  INSTRUMENTS CONSTRUCTED ESPECIALLY FOR OFFERING FACILITY OF TAKING INCLINES—INCLINOMETER—THEODOLITE—GRADIOMETER—CLINOMETERS—ABNEY'S, TROUGHTON'S, DE LISLE'S, STANLEY'S, BARKER'S, BURNIER'S, WATKINS'—CLINOMETER SIGHTS—RULE CLINOMETERS—ROAD TRACER. Certain instruments are constructed specially with the object of taking inclines, where this is the predominant work to be performed with them. They form an important branch of surveying instruments, and for their special kind of work present many time-saving capabilities. 593.—Lister's Inclinometer Theodolite. Fig. 257.—Lister's inclinometer theodolite. Larger image The instrument is also fitted with a mechanical device for repeating the tangential angles when operating on curves, which obviates the necessity of reading them on the horizontal arc, thus facilitating the work. This will be referred to in the following explanation of the manipulation of the instrument as the "angle repeater." The main difference between the method of taking cross sections by the level and by the inclinometer theodolite is in Fig. 258. Fig. 259. Larger image Fig. 258 shows the levelling method and Fig. 259 the method by the inclinometer theodolite. In the first it will be seen that each section requires to be taken singly with repeated changes in the position of the instrument at each section, involving numerous readings on the staff, booking, and reduction of the levels for changes only. Also the sectional measurements require to be taken in short horizontal lengths with the plumbing of the end of the tape at each length. By the inclinometer method this unnecessary labour is avoided, there being no changes in the position of the instrument, as from one setting a series of sections may be The saving of labour is even more marked in the setting out of slope pegs than in the taking of cross sections, for in addition to the transference of level from the centre pegs to the outcrop of the slope several approximate calculations have to be made before the exact position of the slope peg can be found, while by using the inclinometer theodolite it is only necessary to put in normal slope pegs at intervals of a quarter of a mile, or at such distances apart that a ranging rod may be seen from one point to the other, and by setting up the instrument at each alternate peg, or at half mile intervals, the whole of the intermediate pegs for a quarter of a mile on each side of it can be "boned" as simply as ranging a straight line, the telescope being inclined to, and revolving in the plane of the slope. In this manner as much work may be done in a few hours as will take a week with the levelling method, and this without the slightest physical or mental strain to the operator. 594.—Explanation of the Method of Operating with the Inclinometer Theodolite.—For setting out a centre line of railway, etc., and putting in level pegs the instrument may be used as an ordinary theodolite, or even as a level, and the work performed in the usual manner. It may also be used as a level when setting out the normal slope pegs on slightly inclined ground surfaces, but when the inclination is considerable it may be used in a special manner with advantage as hereinafter explained. 595.—To take Cross Sections when the Line is Straight.—It is unnecessary to explain the use of the instrument when the ground surface is comparatively level, so as to require no change in position and resetting of the instrument, it being obvious that in this case it may be used simply as a level with advantage; but when the surface is inclined in the direction of the centre, and also at a right angle thereto Assuming that it is desired to take a series of 15 sections (and this is within the limit of the number that can be taken from one setting of the instrument), set up the inclinometer, preferably over the centre peg of the series, in such a position that the two front legs of the tripod stand across the centre line, and the back leg (which has a distinguishing mark) rests upon the centre line. Set the lower limb of the tribrach stand upon which the instrument is supported to a level condition in its lateral direction by manipulating the back leg, and at the same time observing the bubble on the stand. This will enable the instrument to be subsequently tilted to a certain extent in a perfectly vertical position. Clamp the horizontal arc to zero and direct the telescope to the centre line. Clamp the lower limb and bring the arc round to an angle of 90°. The vertical arc is now at right angles to the centre line and parallel with the section lines. Now release the telescope from the vertical arc and turn it again on the centre line, and by working the back adjusting of the instrument (or in case of necessity manipulating