Chapter XIX

MISCELLANEOUS SURVEYORS' AND ENGINEERS' INSTRUMENTS, APPLIANCES,
AND ACCESSORIES--CROSS STAFF--MECHANICS' LEVELS AND CLINOMETERS--
BONING RODS--FOOTNER'S RAILWAY GAUGE--GIRTH STRAP FOR TIMBER
MEASUREMENT--GIRTH TAPES--TIMBER MARKER--SLASHING KNIFE--BILL-HOOK--
RECONNOITRING GLASS--TELESCOPE--SUN SPECTACLES--WHISTLES--PIONEER
TOOLS--SKETCH BLOCK BOOK--CAMERA--GEOLOGICAL TOOLS--WEALEMEFNA--
OPISOMETER--BOUCHER'S CALCULATOR--SLIDE RULES--FULLER'S CALCULATOR--
ENGINEERS' POCKET BOOKS--CHRONOMETER--OUTFITS.

846.--=Cross Staff.=--Those of Tycho Brahé and of Gunter were very elaborate affairs, consisting of a pair of notched cross-bars sliding on a divided rod which gave directions to form any angle in a quadrant from the eye by sliding the bars further from or nearer to it. The surveying cross staff, after better instruments were invented to take angles, became a cross at right angles, sawn upon a disc of wood and supported upon a staff which was pressed into the ground. This was used by looking along the saw cuts to take offsets to the chain, and for setting out buildings. The fixed cross-head was much improved by making it a cross of metal with turned-up ends, down the centre of which vertical saw cuts were made at right angles, Fig. 400. This, in the author's opinion, is still the best form.

847.--Cylindrical heads superseded the open cross-head. The modern instrument in use is the French form, Fig. 401, which is made of octagon brass tube. This is cut with alternate sight slit and opposite window, with vertical hair on each of four rectangular sides of the octagon. On the other four sides there are plain slits subtending 45° to those first mentioned. The octagon tube is mounted upon a socket-piece which fits upon a conical pointed staff. The defect of this cross-head is the closeness of the slits, due to the small diameter of the tube, which renders the direction given for sighting uncertain.

848.--=Adjustable Cross Staff Head.=--The cross staff head is sometimes made cylindrical, in two parts, Fig. 402. The upper part is centred upon the lower so that the upper series of sights move to any angle in relation to the lower. In this construction a wheel is cut about the axis of the upper part, which works into a pinion in the lower part, so that the upper part may be revolved horizontally by it. The meeting planes of the two cylinders are divided, the lower into degrees and the upper with a vernier. The vernier is almost an unnecessary refinement, as the sighting distance from slit to hair is only about three inches, and no very great exactness can be obtained in the sighting. This instrument has commonly a magnetic compass upon the upper surface. It is about as expensive as the semi-circumferenter, shown Fig. 232, p. 347, and very inferior to that instrument owing to the extreme closeness of the sights. Its use is obvious.

Many of the following articles, briefly described, may be beyond the direct province of this work; but the utility of these implements for completing the equipment of a surveyor or engineer for special work it is hoped will be sufficient apology for their introduction. The subject can scarcely be treated except in a desultory manner.

849.--=Mechanics' Levels.=--In crowded Eastern cities, in levelling through close passages, in many cases the surveyor has to resort to mechanical levelling to carry his levels through. Mechanics' levels are too well known to need much description. The ordinary good kinds are made from 6 inches to 18 inches long, generally of rosewood, as this wood is very hard and stands well. They have a brass plate at the top, and tips of the same metal at the base. The illustration, Fig. 403, is of a 12-inch level. The level tube, which is of blown glass, is fixed in plaster of Paris, and the upper plate screwed down over it.

850.--=The Author's Hand Level= is shown Fig. 404--12 inch. This is made of a casting either of iron or brass. The level tube is ground to curvature and is somewhat superior to the ordinary run of this class of work. The level tube is fitted with ball socket at one end and stiff spring fitting at the other, which is adjustable, so that the tube may be easily replaced if broken.

These levels are commonly fixed upon a stout fir straight-edge of about 5 feet to 10 feet in length by the lugs at the ends. The level is taken by blockings upon the ground. Corrections of error, both in level and straight-edge, may be made for any considerable distance by reversing the forward and backward position of the level with its straight-edge alternately.

851.--=Square Level--Circular Level.=--Fig. 405 represents a very useful class of level for setting up some instrument stands, plane tables, etc., in which a pair of level tubes are placed at right angles to each other. It is generally made very small--1½ inches square only. A circular level, the upper surface of which is formed of a worked concave glass, was lately very popular, and is still used to a small extent. As the spirit cannot be hermetically sealed in, it evaporates, and this level soon fails. Mr. J. J. Hicks has taken out a patent for a hermetically sealed circular level, described p. 96, which appears to answer very well.

852.--=Incline Level.=--For laying railway rails and drainage works the bubble is frequently made adjustable by the tube in which it is contained being hinged at one end and fitted in slides to rise with a screw at the other end, as shown Fig. 406. A scale of percentage of inclination _S_ is commonly divided upon the adjustable end. The tube is raised or lowered by the key _A_, which is removed after setting and cannot be tampered with.

