.994 0.240 15 3 0.999 0.052 1.997 0.105 2.996 0.157 3.995 0.209 4.993 0.262 87 15 0.998 0.057 1.997 0.113 2.995 0.170 3.994 0.227 4.992 0.2S3 45 30 0.998 0.061 1.996 0.122 2.994 0.183 3.993 0.244 4.991 0.305 30 45 0.998 0.065 1.996 0.131 2.994 0.196 3.991 0.262 4.989 0.327 15 4 0.998 0.070 1.995 0.140 2.993 0.209 3.990 0.279 4.988 0.349 86 15 0.997 0.074 1.995 0.148 2.992 0.222 3. 989 0.296 4.986 0.371 45 30 0.997 0.078 1.994 0.157 2.991 0.235 3.988 0.314 4.985 0.392 30 45 0.997 0.083 1.993 0.166 2.990 0.248 3.986 0.331 4.983 0.414 15 5 0.996 0.087 1.992 0.174 2.989 0.261 3.985 0.349 4.9S1 0.436 85 15 0.996 0.092 1.992 0,183 2.987 0.275 3.983 0.366 4.979 0.458 45 30 0.995 0.096 1.991 0.192 2.986 0.2SS 3.982 0.3S3 4.977 0.479 30 45 0.995 0.100 1.990 0.200 2.9S5 0.301 3.980 0.401 4.975 0.501 15 6 0.995 0.105 1.989 0.209 2.984 0.314 3.978 0.418 4.973 0.523 84 15 0.994 0.109 1.988 0.218 2.9S2 0.327 3.976 0.435 4.970 0.544 45 30 0.994 0.113 1.9S7 0.226 2.981 0.340 3.974 0.453 4.968 0566 30 45 0.993 0.118 1.986 0.235 2.979 0.353 3.972 0.470 4.965 0.588 15 7 0.993 0.122 1.985 0.244 2.978 0.366 3.970 0.4S7 4.963 0.609 83 15 0.992 0.126 1.984 0.252 2.976 0.379 3.96S 0.505 4.960 0.631 45 30 0.991 0.131 1.983 0.261 2.974 0.392 3.966 0.522 4.957 0.653 30 45 0.991 0.135 1.982 0.270 2.973 0.405 3.963 0.539 4.954 0.674 15 8 0.990 0.139 1.981 0.278 2.971 0.418 3.961 0.557 4.951 0.696 82 15 0.990 0.143 1.979 0.287 2.969 0.430 3.959 0.574 4.948 0.717 45 30 0.989 0.148 1.978 0.296 2.967 0.443 3.956 0.591 4.945 0.739 30 45 0.988 0.152 1.977 0.304 2.965 0.456 3.953 0.608 4.942 0.761 15 9 0.988 0.156 1.975 0.313 2.963 0.469 3.951 0.626 4.938 0.782 81 15 0.987 0.161 1.974 0.321 2.961 0.4S2 3.948 0.643 4.935 0.804 45 30 0.986 0.165 1.973 0.330 2.959 0.495 3.945 0.660 4.931 0.825 30 45 0.986 0.169 1.971 0.339 2.957 0.508 3.942 0.677 4.928 0.847 15 1O 0.985 0.174 1.970 0.347 2.954 0.521 3.939 0.695 4.924 0.868 80 15 0.984 0.178 1.968 0.356 2.952 0.534 3.936 0.712 4.920 0.890 45 30 0.983 0.182 1.967 0.364 2.950 0.547 3.933 0.729 4.916 0.911 30 45 0.982 0.187 1.965 0.373 2.947 0.560 3.930 0.746 4.912 0.933 15 11 0.982 0.191 1.963 0.382 2.945 0.572 3.927 0.763 4.908 0.954 79 15 0.981 0.195 1.962 0.390 2.942 0.585 3.923 0.780 4.904 0.975 45 30 0.980 0.199 1.960 0.399 2.940 0.598 3.920 0.797 4.900 0.997 30 45 0.979 0.204 1.958 0.407 2.937 0.611 3.916 0.815 4.895 1.018 15 12 0.978 0.208 1.956 0.416 2.934 0.624 3.913 0.832 4.891 1.040 78 15 0.977 0.212 1.954 0.424 2.932 0.637 3.909 0.849 4.886 1.061 45 30 0.976 0.216 1.953 0.433 2.929 0.649 3.905 0.866 4.881 1.082 30 45 0.975 0.221 1.951 0.441 2.926 0.662 3.901 O.S83 4.877 1.103 15 13 0.974 0.225 1.949 0.450 2.923 0.675 3.897 0.900 4.872 1.125 77 15 0.973 0.229 1.947 0.458 2.920 0.6SS 3.894 0.917 4.867 1.146 45 30 0.972 0.233 1.945 0.467 2.917 0.700 3.SS9 0.934 4.S62 1.167 30 45 0.971 0.238 1.943 0.475 2.914 0.713 3.SS5 0.951 4.857 1.188 15 14 0.970 0.242 1.941 0.484 2.911 0.726 3.SS1 0.968 4.851 1.210 76 15 0.969 0.246 1.938 0.492 2.908 0.73S 3.877 0.985 4.846 1.231 45 30 0.968 0.250 1.936 0.501 2.904 0.751 3.873 1.002 4.841 1.252 30 45 0.967 0.255 1.934 0.509 2.901 0.764 3.868 1.018 4.835 1.273 15 15 0.966 0.259 1.932 0.518 2.898 0.776 3.864 1.035 4.830 1.294 75 f Dep. Lat, Dep. Lat. Dep. Lat. Dep. Lat. Dep. Lat. C f Bearing Distance 1. Distance 2. Distance 3. Distance 4. Distance 5. Bearing. 75- 90' 67 Bearing, Distance 6. Distance 7. Distance 8. Distance 9. Distance 1O. Bearing. o t Lat. Dep. Lat. Dep. Lat. Dep, Lat. Dep. Lat. Dep. O f 015 6.000 0.026 7.000 0.031 8.000 0.035 9.000 0.039 10.000 0.044 89 45 30 6.000 0.052 7.000 0.061 8.000 0.070 9.000 0.079 10.000 0.087 30 45 5.999 0.079 6.999 0.092 7.999 0.105 8.999 0.118 9.999 0.131 15 1 5.999 0.105 6.999 0.122 7.999 0.140 8.999 0.157 9.999 0.175 89 15 5.999 0.131 6.998 0.153 7.998 0.175 8.998 0.196 9.998 0.218 45 30 5.998 0.157 6.998 0.183 7.997 0.209 8.997 0.236 9.997 0.262 30 45 5.997 0.183 6.997 0.214 7.996 0.244 8.996 0.275 9.995 0.305 15 2 5.996 0.209 6.996 0.244 7.995 0.279 8.995 0.314 9.994 0.349 88 15 5.995 0.236 6.995 0.275 7.994 0.314 8.993 0.353 9.992 0.393 45 30 5.994 0.262 6.993 0.305 7.992 0.349 8.991 0.393 9.991 0.436 30 45 5.993 0.288 6.992 0.336 7.991 0.384 8.990 0.432 9.989 0.480 15 3 5.992 0.314 6.990 0.366 7.989 0.419 8.988 0.471 9.986 0.523 87 15 5.990 0.340 6.989 0.397 7.987 0.454 8.986 0.510 9.984 0.567 45 30 5.989 0.366 6.987 0.427 7.985 0.488 8.983 0-549 9.981 0.611 30 45 5.987 0.392 6.985 0.458 7.983 0.523 8.981 0.589 9.979 0.654 15 4 5.985 0.419 6.983 0.488 7.981 0.558 8.978 0.628 9.976 0.698 86 15 5.984 0.445 6.981 0.519 7.978 0.593 8.975 0.667 9.973 0.741 45 30 5.982 0.471 6.978 0.549 7.975 0.628 8.972 0.706 9.969 0.785 30 45 5.979 0.497 6.976 0.580 7.973 0.662 S.%9 0.745 9.966 0.828 15 o 5.977 0.523 6.973 0.610 7.970 0.697 8.966 0.784 9.962 0.872 85 15 5.975 0.549 6.971 0.641 7.966 0.732 8.962 0.824 9.958 0.915 45 30 5.972 0.575 6.968 0.671 7.963 0.767 8.959 0.863 9.954 0.959 30 45 5.970 0.601 6.965 0.701 7.960 0.802 8.955 0.902 9.950 1.002 15 6 5.967 0.627 6.962 0.732 7.956 0.836 8.951 0.941 9.945 1.045 84 15 5.964 0.653 6.958 0.762 7.952 0.871 8.947 0.980 9.941 1.089 45 30 5.961 0.679 6.955 0.792 7.949 0.906 8.942 1.019 9.936 1.132 30 45 5.958 0.705 6.951 0.823 7.945 0.940 8.938 1.058 9.931 1.175 15 7 5.955 0.731 6.948 0.853 7.940 0.975 8.933 1.097 9.926 1.219 83 15 5.952 0.757 6.944 0.883 7.936 1.010 8.928 1.136 9.920 1.262 45 30 5.949 0.783 6.940 0.914 7.932 1.044 8.923 1.175 9.914 1.305 30 45 5.945 0.809 6.936 0.944 7.927 1.079 8.918 1.214 9.909 1.349 15 8 5.942 0.835 6.932 0.974 7.922 1.113 8.912 1.253 9.903 1.392 82 15 5.938 0.861 6.928 1.004 7.917 1.148 8.907 1.291 9.897 1.435 45 30 5.934 0.887 6.923 1.035 7.912 1.182 8.901 1.330 9.890 1.478 30 45 5.930 0.913 6.919 1.065 7.907 1.217 8.895 1.369 9.884 1.521 15 9 5.926 0.939 6.914 1.095 7.902 1.251 8.889 1.408 9.877 1.564 81 15 5.922 0.964 6.909 1.125 7.896 1.286 8.883 1.447 9.870 1.607 45 30 5.918 0.990 6.904 1.155 7.890 1.320 8.877 1.485 9.863 1.651 30 45 5.913 1.016 6.899 1.185 7.884 1.355 8.870 1.524 9.856 1.694 16 10 5.909 1.042 6.894 1.216 7.878 1.389 8.863 1.563 9.848 1.737 80 15 5.904 1.068 6.888 1.246 7.872 1.424 8.856 1.601 9.840 1.779 45 30 5.900 1.093 6.883 1.276 7.866 1.458 8.849 1.640 9.833 1.822 30 45 5.895 1.119 6.877 1.306 7.860 1.492 8.842 1.679 9.825 1.865 15 11 5.890 1.145 6.871 1.336 7.853 1.526 8.835 1.717 9.816 1.908 79 15 5.885 1.171 6.866 1.366 7.846 1.561 8.827 1.756 9.808 1.951 45 30 5.880 1.196 6.859 1.396 7.839 1.595 8.S19 1.794 9.799 1.994 30 45 5.874 1.222 6.853 1.425 7.832 1.629 8.811 1.833 9.791 2.036 15 12 5.869 1.247 6.847 1.455 7.825 1.663 8.803 1.871 9.782 2.079 78 15 5.863 1.273 6.841 1.485 7.818 1.697 8.795 1.910 9.772 2.122 45 30 5.858 1.299 6.834 1.515 7.810 1.732 8.787 1.948 9.763 2.164 30 45 5.852 1.324 6.827 1.545 7.803 1.766 8.778 1.986 9.753 2.207 15 13 5.846 1.350 6.821 1.575 7.795 1.800 8.769 2.025 9.744 2.250 77 15 5.840 1.375 6.814 1.604 7.787 1.834 8.760 2.063 9.734 2.292 45 30 5.834 1.401 6.807 1.634 7.779 1.868 8.751 2.101 9.724 2.335 30 45 5.828 1.426 6.799 1.664 7.771 1.902 8.742 2.139 9.713 2.377 15 14 5.822 1.452 6.792 1.693 7.762 1.935 8.733 2.177 9.703 2.419 70 15 5.815 1.477 6.785 1.723 7.754 1.969 8.723 2.215 9.692 2.462 45 30 5.809 1.502 6.777 1.753 7.745 2.003 8.713 2.253 9.682 2.504 30 45 5.802 1.528 6.769 1.782 7.736 2.037 8.703 2.291 9.671 2.546 15 15 5.796 1.553 6.761 1.812 7.727 2.071 8.693 2.329 9.659 2.588 7.-, o t Dep. Lat. Dep. Lat. Dep. Lat. Dep. Lat. Dep. Lat. o t Bearing. Distance 6. Distance 7. Distance 8. Distance 9. Distance 1O. Bearing. 