M

AB

from B so that they nearly touch the same side of the wire MN. In order to have the plumb-lines as far apart as possible, the line at B must be quite long and a can of water provided to keep the bob from swinging. The plumb-line is fastened to a nail B nearly in the proper position. A bar of wood, with a block fastened to it, should be placed to one side and a little below B. The block must have a hole through which a small screw bolt can easily screw. On this bolt is placed a spool in which a groove is turned and which is sandpapered and greased so that the string will slip easily as the bolt is turned. Now, place the transit in line with the two plumb-bobs, as in an ordinary case of shaft plumbing. Repeat this operation below. The plumb-bobs in both cases hang in the same vertical plane and thus the true bearings are found underground. Even the plumb-lines may be dispensed with, but the method will not then be so accurate. The instrument will be set nearly in the vertical plane passing through the wire, leveled and sighted at M. The telescope should be dipped until the lowest point on the wire is visible and the amount by which the cross-hair and wire fail to coincide noted and the instrument shifted accordingly. But if this method is tried, the two points sighted at will not be nearly so far apart horizontally as the plumb-lines, and any error in leveling will also vitiate the result. This method of the single wire, however, provides no way of obtaining the coordinates.

UNDERGROUND, OR MINE, SURVEYING

INTRODUCTION

FIG. 2

The same instruments and the same methods of measuring and recording angles and distances are used on the surface and in the mine. The chief difference between surface and underground work is one of detail only. In the mine, lamps are needed to give light, sights are taken to a string or to the point of a plumb-bob, and stations are placed in the roof and not in the ground. The main-line notes are kept in the same way above and below ground, but the method of taking and recording side notes is materially different.

Mine surveying in flat coal seams differs in minor details from that used in pitching seams, and this difference in detail has been greatly exaggerated until it has become a prevailing belief that anthracite (pitching) and bituminous (flat, usually) mine surveying methods are absolutely distinct. There is, in all underground work, a difference in the organization of the corps and consequently in some minor details in carrying on the work, depending on whether the survey of an entire and extensive mine is to be undertaken or whether, as is commonly the case, the survey is made merely to connect recent developments with those previously surveyed.

FLAT WORK

In

Because it is necessary for the gangways, or entries, in pitching work to follow the foldings and twistings of the seam, the physical difficulties in the way of the surveyor are greater in that kind of work than in flat seams. pitching seams, short sights and many of them are the rule; in flat work, long sights and few are general. In fact, in flat seams the headings or entries are commonly driven on points; that is, they are driven upon some predetermined course for long distances, even 2 or 3 mi. in the case of large properties. At regular intervals, pairs of cross-, or butt, entries are driven at right angles to the main entries; from these, in turn, the rooms are driven. Hence, the surveyor in the average bituminous mine (bituminous mines are commonly flat) is chiefly concerned with prolonging straight lines for several thousand feet in the case of butt entries, and up to 2, 3, or 4 mi. and more in the case of long main entries. The angles measured are chiefly right angles at the points where a butt entry intersects the main entry, or at the mouths of rooms driven from a butt entry.

The bituminous-mine surveyor is very rarely called on to make a complete survey of underground workings. He usually moves up the points (sights) at more or less regular intervals of time or of distance driven, measures the distance from the old set of points to the new, takes the necessary side notes, and at once plots them; the mine map, so far as the main headings and crossentries are concerned, is thus up to date within a month or so at the most.

In fact, whether the sights are moved up with regularity or not, the mine foreman is always able to determine the position of the working face by measuring back from it to the last survey station appearing on the tracing or blueprint furnished him, and adding this distance thereto, laying it off in the direction the heading is being driven.

Stations.-An essential part of the equipment of the mine surveyor is a carpenter's brace and from three to six bits, or drills, which can be made from files thrown away by the miner. With these, a hole from to 1 in. in diameter and from 1 to 1 in. deep may be drilled in the roof where a station is necessary. From ten to fifty plugs should also be carried by the corps. These plugs are pieces of poplar or other softwood about to in. longer than the drill hole. They are square in section, the side being a little longer than the diameter of the hole in which they are to be used; the lower end may be roughly rounded. After the hole is drilled, one of these plugs is fitted in and driven home by blows from the hatchet until from to in. projects below the roof. A spad, spud, or as sometimes called a nail, is then driven into the plug. The spads or nails are made from mule-shoe nails, through the flattened heads of which -in. holes have been drilled or punched. These spads may also be purchased from dealers in surveyors' supplies, but are commonly made by the 'blacksmith's helper at odd times.

