CO885-(19-20) — Page 428

PUBLIC RECORD OFFICE

Reference :-

C.O. 885

ALLY WITHOUT PERMISSION OF THE BE REPRODUCED PHOTOGRAPHIC- COPYRIGHT PHOTOGRAPH—NOT TO

20 PUBLIC RECORD OFFICE, LONDON

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Readings. The value of one division of the microscope-scale was obtained from the standard tape and found to be .00075 foot. The readings were made in terms of whole tape-divisions, and micro-scale divisions to decimal points by esti- mation. The tape-divisions were coarse. In the sketch, showing the field of the microscope, the reading booked would be 1, 2.3*.

The effects of friction often caused variations in readings amounting to three or four micro-divisions. Until a method of elimination of this effect, due to Mr. Rimmer, was discovered, five readings were taken at each setting.

Transferring to Ground-When it was necessary to transfer to the ground, the instrument was accurately, instead of roughly, levelled, and a 4-inch x 2-inch picket, about 2 feet long, driven in flush, in correct position. Cross-lines were then cut on the wood under the cross-hairs of the transferring telescope, and a zinc plate nailed on.

Fine cross-lines were then drawn on the zinc in similar manner, and the whole covered over with earth to prevent likelihood of being meddled with. The height of the instrument was measured and the position of the feet of the tripod marked. On resuming work the same instrument was set up in the same position, the plate brought to approximately the same height by the foot-screws and accurately levelled. The telescope was then adjusted to bring the cross-hairs again exactly over the cross-lines on the zinc, and the work continued.

Elimination of Friction.-Examination of the field-book after the first measure- ment showed that readings at each setting in many cases fell into groups, one high and one low. A trial showed that the high reading was obtained by drawing the tape from one end gently in one direction before allowing it to come to rest, whilst the low reading occurred with the tape drawn from the same end in the opposite direction. A motion of the tape at one support is, owing to friction, not fully compensated at the other, so that when one end of the tape is drawn outwards the sag is smaller than that of a true catenary, whilst when drawn inwards it is larger. The mean of a pair of readings taken in this manner gives, therefore, a practically correct value. Six readings were taken at each setting during the second measure- ment, three in each direction, with the result that balanced groups for each setting were consistently obtained.

The readings of the first measurement were, during reduction, as far as possible selected in groups, and the odd ones cut out. The second measurement is on this and other accounts probably more accurate than the first, but in consideration of small errors such as those due to wind, transferring and setting up, alignment and level, it was thought that definite weights could not be assigned to the two measurements. The accuracy obtained and the time taken did not justify a third measurement. Reduction of Measurement.-The reduction was made on a special form, tables having been previously prepared covering all likely temperature and level correc- tions. The result was as follows:-

--

150*+ 2.1095 feet. 150 +2.2424 feet.

Length by first measurement Length by second measurement (Where T - Mean tape length under 20 lb. tension at 13.72 C°.)

Difference 0.1329 feet.

Applying the method of least squares to a case of only two measurements, and taking T as 100 feet, the probable error of the mean works out to 1/340000, nearly.

After deducting the small correction for height above M.S.L. (p. 11), the mean value of the base line reduces to-

150+ 2.173 feet.

(B.) RECONNAISSANCE and BEACONING.

Maps.-The existing maps used were I.D.W.O. 1844 (1904), scale 11.5 miles to the inch, a tracing of the island on scale 6 miles to 1 inch, and one of the Navua neighbourhood on a scale of 1 mile to 1 inch; the two latter were provided by the Lands Department and proved very useful.

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Instruments.-The instruments brought out for reconnaissance were: Plane- table with sight-vane and telescopic alidade, telescope with plate and stand, prismatic compass, field-glasses, and aneroid.

The plane-table was used at Navua on the inner quadrilateral, but its use in the sugar-cane flats and hills covered with dense forest was so restricted as to nullify its advantages. Moreover, in spite of every precaution, the work done on one sheet was spoilt by the effect of mildew and damp on the paper, and its use was therefore abandoned in favour of the telescope and sketch-book. The experience of work in the field has shown the practical impossibility in this climate of protecting sketches done in the field from these effects.

The telescope was of the stalker pattern, packing up in leather case, and had a similar maximum power to that of the theodolite, ie., of 35 diameters. The 3-inch plate with telescope carrier, also carried in separate leather case, could be screwed to the stand. With a pointer fixed to the carrier and a pocket-level, this forms a rough theodolite, which, used with a sketch-book, is, as was my experience in South Africa, a valuable and handy instrument for purposes of simple triangula-

tion.

The prismatic compass has only been used to roughly sketch a hill-top. No influence of iron in the soil has as yet been observed.

A geographical aneroid by Cary, Porter and Son, which could be read by estimation to single feet, was used during the first three months. During some heavy rains in the hills in February, however, the leather case became soaked, and the instrument ceased work. On examination it was found that the hair-spring and all steel pivots had become so rusted as to stop the action of the vacuum-box. This was probably due to some rain-water creeping in through the key-hole. A fresh aneroid has been ordered with better protection against bad weather.

Nature of Country. With the exception of the valleys of the main rivers, Rewa and Singatoka, and the small alluvial areas formed at many points on the coast by numerous minor streams, Viti Levu is a crumpled mass of hills rising to 4,500 feet elevation, and mainly covered with dense forest. There is one road across the island along the Rewa River, and a few coast roads, but the interior is otherwise roadless, except for narrow native bush-tracks. The crests of the hills are usually very steep, whilst innumerable streams, issuing from them, have cut the forest-clad lower slopes into a network of ravines.

Transport. Travelling in such a country is a very laborious business, but there is no difficulty when once the physical obstacles have been overcome, in carrying out a triangulation, nor, so far, has there been any difficulty in obtaining material for beacons. In the Navua flats the reconnaissance of the base-line was facilitated by tramways belonging to the Sugar Company, whilst villages situated within 2 miles of the base-extension points enabled complete camping outfit to be dispensed with. The provision of a cutter also for reaching coast and island points has proved of great benefit, and doubtless will, in the future, repay the expense involved.

But the main difficulty for Europeans of a survey party consists in being able to keep in health for a sufficient period to carry a line through the interior of a country where transport by carriers is very slow, labour delays inevitable, game and food, except native vegetables, practically non-existent.

Labour. The selection of points being comparatively easy, it is probable that, as heretofore, the beaconing of points can be done at the same time as the reconnais- sance. The carrying party hitherto has consisted of 10 permanent Fijian carriers, and an extra 11 men whenever a move is undertaken. The total weight carried is about 1,000 lbs., mainly tents, food, and cutting tools.

The pay and amount of food required by a Fijian are large, the former, 1s. 6d. to 2s. per day, and the latter about 8 lbs. of yam or other vegetables. Hence a full permanent gang of 21 carriers is expensive and difficult to feed. At the same time the villages are small and the disinclination to work is large, so that delays occur in getting extra labour when wanted.

Clearing-Paths have generally to be cut up the top-slopes of hills through thick undergrowth, whilst the actual tops for some 80 yards have usually to be cleared completely, and many large trees felled. The actual site for a beacon is thus often difficult to fix without considerable waste of labour. The clearing of Kadawa (see sketch*) took 10 men nearly two days.

Sketches. When sufficient clearing had been made, the surrounding hills were, as far as possible, sketched in outline and a round of angles taken to back points and all likely forward points. These were entered on the sketches with estimated

Not reproduced.