of that parallel, which is nearest the equator.. And so likewise, if one of the meridians be supposed to represent the first meridian, the divisions of the parallels must be reckoned thence; but if not, the divisions must be reckoned from the longitude of that meridian, which is nearest the first meridian; that is to say, as far as 180°, and thence back again. Through every tenth division of the meridians drama parallel across the chart; and through every tenth division of the parallels draw a meridian.*

In some convenient part of the chart draw a mariner's compass, and continue the rhumb lines to the extremities of the chart In most charts, the top of the book or paper is made north, consequently the bottom south, the right east, and the left west.

Elaces are delineated or marked on the chart by drawing 2 parallel through the latitude of the place, on each gradnated meridian; and a meridian through the longitude of the place, on each graduated parallel the point of intersection of the parallel and meridian, thus drawn, will give the required situation of the place. Coasts are laid down by marking a sufficient number of points from the known latitudes and longitudes of places on the coast, and the coast itself is draw by the hand through those points. In all sea charts, the line of the coast is gradually shaded off on the land side, to denote the rise of the land above the be done either with the pen or Indian

water.

ink.

This may

On this chart, the situation of a place may be marked, if the bearing and distance from a given place in the chart be known. For, draw a line from the given place, paral

lel

In the figure, which extends from 10° to 23° of longitude, and from 36° to 44° of north latitude, a meridian is drawn to each degice of longitude, and a parallel to each degree of latitude.

lel to that rhumb of the compass, which denotes the bearing, and on this line set off the distance, in parts of the graduated parallel or meridian. The extreme point of the distance marks the place required.

The operator will soon observe, that places may be delineated on the chart by help of the parallels and meridians already drawn, without having recourse to a multiplicity of other lines.

NOTE. Computation is so much more accurate than delineation, and the helps of tables are so many, that charts are seldom used but in coasting navigation.

PLANE SAILING.

PLANE SAILING is the method of deducing a ship's place, or of determining things relating to the navigation of a ship, by the principles of the plane chart.

The course is the acute angle, formed between the line described, or proposed to be described, by a ship under way, and the meridian, from which she is departing.

Distance is the right line, or rather rhumb, described on any single course.

Difference of latitude is the distance between two parallels of latitude, and is measured on the meridian. It is frequently called northing, or southing.

Departure is the distance on the plane chart between two meridians, and is measured on a parallel of latitude. It is frequently called casting, or westing.

Difference

Difference of longitude is the distance between two meridians, and is measured on the equator. On the plane chart it is the same as departure.

It is absolutely necessary, that the navigator should be able to box the compass, as it is called; that is, to repeat the names of the points in order from memory, either backward or forward, and to tell readily the distance of any point of the compass from the meridian, either in points, or degrees and minutes. For this purpose, the figure of the compass is here drawn. The points being 32, each is equal to 11° 15'.

The following rules do not require any explanation.

1. If the latitudes of two places be given, their difference of latitude may be found by taking the difference of the two latitudes, if of the same name; or their sum, if of contrary names.

2. If one of two latitudes be given, together with the difference, the other may be found by taking the sum of the given latitudes, if of the same name; or their difference, if of contrary names; and the latitude found will be of the same name with the greater of those given.

3. If the longitudes of two places be given, their dif ference of longitude may be found by taking the difference of the two longitudes, if of the same name; or their sum, if of contrary names. But if this sum exceed 180°, its supplement is the difference of longitude:

4. If one of two longitudes be given, together with the difference, the other may be found by taking the sum of the given longitudes, if of the same name; or their dif ference, if of contrary names; and the longitude found will be of the same name with the greater of those given. The two last rules are applicable likewise to departure.

EXAMPLES

IN PLANE SAILING ON A SINGLE COURSE.

1. A ship, in latitude 37° 10' N. sails N N E. So miles it is required to find her difference of latitude and departure.

Construction.

Construction.

Draw an unlimited line NS, to represent the meridian sailed from, the upper part N being understood to be north. From any assumed point A, in NS, draw the line AB, making the angle CAB 2 points, or 22° 30′, the angle of the course NNE. the line AB being drawn upward, because the course is northerly, and to the right of NS, because it is likewise easterly; make AB 80 miles, or the distance; and let fall the perpendicular BC from B on the line NS.

The line AC will be the difference of latitude, and CB the departure.

Computation.

N