Sometimes stations are made by driving a tack or nail in a tie, which has been notched or flattened with a hatchet to receive it, or by driving a spad in the collar or cap-piece of a set of timbers. Neither of these methods is to be recommended, as the position of a tie, and with it that of the station tack, is practically sure to be changed in a few months from the pounding it receives from passing cars, mules, and men, or from alining the track. Stations in collars are less liable to be shifted than those in the track, but as the pressure due to mining operations comes upon the timbers they, too, are apt to be shifted out of line. Sometimes stations that must be set at an exact distance from a previous station (as when a butt entry is to be started, say, 225.25 ft. from the main entry station) are of necessity made in a tie if the roof at the exact spot is not in condition to hold a plug (or has been shot down for an overcast). In such a case the station is placed in the tie and as soon as the butt entry or other place has advanced sufficiently to have sight plugs set in, these are placed, and the use of the tack abandoned.

In longwall work, much difficulty is experienced at times through the stations being shifted out of line through the settling of the overlying rocks. This settling may extend over a period of years or may stop after a few months. While the settling is in progress, the timbers must frequently be renewed, so that they and the constantly disturbed roof and floor afford a poor place for permanent stations. Hence, during the period of settlement at least, stations in longwall mines must be placed in the floor. For the foregoing reasons, combined with heavings of the floor as the weight comes unevenly upon the pillars, these stations are almost certain to be disturbed, and should not be used to extend a previous survey until one or more older stations have been reoccupied by the transit and the angles and distances remeasured to be absolutely certain that no such disturbance has taken place. If displacement has occurred, it will be necessary to go back along the line until three stations have been found in their original position. From these a new set of lines must be run, using the old stations if solid enough, remeasuring the angles and distances, but not necessarily retaking the side notes.

Stations are commonly marked by enclosing them in a circle, square, or triangle, or by a + mark of white paint. White lead, or Dutch white, thinned with linseed oil is ordinarily used, and is applied with an ordinary sash tool. If the paint has to be kept a number of days, it should be covered with water, which should be poured off before the paint is used.

In addition to marking the station itself so that it may readily be found, some system of lettering or numbering must be devised so that the stations may be distinguished one from the other. Stations on the main entry frequently have the letter M prefixed and are numbered in regular order from the drift mouth, thus, M-1, M-2, etc. Or the stations on the main entry may use the letter A, those on its air-course the letter B, those on the manway the letter C, and similarly for other parallel entries. As butt entries are usually known by a number corresponding to the order in which they were turned off from the main entry, the stations on such entries, while numbered consecutively, have prefixed to them the letter R or L to indicate whether the entry is turned to the right or the left of the main entry, as well as the serial number proper to the entry. Thus, L1-12 or 1L-12 indicates the twelfth station

on the first left-hand cross-entry, or, as commonly said, on the first left. Similarly R5-6, R-56, or 5R-6, is the sixth station on the fifth cross-entry to the right. If entries are driven from one side only of the main entry, the prefixed letters R and L may be omitted. In this case, the foregoing stations will be numbered 1-12 and 5-6, respectively. Air-courses are not usually run on sights. If they are, the stations in them may be numbered in the same way as those on the heading proper with a letter, such as A, to denote the fact that they are on the air-course. Stations coming between regular stations on an entry commonly receive the number of the preceding station with some letter added. Thus 56 D is a station on the fifth cross-entry at a point between regular stations 6 and 7.

Some corps number the stations in a heading as are stakes in a railroad survey. The station at the mouth of the heading on the main entry is called 0, and the first station in the heading will be, say, 2+56.29, the second 4+81.96, etc. This means that these stations are 256.29 and 481.96 ft., respectively, from the mouth of the entry. The distance between the stations is, of course, 481.96-256.29=225.67 ft. While this system of numbering shows at a glance the exact distance an entry has been driven, such large numbers may be a source of trouble and of possible error when used to describe the backsight, instrument, and foresight stations as entered in the field notes.

Rarely are stations numbered in the order in which they chance to be placed. It may happen that station 56 will be on the main entry, 57 on the fifth right, and 58 on the tenth left and follow, say, stations numbered 36, 48, and 51. This system, or want of system, is not commended, as it leads to confusion.

While the numbers of stations are frequently painted on the roof alongside the station mark, it is better practice to paint them on the rib a short distance before the station is reached. In this way the foresight man can see them without having to walk in a stooping posture.

Sighting. Sights in underground work are commonly taken either to the point of a plumb-bob suspended by a cord passed through the hole in the head of the spad marking the station, or to the cord itself. In the first case, a lamp is held a short distance back of the point of the bob to render it visible against a background of flame. In the latter case, the cord is best illuminated by placing a white paper or cardboard behind it and holding the lamp in front and to one side. The string shows as a dark line against a white ground, but care must be taken not to confuse the string with the shadow it casts upon the paper.