75- 90 58 15- 30 C Bearing, Distance 1. Distance 2. Distance 3. Distance 4. Distance 5. Searing. o t Lat. Dep. Lat. Dep. Lat. Dep. Lat. Dep. Lat. 1 Dep. f 1515 0.965 0.263 1.930 0.526 2.894 0.789 3.859 1.052 4.824 1.315 7445 30 0.964 0,267 1.927 0.534 2.891 0.802 3.855 1.069 4.818 1.336 30 45 0.962 0.271 1.925 0.543 2.887 0.814 3.850 1.086 4.812 1.357 15 16 0.961 0.276 1.923 0.551 2.884 0.827 3.845 1.103 4.806 1.378 74 15 0.960 0.280 1.920 0.560 2.880 O.S39 3.840 1.119 4.800 1.399 45 30 0.959 0.284 1.918 0.568 2.876 0.852 3.835 1.136 4.794 1.420 30 45 0.958 0.2SS 1.915 0.576 2.873 0.865 3.830 1.153 4.788 1.441 15 17 0.956 0.292 1.913 0.585 2.869 0.877 3.825 1.169 4.7S2 1.462 73 15 0.955 0.297 1.910 0.593 2.865 O.S90 3.820 1.186 4.775 1.483 45 30 0.954 0.301 1.907 0.601 2.861 0.902 3.815 1.203 4.769 1.504 30 45 0.952 0.305 1.905 0.610 2.857 0.915 3.810 1.220 4.762 1.524 15 18 0.951 0.309 1.902 0.618 2.853 0.927 3.804 1.236 4.755 1.545 72 15 0.950 0.313 1.899 0.626 2.849 0.939 3.799 1.253 4.748 1.566 45 30 0.948 0.317 1.897 0.635 2.845 0.952 3.793 1.269 4.742 1.587 30 45 0.947 0.321 1.894 0.643 2.841 0.964 3.788 1.286 4.735 r607 15 19 0.946 0.326 1.891 0.651 2.837 0.977 3.782 1.302 4.728 1.628 71 15 0.944 0.330 1.888 0.659 2.832 0.989 3.776 1.319 4.720 1.648 45 30 0.943 0.334 1.885 0.668 2.828 1.001 3.771 1.335 4.713 1.669 30 45 0.941 0.338 1.882 0.676 2.824 1.014 3.765 1.352 4.706 1.690 15 2O 0.940 0.342 1.879 0.684 2.819 1.026 3.759 1.368 4.698 1.710 70 15 0.938 0.346 1.876 0.692 2.815 1.038 3.753 1.384 4.691 1.731 45 30 0.937 0.350 1.873 0.700 2.810 1.051 3.747 1.401 4.683 1.751 30 45 0.935 0.354 1.870 0.709 2.805 1.063 3.741 1.417 4.676 1.771 15 21 0.934 0.358 1.867 0.717 2.801 1.075 3.734 1.433 4.668 1.792 69 15 0.932 0.362 1.864 0.725 2.796 1.087 3.728 1.450 4.660 1.812 45 30 0.930 0.367 1.861 0.733 2.791 1.100 3.722 1.466 4.652 1.833 30 45 0.929 0.371 1.858 0.741 2.786 1.112 3.715 1.482 4.644 1.853 15 22 0.927 0.375 1.854 0.749 2.782 1.124 3.709 1.498 4.636 1.873 68 15 0.926 0.379 1.851 0.757 2.777 1.136 3.702 1.515 4.628 1.893 45 30 0.924 0.383 1.848 0.765 2.772 1.148 3.696 1.531 4.619 1.913 30 45 0.922 0.387 1.844 0.773 2.767 1.160 3.689 1.547 4.611 1.934 15 23 0.921 0.391 1.841 0.781 2.762 1.172 3.682 1.563 4.603 1.954 67 15 0.919 0.395 1.838 0.789 2.756 1.184 3.675 1.579 4.594 1.974 45 30 0.917 0.399 1.834 0.797 2.751 1.196 3.668 1.595 4.585 1.994 30 45 0.915 0.403 1.831 0.805 2.746 1.208 3.661 1.611 4.577 2.014 15 24 0.914 0.407 1.827 0.813 2.741 1.220 3.654 1.627 4.568 2.034 66 15 0.912 0.411 1.824 0.821 2.735 1.232 3.647 1.643 4.559 2.054 45 30 0.910 0.415 1.820 0.829 2.730 1.244 3.640 1.659 4.550 2.073 30 45 0.908 0.419 1.816 0.837 2.724 1.256 3.633 1.675 4.541 2.093 15 25 0.906 0.423 1.813 0.845 2.719 1.268 3.625 1.690 4.532 2.113 65 15 0.904 0.427 1.809 0.853 2.713 1.280 3.618 1.706 4.522 2.133 45 30 0.903 0.431 1.805 0.861 2.708 1.292 3.610 1.722 4.513 2.153 30 45 0.901 0.434 1.801 0.869 2.702 1.303 3.603 1.738 4.503 2.172 15 26 0.899 0.438 1.798 0.877 2.696 1.315 3.595 1.753 4.494 2.192 64 15 0.897 0.442 1.794 0.885 2.691 1.327 3.587 1.769 4.484 2.211 45 30 0.895 0.446 1.790 0.892 2.685 1.339 3.580 1.785 4.475 2.231 30 45 0.893 0.450 1.786 0.900 2.679 1.350 3.572 1.800 4.465 2.250 15 27 0.891 0.454 1.782 0.908 2.673 1.362 3.564 1.816 4.455 2.270 63 15 0.889 0.458 1.778 0.916 2.667 1.374 3.556 1.831 4.445 2.289 45 30 0.887 0.462 1.774 0.923 2.661 1.385 3.548 1.847 4.435 2.309 30 45 0.885 0.466 1.770 0.931 2.655 1.397 3.540 1.862 4.425 2.328 15 28 0.883 0.469 1.766 0.939 2.649 1.408 3.532 1.878 4.415 2.347 62 15 0.881 0.473 1.762 0.947 2.643 1.420 3.524 1.893 4.404 2.367 45 30 0.879 0.477 1.758 0.954 2.636 1.431 3.515 1.909 4.394 2.386 30 45 0.877 0.481 1.753 0.962 2.630 1.443 3.507 1.924 4.384 2.405 15 29 0.875 0.485 1.749 0.970 2.624 1.454 3.498 1.939 4.373 2.424 61 15 0.872 0.489 1.745 0.977 2.617 1.466 3.490 1.954 4.362 2.443 45 30 0.870 0.492 1.741 0.985 2.611 1.477 3.481 1.970 4.352 2.462 30 45 0.868 0.496 1.736 0.992 2.605 1.489 3.473 1.985 4.341 2.481 15 30 0.866 0.500 1.732 1.000 2.598 1.500 3.464 2.000 4.330 2.500 6O f Dep. Lat. Dep. Lat. Dep. Lat. Dep. Lat. Dep. Lat. t Bearing Distance 1. Distance 2. Distance 3. Distance 4. Distance 5. Bearing. 60- 75< 15- 30' 59 Bearing, Distance 6. Distance 7. Distance 8. Distance 9. Distance 10. Bearing. O f Lat. Dep. Lat. Dep. Lat. Dep. Lat. Dep. Lat. Dep. o t 1515 5.789 1.578 6.754 1.841 7.718 2.104 8.683 2.367 9.648 2.630 7445 30 5.782 1.603 6.745 1.871 7.709 2.138 8.673 2.405 9.636 2.672 30 45 5.775 1.629 6.737 1.900 7.700 2.172 8.662 2.443 9.625 2.714 15 16 5.768 1.654 6.729 1.929 7.690 2.205 8.651 2.481 9.613 2.756 74 15 5.760 1.679 6.720 1.959 7.680 2.239 8.640 2.518 9.601 2.798 45 30 5.753 1.704 6.712 1.988 7.671 2.272 8.629 2.556 9.588 2.840 30 45 5.745 1.729 6.703 2.017 7.661 2.306 8.618 2.594 9.576 2.882 15 17 5.738 1.754 6.694 2.047 7.650 2.339 8.607 2.631 9.563 2.924 73 15 5.730 1.779 6.685 2.076 7.640 2.372 8.595 2.669 9.550 2.965 45 30 5.722 1.804 6.676 2.105 7.630 2.406 8.583 2.706 9.537 3.007 30 45 5.714 1.829 6.667 2.134 7.619 2.439 8.572 2.744 9.524 3.049 15 18 5.706 1.854 6.657 2.163 7.608 2.472 8.560 2.781 9.511 3.090 72 15 5.698 1.879 6.648 2.192 7.598 2.505 8.547 2.818 9.497 3.132 45 30 5.690 1.904 6.638 2.221 7.587 2.538 8.535 2.856 9.483 3.173 30 45 5.682 1.929 6.629 2.250 7.575 2.572 8.522 2.893 9.469 3.214 15 19 5.673 1.953 6.619 2.279 7.564 2.605 8.510 2.930 9.455 3.256 71 15 5.665 1.978 6.609 2.308 7.553 2.638 8.497 2.967 9.441 3.297 45 30 5.656 2.003 6.598 2.337 7.541 2.670 8.484 3.004 9.426 3.338 30 45 5.647 2.028 6.588 2.365 7.529 2.703 8.471 3.041 9.412 3.379 15 20 5.638 2.052 6.578 2.394 7.518 2.736 8.457 3.078 9.397 3.420 70 15 5.629 2.077 6.567 2.423 7.506 2.769 8.444 3.115 9.382 3.461 45 30 5.620 2.101 6.557 2.451 7.493 2.802 8.430 3.152 9.367 3.502 30 45 5.611 2.126 6.546 2.480 7.481 2.834 8.416 3.189 9.351 3.543 15 21 5.601 2.150 6.535 2.509 7.469 2.867 8.402 3.225 9.336 3.584 69 15 5.592 2.175 6.524 2.537 7.456 2.900 8.388 3.262 9.320 3.624 45 30 5.582 2.199 6.513 2.566 7.443 2.932 8.374 3.299 9.304 3.665 30 45 5.573 2.223 6.502 2.594 7.430 2.964 8.359 3.335 9.288 3.706 15 22 5.563 2.248 6.490 2.622 7.417 2.997 8.345 3.371 9.272 3.746 68 15 5.553 2.272 6.479 2.651 7.404 3.029 8.330 3.408 9.255 3.787 45 30 5.543 2.296 6.467 2.679 7.391 3.061 8.315 3.444 9.239 3.827 30 45 5.533 2.320 6.455 2.707 7.378 3.094 8.300 3.480 9.222 3.867 15 23 5.523 2.344 6.444 2.735 7.364 3.126 8.285 3.517 9.205 3.907 67 15 5.513 2.368 6.432 2.763 7.350 3.158 8.269 3.553 9.188 3.947 45 30 5.502 2.392 6.419 2.791 7.336 3.190 8.254 3.589 9.171 3.988 30 45 5.492 2.416 6.407 2.819 7.322 3.222 8.238 3.625 9.153 4.028 15 24 5.481 2.440 6.395 2.847 7.308 3.254 8.222 3.661 9.136 4.067 66 15 5.471 2.464 6.382 2.875 7.294 3.286 8.206 3.696 9.118 4.107 45 30 5.460 2.488 6.370 2.903 7.280 3.318 8.190 3.732 9.100 4.147 30 45 5.449 2.512 6.357 2.931 7.265 3.349 8.173 3.768 9.081 4.187 15 25 5.438 2.536 6.344 2.958 7.250 3.381 8.157 3.804 9.063 4.226 65 15 5.427 2.559 6.331 2.986 7.236 3.413 8.140 3.839 9.045 4.266 45 30 5.416 2.583 6.318 3.014 7.221 3.444 8.123 3.875 9.026 4.305 30 45 5.404 2.607 6.305 3.041 7.206 3.476 8.106 3.910 9.007 4.345 15 26 5.393 2.630 6.292 3.069 7.190 3.507 8.089 3.945 8.988 4.384 64 15 5.3S1 2.654 6.278 3.096 7.175 3.538 8.072 3.981 8.969 4.423 45 30 5.370 2.677 6.265 3.123 7.160 3.570 8.054 4.016 8.949 4.462 30 45 5.358 2.701 6.251 3.151 7.144 3.601 8.037 4.051 8.930 4.501 15 27 5.346 2.724 6.237 3.178 7.128 3.632 8.019 4.086 8.910 4.540 63 15 5.334 2.747 6.223 3.205 7.112 3.663 8.001 4.121 8.890 4.579 45 30 5.322 2.770 6.209 3.232 7.096 3.694 7.983 4.156 8.870 4.618 30 45 5.310 2.794 6.195 3.259 7.0SO 3.725 7.965 4.190 8.850 4.656 15 28 5.298 2.817 6.181 3.286 7.064 3.756 7.947 4.225 8.829 4.695 62 15 5.285 2.840 6.166 3.313 7.047 3.787 7.928 4.260 8.809 4.733 45 30 5.273 2.863 6.152 3.340 7.031 3.817 7.909 4.294 8.788 4.772 30 45 5.260 2.886 6.137 3.367 7.014 3.848 7.891 4.329 8.767 4.810 15 29 5.248 2.909 6.122 3.394 6.997 3.878 7.S72 4.363 8.746 4.848 61 15 5.235 2.932 6.107 3.420 6.9SO 3.909 7.852 4.398 8.725 4.886 45 30 5.222 2.955 6.093 3.447 6.963 3.939 7.833 4.432 8.704 4.924 30 45 5.209 2.977 6.077 3.474 6.946 3.970 7.814 4.466 8.682 4.962 15 30 5.196 3.000 6.062 3.500 6.928 4.000 7.794 4.500 8.660 5.000 60 f Dep. Lat. Dep. Lat. Dep. Lat. Dep. Lat. Dep. Lat. o t Bearing. Distance 6. Distance 7. Distance 8. Distance 9. Distance 1O. Bearing. 