IMPORTS AND EXPORTS OF EACH STATE, 1855-6, 1856-7, 1857-8, 1858-9.

The following table will illustrate fully the comparative foreign import and export trade of the State of New-York compared with the other States of the Union, for each year from July 1, 1855, to June 30, 1859:

THE HARBOR OF NEW-YORK AND ITS VICINITY.

From the Report of A. D. BACHE, the Superintendent of the Coast Survey of the United States.

On the Tidal Currents of New-York Harbor near Sandy Hook, by A. D. BACHE, Superintendent United States Coast Survey.

In a former notice of the observations of tidal currents near Sandy Hook I stated the general character of the results obtained, and their specific bearing upon the explanation of the growth of Sandy Hook, and of the changes above and below water in its vicinity. I propose now to describe more in detail the observations themselves, to discuss numerically and by the aid of diagrams the results obtained, and to show from them how the Hook is built up, the False Hook channel deepened, and Sandy Hook bay modified in its shore line, and especially in the configuration of the bottom.

Sketch No. 1 shows the current stations occupied on the outside of the Hook, and in False Hook channel, and the approaches in the different parts of the main ship channel and its approaches, and in the eastern, middle and western portions of Sandy Hook bay.

It will be convenient to discuss the subject under the three divisions already referred to, of (1) the normal currents in the main ship channel and its approaches, of (2) the currents of False Hook channel and the approaches, and (3) the currents of Sandy Hook bay.

1. Normal currents at the entrance to New-York Bay.-Diagram 1 (sketch 2) shows the comparison of the average tidal currents at three groups of stations; the most eastern, comprehending the positions R., R, Q. and H., shows the currents at and within the bar in the vicinity of Gedney's channel; the middle, embracing the stations P., O., I., A., A., lying for the most part between the eastern portions of Flynn's Knoll and the point of Sandy Hook, shows the currents of this part of the main ship channel; while the western group, B. and B., gives the currents for the western part of the main ship channel in the vicinity of the Southwest Spit. Diagram 1 (sketch 2) also exhibits the type form of the tide wave as observed at Sandy Hook. The currents are plotted for flood and ebb, above and below a common axis, which corresponds to the mean level of the sea. These curves are plotted in their true relative positions to the tide wave as regards their epochs.

Table 1 contains the dates, names of stations, localities, luni-current intervals, durations, intervals after the tide wave, velocities and directions of the currents. In this table are given the numerical results from all the stations to which we have referred, reduced to their mean values. In table 2 the averages for the groups are given.

From the first line of table 2 we find that about 56m after the time of high water at Sandy Hook, the ebb current begins to make in the locality

covered by the eastern group of stations running east by south, reaching its greatest rate of about 1.71 miles per hour, (in about three hours,) and then decreasing (in about three hours) to zero, and turning to flood at about 1h 33m after the time of low water, the ebb thus being estimated at 6h 19m. The flood reaches its maximum in about 3h, when its rate is 1.11 miles per hour, running generally northwest for about 5h 43m, and reaching slack water about 56m after the time of high water at Sandy Hook. The times of running ebb and flood are nearly equal. The greatest rates are as 17 to 11, and the average as 10 to 6.

Line 2 of table 2 gives the results from the middle group of stations, from which it appears that in that portion of the main ship channel lying north of Sandy Hook the ebb currents run generally east by south; the flood west by north. The ebb has a less velocity, and the flood a greater, than for the eastern group. The maximum velocity of ebb is 1.49 miles per hour, and of flood 1.68 miles; the mean velocity of ebb 1.09, and of flood 1.04 miles. The reason of this change of proportion between the maximuin and mean velocities of the ebb and flood currents is obvious from an inspection of the type curve. It will be seen that the ebb is

characterized by a uniformity of rate during the second, third and fourth hours of its existence, while the curve for the flood resembles the curve of sines. The ebb current turns earlier, lagging but 22" after low water; thus turning more than 30m before the corresponding currents to the eastward. The 3d line of table 2 shows the results for the westward group in the vicinity of Southwest Spit. Here the currents have a course round the compass, are much less rapid than the other, and are earlier.

It would be curious to know where the earliest turning of the current is to be found; and, indeed, these results open up many questions in regard to the whole bar and the channels through it. For our present purpose we have limited ourselves to obtaining the means of comparison of the normal currents sweeping by the point of Sandy Hook with those secondary ones which we shall next proceed to trace.

2. False Hook Channel and the Approaches.-The results from the current stations S., T., C., D., G., F. and V. (see sketch 1 and table 3) show the movements of the water in this channel and its vicinity. Stations at E. and "off Long Branch" lie quite to the southward. S. shows the action of the northern entrance and V. at the southern; C. in mid-channel. T., at the entrance, is influenced by the shoals of the False Hook; G., F. and V., between the ocean and False Hook channel, are unsatisfactory; D. shows the shore currents of Sandy Hook.

The results from these stations are given in table 3, which is constructed in a manner similar to table 1, already described. Treating S., T., C., F. and G. together as a group, we have for the luni-current interval 8h 20m, or 58m after the time of high water at Sandy Hook for the commencement of ebb, the current of ebb beginning earliest at S., G., T., the flood first at F., S., T. The interval of ebb is about the same as that of the vicinity of Gedney's channel; the flood three-quarters of an hour earlier. This gives above a half hour for the differences of duration between the main ebb and flood, and the corresponding ones of this part of the ap

proach to New-York harbor. The currents at stations T., S. and G. are plotted upon the diagram 2, sketch 2.

