XXIV.

SUCCINCT REVIEW OF THE OBSERVATIONS

OF THE TIDES IN THE INDIAN ARCHI-
PELAGO.

MADE DURING THE YEAR 1839 BY ORDER OF HIS EXCELLENCY THE GOVERNOR-GENERAL OF HIS NETHERLANDISH MAJESTY'S POSSESSIONS, 20TH OCTOBER 1838. NO. 3.

["Journal of the Asiatic Society of Bengal,” vol. x. (1841), pp. 302-316.]

[THIS interesting report was transmitted to the Asiatic Society by the Society of Arts at Batavia. It has been translated for the Journal from the original Dutch by my friend Dr. Röer.]

The tides have been observed at Pulo Chinco, on the west coast of Sumatra, to the southward of Padang, from February 10, 1839, to January 1, 1840, being ten months and three-quarters, by the naval lieutenants of the second class, G. J. Fabricius and J. de Hoon.

At Muntok, on Borneo, from January 15, 1839, to January 1, 1840, being eleven months and a half, by the naval lieutenant of the second class, P. C. Keuchenius.

On the island Onrust, near Batavia, from January 1, 1839, to January 1, 1840, being twelve months, by the naval lieutenant of the first class, Director of Onrust, J. Sigtorel.

At Tagal, on the north coast of Java, from January 1, 1839, to January 1, 1840, being twelve months, by the naval lieutenant of the second class, F. J. E. Van Gorcum.

At Klampies, on the north coast of Madura, from February 10, 1839, to January 1, 1840, being eleven months and three-quarters, by the naval lieutenants of the second class, J. A. K. Van Hasfelt and J. Van Gool.

At Chilichap, on the south coast of Java, from January 1, 1839, to January 1, 1840, being twelve months, by the naval lieutenant of the second class, J. A. G. Rietoeld.

To these have been added some less complete observations on Amboyna, from March 23, 1839, to January 1, 1840, being nine months and a quarter, by the master, J. Keeutebol, and the naval lieutenants of the second class, J. A. Kieffer and J. A. W. High.

At Japara, from the commencement of May 1835 to the close of December 1839, by the assistant resident of Japara, Winkelman.

Also on the Coriman Islands, from July 18, 1838, to April 1839, by deputy of the civil service, Michalosske.

These two latter observations were forwarded by the favour of the Batavian Society of Arts and Sciences, which had already previously made (at the request of Prof. Whewell, Trinity College, Cambridge) some communications with regard to the tides in this archipelago, to the Asiatic Society in Calcutta ; besides these, there were some observations made at Macassar in the year 1840, by the master in the navy, E. Lagto, after they had been finished at the other stations.

These observations furnish the following results concerning the respective stations.

At Pulo Chinco, west coast of Sumatra.

The course of the flood tide and the rise of the water on the coast was observed to run from N.E. to S.W., closely following the direction of the coast.

The ebb tide ran in the opposite direction, and though both. were very trifling, not exceeding a quarter of a mile, yet the force of the ebb generally exceeded that of the flood, though neither were sensibly influenced by the wind.

The tides were, however, very regular. The mean duration was about six hours and a quarter, so that, as usual, there were two tides in a day.

At new and full moon the high water was generally between 5h. 30m. and 6h. 30m.-viz.:

average time about 600, and the time of flood tide during the other days followed the common rule, dependent upon the moon's passing the meridian, according to which, though not always with the same regularity, the tide came in every day generally about three-quarters of an hour later; or rather, in the course of a fortnight the variation amounted to twelve hours. If, then, six hours be supposed as mean number, it was almost always flood tide when the moon was in the horizon.

From the time of high water to the time when it again turns to ebb, as is here noticed, we may be allowed to fix 5h. 30m. as the mean number.

The mean rise and fall was about ebb

78

The difference in the elevation of the succeeding tides is remarkable-viz., a greater rise and a smaller one were perceived to take place alternately, and in the same manner also the ebb tides.* This alternation of flow and ebb, which is very regular, may here, after be shown to be in connection with the moon's decrease, though perhaps more so at this place than at the other stations of the archipelago.

The greatest difference between high and low water, as well as the highest rise, occurred in October and November, and generally in the months when the west monsoon prevails.

At Chilichap, south coast of Java.

On the south coast of Java the tides were most regular in all respects; consequently the observations made upon them are best adapted to furnish a general rule.