60-- 75' 30- 45 C Bearing. Distance 1. Distance 2. Distance 3. Distance 4. Distance 5. Bearing. o r Lat. Dep. Lat. Dep. Lat. Dep. Lat. Dep. Lat. Dep. f 3015 0.864 0.504 1.728 1.008 2.592 1.511 3.455 2.015 4.319 2.519 5945 30 0.862 0.508 1.723 1.015 2.585 1.523 3.447 2.030 4.308 2.538 30 45 0.859 0.511 1.719 1.023 2.578 1.534 3.438 2.045 4.297 2.556 15 31 0.857 0.515 1.714 1.030 2.572 1.545 3.429 2.060 4.286 2.575 59 15 0.855 0.519 1.710 1.038 2.565 1.556 3.420 2.075 4.275 2.594 45 30 0.853 0.522 1.705 1.045 2.558 1.567 3.411 2.090 4.263 2.612 30 45 0.850 0.526 1.701 1.052 2.551 1.579 3.401 2.105 4.252 2.631 15 32 0.848 0.530 1.696 1.060 2.544 1.590 3.392 2.120 4.240 2.650 58 15 0.846 0.534 1.691 1.067 2.537 1.601 3.383 2.134 4.229 2.668 45 30 0.843 0.537 1.687 1.075 2.530 1.612 3.374 2.149 4.217 2.686 30 45 0.841 0.541 1.682 1.082 2.523 1.623 3.364 2.164 4.205 2.705 15 33 0.839 0.545 1.677 1.089 2.516 1.634 3.355 2.179 4.193 2.723 57 15 0.836 0.548 1.673 1.097 2.509 1.645 3.345 2.193 4.181 2.741 45 30 0.834 0.552 1.668 1.104 2.502 1.656 3.336 2.208 4.169 2.760 30 45 0.831 0.556 1.663 1.111 2.494 1.667 3.326 2.222 4.157 2.778 15 34 0.829 0.559 1.658 1.118 2.487 1.678 3.316 2.237 4.145 2.796 56 15 0.827 0.563 1.653 1.126 2.480 1.688 3.306 2.251 4.133 2.814 45 30 0.824 0.566 1.648 1.133 2.472 1.699 3.297 2.266 4.121 2.832 30 45 0.822 0.570 1.643 1.140 2.465 1.710 3.287 2.280 4.108 2.850 15 35 0.819 0.574 1.638 1.147 2.457 1.721 3.277 2.294 4.096 2.868 55 15 0.817 0.577 1.633 1.154 2.450 1.731 3.267 2.309 4.083 2.886 45 30 0.814 0.581 1.628 1.161 2.442 1.742 3.257 2.323 4.071 2.904 30 45 0.812 0.584 1.623 1.168 2.435 1.753 3.246 2.337 4.058 2.921 15 36 0.809 0.588 1.618 1.176 2.427 1.763 3.236 2.351 4.045 2.939 54 15 0.806 0.591 1.613 1.183 2.419 1.774 3.226 2.365 4.032 2.957 45 30 0.804 0.595 1.608 1.190 2.412 1.784 3.215 2.379 4.019 2.974 30 45 0.801 0.598 1.603 1.197 2.404 1.795 3.205 2.393 4.006 2.992 15 37 0.799 0.602 1.597 1.204 2.396 1.805 3.195 ?.407 3.993 3.009 53 15 0.796 0.605 1.592 1.211 2.388 1.816 3.184 2.421 3.980 3.026 45 30 0.793 0.609 1.587 1.218 2.380 1.826 3.173 2.435 3.967 3.044 30 45 0.791 0.612 1.581 1.224 2.372 1.837 3.163 2.449 3.953 3.061 15 38 0.788 0.616 1.576 1.231 2.364 1.847 3.152 2.463 3.940 3.078 52 15 0.785 0.619 1.571 1.238 2.356 1.857 3.141 2.476 3.927 3.095 45 30 0.783 0.623 1.565 1.245 2.348 1.868 3.130 2.490 3.913 3.113 30 45 0.780 0.626 1.560 1.252 2.340 1.878 3.120 2.504 3.899 3.130 15 39 0.777 0.629 1.554 1.259 2.331 1.888 3.109 2.517 3.8S6 3.147 51 15 0.774 0.633 1.549 1.265 2.323 1.898 3.098 2.531 3.872 3.164 45 30 0.772 0.636 1.543 1.272 2.315 1.908 3.086- 2.544 3.858 3.180 30 45 0.769 0.639 1.538 1.279 2.307 1.918 3.075 2.558 3. 844 3.197 15 40 0.766 0.643 1.532 1.286 2.298 1.928 3.064 2.571 3.830 3.214 5O 15 0.763 0.646 1.526 1.292 2.290 1.938 3.053 2.584 3.816 3.231 45 30 0.760 0.649 1.521 1.299 2.281 1.948 3.042 2.598 3.802 3.247 30 45 0.758 0.653 1.515 1.306 2.273 1.958 3.030 2.611 3. 788 3.264 15 41 0.755 0.656 1.509 1.312 2.264 1.968 3.019 2.624 3.774 3.280 49 15 0.752 0.659 1.504 1.319 2.256 1.978 3.007 2.637 3.759 3.297 45 30 0.749 0.663 1.498 1.325 2.247 1.988 2.996 2.650 3.745 3.313 30 45 0.746 0.666 1.492 1.332 2.23S 1.998 2.984 2.664 3.730 3.329 15 42 0.743 0.669 1.486 1.338 2.229 2.007 2.973 2.677 3.716 3.346 48 15 0.740 0.672 1.480 1.345 2.221 2.017 2.961 2.689 3.701 3.362 45 30 0.737 0.676 1.475 1.351 2.212 2.027 2.949 2.702 3.686 3.378 30 45 0.734 0.679 1.469 1.358 2.203 2.036 2.937 2.715 3.672 3.394 15 43 0.731 0.682 1.463 1.364 2.194 2.046 2.925 2.728 3.657 3.410 47 15 0.728 0.685 1.457 1.370 2.185 2.056 2.913 2.741 3.642 3.426 45 30 0.725 0.688 1.451 1.377 2.176 2.065 2.901 2.753 3.627 3.442 30 45 0.722 0.692 1.445 1.383 2.167 2.075 2.889 2.766 3.612 3.458 15 44 0.719 0.695 1.439 1.389 2.158 2.0S4 2.877 2.779 3.597 3.473 46 15 0.716 0.698 1.433 1.396 2.149 2.093 2.865 2.791 3.582 3.489 45 30 0.713 0.701 1.427 1.402 2.140 2.103 2.853 2.804 3.566 3.505 30 45 0.710 0.704 1.420 1.408 2.131 2.112 2.841 2.816 3.551 3.520 15 45 0.707 0.707 1.414 1.414 2.121 2.121 2.828 2.828 3.536 3.536 45 f Dep. Lat. Dep. Lat. Dep. Lat. Dep. Lat. Dep. Lat. o r Bearing Distance 1. Distance 2. Distance 3. Distance 4. Distance 5. Bearing. 45- 60 C 30- 45' Bearing. Distance 6. Distance 7. Distance 8. Distance 9. Distance 1O. Bearing. o / Lat. Dep. Lat. Dep. Lat. Dep. Lat. Dep. Lat. i Dep. o t 3O15 5.183 3.023 6.047 3.526 6.911 4.030 7.775 4.534 8.638 i 5.038 5945 30 5.170 3.045 6.031 3.553 6.893 4.060 7.755 4.568 8.616 5.075 30 45 5.156 3. 068 6.016 3.579 6.875 4.090 7.735 4.602 8.594 5.113 15 31 5.143 3.090 6.000 3.605 6.857 4.120 7.715 4.635 8.572 5.150 59 15 5.129 3.113 5.984 3.631 6.839 4.150 7.694 4.669 8.549 5.188 45 30 5.116 3.135 5.968 3.657 6.821 4.180 7.674 4.702 8.526 5.225 30 45 5.102 3.157 5.952 3.683 6.803 4.210 7.653 4.736 8.504 5.262 15 32 5.088 3.180 5.936 3.709 6.784 4.239 7.632 4.769 8.481 5.299 58 15 5.074 3.202 5.920 3.735 6.766 4.269 7.612 4.802 8.457 5.336 45 30 5.060 3.224 5.904 3.761 6.747 4.298 7.591 4.836 8.434 5.373 30 45 5.046 3.246 5.887 3.787 6.728 4.328 7.569 4.869 8.410 5.410 15 33 5.032 3.268 5.871 3.812 6.709 4.357 7.548 4.902 8.387 5.446 57 15 5.018 3.290 5.854 3.838 6.690 4.386 7.527 4.935 8.363 5. 483 45 30 5.003 3.312 5.837 3.864 6.671 4.416 7.505 4.967 8.339 5.519 30 45 4.989 3.333 5.820 3.889 6.652 4.445 7.483 5.000 8.315 5.556 15 34 4.974 3.355 5.803 3.914 j! 6.632 4.474 7.461 5.033 8.290 5.592 56 15 4.960 3.377 5.786 3.940 6.613 4.502 7.439 5.065 8.266 5.628 45 30 4.945 3.398 5.769 3.965 6.593 4.531 7.417 5.098 8.241 5.664 30 45 4.930 3.420 5.752 3.990 6.573 4.560 7.395 5.130 8.217 5.700 15 35 4.915 3.441 5.734 4.015 6.553 4.589 7.372 5.162 8.192 5.736 55 15 4.900 3.463 5.716 4.040 6.533 4.617 7.350 5.194 8.166 5.772 45 30 4.885 3.484 5.699 4.065 6.513 4.646 7.327 5.226 8.141 5.807 30 45 4.869 3.505 5.681 4.090 6.493 4.674 7.304 5.258 8.116 5.843 15 36 4.854 3.527 5.663 4.115 6-472 4.702 7.281 5.290 8.090 5.878 54 15 4.839 3.548 5.645 4.139 6.452 4.730 7.258 5.322 8.064 5.913 45 30 4.823 3.569 5.627 4.164 6.431 4.759 7.235 5.353 8.039 5.948 30 45 4.808 3.590 5.609 4.188 6.410 4.787 7.211 5.385 8.013 5.983 15 37 4.792 3.611 5.590 4.213 6.389 4.815 7.188 5.416 7.986 6.018 53 15 4.776 3.632 5.572 4.237 6.368 4.842 7.164 5.448 7.960 6.053 45 30 4.760 3.653 5.554 4.261 6.347 4.870 7.140 5.479 7.934 6.088 30 45 4.744 3.673 5.535 4.286 6.326 4.898 7.116 5.510 7.907 6.122 15 38 4.728 3.694 5.516 4.310 6.304 4.925 7.092 5.541 7.880 6.157 52 15 4.712 3.715 5.497 4.334 6.283 4.953 7.068 5.572 7.853 6.191 45 30 4.696 3.735 5.478 4.358 6.261 4.980 7.043 5.603 7.826 6.225 30 45 4.679 3.756 5.459 4.381 6.239 5.007 7.019 5.633 7.799 6.259 15 39 4.663 3.776 5.440 4.405 6.217 5.035 6.994 5.664 7.772 6.293 51 15 4.646 3.796 5.421 4.429 6.195 5.062 6.970 5.694 7.744 6.327 45 30 4.630 3.816 5.401 4.453 6.173 5.089 6.945 5.725 7.716 6.361 30 45 4.613 3.837 5.382 4.476 6.151 5.116 6.920 5.755 7.688 6.394 15 40 4.596 3.857 5.362 4.500 6.128 5.142 6.894 5.785 7.660 6.428 50 15 4.579 3.877 5.343 4.523 6.106 5.169 6.869 5.815 7.632 6.461 45 30 4.562 3.897 5.323 4.546 6.083 5.196 6.844 5.845 7.604 6.495 30 45 4.545 3.917 5.303 4.569 6.061 5.222 6.818 5.875 7.576 6.528 15 41 4.528 3.936 5.283 4.592 6.038 5.248 6.792 5.905 7.547 6.561 49 15 4.511 3.956 5.263 4.615 6.015 5.275 6.767 5.934 7.518 6.594 45 30 4.494 3.976 5.243 4.638 5.992 5.301 6.741 5.964 7.490 6.626 30 45 4.476 3.995 5.222 4.661 5.968 5.327 6.715 5.993 7.461 6.659 15 42 4.459 4.015 5.202 4.684 5.945 5.353 6.688 6.022 7.431 6.691 48 15 4.441 4.034 5.182 4.707 5.922 5.379 6.662 6.051 7.402 6.724 45 30 4.424 4.054 5.161 4.729 5.898 5.405 6.635 6.080 7.373 6.756 30 45 4.406 4.073 5.140 4.752 5.875 5.430 6.609 6.109 7.343 6.788 15 43 4.388 4.092 5.119 4.774 5.851 5.456 6.582 6.138 7.314 6.820 47 15 4.370 4.111 5.099 4.7% 5.827 5.481 6.555 6.167 7.284 6.852 45 30 4.352 4.130 5.078 4.818 5.803 5.507 6.528 6.195 7.254 6.884 30 45 4.334 4.149 5.057 4.841 5.779 5.532 6.501 6.224 7.224 6.915 15 44 4.316 4.168 5.035 4.863 5.755 5.557 6.474 6.252 7.193 6.947 48 15 4.298 4.187 5.014 4.885 5.730 5.582 6.447 6.280 7.163 6.978 45 30 4.2SO 4.206 4.993 4.906 5.706 5.607 6.419 6.308 7.133 7.009 30 45 4.261 4.224 4.971 4.928 5.681 5.632 6.392 6.336 7.102 7.040 15 45 4.243 4.243 4.950 4.950 5.657 5.657 6.364 6.364 7.071 7.071 45 f Dep. Lat. Dep. Lat. Dep. Lat. Dep. Lat. Dep. Lat. o t Bearing, Distance 6. Distance 7. Distance 8. Distance 9. Distance 1O. Bearing. 