the back leg) tilt the instrument until the cross web of the telescope is elevated to a short distance above the seventh or most distant peg of the sections, or site of the first section to be taken. Now tilt the vertical arc until the cross web assumes a position parallel to the general inclination of the ground surface laterally. Clamp the arc to this inclination and note the angle thereon, for this will be the angle of the inclined base from which the whole of the sections will be taken and subsequently plotted. Commencing at the seventh peg at this side of the instrument, the sections may now be taken consecutively to the seventh peg on the other side by taking readings on a level staff held in an inclined position at a right angle to the cross web or base, as shown in Fig. 259, and oscillated that the lowest reading may be taken. A reading must be taken on Fig. 260. Larger image The bases being parallel the angle of inclination remains the same. The tilting of the instrument produces a variation in the angle of the vertical arc, but this is only to such an infinitesimal extent that unless the tilt be excessive it may be disregarded. The correction, however, may be simply made after the instrument has been adjusted for any operation by ascertaining or simply noting approximately the angle of the tilt, and setting off this angle on the horizontal arc towards the tangent line, thus varying the chord or base line to this extent, or it may be found by referring to a table of natural sines, etc., and multiplying the cosine of the angle of the tilt by the tangent of the vertical arc angle, the result being the tangent of the corrected angle, thus:—if the angle of the tilt be 10°, and the vertical arc angle 25°—Referring to tables, cosine 10° = ·98481, tangent 25° = ·46631. ·46631 × ·98481 = ·45924 = tangent 24° 40', the corrected angle making a variation of 20'. 596.—To take Cross Sections when the Line is on a Curve.—This operation is similar to that explained above for taking cross sections when the line is straight, except that being on a curve a variation of the tangential angle must be made at each peg or section. As this is performed mechanically by a single movement of the angle repeater and no reading of the angle is required, the work is just as readily performed. To more clearly elucidate the method, we will take a case in point and assume that the number of sections to be taken is 15 and that the radius of the curve is 50 chains, which the accompanying diagram illustrates. Diagram (Fig. 261) showing the adjustment of the instrument for taking sections on curves and the variation of the tangential angles for each section. Fig. 261. If the centre pegs be taken as slope pegs, the diagram applies to illustrate the setting out of half widths. Larger image Having set up the instrument at A, Fig. 261, over the centre peg of the series in the manner before described, ascertain the tangential angle for the first chain of the curve by dividing the constant, 1719, by the radius of the curve in chains, which gives the angle in minutes or 1719 ÷ 50 = 34' 24, and set the angle repeater to give a movement of double this angle or 1° 8' 48, ready for application at each change of section. Set the horizontal arc to the tangential angle for the seventh peg from the instrument at which the first section has to be taken, or 34' 24 × 7 = 4° 0' 48, and direct the telescope to the peg. Zero is now on the chord line AD, which is parallel to the tangent at the seventh peg, and at an angle of 8° 1' 36, from the tangent line AB, which divided by 7 gives the variation of the tangential angle at each section, or 1° 8' 48, to which the angle repeater has been set. Release the horizontal arc and bring it round to an angle of 90° from zero, and the vertical arc will be at a right angle to the line A D and parallel with the section line at the seventh The movement of the angle repeater brings the vertical arc parallel to the section line at each peg, and the adjustment of the bubble maintains the angle of the inclined base uniform throughout. When the sections are all taken on this side of the instrument, the telescope is turned to the other side and the operation continued until the whole fifteen are completed. From the above detailed description it may be thought that the adjustment of the instrument for the operation is somewhat complicated, but in practice it is not so. After the first experience and the method is understood, it is only a matter of two or three minutes, and once in position the sections may be taken as rapidly as on level ground, and the saving of labour is practically the same as in taking sections when the line is straight. 597.—To set out Half Widths or Slope Pegs when the Line is straight.