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PUBLIC RECORD OFFICE

Reference :-

·। ། ། ‛། །། ། mmmmmim C.O.88

18 PUBLIC RECORD OFFICE, LONDON

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

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in time and trouble to the supervising staff of the Colony where they obtain appoint- ments. A fee of, say, £10 would be very well expended by any applicant for an appointment and would also be well earned. I consider that, at any rate in the case of appointments to the Ceylon survey, it would well repay the Colonial Govern- ment to defray this expenditure out of the Departmental funds, as the eventual saving to the Department would be much greater than could be represented by Rp. 150.

When this training is taken up after the usual month at Southampton, which determines finally the appointment of an applicant, he should be put on half salary during the period.

If my idea is approved I would further suggest that those applicants who cannot show such experience in surveying as will satisfy the Colonial Survey Committee that they are competent to carry out surveys without supervision, which is not often the case, should at once be told that they should place themselves under Mr. Hampton for a month and send in a certificate from him as to their qualifica- tion before their application can be considered, while those gentlemen who can, on making an application, submit a satisfactory certificate from him should where possible receive favourable consideration.

I think that by this means in addition to the very full and clear enquiries, both as regards professional and personal qualification, now made through the printed forms of application and personal interviews, that a continual supply of competent and suitable gentlemen will be available for immediate despatch to the Colònies on receipt of an application in your Office.

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I have, &c.,

P. D. WARREN,

Surveyor-General of Ceylon.

No. 143.

EAST AFRICA PROTECTORATE.

NOTES ON VICTORIA NYANZA SURVEY, BY COMMANDER WHITEHOUSE, R.N. (Received in Colonial Office 12 December, 1908.) Method of Survey.

My instructions in 1899 were to make a compass survey of the British part of the lake and report on likely traffic. As compass surveying was found very unsatisfactory, triangulation on 1-inch scale was resorted to. An astronomical base of about 45 statute miles was obtained from Namenya Hill station, in Inyala, to Gembe Hill station, in Kasagunga; from this base triangulation with 5-inch theodolites was carried round north shore by graphic plotting. The triangulation failed in the Sesse Islands owing to bad weather and want of time, the mainland coast from Dumo Point being put in with patent log and compass.

For the southern, or German, part in 1902, the same system was followed, using the same base. Practically no error was found in the Anglo-German boundary 1° south parallel of latitude, obtained in 1900. The triangulation was extended round the south shore and up to Dumo Point on the west coast. The difference by graphic plotting on 1-inch scale in the distance so found between Mohurn station on east shore and Mizinda station on west shore, about 157 statute miles, and as found by the Anglo-German Boundary Commission, who triangulated over my 1900 map of north part of lake, our stations being identical, was '7 of quarter of a mile on 4-inch scale.

On my southern triangulation being calculated by the War Office, using their base instead of mine, ample connection having been made to their survey beacons on both sides of the lake, the distance between the same stations was found to differ 80 feet from the result given by their triangulation round the north shore.

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In the report on my triangulation issued by the War Office, it is stated that observations were made for most part to hill-tops with a theodolite." The observa- tions were made in every case with a 5-inch theodolite. At first, the hill-top, a prominent or the highest tree on it was observed to. On the next hill being reached,

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it was cleared if necessary, the highest tree being left for a mark. The position of the theodolite was marked by a cairn whenever stones were available, and later a second series of observations were made to the actual station, a small tree being cut and placed in the cairn, or a beacon, built over it, if the hill-top was bare. In clear weather the stations so marked could be easily seen 30 miles, while tree marks were observed to up to 80 miles.

On the survey being started, there was no intention of calculating the triangula- tion, the graphic work plotted very well, and later it was known a check could be obtained from the Boundary Commission triangulated points. The staff of the lake survey was never more than two officers, decreased in 1904 to one.

The connec-

tion to the Commission's work was purposely made on both sides of lake for a check, and the graphic method followed gave a result that was practically correct, and fulfilled the object of the survey, viz., to get as quickly as possible a map of the lake for the purposes of navigation.

Had the survey continued, observations for latitude would have proved its positions without reference to the other survey.

Plane Tables were not used in the survey, and very seldom are in any hydro- graphical work. Reference to topography shows that there is very little that could be done with them, while they would be quite unsuitable for mapping continuous coast-line, the majority of the fixing being done in boats, in which, of course, they would be useless. I was pressed several times to use them by the Manager of the Uganda Railway, but they would, in my opinion, have only been useless lumber in already overloaded boats.

Level.

The level of the lake has been taken from the reduced levels of the Uganda Railway, and is placed at 3,726 feet above mean low-water level at Mombasa. Heights of hills were taken with Watkin mountain aneroids, and are shown above lake level.

The zero of the Port Florence gauge was set, and checked several times, 18.08 feet below the masonry bench mark set for reference, near the points of the shipyard siding, and marked 3744.23.

The soundings shown are reduced to a level of lake at zero of Port Florence gauge.

In shallow parts of the lake it is very important that soundings should be referred to this level, as neglect of this precaution may cause considerable expense in harbour works alterations. (See notes on maps.*)

The lowest level of lake registered to date on the Port Florence gauge has been 1 foot 6 inches below zero on 29th October, 1902, and the highest 3 feet 5 inches above zero on 14th May, 1906. The height above level of old water marks on the shores, measured at various intervals, shows that the level may rise to 5 feet 1 inch on the Port Florence gauge, or about 3 inches above the present dock walls, while a strong S.W. wind, usual in the afternoons, would cause another rise of 1 foot.

The level of Port Florence is much affected by wind, and the afternoon level For this reason only the is always with S.W. winds higher than in the morning. morning readings of the gauge were referred to in the lake survey.

Comparisons of level with other spots was obtained by readings of temporary gauges referred to bench marks for the period of survey, compared with the average morning reading of the Port Florence gauge for same period. The difference of level at various places and times was always found to agree with the Port Florence differences.

It is very important that the same system should be followed in any future survey, and proper attention be paid to Port Florence levels, while working else- where; by this means only will the mystification that was caused by the use of gauges without comparison and bench marks be avoided. Attention should also be paid to the result of wind action on the level. The alteration of level is so slow that automatic recorders are quite useless, while its range at present is only recorded up to 4 feet 11 inches, with older watermark evidence up to 6 feet 7 inches.

Most of the bays are shallow, and have a bottom of very soft mud into which a sounding lead sinks easily. In such places correct soundings for detailed plans were obtained by raising and lowering the lead slightly until on its touching the mud, bubbles rose to the surface.

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