45- 60' TABLE VIII, -NATURAL SINES AND COSINES. t 1 2 3 4 t sin cos gin cos sin cos sin cos sin cos o 0000 one 0175 9998 0349 9994 0523 9986 0698 9976 6O 1 0003 one 0177 9998 0352 9994 0526 9986 0700 9975 59 2 0006 one 0180 9998 0355 9994 0529 9986 0703 9975 58 3 0009 one 0183 9998 0358 9994 0532 9986 0706 9975 57 4 0012 one 0186 9998 0361 9993 0535 9986 0709 9975 56 5 0015 one 0189 9998 0364 9993 0538 9986 0712 9975 55 6 0017 one 0192 9998 0366 9993 0541 9985 0715 9974 54 7 0020 one 0195 9998 0369 9993 0544 9985 0718 9974 53 8 0023 one 0198 9998 0372 9993 0547 9985 0721 9974 52 9 0026 one 0201 9998 0375 9993 0550 9985 0724 9974 51 1O 0029 one 0204 9998 0378 9993 0552 9985 0727 9974 50 11 0032 one 0207 9998 0381 9993 0555 9985 0729 9973 49 12 0035 one 0209 9998 0384 9993 0558 9984 0732 9973 48 13 0038 one 0212 9998 0387 9993 0561 9984 0735 9973 47 14 0041 one 0215 9998 0390 9992 0564 9984 0738 9973 46 15 0044 one 0218 9998 0393 9992 0567 9984 0741 9973 45 16 0047 one 0221 9998 0396 9992 0570 9984 0744 9972 44 17 0049 one 0224 9997 0398 9992 0573 9984 0747 9972 43 18 0052 one 0227 9997 0401 9992 0576 9983 0750 9972 42 19 0055 one 0230 9997 0404 9992 0579 9983 0753 9972 41 2O 0058 one 0233 9997 0407 9992 0581 9983 0756 9971 40 21 0061 one 0236 9997 0410 9992 0584 9983 0758 9971 39 22 0064 one 0239 9997 0413 9991 0587 9983 0761 9971 38 23 0067 one 0241 9997 0416 9991 0590 9983 0764 9971 37 24 0070 one 0244 9997 0419 9991 0593 9982 0767 9971 36 25 0073 one 0247 9997 0422 9991 05% 9982 0770 9970 35 26 0076 one 0250 9997 0425 9991 0599 9982 0773 9970 34 27 0079 one 0253 9997 0427 9991 0602 9982 0776 9970 33 28 0081 one 0256 9997 0430 9991 0605 9982 0779 9970 32 29 0084 one 0259 9997 0433 9991 0608 9982 0782 9969 31 30 0087 one 0262 9997 0436 9990 0610 9981 0785 9969 3O 31 0090 one 0265 9996 0439 9990 0613 9981 0787 9969 29 32 0093 one 0268 9996 0442 9990 0616 9981 0790 9969 28 33 0096 one 0270 9996 0445 9990 0619 9981 0793 9968 27 34 0099 one 0273 9996 0448 9990 0622 9981 0796 9968 26 35 0102 9999 0276 9996 0451 9990 0625 9980 0799 9968 25 36 0105 9999 0279 9996 0454 9990 0628 9980 OS02 9968 24 37 0108 9999 0282 9996 0457 9990 0631 9980 0805 9968 23 38 0111 9999 0285 9996 0459 9989 0634 9980 0808 9967 22 39 0113 9999 0288 9996 0462 9989 0637 9980 0811 9967 21 4O 0116 9999 0291 9996 0465 9989 0640 9980 0814 9967 2O 41 0119 9999 0294 9996 0468 9989 0642 9979 0816 9967 19 42 0122 9999 0297 9996 0471 9989 0645 9979 0819 9966 18 43 0125 9999 0300 9996 0474 9989 0648 9979 0822 9966 17 44 0128 9999 0302 9995 0477 9989 0651 9979 0825 9966 16 45 0131 9999 0305 9995 0480 9988 0654 9979 0828 9966 15 46 0134 9999 0308 9995 0483 9988 0657 9978 0831 9965 14 47 0137 9999 0311 9995 0486 9988 0660 9978 0834 9965 13 48 0140 9999 0314 9995 0488 9988 0663 9978 0837 9965 12 49 0143 9999 0317 9995 0491 9988 0666 9978 08-10 9965 11 5O 0145 9999 0320 9995 0494 9988 0669 9978 0843 9964 1O 51 0148 9999 0323 9995 0497 9988 0671 9977 0845 9964 9 52 0151 9999 0326 9995 0500 9987 0674 9977 0848 9964 8 53 0154 9999 0329 9995 0503 9987 0677 9977 0851 9964 7 54 0157 9999 0332 9995 0506 9987 0680 9977 0854 9963 6 55 0160 9999 0334 9994 0509 9987 0683 9977 0857 9963 5 56 0163 9999 0337 9994 0512 9987 0686 9976 0860 9963 4 57 0166 9999 0340 9994 0515 9987 06S9 9976 0863 9963 3 58 0169 9999 0343 9994 0518 9987 0692 9976 0866 9962 2 59 0172 9999 0346 9994 0520 9986 0695 9976 0869 9962 1 60 0175 9999 cos sin 0349 9994 cos sin 0523 9986 0698 9976 0872 9962 O t 89 88 87 86 86 NATURAL SINES AND COSINES. 5 6 7 8 9 f Mil COS sin cos sin cos sin cos sin COB 0872 9962 1045 9945 1219 9925 1392 9903 1564 9877 '< 1 0874 9962 1048 9945 1222 9925 1395 9902 1567 9876 59 2 0877 9461 1051 9945 1224 9925 1397 9902 1570 9876 58 3 0880 9961 1054 9944 1227 9924 1400 9901 1573 9876 57 4 0883 9961 1057 9944 1230 9924 1403 9901 1576 9875 56 5 0886 9961 1060 9944 1233 9924 1406 9901 1579 9875 55 6 0889 9960 1063 9943 1236 9923 1409 9900 1582 9874 54 7 0892 9960 1066 9943 1239 9923 1412 9900 1584 9874 53 8 0895 9960 1068 9943 1241 9923 1415 9899 1587 9873 52 9 0898 9960 1071 9942. 1245 9922 1418 9899 1590 9S73 51 10 0901 9959 1074 9942 1248 9922 1421 9899 1593 9872 5O 11 0903 9959 1077 9942 1250 9922 1423 9898 1596 9872 49 12 0906 9959 1080 9942 1253 9921 1426 9898 1599 9871 48 13 0909 9959 1083 9941 1256 9921 1429 9897 1602 9871 47 14 0912 9958 1086 9941 1259 9920 1432 9897 1605 9870 46 15 09] 5 9958 1089 9941 1262 9920 1435 9897 1607 9870 45 16 0918 9958 1092 9940 1265 9920 1438 9896 1610 9869 44 17 0921 9958 1094 9940 1268 9919 1441 9896 1613 9869 43 18 0924 9957 1097 9940 1271 9919 1444 9895 1616 9869 42 19 0927 9957 1100 9939 1274 9919 1446 9895 1619 9868 41 20 0929 9957 1103 9939 1276 9918 1449 9894 1622 9868 4O 21 0932 9956 1106 9939 1279 9918 1452 9894 1625 9867 39 22 0935 9956 1109 9938 1282 9917 1455 9894 1628 9867 38 23 0938 9956 1112 9938 1285 9917 1458 9893 1630 9866 37 24 0941 9956 1115 9938 1288 9917 1461 9893 1633 9866 36 25 0944 9955 1118 9937 1291 9916 1464 9892 1636 9865 35 26 0947 9955 1120 9937 1294 9916 1467 9892 1639 9865 34 27 0950 9955 1123 9937 1297 9916 1469 9891 1642 9864 33 28 0953 9955 1126 9936 1299 9915 1472 9891 1645 9864 32 29 0956 9954 1129 9936 1302 9915 1475 9891 1648 9863 31 30 0958 9954 1132 9936 1305 9914 1478 9890 1650 9863 3O 31 0961 9954 1135 9935 1308 9914 1481 9890 1653 9862 29 32 9964 9953 1138 9935 1311 9914 1484 9889 1656 9862 28 33 0967 9953 1141 9935 1314 9913 1487 9889 1659 9861 27 34 0970 9953 1144 9934 1317 9913 1490 9888 1662 9861 26 35 0973 9553 1146 9934 1320 9913 1492 9888 1665 9860 25 36 0976 9952 1149 9934 1323 9912 1495 9888 1668 9860 24 37 0979 9952 1152 9933 1325 9912 1498 9887 1671 9859 23 38 0982 9952 1155 9933 1328 9911 1501 9887 1673 9859 22 39 0985 9951 1158 9933 1331 9911 1504 9886 1676 9859 21 4O 0987 9951 1161 9932 1334 9911 1507 9886 1679 9858 2O 41 0990 9951 1164 9932 1337 9910 1510 9885 1682 9858 19 42 0993 9951 1167 9932 1340 9910 1513 9885 1685 9857 18 43 0996 9950 1170 9931 1343 9909 1515 9884 1688 9857 17 44 0999 9950 1172 9931 1346 9909 1518 9884 1691 9856 16 45 1002 9950 1175 9931 1349 9909 1521 9884 1693 9856 15 46 1005 9949 1178 9930 1351 9908 1524 9883 1696 9855 14 47 1008 9949 1181 9930 1354 9908 1527 9883 1699 9855 13 48 1011 9949 1184 9930 1357 9907 1530 9882 1702 9854 12 49 1013 9949 1187 9929 1360 9907 1533 9882 1705 9854 11 5O 1016 9948 1190 9929 1363 9907 1536 9881 1708 9853 1O 51 1019 9948 1193 9929 1366 9906 1538 9881 1711 9853 9 52 1022 9948 11% 9928 1369 9906 1541 9880 1714 9852 8 53 1025 9947 1198 9928 1372 9905 1544 9880 1716 9852 7 54 1028 9947 1201 9928 1374 9905 1547 9880 1719 9851. 