66 
HINTS fO TRAVELLERS. 
central meridian, and cut off parts C c, c 0 , 0 h, and h H each to repi?e a 
sent a degree in the corresponding latitude on the given scale. Place 
the first quadrilateral with Q R on C c and prick through the point P, 
thus giving the point B: similarly placing the second quadrilateral on 
H li obtain the point G. Join B G and cut off B b = C c, and G# = H h. 
With B b and G g as bases for starting, proceed as before and determine 
the points A and F and the line A F, which will be one of the outside 
meridians. A similar process on the other side of H C will give the 
points D, E, I, K. Join the points A B, BO, CD, D E, etc., and F G, 
G H, H I, IK, etc., and we get the parallels of latitude which cut each 
of the meridians at the same angle, different for each parallel. We have 
now only to divide the lines fa, gb, etc., into parts equal to h 0 and 0 c, 
and unite the points of intersection, and the graticule is complete. The 
practical check on the process is that if it has been constructed accurately, 
the meridians A F, B G, D I, and E K will be sensibly equal to the 
central meridian C H, and the diagonals AH, C F, C K, EH will be 
sensibly equal to each other. 
