CHAP. XX.] GRADUATION OF A GNOMONIC CHART 463 



In Fig. 112 A represents the station whose position is known, 

 and A M the meridian through it. Along A M can be marked 

 the points where the parallels cut it according to the scale, 

 and if L be a point on the parallel which is nearest to the bottom 

 border of the chart, the parallel through L can be constructed 

 thus: Decide upon the number of points considered necessary 

 to enable the curve to be drawn. It will depend upon the 

 scale of the chart whether these points are one, five, ten, or 

 more minutes of longitude apart, and although the position 



Fig. 112. 



of A will be generally intermediate between two whole minutes 

 of longitude, the positions along the parallel through L will 

 be taken on certain meridians. 



There are now, therefore, a certain number of known posi- 

 tions to plot in order to draw the curved j^arallel through L. 

 The positions are known in so far that the latitude and longi- 

 tude of each point are known, and, taking each position indi- 

 vidually, the distance and bearing of it from A can be obtained 

 readily. 



