If the chart is intended to be upon a larger scale, equi-multiples of the inter vals are to be taken, such as will answer to the proposed extent of the chart. A slip of strong paper is to be divided, and numbered in the same manner as the first drawn parallel. Now each place within the limits of the chart is to be laid down, by placing the slip of paper so, that its ex treme points of division may be at the lati tude of the given place on each meridian; then, under the longitude of the place, a mark is to be made, which will represent the position of that place. In like manner all the places on the coast are to be laid down and connected by observations made on the coast : or if no sketch had been previously made, the contour of the coast is to be drawn agreeable to the best charts. Meridians and parallels are to be drawn through every fifth or tenth degree of latitude and longitude, and extended to the coast.
A compass is to be inserted in some convenient part of the chart, and the points extended to the land : an anchor is to be drawn where there is good an choring ground, and in places where it is safe only to stop a tide, an anchor without a stack is to be laid down. The soundings, the quality of the ground, the times of high water at full and change, &c. are to be marked in their proper places.
Ctwers, manner of using.—The princi pal use of a chart is, to find the course and distance between any two places within its limits, and to lay down the place of a ship on it, so that the position of the ship with respect to the intended port, the adjacent land, islands, &c. may be readily perceived.
To find the latitude of a place on the chart.
Rule.—Take the nearest distance be tween the given place and the nearest parallel of latitude, which being applied the same way on the divided meridian, from the point of intersection of the pa rallel and meridian, will give the latitude of the proposed place.
Example.—Required the latitude of Port Louis, in the isle of France. The least distance between Port Louis and the nearest parallel, being laid the same way on the meridian, from the extremity of that parallel, will reach to 20° 8' S., the latitude required.
'Fe find the course and distance between two given places on the chart.
R ale. —Lay the edge of a scale over the given places, and take the nearest dis tance between the centre of any of the compasses on the chart and the edge of the scale; move this extent along, so as one point of the compass may touch the edge of the scale, and the straight line joining the points may be perpendicular thereto ; then will the other point shew the course; and the interval between the places being applied to the scale will give the required distance.
Example.—Required the course. and distance from Cane St. Andre to Cane St. Sebastian, both in the island of Mada gascar. The edge of a scale being laid over the two places, then, by moving the compass as directed, the course will be found to be N. E. E., and the in terval between them will measure 105 leagues.
The course and distance sailed from a known place being given, to find the slap's place on the Chart.
the edge of a scale over the place sailed from, parallel to the given course ; then take the given distance from the scale on the chart, and lay it off from the given place by the edge of the scale, and it will give the point on the chart representing the place on the ship.
Example.—The correct course of a ship from Cape St. Maria, on the north side the entrance of the river La Plata, was N. E. by E. and the distance 238 leagues. Required the place of the ship on the chart. The edge of the scale being laid over Cape St. Maria, in a N. E. by E. di rection, and the distance 238 leagues, laid off from Cape St. Maria by the edge of the scale, will give the place of the ship, which will be found to be in the la titude 28° 15' S.
To find the longitude of a place on the Chart.
Rule.—Take the least distance between the given place and the nearest meridian, which being laid off on the equator, or divided parallel, from the point of inter section of the parallel and meridian, will give its longitude.
Example.—Required the longitude of Funchal in the island of Madeira. The least distance being taken between Fun chal and the nearest meridian,and laid off from the intersection of that meridian with the divided parallel, will give 17° 6' W., the longitude required.
To find the distance between two given places on the Chart.
L When the given places are under the same meridian.
Rule.—Find the latitude of each ; then the difference or sum of their latitudes, according as they are on the same, or on opposite sides of the equator, will be the distance required.
Example.—Required the distance be tween the nearest extremities of the is lands of Grenada and Guadaloupe.
iT Latitude of southermost ex tremity of Guadaloupe 15° 52' N.