312 DESCRIPTION OF GARNETT's 



the line a b equal to the distance ; and cross it at the extremi- 

 ties a, b, by the lines a T, b I; forming the angles of position 

 at those points b a T, a b I, continued on both sides of a b. The 

 latitude of the places a and b, being given, set off from the 

 same scale of equal parts, a sufficient number of degrees of 

 latitudes on the lines a T, and b I produced so that some com- 

 mon latitude shall be on both those lines, (as the latitude of 

 45° on the annexed special chart) and a perpendicular d T, to 

 the middle of two points of the common latitude on the lines 

 aT, bl will be the CENTRAL MERIDIAN, or that which 

 passes through the middle longitude of the chart ; and as the 

 latitude of the point d has been found, the degrees of latitude 

 can also be marked on the line T d produced on both sides of 

 a b. Then the parallels of latitude will be very nearly repre- 

 sented by circles passing through the three points of each de- 

 gree on the three lines aT, dT, b I, produced on both sides 

 of a b; and dividing the extreme parallels into as many parts 

 as there are five degrees of longitude between the two places ; 

 the several meridians can be drawn, shewing the angles of po- 

 sition at every five degrees of longitude, and having the same 

 appearance as on the globe. On this SPECIAL CHART the 

 ship's place can be marked, whenever a good observation of the 

 latitude and longitude is taken, and a new direct course on a 

 great circle to the intended port readily seen, with the angles 

 of position ; and the course which will meet the same great 

 circle, after sailing 5° of longitude, can be found from the 

 Table in page 315, by adding half the inclination of the me- 

 ridians at 5 degrees difference of longitude, to the angle of po- 

 sition ; (the loxodrornic course being always between the great circle, 

 and the equator) or by taking as a course, the angle of position 

 on the special chart at 2 i degrees of longitude farther onwards 

 than the longitude of the ship; which course will serve for 

 sailing the distance corresponding to 5° difference of longitude, 

 (which distance can readily be found by the chart) after which 

 the courjse must be altered either by adding the whole inclination 

 of the meridians for 5° corresponding to the new latitude, or 

 again taking the angle of position at 21 degrees of longitude 

 farther on, as before, which method can be continued at plea- 

 sure. 



