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to be only temporarily located. In case, however, of an accident in dropping an arrow, it becomes doubtful what is the exact number of chains that have been measured, and the position of a peg so placed limits the possibility of an error to a distance of ten chains, and then only this portion of the base line, in which a surveyor has the misfortune to lose an arrow, need be re-measured. Time is a more important element than the cost of labour and material in the use of pegs.

For the purpose of testing the chain employed in an extensive survey during the progress of any work, which will most likely stretch a little every day it is in use, it is well to fix two pegs upon a level piece of ground near a fence, and at a distance apart just sufficient to enable the outside of the handles of a correct chain when drawn tightly to touch the inner sides of the pegs. This arrangement is better than making the chain's length measure from centre to centre of the pegs, but the chain should be pulled quite taut, and the rings cleared of all dirt, and the links straightened, so that the chain may play freely along its whole length. If the chain has been previously pulled over a ploughed field upon a wet day the rings uniting the links will have become clogged with dirt and the chain will need washing, which can be effected by passing it through a stream carefully. The test distance may be set out very accurately with a level staff, or, better still, with two level staves placed end to end in measuring the line, provided each level staff has been previously tested upon the Government standards. It is sometimes well to keep a properly-tested spare chain in reserve, to be used only for the purpose of testing when a level staff is not near to hand, and the distance should be proved prior to each testing of a chain, as pegs have been known to be purposely moved by parties interested in opposition.

No survey can be accurate in which the base lines are ranged in the least degree curved, and in chaining up and down hill by a process called "stepping," as exemplified in fig. 4 (pages 14, 15), the steepness of the slope will regulate the distance between the successive points, P, R, S, as the chain can only be raised to a certain height by hand,

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FICURE 3

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Land Surveying and Leveiling, pp. 14, 15.

ZONTAL LINE

TESTING A CHAIN

FOR STANDARD TESTS SEE FICURES 5 AND 6
30

20

30

20

HILLY CROUND

40

50

$40 OR 60

40

FICURE

THIS DISTANCE MAY BE ACCURATELY SET OUT WITH TWO LEVEL
STAFFS PLACED END TO END AND MEASURED THUS-

(4x 14") + 10° - 66'T

(7x14) 2'100'
(6 x 16)+43 = 100

(4x 16T) + 2'' = 66'T

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NOTE THE OFFSETS WHERE REQUIRED.
ARE TAKEN AT THE PLUMB BOB
POINTS. MARKED P. R.S..

and its top end should in each sub-divided length be held close to the ground. The chain should also be well stretched between the points of sub-division. In chaining downhill a plumb-bob is superior to a dropping arrow, for the reason that the head of such an arrow is liable in falling to displace the point out of the perpendicular. A plumbbob, however, takes longer to manipulate than a dropping arrow, although it can be adjusted with great care. In chaining uphill the follower manages the plumb-bob. In chaining downhill the leader takes charge of it. In either case, at the end of each chain's length, the totals are corrected, by the follower returning all arrows picked up, from intermediate points in a chain's length, to the leader, prior to proceeding with another chain's length.

Tapes. It may be mentioned that there are two descriptions of linen tapes; one is usually known as the metallic tape, and has delicate copper wires or threads interwoven with the substance of which it is composed. The other kind is a plain linen tape without any such additional combination. When really good, either of them may be trusted at any time to half an inch while new, but linen tapes stretch by use in windy weather and shrink. by use in rain. In using a tape in wet weather, or upon any occasion when it gets wet, it should never be rolled up until it is quite dry. Winding up a wet tape and laying it by in its box until it is next wanted, is a certain means of spoiling it. The tape, after being washed, should be coiled loosely up, and after carrying it for a short time in the open air it will be dry enough to wind up. The same remark applies to rolling up a dirty tape. In winding up a tape the box is held in one hand and the portion outside the box is drawn between the first and second fingers of that hand by turning the handle by the other hand. By this means the tape is prevented from twisting as it enters the box or leather case, which is usually of a polished brown colour. (See pages 17-19.)

Metal band tapes are now very much employed instead of chains, as the sub-divisions indicated upon a continuous band are found to remain more accurate than is possible

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Land Surveying and Levelling, pp. 17, 18, 19.

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TAPE

FFSETS WITH A TAPE

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28

B

ARROW

80

FEET

R

100

BASE LINE

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