853.--=Sighted Levels.=--A mechanic's level is commonly made with a hole longitudinally through it of about ½ inch diameter, closed at one end, except a small hole of 1/30 inch or so, and a cross upon a piece of glass at the other end. This plan permits a sight to be taken through it which gives an approximate level. Occasionally the same form of sight as that described is hinged on the top surface at each end of the level. The author has found a better plan of sighting to be given by a pair of sights placed on a centre upon the ends of the level to turn up when required for use, as shown Fig. 408, _P S_ one of the pair of points. This, when turned up, shoulders on the stop-piece _A B_. The stop-piece is made of sufficient thickness to admit the point in the hole near _B_ for protection when it is folded away out of use. The section of the level, as shown by the end view _D_, is the same as that of the level, Fig. 404. Very fair accuracy may be obtained by making these sights appear coincident upon a distant staff or rod.

854.--=Boning-Rods=, Fig. 409. These are very commonly employed with mechanics' levels. They are made somewhat like a stout T-square of 3 feet to 4 feet in length, about 3 inches in width, and ¾ inch in thickness both of the stem and head. They are at first placed at a distance apart, 9 or 10 feet, and a straight-edge of this length is laid from one to the other, upon which the mounted level is afterwards placed, the boning-rod being tapped down in the ground till the bubble is in the centre of its run. A third boning-rod is then placed at the same distance as the first pair, and the straight-edge with the level upon it is reversed end for end. This, if the work be fairly down, leaves the two outer boning-rods level, however imperfect the straight-edge and level may be, if the run of the bubble be taken correctly. By removing the central boning-rod from the outer pair of rods, levels may be continued by sighting over them, or _boning forward_ as it is termed. On the Continent boning-rods are commonly fixed by driving a separate standard into the ground, which has a pair of brass slings by its side to hold the rod, Fig. 410. This is a much neater plan than that in common use of blocking the rod up with stones. Boning-rods are also sometimes used conveniently with a proper surveying level, from the tops of water-pipes, etc.

855.--=Railway Gauge=, combining level and clinometer. This high-class gauge, Fig. 411, is the invention of Mr. H. Footner, C.E., late of the London and North-Western Railway. It is formed of a bar of Spanish mahogany neatly shaped. The end fittings are of steel. The gauging part is formed of two turn-up steel flap-pieces with back stops. A spirit level is sunk in the end fitting, shown in the figure towards the left hand. The clinometer is formed by a gun-metal pin of ½ inch in diameter; 9 inches long. This slides perpendicularly in a spring fitting sufficiently stiff to support the gauge, and is made to fall on the centre of the rail. The pin is divided into inches and eighths. When it is out of use it slides up the end of the gauge and leaves the whole instrument smooth and portable to carry open or go into a leather case. Its use is implied.

856.--=Timber Girth Strap.=--The direction for removal and estimate of the value of timber often falls into the hands of the surveyor. The height of standing timber may be taken by a long rod, or a pair united by a link, art. 775, or by the apomecometer, art. 693. The girth is most conveniently taken by a leather girth strap, of which there are various patterns: but that illustrated below, Fig. 412, is perhaps the most popular form. This strap is made of two straps of bullock's hide 1 inch wide, thinned down to about 1/8 inch in thickness; the two pieces are stitched together to make it 12 feet to 14 feet long. The strap is divided by lines into inches, but figured in units at every 4 inches = single inches of quarter-girth. The figures and lines are stamped. A brass weight, shown at one end of the strap, is thrown by the strap with a swing round the standing tree, and encompasses it in a second of time. The weight is caught by the hand and the strap brought up to it to read the quarter-girth. The _quarter-girth_ gives roughly the equal sides of a square; as, for instance if a quarter-girth reads 10, the size of the tree is 10 × 10 = 100 inches, or 8·4 cubic foot-inches per foot run.

Some surveyors prefer a hook instead of a weight, as being more convenient to measure close timber. This is shown Fig. 413. The hook is stuck into the bark and the tree is girthed by walking round until the hook is met.

857.--=Girth Tapes=, similar to measuring tapes, Fig. 349, p. 506, are occasionally used, but these are more convenient for felled timber. Tapes for the purpose are made from ¾ inch to 1 inch wide, and 6, 12, and 24 feet long. They have the ordinary feet and inches on one side and quarter-girths on the other.

It is customary to allow 1 or 1½ inches, and sometimes more for bark, according to the species of tree and the custom of the country.

858.--=Marking off Timber.=--For this a special tool with a gouge point, Fig. 414, and strong buck-horn handle, termed a _timber-marker_, is used for standing timber intended to be felled. The contents of the tree are sometimes marked with the marker upon it if for sale, good bark allowance being made in cases of difficulty of extraction from the forest, etc. A plain knife is usually put with the marker, which is useful as a food knife.

859.--The author makes a very small, neat surveyor's knife, with marker, for the waistcoat pocket, Fig. 415, which combines--_M_ tree marker (small); _S_ screw-driver for small screws of instruments; _P_ tommy-pin for turning capstan heads; _F_ file for sharpening lead of pencil, when this is used for the field-book; and _E_ _R_ two penknife blades. The knife is similar to the author's architect's knife, which is well known. The tree marker is not strong enough for constant work.

