[iiss ] 
rence of latitude made, the longitude cannot be had by Mer- 
cator’s failing, which makes it neceflary to fubjoin the two fol- 
lowing cafes, 
CASE IX 
Tur difference of longitude between two places in one parallel 
of latitude given, to find the diftance between them. 
Lat. 49° 30 N. 
Difference of Long. 3° 30 E. 
1a WO A a! 2 
Ser the index to the complement of the latitude, 40° 30’, on 
the femicircle, mark the difference of longitude in miles on the 
index, then move the perpendicular until it meets the termina- 
tion of the difference of longitude on the index, and the part 
of the perpendicular intercepted between the limb of the box 
and the point of interfection will reprefent the diftance 136.4 
miles required. 
GAY SB) ek, 
Tue diftance between two places in one parallel of latitude given, 
to find the difference of longitude between them, 
Lat. of the given parallel 49° 30’ N. 
Diftance failed E. 136.4. 
RULE 