The course of the flood tide was to the west into the outlet, and followed the direction of its shore. The ebb tide ran in an opposite course. In the westernly passage or creek of Segara Anakon the tides had a course quite the reverse; here the streams met, consequently the rise and fall took place without stream. In general the stream appears to run, at least in the east monsoon, along the coast to the east, at the rate of half a mile in four hours. In the straits of Chilichap, in the west monsoon, the ebb and flood tides ran at the rate of two and three miles, and in the east monsoon at five and five and a half miles. The tides evidently follow here, as well as at Pulo Chinco, the common rule. The mean duration of rise and fall was about six hours and a half, and this took place with much regularity, two tides in one day; but also smaller rises and falls between the usual ones have been sometimes noticed, amounting to o 20 ebb. The duration of still water is here very regular for ten or fifteen minutes after high and low water. The ebbs and floods are about equal in force and duration. At new and full moon the mean time of the flood tide was between eight and nine hours-viz.:

and therefore, as the time of flood tide is noticed to the moment when the water again commences to decrease, we may fix here, as mean number, 8h. 30m., considering that here also the period of the flood tide during the fortnight passed the space of 12h.

* A nautical friend has pointed out that night tides are generally the highest, thus giving an alternation."

At this station was observed the same remarkable fact as at Pulo Chinco, that at new moon it was high water an hour later than at full moon.

The mean rise and fall of the water was 1.25 ebb.

the greatest 2°42

the smallest o'10.

The greatest difference in the rise and fall of the tide took place some days after the new and full moon, not, however, exceeding 2.63 ebb. The highest water mark was observed in the east

monsoon.

The difference of the rise and fall of the succeeding tides is here very notable, and appears more than elsewhere to be in connection with the decrease of the moon. The morning and evening tides are different, especially at the decrease of the moon, while they were about equal at the time of the moon's passing the equator.

At Amboyna.

Although the streams in the bay are not strong, and sometimes only run from two miles to two and a half, and the turns of the tide very irregularly take place, we may state that the stream of the flood tide in the east monsoon runs into the bay along the northern coast to the E., and runs out along the southern coast to the S.W. The opposite course takes place in the west monsoon, while in the middle of the bay little or no stream is observed.

The duration of the rise and fall of the water is here very regular about six hours and a quarter; so that the flood occurs about twice a day, and in a fortnight loses about twelve hours. At new moon the mean time of high water was about

The month of December makes an exception to this, and might encourage the supposition of another mean number during the west monsoon, unless the observations made in that month exhibited a want of accuracy, on account of which they are not to be relied on.

At new moon here also, as well as at Chilichap and Pulo Chinco, the flood tide appears to come in always later than at full moon.

The smallest rise observed at several places was scarcely perceptible. A small rise was alternately taking place with a great

one, and the same occurred with the fall. The difference of the succeeding rises and falls is here likewise deserving notice. The greatest difference between high and low water took place in April and July.

The highest water mark was in April, November, and December. These remarks are made on observations taken during the period from April to December, and especially during the east monsoon.

At Klampies, on the northern coast of Madura.

It appears from the observations that were made that there was no flood or ebb stream perceptible during the east monsoon, and in the month of May the stream had always during the day a westerly direction, with the velocity from two miles to two and a half, while at night little or no stream was observed; it sometimes likewise ran to the east; the month of July forming the only exception to this, when in the night also the stream ran to the west, with a force of about two to three miles. In this monsoon the water is generally falling during the day, and the stream then strongest, while during the night the water is generally rising; the stream, however, has little force.

These facts suggest the inference, that if ebb and flood tides here actually exist, the ebb tide has a westerly direction, while the flood runs to the east; this latter, however, is almost annihilated by easterly winds. In the west monsoon the stream runs to the east with little force, and the water rises during the day; the flood stream should accordingly run in this season to the east; but then at night scarcely any stream is perceived, and the ebb tide which then runs was observed to be annihilated by the westerly winds.

The mean duration of the rise and fall of the water is during the whole year eleven and a half to twelve and a half, so that here ebb and flood occur only once in the same day; nevertheless, it appears that here often little rises and falls, or those called short tides, have obtained alternately with them. It is worth noticing that during a certain period the flood tide always took place before noon, and during the remainder of the year in the evening -namely, in May, June and July the time of flood tide was daily in the morning about nine o'clock and one o'clock in the afternoon, without regular yet constant retardation; this period from