Against each part draw the appearance of the land marked in the sketches, distinguishing the rocky shore, highland, beach, &c., as in Plate V. or VIII. Thus the sand beaches may be marked as in Plate VIII. figure 8, and the rocky shore as in figure 9, &c. Put in the several soundings, at low water,* in small figures, distinguishing whether they are fathoms or feet. Show the time of high water, on the full and change days, by Roman figures, and note the rise of the tide in feet. The direction and velocity of the flood tide are to be observed; which may be done by heaving the log when the ship or boat is at anchor, and the direction is to be represented by an arrow. Insert a compass and a scale of miles or leagues, such as the vessel's run was laid down by. Add the name of the place, and the latitude and longitude, as true as can be obtained.

If there are shoals or sands on the coast, let them be observed in a boat, sailing round them, keeping account of the courses, distances, and soundings. But to put them in the draught, the observer in the boat must take the bearings of two points on the coasts (the bearings of which have been taken from the ship) from some part of each sand or shoal so sailed round; or the bearing of the boat at some part of the shoal, or of some beacon in that place, must be taken by the ship at each of the stations where the bearings of the shore were taken from the ship; for by either of these means, one point of the sand being obtained, the rest of it can be laid down from the observations taken in the boat. Rocky shoals may be marked on the chart as in Plate VIII.figure 11,and sand-banks as in figure 10.

If the coast be a bay or harbor, winding in such manner that all its parts cannot be seen at two stations, let as many bases or lines be run and measured exactly as may be found necessary, observing that the several distances run should join to one another, in the nature of a traverse, that each new set of objects or points observed should be taken from two stations at the ends of a known distance, and that the objects whose bearings are taken do not so much extend beyond the limits of the base as to make angles with it less than about or of a point, but rather reserve such objects for the next measured base line; for when lines lie very obliquely to one another, their intersections are not easily ascertained.

If any particular parts of the harbor cannot be conveniently seen from either of the stations, take the boat into those places; having well examined them, and made sketches thereof, estimating the lengths and breadths of the several inlets, either by the rowing or sailing of the boat, take as many bearings, soundings, and other notes, as may be thought necessary; then annex these particular views, in their proper places, in the general draught.

If there are any dangerous sands or rocks, besides inserting them in their proper places, you must see if there be any two objects ashore (such as a church, mill, house, noted cliff, &c.) which appear in the same right line when on the shoal, and these objects must be noted on your chart. If none can be found, you must take the bearings of some remarkable points, and note them on your chart. By this means we may know how to avoid the danger.

We must mark in the draught the kind of bottom obtained in sounding, whether mud, sand, shells, coral, rocky ground, &c.; and where there is good anchorage, draw the figure of an anchor; also, if there is any particular channel more convenient than another, it is to be pointed out by lines drawn to its entrance from two or more noted marks ashore.

The positions of objects, taken by a magnetic compass, being liable to great uncertainties, as is well known to those who have had any experience, especially at sea, it has been recommended to observe only the bearings of the station-lines by the compass, and then measure the angles which the other objects make with these lines by a quadrant or sextant, which, for this purpose, must be held in a horizontal position.

EXAMPLE I. (See Plate VII. fig. 1.)

Suppose, in a ship at A, we observe the bearings of the most remarkable points of a bay, C, D, E, F, G, H, and I, and then sail S. 64° E. 13 miles to B, and at B observe the bearings of the same points; it is required to construct the chart.

*If the soundings were not taken at low water, they may be reduced thereto by a method which will be explained hereafter.

It is difficult to ascertain correctly the courses and distances sailed by the boat, on account of the currents and other causes. This inconvenience may be obviated, if the ship be at anchor, and not far from the boat, by observing in the boat the bearing of the ship by compass, and by measuring, with a quadrant, the angle contained between the top-gallant-mast head and that part of the ship which is at the same height as the eye of the observer; for by this angle the distance of the boat from the ship

Draw the line AB, S. 64° E. 14 miles. Through the points A and B draw the lines AC, AD, AE, AF, AG, AH, AI, BC, BD, BE, BF, BG, BH, and BI, with their respective bearings; and where the corresponding lines cut each other, will be the points C, D, E, F, G, H, and I, respectively. Through these points the different curvatures of the land must be drawn, corresponding with your eye-draught. In this manuer may a chart be constructed by observations taken upon the water. manner of surveying upon land is exactly similar.

To survey a harbor by observations on shore.

The

Make an eye-draught of the place to be surveyed, and, in going round the coast, fix station-staves, or straight poles, tall enough to be seen at a considerable distance, in the most remarkable points and bendings of the shore; but if at any of those places there is a noted tree, house, or any other remarkable thing, that object may serve instead of a station-staff; and it will be convenient to black the staves, and tie a piece of white bunting at the top of each; then in the eye-draught put letters or numbers, at the noted points or marks, for the sake of distinction.

Choose the most extensive and level spot of ground you can meet with to measure your base line upon. This line must not be less in length than a tenth part of the distance of the two extreme objects which are to be observed; and the two extreme points of it must be so situated that as many of the station-staves as possible may be seen from both of them. The bearing or position of the base must be well determined in degrees and minutes, and the length accurately measured, either by a measuringchain or a piece of log-line.