—In commencing this operation it is necessary in the first instance to set out two or more half widths, according to the length of the cutting or embankment. These may be a quarter of a mile apart, or so far as a ranging rod may be clearly seen from one point to the other. The pegs put in at these points act as normals from which to Fig. 262. Larger image Assuming that the normals have been put in, set up the instrument at any intermediate peg in such a position that the telescope when set to the angle of the slope shall line with the top of the peg, as per sketch, Fig. 262. Then release the telescope from the vertical arc and direct it to one or other of the nearest normals, adjusting the cross web to cut the top of the peg by turning the instrument on its axis. Clamp in this position and the telescope will revolve in the plane of the slope, and any point on the intermediate surface intersected by the cross web is the outcrop of the slope and the position of the peg. When all the pegs on the one side of the instrument are put in, turn the telescope to the other side to cut the next normal and proceed in the same manner. When all the pegs have been put in for this half mile distance, the instrument may be moved to the next half mile normal and the operation repeated, until the whole cutting or embankment is completed, the last normal point being in all cases the formation width at the ends. In speaking of half-mile distances we are assuming the In fixing the points for the slope pegs, a rod should be held in an inclined position and be brought to line exactly with the cross web of the telescope, the pegs should then be driven level with the ground surface where the foot of the rod has rested. 598.—To set out Slope Pegs when the Line is on a Curve.—The operation is similar to that described above, except as explained for taking cross sections on a curve. A variation of the tangential angle must be made for each peg, and if the centre peg shown on the diagram accompanying that explanation be taken as one of the slope pegs, it will also serve the purpose of illustrating the present one, and a brief recapitulation of the manipulation of the instrument to bring it into adjustment for the operation is all that will be required. The normal slope pegs having been set out and the instrument set up at an intermediate one, as before explained, instead of directing the telescope in the first instance to intersect one of the next normals, set the angle repeater to double the tangential angle for the first chain in the curve, and the horizontal arc to the tangential angle for the distance in chains that the normal is from the instrument. Then turn the telescope to cut the normal peg and clamp the lower limb. Now bring the horizontal arc round to an angle of 90° from zero and clamp. Release the telescope from the vertical arc and turn it at a right angle thereto in the direction of the zero line AD, and by working the back adjusting screw tilt the instrument until the cross web cuts the normal peg again. Adjust the lateral bubble on the instrument to a level condition and it is in adjustment for the operation. To put in the first peg from the normal, make one movement of the angle repeater and adjust the bubble. To put in 599.—Alternative method of setting out the Normal Pegs.—Let the diagram, Fig. 263, represent the section of a cutting at the point opposite which the normal has to be set out, when the section depth may be assumed to be 16 feet, the formation width 30 feet, and the slope 1½ to 1, or at an inclination of 56° 18'. The distance bc for a 1½ to 1 slope is one-third the formation width, or 10 feet. The data required for the operation is the distance ad from the centre peg to the plane of the slope, which is found by multiplying ac by the natural sine of the slope angle 56° 18', thus: 26 × ·831 = 21·60 feet. The operation when the line is straight is to set up the instrument at a centre peg some distance away from the normal in the manner previously described, viz., with the front legs set across the centre line, the back leg on the centre line, and the bubble on the tribrach set level before adjusting the instrument, which manipulation produces a perfectly vertical tilt. After adjustment, set the horizontal arc to zero and direct the telescope to the centre line, clamp the lower limb, set the vertical arc to the angle of the slope, and bring the horizontal arc round to an angle of 90°, or a right angle to the centre line. Liberate the telescope and direct it again to the centre line, and by working the back adjusting screw tilt the instrument until the cross web intersects the top of the centre peg at the normal. The telescope will now revolve in the line ag parallel with the plane of the