PUBLIC RECORD OFFICE
Reference :-
TTL C.O.885
ALLY WITHOUT PERMISSION OF THE BE REPRODUCED PHOTOGRAPHIC- COPYRIGHT PHOTOGRAPH-NOT TO
18 PUBLIC RECORD OFFICE, LONDON
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superintendents to be employed as heads of parties should be fixed at one-tenth of the number of surveyors, making a present total of 15. To these must be added the men wanted for special work, which may be reasonably put at two for levelling and two for triangulation, thus giving a total establishment of 19, an increase of nine. It is recommended that five of these be appointed at once and four more next year.
There is at the present time no grade surveyor qualified for promotion. The levelling and triangulation hands will only be wanted for a few years, so on the completion of the work their posts can be absorbed, unless in the meantime it is decided to add further topographical or block survey parties. The proportion of one assistant superintendent to 10 surveyors, apart from those required for special jobs, should be strictly adhered to in the event either of an increase or a decrease of the total Survey staff.
The requisite qualifications of men selected for these appointments are set forth in the letter of the Surveyor-General, enclosed with Sir II. Blake's despatch to the Secretary of State, No. 568, of 8th November, 1906. It may, however, be added that at the salary offered, with the chance of rising to the highest ranks in the Department, there should be no difficulty in obtaining young men with University degrees and with first-class general and mathematical education In such cases any speciał technical knowledge need not be insisted upon; men of this character would very soon acquire the necessary practical experiênce and would be ideal recruits for the Department.
It does not fall within the province of this report to express an opinion as to the desirability of making any general enlargement of the Survey Department. such a question can only be decided by those in touch with the finances of the Colony. the urgency of land settlement, the probability of data being required for a com- pulsory registration of titles or for the imposition of a land tax and other cognate questions. It may, however, be laid down as a fixed principle that all additions to the staff should be made in the form of complete survey parties, cach comprising:-
1 Assistant superintendent.
2 Grade surveyors.
8 Supernumerary or temporary surveyors.
The only exceptions to this are the cases of isolated men required for application work and demarcation parties required for settlement under the Waste Lands Ordinance. This point will be further dealt with under its proper heading.
At the present time, owing to the shortage of assistant superintendents, grade surveyors have been placed in charge of parties. It is undesirable that this should be continued, nor would it be necessary if the numbers are brought up to the proper proportion as now proposed.
Triangulation and Levelling.-Up to the date of Sir T. Holdich's visit in 1897 the whole question of the principal triangulation of Ceylon was in a state of great confusion. In that year, in accordance with Sir T. Holdich's recommendation, Mr. A. E. Wackrill was appointed Superintendent of Trigonometrical Surveys, two European assistants were put under his orders, and he carried out a laborious recomputation of all the existing work. The method adopted for these calculations was ingenious but unorthodox, though it is probable that the final results thus obtained were as accurate as could be derived from materials of the imperfect nature available. In any case it may now be assumed that the horizontal co-ordinates of all the principal, and a large number of the secondary, points are known with all the precision requisite for mapping purposes. The final chain of secondary work along the north-east coast, connecting the principal chain near Trincomalee with the northern principal chain, was completed in May, 1906. This is not yet com- puted, a task which should be proceeded with and completed at an early date.
While the horizontal positions of these points may now be taken as finally determined the same is unfortunately not true of the vertical co-ordinates or heights of the stations above mean sea-level. The observation of the vertical angles, which should normally form part of the ordinary routine of triangulation, has been much neglected, so that there are, even at this date, no points on the island of which the heights are known with sufficient precision to form initial or datum points for running contour lines. This is a most unfortunate omission, and it is absolutely imperative that it be remedied at once. There are two methods for accomplishing
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this between which choice must be made. Either a large number of the trigono- metrical stations must be re-occupied and reciprocal vertical angles observed or lines of levels must be run across the island, preferably along the main roads, and bench marks established at frequent intervals. For several reasons the second course is preferable. Firstly, to re-observe from the trigonometrical stations would involve the rebuilding of a number of beacons and, in many cases, of the expensive platforms required to raise the observer above the tops of the forest trees; secondly, the accuracy of levelling is substantially superior to that of the method of vertical angles; and thirdly, even were all the vertical angles observed and the heights of the points computed, it would be none the less necessary to run the level lincs along the roads and cut the bench marks. The latter are required not only for the immediate purposes of the survey but also for many questions connected with irriga- tion works, new railways and roads, so that apart from their usefulness as data for the topographical mapping, it may be fairly said that the establishment of these bench marks and their final fixation, referred to mean sea-level at Colombo, is one of the most pressing duties now facing the Survey Department. Some progress has been already made in this work; 150 miles of road in the north were levelled during last year and about 120 miles had been previously accomplished in the Eastern Province, starting at the mean sca at Batticaloa. Before either of these lines can be finally computed they must be connected with datum at Colombo. The work for the present has been discontinued for want of staff.
It is recommended that two men, of the rank of assistant superintendent, be appointed for its completion, a task which should occupy about five years.
The geographical co-ordinates of Ceylon cannot yet he considered as finally fixed, the latitude of Colombo having still a residual uncertainty of three seconds of arc. This should be re-observed. The longitude can be accepted. The arcs Madras- Colombo and Madras-Jaffna were determined by interchange of telegraphic signals in 1871, so that the longitudes of Colombo and Jaffna can now he re-adjusted to conform with the latest position of Madras as fixed by the Survey Department of India.
There is still a large amount of secondary triangulation required for the purpose of "breaking down" the large triangles and providing points for the topo- graphical and block survey parties. Some difficulty has hitherto been experienced in keeping this sufficiently ahead of the detail surveyors, a defect which it may be confidently anticipated will disappear when the proportion of men competent for this work, i.e., men of the rank of assistant surveyors, is increased. In the particular case of the topographical triangulation there has been delay in the past owing to the altogether excessive number of points which have been fixed by the triangulators, one point per each 16 square inches on the paper, or, say, 20 points per plane-table board (171 by 174 inches), may be taken as ample for the requirement of the topo- graphical sheets in ordinary country. Even when the work is thus limited it is not practicable for the detailed triangulation to be carried out by the officers in charge of the topographical parties, and a special triangulation party, of two assistant superintendents, should be formed, working continuously a full season ahead of the plane-tablers. As will be seen below, the area covered by the latter each season may reasonably be estimated at from 1,500 to 1,800 square miles. To cover this area with triangulation, involving the fixation of at most 480 points, is just within the capacity of two men.
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The instruments hitherto used for this class of work have been generally 5-inch Vernier theodolites, reading to 20 seconds of arc, with which the "repetition-are system of observation has been adhered to. The justification for this method of observing depends upon whether the cross wires can be set upon the distant signal with a higher degree of precision than that with which the verniers can be read. This is probably the case with these particular instruments. They are, however, hardly good enough for the work, and greater accuracy, combined with equal or even increased rapidity of observation, could be secured by the substitution of 5-inch micrometer microscope theodolites. The immediate purchase of three of these instruments is recommended. With these the repetition system of observation will naturally be dropped and the ordinary method adopted. Four readings of each vernier on each of two zeros for secondary points and two of each vernier on each of two zeros for intersected points may be taken as the standard practice. Computa- tion should invariably be executed in duplicate.