6 55 1031 9947 1204 9927 1377 9905 1550 9879 1722 9851 5 56 1034 9946 1207 9927 1380 9904 1553 9879 1725 9850 4 57 1037 9946 1210 9927 1383 9904 1556 9878 1728 9850 3 58 1039 9946 1213 9926 1386 9903 1559 9878 1731 9849 2 59 1042 9946 1216 9926 1389 9903 1561 9877 1734 9849 1 60 1045 9945 1219 9925 1392 9903 1564 9877 1736 9848 cos sin cos sin cos ftin cos sin COB Bin f 84 83 82 81 80 64 NATURAL SINES AND COSINES. f 1O 11 12 13 14 r sin cos sin cos sin cos sin cos sin cos o 1736 9848 1908 9816 2079 9781 2250 9744 2419 9703 6O 1 1739 9848 1911 9816 2082 9781 2252 9743 2422 9702 59 2 1742 9847 1914 9815 2085 9780 2255 9742 2425 9702 58 3 1745 9847 1917 9815 2088 9780 2258 9742 2428 9701 57 4 1748 9846 1920 9814 2090 9779 2261 9741 2431 9700 56 5 1751 9846 1922 9813 2093 9778 2264 9740 2433 9699 55 6 1754 9845 1925 9813 2096 9778 2267 9740 2436 9699 54 7 1757 9845 1928 9812 2099 9777 2269 9739 2439 9698 53 8 1759 9844 1931 9812 2102 9777 2272 9738 2442 9697 52 9 1762 9843 1934 9811 2105 9776 2275 9738 2445 9697 51 1O 1765 9843 1937 9811 2108 9775 2278 9737 2447 9696 50 11 1768 9842 1939 9810 2110 9775 2281 9736 2450 9695 49 12 1771 9842 1942 9810 2113 9774 2284 9736 2453 9694 48 13 1774 9841 1945 9809 2116 9774 2286 9735 2456 9694 47 14 1777 9841 1948 9808 2119 9773 2289 9734 2459 9693 46 15 1779 9840 1951 9808 2122 9772 2292 9734 2462 9692 45 16 1782 9840 1954 9S07 2125 9772 2295 9733 2464 9692 44 17 1785 9839 1957 9807 2127 9771 2298 9732 2467 9691 43 18 1788 9839 1959 9806 2130 9770 2300 9732 2470 9690 42 19 1791 9838 1962 9806 2133 9770 2303 9731 2473 9689 41 2O 1794 9838 1965 9805 2136 9769 2306 9730 2476 9689 4O 21 1797 9837 1968 9804 2139 9769 2309 9730 2478 9688 39 22 1799 9837 1971 9804 2142 9768 2312 9729 2481 9687 38 23 1802 9836 1974 9803 2145 9767 2315 9728 2484 9687 37 24 1805 9836 1977 9803 2147 9767 2317 9728 2487 9686 36 25 1808 9835 1979 9802 2150 9766 2320 9727 2490 9685 35 26 1811 9835 1982 9802 2153 9765 2323 9726 2493 9684 34 27 1814 9S34 1985 9801 2156 9765 2326 9726 2495 9684 33 28 1817 9834 1988 9800 2159 9764 2329 9725 2498 9683 32 29 1819 9833 1991 9800 2162 9764 2332 9724 2501 9682 31 30 1822 9833 1994 9799 2164 9763 2334 9724 2504 9681 30 31 1825 9832 1997 9799 2167 9762 2337 9723 2507 9681 29 32 1828 9831 1999 9798 2170 9762 2340 9722 2509 9680 28 33 1831 9831 2002 9798 2173 9761 3343 9722 2512 9679 27 34 1834 9830 2005 9797 2176 9760 2346 9721 2515 9679 26 35 1837 9830 2008 9796 2179 9760 2349 9720 2518 9678 25 36 1840 9829 2011 9796 2181 9759 2351 9720 2521 9677 24 37 1842 9829 2014 9795 2184 9759 2354 9719 2524 9676 23 38 1845 9828 2016 9795 2187 9758 2357 9718 2526 9676 22 39 1848 9828 2019 9794 2190 9757 2360 9718 2529 9675 21 40 1851 9827 2022 9793 2193 9757 2363 9717 2532 9674 20 41 1854 9827 2025 9793 2196 9756 2366 9716 2535 9673 19 42 1857 9826 2028 9792 2198 9755 2368 9715 2538 9673 18 43 1860 9826 2031 9792 2201 9755 2371 9715 2540 9672 17 44 1862 9825 2034 9791 2204 9754 2374 9714 2543 9671 16 45 1865 9825 2036 9790 2207 9753 2377 9713 2546 9670 15 46 1868 9824 2039 9790 2210 9753 2380 9713 2549 9670 14 47 1871 9823 2042 9789 2213 9752 2383 9712 2552 9669 13 48 1474 9823 2045 9789 2215 9751 2385 9711 2554 9668 12 49 1877 9822 2048 9788 2218 9751 2388 9711 2557 9667 11 50 1880 9822 2051 9787 2221 9750 2391 9710 2560 9667 10 51 1882 9821 2054 9787 2224 9750 2394 9709 2563 9666 9 52 1885 9821 2056 9786 2227 9749 2397 9709 2566 9665 8 53 1888 9820 2059 9786 2230 9748 2399 9708 2569 9665 7 54 1891 9820 2062 9785 2233 9748 2402 9707 2571 9664 6 55 1894 9819 2065 9784 2235 9747 2405 9706 2574 9663 5 56 1897 9818 2068 9784 2238 9746 2408 9706 2577 9662 4 57 1900 9818 2071 9783 2241 9746 2411 9705 2580 9662 3 58 1902 9817 2073 9783 2244 9745 2414 9704 2583 9661 2 59 1905 9817 2076 9782 2247 9744 2416 9704 2585 9660 1 60 1908 9816 2079 9781 2250 9744 2419 9703 2588 9659 cos sin cos sill cos sin cos sin cos sin f 79 78 77 76 75 r NATURAL SINES AND COSINES. 65 f 15 16 17 18 19 t sin cos Bin cos sin cos sin cos sin cos o 25S8 9659 2756 9613 2924 9563 3090 9511 3256 9455 6O 1 2591 9659 2759 9612 2926 9562 3093 9510 3258 9454 59 2 2594 9658 2762 9611 2929 9561 30% 9509 3261 9453 58 3 2597 9657 2765 9610 2932 9560 3098 9508 3264 9452 57 4 2599 9656 2768 9609 2935 9560 3101 9507 3267 9451 56 5 2602 9655 2770 9609 2938 9559 3104 9506 3269 9450 55 6 2605 9655 2773 9608 2940 9558 3107 9505 3272 9449 54 7 2608 9654 2776 9607 2943 9557 3110 9504 3275 9449 53 8 2611 9653 2779 9606 2946 9556 3112 9503 3278 9448 52 9 2613 9652 2782 9605 2949 9555 3115 9502 3280 9447 51 10 2616 9652 2784 9605 2952 9555 3118 9502 3283 9446 5O 11 2619 9651 2787 9604 2954 9554 3121 9501 3286 9445 49 12 2622 9650 2790 9603 2957 9553 3123 9500 3289 9444 48 13 2625 9649 2793 9602 2960 9552 3126 9499 3291 9443 47 14 2628 9649 2795 9601 2963 9551 3129 9498 3294 9442 46 15 2630 9648 2798 9600 2965 9550 3132 9497 3297 9441 45 16 2633 9647 2801 9600 2968 9549 3134 94% 3300 9440 44 17 2636 9646 2804 9599 2971 9548 3137 9495 3302 9439 43 18 2639 9646 2807 9598 2974 9548 3140 9494 3305 9438 42 19 2642 9645 2809 9597 2977 9547 3143 9493 3308 9437 41 2O 2644 9644 2812 95% 2979 9546 3145 9492 3311 9436 JO 21 2647 9643 2815 9596 2982 9545 3148 9492 3313 9435 39 22 2650 9642 2818 9595 2985 9544 3151 9491 3316 9434 38 23 2653 9642 2821 9594 2988 9543 3154 9490 3319 9433 37 24 2656 9641 2823 9593 2990 9542 3156 9489 3322 9432 36 25 2658 9640 2826 9592 2993 9542 3159 9488 3324 9431 35 26 2661 9639 2829 9591 29% 9541 3162 9487 3327 9430 34 27 2664 9639 2832 9591 2999 9540 3165 9486 3330 9429 33 28 2667 9638 2835 9590 3002 9539 3168 9485 3333 9428 32 29 2670 9637 2837 9589 3004 9538 3170 9484 3335 9427 31 30 2672 9636 2840 9588 3007 9537 3173 9483 3338 9426 3O 31 2675 9636 2843 9587 3010 9536 3176 9482 3341 9425 29 32 2678 9635 2846 9587 3013 9535 3179 9481 3344 9424 28 33 2681 9634 2849 9586 3015 9535 3181 9480 3346 9423 27 34 2684 9633 2851 9585 3018 9534 3184 9480 3349 9423 26 35 2686 9632 2854 9584 3021 9533 3187 9479 3352 9422 25 36 2689 9632 2857 9583 3024 9532 3190 9478 3355 9421 24 37 2692 9631 2860 9582 3026 9531 3192 9477 3357 9420 23 38 2695 9630 2862 9582 3029 9530 3195 9476 3360 9419 22 39 2698 9629 2865 9581 3032 9529 3198 9475 3363 9418 21 l 2700 9628 2868 9580 3035 9528 3201 9474 3365 9417 20 41 2703 9628 2871 9579 3038 9527 3203 9473 3368 9416 19 42 2706 9627 2874 9578 3040 9527 3206 9472 3371 9415 18 43 2709 9626 2876 9577 3043 9526 3209 9471 3374 9414 17 44 2712 9625 2879 9577 3046 9525 3212 9470 3376 9413 16 45 2714 9625 2882 9576 3049 9524 3214 9469 3379 9412 15 46 2717 9624 2885 9575 3051 9523 3217 9468 3382 9411 14 47 2720 9623 2888 9574 3054 9522 3220 9467 3385 9410 13 48 2723 9622 2890 9573 3057 9521 3223 9466 3387 9409 12 49 2726 9621 2893 9572 3060 9520 3225 9466 3390 9408 11 5O 2728 9621 2896 9572 3062 9520 3228 9465 3393 9407 1O 51 2731 9620 2899 9571 3065 9519 3231 9464 33% 9406 9 52 2734 9619 2901 9570 3068 9518 3234 9463 3398 9405 8 53 2737 9618 2904 9569 3071 9517 3236 9462 3401 9404 7 54 2740 9617 2907 9568 3074 9516 3239 9461 3404 9403 6 55 2742 9617 2910 9567 3076 9515 3242 9460 3407 9402 5 56 2745 9616 2913 9566 3079 9514 3245 9459 3409 9401 4 57 2748 9615 2915 9566 3082 9513 3247 9458 3412 9400 3 58 2751 9614 2918 9565 3085 9512 3250 9457 3415 9399 2 59 2754 9613 2921 9564 30S7 9511 3253 9456 3417 9398 1 60 2756 9613 2924 9563 3090 9511 3256 9455 3420 9397 cos Bin cos sin cos sin cos sin cos sin / 74 o 73 72 71 7O ' 66 NATURAL SINES AND COSINES. t 2O 21 22 23 24 f sin cos sin cos sin cos sin cos sin cos o 3420 9397 3584 9336 3746 9272 3907 9205 4067 9135 6O 1 3423 9396 3586 9335 3749 9271 3910 9204 4070 9134 59 2 3426 9395 3589 9334 3751 9270 3913 9203 4073 9133 58 3 3428 9394 3592 9333 3754 9269 3915 9202 4075 9132 57 4 3431 9393 3595 9332 3757 9267 3918 9200 4078 9131 56 5 3434 9392 3597 9331 3760 9266 3921 9199 4081 9130 55 6 3437 9391 3600 9330 3762 9265 3923 9198 4083 9128 | 54 7 3439 9390 3603 9328 3765 9264 3926 9197 4086 9127 53 8 3442 9389 3605 9327 3768 9263 3929 9196 4089 9126 52 9 3445 9388 3608 9326 3770 9262 3931 9195 4091 9125 51 1O 3448 9387 3611 9325 3773 9261 3934 9194 4094 9124 5O 11 3450 9386 3614 9324 3776 9260 3937 9192 4097 9122 49 12 3453 9385 3616 9323 3778 9259 3939 9191 4099 9121 48 13 3456 9384 3619 9322 3781 9258 3942 9190 4102 9120 47 14 3458 9383 3622 9321 3784 9257 3945 9189 4105 9119 46 15 3461 9382 3624 9320 3786 9255 3947 9188 4107 9118 45 16 3464 9381 3627 9319 3789 9254 3950 9187 4110 9116 44 17 3467 9380 3630 9318 3792 9253 3953 9186 4112 9115 i 43 18 3469 9379 3633 9317 3795 9252 3955 9184 4115 9114 42 19 3472 9378 3635 9316 3797 9251 3958 9183 4118 9113 41 2O 3475 9377 3638 9315 3800 9250 3961 9182 4120 9112 4O 21 3478 9376 3641 9314 3803 9249 3963 9181 4123 9110 39 22 3480 9375 3643 9313 3805 9248 3966 9180 4126 9109 38 23 3483 9374 3646 9312 3808 9247 3969 9179 4128 9108 37 24 3486 9373 3649 9311 3811 9245 3971 9178 4131 9107 36 25 3488 9372 3651 9309 3813 9244 3974 9176 4134 9106 35 26 3491 9371 3654 9308 3816 9243 3977 9175 4136 9104 34 27 3494 9370 3657 9307 3819 9242 3979 9174 4139 9103 ! 