slope and at a distance of 21·60 feet from it. Therefore any point on the surface in the line of the slope where 21·60 can be read on the staff is the outcrop of the slope and the position of the peg. In this example, when the required reading is higher than the ordinary staff, lower the tilt and take an intermediate reading, as at f in the diagram, Fig. 263, which may read, say, 12·00, when the required reading on the peg will be reduced to 9·60. Fig. 263. Larger image In setting out normals on a curve by this method the only difference in the operation to that above described is that instead of in the first instance clamping the instrument with zero on the centre line, it must be clamped with zero on the chord line, i.e., at double the tangential angle for the distance the instrument is from the peg, as before explained in detail for operations on curves. By this method two normals may be set out at least 20 chains apart from one setting of the instrument, or several slope pegs may be set out in like manner, which under certain In this connection there is also an alternative method of putting in the slope pegs after the normals have been set out, which, under certain conditions, may be employed with advantage. Instead of setting up the instrument at the back of the normal with the telescope set to line with the plane of the slope, and to range the pegs in by means of a rod or staff held at the inclination of the slope, as before described, it may be set up in any position in the line of slope where a reading can be taken on the peg, as at a on the sketch (Fig. 264), and at the point read, as at b, a disc should be clamped to the staff, as this can be much more clearly seen than the staff graduations when sighting long distances. The staff should then be transferred to the next normal and held on the peg. If the telescope be now turned in this direction and the cross web adjusted to cut the disc, any point on the intermediate surface where the disc can be intersected is the outcrop of the slope and position of the slope peg. Fig. 264. Larger image It is necessary to observe in the setting out of slope pegs that when there is a change of gradient the operation must cease, but if the point where this occurs be made the position of a normal the operation may be proceeded with, if the instrument be set up at this point. 600.—To set out Slope Pegs on both sides of the Line simultaneously without moving the Instrument from the Centre The point e, Fig. 265, is the extension of the slope lines to cut the centre line, and its depths below formation for 1 to 1 slope is half the formation width, or 7' 6. Fig. 265. Larger image Operation.—The instrument being set over a centre peg with the telescope at the slope angle, turn the telescope to any other peg and adjust the cross web to line therewith (on line c f). Take the section depth cd (14 feet), to which add de (7' 6) = 21' 6. This multiplied by ·707, the natural sine of the slope angle (45°) will give the distance from the axis of the instrument to the slope line, thus: 21·50 × ·707 = 15·20 feet, and the point on the surface at g where 15·20 can be read on the staff is the position of the slope peg. This is similar to that described in the last paragraph, but if the telescope be now changed to the angle of the slope on the other side of the line ch, the peg i is instantly found by the same reading (15·20). 601.—The Use of the Inclinometer in Mining.—A lode having been discovered, it is required to mark out on the The inclinometer, having an adjustable axis at right angles to the horizontal, enables the line of sight to be made to revolve in any plane. If at the spot where the lode has been discovered the instrument be set up in line with the strike, and the movable axis adjusted to the angle of dip, it is evident the line of sight lies wholly in that plane, and a continuous line of outcrop may be pegged out on a flat or undulating country, which can be produced to any length required by taking the instrument to a fresh station. This feature of the instrument is equally, if not more, important than its use for rapidly pegging out railway slopes. 602.—The Gradiometer.—This instrument, while performing all the duties of a first-class level, is designed also for taking vertical inclines at small fixed angles for railways, drainage works, steep incline levelling, etc., etc., and also telemetrical readings up to great distances. In general construction, as regards telescope, stand, etc., it resembles a level, and when set at zero is equal in every way to one of the best, with the additional advantage that it may be used for rapid work without the trouble of setting up by the levelling screws, as the telescope may be levelled at any sight by means of the gradienter drum milled head. The The additional parts do not increase the bulk of the case and add very little to the weight. Fig. 266.