a hind-chainman, or follower. The more careful and expert of the two should be the follower.

The leader, with the marking-pins and one handle of the chain in his right hand, starts off on the line, drawing out the chain to its full length. Both chainmen now examine it to see that there are no inaccuracies in it, either from bent links or kinks in the rings joining the links. Having adjusted the chain for use, the leader resumes his place, to be directed by the follower, who stands behind the staff at the beginning, and sights to the staff at the end of the line, so that the measurement shall be made exactly along the established line.

To facilitate this (on level ground) and to insure the correct alignment of the pin, at its proper distance, the chain and one pin should be held firmly in the right hand, as represented in Figure 28. While the pin is being aligned, it should be held by the leader as far from the body as possible, so that the view of the flag be left unobstructed. To accomplish this, and at the same time draw the chain to the proper degree of tension, the right arm should be braced against the inside of the right knee.

FIG. 28.

The follower directs, by the simple orders "right" or "left," according as the pin, held as described, is to be carried to the right or left to bring it into line with the flag. When the pin is truly in line, the chain at the same time being drawn straight and taut, the order "down" is given, when the leader bringing his left hand to bear on the top of the pin, forces it vertically into the ground, and resumes his course to the length of another

If, for any reason, the pin can not be driven into the ground, the end of the chain length should be marked by driving the pin obliquely, always at right angles to the chain; if this cannot be done, a cross should be scratched on the ground at the exact point, and the pin laid down with its point at the mark.

After one

or two chains have been

measured, on any line, the leader can, by

"DOWN."

FIG. 29.

་་ ས

glancing back to the station just left, place the pin nearly in the right position; the exact aligning should be left, however, to the follower.

When the distance to be measured is more than ten chains, the pins, when exhausted, should be returned to the leader, the distance noted in a field-book provided for the purpose, and the chaining recommenced at the place of the tenth pin. If but ten pins are used, the follower has then but the hole made by the tenth pin to measure from. For this reason, eleven pins are often used, the eleventh being of different material from the others for distinction, and is used by the follower to measure from when the ten pins are returned to the leader.

71. All distances should be measured horizontally. Hence, when the ground slopes, one end of the chain must be elevated. Each chainman should be provided with a small plumb-line, so that the elevated end of the chain may be held directly over the proper point.

When the raised end of the chain is only two, or even three feet above the ground, it will suffice, in many cases, to use a marking-pin, held lightly by the point, between the thumb and finger, instead of a plumb-line. When the chaining is on a steep inclination, other precautions should be observed.

Suppose the chaining to be up hill. The leader draws the chain out to its full length, as in any other case, and then returns

to within such a distance of the follower, that when the chain is drawn out to that length horizontally, it shall not be too high to be held conveniently.

The follower holds his end of the chain carefully over the point or station, by means of the plumb-line, while he directs the leader in the usual manner.

The point fixed in this manner, by the leader, must not be marked by a marking-pin, but by a small peg or nail. At the order, "Down," the leader does not go forward immediately, but waits until the follower comes up and takes the chain by the precise point held, the moment before, to the ground.

This point is now held above the peg by the the follower, who uses the plumb, as before, and aligns the leader, who has taken hold of the chain a few links farther on, and is holding it to the ground. These short distances are not recorded. The end of a full chain is marked by a marking-pin.

In chaining down-hill, the method is essentially the same. The leader uses the plumb, and determines by it where the peg is to be placed.

At the end of a course, the part of a chain is measured by drawing the chain only to the flag, where it is held by the leader, until the follower comes forward to the last pin, and counts the links.

In measuring up the hill from A to C, or down the hill from C to A, the horizontal distances a b, c d, and f C, are measured and their sum is the horizontal distance between A and C.

B

FIG. 31.

Chaining down hill gives more accurate results than chaining up; for in chaining down, the follower holds the chain firmly upon the ground and no ordinary pull by the leader moves it. It is impossible to hold a chain perfectly steady over a point, by means of a long plumb-line, while the leader is pulling out.

72. When the ends of a line can not be seen, each from the other, intermediate points between the two must be established. When a hill intervenes, such points may be established thus: let the surveyor and an assistant, each with a ranging-rod, place themselves as nearly in the line as possible, and in such position that each can see the other and the flag beyond him. The surveyor looking to the flag at the end of the line, directs the assistant into line with it; the assistant then looks to the flag at the beginning of the line and directs the surveyor into line with it; the surveyor from his new position redirects the assistant into line with the end flag-staff; the assistant then realigns the surveyor with the flag-staff at the beginning of the line; the operation is repeated till both stand in the

desired line, when their positions are marked with the ranging-rods.

73. When a valley is to be chained across, intermediate points in the lower portions of it may be fixed, if necessary, by the surveyor holding a plumb-line so as to cover the flag-staffs at both ends of the line and directing an assistant to fix, between. the two, ranging-rods which shall also be covered by the plumbline.

74. When a wood intervenes between the two ends of a line, a trial line may be run out by ranging-rods placed at convenient distances in line with each other and with the staff at the beginning of the line, and as nearly as possible in the required line. Then draw on the ground a perpendicular (by a method to be shown presently) from the staff at the end of the required line to the trial line just run out, and measure the length of this perpendicular. The ranging-rods may then, by the property of similar triangles, be put in their true position in line. Thus,

AG is to be measured; the trial line AF is run out and the ranging-rods B, C, &c., fixed at known distances apart and as nearly in the line as possible; the perpendicular GF' is measured ; then from the similar triangles, AFG and ABH,

AF: AB :: FG: BH.

The distance BH thus becomes known, and the ranging-rod at B is moved, on a perpendicular to AF, the required distance to its true position at H. The other ranging-rods are in like