61

bearings of the adjacent stations are obtained, and thus successively the bearings
between all the stations. The difference of
bearing between any two adjacent stations
is an angle of the rectilineal figure formed
by the traverse. If then the so deduced
bearing from the last station of the tra-
verse to a second Trigonometrical Station
arrived at differs somewhat from the correct
bearing as obtained by resetting the instru-
ment when on this second Trigonometrical
Station to the former one left or to any in
view, this difference will exhibit the amount
of error committed in the measurements of
the interior angles of the rectilineal figure
before alluded to. The best method of
expunging these errors is by equal dispersion
throughout the traversed stations, and
their limit should be confined to one
minute for every two bearings.

Manner of preserving an uniform meridian.

51. Care must therefore be taken to ob-
    serve as many of the traverse stations as
    can be seen from the trigonometrical points
    so that by constantly referring back to such
    data for correction the dispersion of errors
    may be limited to their proper precincts;
    and also in depressed localities such as
    ravines and beds of rivers and streams,
    where stations are liable to become numerous,
    long bearings should be thrown from
    point to point near to the traverse for constant
    and convenient reference, to preserve
    the uniform direction of the meridian.

Detection of errors in the Chain Measure-

ments of a Traverse.

52. If the above rules for preserving an
    uniform meridian throughout the traverse
    have been strictly attended to and provided
    the distances have been fairly chained, the
    sum of northing and southing, or of easting
    and westing by traverse will be found to
    coincide nearly with the trigonometrical
    values in the case of a traverse performed
    between two points fixed by triangulation
    or to closely balance in instances when the
    traverses check by closing circuits. If the
    errors exhibited lie within the limits stated
    in paragraph 49 they may be apportioned
    amongst the several distances according to
    the following rule: as the sum of all the
    chained distances of the traverse is to the
    whole error in northing and southing or
    easting and westing respectively, so is each
    chained distance to its correction, additive
    or substractive from the particular northing
    or southing, easting or westing between the
    two stations, and then the sum of the
    meridian distances so corrected will agree
    with the check data.

Cases in which this system of Traverse may

be modified.

53. When all the co-ordinates on the
    meridian have been referred to some one
    point on the survey, they afford an easy
    method for the deduction of the bearing and
    distance between any two of the points, and
    thus great facilities are acquired for setting
    off and running intersecting lines at certain
    intervals apart, to represent the divisional
    lines of the general purchases or applications
    for land. But when the object of the tra-
    verses is simply to delineate the course of
    streams and other features forming what
    may be termed indefinite boundaries in
    order to compute the areas of blocks,
    but without requiring to base thereon the
    dimensions of definite boundary lines or of
    sectional sub-divisions, then the same
    amount of accuracy is not sought for, and
    it will only be necessary to plot the traversed
    stations by the ordinary method of
    protraction.

Standard length of chain to be obtained from

the Survey Office, and its uniform length
preserved during survey operations.

54. The instrument used for traversing
    is generally a 4-inch theodolite. The length
    of the chain used is a subject of primary
    consideration; the correct standard length
    as obtained from the Survey Office, must
    be carefully preserved by laying down blocks
    to mark this length on the occasion of every
    shift of camp, and the chain should be
    tested with this measure after every day’s
    work. The neglect of this precaution causes
    a vast amount of inconvenience besides
    making use of a wrong measure, which in
    itself is a very reprehensible proceeding;
    and should this measure be constantly
    varying all efforts to test the accuracy of
    the work become unavailable notwithstanding
    the care that may have been bestowed
    in its execution, and thus the survey is
    rendered incapable of being harmoniously
    combined with other surveys.

Reduction of lines measured over uneven

surfaces to the horizontal measure.

55. The dimensions of all lines are to
    be given as if measured on the horizontal
    plane, and the area of land is to be com-
    puted on the same basis. The measure-
    ments of lines, therefore, over the surface
    of hills and slopes of various inclinations
    require to be reduced to the horizontal
    measure, either by calculation or by the
    more practical method of holding the chain
    or part of it at a time as nearly horizontal
    as may be judged and letting a plum line
    fall from the elevated end to the surface of
    the ground.

Field Book.

56. The field book is to be paged and
    indexed, and should be kept in a neat and
    explanatory manner, the reverse case being
    a sure indication of carelessness and neglect.
    Memoranda are to be entered in pencil at
    the time and place of observation, and are
    not to be entrusted to memory nor noted
    on slips of paper, as such are liable to be-
    come lost, and thereby entailing the necessity of going over the work again.