860.--=Slashing Knife--Bill-Hook--Axe.=--In new countries where sight way has to be obtained for the survey through forests and jungles, one or more of the tools illustrated next is most valuable as a part of the surveyor's equipment. The slashing knife, Fig. 416, which is over a yard long, wielded by a strong man will remove light brushwood very quickly. Where the wood is close and of larger growth the bill-hook, Fig. 417, is better; and with thickset timber the axe becomes necessary. The well-known Canadian axe is found to be the best.

861.--_Hedging Gloves--Iron Hooks for Climbing Trees._--For clearing land to avoid spines hedging gloves are generally used; these are made of soft horse-hide, and although pliable resist thorns to a great extent. Clutch hooks are also very convenient to climb trees, to look forward for the easiest direction for sight way.

862.--=Rods for Measuring Standing Timber.=--These are generally made 25 feet long, jointed in 5 feet lengths, similar to a fishing rod, but much stiffer. The rod is set by the side of a tree to be measured and observed from a distance where the first breech cuts its length.

863.--=Reconnoitring Glass.=--At present it is customary to use a binocular field-glass in preference to a telescope. The telescope gives greater penetration from its higher power; the field-glass is preferred for its wider field of view. The field-glass the author has supplied to the Indian Government has neutral-tint glasses centred on the eye-pieces to take off the glare when looking towards the sun, Fig. 418. These have also hinge joints between the pair of bodies, which permit adjustment of distance of centres to the distance of the eyes. The object-glass should be 1¾ inches, not over this. Where a telescope is used, the 30-inch--the original, not the present--India military telescope is to be recommended, Fig. 419. This is portable, has a sling case and a good 2-inch object glass. For lightness, aluminium bodies are preferred by many for both field-glasses and telescopes; at present the price of this metal is very low, so that it is probable it may become in a short time general for the purpose.

864.--=Prism Binoculars.=--These will be found a great improvement on the old form of field-glasses, as owing to the optical arrangement a high power is obtained combined with a larger field of view and good illumination. Fig. 420 shows the most modern form with all refinements; hinged body, central focussing and separate focussing to suit each eye. It has a very compact and strong body, and the size magnifying 8 diameters or about 64 times weighs only 13 ozs.

865.--=Dome Spectacles--Bogles.=--Spectacles of neutral tint are most comfortable for general wear in sunny or snowy countries. The dome or globular form is generally preferred. Where there is hot dust gauze sides are to be preferred. There is a very cheap form with gauze sides, which holds on the head by an elastic band, termed _bogles_. These are rather hot to the face, and the band after a time becomes sticky. The spectacle form is much better. The glasses are made in various shades to choice: some very dark or even black, the latter being made for viewing and tending arc lights.

866.--=Whistles= made very powerful are much used in exploring abroad to bring the party together, and for signalling generally by sound, using the Morse signals, art. 803.

867.--=Pioneers' Tools.=--A small set of these is often very useful to the surveyor in new forest countries. The common set consists of a claw-hammer, wood-chisel, stone-chisel, pincers, screw-driver, gimlet, and brad-awl. The leather case is 8 by 4 by 2½ inches; it weighs 1¾ lbs. with strap. This may be supplemented by a small American saw, cutting both edges, about 20 inches long, and the axe previously described, with a few pounds of wire nails. The tools serve for marking trees or rocks, erecting signals, temporary covers, etc.

868.--=Sketch Block Book--Pocket Book.=--In reconnoitring no better information can be given of a track than forward sketches from commanding station to station. Sketch books about 7 inches by 5 inches are generally found sufficient. The drawing-paper should be thin, and the pocket large enough to contain all the separate sheets as they are taken off by the penknife after completion from the block. The sketches may be made with pencil, or a fine fountain pen; or if the surveyor be a colourist a light box of moist colours and a water bottle will often leave pleasing sketches as reminiscences. Pocket-books with section lines to 1/8 inch or 1/10 inch scale are sometimes used to give approximate plans to scale of buildings, etc., where required, as well as the ordinary field-book record.

869.--=Camera.=--Recently the camera has been much used for reconnoitring. These are now made very light and portable to take ¼ plate or 3 × 3 inch films, either on rollers or in separate films.

870.--=Cement Testers= are made in various manners, generally to test the cohesion of the cement as a homogeneous hard body. Mr. Mann's cement tester, Fig. 421, goes on another principle--it tests the adhesion of the cement to stone, which appears to the author to be its most important function; it is always hard enough.

871.--=Watson's Improved Vicat Needle= is a most refined and accurate instrument for determining the time taken by cement in setting. The cement is placed in the circular container shown in the illustration, and the weighted needle is lowered into it by means of the handle at the top. The depth of penetration is shown in millimetres on the divided arc.

872.--=Geological Tools.=--_Acid-bottle--Blow-pipe--Touch-stone._-- Where countries are prospected for railways it often becomes important to examine the rocks, both to detect the softer rocks for cutting and to find limestone suitable for mortar. A geological hammer, weight about 2 lbs. to 3 lbs., is the ordinary tool. This, with a chisel and sailcloth bag with strap, is all the necessary appliance. In searching for limestone a small bottle of sulphuric acid sewn up in a leather case is useful. A dipper is blown on the stopper of the bottle, and a single drop of acid will detect limestone by the bubble of froth it produces. Where minerals are to be examined, a small blow-pipe apparatus is necessary. This should be accompanied by a book of instructions. Where the surveyor has not been trained to use the blow-pipe, one with constant blast should be employed. For examination for precious metals a touch-stone and two-acid bottle--sulphuric and nitric--for silver and gold, are useful. The metal is merely rubbed on the stone and the acid applied. If the metal is base the acid removes it from the surface of the stone. If precious it removes other matter and leaves it visible.