—Stanley's gradiometer. Larger image By its use a great saving of work is effected. For instance, for a town drainage in which it is desired to work out an inclination, say the levels indicate a fall of 10 feet between the extreme points: if the line the drainage is intended to take be measured, however angular or zigzag it may be, and the length of that line be divided by the amount of fall, this will give the gradient; say the line of streets measures 5,000 feet, this, divided by 10 feet, gives a gradient of 1 foot in 500. Therefore if the drum be set to that proportion, all the pipes may be laid directly without further setting. The gradients for any railway may be instantly found by merely turning the drum until the telescope sights, up or down the incline to be measured, a reading on the staff equal to the height of the For levelling steep inclines it also saves a great number of settings up, as, instead of levelling for, say every 14 feet rise or fall, the gradient of the total distance can be taken and also the distance measured by stadia reading, when the incline is not too great for taking one reading with telescope level, or by gradient reading when this cannot be done, and by adding the staff reading to the distance divided by the gradient, and deducting the height of the instrument the difference of level can at once be ascertained. Example: Sighting a staff at a gradient which falls conveniently upon it, say 1 in 35 and this reads 8·7 feet. Distance measured, as explained later, say 735 feet, then 735/35 = 21 feet + 8·7 feet = 29·7 feet; deduct the height of instrument, say 4·9 feet, difference of level 24·8 feet. For measuring long distances beyond the range of the stadia lines or points in the diaphragm, or for measuring distance on inclines, the gradiometer will also be found very useful, as by taking the difference of any two suitable gradients, the base distance is given without calculation for difference of hypo and base. If the gradient be not very steep or below the height of the staff, the simplest method is to sight the staff with the telescope level and take the staff reading; say this is 12·45 feet, then set the gradient drum to 1 in 100 and again take the staff reading and, say this is 4·30 feet, the difference between these readings = 8·15 feet. Strike out the decimal point which multiplies it by 100 and we have the base distance 815 feet. For shorter distances a larger base upon the staff may be taken, thus giving greater accuracy; for instance, if the gradient drum after taking the level reading be set to 1 in 50 and the resulting difference divided by 2, any error in taking exact readings is reduced by one half, or 1 in 33-1/3 and divide The difference of readings obtained by either of the following two gradients will also give base measurement without any calculation whatever: 100 and 50 " 63-2/3 and 40 " 60 and 37½ " 50 and 33-1/3 " 33-1/3 and 25 " 25 and 20 " 20 and 16-2/3 " 12½ and 11-1/9 " 11-1/9 and 10. Example: Suppose the top of staff is below level altogether, turn the drum until the top of staff is sighted in the telescope; say the gradient of this is 27½ go on turning until gradient 25 is indicated and take the staff reading; say this is 12·75, then move the drum until gradient 20 is indicated and take the staff reading: suppose this to be 3·40, then
Omit the decimal point and the measurement reads 935 feet, which is the horizontal distance. The two most suitable gradients would of course be used according to the position. Distances may be set out with equal facility with the gradiometer by the subtense method, by working out a subtense suitable for the distance. This is easily done by dividing the distance required by any two numbers having a difference of the required subtense, the result being two gradients, which, when worked with, will give that subtense at the required distance. Example: If the distance required to be set out be 650 feet, a suitable size for an object to be plainly visible at this distance would be 10 feet. Then take as divisors two numbers having a difference of 10, say 10 and 20. 650 ÷ 10 = 65 650 ÷ 20 = 32½ These two gradients will give a subtense of 10 feet at a distance of 650 feet, and all that is necessary is to send a man Fig. 267.