What are known as plumb-lamps, or plummet lamps, are a great convenience. These are very heavy plumb-bobs, suspended in gimbals to ensure verticality, which are hollowed to form an oil chamber, and are provided with a wick. The bisection of the lamp flame, if the wick is turned low, affords a sufficiently accurate setting of the transit when placing room sights, surveying rooms, and even in moving up sights in a butt entry, provided the backsight is not too close to the instrument and the flame is not greatly disturbed by the ventilating current. It is obvious that the use of the plummet lamp, which will burn for several hours and is always ready for backsighting on, saves the labor of one man. In accurate sighting, the point or the cord of the plumb-lamp may be used as just explained. Where the velocity of the air is great enough to cause the plumb-bob to oscillate, long narrow bobs must be used, and these must be shielded from the direct current by the backsight man. In drafty places, a hole may be dug out in the ballast between the ties and the bob let into this shelter, the sight being taken to the string. Cords for suspending plumb-bobs should be braided to avoid twisting under the weight of the bob, should be well-oiled, and should be hung with a slip knot so that the point may be raised or lowered.

Various means are employed to illuminate the cross-hairs in the telescope. Commonly this is done by holding a lamp a little beyond, above, and to one side of the object glass. Sometimes a reflector is provided. This consists of a piece of silvered metal, inclined at an angle of about 30°, that is soldered on one edge to a metal ring that fits around the object end of the telescope. The reflector has an oval hole through it to permit the passage of the line of sight. The reflection of the light carried in the surveyor's cap sufficiently illuminates the hairs to permit their being centered upon an object. In some rare cases, transits have the horizontal axis pierced (the opening being closed by a piece of glass), through which hole a lamp held at the end of the telescope axis will throw enough light to render the cross-hairs visible.

Centers. If stations are made in the ties, the transit may be set up over them exactly as in outside work. However, stations are commonly made in the roof. The transit may be set under a station if a center mark is punched in the collar surrounding the telescope and to which the transverse axis is attached. When the telescope is level, this mark is immediately_above_the point of a plumb-bob suspended from beneath the instrument. By slightly loosening the leveling screws, the plate may be shifted until the center of the instrument is exactly below the point of a bob suspended from the station spad. However, care must be taken in tightening the leveling screws, that the instrument is not thrown out of line. Commonly, the station in the roof is transferred to what is called a center placed on the floor, and over this center the instrument is set in the ordinary way.

The center may be made from a large square or hexagonal nut some 2 in. across. A wire nail or spad is set in the center of the hole in the nut, which is filled with melted lead or Babbitt metal. The point of the nail is cut off about in. above the top of the nut and sharpened with a file. Or a very satisfactory center may be made by boring a hole 1 in. in diameter and 1 in. deep in a thick plank, setting a brad in the center with its head down, and filling in with melted lead, at the same time holding the brad in a vertical position with its end projecting slightly above the top of the plank. After cooling, the brad may be sharpened as before.

A plumb-bob is hung from the station and the string adjusted until the point of the bob just clears the point of the center. By sighting across the two points at an angle of 90°, the point in the center may be shifted into coincidence with the point of the bob. If the center has been lost or forgotten, a plank may be laid across the rails under the station and the position of the point of the plumb-bob marked upon it with a pencil. After removing the plumb-bob and its cord, the transit may be set over the center or pencil mark in the usual way.

Placing Stations on Line. Two cases of placing stations on line may arise: (1) The station may be on the prolongation of the heading line and at any indefinite distance from the instrument. (2) The station may (or may not) be on the line of the heading, but is at a fixed, definite distance from the instrument.

The first is the common case when the last station on a straight heading is, say, 200 to 250 ft. back from the face, and a new station must be set ahead and on line so that sight plugs may be placed from it. The transit should be set up at the station nearest the face, a backsight taken on an outer station on the line, and the telescope plunged. Where the roof is solid and from 25 to 50 ft. back from the face, the foresight man should hold his lamp against the roof so that its flame may be lined in by the surveyor, a smear with the lampwick or an X with a piece of chalk should then be made on the roof when the line is secured. The point of the drill may be placed on this mark and the lamp held behind it. If not in line, the drill may be shifted to the right or left until it is. The hole should then be started by pressing upwards and turning the brace. As the point of the drill is apt to slip on smooth rock, as soon as the hole has a grip, another sight should be taken to make sure that the drill is still in line. If it is not in line, a new sight should be taken and a new hole started a few inches away. The hole should be drilled to the required depth and the plug driven firmly home. The point of a spad should then be stuck in the plug near its center with the head hanging vertically and the eye facing the transit. Holding the flame of the lamp behind the spad, it must be moved to the right or left until its point is exactly in line. Still holding the lamp behind it, the spad should be driven firmly home, the blows of the hatchet being inclined so that the head of the spad may be driven to the right or the left as the transitman, who is following the work, may direct. When the spad is driven home, the lamp should be held behind its eye and, with gentle taps of the hatchet, it should be knocked to the right or left until the vertical hair exactly bisects the hole. For many purposes, the alinement is now sufficiently accurate. For important work, however, the plumb-bob should be hung from the spad and the final and exact alinement made by sighting to its point or to the cord. The distance between the old and new stations should be measured and if, in addition, the side notes are taken the work may be placed upon the mine map at once.

