(4) Fourth Method. At 614 S backsight on cross-cut plug 604 x.

NOTE: Clamp the vernier to zero and set on the back point, unclamp upper plate and sight to forward point and book the reading as "positive angle."

2. "Clamp the vernier to zero and set on the forward point, unclamp upper plate and sight to back point and book the reading as "negative angle."

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3. Tape distance to back point and book as "back distance." 4. "Tape distance to forward point and book as "forward distance."

"Repeat operation at every point of traverse."

"Distances are taped horizontally, the plumb bob being raised or lowered till approximately on a level with the instrument." "Measure every line twice, first as a forward distance and then as a back distance; if there is any difference take the mean."

(5) Fifth Method.-Main Reef West Drive. 5th April, 1905.

"Set up instrument at say peg 1128 M and set vernier at oo. Clamp spindle on back sight (1127 M) and read vertical angle, say 93° 42'. Unclamp vernier and read angle 1127-1128—1129 which for convenience call x, also read fore vertical as 89° 05'

"Now, plunge telescope, set vernier at o°, and clamp on foresight (1129), and again read fore vertical as 270° 55. If instrument is in adjustment the sum of both fore verticals will be

360 deg. Unclamp vernier and read angle 1129-1128-1127, for convenience called also read back vertical. The sum of each two

readings should be 360 deg.

"Measure both back and fore distances with a steel tape, and calculate horizontal distances. The back horizontal distance at 1128 M should equal the fore horizontal distance previously obtained at 1127 M.

"Measure the length of the plumb bob at 1127, distance of instrument from peg at 1128, and length of plumb bob at 1129.

"Subtract the rail distance (or add for Government levels) from the level of survey peg, and one obtains the rail level at each peg, and thus can work out the grade of track wherever required."

Peg 1005 E is distance east or west of D.M. 100 E.

SUMMARY OF RESULTS.

(a) Use of Instrument. In method (1) it is impossible to determine the use to which the instrument is placed. Checks, if made, are not recorded. Values of quadrants are completely at variance with Government Surveyors' methods in the Colony.

(2) A clear and concise method of shewing what is done. (3) The actual readings are apparently not recorded, and angles are only taken out mentally. Check recorded.

(4) Without footnote it is impossible to determine how instrument is used. No checks of any kind are applied to eliminate errors of instrument.

negative," after

(5) The actual readings are apparently not recorded; angles taken out mentally, called "positive" and transiting instrument. Working from zero point.

(6) No indication of any check being adopted.

(b) Levelling. In method (1), conducted by use of vertical angles and no record of height of instrument, benchmarks, etc.; (2) carries on levels with azimuth readings; correct checks to angular measurements; (3), (4), and (6) use dumpy level; (5) uses angular method without sufficient check.

(c) Measurements. (2) works without decimals, which is clumsy and contrary to Law; (3) works to 3 places of decimals; (4) measures both fore and back sight, which, since he does not carry out his levels, must necessitate adjustment of all plumb bobs to height of instrument in order to serve as check on previous survey of line. This is cumbersome and unnecessary, except at start of survey, to check starting point. (5) measures fore and back distance, but also takes vertical angles, which he reduces to horizontal. Writer recommends only for inclined distances, e.g., shafts, winzes. (6) gives no indication of method of checking.

(d) Other Data. (1) and (2) adopt an off-set method for position of drive, etc.; (3) measures in reef and sketches in drive; (4), (5), and (6) apparently record no such data.

CONCLUSION.

It is hard to conceive that there is such a sad lack of uniformity in the method of procedure. The writer is of opinion that in recording work, all observations should be noted, and not merely the deductions made at the instrument and at the time. In (a), the use of the instrument, full advantage should be taken of the wonderful accuracy of a transit theodolite when used in such a manner as to eliminate errors of eccentricity, collimation, and of the standards. Opinions must vary as to (b), levelling, whether best conducted in conjunction with azimuth readings or by an independent survey with a dumpy level. The writer would not be pedantic and say one or the other should be adopted; he would point out that the former method, inasmuch as he must reduce all distances to the horizontal and so also can calculate the vertical distance before calculating the co-ordinates of any point, will enable the surveyor to be always up to date in the elevation of his benchmarks.

With regard to (c), measurements, individual practice is scarcely disclosed in a study of these six methods. It is highly probable that errors in underground traversing arise from (1) error in centering the instrument, introducing small angular errors, and (2) errors in measurement, due to the use of native assistants and the surveyor's

personal factor, e.g., variable pull on the tape, rather than any errors in the measurement of angles when the instrument is properly used.

Finally, in considering the record of other data (d), the writer is of opinion that, from the way in which the information has been forwarded to him, there is a loose appreciation of this most important part of a mine surveyor's duty. Minute and careful offsetting is, in the writer's opinion, so much waste of time. By noting the position of benchmark, in hanging of drive relative to the track, and sketching in the contour of the drive as the surveyor walks along, say in winding up his tape, a sufficiently accurate representation of the drive can be obtained on the scales of 1:500 or 1:1000, at which most plans are plotted. The intersection of any fault with the drive is noted in similar manner as the tape is being wound up, whilst the fall or rise of reef in the drive is of no import until the reef enters or leaves the drive.

We now come to:

II. METHODS OF CALCULATION.

(1) does not feel justified in giving his method as the representative one of his group. He remarks that he uses Gurden's Traverse Tables and natural sines and co-sines as a check.

This is systematic, but has weak points, in the writer's opinion. The angle measured is only extracted once from the field book; the angle of direction (or bearing) is only taken down once; the addition of co-ordinates is only effected once.

(3) confuses a calculation with the record of results obtained. In other words, this is no form of calculation, and cannot be criticised as such. As a form of record it contains too much; no practical good can come from laboriously copying out forms of logarithms. The plotted traverse is useful, and gives a finished record of the detail sketches made in the field book.