—Stanley's gradioplane. Larger image It is always preferable to make the subtense as large as possible, as the larger it is the more accurate the result will be. All distances set out by this method are base distances, no matter what the difference of level may be, and such figures for divisors should be used as give the gradients below 100. Gradients between 12 and 65 are the best and quickest to work with, and with care more accurate results are obtained than with chaining. Thus, at one time, a distance may be set out or measured, the difference of level taken, and also the gradient ascertained, and the drum can instantly be set to zero and all ordinary levelling operations continued. If preferred the gradient drum can be divided to percentage gradients ·001 to 8 instead of ordinary gradients 1 in 12 to 1 in 1,200. 603.—Gradioplane.—This is a new instrument, specially designed by the reviser for very accurate underground surveying, such as is required for large sewage work or water works, long tunnels, or any work requiring a very rigid and accurate instrument, with a very powerful telescope for measuring all horizontal and small vertical angles. The horizontal circle is 6 inches diameter, and reads by two verniers to 20 seconds of arc, or it is fitted with micrometer microscopes reading to five seconds of arc if desired. In the former case it carries a floating bevelled aluminium ring compass divided to ¼ degrees, reading by microscope, and in the latter a long trough compass. Vertical angles are measured by a very accurate form of gradiometer screw carrying a drum with open extended scale in exactly the same manner as the foregoing instrument, and the remarks regarding that and its working apply equally to this instrument. The telescope, which is 14 inches long and carries a 1¾ inch object glass is so mounted that it will revolve in the plane of any inclination set by the gradiometer drum, and is provided with a locking arrangement for fixing it absolutely true for fore or back sight, and it carries a long sensitive spirit bubble to enable it to be used as a most accurate level and for rapid levelling; this may instantly be set level by the drum at any sight without troubling to level the instrument. The diaphragm is fitted for subtense measurements. A further refinement is fitted to the telescope when desired, by which any grade may be instantly divided into any desired number of parts; this is effected by means of a A sliding lower plate is provided for accurately centring the instrument, the levelling screws are adjustable for wear, and the tribrach is fitted with quick-setting spherical joint. This instrument will also be found of great utility in mining work, to mark out the general line of the outcrop when a lode has been discovered. This, by the ordinary method, entails a considerable amount of labour and careful work both in the field and office, and then only points at intervals are obtained, not a continuous line. With this instrument the line of sight may be made to revolve in any plane, so that if it be set up in Fig. 268.—Stanley's gradioplane. Larger image The above illustration, Fig. 268, shows the gradioplane fitted with a horizontal circle to the telescope for subdividing the grades of the gradienter drum, and when thus fitted forms the most exact instrument for setting out or ascertaining gradients that has been devised. 604.—Abney's Clinometer.—This very popular little instrument, the invention of Captain Abney, Fig. 269, embraces the same form of sighted level with reflector as that Fig. 269.—Abney's clinometer.. Fig. 270.—Troughton's clinometer. Larger image 605.—Troughton's Abney's Clinometer.—In the Troughton form, Fig. 270, the arc is toothed, and it is moved by a pinion similar to the movement of the box sextant, so that the bubble moves slowly in relation to the motion of the fingers when adjusting. The arc is read by a single index line instead of by a vernier. 606.—Telescopic Hand Clinometer.—The author has recently added a telescope to the Abney form of clinometer, as shown Fig. 271. The arc is moved by rack and Fig. 271.—Telescopic Abney clinometer. Larger image 607.—De Lisle's Reflecting Clinometer.—There have been several arrangements made for converting the Burel level, Fig. 89, into a clinometer; that devised by General A. De Lisle, R.E., with modifications by Colonel Bell and Mr. Alfred Cooke, as represented in Fig. 272, is the most popular. In this a heavy arc is constructed upon the lower part of the instrument. This is jointed upon a vertical axis at C so that it may be revolved to bring the mass of the arc either forward or backward, to take inclines upwards or downwards, or to rest at an intermediate position to make the instrument flat and portable in its case, it takes the position shown in the figure. The arc has a stiff centre axis with a radial bar, the edge of which forms the index. A sliding weight is placed on the radial bar, which is sufficiently heavy Fig. 272.—De Lisle's reflecting clinometer. Larger image 608.—Prismatic Clinometer.