33 28 3497 9369 3660 9306 3821 9241 3982 9173 4142 9102 32 29 3499 9368 3662 9305 3824 9240 3985 9172 4144 9101 31 30 3502 9367 3665 9304 3827 9239 3987 9171 4147 9100 3O 31 3505 9366 3668 9303 3830 9238 3990 9169 4150 9098 29 32 3508 9365 3670 9302 3832 9237 3993 9168 4152 9097 28 33 3510 9364 3673 9301 3835 9235 3995 9167 4155 9096 27 34 3513 9363 3676 9300 3838 9234 3998 9166 4158 9095 26 35 3516 9362 3679 9299 3840 9233 4001 9165 4160 9094 25 36 3518 9361 3681 9298 3843 9232 4003 9164 4163 9092 24 37 3521 9360 3684 9297 3846 9231 4006 9162 4165 9091 23 38 3524 9359 3687 9296 3848 9230 4009 9161 4168 9090 22 39 3527 9358 3689 9295 3851 9229 4011 9160 4171 9089 21 40 3529 9356 3692 9293 3854 9228 4014 9159 4173 9088 2O 41 3532 9355 3695 9292 3856 9227 4017 9158 4176 9086 19 42 3535 9354 3697 9291 3859 9225 4019 9157 4179 9085 18 43 3537 9353 3700 9290 3862 9224 4022 9155 4181 9084 17 44 3540 9352 3703 9289 3864 9223 4025 9154 4184 9083 16 45 3543 9351 3706 9288 3867 9222 4027 9153 4187 9081 15 46 3546 9350 3708 9287 3870 9221 4030 9152 4189 9080 14 47 3548 9349 3711 9286 3872 9220 4033 9151 4192 9079 13 48 3551 9348 3714 9285 3875 9219 4035 9150 4195 9078 12 49 3554 9347 3716 9284 3878 9218 4038 9148 4197 9077 11 50 3557 9346 3719 9283 3881 9216 4041 9147 4200 9075 10 51 3559 9345 3722 9282 3883 9215 4043 9146 4202 9074 9 52 3562 9344 3724 9281 3886 9214 4046 9145 4205 9073 8 53 3565 9343 3727 9279 3889 9213 4049 9144 4208 9072 7 54 3567 9342 3730 9278 3891 9212 4051 9143 4210 9070 6 55 3570 9341 3733 9277 3894 9211 4054 9141 4213 9069 5 56 3573 9340 3735 9276 3897 9210 4057 9140 4216 9068 4 57 3576 9339 3738 9275 3899 9208 4059 9139 4218 9067 3 58 3578 9338 3741 9274 3902 9207 4062 9138 4221 9066 2 59 3581 9337 3743 9273 3905 9206 4065 9137 4224 9064 1 6O 3584 9336 3746 9272 3907 9205 4067 9135 4226 9063 O cos gin cos sin cos sin cos sin cos sin r 69 68 67 66 65 ' NATURAL SINES AND COSINES. 25 26 27 28 2i> t sin cos sin cos sin cos sin cos sin cog o 4226 9063 4384 8988 4540 8910 4695 8829 4848 8746 6O 1 4229 9062 4386 8987 4542 8909 4697 8828 4851 8745 59 2 4231 9061 4389 8985 4545 8907 4700 8827 4853 8743 58 3 4234 9059 4392 8984 4548 8906 4702 8825 4856 8742 57 4 4237 9058 4394 8983 4550 8905 4705 8824 4858 8741 56 5 4239 9057 4397 8982 4553 8903 4708 8823 4861 8739 55 6 4242 9056 4399 8980 4555 8902 4710 8821 4863 8738 54 7 4245 9054 4402 8979 4558 8901 47J 3 8820 4866 8736 53 8 4247 9053 4405 8978 4561 8899 4715 8819 4868 8735 52 9 4250 9052 4407 8976 4563 8898 4718 8817 4871 8733 51 10 4253 9051 4410 8975 4566 8897 4720 8816 4874 8732 5O 11 4255 9050 4412 8974 4568 8895 4723 8814 4876 8731 49 12 4258 9048 4415 8973 4571 8894 4726 8813 4879 8729 48 13 4260 9047 4418 8971 4574 8893 4728 8812 4881 8728 47 14 4263 9046 4420 8970 4576 8892 4731 8810 4884 8726 46 15 4266 9045 4423 8969 4579 8890 4733 8809 4886 8725 45 16 4268 9043 4425 8967 4581 8889 4736 8808 4889 8724 44 17 4271 9042 4428 8966 4584 8888 4738 8806 4891 8722 43 18 4274 9041 4431 S965 4586 8886 4741 8805 4894 8721 42 19 4276 9040 4433 8964 4589 8885 4743 8803 4896 8719 41 20 4279 9038 4436 S962 4592 8884 4746 8S02 4899 8718 40 21 4281 9037 4439 8961 4594 8882 4749 8801 4901 8716 39 22 4284 9036 4441 8960 4597 8881 4751 8799 4904 8715 38 23 4287 9035 4444 8958 4599 8879 4754 8798 4907 8714 37 24 4289 9033 4446 8957 4602 8878 4756 8796 4909 8712 36 25 4292 9032 4449 8956 4605 8877 4759 8795 4912 8711 35 26 4295 9031 4452 8955 4607 8875 4761 8794 4914 8709 34 27 4297 9030 4454 8953 4610 8874 4764 8792 4917 8708 33 28 4300 9028 4457 8952 4612 8873 4766 8791 4919 8706 32 29 4302 9027 4459 8951 4615 8871 4769 8790 4922 8705 31 3O 4305 9026 4462 8949 4617 8870 4772 8788 4924 8704 30 31 4308 9025 4465 8948 4620 8869 4774 8787 4927 8702 29 32 4310 9023 4467 8947 4623 8867 4777 8785 4929 8701 28 33 4313 9022 4470 8945 4625 8866 4779 8784 4932 8699 27 34 4316 9021 4472 8944 4628 8865 4782 8783 4934 8698 26 35 4318 9020 4475 8943 4630 8863 4784 8781 4937 8696 25 36 4321 9018 4478 8942 4633 8862 4787 8780 4939 8695 24 37 4323 9017 4480 8940 4636 8861 4789 8778 4942 8694 23 38 4326 9016 4483 8939 4638 8859 4792 8777 4944 8692 22 39 4329 9015 4485 8938 4641 8858 4795 8776 4947 8691 21 4O 4331 9013 4488 8936 4643 8857 4797 8774 4950 8689 2O 41 4334 9012 4491 8935 4646 8855 4800 8773 4952 8688 19 42 4337 9011 4493 8934 4648 8854 4802 8771 4955 8686 18 43 4339 9010 4496 8932 4651 8853 4805 8770 4957 8685 17 44 4342 9008 4498 8931 4654 8851 4807 8769 4960 8683 16 45 4344 9007 4501 8930 4656 8850 4810 8767 4962 8682 15 46 4347 9006 4504 8928 4659 8849 4812 8766 4965 8681 14 47 4350 9004 4506 8927 4661 8847 4815 8764 4967 8679 13 48 4352 9003 4509 8926 4664 8846 4818 8763 4970 8678 12 49 4355 9002 4511 8925 4666 8844 4820 8762 4972 8676 11 50 4358 9001 4514 8923 4669 8843 4823 8760 4975 8675 1O 51 4360 8999 4517 8922 4672 8842 4825 8759 4977 8673 9 52 4363 8998 4519 8921 4674 8840 4828 8757 4980 8672 8 53 4365 8997 4522 8919 4677 8839 4830 8756 4982 8670 7 54 4368 8996 4524 8918 4679 8838 4833 8755 4985 8669 6 55 4371 8994 4527 8917 4682 8836 4835 8753 4987 8668 5 56 4373 8993 4530 8915 4684 8835 4838 8752 4990 8666 4 57 4376 8992 4532 8914 4687 8834 4840 8750 4992 8665 3 58 4378 8990 4535 8913 4690 8832 4843 8749 4995 8663 2 59 4381 8989 4537 8911 4692 8831 4846 8748 4997 8662 1 60 4384 8988 4540 8910 4695 8829 4848 8746 5000 8660 cos sin cos sin cos sin cos sin cos sin f 64 63 62 01 OO t 68 NATURAL SINES AND COSINES. r 3O 31 32 33 34 t sin cos sin cos sin cos in cos sin cos O 5000 8660 5150 8572 5299 8480 5446 8387 5592 8290 6O 1 5003 8659 5153 8570 5302 8479 5449 8385 5594 8289 59 2 5005 8657 5155 8569 5304 8477 5451 8384 5597 8287 58 3 5008 8656 5158 8567 5307 8476 5454 8382 5599 8285 57 4 5010 8654 5160 8566 5309 8474 5456 8380 5602 8284 56 5 5013 8653 5163 8564 5312 8473 5459 8379 5604 8282 55 6 5015 8652 5165 8563 5314 8471 5461 8377 5606 8281 54 7 5018 8650 5168 8561 5316 8470 5463 8376 5609 8279 53 8 5020 8649 5170 8560 5319 8468 5466 8374 5611 8277 52 9 5023 8647 5173 8558 5321 8467 5468 8372 5614 8276 51 1O 5025 8646 5175 8557 5324 8465 5471 8371 5616 8274 5O 11 5028 8644 5178 8555 5326 8463 5473 8369 5618 8272 49 12 5030 8643 5180 8554 5329 8462 5476 8368 5621 8271 48 13 5033 8641 5183 8552 5331 8460 5478 8366 5623 8269 47 14 5035 8640 5185 8551 5334 8459 5480 8364 5626 8268 46 15 5038 8638 5188 8549 5336 8457 5483 8363 5628 8266 45 16 5040 8637 5190 8548 5339 8456 5485 8361 5630 8264 44 17 5043 8635 5193 8546 5341 8454 5488 8360 5633 8263 43 18 5045 8634 5195 8545 5344 8453 5490 8358 5635 8261 42 19 5048 8632 5198 8543 5346 8451 5493 8356 5638 8259 41 2O 5050 8631 5200 8542 5348 8450 5495 8355 5640 8258 40 21 5053 8630 5203 8540 5351 8448 5498 8353 5642 8256 39 22 5055 8628 5205 8539 5353 8446 5500 8352 5645 8254 38 23 5058 8627 5208 8537 5356 8445 5502 8350 5647 8253 37 24 5060 8625 5210 8536 5358 8443 5505 8348 5650 8251 36 25 5063 8624 5213 8534 5361 8442 5507 8347 5652 8249 35 26 5065 8622 5215 8532 5363 8440 5510 8345 5654 8248 34 27 5068 8621 5218 8531 5366 8439 5512 8344 5657 8246 33 28 5070 8619 5220 8529 5368 8437 5515 8342 5659 8245 32 29 5073 8618 5223 8528 5371 8435 5517 8340 5662 8243 31 30 5075 8616 5225 8526 5373 8434 5519 8339 5664 8241 3O 31 5078 8615 5227 8525 5375 8432 5522 8337 5666 8240 29 32 5080 8613 5230 8523 5378 8431 5524 8336 5669 8238 28 33 5083 8612 5232 8522 5380 8429 5527 8334 5671 8236 27 34 5085 8610 5235 8520 5383 8428 5529 8332 5674 8235 26 35 5088 8609 5237 8519 5385 8426 5531 8331 5676 8233 25 36 5090 8607 5240 8517 5388 8425 5534 8329 5678 8231 24 37 5093 8606 5242 8516 5390 8423 5536 8328 5681 8230 23 38 5095 8604 5245 8514 5393 8421 5539 8326 5683 8228 22 39 5098 8603 5247 8513 5395 8*20 5541 8324 5686 8226 21 40 5100 8601 5250 8511 5398 8418 5544 8323 5688 8225 2O 41 5103 8600 5252 8510 5400 8417 5546 8321 5690 8223 19 42 5105 8599 5255 8508 5402 8415 5548 8320 5693 8221 18 43 5108 8597 5257 8507 5405 8414 5551 8318 5695 8220 17 44 5110 8596 5260 8505 5407 8412 5553 8316 5698 