873.--=Wealemefna--Opisometer.=--The wealemefna is a very neat form of space runner invented by Mr. E. R. Morris, which is found a very convenient instrument for measuring distances on maps in prospecting. It is very small and light, and may be, if desired, attached to the watch-chain. It gives distances run over in inches and eighths, to be afterwards calculated to the scale of the map, Fig. 423. The opisometer for the same purpose, Fig. 424, is formed of a spur wheel at the end of an ivory handle running upon a screw. This instrument gives measurement by reversing its run upon the scale of the map.

874.--Boucher Calculator, the invention of M. Alex. E. M. Boucher, engineer, of Paris.[66] This is one of the most convenient pocket calculators that a civil engineer can desire, being only of the size of an ordinary watch. The instrument was formerly made in France for this country in a very slovenly manner. It is now made in London by the author, of sound work and accurate centring, Fig. 425. It has face back and front. The front one, which is shown in the illustration, carries logarithmic scales of sines, numbers and square roots, and is made to revolve by turning the milled head placed under the handle, as the winder of a keyless watch. The back dial, which is fixed and does not revolve, has upon it a scale of equal parts giving the decimal parts of logarithms, and a logarithmic scale of cube roots. There are three index hands, one fixed on the side of the case over the front dial, as shown in Fig. 425, and one on each end of the central axis made to revolve simultaneously over the back and front dials by means of the milled head at the side of the case. Any operation involving multiplication, division, proportion, powers or roots can be performed approximately with great rapidity by the aid of this calculator, and it is practically as simple to use as an ordinary slide rule, as will be seen from the following explanation of its use:--

Multiplication, using the second circle of divisions from the outside of the front dial:--Bring the first factor under the fixed index, set the movable index to 1, then bring the second factor under the movable index, and the product will be found under the fixed index.

Division is performed on the same scale as follows:--Bring the dividend under the fixed index, set the movable index to the divisor, then bring 1 to the movable index, and the quotient will be found under the fixed index.

For proportion the second circle is also used:--Set the first factor under the fixed index and set the movable index to the second one, then the proportionate equivalent of any number brought under the former will be found at the movable index.

Square roots, using the same scale:--Bring the number under either of the indices, and the square root will be found upon one of the two inner circles of the same dial.

Cube root:--In this case it is necessary to first bring the 1 on the front dial under the fixed index, then set the movable index to the number, and the cube root will be found on one of the inner circles of the back or fixed dial.

To use the trigonometrical dial:--Bring the needle of this dial over the angle of which the sine or tangent is required, and read upon the other dial (indicated by the needle) the natural trigonometrical line upon the inner circle, or its logarithm upon the outer circle.

The book of instructions supplied with the instruments, written by Professor George Fuller, C.E., for the author, gives all directions for working and also gauge points from which calculations are made as with the slide rule.

875.--In reduction of factors of a calculation collectively Boucher's calculator may take more than one turn or less than unity. The author has added a central index to record the number of turns. This is said to be of great value for the perfection of the instrument, Fig. 426.

876.--=Slide Rules=, of which there are great varieties, are of too complex a nature to discuss, except very briefly, in our limited space, particularly as general descriptions have been often given. The ordinary logarithmical scales of Gunter (1619), known as _Gunter's lines_, are placed upon most slide rules. The arithmetical lines are lettered _A_, _B_, _C_, _D_, and _E_. _A_ and _B_ are alike: these are technically termed _double radius log. lines_. They are used for all processes of multiplication and division. _C_ and _D_ are also alike and are termed _single radius log. lines_. They are used together for ordinary multiplication and division, and in conjunction with A and B scales for squares and square roots. The _E_ line, not originally a Gunter's line, but found early in the century on several rules, is termed a _triple radius log. line_. The numbers of the divisions on this line are the cubes of the numbers of the corresponding divisions of the _D_ line, with which it generally works. All these lines work reciprocally together, performing the most complex calculations by simply setting them to numbers or gauge points of which given solutions are required, as for instance, the first four lines in combination give answers to such questions as:--To divide by a number two numbers multiplied together, one of which is squared; to divide the product of two numbers by the square of a third number, etc., each of which calculations is performed at a single setting. By inversion of the slide _A_ to _C_ the reciprocal of a given number is found, also the mean proportional between two numbers, the fourth term is inverse proportion, etc. Trigonometrical calculations are performed by the lines of sines, tangents, etc. Instructions are to be found in the books supplied with the rules, and as a part of many works. Among the most complete books may be mentioned "The Slide Rule," by R. G. Blaine, M.E., and "The Slide Rule," by Chas. N. Pickworth. These both contain very full information on the subject.

877.--_The Slide Rules_ in most general use are A. Nestler's and A. W. Faber's. Both these well-known firms make a very complete series, applicable to a great variety of technical calculations.

878.--The reviser has recently completed from the designs of the author an entirely automatic dividing engine for these rules, which is the only one in existence.