From each end of the base observe, with an azimuth compass, or with a theodolite (if it can be procured), the bearings of each of the station-staves; or else with a sextant measure the angles contained between the staves or remarkable objects and the other end of the station-line, and write them down, in regular order, in your book. These measures and angles, being plotted down, as before directed, will give the most conspicuous points of the shore. The intermediate spaces are to be filled up from the sketches made on the spot.

But if any one of these objects be situated so far beyond the limits of the base as to appear nearly in the same direction, or to make angles not exceeding 10°; or if some of the remarkable objects be visible only from one end of the base; then let the bearings of such objects be taken from a place whose position has been determined from both ends of the measured base: or, if there are several remarked objects which cannot be seen from either end of the base lines, let the bearings of such objects be taken from each of two points whose positions have been determined by bearings taken from both ends of the base or it may, on some occasions, be proper to choose another place on which another base, of a convenient length, may be measured, and from the extremities of which the ends of the first base may be seen, and as many as possible of the remaining objects which lay too obliquely, or which could not be seen from the first base. In such manner proceed until the bearings are taken of all the points judged necessary for completing the survey of the limits of the harbor.

If a right line of a sufficient length for a base line cannot be measured, it may be taken in two adjoining lines, as the two sides of a triangle, the included angle being accurately measured, and the bearing of one of the lines observed.

When the outlines or limits of a harbor, bay, road, &c., are delineated by the preceding precepts, let a small vessel go out to sea to take drawings of the appearance of the land and its bearings. Sail likewise into the harbor, and draw the appearance of its entrance. Take particular notice if there be any false resemblance of the entrance, by which ships may be deceived and run into danger; or if any two objects, being brought in a line, will lead into the harbor without danger. Search for the best anchoring-places, and, if possible, denote those places by bringing two objects in one if not, take the exact bearings of two or three other objects, so that the places may be easily determined. After drawing the chart, we must insert a compass, with the variation, and scale properly fitted to the plan. Then the islands, rocks, sands, &c., must be marked in their proper places, with their soundings at low water; the

anchoring-places, with the best track to get to them; the proper sailing-marks to avoid dangers; the places where fresh water can be obtained; the name of the place, that of the country, or of the sea; the latitude and longitude; a sketch of the appearance the place makes at sea, upon a known bearing, and at an estimated distance; and whatever else a judicious seaman may think proper to insert. Then will the plan be fit for all nautical purposes, and may be embellished with proper colors, if necessary.

EXAMPLE II. (See Plate VII. fig. 2.)

From each end of a base line AB of 1200 fathoms, were observed the points C, D, E, F, and G; and as the points I, K, and L, were not visible from the extremities of the base line, another base line was measured, from the point D to H, of 680 fathoms, from which points the bearings of I, K, and L, were observed. Hence it is required to construct a chart of the place.

Draw the east line AB equal to 1200 fathoms; from each end of this line draw the lines AC, AD, AE, AF, AG, BC, &c., at their respective bearings; the points of intersection will give the points C, D, E, F, and G. From the point D (which was found in this manner) draw the N. W. line DH equal to 680 fathoms, and through these points draw the lines DI, DK, DL, HI, &c., at their respective bearings; the points of intersection of the corresponding lines will be the situation of the points I, K, L. Between these remarkable points, draw the outlines of the land, conformable to your rough draught.

In order to determine the situation of the point M, which was seen too obliquely from the bases AB, DH, you may take the bearing of that point from B, and then from G (whose situation has been determined by bearings taken from the points A, B); the intersection of the lines BM, GM, will determine the situation of M.

Method of surveying a small bank or shoal where great accuracy is required.

The method of determining the extent and situation of shoal ground by sailing round it, and keeping an account of the courses and distances sailed, is well adapted to the taking of an extensive survey, or to the exploring of a large bank, where great accuracy is not required. But the difficulty of ascertaining with precision the courses and distances sailed (which are liable to error on account of the tides, currents, and the different velocity of the boat at different times, owing to the unsteadiness of the wind) prevents this method from being sufficiently accurate to be used in exploring a dangerous shoal or bank at the entrance of a narrow channel of a harbor, or any other place where the exact form of the shoal is to be found; and if to obtain the necessary degree of correctness, the bearings of two remarkable objects are taken at every time of sounding, the time expended in taking the observations, if there be only one observer, will be increased beyond all reasonable bounds. To obviate these difficulties, we may use either of the following methods, by which the necessary observations for determining the situation of the boat, can be made as fast as the soundings are taken.

First Method. Procure a large sail-boat with a high mast, and a small row-boat. Bring the sail-boat to anchor on the bank which is to be explored, and take accurately the bearings of two remarkable points of land, or other objects, whose situation has already been determined by observations taken on shore, or in sailing along the land. By this means the situation of the sail-boat may be accurately marked on the chart. Then enter the small boat, and row from the other in any particular direction, observing to keep the mast of the boat to bear upon any point of the compass, or (which is much