The mean epochs (table 4) are 8h. 14m. and 14h. 02m., being 17m. and 46m. less than those found in the vicinity of Gedney's channel. The flood exceeds the ebb about 24m., whereas for the stations near Gedney's channel the ebb exceeds the flood by about 34m., and in the South channel the ebb has greatly the advantage both in duration and velocity. This shows the influence of the secondary or draught currents through the False Hook channel.

The average maximum velocity at these stations of both flood and ebb is 1.41 miles, which last, in the vicinity of Gedney's channel, was 1.71 miles. The mean velocity of the ebb is but 0.91 miles, which was 1.03 miles for the stations near Gedney's channel, and about the same at station S.

The ebb makes out but slowly through the False Hook channel; the maximum velocity of the flood at C. is 1.62 miles, and of the ebb but 0.78, and the means 1.02 and 0.50 miles per hour. The time during which the ebb runs is 5h. 41m., and the flood 7h. 08m., a difference of 1h. 27m., and this in the axis of the stream. As the scouring action of these currents may be regarded as varying with the product of the square of the mean velocity and the duration, we have for station C. the ratio of about 1 to 5 for the relative work of ebb and flood. At the edge of the False Hook shoal the duration of the ebb appears to be even less, there being but 5h. 20m. of ebb. The currents at C. are plotted with the tide wave on diagram 3, (sketch 2.) It appears that the curve representing the flood drift approaches the type form while the ebb is anomalous—it is weak and inconstant.

We are now prepared to find the shore currents such as the observations prove them to be. The results at station D., off the wreck of the brig Commerce, are shown in diagram 4, (sketch 2,) where they are compared with the tide wave of July 18. The flood runs for 7h. 15m.

out of 12h. 42m. The greatest velocity of the flood is 1.23 miles against 0.62 of the ebb. The directions are nearly opposite. The currents "off Long Branch," at station E., at station D. and at station 9, near point of Sandy Hook, are shown on diagrams 4 and 5, (sketch 2.) The ebb currents are quite feeble in both. It is the shore current, just discussed, which transports materials to the end of Sandy Hook; it is the grand current, in fact, which makes the False Hook channel; and the False Hook occupies the debateable ground between the outside and False Hook channel currents at certain times of tide, and is built up by the slackening ebb. In this point of view the shoal tends to restore equilibrium. The difference of action of flood and ebb is defined by this shoal. At station V., on the southern extremity of the outer middle ground, and in close proximity to the lower entrance of False Hook channel, the currents are feeble, and an equilibrium of ebb and flood drifts seems to be established. It would appear that the scouring action of the tidal currents is insufficient to keep the bar of this channel open.

It is the material carried along the outer shore of Sandy Hook, and deposited at the point, which chiefly causes the growth of the Hook. Whenever it shall be considered desirable to limit this increase, it will be easy to do so by a series of jetties so placed as to arrest the movement

of the sand to the northward, successive structures stopping the material which may pass round the point of the more southwardly jetties.

3. Currents of Sandy Hook Bay.—To obtain a clear idea of the tidal currents of Sandy Hook bay, let us suppose it divided into three sections -eastern, middle and western-and ascertain the relations of direction at successive periods. To this end we arrange the results according to the twelve tidal hours, calling the epoch of low water Oh., the epoch of high water, 6h., &c.

The flood current commences in the main ship channel and in Sandy Hook bay at nearly the same period, viz., about Îh. 04m. after the time of low water. The water of the main ship channel now flows to the westward, that of the eastern section of the bay to the southward, that of the middle to the southwest, and that of the western section to the west. This general condition continues for about two and a half hours, and is exhibited upon diagram 1, (sketch 3.) It will be noticed upon this diagram that a limited region about the point of Sandy Hook is subject to a counter drift or whirl. This whirl is increasing in size, and its axis is moving southward; its existence is due to the lateral draught produced by the strong and steady stream of the ship channel, to which we shall refer hereafter. At 3h. the effect of this lateral draught on the castern section is already seen in the slacking up of the currents, and at 4h. it has completely reversed the direction of the drifts. At this period (4h.) the conditions are exhibited by diagram 2, (sketch 3.)

The currents are northward (with velocities of 1.4 and 0.3 miles per hour at stations near to and more remote from the main ship channel) in the eastern, southwestwardly (with velocity 0.3) in the middle, and westwardly (with velocity 0.4) in the western section of the bay, while the current of the main ship channel, now at its maximum, holds a course due west, with a velocity of 1.9 miles per hour. At 5h. this whirl has extended to the middle section of the bay, reversing the currents of that region. (See diagram 3, sketch 3.) Its axis still moves to the southward, and at 6h. there occurs a space of slack water, near the point of Sandy Hook, where we at first noticed the existence of the whirl that we have followed. The currents are now diminishing rapidly in the main ship channel, as well as in the western section of the bay, and at 7h. we find the ebb current prevailing. At first the course of the ebb currents of Sandy Hook bay may be represented by straight lines converging to a point, in the ship channel north of Sandy Hook, but these lines of direction gradually curve to the southward, until, as in diagram 4, (sketch 3,) which represents the conditions at the 9th hour, the waters of Raritan bay press into Sandy Hook bay, then, escaping along the shore of Sandy Hook, rush into the ship channel, causing a rip and counter drift at the point of the Hook. At this time (9h.) the current of the main ship channel runs east, (velocity 1.3 miles per hour;) that of the eastern section of the bay north, (velocity 0-5;) that of the middle east by south, (velocity 0.5,) and that of the western east by south, (velocity 0.2.)

The point of greatest curvature, in the sweep of the ebb drift through Sandy Hook bay, moves continually to the westward, as will be seen by comparison of the conditions at 9h. and 11h.-(See diagrams 4 and 5,