A great number of slide rules are made for special purposes only: some of these are very useful to the civil engineer.

879.--_Hudson's Slide Rules_ give strength of shafts, beams, and girders; pump duty; and computation of horse-power in engines.

880.--_Honeysett's Hydraulic Slide Rule_ gives discharge of water from channels and pipes of different forms and inclinations.

881.--_Tacheometrical Slide Rules_ with scale of sine^2 and sine × cos. for calculating the horizontal equivalents and vertical heights from tacheometrical observations. These are made either for use with instruments divided sexagesimally to 360° or centesimally to 400.

882.--_Sheppard's Slide Rule_ has duodecimal lines, double reading, for squaring and cubing timber.

883.--_Young's Slide Rule_ is designed for squaring and valuing timber simultaneously, which operations it performs in a very expeditious manner.

884.--Essex's Slide Rule is the best for calculating the rates of velocity and discharge from sewers, water mains, channels, and culverts of different forms, as it works with all formulæ.

885.--=The Slide Rule of Prof. Geo. Fuller, C.E.=, Fig. 427, presents perhaps the highest present refinement of this class of rules, capable of greatly facilitating the numerous arithmetical calculations of the civil engineer. Its range is greater than most calculating machines, and besides the operations of multiplication and division, squaring and cubing, results requiring the reciprocals, powers, roots, or logarithms of numbers can be quickly and easily worked out by its use.

The rule consists of an outer cylinder that can be moved up or down, and turned round upon the cylindrical axis which is held by the handle. Upon the outer cylinder a single spiral, logarithmical scale is continued from end to end, the total length of which makes the scale 500 inches long. This is graduated into 7250 divisions. One index is fixed to the handle. A second index is attached to the inner tube blocked out by a flange to read upon any part of the scale; so that altogether there are three tubes which work together telescopically, by means of which the indices may be set to any position on the graduated cylinder. Stops are placed so that the indices may be brought to zero. By these means, the indices being set to any of the gauge points, the logarithmical scale, moving by itself, will maintain the same proportion for any numbers. In this rule a single log. radius is repeated by coincidence of indices, so that its scale of divisions, 41 feet 8 inches long, if compared with an ordinary double radius slide rule, becomes equal to a slide rule of 83 feet 4 inches long. The ordinary 12-inch slide rule has about 80 divisions to each radius, so that it is easily seen how much more exact quantities may be brought out with a rule of 7250 divisions. It is a most valuable rule for calculations for the tacheometer. Copious tables of gauge points for civil engineers are printed upon the central tube, which is supplemented by a book of instructions. The value of this rule has been much extended by scales to facilitate subtense calculations, by Mr. W. N. Bakewell, C.E., in the "Fuller-Bakewell" slide rule.

An additional improvement, as shown at Fig. 428, has now been effected in these instruments by adapting the case to support the rule when in use, thus overcoming the objection of being always obliged to hold it in the hand.

The use of Professor Fuller's rule is, however, confined to arithmetical computations. The numerical solution of formulæ comprising trigonometrical functions can only be performed by extracting, with considerable loss of time, the values of these functions from a book of tables. To do so requires a certain effort of mind with its consequent risk of mistakes. This limitation has restricted its use in a considerable body of calculations, such, for example, as in the computation of the co-ordinates of surveys from the lengths and bearings of their lines, a method of plotting which is very largely used by land surveyors at present; in astronomical computations; in civil and mechanical engineering, etc.; the use of logarithms being preferred on the score of speed, although the degree of accuracy attained with Professor Fuller's rule is amply sufficient in the large majority of cases.

886.--=The Co-ordinate Spiral Slide Rule= has been designed to meet these requirements by Mr. H. O. Barnard, A.C.H., F.R.A.S., etc., Superintendent of Trigonometrical Surveys, Ceylon, Fig. 429. Like Professor Fuller's rule, upon which it is an improvement, it enables the user to perform with speed and accuracy arithmetical computations involving multiplication, division, proportion, continuous fractions, powers, roots, and logarithms; but in addition, the natural and logarithmic values of trigonometrical functions of any angle can be determined by inspection with the same accuracy as in numerical computation, while the products, quotients, etc., of these functions, by lengths or numbers, integral or fractional, are obtained with equal ease, rapidity and precision. The scope of its operations will be gathered from the examples which are given to illustrate its use in the instructions supplied with the rule.

Although the co-ordinate spiral rule, as all varieties of slide rules, is based primarily upon the theory of logarithms, a knowledge of that theory is by no means essential to its practical use.

887.--=Thacher's Slide Rule.=--Fig. 430. This contains a shorter scale than Professor Fuller's, and the system is not quite so simple. Full printed instructions are given in the book supplied by the inventor, Mr. Edwin Thacher, of Pittsburg, U.S.A., or of the author, who is his agent for this country. The original divisions of this rule were made by the author. The scale is manufactured in the United States. There appears to be found some difficulty in its construction to keep the scales to true length and get them to exact position.

888.--=Pocket Sets of Chain Scales.=--These are made 3, 4, 5, and 6 inch. Three of 6 inch form the ordinary set. The chain scales, if three only, are 10, 20, 30, 40, 50, and 60; if six they generally contain the same scales with feet equal to the links. An extra scale with the ordnance or other scale of the country is found also useful for measuring from maps or plans. Some civil engineers prefer the pocket scales made wide with quite square ends, to be used as offsets or for sketching. These scales are generally made in ivory and placed in a light morocco or Russia leather case. The numbers of divisions of the scales should be stamped on the ends to prevent the wrong scale being drawn from the case.