The second case arises when a branch or cross-entry is driven from the main entry, either to meet a similar place being driven toward it or to intersect another place at a fixed point. The instrument is set up on the main entry at the point nearest to that from which the branch road is to be driven,

a backsight is taken upon an outer station, and the telescope plunged. The foresight must now be placed not only on the entry line, but at an exact distance, say, 186.27 ft., from the transit. The tape must be stretched in line, and at the exact distance from the station, a pencil mark 3 or 4 in. long made at right angles to the line of sight. This mark may be made on the face of a tie that has been cleaned off, if one is at the right distance; or on a piece of plank made to span the space between two ties. The point of a tack or a brad should be placed in this line and a lamp held behind it. The tack must then be shifted until it is in line and driven home. If the distance the branch road is to be driven is short and the station at its mouth will not be needed again, the instrument may be set over the tack, and after setting the vernier at 0 or at the back azimuth or bearing of the entry line, the deflection angle, azimuth, or bearing on which the new place is to be driven may be set off on the upper plate and upon this line the sight plugs may be placed. The surveyor is recommended to always use the system of reading and recording angles with which he is most familiar, except, of course, when the system is inaccurate.

If the station must be preserved (which is commonly the case), the position of the tack just placed in the tie must be transferred to a permanent station in the roof. To do this, leave the transit as it was after setting the tack. Suspend a plumb-bob from the roof, holding the string in such a way between the thumb and forefinger that when the helper says the point is directly over the tack, a smear of chalk (previously applied to the thumb) may easily be made on the roof. Hold the drill on the mark and have it lined in from the transit. After the bit grips the rock, again line in from the transit and check the distance measurement by again dropping a plumb-line upon the tack. Drill the hole and drive home a plug, which may be of somewhat larger surface area than the ordinary station plug. Draw a pencil line across the face of the plug by joining the holes left by the points of two brads set near the inner and outer edges thereof and which have been lined in from the transit. (These brads need not be driven up, as they are used only for giving the ends of the line.) Next suspend the plumb-bob over the edge of a knife blade (the thumb is too blunt), so that the cord is on the pencil line, and when the helper, by sighting across the point and the tack, announces that they are directly over one another (that is, the distance is exact) make a mark, with a pencil, on the plug. A spad may now be placed in this mark and should be on the entry line and at the proper distance from the instrument. However, before driving it home, check the alinement. After driving home, perfect the alinement by sighting to the point of the bob or to its cord. Some prefer, after the plug is driven up, to suspend the plumb-bob from a spad, which is shifted by the transitman to the right or left until in the line of the heading, and by the foresight man's helper inbye and outbye along the heading line until at the exact distance, after which it is slowly driven up, being checked during the process. By the first method, there is no trouble in placing spads within less than o ft. of the exact spot and any desired degree of accuracy may be obtained by taking time.

Placing Sights. The entries always and the rooms usually, in flat seams, are driven on sights. These sights are a pair of plugs set on the predetermined line about 2 ft. apart in which are driven spads that are set exactly on line. Pieces of coal, iron nuts, or other weights are hung from the spads and before an undercut is made the foreman, miner, or machine runner sights across the strings and marks the center line on the face with a piece of chalk. Under ordinary conditions, sights should be moved up about every 200 ft. of advance in the working face; although this distance may be increased where the ventilation is good and lessened where it is poor. While a pair of sights may be placed near the face from an instrument station 200 ft. or more back therefrom, the better practice is to place a station ahead as just explained. The transit is then moved to this station, a backsight taken as before, the telescope plunged and the two sight plugs placed some 10 to 15 ft. ahead of the instrument, the final alinement being effected by bisecting the two eyes. This makes the survey station independent of the sight plugs and the spad in it is not apt to be pulled out of line, as will be the case if the station is one of the sight plugs. The practical certainty of finding the station in good condition more than repays for the labor of setting the extra plug and making the extra set-up.

While entry sights are commonly and naturally placed in the center of the opening, many consider it better to place them to one side and over, say, the right-hand rail. By so doing, a conscientious track foreman can use them to