8218 16 45 S3 13 8594 5262 8504 5410 8410 5556 8315 5700 8216 15 46 5115 8i93 5265 8502 5412 8409 5558 8313 5702 8215 14 47 .5118 8591 5267 8500 5415 8407 5561 8311 5705 8213 13 48 5120 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6161 7877 6298 7768 58 3 5743 8187 5885 8085 6025 7981 6163 7875 6300 7766 57 4 5745 8185 5887 8083 6027 7979 6166 7873 6302 7764 56 5 5748 8183 5890 8082 6030 7978 6168 7871 6305 7762 55 6 5750 8181 5892 8080 6032 7976 6170 7869 6307 7760 54 7 5752 8180 5894 8078 6034 7974 6173 7868 6309 7759 53 8 5755 8178 5897 8076 6037 7972 6175 7866 6311 7757 52 9 5757 8176 5899 8075 6039 7971 6177 7864 6314 7755 51 1O 5760 8175 5901 8073 6041 7969 6180 7862 6316 7753 5O 11 5762 8173 5904 8071 6044 7967 6182 7860 6318 7751 49 12 5764 8171 5906 8070 6046 7965 6184 7859 6320 "7749 48 13 5767 8170 5908 8068 6048 7964 6186 7857 6323 7748 47 14 5769 8168 5911 8066 6051 7962 6189 7855 6325 7746 46 15 5771 8166 5913 8064 6053 7960 6191 7853 6327 7744 45 16 5774 8165 5915 8063 6055 7958 6193 7851 6329 7742 44 17 5776 8163 5918 8061 6058 7956 6196 7850 6332 7740 43 18 5779 8161 5920 8059 6060 7955 6198 7848 6334 7738 42 19 5781 8160 5922 8058 6062 7953 6200 7846 6336 7737 41 2O 5783 8158 5925 8056 6065 7951 6202 7844 6338 7735 40 21 5786 8156 5927 8054 6067 7950 6205 7842 6341 7733 39 22 5788 8155 5930 8052 6069 7948 6207 7841 6343 7731 38 23 5790 8153 5932 8051 6071 7946 6209 7839 6345 7729 37 24 5793 8151 5934 8049 6074 7944 6211 7837 6347 7727 36 25 5795 8150 5937 8047 6076 7942 6214 7835 6350 7725 35 26 5798 8148 5939 8045 6078 7941 6216 7833 6352 7724 34 27 5800 8146 5941 8044 6081 7939 6218 7832 6354 7722 33 28 5802 8145 5944 8042 6083 7937 6221 7830 6356 7720 32 29 5805 8143 5946 8040 6085 7935 6223 7828 6359 7718 31 30 5807 8141 5948 8039 6088 7934 6225 7826 6361 7716 3O 31 5809 8139 5951 8037 6090 7932 6227 7824 6363 7714 29 32 5812 S138 5953 8035 6092 7930 6230 7822 6365 7713 28 33 5814 8136 5955 8033 6095 7928 6232 7821 6368 7711 27 34 5816 8134 5958 8032 6097 7926 6234 7819 6370 7709 26 35 5819 8133 5960 8030 6099 7925 6237 7817 6372 7707 25 36 5821 8131 5962 S02S 6101 7923 6239 781 5 6374 7705 24 37 5824 8129 5965 8026 6104 7921 6241 7813 6376 7703 23 38 5826 8128 5967 8025 6106 7919 6243 7812 6379 7701 22 39 5828 8126 5969 8023 6108 7918 6246 7810 6381 7700 21 4O 5831 8124 5972 8021 6111 7916 6248 7808 6383 7698 20 41 5833 8123 5974 8020 6113 7914 6250 7S06 6385 7696 19 42 5835 8121 5976 8018 6115 7912 6252 7804 6388 7694 18 43 583S 8119 5979 8016 6118 7910 6255 7802 6390 7692 17 44 5840 8117 5981 8014 6120 7909 6257 7801 6392 7690 16 45 5842 8116 5983 8013 6122 7907 6259 7799 6394 7688 15 46 5S45 8114 5986 8011 6124 7905 6262 7797 6397 7687 14 47 5847 8112 5988 8009 6127 7903 6264 7795 6399 7685 13 48 5850 8111 5990 8007 6129 7902 6266 7793 6401 7683 12 49 5852 8109 5993 8006 6131 7900 6268 7792 6403 7681 11 5O 5854 8107 5995 8004 6134 7898 6271 7790 6406 7679 10 51 5857 8106 5997 8002 6136 7896 6273 7788 6408 7677 9 52 5859 8104 6000 8000 6138 7894 6275 7786 6410 7675 8 53 5861 8102 6002 7999 6141 7893 6277 7784 6412 7674 7 54 5864 8100 6004 7997 6143 7891 6280 7782 6414 7672 6 55 5866 8099 6007 7995 6145 7889 6282 7781 6417 7670 5 56 5868 8097 6009 7993 6147 7887 6284 7779 6419 7668 4 57 587 1 8095 6011 7992 6150 7885 6286 7777 6421 7666 3 58 5873 8094 6014 7990 6152 7884 6289 7775 6423 7664 2 59 5875 8092 6016 7988 6154 7882 6291 7773 6426 7662 1 (JO 5S7S 8090 6018 7986 6157 7880 6293 7771 6428 7660 cos sin cos sin cos sin cos sin COS Hill ' 54 r>:$ c r>2^ 5T" 50 ' 70 NATURAL SINES AND COSINES. r 40 41 42 43 44 t sin cos sin cos sin cos sin cos sin cos O 6428 7660 6561 7547 6691 7431 6820 7314 6947 7193 6O 1 6430 7659 6563 7545 6693 7430 6822 7312 6949 7191 59 2 6432 7657 6565 7543 6696 7428 6824 7310 6951 7189 58 3 6435 7655 6567 7541 6698 7426 6826 7308 6953 7187 57 4 6437 7653 6569 7539 6700 7424 6828 7306 6955 7185 56 5 6439 7651 6572 7538 6702 7422 6831 7304 6957 7183 55 6 6441 7649 6574 7536 6704 7420 6833 7302 6959 7181 54 7 6443 7647 6576 7534 6706 7418 6835 7300 6961 7179 53 8 6446 7645 6578 7532 6709 7416 6837 7298 6963 7177 52 9 6448 7644 6580 7530 6711 7414 6839 7296 6965 7175 51 1O 6450 7642 6583 7528 6713 7412 6841 7294 6967 7173 50 11 6452 7640 6585 7526 6715 7410 6843 7292 6970 7171 49 12 6455 7638 6587 7524 6717 7408 6845 7290 6972 7169 48 13 6457 7636 6589 7522 6719 7406 6848 7288 6974 7167 47 14 6459 7634 6591 7520 6722 7404 6850 7286 6976 7165 46 15 6461 7632 6593 7518 6724 7402 6852 7284 6978 7163 45 16 "6463 7630 6596 7516 6726 7400 6854 7282 6980 7161 44 17 6466 7629 6598 7515 6728 7398 6856 7280 6982 7159 43 18 6468 7627 6600 7513 6730 7396 6858 7278 6984 7157 42 19 6470 7625 6602 7511 6732 7394 6S60 7276 6986 7155 41 2O 6472 7623 6604 7509 6734 7392 6862 7274 6988 7153 40 21 6475 7621 6607 7507 6737 7390 6865 7272 6990 7151 39 22 6477 7619 6609 7505 6739 7388 6867 7270 6992 7149 38 23 6479 7617 6611 7503 6741 7387 6869 7268 6995 7147 37 24 6481 7615 6613 7501 6743 7385 6871 7266 6997 7145 36 25 6483 7613 6615 7499 6745 7383 6873 7264 6999 7143 35 26 6486 7612 6617 7497 6747 7381 6875 7262 7001 7141 34 27 6488 7610 6620 7495 6749 7379 6877 7260 7003 7139 33 28 6490 7608 6622 7493 6752 7377 6879 7258 7005 7137 32 29 6492 7606 6624 7491 6754 7375 6881 7256 7007 7135 31 30 6494 7604 6626 7490 6756 7373 6884 7254 7009 7133 3O 31 6497 7602 6628 7488 6758 7371 6886 7252 7011 7130 29 32 6499 7600 6631 7486 6760 7369 6888 7250 7013 7128 28 33 6501 7598 6633 7484 6762 7367 6890 7248 7015 7126 27 34 6503 7596 6635 7482 6764 7365 6892 7246 7017 7124 26 35 6506 7595 6637 7480 6767 7363 6894 7244 7019 7122 25 36 6508 7593 6639 7478 6769 7361 6896 7242 7022 7120 24 37 6510 7591 6641 7476 6771 7359 6898 7240 7024 7118 23 38 6512 7589 6644 7474 6773 7357 6900 7238 7026 7116 22 39 6514 7587 6646 7472 6775 7355 6903 7236 7028 7114 21 40 6517 7585 6648 7470 6777 7353 6905 7234 7030 7112 2O 41 6519 7583 6650 7468 6779 7351 6907 7232 7032 7110 19 42 6521 7581 6652 7466 6782 7349 6909 7230 7034 7108 18 43 6523 7579 6654 7464 6784 7347 6911 7228 7036 7106 17 44 6525 7578 6657 7463 6786 7345 6913 7226 7038 7104 16 45 6528 7576 6659 7461 6788 7343 6915 7224 7040 7102 15 46 6530 7574 6661 7459 6790 7341 6917 7222 7042 7100 14 47 6532 7572 6663 7457 6792 7339 6919 7220 7044 7098 13 48 6534 7570 6665 7455 6794 7337 6921 7218 7046 7096 12 49 6536 7568 6667 7453 6797 7335 6924 7216 7048 7094 11 50 6539 7566 6670 7451 6799 7333 6926 7214 7050 7092 10 51 6541 7564 6672 7449 6801 7331 6928 7212 7053 7090 9 52 6543 7562 6674 7447 6803 7329 6930 7210 7055 7088 8 53 6545 7560 6676 7445 6805 7327 6932 7208 7057 7085 7 54 6547 7559 6678 7443 6807 7325 6934 7206 7059 7083 6 55 6550 7557 6680 7441 6809 7323 6936 7203 7061 7081 5 56 6552 7555 6683 7439 6811 7321 6938 7201 7063 7079 4 57 6554 7553 6685 7437 6814 7319 6940 7199 7065 7077 3 58 6556 7551 6687 7435 6816 7318 6942 7197 7067 7075 2 59 6558 7549 6689 7433 6818 7316 6944 7195 7069 7073 1 6O 6561 7547 6691 7431 6820 7314 6947 7193 7071 7071 O cos sin cos sin cos sin cos sin cos sin f 49 48 47 46 45 f TABLE IX, NATURAL TANGENTS AND COTANGENTS. ' 2 3 4 r tan cot tan cot tan cot tan cot tan cot O 10000 Infinite 0175 57.2900 0349 28.6363 0524 19.0811 0699 14.3007 GO 1 0003 3437.75 0177 56.3506 0352 28.3994 0527 18.9755 0702 14.2411 59 2 i0006 1718.87 0180 55.4415 0355 28.1664 0530 18.8711 0705 14.1821 58 3 10009 1145.92 0183 54.5613 0358 27.9372 0533 18.7678 0708 14.1235 57 4 0012 859.436 0186 53.7086 0361 27.7117 0536 18.6656 0711 14.0655 56 5 0015 687.549 0189 52.8821 0364 27.4899 0539 18.5645 0714 14.0079 55 6 J0017 572.957 0192 52.0807 0367 27.2715 0542 18.4645 0717 13.9507 54 7 0020 491.106 0195 51.3032 0370 27.0566 0544 18.3655 0720 13.8940 53 8 0023 429.718 0198 50.5485 0373 26.8450 0547 18.2677 0723 13.8378 52 9 0026 381.971 0201 49.8157 0375 26.6367 0550 18.1708 0726 13.7821 51 1O 0029 343.774 0204 49.1039 037S 26.4316 0553 18.0750 0729 13.7267 5O 11 0032 312.521 0207 48.4121 0381 26.2296 0556 17.9802 0731 13.6719 49 12 0035 286.478 0209 47.7395 0384 26.0307 0559 17.8863 0734 13.6174 48 13 0038 264.441 0212 47.0853 0387 25.8348 0562 17.7934 0737 13.5634 47 14 0041 245.552 0215 46.4489 0390 25.6418 0565 17.7015 0740 13.5098 46 15 0044 229.182 0218 45.8294 0393 25.4517 0568 17.6106 0743 13.4566 45 16 0047 214.858 0221 45.2261 0396 25.2644 0571 17.5205 0746 13.4039! 