889.--=Anemometers= are used by mining engineers for testing the ventilation of mines. The original and best known form is that of Biram, Fig. 431. This instrument is held in any current of air, and the velocity of the current is registered by the motion of oblique fans, by means of ordinary decimal gearwork on five dials giving feet and multiples by 10. Lowne's anemometer, with the author's improvements, Fig. 432, is of similar principles of construction, but it is arranged in portable form to go in a pocket case. Another well-known form of anemometer is built upon the same principle, but of cubical form. It is customary to take the velocity of the current for one minute by a watch, there being a detent provided in most instruments to start and stop the motion of the hands upon the dials.

890.--=Books of Tables and Formulæ.=--Few British Surveyors are without Molesworth's pocket-book. This contains all the useful tables and notes of reference valuable to the civil engineer in his ordinary work--weight, 5 ozs. Many pocket-books have been written on the same plan. Hurst's pocket-book contains all matters of reference for the town surveyor among buildings. Trautwine's _Civil Engineer's Pocket-book_ (American) is the most complete, but it is of double the weight of the Molesworth. Spon's _Engineers' Tables for the Waistcoat Pocket_--weight, little over ½ oz.--is a very useful little book. Of _Traverse Tables_ both Gurden's and Boileau's are comprehensive and reliable. There are several pocket-books of _Curve Tables_, those of Cutler & Edge, Beazeley, and Kennedy & Hackwood being perhaps in the most general use.

891.--=Technical Books--Ordnance Maps= are published on special districts and subjects which are often relative to the country or the special conditions of work abroad and at home for minerals, etc. It is very useful to possess such of these as may be required, and the note is only made here as a reminder.

892.--=Sling Case for Drawings.=--The most convenient method of carrying maps or drawings for public works in execution is to have a solid leather case similar to a telescope case. This is best if made with the cap or lid of the same length as the body: it can then be drawn out any distance according to the length of the rolled drawing. If thought more convenient, and the map or drawings are heavy, a strap may be added to pass over the shoulder, Fig. 433.

893.--=Chronometer.=--This may be any form of watch with compensated escapement. At present the prices run high for this class of work; but from the simplicity and moderate certainty of compensation it does not appear that this should be necessary for the production of a fair working instrument useful for the surveyor in new countries to check his longitude. Where a good chronometer is used it is better to keep it to Greenwich time without alteration. If there is a gaining or losing rate this will most probably remain constant in equal times, so that corrections may be made _pro ratâ_ for all observations until a check can be taken with certainty when arriving at a town which possesses an observatory. The quality of a chronometer is fully ascertained by having a certificate from one of our observatories, that of Kew being the most popular.

894.--=Chronograph.=--For the observation of stars in transit for the purpose of taking longitude, a dead-stop watch or chronograph is most useful. This can now be had in combination with an otherwise fair going watch at a very moderate price.

895.--=Outfit of a Surveyor for Work in a New Country.=--The ordinary items of strong, dust-coloured woollen clothing, good boots, saddle, firearms, etc., do not come within the province of this work. The instruments he will require will depend partly upon the nature of the country and the kind of work to be done. If for prospecting only, light instruments are commonly selected--the sextant, or box sextant with glass artificial horizon, good pocket chronometer, _telescope_, aneroid barometer, prismatic compass, and clinometer. If a general survey is to be made, the first instrument of importance is the theodolite, the 4 or 5-inch being the most usual. With this, pickets, land chain and arrows, a steel tape for testing, and a linen tape. If for survey in mineral districts, a good mining-dial is required, with all accessories of chains, etc. If for railway work, a 5-inch theodolite, a good level, staves, pickets, clinometer, and prismatic compass. In all cases, field-books, drawing instruments, supply of paper, drawing boards, squares, parallel rule, pencils, Indian ink, colours, stencil plates, and other articles for office use, of which the established optician or trader will give full information from his experience, or general reference may be taken from any complete catalogue of such instruments.

FOOTNOTE:

[66] Patent, No. 4310, November, 1876.

