CHARTS. 



ed from the conformity it bears to the 

 globe itself. This projection was pro- 

 posed by Senex, in which the meridians 

 are inclined, the parallels equidistant and 

 curvilinear, and the rhomb-lines real spi- 

 rals, as on the surface of the globe. From 

 this last property, it is evident it can be 

 of very little use in navigation ; as a map, 

 however, it has its advantages. 



Construction of Charts. 



1. Of the plane chart. The number of 

 degrees of latitude which the chart is in- 

 tended to contain, and the extent from 

 east to west being fixed upon, a line is 

 to be drawn near the side or end of a 

 sheet of paper, in length equal to the 

 whole length of the chart from north to 

 south ; and this line is to be divided into 

 degrees, and numbered accordingly. 

 From each end of this line perpendicu- 

 lars are to be drawn, and made equal to 

 the intended extent of the chart from east 

 to west, and their extremities are to be 

 joined by a straight line. If the chart is to 

 commence at or near the equator, and to 

 extend only a few degrees of latitude, the 

 divisions of the parallels may be equal to 

 those of the meridian; but if the chart be- 

 gins at any considerable distance from the 

 equator, it will conduce to accuracy, to 

 make the length of each degree of the pa- 

 rallel equal to the co-sine of the mean la- 

 titude, the radius being 60 minutes ; or 

 the extreme parallels may be divided ac- 

 cording to the above proportion, and in 

 that case it will become a reduced chart. 

 Meridians and parallels are there to be 

 drawn at convenient distances. 



A scale is now to be made of stiff paper 

 or pasteboard, equal in length to the ex- 

 tent of the chart from east to west, and 

 divided and numbered accordingly. By 

 this scale, the positions of those places 

 contained within the limits of the chart 

 are very easily laid down, by placing the 

 divided edge of the scale over the latitude 

 of the given place ; and under the given 

 longitude, a mark being made will repre- 

 sent the position of the place on the chart. 



A compass is to be inserted in any con- 

 venient place of the chart, an arrow shew- 

 ing the direction of the flood tide or cur- 

 rent. The times of high water at full and 

 change are to be marked in their proper 

 places, expressed in Roman characters ; 

 sounding and quality of the ground at bot- 

 tom, the leading marks to avoid dangers, 

 &c. 



II. Of a Mercator's chart. A Mercator's 

 chart, for any given portion of the surface 



of the globe, is constructed as follows : 

 the limit of the proposed chart is first to 

 be determined ; that is, the number of de- 

 grees of latitude and longitude which it is 

 to contain, and the degree of latitude and 

 longitude of its commencement. Find the 

 meridional parts answering to each degree 

 of latitude, within the intended limits of 

 the chart, and take the difference between 

 each, and that corresponding to the least 

 degree of latitude in the chart; and reduce 

 these differences Jto degrees by dividing 

 by 60. 



A parallel, representing that of the least 

 latitude, is to be drawn ; upon which the 

 number of degrees in the proposed differ- 

 ence of longitude, from a scale of equal 

 parts, is to be laid off, and divided into de- 

 grees, and smaller portions of, if conve- 

 nient, and numbered at each fifth or 

 tenth degree. From each end of this pa- 

 rallel a perpendicular is to be drawn, and 

 made equal to the difference of the meri- 

 dional partsof the extreme latitudes taken 

 from the divided parallel ; and the ends 

 of these meridians are to be joined by a 

 straight line, which will represent the 

 other extreme parallel, and which is to 

 be divided and numbered in the same 

 manner as the first drawn parallel ; the 

 meridians are then to be divided into de- 

 grees, and numbered at every fifth or 

 tenth degree. Take the meridional dif- 

 ference of latitude between the begin- 

 ning of the chart, and the next fifth or 

 tenth degree of latitude from the divided 

 parallel, and lay it off from the first paral- 

 lel on each of the scale meridians, and join 

 these points by a straight line. In like man- 

 ner the meridional difference of latitude, 

 answering to each successive interval of 

 five or ten degrees, is to be taken from the 

 first drawn parallel and laid off, and the 

 corresponding parallels are to be drawn 

 and numbered accordingly, and the inter- 

 mediate spaces are to be subdivided. If the 

 chart is upon a large scale, the meridional 

 difference of latitude answeringto eachde- 

 gree is to b e laid off from the least parallel . 



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 