44 17 0049 202.219 0224 44.6386 0399 25.0798 0574 17.4314 0749 13.3515 43 18 0052 190.984 0227 44.0661 0402 24.8978 0577 17.3432 0752 13.2996 42 19 0055 180.932 0230 43.5081 0405 24.7185 0580 17.2558 0755 13.2480 . 41 20 0058 171.885 0233 42.9641 0407 24.5418 0582 17.1693 0758 13.1%9 4O 21 0061 163.700 0236 42.4335 0410 24.3675 0585 17.0837 0761 13.1461 39 22 0064 156.259 0239 41.9158 0413 24.1957 0588 16.9990 0764 13.0958! 38 23 0067 149.465 0241 41.4106 0416 24.0263 0591 16.9150 0767 13.0458 37 24 0070 143.237 0244 40.9174 0419 23.8593 0594 16.8319 0769 12.9962 36 25 0073 137.507 0247 40.4358 0422 23.6945 0597 16.74% 0772 12.9469 35 26 0076 132.219 0250 39.9655 0425 23.5321 0600 16.6681 0775 12.8981 j 34 27 0079 127.321 0253 39.5059 0428 23.3718 0603 16.5874 0778 12.84% | 33 28 i OOS1 122.774 0256 39.0568 0431 23.2137 0606 16.5075 0781 12.8014 32 29 0084 118.540 0259 38.6177 0434 23.0577 0609 16.4283 0784 12.7536 31 3O 0087 114.589 0262 38.1885 0437 22.9038 0612 16.3499 0787 12.7062 30 31 0090 110.892 0265 37.7686 0440 22.7519 0615 16.2722 0790 12.6591 ! 29 32 0093 107.426 0268 37.3579 0442 22.6020 0617 16.1952 0793 12.6124 i 28 33 0096 104.171 0271 36.9560 0445 22.4541 0620 16.1190 07% 12.5660 j 27 34 0099 101.107 0274 36.5627 0448 22.3081 0623 16.0435 0799 12.5199! 26 35 0102 98.2179 0276 36.1776 0451 22.1640 0626 15.9687 0802 12.4742 25 36 0105 95.4895 0279 35.8006 0454 22.0217 0629 15.8945 0805 12.4288! 24 37 0108 92.9085 0282 35.4313 0457 21.8813 0632 15.8211 0808 12.3838 23 38 0111 90.4633 0285 35.0695 0460 21.7426 0635 15.7483 0810 12.3390 22 39 0113 88.1436 0288 34.7151 0463 21.6056 0638 15.6762 0813 12.29461 21 4O 0116 85.9398 0291 34.3678 0466 21.4704 0641 15.6048 0816 12.2505 2O 41 0119 83.8435 0294 34.0273 0469 21.3369 0644 15.5340 0819 12.20671 19 42 0122 81.8470 0297 33.6935 0472 21.2049 0647 15.4638 0822 12.16321 18 43 1 Q12S 79.9434 0300 33.3662 0475 21.0747 0650 15.3943 0825 12.1201 17 44 0128 78.1263 0303 33.0452 0477 20.9460 0653 15.3254 0828 12.0772 16 45 0131 76.3900 0306 32.7303 0480 20.8188 0655 15.2571 0831 12.03461 IS 46 0134 74.7292 0308 32.4213 0483 20.6932 0658 15.1893 0834 11.9923 14 47 0137 73.1390 0311 32.1181 0486 20.5691 0661 15.1222 0837 11.9504 13 48 0140 71.6151 0314 31.8205 0489 20.4465 0664 15.0557 0840 11.9087 12 49 0143 70.1533 0317 31.5284 0492 20.3253 0667 14.9898 0843 11.8673 11 5O OJ46 68.7501 0320 31.2416 0495 20.2056 0670 14.9244 0846 11.8262 1O 51 0148 67.4019 0323 30.9599 0498 20.0872 0673 14.85% 0849 11.7853 9 52 0151 66.1055 0326 30.6833 0501 19.9702 0676 14.7954 0851 11.7448 8 53 0154 64.8580 0329 30.4116 0504 19.8546 0679 14.7317 0854 11.7045 7 54 0157 63.6567 0332 30.1446 0507 19.7403 0682 14.6685 0857 11.6645 6 55 0160 62.4992 0335 29.8823 0509 19.6273 0685 14.6059 0860 11.6248 5 56 0163 61.3829 0338 29.6245 0512 19.5156 0688 14.5438 0863 11.5853 4 57 0166 60.3058 0340 29.3711 0515 19.4051 0690 14^823 0866 11.5461 3 58 0169 59.2659 0343 29.1220 0518 19.2959 0693 14.4212 0669 11.5072 2 59 0172 58.2612 0346 28.8771 0521 19.1879 0696 14.3607 0872 11.4685 1 6O 0175 57.2900 0349 28.6363 0524 19.0811 0699 14.3007 0875 11.4301 cot tan cot tan cot tan cot tan cot tan ' 89 88 87 80 S.T t 72 NATURAL TANGENTS AND COTANGENTS. t 5 6 7 8 9 o , tan cot tan cot tan cot tan cot tan cot 0875 11.4301 1051 9.5144 1228 8.1443 1405 7.1154 1584 6.3138 ! GO 1 0878 11.3919 1054 9.4878 1231 8.1248 1408 7.1004 1587 6.3019 59 2 0881 11.3540 1057 9.4614 1234 8.1054 1411 7.0855 1590 6.2901 58 3 0884 11.3163 1060 9.4352 1237 8.0860 1414 7.0706 1593 6.2783 57 4 0887 11.2789 1063 9.4090 1240 8.0667 1417 7.0558 1596 6.2666 56 5 0890 11.2417 1066 9.3831 1243 8.0476 1420 7.0410 1599 6.2549 55 6 0892 11.2048 1069 9.3572 1246 8.0285 1423 7.0264 1602 6.2432 i 54 7 OS95 11.1681 1072 9.3315 1249 8.0095 1426 7.0117 1605 6.2316 53 8 0898 11.1316 1075 9.3060 1251 7.9906 1429 6.9972 1608 6.2200 j 52 9 0901 11.0954 1078 9-2806 1254 7.9718 1432 6.9827 1611 6.2085 51 1O 0904 11.0594 1080 9.2553 1257 7.9530 1435 6.9682 1614 6.1970 SO 11 0907 11.0237 1083 9.2302 1260 7.9344 1438 6.9538 1617 6.1856 49 12 0910 10.9882 1086 9.2052 1263 7.9158 1441 6.9395 1620 6.1742 48 13 0913 10.9529 1089 9.1803 1266 7.8973 1444 6.9252 1623 6.1628 47 14 0916 10.9178 1092 9.1555 1269 7.8789 1447 6.9110 1626 6.1515 46 15 0919 10.8829 1095 9.1309 1272 7.8606 1450 6.8969 1629 6.1402 45 16 0922 10.8483 1098 9.1065 1275 7.8424 1453 6.8828 1632 6.1290 44 17 0925 10.8139 1101 9.0821 1278 7.8243 1456 6.8687 1635 6.1178 43 18 0928 10.7797 1104 9.0579 1281 7.8062 1459 6.8548 1638 6.1066 i 42 19 0931 10.7457 1107 9.0338 1284 7.7883 1462 6.8408 1641 6.0955 i 41 2O 0934 10.7119 1110 9.0098 1287 7.7704 1465 6.8269 1644 6.0844 4O 21 0936 10.6783 1113 8.9860 1290 7.7525 1468 6.8131 1647 6.0734 39 22 0939 10.6450 1116 8.9623 1293 7.7348 1471 6.7994 1650 6.0624 38 23 0942 10.6118 1119 8.9387 1296 7.7171 1474 6.7856 1653 6.0514 ! 37 24 0945 10.5789 1122 8.9152 1299 7.6996 1477 6.7720 1655 6.0405 36 25 0948 10.5462 1125 8.8919 1302 7.6821 1480 6.7584 1658 6.0296 | 35 26 0951 10.5136 1128 8.8686 1305 7.6647 1483 6.7448 1661 6.0188 34 27 0954 10.4813 1131 8.8455 1308 7.6473 1486 6.7313 1664 6.0080 ' 33 28 0957 10.4491 1134 8.8225 1311 7.6301 1489 6.7179 1667 5.9972 ; 32 29 0960 10.4172 1136 8.7996 1314 7.6129 1492 6.7045 1670 5.9865 ' 31 3O 0963 10.3854 1139 8.7769 1317 7.5958 1495 6.6912 1673 5.9758 3O 31 0966 10.3538 1142 8.7542 1319 7.5787 1497 6.6779 1676 5.9651 29 32 10969 10.3224 1145 8.7317 1322 7.5618 1500 6.6646 1679 5.9545 28 33 0972 10.2913 1148 8.7093 1325 7.5449 1503 6.6514 1682 5.9439 27 34 0975 10.2602 1151 8.6870 1328 7.5281 1506 6.6383 1685 5.9333 26 35 0978 10.2294 1154 8.6648 1331 7.5113 1509 6.6252 1688 5.9228 25 36 0981 10.1988 1157 8.6427 1334 7.4947 1512 6.6122 1691 5.9124 24 37 0983 10.1683 1160 8.6208 1337 7.4781 1515 6.5992 1694 5.9019 23 38 J0986 10.1381 1163 8.5989 1340 7.4615 1518 6.5863 1697 5.8915 22 39 0989 10.1080 1166 8.5772 1343 7.4451 1521 6.5734 1700 5.8811 21 4O 0992 10.0780 1169 8.5555 1346 7.4287 1524 6.5606 1703 5.8708 2O 41 0995 10.0483 1172 8.5340 1349 7.4124 1527 6.5478 1706 5.8605 19 42 0998 10.0187 1175 8.5126 1352 7.3962 1530 6.5350 1709 5.8502 18 43 i 1001 9.9893 1178 8.4913 1355 7-3800 1533 6.5223 1712 5.8400 17 44 ! 1004 9.9601 1181 8.4701 1358 7.3639 1536 6.5097 1715 5.8298 16 45 ' 1007 9.9310 1184 8.4490 1361 7.3479 1539 6.4971 1718 5.8197 15 46 1010 9-9021 1187 8.4280 1864 7.3319 1542 6.4846 1721 5.8095 14 47 1013 9.8734 1189 8.4071 1367 7.3160 1545 6.4721 1724 5.7994 13 48 1016 9.8448 1192 8.3863 1370 7.3002 1548 6.4596 1727 5.7894 12 49 1019 9.8164 1195 8.3656 1373 7.2844 1551 6.4472 1730 5.7794 11 5O 1022 9.7882 1198 8.3450 1376 7.2687 1554 6.4348 1733 5.7694 1O 51 1025 9.7601 1201 8.3245 1379 7.2531 1557 6.4225 1736 5.7594 9 52 1028 9.7322 1204 8.3041 1382 7.2375 1560 6.4103 1739 5.7495 8 53 | 1030 9.7044 1207 8.2838 1385 7.2220 1563 6.3980 1742 5.7396 7 54 1033 9.6768 1210 8.2636 1388 7.2066 1566 6.3S.S9 1745 5.7297 6 55 1036 9.6499 1213 8.2434 1391 7.1912 1569 6.3737 1748 5.7199 5 56 1039 9.6220 1216 8.2234 1394 7.1759 1572 6.3617 1751 5.7101 4 57 1042 9.5949 1219 8.2035 1397 7.1607 1575 6.3496 1754 5.7004 3 58 1045 9.5679 1222 8.1837 1399 7.1455 1578 6.3376 1757 5.6906 2 59 1048 9.5411 1225 8.1640 1402 7.1304 1581 6.3257 1760 5.6809 1 6O | 1051 9.5144 1228 8.1443 1405 7.1154 1584 6.3138 1763 5.6713 O cot tan cot tan cot tan cot tan cot tan ' 84 83 82 81 80 ' NATURAL TANGENTS AND COTANGENTS. 73 11 12 13 14 f tan cot tan cot tan cot tan cot tan cot 1763 5.6713 1944 5.1446 2126 4.7046 2309 4.3315 2493 4.0108 : ^^^ I 3 & ff u 3 1158 00023 2685 * I -n I-- V ^ AA 001 270133 o "^/mMN.I 3\\\ N I 3 i fe PLEASE DO NOT REMOVE THIS BOOK CARD 2 University Research Library IIBRARYO/