INDEX

Abney's clinometer, 411

Achromatism explained, 35

Adjustable axis, of plane table, 479
of theodolite, 237

Adjustable tripod, 329

Alidades for plane tables, 473

Alloys used for surveying instruments, 7

Altazimuth theodolite, 295

Altitudes, measurements of, 550

Aluminium alloys, 8

Anallatic telescope, 364

Anemometers, 596

Aneroid barometers, Vidie's, 558
Bourdon's, 568

Apomecometer, 469

Arrows, for chain, 494

Artificial horizons, 443

Atmospheric pressure, measurements of, 550

Axes, workmanship in, 11

Bakewell's tangential index, 384

Ball and socket adjustments: Hoffmann's, Pastorelli's, 330

Bands, steel, for measuring land, 449

Barker's clinometer, 415

Barometer, aneroid, 558
mountain, 550
mercurial, 549

Base line apparatus, 517

Beam compass measurements, 510

Bellamy's road tracer, 420

Bill-hook, 582

Binoculars, prism, 584

Black, optical, 14

Boiling-point thermometer, hypsometer, 569

Boning rods, 578

Books, levelling, 173

Boucher's calculator, 587
improved, 590

Box sextant, 451
with continuous arc, 461
with supplementary arc, 458

Bronzing instruments, 14

Brunton mine transit, 353

Bubble trier, 88

Burel's reflecting level, 144

Burnier's clinometer, 416

Caink's rule for correcting inclines, 498

Calculators: Barnard's, 594
Boucher's, 587
Fuller's, 592
Thacher's, 595

Camera, 243, 585

Cases, for carrying maps, 597
leather, for instruments, 23

Cavalry sketching case, 488

Cement tester, Mann's, 585

Centesimal division, 185

Chain scales, pocket sets, 596

Chain vice, 496

Chaining, 497

Chains, land, various, 490

Chains, sounding, 526

Chronometer and chronograph, 598

Circumferentor, 307

Clamp and tangent motions, various, 202

Classification of instruments, 5

Clinometer compasses, 418
hanging, 344

Clinometers, various, 411

Coast survey lines, 527

Coincidence rods, 511

Collimation, 55

Collimator, 121

Compass, surveying with, 80

Compasses: magnetic, bar, 59
Barker's, 84
Burnier's, 80
hanging, 344
Hutchinson's, 79
luminous, 84
mariners', 73
prismatic, 75
pocket, 82
ring, 72
trough, 74, 83

Compensated rods, 512

Connecting link, to extend hand rods, 531

Convex and concave lenses, 32

Cooke's level, 138

Co-ordinate slide rule, 594

Cross-staff heads, 573

Curvature, correction for, 170

Cushing's level, 136

De Lisle's reflecting clinometer, 413

Declination of needles, 67

Deville's theodolite, 263

Diagonal eye-piece, 45

Dials, mining, 309

Diaphragm of telescope, 50, 114, 135

Dip compass, 354

Dip of needles, 66

Dispersion of light, 35

Dividing engine, 176

Division of the circle, 175

Double optical square, 467

Drop arrow, 494

Dumpy level, 110
improved, 123

Dynameter, 43

Edgeworth's stadiometer, 482

Engineer's level, 133

Engraving, note on, 16

Everest's theodolite, 271
tripod, 273

Excise ink bottle, 174

Eye-pieces: Ramsden, 41
erecting, 44
diagonal, 45
reflecting, 46

Field-books, 289, 374, 380

Field-glasses, 582

Finishing of surveying instruments, 14

Formation of images in a telescope, 33

French forms of miners' dials, 336

Fuller's rule, 592

Geological tools, 587

George's artificial horizon, 446

Girth straps, tapes, etc., 579

Glass diaphragm, 53

Glass, working, 16
refraction of, 25

Gradient scale, 213

Gradienter Screw, 386

Gradiometer, 404

Gradioplane, 409

Graduation, 179

Green, William, Subtense instruments, 355

Hadley's quadrant, 423

Hanging mining compass, 344

Hedley's dial, 322
improved, 326, 329, 333

Heliograph, 540

Heliostat and heliotrope, 537

Henderson's miners' dial, 315

Hick's patent level, 96

Historical sketch of surveying instruments, 1

Hoffmann's ball and socket head, 330

Horizontal scale of tangents, 213

Hypotenuse and base, 212

Hypsometer, 569

Illumination of axis of telescope, 234

Inclinometer: Lister's, 389

Lacquering work, 15

Lamp, magnesium, 545
for levelling, 169
mining, 348
theodolite, 235

Land chains, 490
vice for adjusting, 496

Lanterns, oil, 545

Lean's miners' dial, 315

Leather cases, 23

Lenses, 33
achromatic, 36

Level: for levelling staff, 163
mechanics', 575
with inclines, 576

Levels: surveyors', 97
Cooke's, 138
Cushing's, 136
dumpy, 110
same improved, 123
engineers', 133
reflecting, 144
pocket, 142
simple construction of, 141
supplementary parts to, 139
water, 146
Y-form, 98
same improved, 107

Level tubes, 86
circular, 96, 576
curvature of, 87
divisions upon, 90
readers for, 95
Scott's, 93
sensitiveness of, 89
Strange's, 92
with air cell, 93

Level tube trier, 88

Levelling: books, 172
staves, telescopic, 148
semicircular, 150
mining, 158
papering of, 159
preservation of, 161
various patterns of, 151
holder for, 163
pads for, 161
pegs for, 171
practice of, 163

Light for night observations, 169, 545

Light, refraction of, 27

Line, sounding, 527

Lubrication of joints, etc., 20

Luminous compass, 84

Magnesium lamp, 546

Magnetic compasses, 59
correction of, 64
declination of, 67
inclination of, 66
trough, 74
variation of, 68
various forms, 82

Magnetic needles, 59
lifting, 65
mounting, 64

Magnetic needles, various, 59

Magnetism, 59
preservation of, 71

Magnifying power of telescope, 43

Measuring rods, 530

Mechanics' levels, 575

Mercurial barometer, 549

Metals employed in surveying instruments, 7

Micrometer microscopes: various, 192
Stanley's, 197

Micrometer theodolites, 259

Military sketching board, 485
cavalry, 488

Miners' circumferentor, 307

Miners' compasses: French, 336
hanging, 344
Stanley's prismatic, 343

Miners' dials: various, 309
hanging, 344
Hedley's, 322
Henderson's, 315
Lean's, 315
improvements in Hedley's dial, 326, 329, 333

