CHAP. IV.] 



CONVERGENCY 



99 



drawing a line from the centre through K. X is the point 

 in which the axis of the earth, produced, meets the central 

 meridian of the chart, also produced. 



Let us again look at our flat surface, which we may now 

 call the chart, from a different point of view, i.e., from a point 



/i^ 



Fig- 15- 



in the extension of the line joining the centre of the earth and 

 the central point of the chart. 



In Fig. 16, A B C D is the chart as before, touching the 

 spherical earth at the central point J. G and N are the 

 positions on the chart of the points on the earth's surface, 

 F and M in the other figure. G J N is then the central 

 meridian of the chart. X is, as before, the point where the 

 extension of this meridian meets the extended axis of the 



7—2 