—This instrument was originally devised by the author about 1860. The form of the instrument, Fig. 273, is that of a prismatic compass, art. 155. A similar metal or card and talc dial to that of the prismatic is used, but this is centred upon a transverse axis which is pointed at the ends to fit into hollow centres. This card is weighted on one side, so that when the sights are in a truly horizontal position the prism will show the zero of the card cutting the sight line. If the instrument be inclined upwards or downwards, the degrees of elevation or depression will be indicated by the card retaining its pendulous position. This Fig. 273.—Stanley's prismatic clinometer. Fig. 274.—Barker's clinometer. Larger image In Using this Form of Clinometer the prism is raised or lowered in its sliding fitting until the divisions of the card are sharply defined. Then in looking over the edge of the prism through the slot above it, the hair in the window of the back sight will appear to cut the divisions of the card; and the object seen in the distance, in front of the hair to which the instrument is directed, will appear coincident with the number of degrees of inclination indicated by the card. This clinometer is sometimes fitted upon a prismatic compass, so that inclines may be read by the same prism and sight arrangement. This is, however, done more neatly by the arrangement next described, if the instrument is intended to be used with the prismatic compass only, and is not wanted separately for use with the chain. 609.—Barker's Combined Prismatic Compass and Clinometer, Fig. 275.—Continental form of clinometer (Burnier). Fig. 276.—Section of the same. Larger image 610.—Continental Form of Clinometer.—Hand clinometers on the Continent are generally made on Captain Burnier's plan, Fig. 275, which was explained for the prismatic compass, art. 156. Indeed this instrument is more generally combined with the prismatic compass. The graduation is set up on a plated ring vertical to the plane of the Fig. 277.—Major Watkins clinometer. Larger image 611.—Major Watkins' Clinometer. Fig. 278.—Compass with clinometer sight. Larger image 612.—Clinometer Sights.—A clinometer sight is often attached to a light pocket compass, as shown Fig. 278 at the upper part of the engraving, consisting of a pin hole and hair cross. This, used in the manner shown by the position of the eye in the engraving, can only be made to take sight inclines by another person reading the pendulum index, which marks the inclination in the degrees to which the compass is divided. This portable pocket instrument is, however, useful in other ways. Standing face to the instrument it will measure inclines directly very fairly by looking over the top edge and bringing this to the visual rate of inclination at which the pendulum index can be read in front view. Geologists commonly use it in this way to take the dip of strata. It can also be used by putting it on or against any inclined surface. The case is generally gilt or nickel plated, and is about 2 inches diameter, and the instrument weighs about 3 oz. Fig. 279.—Rule form clinometer. Larger image 613.—Rule Form Clinometer.—This is made in the form of a stout 12-inch, one-fold boxwood rule, Fig. 279. It is much used by civil engineers as a working tool, and Fig. 280.—Road tracer. Larger image 614.—The Road Tracer is a balanced clinometer much used by natives in India and China for road making, Fig. 280. It consists of a pendulum, supported upon a stand that carries a sighted tube which indicates the level of the ground when the weight is carried in the axis of suspension. The weight is adjustable to a scale by a screw. The scales read inclines, by displacement of the weight, up and down in percentages or gradients, to which it may be divided. Fig. 281.—Bellamy's road tracer. Larger image This instrument has been improved by Mr. C. V. Bellamy, M.I.C.E., M.I.M.E., F.G.S., &c., Director of Public Works, Lagos, West Africa, a civil engineer who has had great experience in the colonies, and it will be found much more accurate, less liable to get out of order and far more convenient to use than the old forms. It is shown at Fig. 281. The chief feature of this pattern lies in the adoption of the arc of a circle instead of a straight scale, and a pendulum The sighting tube is provided with reversible sliding shutters, so that back readings may be taken without unclamping the instrument or altering the vernier or index. A powerful clamp is provided for locking at any desired grade. A recent further improvement by Mr. Bellamy has been made by making this instrument in a form to give readings in degrees of arc as well as in gradients. Fig. 282. Fig. 282.—Bellamy's improved road tracer. Larger image |
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