Mining, survey lamp, 348
targets, 349
theodolite, 342

Morse signaling, 544

Mountain barometer, 550
theodolite, 258

Nautical sextant, 429

Needles, magnetic, 59

Night signalling stations, 545

Octant or quadrant, 422

Offset rods, 507

Omnimeter, 374

Opisometer, 587

Optical black, 14

Optical principles of telescope, 25

Optical square, 465

Outfits for surveyors abroad, 598

Packing of instruments, 21

Parallax, in eye-piece, 55

Parallel plates, to level, 99
to theodolite, 219

Passometer, 525

Pastorelli's ball and socket head, 330

Pedometer, 524

Perambulator, 521

Permanent stations, 535

Pickets or ranging poles, 533

Pine measuring rods, 508

Pioneer tools, 585

Photographic camera, 243, 585

Plain theodolite, 215, 267

Plane tables, 472

Platinum-iridium points, 53, 129, 135

Plummets, 232

Pocket-books, 534, 596

Pocket levels, 96
sighted, 142, 525

Pocket magnetic compasses, 83

Point diaphragm, 53, 129, 135

Polishing work, 14

Preservation of instruments, 20

Prismatic clinometers, 414

Prismatic compasses, 75
Hutchinson's, 79
stands, 78

Prismatic mining survey compass, 343

Prisms as reflectors, 29

Protectors for the eyes, 584

Protractors, sketching, 82, 374, 485

Quadrant, 422

Qualities of work, 7
of a telescope, 56

Quick-setting surveyor's level, 132

Quick-setting theodolites, 257

Quiver for arrows, 494

Railway gauge, 579
theodolite, 258

Ramsden eye-piece, 41

Ranging poles, 533

Ray shade, 129

Reader for level tube, 95

Reading microscopes, 188

Reconnoitring glass and telescope, 582

Reflecting cap to telescope, 334

Reflecting circle, 424

Reflecting clinometers, 413

Reflecting levels, 144

Reflection of glass, 25

Reflector in eye-piece, 46

Refraction of light, 25

Repairing sleeves for steel bands, 505

Revolving compass to dial, 318

Richmond's tension handle, for steel band, 503

Road tracer, 420

Rods: coincidence, 511
compensated, 512
hand, 530
standard, 508

Rule, civil engineer's, 532

Rule for correcting inclined measurement, 498

Rule form clinometer, 418

Semi-circumferentor, 346

Sextants, 425
box, 451
with supplementary arc, 461
continuous arc, 458
sounding, 449
surveying (open), 464

Sight director to stadium, 364

Sighted pocket level, 142

Silvering sextant glasses, 437

Sketch books, etc., 585

Sketching board, military, 485

Slashing knife, 582

Slide rules, various, 590

Sliding stage to theodolite, 249

Socket for station pole, 535

Solar attachment to theodolite, 239, 259

Soldering, 13

Sounding chain, 526 lines, 527

Sounding sextant, 449

Spectacles for protecting the eyes, 584

Spherical aberration, 33

Spur shod picket, 535

Stadia points, 131
webs, 114

Stadium for tacheometer, 155, 373

Stadiometer, 482

Standard rods, 508

Stands of instruments, 19

Stations for observation, 533

Staves, levelling, 149

Steel bands and tapes, 499, 507

Striding level, 237

Style of work, 16

Subtense, instruments, 355
diaphragm, 114, 363

Supplementary arc to box sextant, 461

Sun glass to telescope, etc., 47

Tacheometers: general description, 370
Stanley's, etc., 371

Tacheometers: stadium for, 155, 373
field book, 374

Tangent motions, 202

Tapes, linen, etc., 505

Targets, mining, 349

Telemeters, 528

Telescope: general description of, 24
Kepler's, Galileo's, 40
body of, 47

Telescope: optical arrangements, 47
optical principles, 25
qualities, 56
reconnoitring, 582

Telescopic pocket level, 143

Tension handles for steel bands, 503

Theodolites, 214
adjustment, 276
adjustable axis, 237, 248
Deville's, 263
Everest's, 271
micrometer, 259
mountain, 258
plain, 265, 267
railway, 258
simple construction, 275
solar attachment to, 239
Souterrain 348
Stanley's, 247
transit, 215, 231, 247
14-inch, 295
36-inch Colonel Strange's, 298
Universal, 265

Thermometer for steel band, 503
boiling point, 569

Timber girth strap, 579
marking knife, 581
rods, 582

Tools used in manufacture of instruments, 11

Triangle for levelling staff, 162

Tribrach adjustments, 126
Everest's, 272
with mechanical stage, 251

Tripods, 114, 217, 322
framed, 250
miners', 313

Tripods, jointed, for mining instruments, 313

Trough compass, 74, 83, 236

Vernier scale readings, 180

Vicat needle, 586

Vice for adjusting land chain, 496

Water levels, 146

Waterproof covers, 23

Watkin's aneroid, 567

Watkin's clinometer, 417

Wealemefna, 587

Webs, collecting and mounting, 51

Whistles, 585

Y-levels, 98
improved construction, 107

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