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11. A ship in the Baltic takes her departure from the Eastholms, bearing W 10 miles, and sails Eb S 15, S E b E 20, N E 34, EN 16, and N N E 22 miles, required her place, and course and distance to Libau ?
Answer, lat 55° 22' W, long 17° 54' E, and course by Mer N 68° 20' E, dist 101 miles.
12. A ship from Memel sails W 34, W SW S 42, S Wb $ 38, and Wb N 21 miles, required her place, and course and distance to the south east point of Bornholm ?
Answer, lat 54° 55' N, long 17° 50' E, course N 88° 5' W, and dist 89.6 miles.
13. If a ship from Heligoland sail N W b N 26, N W N 34, Nb E 12, WIS 42, and NNE 38 miles, required her place, and course and distance to Aberdeen ?
Answer, lat 55° 44' N, long 6° 9' E, course to port N 72° 51' E, and dist 287 miles.
14. If a ship from Cape Horn sail SES 46, S Eb E 72, E SE 90, SW 51, and SSW W 61 miles, required her course and distance to Cape Smith, New Shetland, finding the difference of longitude upon each course?
Answer, lat 59° 32' S, long 63° 14' W, course S 3° 52' W, and dist 200:5 miles.
15. A ship from lat 6° 28' N, lc g 63° 27' E, bound for Bombay, sails N N E 16, N ] W 43, NEI N70, N E b N 43, and N b E À E 14 miles, required her latitude and longitude, the course to be steered, and the distance to be sailed to arrive at her port?
Answer, lat 9° 6' N, long 64° 45' E, course to port N 38° 58' E, and dist 756 miles.
16. By observation, a ship is found to be in lat 41° 50 s, long 68° 14 E, she sails N E 140, and E , S 73 miles, required her place, and course and distance to the Island of St. Paul ?
Answer, lat 40° 18' S, long 72° 2! E, course N 68° 35' E, and dist 262.9 miles.
A CHART is a representation of the whole or part of the surface of the globe, exhibiting particularly every thing calculated to facilitate the husiness of navigation. There are two kinds of charts in use among seamen, the plane chart and the Mercator's chart. In plane charts, in which it is attempted to exhibit the latitudes and longitudes of places, the meridians are drawn parallel to each other, the degrees of the parallels, as well as those of the meridians, being and relative positions of different places must therefore on such charts be exhibited very erroneously; and, in fact, charts of this kind can scarcely be considered as of any practical utility.
But abstracting from the consideration of latitude and longitude, there will be no material error in representing a small portion of the earth's surface as if it were actually a plane ; and coasting charts are generally constructed on that supposition. In plane coasting charts neither latitude nor longitude is considered, and places are repre: sented according to their relative distances and angular positions ; and as these charts in general comprehend but a small extent of coast, they can be drawn on a large scale ; and, in consequence, many things can be inserted in them which it is impracticable to introduce in a more general chart.
Plane charts, which shew in an approximate way the latitudes and longitudes, bearings and distances, of places comprehended within small portions of the earth's surface, may however be constructed thus :
Draw at the bottom of the paper a line to represent the parallel at which it is proposed the chart should begin, erect a perpendicular by the side of the page, and set off upon it as many degrees of latitude as it is intended the chart should extend to, and of such a magnitude as may be thought proper, subdividing the degrees into such smaller portions as the size will admit; and at convenient intervals draw lines parallel to the bottom one to represent the parallels of latitude. Then to determine the proper length of a degree on the parallels, add the logarithm of 60' to the logarithm cosine of the latitude of the middle parallel on the chart, and the sum will be the length of a degree of the parallel in that latitude; which being taken from the previously divided meridian, and laid off on the bottom parallel, will divide it into degrees of longitude nearly. From such points of the divided parallel as may be thought proper, (say at every degree) meridians may be drawn parallel to the divided one, and the degrees of longitude which the chart is intended to embrace, may be marked on the parallels at the bottom and top of the page ; and the degrees of latitude on each side of the middle latitude, used in computing the degrees of the parallel, may be marked at their proper places. Then, a compass being drawn in any convenient situation on the chart, and the different places included in it marked according to their latitudes and longitudes, the coasts, &c. may be shaded, and the chart will be completed.
Such charts are of limited use to seamen however when compared with the Mercator's chart, the construction of which may be thus explained.
Having drawn at the bottom of the paper a line to represent the lowest parallel on the chart, and divided and subdivided it as may
be thought convenient for degrees, &c. of longitude, let this line be considered as a general line of measures, and draw perpendiculars at the extremities of it to represent the extreme meridians. Then to obtain the proper length of the degrees in the different parts of the meridian proceed as follows.
