CO882-(3-4) — Page 524

Method of observing. Floats put in nt 2 hourly

intervals, and sul- sequent positions determined

Tide gauge recorded. Method of recording results,

reference to

tide curves for the day.

Nature of long Kong tides.

Similarity to

5. The floats or drags were put in at the points of proposed outfall, successively at intervals of about two hours, and their subsequent positions determined as often as possible during the remaining daylight hours (if they did not run ashore, get foul of shipping, or get stolen). Meanwhile, half-hourly readings of a tide gauge were taken at the Dockyard Pier. These were also continued night and day until my departure to ascertain mean sea level, and to furnish data for predicting the tides for the future. 6. The results are shown on the drawings, each of which contains a day's work. coloured lines shows the paths described by the floats, and the figures show the hours at which they occupied the positions indicated by the small circles. The tidal curves for the day is also shown on each sheet.

The

The path of the float during rising tide is shown in full lines, that during falling tide

in dotted lines. The successive colours-blue, yellow, and red-show those parts of the path which correspond to periods of rise or fall, marked in the same colours on the tide

curve.

7. On plotting the tide curve, from the observations taken at the dockyard, it became apparent that the tides of Hong Kong resemble those of the Indian Ocean, in that the semi-diurnal inequality is great. A large morning tide is followed by a small afternoon tide, or vice versa.

Sometimes, indeed, the second tide disappears wholly, so that there is a rise or fall, Semi-diurne lasting for nearly 18 hours.

tides of

Indian

Ocean.

inequality.

During the part of the year when the observations were taken the morning tide is Observations small, so that observations on the rising tide unduly preponderate.

must be

taken in

second half

of year,

Monsoon

will probably

be found to

live little

effect on

tirles which depend on Kolar and Junar

To complete the investigation, therefore, another set must be taken during another part of the year, when the morning tide is greatest, for I need hardly say that it is practically impossible to make these observations at night. With a steam launch and three guard boats it needed the utmost vigilance to keep all the floats in sight.

8. I would here observe that the monsoons will almost certainly be found to have little or no effect on the height of the tide (not the surface drift), which depends almost wholly on the relative movements of the sun and moon. Were it not so, the tides of the Indian ports could not be predicted, as they are year after year, within an inch or two as to height, and within a minute or two of time, from these elements alone, and without any regard to monsoons.

It merely happens that the combinations of the sun and moon producing extremely motions only. high or low tides takes place during certain states of the monsoon.

9. I have the highest authority for saying that the tides of Hong Kong closely resemble those of the Indian Ocean, and that, like them, they may be predicted with accuracy, and further, that the "elements" for prediction may be computed, with tolerable accuracy, from the observations in my possession.

Considering the great value that this information will be, not only to the Government engineers, but to the seafaring public at large, I think it would be most desirable if the Government would incur the trifling expense involved in the investigation of the data and the preparation of the tide tables,

PUBLIC RECORD OFFICE

Reference:-

C.O. 882

4 PUBLIC RECORD OFFICE, LONDON ALLY WITHOUT PERMISSION OF THE BE REPRODUCED PHOTOGRAPHIC- COPYRIGHT PHOTOGRAPH—NOT TO