Take from Table 3, the meridional parts for the latitude at which it is proposed the chart should commence, and also for each successive degree of latitude intended to be contained in it. Then find the meridional difference of latitude between the latitude of the lowest parallel, and every other one intended to be contained in the chart, and dividing them by 60, for degrees, &c. take the quotients from the bottom line, or the line of measures, and apply them from the bottom on the extreme meridians, and the degrees of latitude will thus be determined ; and they may be farther subdivided, in a manner similar to the degrees of longitude. The meridians and parallels of latitude being then drawn at such intervals as may be judged, convenient, the situation of every remarkable place, rock, island, shoal, &c. comprised within the space represented by the chart, may be laid down from its known latitude and longitude ; and a compass (or more than one if the chart be large) being inserted in any convenient situation, to determine the relative bearings of the different points on the chart, the coasts, sands, rocks, &c. may be shaded, and the chart will be completed.
USE OF MERCATOR'S CHART. To find the latitude and longitude of any place on the chart. Take the perpendicular distance of the given place from any convenient parallel, and from the point where that parallel cuts, the graduated meridian, apply the distance upon the meridian in the same direction that the place lies with respect to the parallel, and the point to which the distance reaches will be the latitude of the place.
In the same way, if the perpendicular distance of the place from a meridian be taken and applied from the place where the meridian cuts the divided parallel, the longitude of the place will be determined. From the latitude and longitude of a place to find its situation on the chart.
Lay the edge of a scale over the parallel of the given latitude measure on one of the graduated parallels the distance of any convenient meridian from the given longitude, and apply this distance along the edge of the scale from the place where the meridian measured from cuts it, in the same direction that the longitude lies from the meridian ; and the point to which the distance reaches will To find the course between two places on the chart.
Lay the edge of a scale over both the places, and applying a parallel ruler to the edge of it, move the two parts of the ruler in succession till the edge of one of them passes through the centre of a compass, and that edge will on the compass indicate the course.
Or draw a line in pencil along the edge of the scale, cutting any meridian, and the angle included between the line and the meridian will be the course.
Or, lastly, having laid the scale over the places as before, place one foot of a pair of compasses in the centre of any convenient compass on the chart, and with the other take the nearest distance to the edge of the scale. Then carry both points of the compasses forward, keeping one of them by the edge of the scale, and the imaginary line which joins them perpendicular to the edge, and the line which the other point describes from the centre of the compass will indicate the course.
To find the distance between two places on the chart. If the places are in the same longitude, find the latitude of each, and if their latitudes are of the same denomination, take their difference; otherwise; their sum for the distance of the places.
If they are in the same latitude, or on the same parallel, take half their distance, and apply it on the graduated meridian on both sides of the parallel on which the places are situated, and the degrees of the meridian intercepted between the two points to which the distance reaches will be the distance of the two places nearly.
But if the places differ both in latitude and longitude, lay a scale over them both, and taking half their distance, apply it both upwards and downwards on the graduated meridian from the middle parallel between the two places, and the degrees of the meridian intercepted between the points to which the distance reaches will be the distance of the places nearly.
If half the distance is too great to be conveniently measured at once, one fourth, or one eighth of it may be taken, and applied upwards and downwards from the middle parallel as before, and the intercepted degrees of the meridian will be one half, or one fourth of the required distance nearly.
The distance may be found by the following method, which is exact in principle, and is in fact only an abridged solution of the question by construction, on the principles of Mercator's sailing.
Find the difference of latitude between the two places, and take it from the graduated parallel ; then, having laid the edge of a scale over the two places, lay the difference of latitude, before taken off, on the meridian from the latitude of either of the places. Through the point to which this difference of latitude extends draw a parallel of latitude in pencil, cutting the edge of the scale, and the distance of this point from the place whose latitude the difference of latitude was extended from, will, if measured on the graduated parallel, or general line of measures, be the true distance of the places. From the course and the distance which a ship has run from a known
place, to determine her situation on the chart. Lay the edge of a scale over the given place in the direction of the ship's course, and take the distance, reduced to degrees, &c. from that part of the graduated meridian opposite the place on which the ship had been sailing, and this distance, applied from the given place along the edge of the scale, will determine the situation of the ship.
The method of using a plane chart, on which the latitude and longitude are marked, is the same as the method of using a Mercator's one, except that the distance between places is in all cases determined by applying their distance on the chart to the graduated meridian.
But in coasting charts, where latitude and longitude are not in general noticed, the distances of places are measured on a scale adapted to the chart, and inserted in some part of it; and the magnetic bearings and courses between places are deterinined by their situations with respect to the points of a compass drawn also in some convenient part of the chart, and adapted to the magnetic, not the true meridian.
ON A SEA JOURNAL.
À JOURNAL is a register of occurrences that take place on board a ship, either in a harbour or during a voyage, and ought to contain a particular detail of every thing relative to the navigation of the ship, as the courses, winds, currents, &c. that her situation may be known at any instant at which it may be required.
On commencing a voyage, the true course to the first place which it is intended to reach, is either taken from a chart or calculated ; and thence, from the variation, the compass course is found ; and the ship is kept as near that course as the wind and other circumstances will admit. When the ship leaves the land, the bearing of some known place is taken by the compass, and its distance is in general estimated by the eye, which seainen soon acquire considerable skill in doing. This is called taking the departure. But the distance may be otherwise determined by taking the bearing of an object at two